Geostress calculation method and device for tight gas reservoirs with sandstone and mudstone interlayers

Abstract

The present invention provides a method for calculating geostress for tight gas reservoirs with interlayers of sand and mudstone, which comprises: calculating and obtaining shear wave time difference, performing correlation analysis between the shear wave time difference and the logging shear wave time difference obtained by actual logging, and obtaining a corrected shear wave time difference; calculating and obtaining rock dynamic mechanical parameters, and converting the rock dynamic mechanical parameters into continuous static parameters in combination with discontinuous static parameters obtained by indoor core tests; obtaining geostress data through a geostress calculation model based on the continuous static parameters, and correcting the geostress data using a field fracturing construction curve and a calculated fracture pressure calculated by a fracture pressure calculation model, so as to obtain a geostress profile. The present invention obtains relatively reliable rock dynamic mechanical parameters through the calculation and correction of the shear wave time difference, and obtains continuous static parameters through correlation conversion with the rock static mechanical parameters, laying a relatively reliable data foundation for subsequent geostress calculation.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, and in particular to a method and a device for calculating ground stress in a sand-shale interbedded tight gas reservoir. Background Art

[0002] Geostress is a local load acting on underground rock formations. It is a force per unit area caused by the combined effects of the gravity of the overlying rock formations, the vertical and horizontal movements of the crust, and other factors. It can be decomposed into one vertical stress and two horizontal stresses, of which the two horizontal stresses are usually unequal. The geostress profile can reflect the longitudinal variation of the geostress field. Accurately obtaining the layered geostress parameters can provide a basis for decision-making and design in various links such as drilling engineering, oil and gas reservoir engineering, and oil production engineering. Especially in hydraulic fracturing operations, geostress and rock mechanics parameters have important guiding significance for the formulation of perforation schemes, three-dimensional fracturing simulation, and optimization of engineering parameters.

[0003] At present, the methods for measuring geostress mainly include three technologies: core laboratory test, logging data inversion and field measurement. The logging method can continuously measure the mechanical properties of rocks, but conventional logging data usually lacks shear wave logging data, and the data error is large when used to simulate and calculate stress; the mechanical properties measured by core laboratory test are accurate, but its test accuracy is affected by many factors, and the test cost is high and the data is limited; field fracturing test is currently the most accurate method for measuring geostress, and its test results can often be used as a standard to verify the accuracy of other tests, but due to conditions, this method is rarely used and cannot obtain continuous geostress profiles. Therefore, how to use conventional logging data (excluding shear wave logging data) to obtain geostress profiles and correct them in combination with fracturing construction data is of great significance for the development of oil and gas fields.

[0004] Therefore, the present invention provides a method and device for calculating ground stress in a tight gas reservoir with sandstone and mudstone interlayers. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for calculating geostress for a tight gas reservoir with sandstone and mudstone interlayers, the method comprising the following steps:

[0006] Step 1: Based on the natural gamma curve, rock volume density and P-wave time difference in conventional logging data, the S-wave time difference is calculated, and the S-wave time difference is correlated with the well logging S-wave time difference obtained by actual logging to obtain the corrected S-wave time difference;

[0007] Step 2: According to elastic wave theory, the rock dynamic mechanical parameters are calculated based on the longitudinal wave time difference, the rock volume density and the corrected shear wave time difference, and the rock dynamic mechanical parameters are converted into continuous static parameters in combination with the discontinuous static parameters obtained from the indoor core test;

[0008] Step 3: Based on the continuous static parameters, the in-situ stress data is obtained through the in-situ stress calculation model, and the in-situ stress data is corrected using the on-site fracturing construction curve and the calculated fracture pressure calculated by the fracture pressure calculation model to obtain the in-situ stress profile.

[0009] According to one embodiment of the present invention, the step 1 specifically includes the following steps:

[0010] The shale content is calculated based on the natural gamma curve in the conventional logging data, and the sandstone or mudstone is determined based on the shale content;

[0011] Obtain the rock volume density and the P-wave time difference in the conventional logging data, and calculate the S-wave time difference in combination with the shale content;

[0012] The shear wave time difference is compared with the well logging shear wave time difference, and the calculation parameters are corrected to obtain a fitting curve, and further obtain the corrected shear wave time difference.

[0013] According to one embodiment of the present invention, the sandstone shear wave time difference and the mudstone shear wave time difference are calculated by the following formulas:

[0014]

[0015]

[0016] Among them, △t p1 , △t s1 Respectively represent the sandstone longitudinal wave time difference and sandstone transverse wave time difference, μs / m; △t p2 , △t s2 represents the longitudinal wave time difference and the transverse wave time difference of mudstone, μs / m; ρ represents the volume density of rock, ρ≤2.2g / cm 3 ; A represents the density of sandstone rock, g / cm 3 ρ sh Indicates the bulk density of mudstone, g / cm 3 .

[0017] According to one embodiment of the present invention, the rock dynamic mechanical parameters include: Young's modulus, Poisson's ratio, shear modulus and bulk modulus.

[0018] According to one embodiment of the present invention, the Poisson's ratio is calculated by the following formula:

[0019]

[0020] Among them, v d Represents the dynamic Poisson's ratio, dimensionless; △t s Indicates the shear wave time difference, μs / m; △t p Indicates the longitudinal wave time difference, μs / m.

[0021] According to one embodiment of the present invention, the Young's modulus is calculated by the following formula:

[0022]

[0023] Among them, E d represents the dynamic Young's modulus, GPa; ρ represents the volume density of rock, g / cm 3 ; △t s Indicates the shear wave time difference, μs / m; △t p Indicates the longitudinal wave time difference, μs / m.

[0024] According to an embodiment of the present invention, the step 2 specifically includes the following steps:

[0025] The rock static mechanical parameter test was carried out based on the triaxial stress tester to measure the static parameters of the test area, and linear regression was performed with the dynamic parameters of the same depth obtained by logging in the test area to obtain the correlation between the dynamic and static parameters of the test area;

[0026] The rock dynamic mechanical parameters are inverted using the correlation to obtain the continuous static parameters that are continuous in the vertical direction.

[0027] According to an embodiment of the present invention, the step three specifically includes the following steps:

[0028] Based on the continuous static parameters, the minimum horizontal stress and the maximum horizontal stress in the geostress data are calculated by the geostress calculation model;

[0029] Performing net pressure fitting on the on-site fracturing construction curve to obtain a longitudinal stress difference range of the minimum horizontal principal stress as a constraint condition;

[0030] Taking the measured rupture pressure as the target value and combining the constraint conditions, a regression analysis is performed on the calculated rupture pressure to obtain a regression relationship between the corrected rupture pressure and the calculated rupture pressure;

[0031] The regression factor in the regression relationship is extracted, and the geostress data is corrected to obtain the geostress profile.

[0032] According to one embodiment of the present invention, the geostress data is calculated by the following formula:

[0033]

[0034]

[0035]

[0036] Among them, σ h represents the minimum horizontal stress, MPa; σ H represents the maximum horizontal stress, MPa; v represents Poisson's ratio, dimensionless; β and γ represent geological structural stress coefficients; σ v represents the overburden pressure, MPa; α represents the effective stress coefficient; P p Indicates formation pore pressure, MPa; △D i represents the thickness of the stratum in the i-th section, m; ρ i Indicates the average bulk density of the i-th segment on the density logging curve, g / cm 3 ; g represents the acceleration due to gravity, m / s 2 .

[0037] According to another aspect of the present invention, there is also provided a device for calculating ground stress for a tight gas reservoir with sandstone and mudstone interlayers, the device comprising:

[0038] A shear wave time difference correction module is used to calculate the shear wave time difference based on the natural gamma curve, rock volume density and P-wave time difference in conventional logging data, and to perform correlation analysis between the shear wave time difference and the logging shear wave time difference obtained by actual logging to obtain the corrected shear wave time difference;

[0039] A continuous static parameter calculation module, which is used to calculate the rock dynamic mechanical parameters based on the longitudinal wave time difference, the rock volume density and the corrected shear wave time difference according to the elastic wave theory, and convert the rock dynamic mechanical parameters into continuous static parameters in combination with the discontinuous static parameters obtained from the indoor core test;

[0040] The in-situ stress profile module is used to obtain in-situ stress data through an in-situ stress calculation model based on the continuous static parameters, and to correct the in-situ stress data using an on-site fracturing construction curve and a calculated fracture pressure calculated by a fracture pressure calculation model to obtain a in-situ stress profile.

[0041] The geostress calculation method and device for sandstone-mudstone interbedded tight gas reservoirs provided by the present invention obtain relatively reliable rock dynamic mechanical parameters through the calculation and correction of shear wave time difference, and obtain continuous static parameters through correlation conversion with rock static mechanical parameters, thereby laying a relatively reliable data foundation for subsequent geostress calculation; and the calculated geostress is further corrected by fracture pressure and net pressure curve fitting, and the final geostress profile more reliably depicts and reflects the longitudinal variation law of the geostress field, thereby providing a reliable basis for subsequent oil and gas field development.

[0042] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0044] Figure 1 A flow chart of a method for calculating ground stress in a sand-shale interbedded tight gas reservoir according to an embodiment of the present invention is shown;

[0045] Figure 2 A flow chart of a method for calculating ground stress for a sand-shale interbedded tight gas reservoir according to another embodiment of the present invention is shown;

[0046] Figure 3 A diagram showing the calculation results of rock mechanics parameters according to an embodiment of the present invention is shown;

[0047] Figure 4 A schematic diagram of input parameters for fracture simulation of Well J119 according to an embodiment of the present invention is shown;

[0048] Figure 5 A diagram showing calculation and correction results of geostress data according to an embodiment of the present invention; and

[0049] Figure 6 The structure block diagram of a ground stress calculation device for a sandstone-mudstone interbedded tight gas reservoir according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0051] In order to better carry out fracturing construction and transformation of the reservoir, it is necessary to evaluate the rock mechanical parameters and geostress of the reservoir. However, the rock mechanical parameters are functions of the time difference between the longitudinal and transverse waves of the formation. In wells with array acoustic wave data, the rock mechanical parameters of the formation can be calculated based on the longitudinal and transverse wave time difference and lithology density data obtained from the logging data. However, array acoustic logging is costly and risky, so most wells rarely perform array acoustic logging unless necessary. Therefore, it is necessary to use conventional logging data to establish a method for calculating the transverse wave time difference, calculate the rock mechanical parameters in wells that lack array acoustic wave data, and further calculate the geostress.

[0052] In view of the current status of existing technologies, a method is needed to obtain rock mechanical parameters and geostress profiles based on conventional logging data and to correct them, so as to accurately characterize the geostress profile of the reservoir and provide a reference for the formulation of reservoir reconstruction plans for oil and gas reservoirs.

[0053] Figure 1 A flow chart of a method for calculating in-situ stress for a tight gas reservoir with interbedded sandstone and mudstone is shown according to an embodiment of the present invention.

[0054] like Figure 1 In step S101, the shear wave time difference is calculated based on the natural gamma curve, rock volume density and longitudinal wave time difference in conventional logging data, and the shear wave time difference is correlated with the logging shear wave time difference obtained by actual logging to obtain the corrected shear wave time difference.

[0055] Specifically, step S101 includes the following steps:

[0056] S1011. Calculate the mud content based on the natural gamma curve in conventional logging data, and determine whether it is sandstone or mudstone based on the mud content.

[0057] Furthermore, the mud content is calculated by the following formula:

[0058]

[0059]

[0060] Among them, I sh Represents the mud index, dimensionless; GR represents the natural gamma value of the target layer, API; GR min Indicates the natural gamma value of pure sandstone layer, API; GR max Indicates the natural gamma value of pure mudstone layer, API; V sh represents the mud content; G represents the empirical index, which is 3.7 for Cenozoic strata and 2 for old strata.

[0061] In one embodiment, when the mud content is greater than a preset threshold (the mud content of mudstone is higher than that of sandstone), it is determined to be mudstone and the mudstone shear wave time difference calculation formula is applicable. In practical applications, the mud and sandstone mud content discrimination standards corresponding to different blocks are different, and other methods can be used to determine whether it belongs to sandstone or mudstone, and the present invention does not limit this.

[0062] S1012. Obtain rock volume density and P-wave time difference from conventional logging data, and calculate S-wave time difference in combination with mud content.

[0063] Furthermore, the sandstone shear wave time difference and mudstone shear wave time difference are calculated by the following formulas:

[0064]

[0065]

[0066] Among them, △t p1 , △t s1 Respectively represent the sandstone longitudinal wave time difference and sandstone transverse wave time difference, μs / m; △t p2 , △t s2 represents the longitudinal wave time difference and the transverse wave time difference of mudstone, μs / m; ρ represents the volume density of rock, ρ≤2.2g / cm 3 ; A represents the density of sandstone rock, g / cm 3 ρ sh Indicates the bulk density of mudstone, g / cm 3 . A=2.5g / cm 3 ρ sh ≥2.65g / cm 3 .

[0067] S1013, comparing the shear wave time difference with the logging shear wave time difference, correcting the calculation parameters, obtaining a fitting curve, and further obtaining a corrected shear wave time difference.

[0068] like Figure 1 In step S102, according to the elastic wave theory, the dynamic mechanical parameters of the rock are calculated based on the longitudinal wave time difference, the rock volume density and the corrected shear wave time difference, and the dynamic mechanical parameters of the rock are converted into continuous static parameters in combination with the discontinuous static parameters obtained from the indoor core test.

[0069] Specifically, the dynamic mechanical parameters of rocks include: Young's modulus, Poisson's ratio, shear modulus and bulk modulus.

[0070] Furthermore, the Poisson's ratio is calculated by the following formula:

[0071]

[0072] Among them, v d Represents the dynamic Poisson's ratio, dimensionless; △t s Indicates the shear wave time difference, μs / m; △t p Indicates the longitudinal wave time difference, μs / m.

[0073] Furthermore, the Young's modulus is calculated by the following formula:

[0074]

[0075] Among them, E d represents the dynamic Young's modulus, GPa; ρ represents the volume density of rock, g / cm 3 ; △t s Indicates the shear wave time difference, μs / m; △t p Indicates the longitudinal wave time difference, μs / m.

[0076] Specifically, step S102 includes the following steps:

[0077] S1021. Conduct rock static mechanical parameter tests based on a triaxial stress tester to measure the static parameters of the test area. Perform linear regression with the dynamic parameters of the same depth obtained by logging in the test area to obtain the correlation between the dynamic and static parameters of the test area.

[0078] S1022. Invert the dynamic mechanical parameters of the rock using the correlation relationship to obtain vertically continuous static parameters.

[0079] like Figure 1 In step S103, based on the continuous static parameters, the in-situ stress data is obtained through the in-situ stress calculation model, and the in-situ stress data is corrected using the field fracturing construction curve and the calculated fracture pressure calculated by the fracture pressure calculation model to obtain the in-situ stress profile.

[0080] Specifically, step S103 includes the following steps:

[0081] S1031. Based on the continuous static parameters, the minimum horizontal stress and the maximum horizontal stress in the geostress data are calculated by a geostress calculation model.

[0082] S1032. Perform net pressure fitting on the on-site fracturing construction curve to obtain the stress difference range of the minimum horizontal principal stress in the longitudinal direction as a constraint condition.

[0083] S1033. Taking the measured rupture pressure as the target value and combining the constraint conditions, a regression analysis is performed on the calculated rupture pressure to obtain a regression relationship between the corrected rupture pressure and the calculated rupture pressure.

[0084] S1034. Extract the regression factor in the regression relationship and correct the geostress data to obtain a geostress profile.

[0085] Furthermore, the ground stress data is calculated by the following formula:

[0086]

[0087]

[0088]

[0089] Among them, σ h represents the minimum horizontal stress, MPa; σ H represents the maximum horizontal stress, MPa; v represents Poisson's ratio, dimensionless; β and γ represent geological structural stress coefficients; σ v represents the overburden pressure, MPa; α represents the effective stress coefficient; P p Indicates formation pore pressure, MPa; △D i represents the thickness of the stratum in the i-th section, m; ρ i Indicates the average bulk density of the i-th segment on the density logging curve, g / cm 3 ; g represents the acceleration due to gravity, m / s 2 .

[0090] Figure 2 A flow chart of a method for calculating in-situ stress for a tight gas reservoir with interbedded sandstone and mudstone according to another embodiment of the present invention is shown.

[0091] like Figure 2 The mud content is calculated based on the natural gamma curve in the conventional logging data, and the shear wave time difference is calculated by combining the conventional logging data such as volume density and longitudinal wave time difference. The correlation analysis is carried out with the measured logging shear wave time difference to obtain the corrected shear wave time difference. The accuracy of the shear wave time difference directly affects the subsequent mechanical parameter calculation, so the accuracy of the shear wave time difference is very important.

[0092] Specifically, in a sedimentary environment, the mud contained in sandstone is often distributed in layers to form sand-mud interlayers. The natural gamma curve is a curve that measures the change in the radioactivity intensity of the formation with depth. It can be used to calculate the mud content in sandstone, divide the lithology, and determine the permeability of the formation. The formula for calculating the mud content is as follows:

[0093]

[0094]

[0095] Among them, I sh Represents the mud index, dimensionless; GR represents the natural gamma value of the target layer, API; GR minIndicates the natural gamma value of pure sandstone layer, API; GR max Indicates the natural gamma value of pure mudstone layer, API; V sh represents mud content; G represents the empirical index.

[0096] Specifically, the P-wave and S-wave time difference is the necessary acoustic logging data for calculating the formation rock mechanical parameters, which can be extracted from the full wave logging data. However, most wells only have conventional P-wave logging data. Therefore, it is necessary to use the conventional P-wave time difference to obtain the S-wave time difference value. The S-wave time difference calculation formula is as follows:

[0097] sandstone:

[0098] Mudstone:

[0099] Among them, △t p1 , △t s1 Respectively represent the sandstone longitudinal wave time difference and sandstone transverse wave time difference, μs / m; △t p2 , △t s2 represents the longitudinal wave time difference and the transverse wave time difference of mudstone, μs / m; ρ represents the volume density of rock, ρ≤2.2g / cm 3 ; A represents the density of sandstone rock, g / cm 3 ρ sh Indicates the bulk density of mudstone, g / cm 3 . A=2.5g / cm 3 ρ sh ≥2.65g / cm 3 .

[0100] The calculated shear wave time difference cannot be directly used for the calculation of rock mechanical parameters. It needs to be correlated with the actual logging shear wave time difference and corrected to obtain the following: Figure 3 The DTS (logging shear time difference) and TS (calculated shear time difference) are shown, where AC is the measured P-wave time difference. It can be seen that the corrected calculated shear time difference (TS) has a high degree of fit with the logging shear time difference DTS, with a small error, and can be used for the subsequent calculation of rock mechanical parameters. Figure 3 SP stands for spontaneous potential, GR stands for natural gamma, YMOD stands for Young's modulus, POIS stands for Poisson's ratio, SH stands for shale content, and POR stands for porosity.

[0101] like Figure 2, rock mechanical parameters (Young's modulus, Poisson's ratio, shear modulus, bulk modulus, etc.) are obtained based on the corrected shear wave time difference. The parameters calculated by the well logging method are called dynamic rock mechanical parameters. In general, the dynamic parameter value is greater than the static value, and the static elastic parameters of rock should be used in ground stress calculation and actual engineering. Therefore, a large number of dynamic parameters are converted into continuous static parameters in combination with the static parameters (a small amount, discontinuous) obtained from indoor core tests, thus laying a reliable foundation for stress field analysis and actual engineering applications.

[0102] Specifically, according to the elastic wave theory, the P-wave time difference (Δt p ), rock volume density (ρ), combined with the calculated shear wave time difference (Δt s ), the dynamic Poisson’s ratio (v d ), dynamic Young's modulus (E d )wait.

[0103] Furthermore, the Poisson's ratio is calculated by the following formula:

[0104]

[0105] Among them, v d Represents the dynamic Poisson's ratio, dimensionless; △t s Indicates the shear wave time difference, μs / m; △t p Indicates the longitudinal wave time difference, μs / m.

[0106] Furthermore, the Young's modulus is calculated by the following formula:

[0107]

[0108] Among them, E d represents the dynamic Young's modulus, GPa; ρ represents the volume density of rock, g / cm 3 ; △t s Indicates the shear wave time difference, μs / m; △t p Indicates the longitudinal wave time difference, μs / m.

[0109] Specifically, conventional rock static mechanical parameter tests are conducted on triaxial stress testers. By measuring a series of static parameters for a certain block and performing linear regression with a series of dynamic parameters at the same depth obtained by logging, the correlation between the dynamic and static elastic parameters of the block can be obtained. Using the obtained relationship, a large number of dynamic parameters can be inverted to obtain vertically continuous static elastic mechanical parameters.

[0110] like Figure 2The geostress data (including minimum horizontal stress and maximum horizontal stress) are obtained by applying the geostress calculation model based on the relevant data obtained above, and then the geostress is corrected using the on-site fracturing construction curve or the calculated fracture pressure obtained by the fracture pressure calculation model, and finally a more reliable geostress profile is obtained.

[0111] Specifically, there are three main geostresses in the underground rock mass that are perpendicular to each other, namely the vertical geostress caused by the deadweight of the rock mass, and the maximum and minimum horizontal stresses. The fracturing effect of the rock formation is often closely related to the minimum horizontal stress.

[0112] Furthermore, the ground stress data is calculated by the following formula:

[0113] Minimum horizontal stress calculation formula:

[0114]

[0115] The maximum horizontal stress calculation formula is:

[0116]

[0117] The calculation formula of overburden rock pressure is:

[0118]

[0119] Among them, σ h represents the minimum horizontal stress, MPa; σ H represents the maximum horizontal stress, MPa; v represents Poisson's ratio, dimensionless; β and γ represent geological structural stress coefficients; σ v represents the overburden pressure (which can be calculated by integrating the formation density along the depth), MPa; α represents the effective stress coefficient; P p Indicates formation pore pressure, MPa; △D i represents the thickness of the stratum in the i-th section, m; ρ i Indicates the average bulk density of the i-th segment on the density logging curve, g / cm 3 ; g represents the acceleration due to gravity, m / s 2 .

[0120] Specifically, the full three-dimensional fracturing simulation software Meyer is used to fit the net pressure of the on-site fracturing construction curve, and the stress difference range of the minimum horizontal principal stress in the longitudinal direction is obtained. This is used as a constraint condition, and the ground stress value is inversely calculated by combining the fracture pressure calculation model with the actual fracture pressure data on site. The fracture pressure calculation formula is as follows:

[0121] P f =3σ H -σ h -P p +St

[0122] Where P f is the bursting pressure, MPa; S t is the tensile strength of rock, MPa.

[0123] Afterwards, the calculated burst pressure was subjected to regression analysis with the measured burst pressure as the target value, and the regression relationship shown in the following formula was obtained.

[0124] P f ′=AP f +B

[0125] Where P f ' is the corrected burst pressure, MPa; A and B are regression factors.

[0126] The A and B regression coefficients obtained in this way are also the correction coefficients of the minimum horizontal stress calculation formula and the maximum horizontal stress calculation formula, and finally the correction values ​​of the maximum horizontal principal stress and the minimum horizontal principal stress are obtained.

[0127] Furthermore, the burst pressure calculation formula also specifically includes the following formula:

[0128]

[0129] k=α-3β

[0130] Where k represents the non-uniform geological tectonic stress coefficient, which is dimensionless; α and β represent the maximum and minimum tectonic stress coefficients in the horizontal direction, respectively, which are dimensionless; S represents the overlying rock pressure of the formation, MPa.

[0131] According to the conventional logging curve of the actual sand-shale alternating strata, the present invention first calculates the shear wave time difference from the longitudinal wave time difference and the volume density, and makes a fitting comparison with the actual shear wave time difference to obtain the corrected shear wave time difference, and then obtains the dynamic mechanical parameters of the rock. A small amount of discontinuous static mechanical parameters of the rock measured by the core test are used to convert the dynamic parameters to static state, and continuous static mechanical parameters are obtained for the calculation of the geostress model to obtain a continuous geostress profile. The obtained geostress is then corrected by the net pressure fitting of the actual on-site fracturing construction curve and the fracture pressure, and finally a more reliable longitudinally continuously distributed geostress profile is obtained.

[0132] Figure 4 A schematic diagram of input parameters for fracture simulation of Well J119 according to an embodiment of the present invention is shown. In one embodiment, the XX block of the Ordos Basin is used as a test area, and the in-situ stress calculation method for sandstone-mudstone interbedded tight gas reservoirs proposed in the present invention is applied to construct an in-situ stress profile.

[0133] The reservoir of Block XX in the Ordos Basin is a sand-shale interlayer tight gas reservoir. The geostress calculation method of the present invention is used to calculate and correct the geostress of Well J119. The shear wave time difference is obtained based on its conventional logging data such as P-wave time difference and gamma, and then compared with the measured shear wave time difference to correct the calculation parameters. The fitting curve formula of the shear wave time difference is as follows:

[0134] TS=0.7825DTS+24.226

[0135] According to the measured P-wave time difference and the corrected S-wave time difference, the dynamic mechanical parameters of the formation rock, such as the dynamic Young's modulus and Poisson's ratio, are calculated and then compared with the static mechanical parameters measured by the triaxial mechanical experiment of the rock to determine the conversion formula between the dynamic and static mechanical parameters of the J119 well rock, as shown in the following formula:

[0136] E s =0.4090E d +0.5224

[0137] In the formula, E S represents the static Young's modulus.

[0138] The determined rock mechanics parameters are used to calculate the in-situ stress profile of Well J119, and the actual in-situ stress is corrected by integrating the actual fracture pressure data of the construction, the net pressure curve fitting and other data, such as Figure 5 As shown, Figure 5 SDYM represents the minimum horizontal principal stress, SDXM represents the maximum horizontal principal stress, and PFM represents the fracture pressure. It is used in the full three-dimensional fracturing simulation software Meyer to simulate the fracture morphology of the J119 well. The input parameters are as follows Figure 4 shown.

[0139] The present invention aims at the unique geological characteristics of tight gas reservoirs with interlayers of sand and mudstone, and uses the correlation between the longitudinal wave time difference and the transverse wave time difference to calculate and correct the transverse wave time difference. The dynamic mechanical parameters of the rock formation are calculated based on the corrected transverse wave time difference, and the relationship between dynamic and static mechanical parameters is established. Then, the longitudinally continuous static rock mechanical parameters are obtained, and the ground stress is obtained. The calculated ground stress is corrected in combination with the fracturing construction curve and the fracture pressure calculation model to obtain a more reliable ground stress profile. Using this method, a layered ground stress profile model was established for the XX block in the Ordos Basin. The calculated results are highly consistent with the measured results, which confirms the reliability of the calculation method and provides effective technical parameters for subsequent development.

[0140] Figure 6 The structure block diagram of a ground stress calculation device for a sandstone-mudstone interbedded tight gas reservoir according to an embodiment of the present invention is shown.

[0141] like Figure 6The ground stress calculation device 600 includes a shear wave time difference correction module 601, a continuous static parameter calculation module 602 and a ground stress profile module 603.

[0142] The shear wave time difference correction module 601 is used to calculate the shear wave time difference based on the natural gamma curve, rock volume density and compressional wave time difference in conventional logging data, and perform correlation analysis on the shear wave time difference and the logging shear wave time difference obtained by actual logging to obtain the corrected shear wave time difference.

[0143] The continuous static parameter calculation module 602 is used to calculate the rock dynamic mechanical parameters based on the elastic wave theory, the longitudinal wave time difference, the rock volume density and the corrected shear wave time difference, and convert the rock dynamic mechanical parameters into continuous static parameters in combination with the discontinuous static parameters obtained from the indoor core test.

[0144] The geostress profile module 603 is used to obtain geostress data through a geostress calculation model based on continuous static parameters, and to correct the geostress data using a field fracturing construction curve and a calculated fracture pressure calculated by a fracture pressure calculation model to obtain a geostress profile.

[0145] In summary, the geostress calculation method and device for sandstone-mudstone interlayer tight gas reservoirs provided by the present invention obtain relatively reliable rock dynamic mechanical parameters through the calculation and correction of shear wave time difference, and obtain continuous static parameters through correlation conversion with rock static mechanical parameters, thus laying a relatively reliable data foundation for subsequent geostress calculation; and the calculated geostress is further corrected by fracture pressure and net pressure curve fitting, and the final geostress profile more reliably depicts and reflects the longitudinal variation law of the geostress field, thus providing a reliable basis for subsequent oil and gas field development.

[0146] It should be understood that the embodiments disclosed in the present invention are not limited to the specific structures, processing steps or materials disclosed herein, but should be extended to equivalent substitutions of these features understood by ordinary technicians in the relevant field. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not meant to be limiting.

[0147] The "one embodiment" or "embodiment" mentioned in the specification means that the specific features, structures or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment" or "embodiment" appearing in various places throughout the specification do not necessarily refer to the same embodiment.

[0148] Although the embodiments disclosed in the present invention are as above, the contents described are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for calculating geostress for tight gas reservoirs with interbedded sandstone and mudstone, characterized in that: The method comprises the following steps: Step 1: Based on the natural gamma curve, rock volume density and P-wave time difference in conventional logging data, the S-wave time difference is calculated, and the S-wave time difference is correlated with the well logging S-wave time difference obtained by actual logging to obtain the corrected S-wave time difference; Step 2: According to elastic wave theory, the rock dynamic mechanical parameters are calculated based on the longitudinal wave time difference, the rock volume density and the corrected shear wave time difference, and the rock dynamic mechanical parameters are converted into continuous static parameters in combination with the discontinuous static parameters obtained from the indoor core test; Step 3: Based on the continuous static parameters, the in-situ stress data is obtained through the in-situ stress calculation model, and the in-situ stress data is corrected using the on-site fracturing construction curve and the calculated fracture pressure calculated by the fracture pressure calculation model to obtain a in-situ stress profile, wherein the in-situ stress data includes the minimum horizontal stress, the maximum horizontal stress, and the overburden formation pressure; The step three specifically includes the following steps: based on the continuous static parameters, the minimum horizontal stress and the maximum horizontal stress in the in-situ stress data are calculated by the in-situ stress calculation model; the net pressure fitting is performed on the on-site fracturing construction curve to obtain the stress difference range of the minimum horizontal stress in the longitudinal direction as a constraint condition; with the measured fracture pressure as the target value, combined with the constraint condition, the calculated fracture pressure is regressed and analyzed to obtain the regression relationship between the corrected fracture pressure and the calculated fracture pressure; the regression factor in the regression relationship is extracted to correct the in-situ stress data to obtain the in-situ stress profile; The burst pressure calculation model is: P f =3σ H -s h -P p +S t The regression relationship is: P f "AP" f +B In the formula, σ h represents the minimum horizontal stress, MPa; σ H Indicates the maximum horizontal stress, MPa; P p Indicates formation pore pressure, MPa; S t is the tensile strength of rock, MPa; P f ' is the corrected burst pressure, MPa; P f To calculate the burst pressure, MPa; A and B are regression factors; the obtained A and B regression coefficients are the correction coefficients of the minimum horizontal stress calculation formula and the maximum horizontal stress calculation formula, and finally the correction values ​​of the maximum horizontal stress and the minimum horizontal stress are obtained.

2. The method according to claim 1, characterized in that The step 1 specifically includes the following steps: The shale content is calculated based on the natural gamma curve in the conventional logging data, and the sandstone or mudstone is determined based on the shale content; Obtain the rock volume density and the P-wave time difference in the conventional logging data, and calculate the S-wave time difference in combination with the shale content; The shear wave time difference is compared with the well logging shear wave time difference, and the calculation parameters are corrected to obtain a fitting curve, and further obtain the corrected shear wave time difference.

3. The method according to claim 2, characterized in that The sandstone shear wave time difference and mudstone shear wave time difference are calculated by the following formulas: Among them, △t p1 , △t s1 Respectively represent the sandstone longitudinal wave time difference and sandstone transverse wave time difference, μs / m; △t p2 , △t s2 represents the longitudinal wave time difference and the transverse wave time difference of mudstone, μs / m; ρ represents the volume density of rock, ρ≤2.2g / cm 3 ; A1 represents the density of sandstone rock, g / cm 3 ρ sh Indicates the bulk density of mudstone, g / cm 3 .

4. The method according to claim 1, characterized in that The rock dynamic mechanical parameters include: Young's modulus, Poisson's ratio, shear modulus and bulk modulus.

5. The method according to claim 4, characterized in that The Poisson's ratio is calculated by the following formula: Among them, v d Represents the dynamic Poisson's ratio, dimensionless; △t s Indicates the shear wave time difference, μs / m; △t p Indicates the longitudinal wave time difference, μs / m.

6. The method according to claim 4, characterized in that The Young's modulus is calculated by the following formula: Among them, E d represents the dynamic Young's modulus, GPa; ρ represents the volume density of rock, g / cm 3 ; △t s Indicates the shear wave time difference, μs / m; △t p Indicates the longitudinal wave time difference, μs / m.

7. The method according to claim 1, characterized in that The step 2 specifically includes the following steps: The rock static mechanical parameter test was carried out based on the triaxial stress tester to determine the static parameters of the test area, and linear regression was performed with the dynamic parameters of the same depth obtained by logging in the test area to obtain the correlation between the dynamic and static parameters of the test area; The rock dynamic mechanical parameters are inverted using the correlation to obtain the continuous static parameters that are continuous in the vertical direction.

8. The method according to claim 1, characterized in that The ground stress data is calculated by the following formula: Among them, σ h represents the minimum horizontal stress, MPa; σ H represents the maximum horizontal stress, MPa; v represents Poisson's ratio, dimensionless; β and γ represent geological structural stress coefficients; σ v represents the overburden pressure, MPa; α represents the effective stress coefficient; P p Indicates formation pore pressure, MPa; △D i represents the thickness of the i-th layer, m; n represents the number of layers; ρ i Indicates the average bulk density of the i-th segment on the density logging curve, g / cm 3 ; g represents the acceleration due to gravity, m / s 2 .

9. A device for calculating ground stress in a tight gas reservoir with sandstone and mudstone interlayers, characterized in that: The method according to any one of claims 1 to 8 is performed, wherein the device comprises: A shear wave time difference correction module is used to calculate the shear wave time difference based on the natural gamma curve, rock volume density and P-wave time difference in conventional logging data, and to perform correlation analysis between the shear wave time difference and the logging shear wave time difference obtained by actual logging to obtain the corrected shear wave time difference; A continuous static parameter calculation module, which is used to calculate the rock dynamic mechanical parameters based on the longitudinal wave time difference, the rock volume density and the corrected shear wave time difference according to the elastic wave theory, and convert the rock dynamic mechanical parameters into continuous static parameters in combination with the discontinuous static parameters obtained from the indoor core test; The in-situ stress profile module is used to obtain in-situ stress data through an in-situ stress calculation model based on the continuous static parameters, and to correct the in-situ stress data using an on-site fracturing construction curve and a calculated fracture pressure calculated by a fracture pressure calculation model to obtain a in-situ stress profile.

Images