Quantitative evaluation method for micro-compressibility of tight sandstone reservoir

Abstract

The application provides a kind of compact sandstone reservoir microcosmic compressibility quantitative evaluation method, comprising the following steps: step one: using X-ray diffraction whole rock analysis technique and energy dispersive X-ray fluorescence spectrum technology analysis compact sandstone reservoir mineral composition;Step two: according to the requirement of nanoindentation experiment, the compact sandstone core sample is cut and sampled;Step three: record the load-displacement curve in the process of nanoindentation;Step four: establish the equivalent rock mechanics parameter calculation model of compact sandstone mineral composition complex;Step five: comprehensive consideration natural microcrack and bedding development degree;Step six: when establishing comprehensive compressibility evaluation model, the range transformation standardization method is needed for normalization processing to each parameter;Step seven: using the normalized parameters to establish the final compact sandstone reservoir comprehensive compressibility model.The application overcomes the high cost of existing rock mechanics test technology, and the core is not easy to obtain, and considers the inherent weak structural plane characteristics of deep compact sandstone, so as to realize the accurate and rapid evaluation of deep compact sandstone reservoir microcosmic compressibility.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of rock evaluation, and particularly relates to a method for quantitatively evaluating micro-compressibility of a tight sandstone reservoir. BACKGROUND

[0002] Quantitative evaluation of reservoir compressibility has very important guiding significance for engineering sweet spot optimization and fracturing reconstruction design optimization of deep tight sandstone reservoirs. At present, the research mainly adopts macro rock mechanics parameters and mineral content brittleness index to quantitatively evaluate the compressibility of tight sandstone reservoirs. First, the rock mechanics parameters, as one of the important evaluation indexes, not only affect the formation and evolution of natural fractures, but also control the expansion of artificial fractures. At present, the rock mechanics parameters are mainly obtained by experimental testing means to obtain static parameters or calculated by using geophysical logging data to obtain dynamic parameters.

[0003] The former uses triaxial rock mechanics experiment to simulate the three-dimensional stress state of deep strata by loading the confining pressure on the rock sample, measures the axial and lateral strain and axial load of the rock sample by using the sensor until the rock sample is damaged, and finally calculates the static rock mechanics parameters by using the obtained stress-strain curve. The latter uses the longitudinal and transverse wave velocities and density data in the array acoustic logging data to obtain the dynamic rock mechanics parameters reflecting the mechanical properties of the stratum under instantaneous loading. In view of the characteristics that the dynamic rock mechanics parameter data are large and the static rock mechanics parameters are relatively more real, a mathematical model is established to correct the dynamic and static rock mechanics parameters, so as to obtain the continuous rock mechanics distribution under the stratum condition.

[0004] The mineral content brittleness index method is to quantitatively characterize the reservoir compressibility by calculating the content of brittle minerals (such as quartz and carbonate minerals) in the tight sandstone reservoir. Finally, the rock mechanics parameters and the brittleness index are used to comprehensively establish a reservoir compressibility index model, so as to realize the quantitative characterization of the compressibility of the tight sandstone reservoir.

[0005] The complex microstructure and mineral composition inside the tight sandstone make it have strong heterogeneity. At the same time, the tight sandstone is influenced by the mineral type, sediment source and environmental mechanical properties during its formation, and the micro-pores, micro-fractures and fractures developed inside the tight sandstone all lead to the strong anisotropy of the mechanical properties of the tight sandstone. At present, the rock mechanics parameters of the reservoir are obtained by using triaxial rock mechanics experiment and other methods, and the heterogeneity of the tight sandstone reservoir is not fully considered, which leads to large discreteness of the experimental data, and a large number of experimental data are needed to overcome this problem.

[0006] But the traditional experiment needs large size core and cannot be reused, combined with the high cost and difficulty of drilling core, it is difficult to obtain a large number of cores under normal circumstances. In order to eliminate the influence of anisotropy on the experimental results, the vertical bedding direction and the direction with a certain angle with the bedding are sampled respectively, which has great difficulty in sample preparation and low success rate, so that the reliability of the experimental results cannot be effectively improved. Due to the influence of wellbore quality, drilling fluid system and other factors, the rock mechanics parameters calculated by acoustic logging data have large error, which is difficult to meet the design of drilling and completion and numerical simulation analysis. Moreover, the mechanical properties, content and micro mechanical properties of minerals or organic matter will strongly affect the rock mechanics properties of the reservoir, and the above method cannot obtain the rock mechanics properties of single mineral and accurately represent the rock mechanics properties of the rock with natural weak structural plane.

[0007] For the calculation of brittleness index, only the mineral types and their contents are considered, and the internal fabric and weak structural plane of the rock are not fully considered, and the definition of brittle mineral is still ambiguous at present, so the brittleness characteristics of the rock cannot be accurately represented.

[0008] Therefore, the above methods cannot provide stable and reliable technical support for the quantitative evaluation of the compactness of the tight sandstone reservoir. SUMMARY

[0009] In order to solve the problems of large error of test value of macro rock mechanics parameters caused by the heterogeneity of the tight sandstone reservoir in the background art, and the low accuracy of comprehensive fracturing property evaluation model caused by the insufficient consideration of the influence of natural weak structural plane such as natural fracture and bedding on the compactness of the tight sandstone reservoir, the present application provides a quantitative evaluation method for micro compactness of the tight sandstone reservoir.

[0010] The nanoindentation experiment overcomes the shortcomings of high cost and difficulty in obtaining core in the existing rock mechanics test technology. The equivalent rock mechanics parameter model of micro mineral component complex is established to improve the accuracy of the rock mechanics parameters of the strong heterogeneous tight sandstone. The quantitative evaluation index of the development degree of the natural weak structural plane is constructed by considering the influence of the natural micro fracture, bedding and other natural weak structural planes on the compactness of the tight sandstone reservoir. The quantitative comprehensive evaluation model of the reservoir compactness under the coupling of multiple factors is established by comprehensively considering the mechanical parameters of the minerals, the characteristics of the mineral components and the natural weak structural planes.

[0011] A quantitative evaluation method for micro compactness of the tight sandstone reservoir, comprising the following steps:

[0012] Step 1: analyze the mineral components of the tight sandstone reservoir by using X-ray diffraction (XRD) whole rock analysis technology and energy dispersive X-ray fluorescence spectrum (EDS) technology, and determine the proportion of each mineral component.

[0013] Step two: The sample is cut according to the requirements of the nanoindentation experiment. The sample needs to be a small piece with an intact interior. Microscopic imaging technology is used to target the nanoindentation experiment of the selected mineral.

[0014] Step three: The load-displacement curve (P-h curve) during the nanoindentation process is recorded. The Oliver-Pharr (O-P) method is used to identify the elastic modulus E, indentation hardness H, and fracture toughness K. The specific calculation method is as follows:

[0015]

[0016]

[0017]

[0018] For the indentation crack clear pressure point, the fracture toughness K is determined according to the radial crack length generated by the indenter on the surface of the specimen. The specific calculation method is as follows:

[0019]

[0020] For the indentation crack shape complex, length difficult to measure of pressure point, generally using energy analysis method to determine the fracture toughness K, the specific calculation method is as follows:

[0021] U t =U e +U PP +U c =U e +U ir

[0022]

[0023]

[0024]

[0025]

[0026] In the formula: A is the contact area of the indenter (m 2 ); A max is the maximum contact area of the indenter (m 2); Ei is the elastic modulus of the diamond indenter, taken as 1140 GPa; Er is the indentation reduced modulus (Pa); Pmax is the maximum indentation load (N); h is the indenter contact depth (m); S is the contact stiffness (N / m); v is the Poisson's ratio of the sample, taken as 0.25; vi is the Poisson's ratio of the diamond indenter, taken as 0.07; a is a constant related to the indenter geometry, taken as 1.034 for a Berkovich indenter; K is the fracture toughness of the rock; d is the indenter shape parameter: d = 0.032 for a cube corner indenter, and d = 0.016 for a Berkovich indenter; c is the average crack length; U t is the total energy; U e is the elastic energy; U pp is the plastic energy; U c is the fracture energy; U ir is the irreversible energy; G c is the critical energy release rate; h f is the indentation depth after complete unloading; through the experiment, the mechanical parameters of different minerals in the tight sandstone reservoir can be obtained, and the mean value of the test value of the mineral mechanical parameter is selected as the mechanical parameter value of the typical mineral.

[0027] Step four: a calculation model of equivalent rock mechanical parameters of the tight sandstone mineral component complex is established, the micro elastic modulus parameters, hardness parameters and fracture toughness parameters of the tight sandstone are combined according to different mineral types, and then the scale is upgraded, and the specific calculation method is as follows:

[0028]

[0029]

[0030]

[0031] In the formula, E z is the elastic modulus of the tight sandstone after scale upgrading, MPa; E1, E2, E3, E4 and E5 are the elastic moduli of clay minerals, quartz, potassium feldspar, plagioclase and calcite in the tight sandstone, MPa;

[0032] H z is the rock hardness of the tight sandstone after scale upgrading, MPa; H1, H2, H3, H4 and H5 are the hardnesses of clay minerals, quartz, potassium feldspar, plagioclase and calcite in the tight sandstone, MPa;

[0033] K z is the fracture toughness of the tight sandstone after scale upgrading, MPa·m1 / 2; K1, K2, K3, K4 and K5 are the fracture toughnesses of clay minerals, quartz, potassium feldspar, plagioclase and calcite in the tight sandstone, MPa·m1 / 2;

[0034] f1, f2, f3, f4, f5 are the contents of clay minerals, quartz, potassium feldspar, plagioclase and calcite in the deep dense sandstone, and f1+f2+f3+f4+f5=1

[0035] Step five: considering the natural microcrack and the development degree of bedding, a corresponding mathematical model is established, and finally the above two parameters are integrated to obtain an index model reflecting the development degree of natural weak structure surface, and the specific process is as follows:

[0036] (1) The development degree of microcracks is quantitatively described by using the natural microcrack surface density, and the formula is as follows:

[0037]

[0038] In the formula, I Z is the natural microcrack surface density; l is the length of a single crack; n is the number of visible microcracks on the slice; and AB is the area of the slice.

[0039] (2) The regression model is established by using quartz and calcite minerals which respond to stress weak surface, and the bedding development index is calculated:

[0040] S Z =f(f2, f5)

[0041]

[0042] In the formula, S Z is the bedding development index, f2 is the content of quartz, and f5 is the content of calcite.

[0043] (3) The natural microcrack surface density I Z and the bedding development index S Z are integrated to establish the natural weak structure surface index which can quantitatively evaluate the influence of microcracks and bedding on the compactibility of dense sandstone reservoirs:

[0044]

[0045] In the formula, F Z is the natural weak structure surface index; S Z is the bedding development index; and I Z is the natural microcrack surface density.

[0046] Step six: when establishing the comprehensive compactibility evaluation model, each evaluation index E Z , H Z , K Z , F Z has different dimensions, and the range transformation standardization method is needed for normalization processing. The normalized elastic modulus E Zj , the normalized hardness H Zjand normalized natural structure weakness index F Zj is a positive index, normalized fracture toughness K Zj is a negative index. The specific calculation method is as follows:

[0047]

[0048]

[0049]

[0050]

[0051] Step seven: using the normalized parameters to establish the final compacted sandstone reservoir comprehensive compressibility model, and using the analytic hierarchy process to compare each other to determine the relative importance of each element in each level and the scale, to establish the judgment matrix with the scale value, to determine the characteristic vector of the judgment matrix by using the sum product method, and the elements in the characteristic vector are the weight coefficients of the four parameters. The specific calculation method is as follows:

[0052] J=aE Zj +bH Zj +cK Zj +dF Zj

[0053] a+b+c+d=1

[0054] In the formula, a, b, c, d, e are the weight coefficients of various characteristic parameters reflecting the compressibility of compacted sandstone reservoir.

[0055] The calculated compressibility index can divide the compacted sandstone reservoir into the following three types: the compressibility coefficient is distributed in 0-0.3 for grade III reservoir, indicating poor compressibility; the compressibility index is distributed between 0.3-0.6 for grade II reservoir, indicating general compressibility; when the compressibility index is between 0.6-1, it is grade I reservoir, indicating good compressibility, and the actual production after fracturing is used to verify the accuracy of the compressibility model.

[0056] Beneficial effects:

[0057] The present application is based on the measurement of micro rock mechanics parameters of different minerals by nanoindentation experiment and scale upgrading of the equivalent rock mechanics parameters of mineral component synthesis, which not only solves the problems of high cost and difficult sample preparation in conventional rock mechanics parameter measurement experiment, but also solves the problems of large data dispersion and low accuracy caused by the heterogeneity of dense sandstone from the micro scale. At the same time, when building the comprehensive compressibility index model, the influence of the easily ignored natural weak structural surface on the reservoir compressibility is considered, and the natural weak structural surface index is established. The compressibility of deep dense sandstone reservoir can be more comprehensively, reasonably and accurately predicted, which can provide more scientific basis for the subsequent optimization of dense sandstone reservoir fracturing and sweet spot evaluation.

[0058] The analysis of dense sandstone reservoir mineral components and the targeted nanoindentation experiment by using X-ray diffraction (XRD) whole rock analysis technology and energy dispersive X-ray fluorescence spectroscopy (EDS) technology in steps one and two well solve the problems of high cost, long time consumption and difficult core sample acquisition in conventional triaxial rock mechanics experiment, and the micro rock mechanics properties of different mineral components are measured in a targeted manner.

[0059] The calculation model of equivalent rock mechanics parameters of dense sandstone component synthesis is established in step four to perform scale upgrading of micro rock mechanics parameters, which effectively solves the problem of low reliability of mineral content brittleness index caused by unclear brittle minerals, and more reasonably represents the real brittleness characteristics of dense sandstone. It fully considers the heterogeneity of dense sandstone reservoir, thereby weakening the influence of factors such as mechanical properties of minerals, mineral component content on the macro rock mechanics parameters of dense sandstone, so that the scale upgraded rock mechanics parameters have higher accuracy.

[0060] The natural weak structural surface index model is established by integrating the development degree of natural micro cracks and the development degree of bedding in step five, so as to quantitatively represent the influence of natural structural weak surfaces such as micro cracks and bedding on the compressibility of dense sandstone reservoir, so that the subsequent compressibility model has higher reliability and higher feasibility.

[0061] The normalization processing of each evaluation index of compressibility and the establishment of the compressibility index model of dense sandstone reservoir are performed in steps six and seven, the dimension of all parameters is unified by the range transformation standardization method, the unified evaluation under different meaning parameters is realized, the weight coefficients of the four parameters are determined by using the analytic hierarchy process, so that the compressibility model is more scientific. According to the size range of the compressibility index, the dense sandstone reservoir is divided into three categories, which more intuitively evaluates the compressibility, and provides reliable scientific basis and theoretical support for the exploration and development research of dense sandstone reservoir fracturing and sweet spot evaluation. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1A flow chart of a quantitative evaluation method for micro-compressibility of a tight sandstone reservoir;

[0063] Figure 2 A whole rock mineral diffraction pattern analysis chart;

[0064] Figure 3 An EDS mineral component analysis result chart;

[0065] Figure 4A A schematic diagram of selecting typical mineral measurement points under a microscope after polishing of a sample Figure I ;

[0066] Figure 4B A schematic diagram of selecting typical mineral measurement points under a microscope after polishing of a sample Figure II ;

[0067] Figure 5 A typical load-displacement (P-h) curve chart of a nanoindentation experiment;

[0068] Figure 6 A statistical chart of test results of mechanical parameters of typical minerals in a tight sandstone reservoir;

[0069] Figure 7 A comprehensive compressibility model application effect chart of a tight sandstone reservoir. DETAILED DESCRIPTION

[0070] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the present application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0071] According to Figure 1 , a quantitative evaluation method for micro-compressibility of a tight sandstone reservoir comprises the following steps:

[0072] Step 1: Use X-ray diffraction (XRD) whole rock analysis technology and energy dispersive X-ray fluorescence spectroscopy (EDS) technology to analyze mineral components of the tight sandstone reservoir and determine the proportion of each mineral component.

[0073] Step 2: According to the requirements of the nanoindentation experiment, cut and sample the tight sandstone core sample, and ensure that the sample is a small piece with an intact interior. Use micro-imaging technology to target the nanoindentation experiment of the selected mineral.

[0074] Step 3: Record the load-displacement curve (P-h curve) during the nanoindentation process, and use the Oliver-Pharr (O-P) method to identify the elastic modulus E, indentation hardness H and fracture toughness K. The specific calculation method is as follows:

[0075]

[0076]

[0077]

[0078] For the clear indentation crack of the indentation point, the fracture toughness K is determined according to the radial crack length generated by the indenter on the surface of the test piece, and the specific calculation method is as follows:

[0079]

[0080] For the indentation point with complex indentation crack shape and difficult to measure the length, the energy analysis method is generally used to determine the fracture toughness K, and the specific calculation method is as follows:

[0081] U t = U e + U PP + U c = U e + U ir

[0082]

[0083]

[0084]

[0085]

[0086] In the formula: A is the contact area of the indenter (m 2 ); A max is the maximum contact area of the indenter (m 2 ); Ei is the elastic modulus of the diamond indenter, which is 1140GPa; Er is the equivalent modulus of indentation (Pa); Pmax is the maximum indentation load (N); h is the contact depth of the indenter (m); S is the contact stiffness (N / m); v is the Poisson's ratio of the test piece, which is 0.25; vi is the Poisson's ratio of the diamond indenter, which is 0.07; α is a constant related to the geometry of the indenter, which is 1.034 for a Vickers indenter; K is the fracture toughness of the rock; δ is the shape parameter of the indenter: for a cubic indenter, δ = 0.032; and for a Berkovich type indenter, δ = 0.016; c is the average crack length; U t is the total energy; U e is the elastic energy; U pp is the plastic energy; U c is the fracture energy; U ir is the irreversible energy; G c is the critical energy release rate; h fThe indentation depth after complete unloading; through the experiment, the mechanical parameters of different minerals in the tight sandstone reservoir can be obtained, and the mean value of the test value of the mineral mechanical parameter is selected as the mechanical parameter value of the typical mineral.

[0087] Step four: establish a calculation model of equivalent rock mechanics parameters of tight sandstone mineral component complex, combine the micro elastic modulus parameters, hardness parameters and fracture toughness parameters of the tight sandstone according to different mineral types, and then realize scale upgrading, and the specific calculation method is as follows:

[0088]

[0089]

[0090]

[0091] In the formula, E z is the elastic modulus of the tight sandstone after scale upgrading, MPa; E1, E2, E3, E4 and E5 are the elastic moduli of clay minerals, quartz, potassium feldspar, plagioclase and calcite in the tight sandstone, MPa;

[0092] H z is the rock hardness of the tight sandstone after scale upgrading, MPa; H1, H2, H3, H4 and H5 are the hardnesses of clay minerals, quartz, potassium feldspar, plagioclase and calcite in the tight sandstone, MPa;

[0093] K z is the fracture toughness of the tight sandstone after scale upgrading, MPa·m1 / 2; K1, K2, K3, K4 and K5 are the fracture toughnesses of clay minerals, quartz, potassium feldspar, plagioclase and calcite in the tight sandstone, MPa·m1 / 2;

[0094] f1, f2, f3, f4 and f5 are the contents of clay minerals, quartz, potassium feldspar, plagioclase and calcite in the tight sandstone at the depth, and f1+f2+f3+f4+f5=1

[0095] Step five: considering the development degree of natural micro cracks and bedding, a corresponding mathematical model is established, and finally the above two parameters are integrated to obtain an index model reflecting the development degree of natural weak structural plane, and the specific process is as follows:

[0096] (1) The development degree of micro cracks is quantitatively described by using the natural micro crack surface density, that is,

[0097]

[0098] In the formula, I Z is the natural micro crack surface density; l is the length of a single crack; n is the number of visible micro cracks on the slice; AB For the area of the sheet.

[0099] (2) The regression model was established by using quartz and calcite mineral content which has a larger response to stress weak surface, and the bedding development index was calculated:

[0100] S Z = f(f2, f5)

[0101]

[0102] In the formula, S Z is the bedding development index, f2 is the quartz content, and f5 is the calcite content.

[0103] (3) The natural microcrack surface density I Z and the bedding development index S Z were integrated to establish the natural weak structure surface index which can quantitatively evaluate the influence of microcracks and bedding on the compactibility of tight sandstone reservoirs:

[0104]

[0105] In the formula, F Z is the natural weak structure surface index; S Z is the bedding development index; and I Z is the natural microcrack surface density.

[0106] Step six: In the establishment of the comprehensive compactibility evaluation model, each evaluation index E Z , H Z , K Z , and F Z has different dimensions, and the range transformation standardization method needs to be used for normalization processing. The normalized elastic modulus E Zj , the normalized hardness H Zj , and the normalized natural structure weak surface index F Zj are positive indexes, and the normalized fracture toughness K Zj is a negative index. The specific calculation method is as follows:

[0107]

[0108]

[0109]

[0110]

[0111] Step seven: the normalized parameters are used to establish the final compacted sandstone reservoir comprehensive compressibility model, and the relative importance of each element in each level and the scale are determined by using the analytic hierarchy process, a judgment matrix is established by using the scale value, the characteristic vector of the judgment matrix is determined by using the sum product method, and the elements in the characteristic vector are the weight coefficients of the four parameters. The specific calculation method is as follows:

[0112] J = aE Zj +bH Zj +cK Zj +dF Zj

[0113] a + b + c + d = 1

[0114] In the formula, a, b, c, d, and e are weight coefficients of various characteristic parameters reflecting the compressibility of compacted sandstone reservoirs.

[0115] The calculated compressibility index can divide the compacted sandstone reservoir into the following three types: the compressibility coefficient is distributed in 0-0.3, which is grade III reservoir, indicating poor compressibility; the compressibility index is distributed between 0.3-0.6, which is grade II reservoir, indicating general compressibility; when the compressibility index is between 0.6-1, it is grade I reservoir, indicating good compressibility, and the actual production after fracturing is used to verify the accuracy of the compressibility model.

[0116] Example

[0117] According to Figures 2-3 , step one: first, the X-ray diffraction (XRD) whole rock analysis technology is used to determine the mineral composition of the compacted sandstone reservoir, and the energy dispersive X-ray fluorescence spectrum (EDS) technology is used to determine the existence form and specific distribution of each mineral.

[0118] According to Figure 4A -fig. B, step two: collect rock samples, standard sample preparation of 1cm x 1cm x 5mm is carried out for samples that need to be subjected to nanoindentation experiment, polishing treatment is carried out for the experimental samples, typical test pressure points are found in high power microscope, and the range of minerals to be tested is preliminarily circled, and targeted nanoindentation experiment is carried out for different minerals.

[0119] According to Figures 5-6 , step three: based on the targeted nanoindentation experiment of step two, the Oliver-Pharr (O-P) method is used to calculate the load-displacement (P-h) curve collected, and then the elastic modulus, indentation hardness and fracture toughness of the micro mineral are obtained.

[0120] Step four: based on the influence of mineral composition and its distribution characteristics on the macroscopic rock mechanics parameters of the reservoir, a comprehensive equivalent rock mechanics parameter calculation model for the mineral composition of the heterogeneous tight sandstone reservoir is established, and the micro-elastic modulus, indentation hardness and fracture toughness obtained in step three are scaled up.

[0121] Step five: the natural structural weak surface, one of the main factors affecting the crack propagation in the actual fracturing process, is quantitatively characterized, and a forward index of the natural structural weak surface index is established.

[0122] According to Figure 7 Step six: the elastic modulus, indentation hardness, fracture toughness and natural structural weak surface index after homogenization are combined, the weight coefficients of the four compressibility parameters are determined by using the analytic hierarchy process and the sum method, the final comprehensive compressibility model of the tight sandstone reservoir is constructed, the compressibility index calculated by using the model is between 0 and 1, and the reservoir can be divided into three categories according to the compressibility index.

[0123] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present application, which are used to illustrate the technical solutions of the present application, but not to limit them, and the protection scope of the present application is not limited thereto. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can modify or easily think of changes to the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some technical features, without departing from the technical range disclosed by the present application. These modifications, changes or replacements do not make the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for quantitative evaluation of micro-compressibility of tight sandstone reservoirs, characterized in that, The method comprises the following steps: Step 1: analyze the mineral components of the tight sandstone reservoir by using X-ray diffraction whole rock analysis technology and energy dispersive X-ray fluorescence spectrum technology, and determine the proportion of each mineral component; Step 2: according to the requirements of nanoindentation experiment, the tight sandstone core sample is cut and sampled, the sample needs to be an internally complete small piece, and the micro imaging technology is used for targeted nanoindentation experiment on the selected mineral; Step 3: record the load-displacement curve in the process of nanoindentation; Step 4: establish a calculation model of equivalent rock mechanics parameters of tight sandstone mineral component synthesis; The micro elastic modulus parameters, hardness parameters and fracture toughness parameters of the tight sandstone are combined according to different mineral types, and then scale upgrading is realized, and the specific calculation method is as follows: ; wherein Eres is the elastic modulus of the compacted sandstone, MPa; , , , , Eclay, Eq, Epot, Epl, Ef is the elastic modulus of the clay mineral, quartz, potassium feldspar, plagioclase, and calcite in the compacted sandstone, MPa; Hardness of the rock after the tight sandstone scale upgrade, N / m 2 ; , , , , Hardness of clay minerals, quartz, potassium feldspar, plagioclase, calcite in tight sandstone, respectively, N / m 2 ; Fracture toughness for tight sandstone scale-up, MPa.m 1 / 2 ; , , , , Fracture toughness for clay minerals, quartz, potassium feldspar, plagioclase, calcite in tight sandstone, MPa.m 1 / 2 ; , , , , are the contents of clay minerals, quartz, potassium feldspar, plagioclase, and calcite in the tight sand, respectively, and ; Step 5: considering the development degree of natural microcracks and bedding, the corresponding mathematical model is established, and the above two parameters are integrated to obtain an exponential model reflecting the development degree of natural weak structural plane; Step 6: when establishing the comprehensive compressibility evaluation model, the range transformation standardization method is used to normalize each parameter; Step 7: using the normalized parameters, the final comprehensive compressibility model of tight sandstone reservoir is established, and the analytic hierarchy process is used to compare each other to determine the relative importance and scale value of each element in each level, and the scale value is used to establish a judgment matrix, and the sum product method is used to determine the characteristic vector of the judgment matrix; The calculated compressibility index divides the tight sandstone reservoir into the following three types: the compressibility coefficient is distributed in 0-0.3, which is grade III reservoir, indicating poor compressibility; the compressibility index is distributed between 0.3 and 0.6, which is grade II reservoir, indicating general compressibility; when the compressibility index is between 0.6 and 1, it is grade I reservoir, indicating good compressibility, and the actual production after fracturing is used to verify the accuracy of the compressibility model.

2. The method for quantitatively evaluating the micro-compressibility of a tight sandstone reservoir according to claim 1, characterized in that, Step 3 specifically comprises: The elastic modulus E, the indentation hardness H and the fracture toughness K are identified using the Oliver-Pharr method, and the specific calculation method is as follows: ; For the clear indentation crack of the indentation crack, the fracture toughness K is determined according to the radial crack length generated by the indenter on the surface of the test piece, and the specific calculation method is as follows: ; For the indentation crack morphology complex, length is difficult to measure the pressure point, the energy analysis method to determine the fracture toughness K, the specific calculation method as follows: ; where: A is the contact area of the indenter, m 2 ; Amax is the maximum contact area of the indenter, m 2 ; E is the elastic modulus of the diamond indenter, taken as 1140 GPa; Eeff is the indentation equivalent modulus, Pa; Pmax is the maximum indentation load, N; h is the contact depth of the indenter, m; S is the contact stiffness, N / m; v is the Poisson's ratio of the sample, taken as 0.25; v is the Poisson's ratio of the diamond indenter, taken as 0.07; K is a constant related to the indenter geometry, taken as 1.034 for a Berkovich indenter; KIC is the fracture toughness of the rock; a is the indenter shape parameter: for a cube corner indenter, ; and for a Berkovich indenter, ; L is the average crack length; G is the total energy; Gel is the elastic energy; Gpl is the plastic energy; Gf is the fracture energy; Girr is the irreversible energy; Gc is the critical energy release rate; hres is the residual indentation depth after complete unloading; through the experiment, the mechanical parameters of different minerals in the dense sandstone reservoir are obtained, and the mean value of the test value of the mineral mechanical parameter is selected as the mechanical parameter value of the mineral.

3. The method of claim 1, wherein the method is characterized by, Step 5 specifically comprises: (1) Using the natural microfracture surface density to quantitatively depict the microfracture development degree: ; wherein is the natural microfracture surface density; is the length of a single fracture; is the number of microfracture lines visible on the slice; is the area of the slice sample; (2) The regression model is established by using the quartz and calcite minerals with large response to stress weak surface to obtain the bedding development index: ; wherein is the bedding development index, is the quartz content, is the calcite content; (3) the natural microfracture surface density and the bedding development index are integrated to establish a natural weak structure surface index that quantitatively evaluates the influence of microfractures and bedding on the compactibility of tight sandstone reservoirs: ; In the formula, is the natural weak structural plane index; is the bedding development index; is the natural microcrack plane density.

4. The method of claim 1, wherein, Step 6 specifically comprises: In the establishment of comprehensive compressibility evaluation model, each evaluation index , , , has different dimensions, and needs to be normalized by using the range transformation standardization method. normalized elastic modulus , normalized hardness , and normalized natural weak plane index normalized fracture toughness as a positive indicator, and normalized fracture toughness as a negative indicator, calculated as follows:

5. The method of claim 1, wherein the method is used for quantitatively evaluating the micro-compressibility of a tight sandstone reservoir. Step 7 specifically comprises: The normalized parameters are used to establish a final comprehensive compactability model of the tight sandstone reservoir, and the relative importance and scale value of each element in each level are determined by using the analytic hierarchy process (AHP) to compare each other, a judgment matrix is established according to the scale value, the characteristic vector of the judgment matrix is determined by using the sum product method, and the elements in the characteristic vector are the weight coefficients of the four parameters, and the specific calculation method is as follows: ; In the formula, is the weight coefficient of various characteristic parameters reflecting the compactibility of the tight sandstone reservoir.

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