HK1128746A

HK1128746A - Controlling pressure and static charge within a wellbore

Info

Publication number: HK1128746A
Application number: HK09106310.1A
Authority: HK
Inventors: D．M．寇特斯; J．M．丹尼尔
Original assignee: 雪佛龙美国公司; 璐彩特国际公司
Priority date: 2006-11-07
Filing date: 2006-11-16
Publication date: 2009-11-06

Description

Controlling pressure and static charge in a wellbore

Technical Field

The present invention relates to a method of controlling the pressure generated by a fluid contained within a confined volume when the fluid within the confined volume is being heated. In a preferred embodiment, the present invention relates to a method of controlling the pressure within an annular volume described by a casing string assembly within a wellbore.

Background

In the drilling of a wellbore, such as an oil well, it is common to secure together individual sections of larger diameter metal tubing to form a casing string or liner disposed within each section of the wellbore. Each casing string may be suspended from wellhead equipment near the surface. Alternatively, some casing strings may be in the form of a liner string extending from near the setting depth of a previous section of casing. In this case, the liner string will be suspended from the forward portion of the casing on the liner hanger. The casing string is typically made up of a number of joints or segments, each approximately forty feet long, connected to each other by threaded joints or other connection devices. These joints are typically metal pipes, but may also be non-metallic materials such as composite pipes. Such casing strings are used to improve wellbore integrity by preventing collapse of the cavity walls. In addition, the casing string prevents the movement of fluids from one formation to another formation through which the wellbore passes.

Typically, each section of casing string is secured within the wellbore before the next section of the wellbore is drilled. Thus, each subsequent section of the wellbore must have a smaller diameter than the previous section. For example, a first portion of the wellbore may receive a surface (or guide) casing string that is 20 inches in diameter. Subsequent sections of the wellbore may receive intermediate (or protective) casing strings having diameters of 16 inches, 133/8 inches, and 95/8 inches, respectively. The last section of the wellbore may receive production casing strings having diameters of 7 inches and 41/2 inches, respectively. When the cementing operation is completed and the cement sets, there is a column of cement in the annulus described by the outer surface of each casing string.

Subterranean zones penetrated by wellbores are typically sealed by hydraulic cement compositions. In such applications, hydraulic cement compositions are used to secure pipe strings, such as casings and liners, in the wellbore. In performing these primary cementing operations, a hydraulic cement composition is pumped into an annular space bounded by the borehole wall and the outer surface of the tubular string disposed therein. The cement composition is allowed to cure in the annular space to form an annular sheath of hardened substantially impermeable cement that supports and positions the tubing string in the wellbore and seals the outer surface of the tubing string to the wall of the wellbore. Hydraulic cement compositions are also used in various other cementing operations, such as sealing a high permeability zone or fracture in a subterranean zone, plugging a crack or hole in a pipe string, and the like.

A casing assembly comprising more than one casing string bounds one or more annular volumes between adjacent concentric casing strings within the wellbore. Typically, each annular volume is at least to some extent filled with the fluid present in the wellbore when the casing string is installed. In deep wells, the amount of fluid within the annular volume (i.e., the annular fluid) may be significant. Each 1 inch thick by 5000 feet long annulus will accommodate approximately 50,000 gallons, depending on the diameter of the casing string.

In oil and gas wells, it is common that a portion of the formation must be isolated from the rest of the well. This is typically achieved as follows: the top of the cement column of the subsequent column is led to the annular space above the front casing shoe. While this isolates the formation, having the cement up inside the casing shoe effectively blocks the safety valve provided by the natural fracture gradient. Instead of leaking at the shoe, any pressure increase will be exerted on the casing unless it can be bled off at the surface. Most land wells and some offshore platform wells are equipped with wellheads that provide access to each casing annulus and can quickly vent apparent pressure increases. On the other hand, most subsea wellhead installations do not provide access to the casing annulus and may create a sealed annulus. Because the annulus is sealed, the internal pressure may increase significantly in response to the increase in temperature.

The fluid in the annular volume will typically be at or near the ambient temperature of the seafloor during installation of the casing string. When the annular fluid is heated, it expands and may cause a substantial pressure increase. Such conditions are typically present in all production wells, but are most pronounced in deep water wells. Deep water wells are likely to be damaged by the increase in annulus pressure due to the low temperature of the displacement fluid compared to the high temperature of the produced fluid during production. The temperature of the fluid in the annular volume (when it is sealed) will typically be ambient temperature, which may be in the range of 0 ° F to 100 ° F (e.g. 34 ° F), with the lower temperatures most commonly occurring in subsea wells with considerable water depth above the well. During production from a reservoir, produced fluids pass through production tubing at relatively high temperatures. Temperatures of 50 ° F to 300 ° F are contemplated and temperatures of 125 ° F to 250 ° F are often encountered.

The higher temperature of the produced fluid increases the temperature of the annular fluid between the casing strings and increases the pressure to each casing string. Conventional liquids for annular volumes expand with temperature at constant pressure; in a constant volume of the annular space, the increased fluid temperature results in a significant pressure increase. At constant pressure, a substantially incompressible aqueous fluid may increase in volume by more than 5% during the temperature change from ambient conditions to production conditions. At constant volume, this increase in temperature can result in an increase in pressure up to about 10,000 psig. The increased pressure significantly increases the probability of casing string failure with catastrophic consequences to the operation of the well.

What is needed is a method of replacing at least a portion of a conventional fluid within an annular volume with a fluid system that decreases in specific volume as the temperature of the fluid increases. What is also needed is a method of controlling any static charge build-up within the fluid system in the annular volume to reduce the risk of sparking.

The problem of Annular Pressure Buildup (APB) is well known in the oil drilling/recovery industry. See: moe and p. edition, "Annular pressure build: what it and What to do about it, "deep water Technology, p.21-23, 8 months (2000) and P.Oudeman and M.Kerem," Transmission behavor of annular pressure build in HP/HT wells, "J.of Petroleum Technology, v.18, No.3, p.58-67 (2005). Several possible solutions have been reported previously: A. such as "Practical and scientific stability preference and exclusion" of "Nitrogen-foamed Cement barriers, p.1235-1244, (2002) Cement barriers injected with nitrogen, B. such as" Application of Vacuum Insulated tubular barriers ", J.H.Azzola et al, Vacuum Insulated pipes, C. such as C.P.Leach and A.J.Adams," A.N.for molecular Control of the Vacuum Insulated pipe, (2004), C. such as "C.P.Leach and A.J.Adams", A.P.P.P.P.P.P.P.P.P.P.P.P.A.P.P.A.P.P.P.P.A.P.P.P.P.P.P.A.P.P.P.P.A.P.P.P.P.P.P.P.P.A.P.P.P.P.P.P.P.P.P.P.P.P.A.P.P.P.P.P.P.A.P.P.P.P.A.P.P.P.P.A.A.P.P.P.P.P.P.A.P.P.A.P.P.A.P.P.P.P.P.P.A.A.A.A.A.A.A.P.P.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A.A., reinforced casing (stronger) and the use of compressible fluids, and e.g. staudt in U.S. patent No. 6,457,528(2002) and U.S. patent No. 6,675,898(2004) using burst disk assemblies. These prior art examples, while potentially useful, do not provide complete protection against APB problems due to implementation difficulties or prohibitive costs, or both. Our invention is relatively easy to implement and cost effective.

Disclosure of Invention

As described herein, methods of controlling pressure within a confined volume and controlling any static charge buildup are provided.

In one embodiment, the present invention relates to a method of controlling pressure and reducing static charge buildup within a confined volume, the method comprising:

a) providing a volume containing a first fluid within the volume, the first fluid having a first pressure and a first temperature;

b) replacing at least a portion of the first fluid within the volume with a second fluid comprising (i) at least one polymerizable monomer and (ii) at least one antistatic agent;

c) sealing the volume to create a confined volume; and

d) heating the fluid within the confined volume to bring the fluid to a second pressure and a second temperature,

wherein the monomer polymerizes at a temperature between the first temperature and a second temperature, the monomer polymerizing with a pressure decrease within the confined volume such that the second pressure is lower than the pressure at the second temperature when the confined volume contains only the first fluid.

In the above methodThe antistatic agent preferably comprises a hydrophilic group and a hydrophobic group. The antistatic agent is preferably a neutral and/or ionic surfactant. In one embodiment, the antistatic agent is preferably an anionic phosphate ester. In other embodiments, the antistatic agent is selected from ZELECTY^TM、ZELEC UN^TMAnd mixtures thereof. In additional embodiments, the antistatic agent is a quaternary ammonium salt. Preferably, the antistatic agent is added to the above process in an amount of about 0.05 vol% to about 5 vol% of the total volume of the second fluid, more preferably in an amount of about 0.1 vol% to about 1 vol% of the total volume of the second fluid.

In a separate embodiment, a method of controlling pressure and reducing static charge buildup within a casing structure of a wellbore is provided, wherein the pressure may vary depending on location within the wellbore. In this embodiment, the pressure and temperature relate to a single location within the annular volume. Thus, the method comprises:

a) providing an annular volume described by two casing strings within a wellbore and containing a first fluid having a first pressure and a first temperature at a selected location within the annular volume;

b) replacing at least a portion of the first fluid within the annular volume with a second fluid comprising (i) a monomer that polymerizes at a second pressure and a temperature between the first temperature and the second temperature, and (ii) at least one antistatic agent;

c) sealing the annular volume to create a confined volume; and

d) heating the fluid within the confined volume so that the fluid at the selected location is at a second pressure and a second temperature;

wherein the second fluid is preselected such that the second pressure at the selected location is lower than the pressure at the selected location within the confined volume when the confined volume contains only the first fluid at the second temperature.

In one embodiment, the second pressure present at the selected location within the annular volume at the second temperature is equal to the first pressure at the location, despite the increased temperature of the fluid within the annular volume. In another embodiment, the second pressure at the selected location is at most 50%, preferably at most 30%, more preferably at most 15% higher than the first pressure at the selected location.

In a separate embodiment, the method involves a reduction in the maximum pressure and electrostatic charge buildup within the annular volume. For an annular volume of substantial vertical length, the hydrostatic pressure created by the annular fluid causes a pressure gradient across the vertical distance, with the pressure at the deepest location of the annular volume being greater than the pressure at the top of the wellbore, where location is relative to the center of the earth. Thus, there is a location within the annular volume where the pressure is the highest pressure. Accordingly, in this embodiment, there is provided a method of controlling maximum pressure and reducing static charge buildup within a casing structure of a wellbore, the method comprising:

a) providing an annular volume described by two casing strings within a wellbore and containing within the annular volume a first fluid having a first maximum pressure at a first temperature;

b) replacing at least a portion of the first fluid within the annular volume with a second fluid comprising (i) a monomer that polymerizes at a temperature between the first temperature and the second temperature, and (ii) at least one antistatic agent;

c) sealing the annular volume to create a confined volume; and

d) heating the fluid within the confined volume to an elevated temperature above the first temperature such that at least a portion of the fluid is at a second maximum pressure;

wherein the second fluid is preselected such that the second highest pressure is lower than the highest pressure within the confined volume when the confined volume contains only the first fluid at the elevated temperature.

In one embodiment, the second highest pressure within the annular volume is equal to the first highest pressure. In this embodiment, there is no net pressure increase within the sealed annular volume despite the increased temperature of the fluid within the annular volume. In another embodiment, the second highest pressure is at most 50%, preferably at most 30%, more preferably at most 15% higher than the first highest pressure.

In another independent embodiment, a method of controlling pressure and reducing static charge buildup within a confined volume is provided, the method comprising:

a) providing a volume at a first pressure and a first temperature containing a first fluid and a second fluid, the second fluid comprising (i) a monomer that polymerizes at a temperature between the first temperature and a second temperature, and (ii) at least one antistatic agent;

b) sealing the volume to create a confined volume;

c) heating the first and second fluids within the confined volume to bring the first and second fluids to a second pressure and a second temperature;

wherein the second fluid is preselected such that the second pressure is lower than the pressure at the second temperature when the confined volume contains only the first fluid.

In a particular embodiment, the second fluid comprises a monomer and at least one antistatic agent, wherein when the monomer is polymerized (reduced in volume) at a temperature and pressure according to the conditions within the sealed annular volume, static charge build-up is dissipated by the antistatic agent. Accordingly, there is provided a method of controlling pressure and reducing static charge buildup in an annular volume within a wellbore, comprising:

a) filling the annular volume with a first fluid;

b) replacing at least a portion of the first fluid with a second fluid comprising a polymerization system and at least one antistatic agent within the annular volume; and

c) the annular volume is sealed.

The antistatic agent in the above method preferably comprises a hydrophilic group and a hydrophobic group, wherein the hydrophobic group of the antistatic agent is attracted by the second fluid containing the monomer and/or polymer, and wherein the hydrophilic group of the antistatic agent is held at the interface of the second fluid and the surrounding air to conductively dissipate static charges, thereby preventing arcing. In a preferred embodiment, the antistatic agent is a neutral and/or ionic surfactant. Preferably, the antistatic agent is added in an amount of about 0.05 vol% to about 5 vol% of the total volume of the second fluid, more preferably in an amount of about 0.1 vol% to about 1 vol% of the total volume of the second fluid.

Among other factors, the present invention is based on the discovery of fluid systems having unusual thermal expansion properties, as the fluid expands at constant pressure to a lesser extent than would be expected for an incompressible fluid. The present invention is further based on the discovery that the risk of sparking and burning is reduced by controlling the build-up of static charge within fluid systems via the addition of the aforementioned antistatic agents to these fluid systems. Thus, while confined in the sealed volume, the fluid of the present invention, when heated, causes a lower pressure increase within the sealed volume and shows more control over the build-up of static charge than would be expected for conventional fluids.

Drawings

Figure 1 shows an embodiment of the method of the invention showing an open annular volume during which a second fluid is being added to the annular volume.

Fig. 2 illustrates one embodiment of the inventive method, showing a sealed annular volume containing a second fluid disclosed herein at a second temperature and a second pressure.

Figure 3 shows the results of an experiment testing one embodiment of the present invention.

Fig. 4 shows the results of an experiment testing one embodiment of the present invention.

Detailed Description

Following abbreviations and definitions apply in light of this detailed description. It must be noted that, as used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a compound" includes a number of compounds.

The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such disclosure by virtue of prior invention. In addition, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

Unless otherwise indicated, the following terms used in the specification and claims have the meanings given below:

"halogen" means fluorine, chlorine, bromine or iodine.

"Nitro" means the radical-NO₂。

"nitroso" refers to the group-NO.

"hydroxy" refers to the group-OH.

"carboxyl" refers to the group-COOH.

"lower alkyl" refers to monovalent alkyl groups containing 1 to 6 carbon atoms, including straight and branched chain alkyl groups. This term is exemplified by groups such as methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, and the like.

"substituted lower alkyl" refers to an alkyl group containing one or more substituents, preferably one to three substituents, wherein the substituents are selected from the group consisting of amino, nitroso, nitro, halogen, hydroxy, carboxy, acyloxy, acyl, aminoacyl, and aminocarbonyloxy. "lower alkenyl" refers to a linear unsaturated monovalent hydrocarbon radical containing 2 to 6 carbon atoms or a branched monovalent hydrocarbon radical having 3 to 8 carbon atoms containing at least one double bond (-C-). Examples of alkenyl groups include, but are not limited to, allyl, vinyl, 2-butenyl, and the like.

"substituted lower alkenyl" refers to alkenyl groups containing one or more substituents, preferably one to three substituents, wherein the substituents are selected from the group consisting of amino, nitroso, nitro, halogen, hydroxy, carboxy, acyloxy, acyl, aminoacyl, and aminocarbonyloxy.

The term "cycloalkyl" refers to a cyclic alkyl group containing 3 to 6 carbon atoms and having a single cyclic ring, including, for example, cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.

"alkoxy" means the group "lower alkyl-O-", the latter including, for example, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, tert-butoxy, sec-butoxy, n-pentoxy, 1, 2-dimethylbutoxy, and the like.

"amino" refers to the group NR^aR^bWherein R is^aAnd R^bIndependently selected from hydrogen, lower alkyl, substituted lower alkyl and cycloalkyl.

"acyloxy" refers to the groups H-C (O) O-, lower alkyl-C (O) O-, substituted lower alkyl-C (O) O-, lower alkenyl-C (O) O-, substituted lower alkenyl-C (O) O-, and cycloalkyl-C (O) O-, wherein lower alkyl, substituted lower alkyl, lower alkenyl, substituted lower alkenyl, and cycloalkyl are as defined herein.

"acyl" refers to the groups H-C (O) -, lower alkyl-C (O) -, substituted lower alkyl-C (O) -, lower alkenyl-C (O) -, substituted lower alkenyl-C (O) -, cycloalkyl-C (O) -, wherein lower alkyl, substituted lower alkyl, lower alkenyl, substituted lower alkenyl, and cycloalkyl are as defined herein.

"aminoacyl" refers to the groups-NRC (O) lower alkyl, -NRC (O) substituted lower alkyl, -NRC (O) cycloalkyl, -NRC (O) lower alkenyl, and-NRC (O) substituted lower alkenyl, wherein R is hydrogen or lower alkyl, wherein lower alkyl, substituted lower alkyl, lower alkenyl, substituted lower alkenyl, and cycloalkyl are as defined herein.

"Aminocarbonyloxy" refers to the group-NRC (O) O-lower alkyl, -NRC (O) O-substituted lower alkyl, -NRC (O) O-lower alkenyl, -NRC (O) O-substituted lower alkenyl, -NRC (O) O-cycloalkyl, wherein R is hydrogen or lower alkyl, wherein lower alkyl, substituted lower alkyl, lower alkenyl, substituted lower alkenyl and cycloalkyl are as defined herein.

"aliphatic compound" refers to a non-aromatic organic compound in which the carbon atoms are joined together in a straight or branched chain rather than in a benzene ring. An example of an aliphatic compound is methane. Aliphatic compounds include not only fatty acids and other derivatives of alkanes (e.g., alkanes), but also unsaturated compounds such as ethylene (e.g., alkenes) and acetylene (e.g., alkynes).

"antistatic agent" refers to any compound that reduces or dissipates the buildup of static charge in the polymerizable monomers described herein. In a preferred embodiment of the invention, the antistatic agent has both hydrophilic and hydrophobic groups. The hydrophobic groups of the antistatic agent are attracted to the second fluid containing the monomer and/or polymer. The hydrophilic group of the antistatic agent remains at the interface of the second fluid and the surrounding air to conductively dissipate static charges, thereby preventing arcing. In a preferred embodiment of the invention, the antistatic agent is a surfactant.

"fatty acid" means having the formula C_nH_2n+1Carboxylic acid derivatives of COOH, including saturated or unsaturated aliphatic compounds containing at least four carbon atoms, preferably at least eight carbon atoms.

"neutral or ionic surfactant" refers to a compound having a hydrophilic group and a hydrophobic group. The hydrophobic groups of the surfactant are attracted by the second fluid containing the monomer and/or polymer, and wherein the hydrophilic groups of the surfactant are held at the interface of the second fluid and the surrounding air to conductively dissipate static charges to prevent arcing. In a preferred embodiment, surfactants may be used as antistatic agents in various embodiments of the present invention.

"salt" refers to salts derived from a variety of organic and inorganic counterions well known in the art and includes, by way of example only, sodium, potassium, calcium, magnesium, ammonium, tetraalkylammonium, and the like; and when the molecule contains a basic functional group, salts of organic or inorganic acids such as hydrochloride, hydrobromide, tartrate, mesylate, acetate, maleate, oxalate and the like are included. Preferably, the salt is an inorganic acid salt, such as a hydrochloride salt.

"optional" or "optionally" means that the subsequently described event or circumstance can, but need not, occur, and that the description includes instances where said event or circumstance occurs and instances where it does not. For example, "aryl optionally mono-or disubstituted with alkyl" means that the alkyl may, but need not, be present, and the description includes instances where the aryl is mono-or disubstituted with alkyl and instances where the aryl is not substituted with alkyl.

The present invention provides a fluid system that increases in pressure when heated within a confined volume to a lower value than conventional systems and that reduces the risk of sparking and burning due to a reduction in the build-up of electrostatic charges. The confined volume is sealed to prevent escape of fluid. The present invention therefore provides fluids and methods for reducing the effect of pressure increase within a sealed or confined volume when the fluid within the volume is heated to an elevated temperature.

In one embodiment, the volume may be any fluid-containing volume that is sealed and then heated. A non-limiting example of a volume of the present invention is a reaction vessel for performing, for example, a chemical reaction. The volume (initially filled with the first fluid) is open, meaning that fluid can be made to enter and leave the volume. A second fluid is caused to enter the volume, displacing at least a portion of the first fluid in the volume, before the volume is sealed. The volume is then sealed to prevent further flow of fluid into and out of the volume, and the fluid within the volume is heated. This heating causes the pressure within the volume to increase to a considerable extent, particularly with liquid phase fluids, and more particularly with liquid phase fluids that are substantially incompressible. The invention therefore provides a second fluid having the property that, when contained within a sealed volume and heated to a target temperature, the pressure within that volume is lower than when that volume contains only the first fluid. Because the confined volume and the second fluid may accumulate static charge, the second fluid also contains an antistatic agent to reduce static charge accumulation and reduce the risk of sparking and burning.

In a particular embodiment, the present invention provides a method of controlling pressure within an annular volume within a wellbore, particularly within a casing assembly that has been installed in a wellbore intended to extract resources, for example, from a reservoir. Examples of resources include crude oil, natural gas liquids, petroleum vapors (e.g., natural gas), syngas (e.g., carbon monoxide), other gases (e.g., carbon dioxide, nitrogen), and water or aqueous solutions. Control of pressure is achieved using the second fluid described herein. These embodiments are particularly sensitive to spark and combustion. Thus, it has surprisingly been found that the addition of an antistatic agent to the second fluid allows to reduce the risk of sparking and burning.

The casing assembly includes a casing string for protecting the sides of a wellbore formed by drilling into the earth. The annular volume is bounded by two adjacent concentric casing strings within the casing assembly. During the construction of oil and gas wells, a rotary drilling rig is typically used to drill into earth formations to form the wellbore. As the rotary drill rig drills into the earth, drilling fluid (referred to in the industry as "mud") is circulated through the wellbore. The mud is typically pumped from the surface via the interior of the drill pipe. By continuously pumping drilling fluid through the drill pipe, the drilling fluid may flow out of the bottom of the drill pipe and back to the well surface via the annular space between the borehole wall and the drill pipe. The mud is typically returned to the surface when certain geological information is desired and when it is to be recycled. The mud is used to help lubricate and cool the drill bit and to facilitate the removal of cuttings as the borehole is drilled. In addition, the hydrostatic pressure created by the column of mud in the hole prevents blow-outs that may occur due to the high pressures encountered within the wellbore. To prevent blowout caused by high pressure, heavy weights are put into the mud so that the mud has a hydrostatic pressure greater than any pressure expected in drilling.

Different types of mud must be used at different depths because the pressure in the wellbore increases as the depth of the wellbore increases. For example, the pressure at 2,500ft is much higher than the pressure at 1,000ft. The weight of mud used at 1,000ft is not sufficient to be used at a depth of 2,500ft, otherwise blow out may occur. The weight of the mud at extreme depths in subsea wells must be particularly heavy to counteract the high pressure. However, the hydrostatic pressure of this particularly heavy mud may cause the mud to begin to invade or leak into the formation, thereby creating lost circulation of the mud. Casing strings are used to line the wellbore to prevent leakage of drilling mud.

To enable the use of different types of mud, different casing strings are employed to eliminate the wide pressure gradient that occurs in the wellbore. To begin, a borehole is drilled using a light mud to a depth where a heavy mud is required. This typically occurs slightly over 1,000ft. At this stage, a casing string is inserted into the wellbore. A cement slurry is pumped into the casing and a plug flow of fluid, such as drilling mud or water, is pumped behind the cement slurry to push the cement into the annulus between the outside of the casing and the inside of the wellbore. The amount of water used to form the cement slurry will vary over a wide range depending on the type of hydraulic cement selected, the desired consistency of the slurry, the strength requirements of the particular job and the general job conditions at hand.

Typically, hydraulic cement, especially portland cement, is used to secure the well casing within the wellbore. Hydraulic cements are cements that set and exhibit compressive strength due to the occurrence of a hydration reaction that allows them to set or cure underwater. The cement slurry is allowed to set and harden to hold the casing in place. The cement also provides zonal isolation of the subsurface formation and helps prevent collapse or erosion of the wellbore.

After setting the first casing, drilling continues until the wellbore is again drilled to a depth where heavier mud is needed and the needed heavier mud begins to invade and leak into the formation, typically at about 2,500 feet. Again, a casing string is inserted into the wellbore inside the previously installed casing string and cement slurry is added as before.

Multiple casing strings may also be used in a wellbore to isolate two or more formations that should not be in communication with each other. For example, a special case found in the gulf of mexico is high pressure freshwater sand flowing at a depth of about 2,000 feet. Due to the high pressures, additional casing strings are typically required at that level. Otherwise, the sand will leak into the mud or production fluid.

A subsea wellhead typically has an outer housing secured to the seafloor and an inner wellhead housing received within the outer wellhead housing. During completion of an offshore well, a casing and tubing hanger is lowered into a support position within a wellhead housing via a BOP stack mounted above the housing. After completion of the well, the BOP stack is replaced with a Christmas tree (Christmas tree) with appropriate valves for controlling production of well fluids. The casing hanger is sealed with respect to the casing bore and the pipe hanger is sealed with respect to the casing hanger or casing bore so that a fluid barrier is effectively formed in the annulus between the casing and the pipe string and the casing bore above the pipe hanger. After deployment and sealing of the casing hanger, a casing annulus seal is installed for pressure control. If the seal is on the surface wellhead, typically the seal may have a port communicating with the casing annulus. However, in a subsea wellhead housing, there is a large diameter low pressure housing and a smaller diameter high pressure housing. Because of the high pressure, the high pressure housing must be free of any ports for safety. Once the high pressure casing is sealed, there is no way for a hole to be under the casing hanger for blowout prevention.

Representatively illustrated in fig. 1 is a method of practicing the principles of the present invention. In the following description of the methods and other apparatus and methods described herein, directional terms such as "above", "below", "upper", "lower", "upper,the section "and the like are used only for convenience in referring to the drawings. Moreover, it is to be understood that the various embodiments of the invention described herein can be used in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present invention. The methods described herein may be applied to wellbores in both land and underwater locations. It should be understood that the wellbore terminates at the end of the wellbore that enters the earth. In the case of an underwater location, the endpoint is at the water/land interface.

It should be understood that the use of the terms "wellbore" and "casing string" herein should not be construed to limit the present invention to the specifically illustrated elements of the methods. A wellbore may be any wellbore, such as a branch of another wellbore, and does not necessarily extend directly to the surface. The casing string may be any type of tubular string, such as a liner string, etc. The terms "casing string" and "liner" are used herein to refer to any type of tubular string, such as a segmented or non-segmented tubular string, a tubular string made of any material (including non-metallic materials), and the like. Accordingly, the reader will appreciate that these and other descriptive terms used herein are merely for purposes of facilitating clear explanation of exemplary embodiments of the present invention and are not intended to limit the scope of the present invention.

Figure 1 shows one embodiment of the present invention. The wellbore 10 has been drilled using a drill string 50, and a casing assembly 20 has been pre-installed, comprising at least two casing strings concentrically arranged with respect to each other. Not shown is a drilling rig having a support device for supporting a drill string, installing a casing string and supplying fluid to the wellbore. In FIG. 1, a casing string 22 has been installed and sealed at or near the end opposite the wellbore 10 by a cement plug 24.

Attention is now directed in particular to casing string 40 which has been installed to extend to wellbore destination 34. It will be apparent that the termination point 34 may be a temporary termination point so that the wellbore may be extended further after the casing string 40 is installed. Alternatively, the casing string 40 may be run to the final depth in the formation 5 and the wellbore is not run until production begins. When casing string 40 is installed, an annular volume 42 bounded by the inner surface of casing string 22 and the outer surface of casing string 40 is filled with a fluid, and is typically filled with the fluid present within wellbore volume 36. Conventional fluids that may be initially present in the annular volume include drilling fluids or completion fluids, depending on the environment of the drilling operation. The properties of the fluid (referred to herein as the first fluid) initially within the annular volume are selected to meet the needs of a drilling professional drilling the well to complete the well. In one embodiment, the first fluid is an incompressible fluid using conventional definitions.

The composition of the first fluid is not critical to the present invention and is typically one of a variety of fluids used in drilling and completion, including, for example, drilling fluids or completion fluids. The drilling fluid may be water or oil based and may further comprise surfactants, salts, weighting agents and any materials needed to effectively cool the drill bit, remove cuttings and protect and condition the wellbore for fluid production. Likewise, completion fluids may be water or oil based and may further comprise materials used to clean the wellbore and to prepare the installation structure for recovery of fluids from the formation.

At a stage in the method shown in fig. 1, the annular volume 42 is in fluid communication with the wellbore volume 36 via an opening 44 at one end of the casing. The other end of the annular volume, indicated at 46, is in fluid communication with surface equipment, such as a drilling rig (not shown), which has means to recover fluid exiting the annular volume via 46. Environmental concerns provide incentive to minimize the amount of fluid lost to the environment via 46.

In the method of the present invention, a second fluid comprising at least one polymerizable monomer and at least one antistatic agent is introduced into the wellbore volume 36 via the opening 48 to replace at least a portion of the first fluid in the annular volume 42. The opening 48 is in fluid communication with the means for supplying the second fluid. For example, a pumping device for this purpose may be provided on a drilling or production machine. The second fluid is supplied to the volume as a plug flow or slug and passes down through the wellbore volume 36 in a relatively pure form. At the wellbore terminus 34, the second fluid enters the annular volume 42 via opening 44 and flows upward, driving the first fluid initially in the annular volume 42 ahead of the second fluid slug and exiting the annular volume via opening 46. The amount of second fluid supplied to the annular volume is a matter of engineering choice, depending on the amount of pressure that can be tolerated inside the sealed annular volume 42. Such amount is further influenced by, for example, the size of the well system, the temperature of the second fluid when supplied to the annular volume, the temperature of the fluid to be produced in the well, the expected temperature of the fluid in the annular volume during production, the design and specifications of the casing string, etc.

After a sufficient amount of the second fluid has been added to the annular volume 42 to replace at least a portion of the first fluid contained therein, the annular volume 42 is sealed. Figure 2 shows an annular volume 42 sealed by a cement plug at 26 and a casing annulus plug at 28. Typically, casing annulus seals seal the top of the wellbore, preventing fluid from escaping from the wellbore to the environment. Thus, the sealed or confined volume represented by the annular volume 42 of the casing string contains fluid that is confined in place and prevented from leaking from the volume to any significant extent.

In the embodiment shown in fig. 2, at least a portion of the first fluid contained within a volume, such as annular volume 42, and having a first pressure and a first temperature within the volume is replaced with a second fluid comprising at least one polymerizable monomer and at least one antistatic agent such that the volume is filled with a mixture of the first and second fluids. The annular volume 42 between the casing strings 22 and 40 is sealed by cement plug 26 and casing annulus plug 28. The temperature of the fluid containing the second fluid within the annular volume 42 is typically in the range of 0-100F. For subsea installations, the fluid temperature (i.e., the first temperature) is typically less than 60 ° F, or less than 40 ° F, or, for example, in the temperature range of 25 ° F to 35 ° F.

When hydrocarbon fluids begin to be produced and flow upward through the production conduit 52 and out of the wellbore 10, these fluids are typically at a higher temperature than the first temperature. Production fluid temperatures of 50 ° F to 300 ° F are contemplated and temperatures of 125 ° F to 250 ° F are often encountered. The hotter production fluid in the conduit 52 heats the fluid in the confined annular volume 42 to bring the fluid to a second pressure and a second temperature. In conventional systems, the fluid pressure within the sealed annular volume will begin to increase to significantly higher pressures as the temperature increases.

In contrast, according to the present invention, the second fluid comprising at least one polymerizable monomer is preselected such that after the temperature of the fluid within the confined volume is increased to a second temperature, the second pressure within the confined volume is lower than when the confined volume contains only the first fluid at the second temperature. Thus, after increasing the temperature of the fluid within the volume to a second temperature, the polymerizable monomer in the second fluid polymerizes, with a concomitant decrease in pressure within the confined volume, such that the second pressure is lower than the pressure at the second temperature when the confined volume contains only the first fluid. The second fluid also includes at least one antistatic agent that reduces the build-up of static charge.

In a preferred embodiment of the invention, the antistatic agent has both hydrophilic and hydrophobic groups. The hydrophobic groups of the antistatic agent are attracted to the second fluid containing the monomer and/or polymer. The hydrophilic group of the antistatic agent remains at the interface of the second fluid and the surrounding air to conductively dissipate static charges, thereby preventing arcing. In a preferred embodiment, the antistatic agent is a surfactant.

Examples of the antistatic agent having a hydrophilic group and a hydrophobic group include, but are not limited to, anionic phosphate esters and quaternary ammonium salts selected from the group consisting of: dioctadecyl dimethyl ammonium chloride, ditallowdimethyl ammonium chloride, dihexadecyl dimethyl ammonium chloride, bis (docosyl) dimethyl ammonium chloride, didodecyl dimethyl ammonium chloride, ditallowdimethyl ammonium bromide, dioleyldimethyl ammonium hydroxide, ditallowdimethyl ammonium chloride, ditallowdimethyl ammonium bromide, ditallowdimethyl dibutylammonium fluoride, hexadecyldecylmethylethyl ammonium chloride, bis [ ditallowdimethyl ammonium ] sulfate, tris [ ditallowdimethyl ammonium ] phosphate and mixtures thereof.

The anionic phosphate is preferably selected from ZELEC TY^TMAnd/or ZELEC UN^TM(all available from DuPont, Wilmington, DE).

Due to the reduced build-up of static charge in the second fluid, it is possible to significantly reduce the risks associated with sparking and combustion.

The benefits and advantages obtained from the practice of the present invention are in contrast to the drawbacks of conventional processes. The annular volume is initially filled with a first fluid. The temperature of the first fluid may be at or below ambient temperature, depending on the conditions of the wellbore during the addition of the first fluid. For a subsea wellbore, a first fluid may be cooled by water, through which the first fluid flows en route to the wellbore from a source at the drilling platform. Under these conditions, the first fluid will typically be at a temperature in the range of 0 ° F to 100 ° F. For subsea installations, the fluid temperature (i.e., the first temperature) is typically less than 60 ° F, or less than 40 ° F, or, for example, in the temperature range of 25 ° F to 35 ° F. After the fluid is sealed within the annular volume, it is heated by production fluid passing up through the production tubing 52 in the wellbore; elevated temperatures often result in increased pressures, sometimes to a catastrophic extent. Furthermore, there may be a risk of sparking and burning due to the build-up of static charge in the confined volume, which may lead to catastrophic failure.

Annular pressure

Rather, according to the present invention, such pressure within the annular volume is controlled to a manageable degree by the methods disclosed herein. In the practice of the present invention, a confined volume containing a fluid is heated so that the fluid within the confined volume is at a second pressure and a second temperature. In one embodiment, the second pressure is uniform throughout the confined volume. In another embodiment, the second pressure may be different from place to place within the volume. In this embodiment, therefore, the second pressure (and second temperature) is associated with a particular location (referred to as a selected location) within the annular volume. For example, an annular volume within a casing assembly in a wellbore may have a depth (vertical extent) of hundreds, or even thousands of feet. The hydrostatic pressure within the fluid-filled wellbore is therefore expected to be higher at the bottom of the wellbore than at its top. In another embodiment, therefore, the present method involves controlling the maximum pressure within the annular volume (taking into account the hydrostatic head within that volume and other factors).

For purposes of this disclosure, the target pressure is the pressure required within the annular volume during practice of the invention. In one embodiment, the target pressure in the practice of the invention is a second pressure that is lower than when the confined volume contains only the first fluid. In another embodiment, the second pressure is equal to the first pressure within the annular volume. In another embodiment, the second fluid comprising at least one polymerizable monomer is preselected to reduce static charge build-up, and the second pressure at the second temperature of the second fluid contained within the sealed annular volume is at most 50%, preferably at most 30%, more preferably at most 15% higher than the first pressure of the unsealed annular volume at the first temperature and containing only the first fluid.

In many cases, the first pressure, the first temperature, the second pressure, and the second temperature may be measured and the respective values may be known. However, those skilled in the art will recognize that the invention may be fully practiced without knowledge of the numerical values of these parameters. It is sufficient for the practice of the invention that the second pressure be maintained at less than the pressure limit at which the integrity of the vessel (e.g., casing string) in which the fluid is contained would be compromised to an unacceptable degree.

Second fluid system

In the practice of the invention, the first fluid within the annular volume is at least partially replaced by a second fluid. As used herein, the fluid added to the annular volume to control the pressure within the annular volume is referred to as the second fluid or, in the alternative, as the annular fluid.

Generally, the second fluid comprises a liquid componentAnd additional components that contribute to the properties described herein. According to the invention, the additional component comprises at least one polymerizable monomer and at least one antistatic agent. The liquid component may comprise water, hydrocarbons, or both, including, for example, one or more components of the drilling fluid. An aqueous solution containing dissolved organic and/or inorganic salts, acids or bases may be included in the second fluid system. May include hydrocarbon mixtures including materials typically found in drilling fluids or completion fluids. Examples include diesel, C₆-C₂₀Mixtures, alcohols, aldehydes, ketones, ethers, carbonyls, aromatics, paraffins and naphthenes. May include an emulsion having a continuous aqueous phase and a discontinuous organic phase; alternatively, an emulsion having a continuous organic phase and a discontinuous aqueous phase may be included.

In addition, the second fluid may comprise a liquid phase as a continuous phase and also solids, which may be present as a slurry or as bulk particles. Alternatively, the second fluid may comprise a liquid as the continuous phase, the continuous phase having a layer of a gas phase, or a gas phase in the form of a foam within a liquid. In another embodiment, the second fluid comprises a liquid, a gas, and a solid phase in any or all of the above forms. In each alternative, the second fluid has unexpected expansion properties with respect to an increase in fluid temperature.

Static charge buildup can occur within the confined volume. Additionally, replacing a portion of the first fluid within the annular volume with the second fluid may result in the buildup of additional second fluid static charges. This build-up of static charge leads to an increased risk of sparking and burning, which can have catastrophic consequences.

According to the invention, the second fluid comprises at least one polymerizable monomer and at least one antistatic agent. The second fluid has thermal expansion properties which cause a lower pressure increase in the annular volume than would be expected for a substantially incompressible liquid. The second fluid also has the property of reducing the build-up of static charges, since it contains at least one antistatic agent. In a preferred embodiment of the invention, the antistatic agent has both hydrophilic and hydrophobic groups. The hydrophobic groups of the antistatic agent are attracted to the second fluid containing the monomer and/or polymer. The hydrophilic group of the antistatic agent remains at the interface of the second fluid and the surrounding air to conductively dissipate static charges, thereby preventing arcing. In a preferred embodiment, the antistatic agent is a surfactant.

The addition of at least one antistatic agent to the second fluid reduces the risks associated with static charge build-up.

Polymerizable monomer

According to the invention, the second fluid comprises at least one polymerizable monomer. Thus, according to the present invention, there is provided a method of controlling pressure within a confined volume as follows: providing a second fluid comprising a monomer that polymerizes at a second pressure and a temperature between the first temperature and the second temperature, with a concomitant reduction in specific volume. Thus, the pressure within the sealed annular volume is reduced when heated due to the polymerization of the monomer added to the annular fluid prior to sealing the annular volume. When added to the annular volume, both water-soluble monomers and water-insoluble monomers can polymerize with a concomitant volume reduction (and associated pressure reduction within the annular volume). In the confined volume of the sealed annulus, this volume reduction results in a reduction in pressure within the confined volume relative to a similar system without polymerization of the specific monomers of the invention,

the monomers of the invention may be mixed with water, oil or more complex mixtures having the characteristics of drilling muds, including the high density component of the second fluid preparation. The monomer is present in the second fluid in an amount of 1 to 99 vol%, more preferably 5 to 75 vol%, still more preferably 10 to 50 vol%. Example the second fluid comprises 20 vol% monomer and 80 vol% of a second component comprising water and a high density material such as barium sulphate.

As monomers polymerize, including acrylates, such as methyl acrylate and methyl methacrylate, volume shrinkage between liquid monomers and solid polymers of up to 25% may result from the polymerizationThe synthesis process is initiated. See, for example, "Acrylic and Methacrylic ester polymers",Encyclopedia of Polymer Science and Engineeringsecond edition, edited by j.kroschwitz, John Wiley&Sons, inc., vol.1, table 20, p.266, (1985) and d.a.tildbrook et al, "diagnosis of polymerizable shrinkage Using Molecular Modeling," j.poly.sci; part B: polymer Physics, 41, 528 and 548 (2003). In a preferred embodiment of the invention, the monomer is suspended or emulsified (using soap) in water as a water/oil mixture containing a suitable polymerization initiator, pumped into the annular space, and after cementation, polymerization occurs (again, using slow kinetics at near setting temperature), wherein a total volume reduction of up to 5% can be achieved with a 20% vol/vol mixture of monomer and water.

Non-limiting examples of acrylic monomers include acrylamide, methacrylamide, their derivatives, acrylic acid, methacrylic acid, their salts, acid salts and quaternary salts of N, N-dialkylaminoalkyl acrylates or methacrylates, acid salts of diallylamine, diallyldialkylammonium salts, sulfoalkyl acrylates or methacrylates, acrylamidoalkylsulfonic acids and their salts, and the like. More preferably, the acrylic monomer comprises methyl acrylate, methyl methacrylate, and mixtures thereof. Non-limiting examples of other vinyl monomers that may be useful in such in situ polymerization processes include other acrylic esters, methacrylic esters, butadiene, styrene, vinyl chloride, N-vinyl pyrrolidone, N-vinyl caprolactam, or other such oil and/or water soluble monomers.

Additional benefits may be obtained from the selection of initiators for the polymerization process. Azo-type initiators generate nitrogen as a by-product during the polymerization process. The resulting gas phase component (which is a compressible fluid) produced in the confined annular volume can help control the pressure within the confined annular volume as the annular fluid is being heated by the product fluid passing through the production tubing. Peroxide initiators may also be used depending on the temperature and chemical constraints of the product fluid. Alternatively, if encapsulated as described above to control the timing at which polymerization occurs, a redox initiator system such as ammonium persulfate and the activator N, N, N 'N' -tetramethylethylenediamine, or potassium persulfate and the activator ferrous sulfate/sodium bisulfite may also be used.

The second fluid also includes at least one antistatic agent that reduces the build-up of static charge.

Antistatic agent

The confined volume can accumulate static charge after sealing. In addition, static charges can build up during handling of the monomers and during polymerization of the monomers. Static charge build-up increases the risk of sparking and increases the risk of ignition and explosion. Static charge buildup can be controlled by increasing the conductivity of the second fluid containing polymerized monomer. The increase in conductivity can be achieved by increasing the ionic or electronic conductivity. Static charge buildup can also be controlled by increasing conductivity through moisture absorption. Moisture absorption can be achieved using hygroscopic antistatic agents, commonly referred to as humectants, because they rely on the adsorption of atmospheric moisture to exert their effectiveness. Antistatic agents may further work by dissipating static charges as they build up; therefore, the rate of static decay and surface conductivity are common measures of the effectiveness of antistatic agents. According to the present invention, an antistatic agent that functions to dissipate static charges is added to the polymerization system.

According to the invention, an antistatic agent refers to a compound that reduces or dissipates the build-up of static charge in the second fluid. Thus, according to the invention, an antistatic agent is added to the second fluid containing polymerizable monomers.

Examples of the antistatic agent include amines and amides, esters of fatty acids, organic acids, polyoxyethylene derivatives, polyhydric alcohols, neutral or ionic surfactants, quaternary ammonium salts, and mixtures thereof. Other examples of antistatic agents include combinations of fatty acid salts and tertiary amines, fatty amide condensates, hydroxyalkyl fatty acid amides, tetraalkylammonium compounds, alkyl propylamines, ethoxylated amines, and mixtures thereof. Still other examples of antistatic agents include (i) N- (2-hydroxyalkyl) ethanolamine; (ii) a combination of a N, N-bis (2-hydroxyethyl) higher aliphatic amine and a higher aliphatic alcohol; (iii) a combination of N- (2-hydroxy-3-dodecyloxypropyl) ethanolamine and N, N-bis (2-hydroxyethyl) alkylamine; (iv) tetrahydropyrimidine; and (v) mixtures thereof. Other exemplary antistatic agents may be selected from the group consisting of glyceryl monostearate, sodium stearyl sulfonate, sodium dodecylbenzenesulfonate, triethanolamine stearate, and mixtures thereof.

Additional examples of antistatic agents include (i) N-acyl derivatives of N-methylglycine, where the acyl group is lauroyl, oleoyl, or a mixed fatty acid derived from coconut oil; (ii) n-acyl sarcosinates and their salts; (iii) n, N-bis (2-hydroxyethyl) higher aliphatic amines; and (iv) mixtures thereof, each of which is described in U.S. patent No. 4,785,032. N-acyl sarcosinates can be prepared by various methods, including those described in U.S. patent No. 2,063,987 and U.S. patent nos. 2,729,657, 3,074,980 and 3,836,551.

Preferred examples of the antistatic agent having a hydrophilic group and a hydrophobic group include, but are not limited to, anionic phosphate esters and quaternary ammonium salts selected from the group consisting of: dioctadecyl dimethyl ammonium chloride, ditallowdimethyl ammonium chloride, dihexadecyl dimethyl ammonium chloride, bis (docosyl) dimethyl ammonium chloride, didodecyl dimethyl ammonium chloride, ditallowdimethyl ammonium bromide, dioleyldimethyl ammonium hydroxide, ditallowdimethyl ammonium chloride, ditallowdimethyl ammonium bromide, ditallowdimethyl dibutylammonium fluoride, hexadecyldecylmethylethyl ammonium chloride, bis [ ditallowdimethyl ammonium ] sulfate, tris [ ditallowdimethyl ammonium ] phosphate and mixtures thereof.

The anionic phosphate is preferably selected from ZELEC TY^TMAnd/or ZELEC UN^TM(all available from DuPont, Wilmington, DE). ZELEC UN^TMIs an anionic phosphate ester which is an unneutralized phosphate ester and is insoluble in water. In addition, ZELEC UN^TMHaving a structure containing C₈-C₁₆High molecular weight of the fatty alcohol backbone. Thus, ZELEC UN^TMIs an unneutralized water-insoluble, anionic phosphoric ester C of phosphoric acid and fatty alcohol₈-C₁₆An alkyl ester. ZELEC TY^TMIs a neutralized, water-soluble anionic phosphate ester containing a low molecular weight fatty alcohol backbone.

In a preferred embodiment, the at least one antistatic agent is added to the second fluid in an amount of about 0.01 vol% to about 10 vol%, more preferably, the at least one antistatic agent is added to the second fluid in an amount of about 0.05 vol% to about 5 vol%, and most preferably, the at least one antistatic agent is added to the second fluid in an amount of about 0.1 vol% to about 1 vol%.

Examples

Laboratory experiments confirmed the effective volume shrinkage of the methyl methacrylate mixture in the emulsion polymerization process and by the following example, the process proved to be effective in an apparatus that maintained the volume constant while monitoring the pressure during the heating cycle (example 1), and in field trials using a 500 foot test well (example 2). A field test using a second fluid containing methyl methacrylate and an antistatic agent was conducted using a 500 foot test well (example 3).

Example 1

The pressure vessel (bomb) is filled with an aqueous fluid at 200psig start-up pressure. The container was then sealed to prevent the fluid from escaping from the container and heated from 24 ℃ to 100 ℃. As shown in fig. 3, the pressure of the fluid within the vessel increased to 14,000psig during the heating cycle.

The pressure vessel used above was filled at 200psig start-up pressure with an aqueous emulsion fluid containing 20% volume fill of methyl methacrylate (with azo-type initiator). The container was then sealed to prevent the fluid from escaping from the container and heated from 24 ℃ to 100 ℃. As shown in fig. 3, the pressure of the fluid within the vessel increased to about 3000psig, but at a lower rate than the aqueous fluid alone. Polymerization of the methyl methacrylate monomer is initiated at about 70 ℃, and the pressure within the vessel is reduced to less than the initial pressure within the vessel.

Example 2

Scale up field trials were also performed. Water was used for 500 foot deep test wells in the annular space bounded by 7 inch and 9-5/8 inch casing. After placing the fluid, the annular space was pre-pressurized to 500psig and then heated by circulating hot water inside the 7 inch tube. Over a 2 hour period, the temperature input was 190 ° F and the temperature output was 160 ° F (due to heat absorption by the lower void formation). The resulting pressure was about 2100psig (figure 4).

A similar emulsion fluid as described in example 1, containing 20% volume-fill of methyl methacrylate (with azo-type initiator), was used for the same test well. Within minutes after the initial 500 pre-pressurization, it was noted that the pressure had dropped to zero, so the annulus was again pressurized to 500 psig. During the 2 hours, the temperature rose as previously described, and it was noted that the input and output temperatures were almost the same due to the heat generated by the polymerization reaction. The pressure was again reduced to zero and then slowly increased to a final stable pressure of 240psig (figure 4). The significant drop in pressure is due to monomer to polymer shrinkage. Samples collected at the end of the experiment were analyzed for monomers and polymers. The presence of traces of monomer (< 1%) was confirmed and the polymer had a weight average molecular weight close to 3 million.

Example 3

A similar emulsion fluid as described in example 1 but also containing an antistatic agent was used for scale up field trials. The emulsion fluid contained 20% volume-filled methyl methacrylate (with azo-type initiator) and 1% volume-filled Dupont Zelec TY or Zelec UN (Dupont, Wilmington, DE). The emulsion fluid was used for a 500 foot deep test well in the annular space bounded by 7 inch and 9-5/8 inch casing. After placing the fluid, the annular space was pre-pressurized to 500psig and then heated by circulating hot water inside the 7 inch tube. The temperature input was increased over a period of 2 hours. The pressure is reduced due to monomer to polymer shrinkage. The antistatic agent prevents any build up of static charge.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims

1. A method of controlling pressure and reducing static charge buildup within a confined volume comprising:

c) sealing the volume to create a confined volume; and

wherein the polymerizable monomer is polymerized at a temperature between the first temperature and the second temperature, and

wherein polymerization of the polymerizable monomer is accompanied by a reduction in pressure within the confined volume such that the second pressure is lower than the pressure at the second temperature when the confined volume contains only the first fluid.

2. The method of claim 1, wherein the volume is an annular volume.

3. The method of claim 1, wherein the annular volume is described by two concentric casing strings within the wellbore.

4. The method according to claim 1, wherein the first temperature is in the range of 0 ° F to 100 ° F.

5. The method according to claim 1, wherein the second temperature is in the range of 50 ° F to 300 ° F.

6. The method according to claim 5, wherein the second temperature is in the range of 125 ° F to 250 ° F.

7. The method of claim 1, wherein the fluid within the confined volume of step (c) is at a first pressure and a first temperature.

8. The method of claim 1, wherein the first pressure is the maximum pressure of the first fluid within the volume of step (a), wherein the second pressure is the maximum pressure of the fluid within the volume of step (d).

9. The method of claim 1, wherein a first pressure of the fluid within the volume of step (a) at a first temperature is at a selected location within the volume, and wherein a second pressure of the fluid within the volume of step (d) at a second temperature is at said selected location within the volume.

10. The method according to claim 1, wherein the polymerizable monomer is selected from the group consisting of acrylates and methacrylates.

11. The method according to claim 1, wherein the polymerization of the polymerizable monomer is initiated by an initiator selected from the group consisting of: azo type initiator, peroxide initiator or ammonium persulfate/N, N, N ', N' -tetramethylethylenediamine redox initiator system.

12. The method according to claim 1, wherein the antistatic agent has a hydrophilic group and a hydrophobic group.

13. The process according to claim 1, wherein the antistatic agent is a neutral and/or ionic surfactant.

14. The process according to claim 1, wherein the antistatic agent is an anionic phosphate ester.

15. The method according to claim 14, wherein the antistatic agent is selected from ZELEC TY^TM、ZELECUN^TMAnd mixtures thereof.

16. The process according to claim 1, wherein the antistatic agent is selected from the group consisting of dioctadecyl dimethyl ammonium chloride, ditallowdimethyl ammonium chloride, dihexadecyl dimethyl ammonium chloride, bis (docosyl) dimethyl ammonium chloride, didodecyl dimethyl ammonium chloride, ditallowdimethyl ammonium bromide, dioleyldimethyl ammonium hydroxide, ditallowdiethyl ammonium chloride, ditallowdimethyl dipropyl ammonium bromide, ditallowdimethyl ammonium fluoride, hexadecyldecylmethylethyl ammonium chloride, bis [ ditallowdimethyl ammonium ] sulfate, tris [ ditallowdimethyl ammonium ] phosphate and mixtures thereof.

17. The method according to claim 1, wherein the antistatic agent is added to the second fluid in an amount of about 0.05 vol% to about 5 vol% of the total volume of the second fluid.

18. The method according to claim 1, wherein the antistatic agent is added to the second fluid in an amount of about 0.1 vol% to about 1 vol% of the total volume of the second fluid.

19. A method of controlling pressure and reducing static charge buildup within a casing structure of a wellbore, comprising:

b) replacing at least a portion of the first fluid within the annular volume with a second fluid comprising (i) a monomer that polymerizes at a temperature between the second pressure, the first temperature, and the second temperature, and (ii) at least one antistatic agent;

c) sealing the annular volume to create a confined volume; and

20. The method of claim 19, wherein the second pressure is at most 50% higher than the first pressure.

21. The method according to claim 19, wherein the second pressure is at most 30% higher than the first pressure.

22. The method of claim 19, wherein the second pressure is at most 15% higher than the first pressure.

23. The method of claim 19, wherein the second pressure is equal to the first pressure.

24. The method according to claim 19, wherein the antistatic agent has a hydrophilic group and a hydrophobic group.

25. The process according to claim 19, wherein the antistatic agent is a neutral and/or ionic surfactant.

26. The method according to claim 19, wherein the antistatic agent is an anionic phosphate ester.

27. The method according to claim 26, wherein the antistatic agent is selected from ZELEC TY^TM、ZELECUN^TMAnd mixtures thereof.

28. The method according to claim 19, wherein the antistatic agent is selected from the group consisting of dioctadecyl dimethyl ammonium chloride, ditallowdimethyl ammonium chloride, dihexadecyl dimethyl ammonium chloride, bis (docosyl) dimethyl ammonium chloride, didodecyl dimethyl ammonium chloride, ditallowdimethyl ammonium bromide, dioleyldimethyl ammonium hydroxide, ditallowdiethyl ammonium chloride, ditallowdimethyl dipropyl ammonium bromide, ditallowdimethyl ammonium fluoride, hexadecyldecylmethylethyl ammonium chloride, bis [ ditallowdimethyl ammonium ] sulfate, tris [ ditallowdimethyl ammonium ] phosphate and mixtures thereof.

29. The method according to claim 19, wherein the antistatic agent is added to the second fluid in an amount of about 0.05 vol% to about 5 vol% of the total volume of the second fluid.

30. The method according to claim 19, wherein the antistatic agent is added to the second fluid in an amount of about 0.1 vol% to about 1 vol% of the total volume of the second fluid.

31. A method of controlling pressure and reducing static charge buildup within a casing structure of a wellbore, comprising:

a) providing an annular volume described by two casing strings within a wellbore and containing a first fluid having a first maximum pressure at a first temperature within the annular volume;

c) sealing the annular volume to create a confined volume; and

32. The method according to claim 31, wherein the antistatic agent has a hydrophilic group and a hydrophobic group.

33. The method according to claim 31, wherein the antistatic agent is a neutral and/or ionic surfactant.

34. The method according to claim 31, wherein the antistatic agent is an anionic phosphate ester.

35. The method according to claim 34, wherein the antistatic agent is selected from ZELEC TY^TM、ZELECUN^TMAnd mixtures thereof.

36. The method according to claim 31, wherein the antistatic agent is selected from the group consisting of dioctadecyl dimethyl ammonium chloride, ditallowdimethyl ammonium chloride, dihexadecyl dimethyl ammonium chloride, bis (docosyl) dimethyl ammonium chloride, didodecyl dimethyl ammonium chloride, ditallowdimethyl ammonium bromide, dioleyldimethyl ammonium hydroxide, ditallowdiethyl ammonium chloride, ditallowdimethyl dipropyl ammonium bromide, ditallowdimethyl ammonium fluoride, hexadecyldecylmethylethyl ammonium chloride, bis [ ditallowdimethyl ammonium ] sulfate, tris [ ditallowdimethyl ammonium ] phosphate and mixtures thereof.

37. The method according to claim 31, wherein the antistatic agent is added to the second fluid in an amount of about 0.05 vol% to about 5 vol% of the total volume of the second fluid.

38. The method according to claim 31, wherein the antistatic agent is added to the second fluid in an amount of about 0.1 vol% to about 1 vol% of the total volume of the second fluid.

39. A method of controlling pressure and reducing static charge buildup within a confined volume comprising:

a) providing a volume containing a first fluid and a second fluid at a first pressure and a first temperature, the second fluid comprising (i) a monomer that polymerizes at a temperature between the first temperature and a second temperature, and (ii) at least one antistatic agent;

b) sealing the volume to create a confined volume;

40. The method according to claim 39, wherein the antistatic agent has a hydrophilic group and a hydrophobic group.

41. The method according to claim 39, wherein the antistatic agent is a neutral and/or ionic surfactant.

42. The method according to claim 39, wherein the antistatic agent is an anionic phosphate ester.

43. The method according to claim 42, wherein the antistatic agent is selected from ZELEC TY^TM、ZELECUN^TMAnd mixtures thereof.

44. The method according to claim 39, wherein the antistatic agent is selected from the group consisting of dioctadecyl dimethyl ammonium chloride, ditallowdimethyl ammonium chloride, dihexadecyl dimethyl ammonium chloride, bis (docosyl) dimethyl ammonium chloride, didodecyl dimethyl ammonium chloride, ditallowdimethyl ammonium bromide, dioleyldimethyl ammonium hydroxide, ditallowdiethyl ammonium chloride, ditallowdimethyl dipropyl ammonium bromide, ditallowdimethyl ammonium fluoride, hexadecyldecylmethylethyl ammonium chloride, bis [ ditallowdimethyl ammonium ] sulfate, tris [ ditallowdimethyl ammonium ] phosphate and mixtures thereof.

45. The method according to claim 39, wherein the antistatic agent is added to the second fluid in an amount of about 0.05 vol% to about 5 vol% of the total volume of the second fluid.

46. The method according to claim 39, wherein the antistatic agent is added to the second fluid in an amount of about 0.1 vol% to about 1 vol% of the total volume of the second fluid.

47. A method of controlling pressure and reducing static charge buildup in an annular volume within a wellbore, comprising:

a) filling the annular volume with a first fluid;

c) the annular volume is sealed.

48. The method according to claim 47, wherein the polymerization system comprises a monomer selected from the group consisting of acrylates and methacrylates.

49. The method of claim 47, wherein the polymerization system comprises an initiator selected from the group consisting of: azo type initiator, peroxide initiator or ammonium persulfate/N, N, N ', N' -tetramethylethylenediamine redox initiator system.

50. The method according to claim 47, wherein the antistatic agent has a hydrophilic group and a hydrophobic group.

51. The method according to claim 47, wherein the antistatic agent is a neutral and/or ionic surfactant.

52. The method according to claim 47, wherein the antistatic agent is an anionic phosphate ester.

53. The method according to claim 52, wherein the antistatic agent is selected from ZELEC TY^TM、ZELECUN^TMAnd mixtures thereof.

54. The method according to claim 47, wherein the antistatic agent is selected from the group consisting of dioctadecyl dimethyl ammonium chloride, ditallowdimethyl ammonium chloride, dihexadecyl dimethyl ammonium chloride, bis (docosyl) dimethyl ammonium chloride, didodecyl dimethyl ammonium chloride, ditallowdimethyl ammonium bromide, dioleyldimethyl ammonium hydroxide, ditallowdiethyl ammonium chloride, ditallowdimethyl dipropyl ammonium bromide, ditallowdimethyl ammonium fluoride, hexadecyldecylmethylethyl ammonium chloride, bis [ ditallowdimethyl ammonium ] sulfate, tris [ ditallowdimethyl ammonium ] phosphate and mixtures thereof.

55. The method according to claim 47, wherein the antistatic agent is added to the second fluid in an amount of about 0.05 vol% to about 5 vol% of the total volume of the second fluid.

56. The method according to claim 47, wherein the antistatic agent is added to the second fluid in an amount of about 0.1 vol% to about 1 vol% of the total volume of the second fluid.