CN119827547A - Method for calculating shale movable oil saturation based on nuclear magnetism-centrifugation principle - Google Patents
Method for calculating shale movable oil saturation based on nuclear magnetism-centrifugation principle Download PDFInfo
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Abstract
The invention relates to the technical field of reservoir evaluation in petroleum geological exploration and deposition reservoirs, in particular to a method for calculating shale movable oil saturation based on a nuclear magnetism-centrifugation principle, which comprises the steps of processing a sample after oil washing, preparing sample by utilizing crude oil and natural gas based on underground real gas-oil ratio to obtain prepared crude oil, pressurizing and saturating the prepared crude oil to obtain a saturated oil core sample, calculating the total pore volume V of the core under the real underground temperature and pressure condition, obtaining the total volume V 1 of the saturated oil core sample under the normal temperature and pressure condition, calculating the oil saturation S 1 of a light hydrocarbon loss part under the room temperature condition, calculating the ground movable fluid saturation S 2, and finally calculating the real movable oil saturation S of the shale. By the method, the gas-oil ratio is recovered under the condition closer to the geological reality, the viscosity of crude oil can be reduced, the condition is closer to the reality, the experimental error is reduced to the greatest extent, and the calculation result is more accurate.
Description
Technical Field
The invention relates to the technical field of reservoir evaluation in petroleum geological exploration and deposition reservoirs, in particular to a method for calculating shale movable oil saturation based on a nuclear magnetism-centrifugation principle.
Background
The increasing rise of energy demands and the continuous consumption of conventional oil gas resources make the contradiction between oil gas supply and demand increasingly prominent. Therefore, unconventional energy sources are increasingly gaining importance, shale oil being an important component. At present, shale oil becomes a hotspot for unconventional exploration and development, and compared with a conventional oil reservoir, the shale oil reservoir is rich in organic matters, various in pore types, and complex in spatial structure, and the exploration strength is enhanced at home and abroad. Shale oil is a typical unconventional resource, the mobility of the shale oil is an important factor for influencing whether an oil reservoir can be put into development and production, the shale oil mobility evaluation is one of the essential steps of shale oil exploration, the final purpose of the shale oil exploration is to guide the scale development of soluble organic matters in a shale layer, and the shale oil mobility evaluation is one of key reference factors for determining the favorable enrichment layer section of the shale oil.
At present, the shale oil exists in the shale layer mainly in three forms of a free state, an adsorption state and a dissolution state, but the shale oil which can be mined under the current technical conditions is mainly free shale oil, and the constraint oil is difficult to have practical utilization value, so the quantitative evaluation of the saturation degree of the free shale oil (movable oil) is the most core content in the shale oil research. The shale oil mobility quantitative characterization method currently and commonly used mainly comprises an empirical method, multi-temperature-stage pyrolysis, a geochemical parameter method, an adsorption-free oil model method, a nuclear magnetic resonance-high-speed centrifugation method, a numerical simulation method and a gas chromatography-mass spectrometry (GC-MS) technology.
The multi Wen Jiere solutions, the geochemistry parameter method and the gas chromatography-mass spectrometry (GC-MS) technology require a large amount of geochemistry experimental data to draw parameter change trend graphs, so that the movable oil saturation of shale oil in different evolution stages is quantitatively represented, the required data amount is large, the cost is high, and the application effect is good in an exploration maturation area. The adsorption-free oil model method, the numerical simulation method and the molecular dynamics simulation are all based on the idealized state for simulation, and have large human factors and poor representativeness. The movable oil quantity obtained by empirical calculation is a theoretical value, the oil saturation index is a shale oil mobility evaluation parameter based on North American sea shale oil exploration and development practice, and has great difference with the land shale layer in China in terms of mineral composition, organic matters and the like, and whether the limit of the oil saturation index of 100mg/g is suitable for land shale oil mobility evaluation is also controversial. The multi-temperature-stage pyrolysis method has the advantages that the amount of samples required by experiments is small (2 mg), the original structure of rock is damaged by powdery samples, the real underground environment under the conditions of high temperature and high pressure cannot be simulated, the seepage performance of crude oil in the underground is difficult to judge, and therefore, the movable condition of the crude oil cannot be determined.
Nuclear magnetic resonance technology is an important research means for calculating the porosity of a reservoir and representing the pore structure, and can obtain the numerical value of the movable porosity through nuclear magnetic measurement before and after core centrifugation, but is less applied to the aspect of saturation research. The nuclear magnetic resonance technology is characterized in that a pore classification method is formulated according to the relation between the transverse relaxation time T2 of the rock and the pore radius r and according to a T2 energy spectrum distribution diagram, the internal pore distribution rule of the rock can be analyzed based on the relaxation characteristics of the fluid, and the basic physical characteristics of the rock can be accurately measured. At this time, if a radio frequency field with a certain frequency (larmor frequency) is applied to the sample, nuclear magnetic resonance is generated, a signal whose amplitude decays exponentially with time can be received after the radio frequency field is removed, and the decay degree of the signal can be described by the transverse relaxation time T2. After the high-speed centrifugation experiment, crude oil still existing in the core after centrifugation can be regarded as the immovable oil, crude oil which is centrifuged out at a high speed is regarded as movable oil, the numerical value of the movable porosity is obtained through nuclear magnetism measurement before and after the core is centrifuged, and the method for testing the saturation of the movable oil by combining the nuclear magnetism and the centrifugation experiment is economical and efficient in performability and is the best scheme for solving the problem of the saturation of the shale movable oil under the current technical conditions. For example, in a Ji-Texal shale oil reservoir, nuclear magnetic resonance results are measured through an oil flooding experiment using a rock sample, 3 types of adsorbed water, adsorbed oil and free oil which are generated by shale oil are provided, wettability characteristics of macroporous oleophylic oil and hydrophilic water and a crude oil generation mode are provided, a cut-off value is determined through a nuclear magnetic experiment result, free oil saturation is calculated, and the application effect is good. However, the method is used for saturating water or chemical reagent (such as MnCl 2) in the rock core, and does not reduce the underground real condition, so that a certain difference exists between the calculated result and the actual condition.
In research on tight reservoirs such as shale, researchers have developed nuclear magnetic resonance-centrifugation methods to study the mobility of crude oil, and the crude oil still present in the core after high-speed centrifugation is regarded as an immovable oil, and crude oil centrifuged at high speed is regarded as a movable oil. In addition, under the high-temperature and high-pressure environment in the underground, the viscosity and the density of shale oil can be changed greatly, as shown in an attached drawing 4 of the specification and an attached drawing 5 of the specification, the current experimental method can not always obtain a relatively real actual environment in the underground, and the obtained result has a great difference from the actual result in the underground.
Disclosure of Invention
In order to solve the technical problems, the invention provides a method for calculating the movable oil saturation of shale based on a nuclear magnetic resonance-centrifugation principle, which recovers the gas-oil ratio under the real condition closer to geology, can reduce the viscosity of crude oil, is closer to the real condition, furthest reduces experimental errors and ensures that the calculation result is more accurate.
The invention is realized by adopting the following technical scheme:
A method for calculating shale movable oil saturation based on a nuclear magnetism-centrifugation principle, which comprises the following steps:
The method comprises the steps of firstly, obtaining an original core sample, washing oil and drying to obtain a washed oil sample, and preparing the sample by utilizing crude oil and natural gas based on the underground real gas-oil ratio to obtain prepared crude oil, wherein the volume of the prepared crude oil is V 0;
vacuumizing the washed oil sample, pressurizing and saturating to prepare crude oil, and obtaining a saturated oil core sample;
Taking out a saturated oil core sample, measuring the volume V' of the residual configuration crude oil, and calculating the total pore volume V of the core under the real underground temperature and pressure condition:
V=V0-V’;
fourthly, performing nuclear magnetic resonance experiments on the saturated oil core sample under the room temperature condition, inverting to obtain a T2 relaxation time spectrum, obtaining the total volume V 1 of the saturated oil core sample under the normal temperature and pressure, comparing the pore volume difference between the room temperature condition and the real underground temperature and pressure condition, and calculating to obtain the oil saturation S 1 of the light hydrocarbon loss part under the room temperature condition:
S1＝(V-V1)/V;
respectively carrying out high-speed centrifugation on the same saturated oil core sample by using different centrifugal rotating speeds, and respectively carrying out nuclear magnetic resonance test after each centrifugation to obtain the optimal centrifugal rotating speed;
Step six, centrifuging all the saturated oil core samples by utilizing the optimal centrifugal rotating speed selected in the step five, then performing nuclear magnetic resonance experiments to obtain a centrifuged core total pore volume V 2, comparing the centrifuged core total pore volume V 2 with the total volume V 1 of the saturated oil core samples at normal temperature and normal pressure in the step four, and calculating to obtain the ground movable fluid saturation S 2:
S2＝(V1-V2)/V1;
Step seven, calculating the true movable oil saturation S of the shale:
S=S1+S2。
the wash oil in the first step specifically refers to extraction of the wash oil by using chloroform.
The sample after oil washing obtained in the first step concretely comprises the steps of drilling an original core sample, extracting the oil washing by using chloroform, drying the core sample in a vacuum drying oven at the temperature of 60 ℃ for 4 hours, and sealing by using a preservative film after cooling to obtain the sample after oil washing.
The step of extracting washing oil with chloroform is to wrap the original core sample with filter paper, load the core sample into the sample chamber of the extractor, then add chloroform into the extractor, extract the original core sample at 75-80 deg.C until the reflux liquid is colorless, then take out the core sample, volatilize chloroform completely at room temperature.
The method for preparing the crude oil comprises the following steps of calculating crude oil and natural gas based on underground real gas-oil ratio, conveying the crude oil and the natural gas to a high-temperature high-pressure sample preparation device, setting corresponding temperature and pressure according to real underground conditions, and keeping the temperature and the pressure constant for 1h to obtain the prepared crude oil.
And the second step is to vacuumize the washed oil sample for over 12h, wherein the vacuumized sample has the pressure P < -0.098Mpa, the vacuum degree reaches 0.1Pa, the saturated crude oil is prepared under pressure, and the saturated core sample is obtained after 12 hours.
And step five, obtaining the optimal centrifugal rotation speed, namely, if the porosity obtained by the previous nuclear magnetic resonance test, the porosity obtained by the next nuclear magnetic resonance test and the porosity data obtained by the previous nuclear magnetic resonance test are multiplied by 100 percent <5 percent, determining the centrifugal rotation speed corresponding to the previous nuclear magnetic resonance test as the optimal centrifugal rotation speed and the corresponding centrifugal force as the optimal centrifugal force.
The fifth step specifically comprises the steps of centrifuging a saturated oil core sample at a centrifugal speed of 5000r/min for one time, performing nuclear magnetic resonance experiment, inverting to obtain a T2 relaxation time spectrum, obtaining porosity, centrifuging at a centrifugal speed of 6000r/min for one time, performing nuclear magnetic resonance experiment, inverting to obtain a T2 relaxation time spectrum, obtaining the porosity, and the like until the optimal centrifugal speed is obtained.
In the fifth step, the centrifugation time is 60min each time.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the calculation method, after the influence of similar compatibility and gas-driven crude oil is fully considered, a more accurate calculation value of the saturation of the movable oil can be obtained, the experimental error is reduced, and the method is more in line with the actual geological condition. Specifically, compared with the old method, the method has the advantage that the calculated movable oil saturation is 3-4 percent higher.
2. According to the invention, the high-temperature high-pressure sample preparation device is utilized to inject natural gas into crude oil with high viscosity in proportion, so that the gas-oil ratio under the condition close to the geological reality is recovered, the viscosity of the crude oil is reduced, the condition is closer to the reality, and the experimental error is reduced to the greatest extent. And the gas-oil ratio of the core sample can be directly changed in the process of directly filling methane gas into the core sample, so that accurate calculation cannot be performed, and the actual mobility of underground crude oil cannot be reflected.
3. According to the invention, the original core sample is subjected to oil washing operation, and the original hydrocarbons in the original core sample can be removed, so that the saturated oil of the core can be more similar to the actual gas-oil ratio in the underground. The chloroform is used for extracting the wash oil, and is an anionic surfactant, so that the chloroform has strong dissolving capacity, is easy to volatilize and is easy to remove.
4. The oil saturation of the core is different at different centrifugal speeds, and gradually decreases when the centrifugal speed is gradually increased. According to the invention, the measured movable fluid saturation is closer to the actual movable oil saturation by calculating the optimal centrifugal rotating speed.
Drawings
The invention will be described in further detail with reference to the drawings and detailed description, wherein:
FIG. 1 is a schematic flow chart of the present invention;
FIG. 2 is a graph showing the comparison of the saturation of the mobile oil calculated by different methods according to the present invention;
FIG. 3 is a chart showing nuclear magnetic resonance T2 relaxation time spectra obtained by inversion calculation of different centrifugal rotational speeds for a saturated core sample;
FIG. 4 is a graph of density of surface shale oil as a function of temperature;
fig. 5 is a graph of viscosity versus temperature for surface shale oil.
Detailed Description
Example 1
As a basic embodiment of the invention, the invention comprises a method for calculating the shale movable oil saturation based on the nuclear magnetic-centrifugal principle, which comprises the following steps:
and firstly, obtaining an original core sample, washing oil, drying to obtain a washed oil sample, and preparing the sample by utilizing crude oil and natural gas based on the underground real gas-oil ratio to obtain prepared crude oil, wherein the volume of the prepared crude oil is V 0.
And secondly, vacuumizing the oil washed sample, pressurizing and saturating to prepare crude oil, and obtaining a saturated oil core sample.
Taking out a saturated oil core sample, measuring the volume V' of the residual configuration crude oil, and calculating the total pore volume V of the core under the real underground temperature and pressure condition:
V=V0-V’。
fourthly, performing nuclear magnetic resonance experiments on the saturated oil core sample under the room temperature condition, inverting to obtain a T2 relaxation time spectrum, obtaining the total volume V 1 of the saturated oil core sample under the normal temperature and pressure, comparing the pore volume difference between the room temperature condition and the real underground temperature and pressure condition, and calculating to obtain the oil saturation S 1 of the light hydrocarbon loss part under the room temperature condition:
S1＝(V-V1)/V。
And fifthly, respectively carrying out high-speed centrifugation on the same saturated oil core sample by using different centrifugal rotating speeds, and respectively carrying out nuclear magnetic resonance test after each centrifugation to obtain the optimal centrifugal rotating speed.
Step six, centrifuging all the saturated oil core samples by utilizing the optimal centrifugal rotating speed selected in the step five, then performing nuclear magnetic resonance experiments to obtain a centrifuged core total pore volume V 2, comparing the centrifuged core total pore volume V 2 with the total volume V 1 of the saturated oil core samples at normal temperature and normal pressure in the step four, and calculating to obtain the ground movable fluid saturation S 2:
S2＝(V1-V2)/V1。
Step seven, calculating the true movable oil saturation S of the shale:
S=S1+S2。
Example 2
As a preferred embodiment of the invention, the invention comprises a method for calculating the saturation of shale movable oil based on a nuclear magnetism-centrifugation principle, which comprises the following steps:
Step one, an original core sample is obtained, washing oil is extracted by using chloroform and dried, and a sample after washing oil is obtained. And calculating crude oil and natural gas quantity based on the underground real gas-oil ratio, conveying the crude oil and the natural gas quantity to a high-temperature high-pressure sample preparation device, setting corresponding temperature and pressure according to real underground conditions, and keeping the temperature and the pressure constant for 1h to obtain the prepared crude oil. The volume of the configured crude oil is V 0.
And secondly, vacuumizing the oil washed sample, pressurizing and saturating to prepare crude oil, and obtaining a saturated oil core sample.
Taking out a saturated oil core sample, measuring the volume V' of the residual configuration crude oil, and calculating the total pore volume V of the core under the real underground temperature and pressure condition:
V=V0-V’。
Fourthly, performing nuclear magnetic resonance experiments on the saturated oil core sample under the room temperature condition, inverting to obtain a T2 relaxation time spectrum, obtaining the total volume V 1 of the saturated oil core sample under normal temperature and normal pressure, comparing the pore volume difference between the room temperature condition and the real underground temperature and pressure condition, and calculating to obtain the oil saturation S 1 of the light hydrocarbon loss part under the room temperature condition:
S1＝(V-V1)/V。
And fifthly, respectively carrying out high-speed centrifugation on the same saturated oil core sample by using different centrifugal rotating speeds, and respectively carrying out nuclear magnetic resonance test after each centrifugation to obtain the optimal centrifugal rotating speed. Specifically, if the porosity obtained in the previous nuclear magnetic resonance test-the porosity obtained in the next nuclear magnetic resonance test)/the porosity data obtained in the previous nuclear magnetic resonance test is x 100% <5%, the centrifugal speed corresponding to the previous nuclear magnetic resonance test is determined to be the optimal centrifugal speed, and the corresponding centrifugal force is determined to be the optimal centrifugal force.
Step six, centrifuging all the saturated oil core samples by utilizing the optimal centrifugal rotating speed selected in the step five, then performing nuclear magnetic resonance experiments to obtain a centrifuged core total pore volume V 2, comparing the centrifuged core total pore volume V 2 with the total volume V 1 of the saturated oil core samples at normal temperature and normal pressure in the step four, and calculating to obtain the ground movable fluid saturation S 2:
S2＝(V1-V2)/V1。
Step seven, calculating the true movable oil saturation S of the shale:
S=S1+S2。
example 3
As another preferred embodiment of the invention, the invention comprises a method for calculating the saturation of shale movable oil based on the principle of nuclear magnetism-centrifugation, which comprises the following steps:
And step one, obtaining an original core sample, washing oil and drying to obtain a washed oil sample. Specifically, under the condition of room temperature, an original core sample, namely a plunger sample, is wrapped by filter paper and is put into a sample chamber of a rope type extractor, chloroform is added into the extractor, the original core sample is extracted at the temperature of 75-80 ℃ until reflux liquid is colorless, the core sample is taken out, and the chloroform is completely volatilized at room temperature.
And (3) based on the underground real gas-oil ratio, carrying out sample preparation by using crude oil and natural gas to obtain prepared crude oil, wherein the volume of the prepared crude oil is V 0. Specifically, a CP-2 high temperature and high pressure sample preparation instrument is utilized to inject a certain volume of crude oil into an oil storage cylinder, a certain volume of natural gas is injected into the oil storage cylinder, the crude oil and the natural gas are calculated based on the underground real gas-oil ratio, the calculated crude oil and natural gas are conveyed into the high temperature and high pressure sample preparation instrument by a constant speed and constant pressure metering pump, the temperature and the pressure are set according to the real underground condition of the shale oil reservoir under study, and the constant temperature and the constant pressure are kept for 1h.
And secondly, vacuumizing the oil washed sample, pressurizing and saturating to prepare crude oil, and obtaining a saturated oil core sample. Specifically, the sample is vacuumized for more than 12 hours after oil washing, the pressure P < -0.098Mpa during vacuumization is carried out, and the vacuum degree reaches 0.1Pa. Connecting a high-temperature high-pressure sample preparation instrument and a core vacuumizing and pressurizing saturation experimental device, directly pressurizing and saturating prepared oil, and maintaining for 12 hours to obtain a saturated oil sample.
Taking out a saturated oil core sample, measuring the volume V' of the residual configuration crude oil, and calculating the total pore volume V of the core under the real underground temperature and pressure condition:
V=V0-V’。
fourthly, performing nuclear magnetic resonance experiments on the saturated oil core sample under the room temperature condition, inverting to obtain a T2 relaxation time spectrum, obtaining the total volume V 1 of the saturated oil core sample under the normal temperature and pressure, comparing the pore volume difference between the room temperature condition and the real underground temperature and pressure condition, and calculating to obtain the oil saturation S 1 of the light hydrocarbon loss part under the room temperature condition:
S1＝(V-V1)/V。
And fifthly, respectively carrying out high-speed centrifugation on the same saturated oil core sample by using different centrifugal rotating speeds, and respectively carrying out nuclear magnetic resonance test after each centrifugation to obtain the optimal centrifugal rotating speed. Specifically, a saturated oil core sample is centrifuged once at a centrifugal speed of 5000r/min, a nuclear magnetic resonance experiment is carried out, a T2 relaxation time spectrum is obtained through inversion, the porosity is obtained, then the saturated oil core sample is centrifuged once at a centrifugal speed of 6000r/min, a nuclear magnetic resonance experiment is carried out, a T2 relaxation time spectrum is obtained through inversion, the porosity is obtained, and the like. Wherein, the centrifugation time can be 60min each time.
And if the porosity obtained by the previous nuclear magnetic resonance test, the porosity obtained by the next nuclear magnetic resonance test and the porosity data obtained by the previous nuclear magnetic resonance test are multiplied by 100 percent <5 percent, the centrifugal speed corresponding to the previous nuclear magnetic resonance test is considered to be the optimal centrifugal speed, and the corresponding centrifugal force is considered to be the optimal centrifugal force.
Step six, centrifuging all the saturated oil core samples by utilizing the optimal centrifugal rotating speed selected in the step five, then performing nuclear magnetic resonance experiments to obtain a centrifuged core total pore volume V 2, comparing the centrifuged core total pore volume V 2 with the total volume V 1 of the saturated oil core samples at normal temperature and normal pressure in the step four, and calculating to obtain the ground movable fluid saturation S 2:
S2＝(V1-V2)/V1。
Step seven, calculating the true movable oil saturation S of the shale:
S=S1+S2。
Example 4
As yet another embodiment of the present invention, referring to fig. 1 of the drawings, the present invention comprises a method for calculating shale movable oil saturation based on the principles of nuclear magnetism-centrifugation, comprising the steps of:
and step one, drilling a core column sample to obtain an original core sample, extracting wash oil by using chloroform, drying the core sample in a vacuum drying oven at 60 ℃ for 4 hours, and sealing by using a preservative film after cooling.
And (3) respectively injecting a certain volume of crude oil and natural gas into the sample preparation instrument by utilizing a CP-2 type high-temperature high-pressure sample preparation instrument, calculating crude oil and natural gas based on the underground real gas-oil ratio, conveying the calculated crude oil and natural gas into the high-temperature high-pressure sample preparation instrument by utilizing a constant-speed constant-pressure metering pump, setting the temperature and pressure according to the real underground condition of the researched shale oil reservoir, and keeping the constant temperature and pressure for 1h to obtain the prepared crude oil. The volume of the configured crude oil is V 0.
And secondly, vacuumizing the washed oil sample for more than 12 hours, wherein the pressure P < -0.098Mpa during vacuumizing is 0.1Pa, pressurizing saturated configured crude oil, and maintaining for 12 hours to obtain a saturated oil core sample.
And thirdly, taking out a saturated oil core sample, and measuring the volume V 'of the residual prepared crude oil, wherein the volume difference of the crude oil in the sample preparation barrel before and after the saturated oil is V 0 -V', namely the total pore volume V of the core under the real underground temperature and pressure condition and the total pore volume V of the pressure-maintaining core.
Step four, performing nuclear magnetic resonance experiments on the saturated oil core sample under the room temperature condition, inverting to obtain a T2 relaxation time spectrum, obtaining the total volume V 1 of the saturated oil core sample under the normal temperature and pressure, namely the total pore volume V 1 of the normal pressure core, comparing the pore volume difference between the room temperature condition and the real underground temperature and pressure condition, and calculating to obtain the oil saturation S 1 of the light hydrocarbon loss part under the room temperature condition:
S1＝(V-V1)/V。
And fifthly, respectively carrying out high-speed centrifugation on the same saturated oil core sample by using different centrifugal rotational speeds (5000 r/min, 6000r/min, 7000r/min and the like), respectively carrying out nuclear magnetic resonance test after each centrifugation, and carrying out inversion calculation on the obtained nuclear magnetic resonance T2 relaxation time spectrum by using different centrifugal rotational speeds, wherein the nuclear magnetic resonance T2 relaxation time spectrum is shown in figure 3 of the detailed description. The last centrifugal speed is selected as a centrifugal standard, namely the last centrifugal nuclear magnetic volume-the last centrifugal nuclear magnetic volume)/the last centrifugal nuclear magnetic volume multiplied by 100% <5%, and the optimal centrifugal speed is obtained.
Step six, centrifuging all the saturated oil core samples by utilizing the optimal centrifugal rotating speed selected in the step five, then performing nuclear magnetic resonance experiments to obtain a centrifuged core total pore volume V 2, comparing the centrifuged core total pore volume V 2 with the total volume V 1 of the saturated oil core samples at normal temperature and normal pressure in the step four, and calculating to obtain the ground movable fluid saturation S 2:
S2＝(V1-V2)/V1。
Step seven, calculating the true movable oil saturation S of the shale:
S=S1+S2。
Referring to fig. 2 of the drawings, the old method is specifically referred to in the background art, and the scholars develop nuclear magnetic resonance-centrifugation to study the mobility of crude oil, consider crude oil still existing in the core after high-speed centrifugation as non-mobile oil, and consider crude oil centrifuged out at high speed as mobile oil, but in these studies, nuclear magnetic resonance is usually performed when n-dodecane fluid is used to saturate the core, so as to obtain the saturation of mobile oil. The new method refers to the method employed in this embodiment. As can be seen from the attached figure 2 of the specification, the movable oil saturation obtained by the method is obviously 3-4 percent higher than that obtained by the old method, and the more accurate movable oil saturation calculated value obtained by fully considering the influence of similar compatible and gas-driven crude oil reduces experimental errors and accords with the actual geological condition.
In view of the foregoing, it will be appreciated by those skilled in the art that, after reading the present specification, various other modifications can be made in accordance with the technical scheme and concepts of the present invention without the need for creative mental efforts, and the modifications are within the scope of the present invention.
Claims (9)
1. A method for calculating the saturation of shale movable oil based on a nuclear magnetism-centrifugation principle is characterized by comprising the following steps:
The method comprises the steps of firstly, obtaining an original core sample, washing oil and drying to obtain a washed oil sample, and preparing the sample by utilizing crude oil and natural gas based on the underground real gas-oil ratio to obtain prepared crude oil, wherein the volume of the prepared crude oil is V 0;
vacuumizing the washed oil sample, pressurizing and saturating to prepare crude oil, and obtaining a saturated oil core sample;
Taking out a saturated oil core sample, measuring the volume V' of the residual configuration crude oil, and calculating the total pore volume V of the core under the real underground temperature and pressure condition:
V=V0-V’;
fourthly, performing nuclear magnetic resonance experiments on the saturated oil core sample under the room temperature condition, inverting to obtain a T2 relaxation time spectrum, obtaining the total volume V 1 of the saturated oil core sample under the normal temperature and pressure, comparing the pore volume difference between the room temperature condition and the real underground temperature and pressure condition, and calculating to obtain the oil saturation S 1 of the light hydrocarbon loss part under the room temperature condition:
S1＝(V-V1)/V;
respectively carrying out high-speed centrifugation on the same saturated oil core sample by using different centrifugal rotating speeds, and respectively carrying out nuclear magnetic resonance test after each centrifugation to obtain the optimal centrifugal rotating speed;
Step six, centrifuging all the saturated oil core samples by utilizing the optimal centrifugal rotating speed selected in the step five, then performing nuclear magnetic resonance experiments to obtain a centrifuged core total pore volume V 2, comparing the centrifuged core total pore volume V 2 with the total volume V 1 of the saturated oil core samples at normal temperature and normal pressure in the step four, and calculating to obtain the ground movable fluid saturation S 2:
S2＝(V1-V2)/V1;
Step seven, calculating the true movable oil saturation S of the shale:
S=S1+S2。
2. the method for calculating the saturation of shale movable oil based on the nuclear magnetism-centrifugation principle according to claim 1, wherein the washing oil in the first step is specifically washing oil extracted by using chloroform.
3. The method for calculating the movable oil saturation of shale based on the nuclear magnetism-centrifugation principle according to claim 2, wherein the sample obtained after oil washing in the first step specifically comprises the steps of drilling an original core sample, extracting the oil washing by using chloroform, drying the core sample in a vacuum drying oven for 4 hours at the temperature of 60 ℃, waiting for cooling, and sealing by using a preservative film to obtain the sample after oil washing.
4. The method for calculating the movable oil saturation of shale based on the nuclear magnetism-centrifugation principle according to claim 3, wherein the step of extracting the wash oil by using chloroform is specifically to wrap an original core sample by using filter paper, put the core sample into a sample chamber of an extractor, then add the chloroform into the extractor, extract the original core sample at the temperature of 75-80 ℃ until a reflux liquid is colorless, then take out the core sample, and volatilize the chloroform completely at room temperature.
5. The method for calculating the movable shale oil saturation based on the nuclear magnetism-centrifugation principle according to claim 1, wherein the step one is to obtain the configured crude oil, specifically, calculate crude oil and natural gas quantity based on the underground real gas-oil ratio, convey the crude oil and natural gas quantity to a high-temperature high-pressure sample preparation device, set corresponding temperature and pressure according to the real underground condition, and keep the temperature and pressure constant for 1h to obtain the configured crude oil.
6. The method for calculating the movable oil saturation of shale based on the nuclear magnetism-centrifugation principle, which is characterized by comprising the following steps of vacuumizing a sample after oil washing for more than 12 hours, wherein the pressure P < -0.098Mpa during vacuumizing is equal to 0.1Pa, pressurizing saturated configuration crude oil, and maintaining for 12 hours to obtain a saturated core sample.
7. The method for calculating the saturation of shale mobile oil based on the nuclear magnetic resonance-centrifugation principle according to claim 1, wherein the optimal centrifugation speed obtained in the fifth step is specifically that if (the porosity obtained in the previous nuclear magnetic resonance test-the porosity obtained in the next nuclear magnetic resonance test)/the porosity data obtained in the previous nuclear magnetic resonance test is multiplied by 100% <5%, the centrifugation speed corresponding to the previous nuclear magnetic resonance test is determined to be the optimal centrifugation speed, and the corresponding centrifugal force is determined to be the optimal centrifugal force.
8. The method for calculating the movable shale oil saturation based on the nuclear magnetism-centrifugation principle according to claim 7, wherein the fifth step is characterized in that a saturated oil core sample is centrifuged once at a centrifugation speed of 5000r/min, a nuclear magnetic resonance experiment is conducted, a T2 relaxation time spectrum is obtained through inversion, the porosity is obtained, the nuclear magnetic resonance experiment is conducted once at a centrifugation speed of 6000r/min, the T2 relaxation time spectrum is obtained through inversion, the porosity is obtained, and the method is conducted in the same manner until the optimal centrifugation speed is obtained.
9. The method for calculating the saturation of shale movable oil based on the nuclear magnetism-centrifugation principle according to claim 8, wherein in the fifth step, the centrifugation time is 60min each time.
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