Method for recovering oil saturation of shale

Abstract

The invention provides a method for recovering oil saturation of shale. The method comprises the following steps: S1, preparing a sample and acquiring experimental test analysis data; s2, establishing a mathematical model for recovering the oil saturation; actually measuring the oil saturation S0 original of a plurality of original samples with the same depth and the oil saturation S0 recovery of a plurality of recovered oil-water samples in the same reference well; establishing a linear regression equation for recovering the oil saturation according to the mathematical model for recovering the oil saturation and actually measured S0 original and S0 recovery results; and S3, determining the oil saturation S0 recovery of the recovered oil-water sample of the to-be-researched area based on the linear regression equation of the recovered oil saturation. According to the method, the accuracy of oil saturation analysis is ensured, the complexity of oil saturation parameter acquisition is reduced, the method is applied to five wells in a block, the accuracy rate reaches 95%, the working efficiency is improved by more than 50%, and the shale oiliness can be objectively evaluated.

Description

Technical Field

[0001] The present invention belongs to the technical field of unconventional oil and gas exploration, and in particular, relates to a method for restoring the oil saturation of shale. Background Art

[0002] The oil saturation parameter of mudstone is one of the important indicators for parameter evaluation during sweet spot evaluation and reserve declaration, and can characterize the oil content of mudstone. Light hydrocarbon components are easily lost after coring. The industry usually collects core samples as soon as possible after coring and seals the samples with wax, which can reduce the loss of light hydrocarbon components to a certain extent. However, there is still loss during the experimental test and analysis process. At the same time, most core samples have the problem of almost completely losing light hydrocarbons after being placed for a long time. These all affect the accuracy of oil saturation detection. How to use the placed core to obtain the oil saturation in its non-volatile state is a current problem.

[0003] Yan Weilin et al. published an article titled "A New Method for Oil Saturation Evaluation of Gulong Shale Based on Nuclear Magnetic Resonance Technology" in the 5th issue of Volume 40 of Daqing Petroleum Geology and Development in 2021. The article points out that Gulong Shale has the characteristics of high clay content, high gas-oil ratio, developed lamellar and micro-nano pores, and complex pore structure and rock-electricity relationship. Traditional saturation experimental analysis and logging saturation evaluation face challenges. Experimental analysis shows that Gulong Shale has the characteristics of large pores containing movable oil, no movable water in pores, and oil in micro-nano pores. By analyzing the shortcomings of the existing pressure-maintained closed coring oil saturation experimental technology, it is proposed to establish a saturation interpretation template for two-dimensional nuclear magnetic logging (specifically Schlumberger's CMR-NG) suitable for Gulong shale oil based on the saturation analysis of the on-site one-dimensional nuclear magnetic experiment. The cluster analysis mathematical algorithm is used to process and interpret the two-dimensional nuclear magnetic logging data, and the quantitative calculation of movable oil and total oil saturation is realized. Compared with the oil saturation of the on-site one-dimensional nuclear magnetic experiment, the average absolute error is 4%, which greatly improves the accuracy of oil saturation interpretation and provides technical support for the preparation and implementation of reserve calculations and development plans. The technical process and method formed by the research are also of guiding significance for the evaluation of oil saturation of similar shale oil.

[0004] Bai Longhui et al. published an article titled "Application of Two-Dimensional Nuclear Magnetic Resonance Technology to Characterize Fluid Characteristics in Shale - Taking Organic-Rich Shale of Qingshankou Formation in Songliao Basin as an Example" in Vol. 42, No. 6 of Petroleum & Natural Gas Geology in 2021. The article points out that shale has been proven to contain a large amount of recoverable oil and gas resources. Clarifying the content and occurrence state of heterogeneous fluids in shale is crucial to the development of shale oil. Two-dimensional nuclear magnetic resonance technology can characterize the hydrogen content ( 1H) compounds for non-destructive, rapid and quantitative detection. NMR detection was performed on shale samples of the first member of the Qingshankou Formation in the Songliao Basin before and after extraction, spontaneous imbibition and during heating to quantitatively evaluate the heterogeneous fluid content, occurrence state and fluid loss during shale placement in the first member of the Qingshankou Formation. The results show that in the two-dimensional NMR spectrum, solid-like organic matter and light hydrocarbons are mainly distributed in T 1 The upper area is greater than 10ms, and the interval between them is basically T 2 =0.1ms, respectively related to the organic carbon content TOC and S 1 (free hydrocarbons) have a good linear relationship. The shale oil in the Qingyi 1st member in the southern Songliao Basin is mainly present in free and adsorbed states. The higher the clay content of the shale, the higher the content of adsorbed shale oil and the less free state. The results of nuclear magnetic resonance detection during the spontaneous imbibition of shale show the swelling effect of clay minerals absorbing water. During the vacuum heating process of shale, light hydrocarbons are volatilized and lost, and a large amount of water is also lost. Using closed coring samples combined with two-dimensional nuclear magnetic resonance technology, its original oil saturation and water saturation can be restored.

[0005] Xu Bodong et al. published an article titled "Analysis of Geochemical Characteristics of Low Oil Saturation Reservoirs in Badaowan Formation, Mahu Slope, Junggar Basin" in Volume 31, Issue 1 of Special Oil and Gas Reservoirs in 2024. The article states: Abstract: Low oil saturation reservoirs of the Jurassic Badaowan Formation were discovered in the shallow and middle layers of the slope of the Mahu Sag in the Junggar Basin. However, the production of old wells varied after oil testing, and it was difficult to identify the "sweet spots" of the reservoirs. To this end, the geochemical characteristics of the Badaowan Formation reservoirs were studied using oil and gas geochemical parameters. The results show that the biomarker compound characteristics of crude oil in the low oil saturation reservoirs of the Badaowan Formation have significant characterization significance for analyzing the characteristics and genesis of crude oil. The crude oil generally has the characteristics of high abundance of β-carotene and γ-cerane, which is a typical product of the Permian Fengcheng Formation source rock. Among them, the abundance of γ-cerane in crude oil from low-yield wells is relatively low, and Ts / Tm is relatively large; the abundance of γ-cerane in crude oil from high-yield wells is relatively high, and Ts / Tm is relatively small. The chromatographic effect is the main reason for the difference in biomarker compounds between crude oils. Comprehensive analysis shows that the fault communication mode and reservoir filling process affect the accumulation of oil and gas, and the low oil saturation reservoirs of the Badaowan Formation formed by the late structural tilt adjustment have more exploration potential. The research results can provide ideas and directions for the next exploration and development of the Mahu Sag.

[0006] Jia Mengyao et al. published an article titled "Field Analysis Technology and Preliminary Application of Water Content in Continental Shale Cores" in the 2024 issue of "Experimental Petroleum Geology" titled: Fluid analysis of continental shale formations is an important basis for shale oil layer selection and evaluation. In view of the current status of fluid characterization technology in continental shale formations and the needs of drilling sites, based on the characteristics of easy loss of water in core samples, a rapid microwave-based rock sample water content test method suitable for well sites was explored and established. After the core is removed from the barrel to wipe off the drilling fluid on the surface, a representative block rock sample is collected and loaded onto the crushing host for crushing and processing into granular form. The granular sample is poured into the sample cup loaded into the microwave water content meter. The mass fraction of the water content of the rock sample can be obtained after 2 seconds, and the average absolute error of the test is 0.15%. Preliminary application research shows that: first, the results of rock sample moisture detection can be converted into the pore space occupied by moisture in the sample pore system, and the apparent porosity of the sample can be quickly calculated in combination with well site pyrolysis data, providing data support for well site decision-making; second, the apparent oil saturation and apparent water saturation of the core sample can be calculated in combination with rock sample block density and pyrolysis data, so as to achieve rapid evaluation of well site rock sample fluid. The application of this method does not require oil washing and drying of rock samples, shortens the analysis cycle, and enriches the core porosity and fluid analysis experimental technical means and methods applicable to well sites.

[0007] The technical solution of the China patented platform for dynamic monitoring of oil saturation based on microscopic rock slices (CN109025924B) is: automatic control motor to realize positioning of observation points of rock slices fixed on the experimental platform; optical fiber channel setting to realize ultraviolet spectrum acquisition of micro-area of ​​rock slices; ultraviolet spectrum generation and acquisition combined instrument to realize image acquisition of rock slices; microcomputer automatic processing system to realize conversion of spectrum peak value and fluid saturation. This platform can be used in the petroleum industry for research on the mechanism of microscopic water flooding, verification of the effect of enhanced oil recovery technology, etc., and can also be used to explore the mechanism of fluid flow under different microstructures. It has the characteristics of high degree of automation, quantitative monitoring and characterization.

[0008] Chinese patent "Saturation calculation method and device based on conventional well logging data" (CN111561312B) provides a saturation calculation method based on conventional well logging data, including: determining the relationship between the saturation and the oil column height according to the well logging data of the target block; generating the saturation height function of the target block according to the relationship between the saturation and the oil column height; calculating the saturation of the target block according to the saturation height function. Based on conventional well logging data, the present invention can quickly and effectively determine the saturation height function, and then accurately determine the saturation, laying a solid foundation for the fine evaluation of reservoirs in oil and gas field exploration and development, reserve calculation, and the establishment of saturation field attribute models in three-dimensional geological models.

[0009] The scheme of a Chinese patent for an oil shale oil saturation detection device and its use method (CN115825402B) includes a fixed detection frame, a mounting sleeve is arranged in the middle of the fixed detection frame, and also includes: a lifting heating frame, which is arranged directly above the mounting sleeve, and a vertical heating tube is arranged vertically in the middle of the lifting heating frame; a dry distillation sealing cylinder, which is nested and detachably arranged on the inner side of the mounting sleeve. The present invention completes the heating dry distillation, gas condensation and liquid collection and storage required for detection through a dry distillation sealing cylinder, a condensation sealing cylinder and a collection sealing cylinder, respectively, and the dry distillation sealing cylinder, the condensation sealing cylinder and the collection sealing cylinder can be stacked and detachably connected to form a whole, so as to facilitate rapid movement, combination and replacement, so that by setting multiple groups of dry distillation sealing cylinders, condensation sealing cylinders and collection sealing cylinders, multiple oil shale sample detections can be carried out quickly, and the detection operation is more convenient and quick.

[0010] A Chinese patent, a method and system for calculating the oil saturation of muddy sandstone reservoirs (CN116341170A), discloses: obtaining oilfield data; obtaining 100% water-bearing reservoir logging data points based on the oilfield data, fitting the apparent water layer resistivity; calculating the oil saturation based on the apparent water layer resistivity. The oilfield data acquisition includes obtaining the reservoir logging natural gamma curve GR, logging density curve DEN and reservoir resistivity curve Rt; a system for calculating the oil saturation of muddy sandstone storage, the system includes a data acquisition unit for acquiring oilfield data; a data fitting unit for reading 100% water-bearing reservoir logging data points based on the oilfield data, fitting the apparent water layer resistivity; a data calculation unit for calculating the oil saturation based on the water saturation. The calculation by this method has the effect of small error and high accuracy.

[0011] A Chinese patent for a method, device, system and medium for calculating oil saturation of shale oil (CN116357308A) discloses: based on the interval porosity of nuclear magnetic logging data, the porosity after the interval porosity cutoff value is determined and the porosity S 1 The correlation between the oil-bearing reservoir space and the oil content of shale can be indicated. It can solve the problem that the conventional reservoir oil content evaluation methods such as closed coring to determine the saturation, logging saturation interpretation model based on rock physics experiments, and the use of capillary pressure curve to calculate the original oil saturation are not applicable to shale oil reservoirs. Accurately calculate the oil and gas saturation of shale reservoirs, provide assistance for logging evaluation of reservoirs and oilfield exploration and development, and have unparalleled advantages over other saturation models in calculating the oil saturation of shale reservoirs. The actual application effect is remarkable and has great promotion value.

[0012] The Chinese patented method for converting nuclear magnetic resonance to residual oil diameter in a core at different saturations (CN117672402A) discloses the following steps: obtaining the cumulative pore size ratio data of the core and the T2 spectrum data at different oil saturations; establishing a relationship equation 1 between the nuclear magnetic resonance conversion coefficient and the oil saturation, and a relationship equation 2 between the nuclear magnetic resonance relaxation time and the residual oil diameter; determining the nuclear magnetic resonance conversion coefficient value under the saturated oil state, and combining the relationship equation 1 to calculate the nuclear magnetic resonance conversion coefficient value at another oil saturation, repeating and fitting to obtain the relationship equation 3 between the oil saturation and the nuclear magnetic resonance conversion coefficient; according to the relationship equation 3, calculating the nuclear magnetic resonance conversion coefficient value at the target oil saturation, and combining the relationship equation 2 to calculate the residual oil diameter at the target oil saturation.

[0013] A Chinese patent for a method for calculating the oil saturation of complex fluids in shale oil (CN117761100A) discloses: measuring the multi-frequency one-dimensional and two-dimensional nuclear magnetic resonance of each group of core samples in the original state and under different wetting conditions, and determining the nuclear magnetic resonance relaxation position; statistically analyzing the conversion relationship of the nuclear magnetic resonance relaxation position of different fluids at different frequencies; applying the conversion relationship of the nuclear magnetic resonance relaxation position of different frequencies under different wetting conditions, converting the low-frequency logging data into high-frequency experimental data, and calculating the saturation of different fluids. The present invention establishes a detailed experimental scheme, while considering the influence of high and low frequencies and signal-to-noise ratio on the T1 / T2 ratio of different fluids, establishing a new high and low frequency conversion method and original echo noise reduction technology, forming an applicable two-dimensional nuclear magnetic resonance fluid saturation calculation method, and realizing high-precision saturation calculation.

[0014] A Chinese patent for a method for evaluating post-casing oil saturation based on the distribution of secondary gamma rays and thermal neutrons (CN117780332A) discloses: it is mainly used to evaluate the post-casing oil saturation after the development of an oil field, determine the distribution of remaining oil, and provide guidance for the mid- and late-stage development of an oil field. The present invention first establishes interpretation parameters for characterizing post-casing oil saturation based on the gamma detector counts and thermal neutron detector counts of the logging instrument. Then, a simulation model is established by combining the Monte Carlo numerical simulation technology with the actual instrument structure to obtain the correction chart of the oil-water layer response envelope under different measurement conditions, so as to realize the correction of the influencing factors of the interpretation chart. Finally, the measurement data of the actual well is used to construct a cross-plot of porosity and interpretation parameters to calibrate the interpretation chart, and the post-casing oil saturation is quantitatively evaluated based on the calibrated oil-water layer envelope, laying the foundation for the formulation of subsequent oilfield development plans.

[0015] A Chinese patent for a method for continuously characterizing the oil content distribution of mixed shale oil (CN117784220A) discloses: testing the core porosity and oil content of mixed rock samples of different lithologies; selecting logging curves, and constructing a porosity interpretation model and a clay interpretation model for mixed shale reservoirs according to different lithologies; constructing a porosity and clay interpretation model for mixed shale reservoirs based on the constructed different lithologies, determining rock electrical parameters for different lithologies, establishing a rock electrical parameter interpretation model, and establishing a saturation index interpretation model for different lithologies; inverting the formation water resistivity value based on the measured oil saturation data and the rock electrical parameter interpretation model, and establishing a resistivity value interpretation model for different strata; determining the oil content based on the established resistivity interpretation model, and realizing continuous characterization of the oil content based on conventional logging curves.

[0016] A Chinese patent, a system, method and device for determining multi-scale shale oil occurrence characteristics (CN117890398A) discloses: Based on the system, the processor controls the drilling sample module, the oil saturation module, the oil washing and drying module, the CT scanning module, the infrared positioning sensor, and the transportation structure, and uses the first CT scanning device to process the first scale sample according to the preset processing rules to obtain the first-level scale detection result; according to the preset drilling rules, the first scale sample is used to drill to obtain the second scale sample; according to the preset processing rules, the second scale sample is used to process the second scale sample using the second CT scanning device to obtain the second-level scale detection result; according to the preset drilling rules, the second scale sample is used to drill to obtain the third scale sample; according to the preset processing rules, the third scale sample is used to process the third scale sample using the third CT scanning device to obtain the third-level scale detection result; and then the above multiple detection results are combined to accurately determine the multi-scale shale oil occurrence characteristics of the target area.

[0017] A Chinese patent for an original oil saturation logging evaluation method based on pore structure classification (CN117890987A) discloses: on the basis of conventional logging data combined with core experimental analysis data, the reservoir pore structure is divided by nuclear magnetic resonance, and the four logging parameter values ​​of AC, CNL, DEN, and GR are introduced by the canonical discriminant function method. Starting from the high-dimensional space, the pore structure type is further determined. The concept of multiple fractals is adopted, and the partition function, quality index, multiple fractal spectrum, singular intensity and multiple fractal dimension are used to characterize the heterogeneity, continuity and separation of the logging parameters. An original oil saturation logging interpretation model based on pore structure classification is established, which can accurately evaluate reservoir physical parameters and oil layer identification. The method has high oil saturation calculation accuracy and is of great significance for the efficient use and economic development of the area.

[0018] A Chinese patent for a method for changing the back pressure value to establish an indicator chart of initial oil saturation (CN117905454A) discloses: determining the back pressure value through the indicator chart to determine the number of seepage channels participating in the flow in the sand-filled pipe, so as to achieve the purpose of establishing the initial oil saturation under a specific permeability. The method of the present invention is simple to operate, has strong repeatability, fast simulation speed and relatively low experimental cost. The biggest advantage of this method is that by setting the back pressure to control the number of seepage channels participating in the flow, the specified initial oil saturation of sand-filled pipes with different permeabilities can be accurately established, thereby simulating the actual oil saturation of the formation reservoir. Compared with other conventional methods, it can greatly shorten the experimental cycle and improve the repeatability and controllability of the experiment.

[0019] Although the above solution solves some problems, it is still subject to certain limitations in the above background technology when applied to restore the oil saturation of shale. Summary of the invention

[0020] The embodiment of the present application provides a method for restoring the oil saturation of shale, which improves the accuracy, simplicity and operability of obtaining the oil saturation parameters.

[0021] The present application embodiment provides a method for restoring oil saturation of shale, comprising:

[0022] S1, sample preparation and experimental test analysis data acquisition;

[0023] S2, establish a mathematical model for recovering oil saturation; the oil saturation S of multiple original samples at the same depth in the same reference well 0原始 and recover the oil saturation S of the oil-water sample 0恢复 According to the mathematical model of oil saturation recovery and the measured S 0原始 , S 0恢复 Results A linear regression equation for recovering oil saturation was established;

[0024] S3, determining the oil saturation S of the recovered oil-water sample in the study area based on the linear regression equation of the recovered oil saturation 0恢复 .

[0025] Among them, in step S1, for the full-diameter cylindrical core or 1 / 2 or 2 / 3 cut core that has been stored for more than 30 days, a core cylindrical sample with a diameter of 25 mm and a length of not less than 35 mm is drilled parallel to the core bedding plane using a 2 mm diameter diamond wire, i.e., the original sample; the oil saturation S of the original sample is first tested and calculated using the two-dimensional nuclear magnetic resonance test method. 0原始 ; Then restore the oil and water based on the original sample, that is, restore the oil and water sample, using saturated K 2 SO 4 Solution, using saturated K 2SO 4 The solution was set up in a space where the relative air humidity was maintained above 98%. The original sample was placed in the space for 14-30 days, during which time the one-dimensional nuclear magnetic resonance (T) was continuously monitored. 2 The spectrum is recovered if there is no change in the spectrum. Then the recovered water sample is pressurized to 10 MPa and saturated with n-dodecane for 24-30 hours. Then it is left to stand for 24 hours. During this period, one-dimensional nuclear magnetic resonance (T) is continuously monitored. 2 The spectrum is unchanged, and the oil-water recovery is completed. The oil saturation S of the oil-water sample can be restored by two-dimensional NMR calculation. 0恢复 .

[0026] In step S2, the oil saturation S of multiple original samples of the same depth in the same reference well is 0原始 and recover the oil saturation S of the oil-water sample 0恢复 The actual measurement includes: measuring the oil saturation S of n original samples at the same depth 0原始 and recover the oil saturation S of the oil-water sample 0恢复 Conduct actual measurement to obtain the oil saturation S of the recovered oil-water sample 0恢复 The measured value array Y a =[Y 1 ,Y 2 ,…,Y n ], and obtain the original sample oil saturation S 0原始 The measured value array X a =[X 1 ,X 2 ,…,X n ], where Y n is the oil saturation S of the nth restored oil-water sample 0恢复 , X n is the oil saturation S of the nth original sample 0原始 , n≥30.

[0027] In step S2, the mathematical model for recovering the oil saturation is: Y = a + bX, where Y is the oil saturation S of the recovered oil-water sample. 0恢复 , X is the oil saturation S of the original sample 0原始 , a is the regression constant, and b is the regression coefficient.

[0028] In step S2, the regression constant and regression coefficient are calculated according to formula (1):

[0029]

[0030] In formula (1), Y i is the oil saturation S of the i-th restored oil-water sample 0恢复 , The oil saturation S of all recovered oil-water samples 0恢复The average value of the measured values, X i is the oil saturation S of the i-th original sample 0原始 , is the oil saturation S of all original samples 0原始 The average value of the measured values, a is the regression constant, and b is the regression coefficient;

[0031] Substituting the regression constant and regression coefficient into the mathematical model for recovering oil saturation, the linear regression equation for recovering oil saturation is obtained.

[0032] This also includes verifying the linear regression equation.

[0033] The verification of the linear regression equation includes: verifying the linear regression equation using the correlation coefficient according to formula (2):

[0034]

[0035] In formula (2), R is the correlation coefficient, Y i is the oil saturation S of the i-th restored oil-water sample 0恢复 , Y i ′ is X i The corresponding fitted value obtained according to the linear regression equation, The oil saturation S of all recovered oil-water samples 0恢复 The average of the measured values.

[0036] The verifying of the linear regression equation includes: verifying the linear regression equation using the significance of the regression coefficient according to formula (3):

[0037]

[0038] In formula (3), t b is the significance of the regression coefficient, b is the regression coefficient, X i is the oil saturation S of the i-th original sample 0原始 , is the oil saturation S of all original samples 0原始 The average value of the measured values, Y i is the oil saturation S of the i-th restored oil-water sample 0恢复 , Y i ′ is X i The corresponding fitted value obtained according to the linear regression equation;

[0039] According to formula (4), the linear regression equation is verified by using the significance of the regression equation.

[0040]

[0041] In formula (4), F is the significance of the regression equation, Y i ′ is X i The corresponding fitted value obtained according to the linear regression equation, To restore the oil saturation S of the oil-water sample 0恢复 The average value of the measured values, Y i is the oil saturation S of the i-th restored oil-water sample 0恢复 .

[0042] In step S3, the oil saturation S of the original sample in the area to be studied is measured. 0原始 ; According to the oil saturation S of the original sample in the study area 0原始 The oil saturation S of the recovered oil-water sample in the study area is calculated using the linear regression equation 0恢复 .

[0043] The method for restoring oil saturation of shale in the application example has the following beneficial effects:

[0044] The method of restoring oil saturation of shale in this application is used to determine the oil saturation S of the restored oil-water samples in the study area. 0恢复 , establish and verify the mathematical model for recovering oil saturation, according to the oil saturation S of the original sample in the study area 0原始 , the oil saturation S of the restored oil-water sample in the study area can be obtained 0恢复 , and then evaluate the oil content of the shale in the study area, ensuring the accuracy of oil saturation analysis and reducing the complexity of obtaining oil saturation parameters. It has been applied to 5 wells in the block, with an accuracy rate of 95%, and work efficiency increased by more than 50%, which can objectively evaluate the oil content of the shale. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a schematic flow chart of a method for restoring oil saturation in shale according to an embodiment of the present application. DETAILED DESCRIPTION

[0046] The principle and design idea of ​​the technical solution of the present invention are:

[0047] The oil saturation of shale can characterize the oil content of shale and is one of the important evaluation parameters for sweet spot evaluation and reserve declaration. The light hydrocarbon components in the core are easy to dissipate after coring, resulting in low oil saturation data. The industry usually collects core samples as soon as possible after coring and seals the samples with wax, which can reduce the loss of light hydrocarbon components to a certain extent, but there is still loss during the experimental test and analysis process; at the same time, some core samples have the problem of almost completely losing light hydrocarbons after being placed for a long time; these all affect the accuracy of oil saturation detection. How to use the placed cores to obtain the oil saturation in its non-volatile state is a current problem.

[0048] At present, experts and scholars have used a variety of methods to test oil saturation, using a combination of one-dimensional nuclear magnetic resonance of cores and two-dimensional nuclear magnetic resonance of well logging to obtain cutoff values ​​or establish charts to calculate oil saturation; or conducting rapid water testing on rock samples based on microwaves at the well site to calculate the apparent oil saturation and apparent water saturation of core samples; or using saturation calculation methods based on conventional logging data; or using measured values ​​and logging curves to establish a saturation index interpretation model; or using CT scanning to obtain oil characteristics of samples at different scales; or various methods are applicable to conventional sandstone reservoirs or tight sandstone reservoirs, but not to shale reservoirs. The above methods have the problems of high cost and strong timeliness, which are different from the method of restoring oil saturation in shale in this scheme.

[0049] The present invention has carried out a lot of research on the above-mentioned problems, with the aim of solving the problem that the accuracy of oil saturation detection may be affected due to the loss of light hydrocarbon components after drilling and coring, and solving the technical problem of restoring the oil saturation of samples that have been stored for a long time or samples where some light hydrocarbons have been lost. This overcomes the timeliness requirement to a certain extent and reduces the testing cost.

[0050] Under the guidance of the above ideas, the technical means adopted by the present invention are: determining the oil saturation S of the restored oil-water sample in the study area 0恢复 , establish and verify the mathematical model for recovering oil saturation, according to the oil saturation S of the original sample in the study area 0原始 , the oil saturation S of the restored oil-water sample in the study area can be obtained 0恢复 , and then evaluate the oil content of the shale in the study area, ensure the accuracy of oil saturation analysis, reduce the complexity of obtaining oil saturation parameters, and realize the recovery of oil saturation.

[0051] Embodiment 1

[0052] like Figure 1 As shown, the method for recovering the oil saturation of shale in the present application includes: S1, sample preparation and experimental test analysis data acquisition; S2, establishing a mathematical model for recovering the oil saturation; and calculating the oil saturation S of multiple original samples of the same depth from the same reference well. 0原始 and recover the oil saturation S of the oil-water sample 0恢复 According to the mathematical model of oil saturation recovery and the measured S 0原始 , S 0恢复 As a result, a linear regression equation for restoring oil saturation is established; S3, based on the linear regression equation for restoring oil saturation, the oil saturation S of the restored oil-water sample in the study area is determined. 0恢复 , the oil content of shale in the study area can be evaluated.

[0053] The method for restoring the oil saturation of shale in the present application ensures the simplicity and accuracy of oil saturation analysis and improves the ease of operation.

[0054] Embodiment 2

[0055] like Figure 1 As shown, the present application provides a method for restoring the oil saturation of mudstone, taking the XX well in the XX depression of the XX basin as an example, comprising the following steps:

[0056] Step 1: Sample preparation and experimental test analysis data acquisition. For full-diameter cylindrical cores that have been stored for more than 30 days, a 2mm diameter diamond wire is used to drill a 25mm diameter and 40mm length core cylinder sample parallel to the core bedding plane, i.e., the original sample; using the two-dimensional nuclear magnetic resonance test method, first test and calculate the oil saturation S of the original sample 0原始 ; Then restore the oil and water based on the original sample, that is, restore the oil and water sample, using saturated K 2 SO 4 Solution, using saturated K 2 SO 4 The solution was set up in a space where the relative air humidity was maintained above 98%. The original sample was placed in the space and continuously monitored by one-dimensional nuclear magnetic resonance (T) after 25 days. 2 The spectrum did not change, completing the water recovery process. Then the recovered water sample was pressurized to 10 MPa and saturated with n-dodecane for 26 hours. It was then left to stand for 24 hours and continuously monitored by one-dimensional nuclear magnetic resonance (T) 2 The spectrum does not change, and the oil-water recovery is completed. The oil saturation S of the oil-water sample can be restored by two-dimensional NMR calculation. 0恢复 .

[0057] Step 2: Establish a mathematical model for recovering oil saturation;

[0058] The oil saturation S of 31 original samples of the same depth in the same reference well XX is 0原始 and recover the oil saturation S of the oil-water sample 0恢复 According to the mathematical model of oil saturation recovery and the measured S 0原始 , S 0恢复 Results A linear regression equation for recovering oil saturation was established.

[0059] In some implementations of this embodiment, the mathematical model is: Y = a + bX, where Y is the oil saturation S of the restored oil-water sample. 0恢复 , X is the oil saturation S of the original sample 0原始 , a is the regression constant, and b is the regression coefficient.

[0060] As shown in Table 1, in some embodiments, the oil saturation S of 31 original samples of the same depth in the same reference well XX is0原始 and recover the oil saturation S of the oil-water sample 0恢复 The actual measurement includes: for the same reference well, the oil saturation S of n original samples at the same depth 0原始 and recover the oil saturation S of the oil-water sample 0恢复 Conduct actual measurement to obtain the oil saturation S of the recovered oil-water sample 0恢复 The measured value array Y a =[Y 1 ,Y 2 ,…,Y n ], and obtain the original sample oil saturation S 0原始 The measured value array X a =[X 1 ,X 2 ,…,X n ], where Y n is the oil saturation S of the nth restored oil-water sample 0恢复 , X n is the oil saturation S of the nth original sample 0原始 , n=31.

[0061] Table 1

[0062]

[0063]

[0064] In some embodiments, based on the mathematical model of oil saturation recovery and the measured S 0原始 , S 0恢复 Results The linear regression equation for recovering oil saturation includes:

[0065] The regression constant and regression coefficient are calculated according to formula (1):

[0066]

[0067] In formula (1), Y i is the oil saturation S of the i-th (i=1, 2, 3...n) restored oil-water sample 0恢复 , The oil saturation S of all recovered oil-water samples 0恢复 The average value of the measured values, X i is the oil saturation S of the i-th original sample 0原始 , is the oil saturation S of all original samples 0原始 The average value of the measured value, a is the regression constant, b is the regression coefficient, a is 16.9867, b is 0.6749. Substituting the regression constant and regression coefficient into the mathematical model of recovering oil saturation, the linear regression equation is obtained.

[0068] In some implementations of this embodiment, the linear regression equation is: Y=16.9867+0.6749X, where Y is the oil saturation S of the restored oil-water sample. 0恢复 , X is the oil saturation S of the original sample 0原始 .

[0069] In some implementations of this embodiment, the method for restoring the oil saturation of shale in this application further includes: verifying the linear regression equation; if the linear regression equation is verified to be reasonable, determining the oil saturation S of the restored oil-water sample in the study area based on the linear regression equation 0恢复 , according to the oil saturation S of the restored oil-water sample in the area to be studied 0恢复 Evaluate the oil content of shale in the study area.

[0070] As shown in Table 2, in some implementations of this embodiment, verifying the linear regression equation includes: verifying the linear regression equation using the correlation coefficient R according to formula (2),

[0071]

[0072] In formula (2), R is the correlation coefficient, Y i is the oil saturation S of the i-th restored oil-water sample 0恢复 , Y i ′ is X i The corresponding fitted value obtained according to the linear regression equation, The oil saturation S of all recovered oil-water samples 0恢复 The average value of the measured values ​​of the content.

[0073] Y i The definition of ' is recorded on page 35 of the book "Modern Consulting Methods and Practices", first edition published by China Planning Press in April 2003.

[0074] When the degree of freedom is n-2 (n is the number of samples 31) and the significance level is a=0.05, R=0.9509, which is greater than the critical value of 0.361, indicating that the linear relationship between X and Y is established.

[0075] The correlation coefficient critical value table is recorded on page 257 of the book "Modern Consulting Methods and Practices", first edition published by China Planning Press in April 2003.

[0076] Table 2

[0077]

[0078]

[0079] As shown in Table 3, in some implementations of this embodiment, verifying the linear regression equation includes: verifying the linear regression equation using the significance t of the regression coefficient according to formula (3),

[0080]

[0081] In formula (3), t b is the significance of the regression coefficient, b is the regression coefficient, X i is the oil saturation S of the i-th original sample 0原始 , is the oil saturation S of all i-th original samples 0原始 The average value of the measured values, Y i is the oil saturation S of the i-th restored oil-water sample 0恢复 , Y i ′ is X i The corresponding fitted value obtained according to the linear regression equation.

[0082] The significance of the regression coefficient is used to determine whether the linear hypothesis between variables X and Y is reasonable; the calculated result t b =48.9702, which is greater than t(a / 2,n-2)=2.0452. The parameter t test passes, and the linear assumption between variables X and Y is reasonable. The t(a / 2,n-2) distribution table is recorded on page 258 of the book Modern Consulting Methods and Practices, first published in April 2003 by China Planning Press.

[0083] Table 3

[0084]

[0085]

[0086] As shown in Table 4, in some implementations of this embodiment, verifying the linear regression equation includes: verifying the linear regression equation using the significance F of the regression equation according to formula (4),

[0087]

[0088] In formula (4), F is the significance of the regression equation, Y i ′ is X i The corresponding fitted value obtained according to the linear regression equation, The oil saturation S of all recovered oil-water samples 0恢复 The average value of the measured values, Y i is the oil saturation S of the i-th restored oil-water sample 0恢复 .

[0089] The calculation result is F = 6.0162, which is greater than the significance level a = 0.05, and the degree of freedom n 1 =1,n 2 =n-2, the F value is 4.18, and the F test is passed. The regression equation reflects the linear relationship between variables X and Y well. The F distribution table of the significance F test of the regression equation is recorded in the book "Modern Consulting Methods and Practices" first published by China Planning Press in April 2003, pages 259-260.

[0090] Table 4

[0091]

[0092]

[0093] Step 3: Determine the oil saturation S of the restored oil-water sample in the study area based on the linear regression equation 0恢复 Includes: measuring the oil saturation S of the original sample in the area to be studied 0原始 ; According to the oil saturation S of the original sample in the study area 0原始 The oil saturation S of the recovered oil-water sample in the study area is calculated using the linear regression equation 0恢复 .

[0094] Among them, the oil saturation S of the restored oil-water sample in the study area is determined based on the linear regression equation 0恢复 ; According to the oil saturation S of the restored oil-water samples in the study area 0恢复 Evaluate the oil content of the area to be predicted.

[0095] Taking the HY7 well (the area to be studied) as an example, the application of the mathematical model of the present invention is described in detail.

[0096] Well HY7, original sample oil saturation S 0原始 The oil saturation of the oil-water sample is 23.31% according to the mathematical model Y = 16.9867 + 0.6749X. 0恢复 )=32.08%, which is close to the oil saturation of 33.62% of the recovered oil-water sample of the well, and the data is reliable.

[0097] In summary, based on the measured oil saturation S of 31 original samples, 0原始 and recover the oil saturation S of the oil-water sample 0恢复 The established mathematical model, using the correlation coefficient R test, the regression coefficient significance t test, and the regression equation significance F test, all reflect that the linear relationship between variables X and Y is reasonable. Therefore, Y = 16.9867 + 0.6749X can be used to determine the oil saturation S of the restored oil-water sample in the study area. 0恢复 , further evaluate the oil content of shale.

[0098] In this application, the original sample oil saturation S 0原始 The test is relatively simple, and the original sample oil saturation S is established through the measured results. 0原始 The oil saturation S of the recovered oil-water sample 0恢复 The regression equation between them only needs to measure the oil saturation S of the original sample of a well. 0原始 According to the regression equation, the oil saturation S of the restored oil-water sample in the predicted area is calculated. 0恢复 , the oil content of shale in the study area can be evaluated.

[0099] The method of recovering the oil saturation of shale in this embodiment ensures the accuracy and operability of the oil saturation analysis, improves the ease of operation, and is applied to 5 wells in the block with an accuracy rate of 95%. The work efficiency is improved by more than 50%, and the oil content of shale can be objectively evaluated.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for restoring oil saturation in shale, characterized in that: include: S1, sample preparation and experimental test analysis data acquisition; S2, establish a mathematical model for restoring oil saturation; The oil saturation S of multiple original samples of the same depth from the same reference well 0原始 and recover the oil saturation S of the oil-water sample 0恢复 Conduct actual measurements; According to the mathematical model of recovering oil saturation and the measured S 0原始 , S 0恢复 Results A linear regression equation for recovering oil saturation was established; S3 , based on the linear regression equation of the restored oil saturation, determine the oil saturation S of the restored oil-water sample in the study area 0恢复 .

2. The method for restoring oil saturation of shale according to claim 1, characterized in that: In step S1, for a full-diameter cylindrical core or a 1 / 2 or 2 / 3 cut core stored for more than 30 days, a core cylindrical sample with a diameter of 25 mm and a length of not less than 35 mm is drilled parallel to the core bedding plane using a 2 mm diameter diamond wire, i.e., the original sample; the oil saturation S of the original sample is first tested and calculated using a two-dimensional nuclear magnetic resonance test method. 0原始 ; Then, oil and water are restored on the basis of the original sample, that is, the oil and water sample is restored, a saturated K2SO4 solution is used, and a space with a relative air humidity maintained above 98% is established using the saturated K2SO4 solution, and the original sample is placed in the space for 14-30 days, during which the one-dimensional nuclear magnetic resonance T2 spectrum is continuously monitored. If there is no change in the spectrum, the water is restored. Then, the restored water sample is pressurized to 10MPa and saturated with n-dodecane for 24-30 hours, and then allowed to stand for 24 hours, during which the one-dimensional nuclear magnetic resonance T2 spectrum is continuously monitored. If there is no change in the spectrum, the oil and water are restored. The oil saturation S of the restored oil and water sample can be calculated using two-dimensional nuclear magnetic resonance 0恢复 .

3. The method for restoring oil saturation of shale according to claim 1 or 2, characterized in that: In step S2, the oil saturation S of multiple original samples of the same depth in the same reference well is calculated. 0原始 and recover the oil saturation S of the oil-water sample 0恢复 The actual measurement includes: measuring the oil saturation S of n original samples at the same depth 0原始 and recover the oil saturation S of the oil-water sample 0恢复 Conduct actual measurement to obtain the oil saturation S of the recovered oil-water sample 0恢复 The measured value array Y a =[Y1,Y2,…,Y n ], and obtain the original sample oil saturation S 0原始 The measured value array X a =[X1,X2,…,X n ], where Y n is the oil saturation S of the nth restored oil-water sample 0恢复 , X n is the oil saturation S of the nth original sample 0原始 , n≥30.

4. The method for restoring oil saturation of shale according to claim 1 or 2, characterized in that: In step S2, the mathematical model for recovering the oil saturation is: Y = a + bX, where Y is the oil saturation S of the recovered oil-water sample. 0恢复 , X is the oil saturation S of the original sample 0原始 , a is the regression constant, and b is the regression coefficient.

5. The method for restoring oil saturation of shale according to claim 1 or 2, characterized in that: In step S2, the regression constant and regression coefficient are calculated according to formula (1): In formula (1), Y i is the oil saturation S of the i-th restored oil-water sample 0恢复 , The oil saturation S of all recovered oil-water samples 0恢复 The average value of the measured values, X i is the oil saturation S of the i-th original sample 0原始 , is the oil saturation S of all original samples 0原始 The average value of the measured values, a is the regression constant, and b is the regression coefficient; Substituting the regression constant and regression coefficient into the mathematical model for recovering oil saturation, the linear regression equation for recovering oil saturation is obtained.

6. The method for restoring oil saturation of shale according to claim 1 or 2, characterized in that: Validation of the linear regression equation is also included.

7. The method for restoring oil saturation of shale according to claim 6, characterized in that: The verification of the linear regression equation includes: verifying the linear regression equation using the correlation coefficient according to formula (2): In formula (2), R is the correlation coefficient, Y i is the oil saturation S of the i-th restored oil-water sample 0恢复 , Y′ i For X i The corresponding fitted value obtained according to the linear regression equation, The oil saturation S of all recovered oil-water samples 0恢复 The average of the measured values.

8. The method for restoring oil saturation of shale according to claim 6, characterized in that: The verifying the linear regression equation includes: verifying the linear regression equation using the significance of the regression coefficient according to formula (3): In formula (3), t b is the significance of the regression coefficient, b is the regression coefficient, X i is the oil saturation S of the i-th original sample 0原始 , is the oil saturation S of all original samples 0原始 The average value of the measured values, Y i is the oil saturation S of the i-th restored oil-water sample 0恢复 , Y′ i For X i The corresponding fitted value obtained according to the linear regression equation; According to formula (4), the linear regression equation is verified by using the significance of the regression equation. In formula (4), F is the significance of the regression equation, Y′ i For X i The corresponding fitted value obtained according to the linear regression equation, To restore the oil saturation S of the oil-water sample 0恢复 The average value of the measured values, Y i is the oil saturation S of the i-th restored oil-water sample 0恢复 .

9. The method for restoring oil saturation of shale according to claim 1 or 2, characterized in that: In step S3, the oil saturation S of the original sample in the area to be studied is measured. 0原始 ; According to the oil saturation S of the original sample in the study area 0原始 The oil saturation S of the recovered oil-water sample in the study area is calculated using the linear regression equation 0恢复 .

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