CN113777668A - Geostress calculation method and device for tight gas reservoir of sand-shale interbed - Google Patents
Geostress calculation method and device for tight gas reservoir of sand-shale interbed Download PDFInfo
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Abstract
The invention provides a geostress calculation method for a sand-shale interbed compact gas reservoir, which comprises the following steps: calculating to obtain a transverse wave time difference, and performing correlation analysis on the transverse wave time difference and a logging transverse wave time difference obtained by actually-measured logging to obtain a corrected transverse wave time difference; calculating to obtain dynamic mechanical parameters of the rock, and converting the dynamic mechanical parameters of the rock into continuous static parameters by combining discontinuous static parameters obtained by an indoor rock core test; and (3) solving to obtain ground stress data through a ground stress calculation model based on the continuous static parameters, and correcting the ground stress data by using the site fracturing construction curve and the calculated fracture pressure calculated by the fracture pressure calculation model to obtain a ground stress profile. According to the method, through calculation and correction of the transverse wave time difference, reliable dynamic mechanical parameters of the rock are obtained, and continuous static parameters are obtained through correlation conversion of the dynamic mechanical parameters and the static mechanical parameters of the rock, so that a reliable data base is laid for subsequent calculation of the ground stress.
Description
Technical Field
The invention relates to the technical field of oil and gas field development, in particular to a ground stress calculation method and a ground stress calculation device for a sand-shale interbed compact gas reservoir.
Background
The ground stress is a local load acting on the underground rock formation, and is a force per unit area in the earth caused by the combined action of the gravity of the overlying rock formation, the vertical motion and the horizontal motion in the earth crust and other factors, and can be decomposed into 1 vertical stress and 2 horizontal stresses, wherein the 2 horizontal stresses are usually unequal. The crustal stress profile can reflect the change rule of a crustal stress field in the longitudinal direction, and the accurate acquisition of the layered crustal stress parameters can provide a basis for the decision and design of each link of drilling engineering, oil and gas reservoir engineering, oil extraction engineering and the like, and particularly in hydraulic fracturing operation, the crustal stress and rock mechanical parameters have important guiding significance for the formulation of a perforation scheme, three-dimensional fracturing simulation and engineering parameter optimization.
At present, the crustal stress measurement method mainly comprises 3 technologies of indoor core test, inversion of logging data and field actual measurement. The logging method can continuously measure the mechanical properties of rocks, but conventional logging information usually lacks transverse wave logging data, and when the method is used for simulating and calculating stress, the data error is larger; the mechanical characteristics measured by the core indoor test are accurate, but the test precision is influenced by various factors, the test cost is high, and the data is limited; the field fracturing test is the most accurate method for measuring the ground stress at present, the test result of the method can be used as a standard for testing the precision of other tests, but the method is limited by conditions, is less applied and cannot obtain a continuous ground stress profile. Therefore, how to acquire the ground stress profile by using the conventional logging information (excluding the shear wave logging data) and correct the ground stress profile by combining the fracturing construction data has great significance for the development of oil and gas fields.
Therefore, the invention provides a geostress calculation method and device for a sand-shale interbed compact gas reservoir.
Disclosure of Invention
In order to solve the problems, the invention provides a geostress calculation method for a sand-shale interbed compact gas reservoir, which comprises the following steps:
the method comprises the following steps: calculating to obtain a transverse wave time difference based on a natural gamma curve, rock volume density and longitudinal wave time difference in conventional logging data, and performing correlation analysis on the transverse wave time difference and a logging transverse wave time difference obtained by actually-measured logging to obtain a corrected transverse wave time difference;
step two: according to an elastic fluctuation theory, calculating to obtain rock dynamic mechanical parameters based on the longitudinal wave time difference, the rock volume density and the corrected transverse wave time difference, and converting the rock dynamic mechanical parameters into continuous static parameters by combining discontinuous static parameters obtained by an indoor core test;
step three: and based on the continuous static parameters, calculating the ground stress data through a ground stress calculation model, and correcting the ground stress data by using the site fracturing construction curve and the calculated fracture pressure calculated by the fracture pressure calculation model to obtain a ground stress profile.
According to an embodiment of the present invention, the step one specifically includes the following steps:
calculating to obtain the shale content based on the natural gamma curve in the conventional logging data, and judging to belong to sandstone or mudstone based on the shale content;
obtaining the rock volume density and the longitudinal wave time difference in the conventional logging information, and calculating by combining the shale content to obtain the transverse wave time difference;
and comparing the transverse wave time difference with the logging transverse wave time difference, correcting the calculation parameters to obtain a fitting curve, and further obtaining the corrected transverse wave time difference.
According to an embodiment of the invention, the sandstone transverse wave time difference and the mudstone transverse wave time difference are respectively calculated by the following formulas:
wherein, Δ tp1、△ts1Respectively representing sandstone longitudinal wave time difference and sandstone transverse wave time difference, mu s/m; delta tp2、△ts2Respectively representing mudstone longitudinal wave time difference and mudstone transverse wave time difference, mu s/m; rho represents the volume density of the rock, and rho is less than or equal to 2.2g/cm3(ii) a A represents sandstone rock density, g/cm3；ρshRepresents the bulk density of the mudstone in g/cm3。
According to one embodiment of the invention, the rock dynamics parameters comprise: young's modulus, poisson's ratio, shear modulus, and bulk modulus.
According to one embodiment of the present invention, the poisson's ratio is calculated by the following formula:
wherein v isdRepresents the dynamic Poisson's ratio, dimensionless; delta tsRepresents the transverse wave time difference, mu s/m; delta tpRepresents the longitudinal wave time difference, μ s/m.
According to one embodiment of the invention, the young's modulus is calculated by the following formula:
wherein E isdRepresents the dynamic young's modulus, GPa; rho represents the rock bulk density, g/cm3；△tsRepresents the transverse wave time difference, mu s/m; delta tpRepresents the longitudinal wave time difference, μ s/m.
According to an embodiment of the present invention, the second step specifically includes the following steps:
performing a rock static mechanical parameter test based on a triaxial stress tester, determining a static parameter of a test area, and performing linear regression with a dynamic parameter of the same depth obtained by logging in the test area to obtain a correlation between the dynamic parameter and the static parameter of the test area;
and inverting the dynamic mechanical parameters of the rocks by using the correlation to obtain the continuous static parameters which are continuous in the longitudinal direction.
According to an embodiment of the present invention, the step three specifically includes the following steps:
calculating the minimum horizontal stress and the maximum horizontal stress in the geostress data through the geostress calculation model based on the continuous static parameters;
carrying out net pressure fitting on the site fracturing construction curve to obtain a stress difference range of the minimum horizontal principal stress in the longitudinal direction as a constraint condition;
performing regression analysis on the calculated rupture pressure by taking the measured rupture pressure as a target value and combining the constraint condition to obtain a regression relation between the corrected rupture pressure and the calculated rupture pressure;
and extracting regression factors in the regression relationship, and correcting the ground stress data to obtain the ground stress profile.
According to one embodiment of the invention, the ground stress data is calculated by the following formula:
wherein σhRepresents the minimum horizontal stress, MPa; sigmaHRepresents the maximum horizontal stress, MPa; v represents the poisson's ratio, dimensionless; beta and gamma represent the stress coefficient of the geological structure; sigmavRepresents overburden pressure, MPa; α represents an effective stress coefficient; ppRepresents the formation pore pressure, MPa; delta DiRepresents the thickness of the ith stratum, m; rhoiRepresents the average bulk density, g/cm, of the i-th section on the density log3(ii) a g represents the acceleration of gravity, m/s2。
According to another aspect of the present invention, there is also provided a geostress calculation apparatus for a tight gas reservoir of a sandstone-shale interbed, the apparatus comprising:
the transverse wave time difference correction module is used for calculating to obtain transverse wave time difference based on a natural gamma curve, rock volume density and longitudinal wave time difference in conventional logging data, and performing correlation analysis on the transverse wave time difference and logging transverse wave time difference obtained by actually-measured logging to obtain corrected transverse wave time difference;
the continuous static parameter calculation module is used for calculating rock dynamic mechanical parameters based on the longitudinal wave time difference, the rock volume density and the corrected transverse wave time difference according to an elastic fluctuation theory, and converting the rock dynamic mechanical parameters into continuous static parameters by combining discontinuous static parameters obtained by an indoor core test;
and the ground stress profile module is used for solving ground stress data through a ground stress calculation model based on the continuous static parameters, and correcting the ground stress data by utilizing the site fracturing construction curve and the calculated fracture pressure calculated by the fracture pressure calculation model to obtain a ground stress profile.
According to the method and the device for calculating the geostress of the tight gas reservoir of the sand-mud-rock interbed, provided by the invention, the more reliable dynamic mechanical parameters of the rock are obtained through calculation and correction of the transverse wave time difference, and the continuous static parameters are obtained through the correlation conversion of the dynamic mechanical parameters and the static mechanical parameters of the rock, so that a more reliable data base is laid for the calculation of the follow-up geostress; and the calculated crustal stress is corrected again through fracture pressure and net pressure curve fitting, and the finally obtained crustal stress profile is more reliably depicted and reflects the change rule of a crustal stress field in the longitudinal direction, so that a reliable basis is provided for the subsequent development of oil and gas fields.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
FIG. 1 shows a flow chart of a method for geostress calculation of a tight gas reservoir of a sand-shale interbed according to an embodiment of the invention;
FIG. 2 shows a flow chart of a geostress calculation method for a tight gas reservoir of a sand-shale interbed according to another embodiment of the invention;
FIG. 3 shows a graph of results of rock-mechanics parameter calculations according to an embodiment of the invention;
FIG. 4 shows a schematic of J119 well fracture simulation input parameters according to one embodiment of the present invention;
FIG. 5 is a graph illustrating the results of calculation and correction of geostress data according to one embodiment of the invention; and
FIG. 6 shows a block diagram of a geostress calculation device for a tight gas reservoir of a sand-shale interbed according to an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in further detail below with reference to the accompanying drawings.
In order to better perform fracturing construction transformation on a reservoir stratum, rock mechanical parameters and ground stress of the reservoir stratum need to be evaluated. However, the rock mechanics parameters are a function of the time difference between the longitudinal wave and the transverse wave of the stratum, in the well with the array acoustic wave data, the stratum rock mechanics parameters can be calculated according to the longitudinal wave time difference, the transverse wave time difference and the lithologic density data obtained by the logging data, and the array acoustic wave logging is high in cost and high in risk, so most wells rarely carry out the array acoustic wave logging unless necessary, therefore, a method for calculating the transverse wave time difference needs to be established by using the conventional logging data, the rock mechanics parameters are calculated for the well lacking the array acoustic wave data, and the ground stress is further calculated.
Aiming at the current situation of the prior art, a method for acquiring rock mechanical parameters and a ground stress profile based on conventional logging data and correcting the rock mechanical parameters and the ground stress profile is needed, the ground stress profile of a reservoir is precisely described, and a reference basis is provided for formulating a reservoir transformation scheme of an oil and gas reservoir.
FIG. 1 shows a flow chart of a method for calculating geostress for a tight gas reservoir of a sand-shale interbed according to an embodiment of the invention.
As shown in fig. 1, in step S101, a transverse wave time difference is calculated based on a natural gamma curve, a rock volume density, and a longitudinal wave time difference in conventional logging data, and correlation analysis is performed between the transverse wave time difference and a logging transverse wave time difference obtained by actual logging, so as to obtain a corrected transverse wave time difference.
Specifically, step S101 specifically includes the following steps:
s1011, calculating to obtain the argillaceous content based on a natural gamma curve in the conventional logging data, and judging to belong to sandstone or mudstone based on the argillaceous content.
Further, the argillaceous content is calculated by the following formula:
wherein, IshExpressing the mud index without dimension; GR denotes the natural gamma value, API, of the destination layer; GRminRepresenting the natural gamma value, API, of the pure sandstone interval; GRmaxRepresenting the natural gamma value, API, of the pure shale interval; vshExpressing the mud content; g represents the empirical index, with 3.7 for the new world formation and 2 for the old formation.
In one embodiment, when the shale content is larger than a preset threshold (the shale content is higher than the sandstone shale content), the shale is judged to be suitable for the shale transverse wave time difference calculation formula. In practical application, the muds and sandstone shale content corresponding to different blocks have different judgment standards, and whether the sandstone or the mudstone belongs to the sandstone or the mudstone can be judged by adopting other modes, which is not limited by the invention.
S1012, obtaining the rock volume density and the longitudinal wave time difference in the conventional logging data, and calculating by combining the shale content to obtain the transverse wave time difference.
Further, the sandstone transverse wave time difference and the mudstone transverse wave time difference are respectively calculated by the following formulas:
wherein, Δ tp1、△ts1Respectively representing sandstone longitudinal wave time difference and sandstone transverse wave time difference, mu s/m; delta tp2、△ts2Respectively representing mudstone longitudinal wave time difference and mudstone transverse wave time difference, mu s/m; rho represents the volume density of the rock, and rho is less than or equal to 2.2g/cm3(ii) a A represents sandstone rock density, g/cm3；ρshRepresents the bulk density of the mudstone in g/cm3。A＝2.5g/cm3；ρsh≥2.65g/cm3。
And S1013, comparing the transverse wave time difference with the logging transverse wave time difference, correcting the calculation parameters to obtain a fitting curve, and further obtaining the corrected transverse wave time difference.
As shown in fig. 1, in step S102, according to the elastic fluctuation theory, rock dynamic mechanical parameters are obtained by calculation based on the longitudinal wave time difference, the rock volume density, and the corrected transverse wave time difference, and the rock dynamic mechanical parameters are converted into continuous static parameters by combining the discontinuous static parameters obtained by the indoor core test.
In particular, the rock dynamic mechanical parameters include: young's modulus, poisson's ratio, shear modulus, and bulk modulus.
Further, the poisson's ratio is calculated by the following formula:
wherein v isdRepresents the dynamic Poisson's ratio, dimensionless; delta tsRepresents the transverse wave time difference, mu s/m; delta tpRepresents the longitudinal wave time difference, μ s/m.
Further, the young's modulus is calculated by the following formula:
wherein E isdRepresents the dynamic young's modulus, GPa; rho represents the rock bulk density, g/cm3；△tsRepresents the transverse wave time difference, mu s/m; delta tpRepresents the longitudinal wave time difference, μ s/m.
Specifically, step S102 specifically includes the following steps:
and S1021, performing a rock static mechanical parameter test based on a triaxial stress tester, determining a static parameter of a test area, and performing linear regression with a dynamic parameter of the same depth obtained by logging in the test area to obtain a correlation between the dynamic parameter and the static parameter of the test area.
And S1022, inverting the dynamic mechanical parameters of the rock by utilizing the correlation to obtain continuous static parameters in the longitudinal direction.
As shown in fig. 1, in step S103, the geostress data is obtained by the geostress calculation model based on the continuous static parameters, and is corrected by using the on-site fracture construction curve and the calculated fracture pressure calculated by the fracture pressure calculation model to obtain the geostress profile.
Specifically, step S103 specifically includes the following steps:
and S1031, calculating the minimum horizontal stress and the maximum horizontal stress in the geostress data through a geostress calculation model based on the continuous static parameters.
S1032, carrying out net pressure fitting on the site fracturing construction curve to obtain a stress difference range of the minimum horizontal principal stress in the longitudinal direction, and using the stress difference range as a constraint condition.
And S1033, performing regression analysis on the calculated rupture pressure by taking the measured rupture pressure as a target value and combining constraint conditions to obtain a regression relation between the corrected rupture pressure and the calculated rupture pressure.
S1034, extracting regression factors in the regression relationship, and correcting the ground stress data to obtain a ground stress profile.
Further, the ground stress data is calculated by the following formula:
wherein σhRepresents the minimum horizontal stress, MPa; sigmaHRepresents the maximum horizontal stress, MPa; v represents the poisson's ratio, dimensionless; beta and gamma represent the stress coefficient of the geological structure; sigmavTo representOverburden pressure, MPa; α represents an effective stress coefficient; ppRepresents the formation pore pressure, MPa; delta DiRepresents the thickness of the ith stratum, m; rhoiRepresents the average bulk density, g/cm, of the i-th section on the density log3(ii) a g represents the acceleration of gravity, m/s2。
FIG. 2 shows a flow chart of a method for calculating geostress for a tight gas reservoir of a sand-shale interbed according to another embodiment of the invention.
As shown in fig. 2, the shale content is calculated based on the natural gamma curve in the conventional logging data, the transverse wave time difference is calculated by combining the conventional logging data such as the volume density and the longitudinal wave time difference, and the correlation analysis is performed with the actually measured logging transverse wave time difference to obtain the corrected transverse wave time difference, and the subsequent mechanical parameter calculation is directly influenced by the accuracy of the transverse wave time difference, so the accuracy of the transverse wave time difference is very important.
In particular, in a sedimentary environment, the muds contained in the sand tend to be distributed in layers forming an alternating layer of sand and muds. The natural gamma curve is a curve measuring the change of stratum radioactive intensity along with depth, and can be used for calculating the shale content in sandstone, dividing lithology and determining a permeable stratum. The calculation formula of the argillaceous content is as follows:
wherein, IshExpressing the mud index without dimension; GR denotes the natural gamma value, API, of the destination layer; GRminRepresenting the natural gamma value, API, of the pure sandstone interval; GRmaxRepresenting the natural gamma value, API, of the pure shale interval; vshExpressing the mud content; g represents an empirical index.
Specifically, the longitudinal and transverse wave time differences are acoustic logging data necessary for calculating the mechanical parameters of the formation rock, and can be extracted from full wave train logging data, but most wells only have conventional longitudinal wave logging data, so that the transverse wave time differences need to be obtained by using the conventional longitudinal wave time differences. The transverse wave time difference calculation formula is as follows:
sandstone:
mudstone:
wherein, Δ tp1、△ts1Respectively representing sandstone longitudinal wave time difference and sandstone transverse wave time difference, mu s/m; delta tp2、△ts2Respectively representing mudstone longitudinal wave time difference and mudstone transverse wave time difference, mu s/m; rho represents the volume density of the rock, and rho is less than or equal to 2.2g/cm3(ii) a A represents sandstone rock density, g/cm3；ρshRepresents the bulk density of the mudstone in g/cm3。A＝2.5g/cm3；ρsh≥2.65g/cm3。
The calculated transverse wave time difference cannot be directly used for calculating rock mechanical parameters, correlation analysis needs to be performed on the calculated transverse wave time difference and the measured transverse wave time difference of actual logging, and DTS (logging transverse wave time difference) and TS (calculated transverse wave time difference) shown in FIG. 3 are obtained after correction, wherein AC is the measured longitudinal wave time difference. It can be seen that the corrected calculated transverse wave time difference (TS) and the well logging transverse wave time difference DTS have high fitting degree and small error, and can be used for calculating subsequent rock mechanics parameters. In FIG. 3, SP represents the natural potential, GR represents the natural gamma, YMOD represents the Young's modulus, POIS represents the Poisson's ratio, SH represents the argillaceous content, and POR represents the porosity.
As shown in fig. 2, rock mechanical parameters (young's modulus, poisson's ratio, shear modulus, bulk modulus, etc.) are obtained from the corrected transverse wave time difference. The parameters obtained by the logging method are called dynamic mechanical parameters of rocks, the dynamic parameter values are generally larger than static values, and the static elastic parameters of the rocks are adopted in the crustal stress calculation and the actual engineering. Therefore, a large amount of dynamic parameters are converted into continuous static parameters by combining the static parameters (small amount and discontinuity) obtained by the indoor core test, thereby laying a reliable foundation for stress field analysis and practical engineering application.
Specifically, the time difference (Δ t) of longitudinal waves obtained from the well log data according to the elastic wave theoryp) Rock bulk density (p) in combination with a calculated transverse wave time difference (Δ t)s) The dynamic Poisson's ratio (v) can be obtainedd) Dynamic Young's modulus (E)d) And the like.
Further, the poisson's ratio is calculated by the following formula:
wherein v isdRepresents the dynamic Poisson's ratio, dimensionless; delta tsRepresents the transverse wave time difference, mu s/m; delta tpRepresents the longitudinal wave time difference, μ s/m.
Further, the young's modulus is calculated by the following formula:
wherein E isdRepresents the dynamic young's modulus, GPa; rho represents the rock bulk density, g/cm3；△tsRepresents the transverse wave time difference, mu s/m; delta tpRepresents the longitudinal wave time difference, μ s/m.
Specifically, conventional static mechanical parameter tests of rock are performed on a triaxial stress tester. A series of static parameters are measured for a certain block, and linear regression is carried out on the static parameters and a series of dynamic parameters with the same depth obtained by well logging, so that the correlation between the dynamic and static elastic parameters of the block can be obtained. A large number of dynamic parameters can be inverted by using the obtained relation, and the longitudinally continuous static elastomechanics parameters are obtained.
As shown in fig. 2, the geostress data (including the minimum horizontal stress and the maximum horizontal stress) is obtained from the obtained related data by applying a geostress calculation model, and then the geostress is corrected by using the on-site fracturing construction curve or the calculated fracture pressure obtained from the fracture pressure calculation model, so as to finally obtain a more reliable geostress profile.
Specifically, there are three principal earth stresses in the underground rock mass that are mutually perpendicular in direction, namely a vertical earth stress, a maximum and a minimum horizontal stress caused by the self weight of the rock mass. The fracturing effect of the formation is often closely related to the minimum level of stress.
Further, the ground stress data is calculated by the following formula:
minimum horizontal stress calculation formula:
maximum horizontal stress calculation formula:
overburden pressure calculation formula:
wherein σhRepresents the minimum horizontal stress, MPa; sigmaHRepresents the maximum horizontal stress, MPa; v represents the poisson's ratio, dimensionless; beta and gamma represent the stress coefficient of the geological structure; sigmavRepresents overburden pressure (which may be given by an integral calculation of formation density along depth), MPa; α represents an effective stress coefficient; ppRepresents the formation pore pressure, MPa; delta DiRepresents the thickness of the ith stratum, m; rhoiRepresents the average bulk density, g/cm, of the i-th section on the density log3(ii) a g represents the acceleration of gravity, m/s2。
Specifically, net pressure fitting is carried out on the site fracturing construction curve by applying full three-dimensional fracturing simulation software Meyer to obtain the stress difference range of the minimum horizontal principal stress in the longitudinal direction, and the stress difference range is used as a constraint condition to reversely calculate the earth stress value by combining a fracture pressure calculation model and site actual fracture pressure data. The cracking pressure calculation formula is as follows:
Pf＝3σH-σh-Pp+St
in the formula, PfRupture pressure, MPa; stThe tensile strength of rock is MPa.
Then, regression analysis is performed on the calculated burst pressure with the measured burst pressure as a target value to obtain a regression relationship shown by the following formula.
Pf′＝APf+B
In the formula, Pf' to correct for burst pressure, MPa; A. b is a regression factor.
The A, B regression coefficients thus obtained are also the correction coefficients of the minimum level stress calculation formula and the maximum level stress calculation formula, and finally the correction values of the maximum level principal stress and the minimum level principal stress are obtained.
Further, the calculation formula of the burst pressure specifically includes the following formula:
k＝α-3β
in the formula, k represents a non-uniform geologic structure stress coefficient and has no dimension; alpha and beta respectively represent the maximum and minimum structural stress coefficients in the horizontal direction, and have no dimension; s represents overburden pressure, MPa, of the formation.
According to the conventional well logging curve of the actual sand-shale interaction stratum, firstly, the longitudinal wave time difference and the volume density are used for calculating the transverse wave time difference, and the transverse wave time difference is matched and compared with the actual transverse wave time difference to obtain the corrected transverse wave time difference, so that the dynamic mechanical parameters of the rock are obtained. And carrying out dynamic and static conversion by using a small amount of discontinuous static mechanical parameters and dynamic parameters of the rock measured by a rock core test to obtain continuous static mechanical parameters for calculating an earth stress model to obtain a continuous earth stress profile. And then correcting the obtained ground stress by net pressure fitting and fracture pressure of an actual site fracturing construction curve, and finally obtaining a reliable ground stress profile with longitudinal continuous distribution.
FIG. 4 shows a schematic of J119 well fracture simulation input parameters according to one embodiment of the present invention. In one embodiment, the XX block of the Ordos basin is used as a test area, and the crustal stress profile is constructed by applying the crustal stress calculation method for the sand-shale interbed compact gas reservoir.
The reservoir of the XX block of the Ordors basin belongs to a sand-shale interbed compact gas reservoir, and the crustal stress calculation method is adopted to calculate and correct the crustal stress of the J119 well under the flag. And acquiring transverse wave time difference according to conventional logging data such as longitudinal wave time difference, gamma and the like, comparing with the actually measured transverse wave time difference, and correcting the calculation parameters. The fitting curve formula of the transverse wave time difference is as follows:
TS＝0.7825DTS+24.226
according to the actually measured longitudinal wave time difference and the corrected transverse wave time difference, dynamic mechanical parameters such as the dynamic Young modulus, the Poisson ratio and the like of the stratum rock are obtained through calculation, then the dynamic mechanical parameters are compared and analyzed with static mechanical parameters measured through a rock triaxial mechanical experiment, and a J119 well rock dynamic and static mechanical parameter conversion formula is determined, and the formula is as follows:
Es＝0.4090Ed+0.5224
in the formula, ESThe Young's modulus in the static state is shown.
And (3) correcting the actual ground stress by using the determined rock mechanics parameter meter J119 well ground stress profile and integrating data such as construction actual fracture pressure data, net pressure curve fitting and the like, wherein SDYM represents the minimum horizontal main stress, SDXM represents the maximum horizontal main stress and PFM represents the fracture pressure in FIG. 5. The method is applied to simulation research of J119 well fracture morphology in full three-dimensional fracture simulation software Meyer, and input parameters of the method are shown in the following figure 4.
The method aims at the specific geological characteristics of the sand-shale interbed compact gas reservoir, and calculates and corrects the transverse wave time difference by utilizing the correlation between the longitudinal wave time difference and the transverse wave time difference. And then calculating dynamic mechanical parameters of the rock stratum according to the corrected transverse wave time difference, establishing a dynamic and static mechanical parameter relation, then obtaining longitudinal continuous static rock mechanical parameters, and further obtaining the ground stress. And correcting the calculated crustal stress by combining the fracturing construction curve and the fracture pressure calculation model so as to obtain a more reliable crustal stress profile. By utilizing the method, a layered ground stress profile model is established for the XX block of the Ordos basin, the coincidence degree of the calculation result and the actual measurement result is very high, the reliability of the calculation method is verified, and effective technical parameters are provided for subsequent development.
FIG. 6 shows a block diagram of a geostress calculation device for a tight gas reservoir of a sand-shale interbed according to an embodiment of the invention.
As shown in fig. 6, the geostress calculation apparatus 600 includes a transverse wave time difference correction module 601, a continuous static parameter calculation module 602, and a geostress profile module 603.
The transverse wave time difference correction module 601 is configured to calculate a transverse wave time difference based on a natural gamma curve, a rock volume density, and a longitudinal wave time difference in conventional logging data, perform correlation analysis on the transverse wave time difference and a logging transverse wave time difference obtained by actually-measured logging, and obtain a corrected transverse wave time difference.
The continuous static parameter calculation module 602 is configured to calculate, according to an elastic fluctuation theory, dynamic rock mechanical parameters based on the longitudinal wave time difference, the rock volume density, and the corrected transverse wave time difference, and convert the dynamic rock mechanical parameters into continuous static parameters by combining discontinuous static parameters obtained by an indoor core test.
The ground stress profile module 603 is configured to obtain ground stress data through a ground stress calculation model based on the continuous static parameters, and correct the ground stress data by using the on-site fracture construction curve and the calculated fracture pressure calculated by the fracture pressure calculation model to obtain a ground stress profile.
In conclusion, the geostress calculation method and the device for the sand-shale interbed compact gas reservoir provided by the invention obtain more reliable dynamic mechanical parameters of the rock through calculation and correction of the transverse wave time difference, and perform related conversion with the static mechanical parameters of the rock to obtain continuous static parameters, thereby laying a more reliable data base for the calculation of the follow-up geostress; and the calculated crustal stress is corrected again through fracture pressure and net pressure curve fitting, and the finally obtained crustal stress profile is more reliably depicted and reflects the change rule of a crustal stress field in the longitudinal direction, so that a reliable basis is provided for the subsequent development of oil and gas fields.
It is to be understood that the disclosed embodiments of the invention are not limited to the particular structures, process steps, or materials disclosed herein but are extended to equivalents thereof as would be understood by those ordinarily skilled in the relevant arts. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase "one embodiment" or "an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.
Although the embodiments of the present invention have been described above, the above description is only for the convenience of understanding the present invention, and is not intended to limit the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A geostress calculation method for a tight gas reservoir of a sand-shale interbed, the method comprising the steps of:
the method comprises the following steps: calculating to obtain a transverse wave time difference based on a natural gamma curve, rock volume density and longitudinal wave time difference in conventional logging data, and performing correlation analysis on the transverse wave time difference and a logging transverse wave time difference obtained by actually-measured logging to obtain a corrected transverse wave time difference;
step two: according to an elastic fluctuation theory, calculating to obtain rock dynamic mechanical parameters based on the longitudinal wave time difference, the rock volume density and the corrected transverse wave time difference, and converting the rock dynamic mechanical parameters into continuous static parameters by combining discontinuous static parameters obtained by an indoor core test;
step three: and based on the continuous static parameters, calculating the ground stress data through a ground stress calculation model, and correcting the ground stress data by using the site fracturing construction curve and the calculated fracture pressure calculated by the fracture pressure calculation model to obtain a ground stress profile.
2. The method of claim 1, wherein the first step comprises the steps of:
calculating to obtain the shale content based on the natural gamma curve in the conventional logging data, and judging to belong to sandstone or mudstone based on the shale content;
obtaining the rock volume density and the longitudinal wave time difference in the conventional logging information, and calculating by combining the shale content to obtain the transverse wave time difference;
and comparing the transverse wave time difference with the logging transverse wave time difference, correcting the calculation parameters to obtain a fitting curve, and further obtaining the corrected transverse wave time difference.
3. The method of claim 2, wherein the sandstone transverse wave time difference and the mudstone transverse wave time difference are calculated by the following formulas:
wherein, Δ tp1、△ts1Respectively representing sandstone longitudinal wave time difference and sandstone transverse wave time difference, mu s/m; delta tp2、△ts2Respectively represents the mudstone longitudinal wave time difference and the mudstone transverse wave time difference, mu s-m; rho represents the volume density of the rock, and rho is less than or equal to 2.2g/cm3(ii) a A represents sandstone rock density, g/cm3；ρshRepresents the bulk density of the mudstone in g/cm3。
4. The method of claim 1, wherein the rock dynamics parameters comprise: young's modulus, poisson's ratio, shear modulus, and bulk modulus.
5. The method of claim 4, wherein the Poisson's ratio is calculated by the formula:
wherein v isdRepresents the dynamic Poisson's ratio, dimensionless; delta tsRepresents the transverse wave time difference, mu s/m; delta tpRepresents the longitudinal wave time difference, μ s/m.
6. The method of claim 4, wherein the young's modulus is calculated by the formula:
wherein E isdRepresents the dynamic young's modulus, GPa; rho represents the rock bulk density, g/cm3；△tsRepresents the transverse wave time difference, mu s/m; delta tpRepresents the longitudinal wave time difference, μ s/m.
7. The method of claim 1, wherein the second step specifically comprises the steps of:
performing a rock static mechanical parameter test based on a triaxial stress tester, determining a static parameter of a test area, and performing linear regression with a dynamic parameter of the same depth obtained by logging in the test area to obtain a correlation between the dynamic parameter and the static parameter of the test area;
and inverting the dynamic mechanical parameters of the rocks by using the correlation to obtain the continuous static parameters which are continuous in the longitudinal direction.
8. The method of claim 1, wherein the third step comprises the steps of:
calculating the minimum horizontal stress and the maximum horizontal stress in the geostress data through the geostress calculation model based on the continuous static parameters;
carrying out net pressure fitting on the site fracturing construction curve to obtain a stress difference range of the minimum horizontal principal stress in the longitudinal direction as a constraint condition;
performing regression analysis on the calculated rupture pressure by taking the measured rupture pressure as a target value and combining the constraint condition to obtain a regression relation between the corrected rupture pressure and the calculated rupture pressure;
and extracting regression factors in the regression relationship, and correcting the ground stress data to obtain the ground stress profile.
9. The method of claim 8, wherein the geostress data is calculated by the formula:
wherein σhRepresents the minimum horizontal stress, MPa; sigmaHRepresents the maximum horizontal stress, MPa; v representsPoisson's ratio, dimensionless; beta and gamma represent the stress coefficient of the geological structure; sigmavRepresents overburden pressure, MPa; α represents an effective stress coefficient; ppRepresents the formation pore pressure, MPa; delta DiRepresents the thickness of the ith stratum, m; rhoiRepresents the average bulk density, g/cm, of the i-th section on the density log3(ii) a g represents the acceleration of gravity, m/s2。
10. A geostress calculation apparatus for a tight gas reservoir of a sand-shale interbed, the apparatus comprising:
the transverse wave time difference correction module is used for calculating to obtain transverse wave time difference based on a natural gamma curve, rock volume density and longitudinal wave time difference in conventional logging data, and performing correlation analysis on the transverse wave time difference and logging transverse wave time difference obtained by actually-measured logging to obtain corrected transverse wave time difference;
the continuous static parameter calculation module is used for calculating rock dynamic mechanical parameters based on the longitudinal wave time difference, the rock volume density and the corrected transverse wave time difference according to an elastic fluctuation theory, and converting the rock dynamic mechanical parameters into continuous static parameters by combining discontinuous static parameters obtained by an indoor core test;
and the ground stress profile module is used for solving ground stress data through a ground stress calculation model based on the continuous static parameters, and correcting the ground stress data by utilizing the site fracturing construction curve and the calculated fracture pressure calculated by the fracture pressure calculation model to obtain a ground stress profile.
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