RU2667255C1 - Method of hydraulic fracturing of a reservoir - Google Patents

Abstract

FIELD: oil and gas industry.SUBSTANCE: invention relates to the petroleum industry and can be used in the hydraulic fracturing of a carbonate formation or a reservoir of high viscosity oil. Method includes perforating the walls of the well in its necessary interval with channels of a depth not less than the extent of the stress concentration zone in the rocks from the wellbore, draining the pipe string into the fracturing zone, sealing the annular space with a packer above the perforation interval, pumping a gel-like fracturing fluid and acid in portions along the tubing string, aging, removal of acid reaction products from the rock, unpacking the packer, and extracting it from the tubing string from the well. According to the invention, a gel-like fracturing fluid is injected with 1 ton of quartz sand with a stepwise increase in the concentration of quartz sand during the injection of the gel-like fracturing fluid. Further, a cyclic injection of the sulfamic acid composition in 4 cycles is performed with an increase in the portion of the injected composition of sulfamic acid by 1.5 mwith each cycle. At the end of the injection of the last portion of the sulfamic acid composition, COin the liquid state in a volume of 10 % of the total volume of the sulfamic acid composition. Then, a 2 % aqueous KCl solution is extruded in a volume of 1.1 from the volume of the well. In the process, all components are pumped with a single flow rate, stop the fracturing process, hold for 24 hours, the pressure is gradually depressurized to zero at 5.0 MPa with an exposure time of 10 min, the reaction products of the acid are removed from the rock formation by swabbing, the packer is unpacked and extracted with the tubing string from the well.EFFECT: technical result is to increase fracture growth during fracturing; increasing the efficiency of the method in carbonate reservoirs and deposits of high-viscosity oil; increasing the productivity of the well in its subsequent operation; preservation of reservoir properties of the bottomhole formation zone; reduction of wear of the equipment used.1 cl

Description

The invention relates to the oil industry and may find application in hydraulic fracturing of a carbonate formation or deposits of high viscosity oil.

A known method of hydraulic fracturing of a carbonate formation (patent RU No. 2460875, IPC ЕВВ 43/26, publ. 09/10/2012, bull. No. 25), including the descent into the well of a string of tubing with a packer and its subsequent landing , descending into the tubing string string of flexible pipes (GT) below the lower end of the tubing, pumping water-insulating cement along the GT, hydraulic fracturing of the carbonate formation with bottom water. According to the method, the lower end of the GT is lowered to the level of the oil-water contact (WOC), the space between the tubing strings and the HT is sealed, the injection of water-insulating cement through the HT is used to isolate the bottom water in the carbonate formation with the well being poured from the bottom to the level of the WOC. The space between the tubing and GT columns is depressurized and the GT column is lifted so that its lower end is 1-2 m below the roof of the carbonate formation, after which the total volume of fracturing fluid (V _g ) is determined, the space between the tubing and GT columns is sealed. The first portion of the fracture fluid is injected into the GT in a volume of 60-70% of the total volume (V _g ) under a pressure of not more than 25 MPa and at a speed of not more than 2 m ³ / min, after which the remaining volume of the fracture fluid is pumped into the GT in 3- 5 cycles, alternating with the injection of a proppant, which is used as 25% hydrochloric inhibited acid. The volume of acid is determined depending on the thickness of the productive part of the carbonate formation, based on the volume of 0.2 m ^{3 of} acid per 1 m of thickness of the formation for each injection cycle. At the end of the last injection cycle, acid is pumped with an aqueous solution of a surfactant in the volume of the HT column, followed by 1-2 hours, after which the GT column is removed from the tubing string. Launch the well into operation.

The disadvantages of this method are:

- firstly, the low efficiency of its implementation in carbonate reservoirs and deposits of highly viscous oil due to the high reaction rate and the short range of penetration of unreacted acid into the formation and the formation of persistent emulsions in the bottomhole formation zone;

- secondly, the restriction of crack growth during hydraulic fracturing due to high frictional pressure losses in perforations and the presence of small competing cracks;

- thirdly, the duration of the implementation of the method associated with the need to lower the tubing string into the tubing string below the lower end of the tubing, sealing (depressurization) of the space between the tubing string and the tubing string, moving the tubing string inside the tubing string during the process;

- fourthly, a decrease in the reservoir properties of the bottomhole formation zone due to precipitation of insoluble sediments from the reaction products;

fifthly, intensive wear of the equipment used due to the formation of organochlorine compounds, leading to corrosion of the equipment.

The closest in technical essence and the achieved result is a method of hydraulic fracturing of a carbonate formation (hydraulic fracturing) in a well (patent RU No. 2455478, IPC ЕВВ 43/26, published on July 10, 2012, Bull. No. 19), including perforation of the walls of the well in the required interval of the borehole with channels of depth not less than the length of the zone of stress concentration in the rocks from the borehole, the descent of the pipe string into the hydraulic fracturing zone with the packer sealing the annulus above the perforation interval and cyclic injection of a gel-like fracturing fluid into the borehole. Before hydraulic fracturing, the well is filled with process fluid for 0.2-0.4 wellbore volumes. The total volume of injected gel-like fracturing fluid is calculated by the formula:

V _g = k⋅H _p ,

where V _g - the volume of the gel-like fluid rupture, m ³ ;

k is the conversion coefficient, m ³ / m (k = 1.4-1.6);

N _p - reservoir height, m,

moreover, the gel-like liquid of rupture is pumped in equal portions in 3-5 cycles with the injection of acid portions of 0.7-0.75 volumes of the gel-like liquid of rupture after them. At the end of the last injection cycle, salable oil or fresh water is pumped into a 1.5-fold volume of the pipe string, followed by 1-2 hours. The reaction products of the acid with the rock are removed, the packer is removed and it is removed from the pipe string from the well.

The disadvantages of the method:

- firstly, the restriction of crack growth during hydraulic fracturing due to the high pressure loss due to friction in the perforations and the presence of small competing cracks;

- secondly, the low efficiency of the implementation of the method in carbonate reservoirs and deposits of highly viscous oil due to the high reaction rate and the short range of penetration of unreacted acid into the formation and the formation of persistent emulsions in the bottomhole formation zone;

- thirdly, low well productivity after hydraulic fracturing, associated with incomplete removal of reaction products from the fracture and low permeability of the resulting hydraulic fracture;

- fourthly, a decrease in the reservoir properties of the bottom-hole formation zone after hydraulic fracturing due to precipitation of insoluble sediments from the reaction products;

fifthly, intensive wear of the equipment used during hydraulic fracturing due to the formation of organochlorine compounds, leading to corrosion of the equipment.

The technical objectives of the invention are to increase crack growth during hydraulic fracturing, increase the efficiency of the method in carbonate reservoirs and high-viscosity oil reservoirs, increase well productivity after hydraulic fracturing, preserve reservoir properties of the bottom-hole formation zone after hydraulic fracturing, and reduce wear on equipment used during hydraulic fracturing.

The stated technical problems are solved by the method of hydraulic fracturing - hydraulic fracturing in a well, including perforation of the walls of the well in the required interval of the well with channels at least the depth of the stress concentration zone in the rocks from the well bore, the descent of the pipe string into the hydraulic fracturing zone with the packer sealing the annulus above the perforation interval, injection of gelled fracture and acid gel in portions along the pipe string into the well, aging, removal of the reaction products of the acid with the rock, unpacking the packer extracting it from the tubular string from the well.

What is new is that a gel-like fracturing fluid is injected from 1 ton of quartz sand with a stepwise increase in the concentration of silica sand during the injection of the gel-like fracturing fluid, then the composition of sulfamic acid is cyclically injected in 4 cycles with an increase in the portion of the injected composition of sulfamic acid by 1.5 m ³ with each cycle at the end of injection of the last portion of the composition of sulfamic acid is pumped into the well CO ₂ in a liquid state at 10% of the total composition of sulfamic acid, and then pressurize a 2% aqueous KCl solution in a volume of 1.1 of the well’s volume, while during the hydraulic fracturing process, all components are pumped with the same flow rate, the hydraulic fracturing process is stopped, the shutter speed is held for 24 hours, and the pressure is relieved to zero by 5.0 MPa with a holding time of 10 min, remove the reaction products of the acid with the formation rock by swabbing, unpack the packer and remove it from the pipe string from the well.

The proposed hydraulic fracturing method is implemented as follows.

Perforation of the walls of the well is carried out by channels with a depth not less than the extent of the zone of stress concentration in the rocks from the wellbore. Next, into the well, into the hydraulic fracturing zone, the pipe string with the packer is lowered so that the packer is 5-10 m above the roof of the formation to be fractured, after which the annulus is sealed, i.e. they make a landing packer of any known design, for example a packer with a mechanical axial installation of any manufacturer.

Determine the volume of injected gel-like fracturing fluid:

V _g = k⋅N _p ,

where V _g - the volume of the gel-like fluid rupture, m ³ ;

k is the conversion coefficient, m ³ / m (k = 1.4-1.6);

N _p - the height of the reservoir, m

For example, the height of the reservoir N _p is 5 m. Then, substituting the value in the formula, we obtain the volume of the injected gel-like fracturing fluid:

V _g = 1.4-1.6 m ³ / m⋅5 m = 7-8 m ³ .

We take the total volume of injected gel-like fracture fluid

V _g = 8 m ³ .

As a gel-like fracturing liquid, known crosslinked or linear gels are used, for example, developed by Khimekogang CJSC.

The procedure for the preparation of gelled liquid and its injection using the pump unit CA-320 is described in patent RU No. 2358100, IPC Е21В 43/26, publ. 06/10/2009, bull. No. 16. As an additional example of the use of a gel-like liquid, the use of a structured hydrocarbon gel-like composition for hydraulic fracturing, described in patent No. 2043491 IPC ЕВВ 43/26, publ. 09/10/1995, bull. Number 25.

After sealing the annular space with a packer along the pipe string into the under-packer space of the well, a gel-like fracturing fluid is injected in a volume of 8 m ³ from 1 t of silica sand with a stepwise increase in the concentration of silica sand in the gel-like fluid during the injection, for example, from 110 to 140 kg / m ³ , namely:

- 2 m ³ gelled fracturing fluids with quartz sand at a concentration of 110 kg / m ^3:

2 m ³ ⋅110 kg / m ³ = 220 kg;

- 2 m ³ gel-like fluid rupture with quartz sand at a concentration of 120 kg / m ³ :

2 m ³ ⋅120 kg / m ³ = 240 kg;

- 2 m ³ gel-like fracturing fluid with silica sand at a concentration of 130 kg / m ³ :

2 m ³ ⋅130 kg / m ³ = 260 kg;

- 2 m ³ gel-like fracturing fluid with silica sand at a concentration of 140 kg / m ³ :

2 m ³ ⋅140 kg / m ³ = 280 kg.

Total injected (2 m ³ + 2 m ³ + 2 m ³ + 2 m ³ ) = 8 m ^{3 of} gel-like liquid with a gap of (220 kg + 240 kg + 260 kg + 280 kg) = 1000 kg = 1 ton of quartz sand.

The injection of a gel-like liquid with quartz sand at the beginning of the hydraulic fracturing process allows the perforations to be processed in order to reduce friction (to reduce injection pressure loss) and to block small competing cracks with quartz sand, which in general allows increasing the initial crack growth in the future (during cyclic injection of sulfamic composition acid).

Next, produce a cyclic injection of the composition of sulfamic acid. To do this, determine the total volume of the injected composition of sulfamic acid according to the formula:

V _k = k⋅H _p ,

where V _to - the volume of the composition of sulfamic acid, m ³ ;

k is the transfer coefficient (obtained experimentally), m ³ / m (k = 4-5);

N _p - the height of the formation susceptible to hydraulic fracturing, m

As noted above, the height of the reservoir N _p equal to 5 m

Then, substituting the numerical values in the formula, we get:

V _к = k⋅Н _p = 4-5 m ³ / m ⋅ 5 m = 20-25 m ³ .

We take V _to = 21 m ³ .

The composition of sulfamic acid contains in 1 m ^{3 the} following substances,%:

- sulfamic acid - 10%;

- ammonium organic salt - 3%;

- nonionic surfactant - 1%;

- anionic surfactant - 1%;

- xanthan gum - 0.1%;

- water - the rest.

Sulfamic acid (GOST 5821-78) is a substance that is a colorless crystals of a rhombic shape. The formula of this compound is NH ₂ SO ₂ OH or NH ₂ SO ₃ H; it has a density of 2.126 kg / m ³ .

Ammonium organic salt (GOST 17444-2016) - colorless crystalline substances, well soluble in water.

As nonionic surfactants (GAS) (GOST 25163-82), for example, ethoxylates of alcohols, alkanolamides of fatty acids are used. Nonionic surfactants are used in combination with anionic surfactants as a secondary purifier, as well as a thickener and stabilizer of sulfamic acid composition.

As anionic surfactants (GOST 30828-2002), for example, alkyl benzene sulfonates, alcohol sulfoethoxylates, fatty alcohol sulfates, alkanesulfonates, alpha oleinsulfonates are used.

Xanthan gum (xanthan gum) (GOST 33333-2015) - a natural polysaccharide obtained by fermentation of glucose by microorganisms of the genus Xanthomonas campestris, belongs to the group of stabilizers. The use of xanthan allows you to get a more stable and plastic structure of the finished composition of sulfamic acid, increasing elasticity and viscosity.

Technical water with a density of 1000 kg / m ³ .

Then, at the wellhead, a composition of sulfamic acid is prepared, and the above chemicals are imported.

In the tank located at the wellhead, add the above chemicals in the following sequence in the following volume:

- sulfamic acid (10% ⋅21 m ³ ) / 100% = 2.1 m ³ ;

- ammonium organic salt (3% ⋅21 m ³ ) / 100% = 0.63 m ³ ;

- nonionic surfactant (1% ⋅21 m ³ ) / 100% = 0.21 m ³ ;

- anionic surfactant (1% ⋅21 m ³ ) / 100% = 0.21 m ³ ;

- xanthan gum (0.1% ⋅21 m ³ ) / 100% = 0.021 m ³ ;

- water (technical) (84.9% ⋅21 m ³ ) / 100% = 17.829 m ³ .

Next, the above chemicals are mixed in a container.

Also wellhead CO ₂ is brought in the liquid state.

Further produce cyclic download composition sulfamic acid in 4 cycles, with increasing portions of the injected composition sulfamic acid per 1.5 m ³ with each cycle (see. Table).

An increase in the portions of the injected sulfamic acid composition by 1.5 m ³ with each cycle allows the acid to be pushed deeper into the reservoir, widening the fracture.

Sulfamic acid used in the implementation of this method allows you to save the reservoir properties of the bottomhole formation zone due to the absence of insoluble sediments in the reaction products, since the reaction products are highly soluble and do not reduce the permeability of the fracture, in addition, low temperatures are sufficient for the reaction to proceed (about 30 ° FROM).

At the end of the injection of the fourth portion of the sulfamic acid composition, carbon dioxide CO ₂ in the liquid state is pumped into the well in a volume of 10% of the total volume of sulfamic acid composition, i.e.

Substituting the numerical values in the formula, we get:

Injection of liquid CO ₂ allows the acid to be pushed further into the fractured formation during the fracturing process.

Then push 2% aqueous KCl solution in a volume of 1.1 of the well volume, for example 13 m ³ .

2% aqueous KCl solution contains:

- KCl - 2%, i.e. (2% ⋅13 m ³ ) / 100% = 0.26 m ³ ;

- water (technical) - 98%, i.e. (98% ⋅13 m ³ ) / 100% = 12.74 m ³ .

A 2% aqueous KCl solution is prepared in a container at the mouth by mixing the components in the proportions indicated above, or delivered to the well in a tank truck in the finished form. In the process of hydraulic fracturing, all components are pumped with one flow rate, as indicated in the table, with a flow rate of 2.5 m ³ / min.

They stop the hydraulic fracturing process, hold for 24 hours.

Gradually bleed pressure to zero at 5.0 MPa with a shutter speed of 10 minutes. For example, the pressure of the end of the sale is 25.0 MPa, can withstand 10 minutes; vent to 20 MPa, incubated for 10 minutes; vent to 15 MPa, incubated for 10 minutes; bleed to 10 MPa, incubated for 10 minutes; vent to 5 MPa, incubated for 10 minutes; then bleed to zero.

Stepwise pressure relief after completion of hydraulic fracturing at 5.0 MPa with a shutter speed of 10 min ensures a smooth transition of carbon dioxide CO ₂ from liquid to gaseous state. This provides a more complete removal of reaction products from the fracture and improves the permeability of the resulting hydraulic fracture, which increases the productivity of the well during its subsequent operation.

The reaction products of the acid with the formation rock are removed by swabbing using a geophysical elevator.

Unpack the packer and remove it with the pipe string from the well.

The efficiency of the method implementation in carbonate reservoirs and high-viscosity oil deposits increases due to the possibility of transporting the reacted sulfamic acid along the hydraulic fracture to the far zones of the formation due to the low dissolution rate of carbonate rocks, which increases the radius of impact on the formation. In addition, during hydraulic fracturing in highly viscous oil deposits, formation of persistent emulsions in the bottomhole formation zone after hydraulic fracturing is excluded.

In the proposed method, in contrast to the prototype, where hydrochloric acid is used, chlorine-free acid (sulfamic acid) is used, which eliminates the formation of corrosive organochlorine compounds, thereby reducing the wear of equipment used in the hydraulic fracturing process. In addition, the low corrosivity of sulfamic acid eliminates the use of corrosion inhibitors.

The proposed method of hydraulic fracturing allows you to:

- increase crack growth during hydraulic fracturing;

- increase the efficiency of the method in carbonate reservoirs and deposits of high viscosity oil;

- increase well productivity during its subsequent operation;

- save the reservoir properties of the bottomhole formation zone;

- reduce the wear of the equipment used.

Claims (1)

The method of hydraulic fracturing - hydraulic fracturing in a well, including perforation of the walls of the well in the required interval of the well with channels of depth not less than the length of the stress concentration zone in the rocks from the wellbore, lowering the pipe string into the hydraulic fracturing zone with the packer sealing the annulus above the perforation interval, injecting portions along the column pipes into the well of a gel-like fracturing fluid and acid, holding, removing the reaction products of the acid with the rock, unpacking the packer and removing it from the pipe string from the well, characterized in that a gel-like fracturing fluid is pumped from 1 ton of quartz sand with a stepwise increase in the concentration of silica sand during the injection of the gel-like fracturing fluid, then the composition of sulfamic acid is cyclically injected in 4 cycles with an increase in the portion of the injected composition of sulfamic acid by 1.5 m ³ s each cycle, after the last portion of the injection composition of sulfamic acid is pumped into the well CO ₂ in a liquid state at 10% of the total composition of sulfamic acid, and then pressurize a 2% aqueous KCl solution in a volume of 1.1 of the well’s volume, while during the hydraulic fracturing process, all components are pumped with the same flow rate, the hydraulic fracturing process is stopped, the shutter speed is held for 24 hours, and the pressure is relieved to zero by 5.0 MPa with a holding time of 10 min, remove the reaction products of the acid with the formation rock by swabbing, unpack the packer and remove it from the pipe string from the well.