METHOD FOR EVALUATING BRITTLENESS OF DEEP SHALE RESERVOIR AND COMPUTER READABLE STORAGE MEDIUM

Abstract

A method for evaluating brittleness of a deep shale reservoir and a computer readable storage medium. The method includes determining a Rickman brittleness index of the deep shale reservoir and determining an effective pressure of the deep shale reservoir according to a pore pressure and an overlying formation pressure of the deep shale reservoir. The Rickman brittleness index is adjusted to obtain the brittleness index of the deep shale reservoir according to an exponential relationship of the brittleness index with the effective pressure of the deep shale reservoir. Inherent properties, such as rock brittle mineral content and the like, are better indicated by the Rickamn brittleness index, and then the brittleness index of the deep shale reservoir is obtained by utilizing the exponential relationship of the brittleness index with the effective pressure of the deep shale reservoir, to realize reasonable evaluation for the brittleness of the deep shale reservoir.

Claims

1. A method for evaluating brittleness of a deep shale reservoir, characterized by comprising: determining a Rickman brittleness index BI.sub.Rickman of the deep shale reservoir; determining an effective pressure Pe of the deep shale reservoir according to a pore pressure P.sub.p and an overlying formation pressure P of the deep shale reservoir; and adjusting BI.sub.Rickman to obtain BI according to an exponential relationship of the brittleness index BI with Pe of the deep shale reservoir.

2. The method for evaluating the brittleness of the deep shale reservoir according to claim 1, wherein the determining an effective pressure Pe of the deep shale reservoir according to a pore pressure P.sub.p and an overlying formation pressure P of the deep shale reservoir comprises: determining the overlying formation pressure P of the deep shale reservoir according to P=∫.sub.t.sub.0.sup.tρ(t)V(t)gdt, wherein g is gravity acceleration, ρ(t) is measured rock density, V(t) is measured rock velocity, t is time depth of the deep shale reservoir, and t.sub.0 is time depth of a reference datum plane; determining a hydrostatic pressure P.sub.0 of the deep shale reservoir according to P.sub.0=ρ.sub.wgH, wherein H is formation burial depth, and ρ.sub.w is formation water density; determining a pore pressure P.sub.p of the deep shale reservoir according to the Eaton method, wherein, $P_p=P-\left(P-P_0\right){\left(\frac{\Delta t_n}{\Delta t_s}\right)}^c,$ c is the Eaton coefficient, Δt.sub.s is measured interval transit time, and Δt.sub.n is normal compaction interval transit time; and determining the effective pressure Pe of the deep shale reservoir according to Pe=P−P.sub.p.

3. The method for evaluating the brittleness of the deep shale reservoir according to claim 2, further comprising: determining Δt.sub.n according to Δt.sub.n=Δt.sub.m+(Δt.sub.ml−Δt.sub.m)e.sup.−aH, wherein Δt.sub.m is the interval transit time of rock matrix, Δt.sub.ml is the interval transit time of the surface or seabed, H is the formation buried depth, and a is the regional index.

4. The method for evaluating the brittleness of the deep shale reservoir according to claim 1, wherein the adjusting BI.sub.Rickman to obtain BI according to an exponential relationship of the brittleness index BI with Pe of the deep shale reservoir comprises: determining BI as follows:
BI=B.sub.Rickman[e.sup.m(40−Pe)−n]/l; wherein, l is amplitude modulation factor, and m and n are obtained by fitting laboratory rock core stress-strain analysis data.

5. The method for evaluating the brittleness of the deep shale reservoir according to claim 4, wherein the determining an effective pressure Pe of the deep shale reservoir according to a pore pressure P.sub.p and an overlying formation pressure P of the deep shale reservoir comprises: determining the overlying formation pressure P of the deep shale reservoir according to P=∫.sub.t.sub.0.sup.tρ(t)V(t)gdt, wherein g is gravity acceleration, ρ(t) is measured rock density, V(t) is measured rock velocity, t is time depth of the deep shale reservoir, and t.sub.0 is time depth of a reference datum plane; determining a hydrostatic pressure P.sub.0 of the deep shale reservoir according to P.sub.0=ρ.sub.wgH, wherein H is formation burial depth, and ρ.sub.w is formation water density; determining a pore pressure P.sub.p of the deep shale reservoir according to the Eaton method, wherein, $P_p=P-\left(P-P_0\right){\left(\frac{\Delta t_n}{\Delta t_s}\right)}^c,$ c is the Eaton coefficient, Δt.sub.s is measured interval transit time, and Δt.sub.n is normal compaction interval transit time; and determining the effective pressure Pe of the deep shale reservoir according to Pe=P−P.sub.p.

6. The method for evaluating the brittleness of the deep shale reservoir according to claim 5, further comprising: determining Δt.sub.n according to Δt.sub.n=Δt.sub.m+(Δt.sub.ml−Δt.sub.m)e.sup.−aH, wherein Δt.sub.m is the interval transit time of rock matrix, Δt.sub.ml is the interval transit time of the surface or seabed, H is the formation buried depth, and a is the regional index.

7. A computer device comprising: a memory, a processor, and a computer program stored on the memory and being operable on the processor; wherein the computer program, when executed by the processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 1.

8. A computer device comprising: a memory, a processor, and a computer program stored on the memory and being operable on the processor; wherein the computer program, when executed by the processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 2.

9. A computer device comprising: a memory, a processor, and a computer program stored on the memory and being operable on the processor; wherein the computer program, when executed by the processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 3.

10. A computer device comprising: a memory, a processor, and a computer program stored on the memory and being operable on the processor; wherein the computer program, when executed by the processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 4.

11. A computer device comprising: a memory, a processor, and a computer program stored on the memory and being operable on the processor; wherein the computer program, when executed by the processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 5.

12. A computer device comprising: a memory, a processor, and a computer program stored on the memory and being operable on the processor; wherein the computer program, when executed by the processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 6.

13. A computer readable storage medium having stored thereon a brittleness evaluation program for a deep shale reservoir which, when executed by a processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 1.

14. A computer readable storage medium having stored thereon a brittleness evaluation program for a deep shale reservoir which, when executed by a processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 2.

15. A computer readable storage medium having stored thereon a brittleness evaluation program for a deep shale reservoir which, when executed by a processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 3.

16. A computer readable storage medium having stored thereon a brittleness evaluation program for a deep shale reservoir which, when executed by a processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 4.

17. A computer readable storage medium having stored thereon a brittleness evaluation program for a deep shale reservoir which, when executed by a processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 5.

18. A computer readable storage medium having stored thereon a brittleness evaluation program for a deep shale reservoir which, when executed by a processor, performs the steps of the method for evaluating the brittleness of the deep shale reservoir of claim 6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, reference will now be made briefly to the accompanying drawings, which are used in the description of the embodiments or the prior art, and it will be obvious to a person skilled in the art that other drawings may be obtained from these drawings without involving any inventive effort.

[0018] FIG. 1 is a crossplot of brittle mineral contents (i.e., brittle mineral index) with Rickman brittleness index of a deep shale reservoir in a working area;

[0019] FIG. 2 is a schematic diagram showing the relationship of rock brittleness index with effective pressure of a deep shale reservoir in a working area;

[0020] FIG. 3 is a flow chart of an implementation of a method for evaluating brittleness of a deep shale reservoir provided by an embodiment of the present application;

[0021] FIG. 4a is a Rickman brittleness index prediction result of a deep shale reservoir in a working area;

[0022] FIG. 4b is a brittle index prediction result incorporating effective pressure of a deep shale reservoir in a working area;

[0023] FIG. 5 is a hardware schematic diagram of an implementation of a computer device provided by an embodiment of the present application.

DETAILED DESCRIPTION

[0024] It should be understood that the specific embodiments described herein are merely illustrative of and not intended to limit the present application.

[0025] In the following description, suffixes such as “module”, “component”, or “unit” used to represent elements are used merely to facilitate the description of the present application and have no particular meaning in itself. Thus, “module”, “component”, or “unit” may be used in combination.

[0026] FIG. 1 is a crossplot of brittle mineral contents with Rickman brittleness index of a deep shale reservoir in a working area, the degree of dispersion of which is affected by non-mineral inherent properties such as rock cracks. Referring to FIG. 1, Rickamn brittleness index has a good mapping relationship with brittle mineral contents, i.e., the Rickamn brittleness index is a good indicator of rock brittle mineral content without changing other rock conditions. Thus, in an embodiment of the present application, the effects of rock intrinsic properties (e.g., brittle mineral content) and external factors (e.g., effective pressure of formation) on the brittle characteristics of deep shale reservoirs are considered.

[0027] FIG. 2 shows the relationship between rock brittleness and effective pressure calculated by laboratory stress-strain analysis of a rock core sample from the same section of the deep shale reservoir under different effective pressures. As can be seen from FIG. 2, the relationship curve is roughly divided into the following three sections.

[0028] {circle around (1)} A shallow surface layer abrupt area: this area simulates effective pressure environment of a shallow formation.

[0029] {circle around (2)} A conventional reservoir flat area: this area simulates relationship of the brittleness with the effective pressure of the shale reservoir in the conventional shallow part, and it is found that effective pressure has little effect on rock brittleness.

[0030] {circle around (3)} A deep reservoir falling area: this area simulates relationship between the brittleness with the effective pressure of the deep shale reservoir.

[0031] The inventors of the present application have found that the brittleness of the deep shale reservoir is exponentially related to the effective pressure. In an embodiment of the invention, the brittleness influencing factors of the deep shale reservoir are integrated, and the brittleness index of the deep shale reservoir based on the effective pressure is constructed as follows:

[00005]$\begin{array}{cc}\mathrm{BI}={\mathrm{BI}}_{\mathrm{Rickman}}\left[e^{m\left(40-\mathrm{Pe}\right)}-n\right]/l=\frac{1}{2}\left(\frac{E-E_{min}}{E_{\mathrm{ma}x}-E_{min}}+\frac{\sigma -{\sigma }_{\mathrm{ma}x}}{{\sigma }_{min}-{\sigma }_{max}}\right)\frac{\left[e^{m\left(40-\mathrm{Pe}\right)}-n\right]}{l}& \left(5\right)\end{array}$

wherein, BI.sub.Rickman is Rickman brittleness index (see Formula 4) for characterizing inherent properties such as the brittle mineral content; l is amplitude modulation factor, and if only the relative change of the brittleness of the working area is analyzed, the parameter can be set to 1; m and n can be obtained by fitting laboratory rock core stress-strain analysis data; for example, the data fitting result of FIG. 2 is m=−0.06982, n=−98.4.

[0032] In an embodiment of the application, the pore pressure P.sub.p and the overlying formation pressure P in the formula (5) are estimated by using seismic data, and Young's modulus E, Poisson's ratio σ, density ρ and velocity V of a target area are inverted, so that the deep shale reservoir brittleness evaluation is realized.

[0033] FIG. 3 is a flow chart of an implementation of a method for evaluating brittleness of a deep shale reservoir provided by an embodiment of the present application. As shown in FIG. 3, the method includes steps S302 to S306.

[0034] Step S302, determining a Rickman brittleness index of the deep shale reservoir.

[0035] In certain embodiments, the Rickman brittleness index is determined as follows.

[0036] First step, elastic impedance inversion. Under the prior constraint of the model, a maximum posterior probability solution of target inversion is derived based on the Bayesian theory:

(G.sup.TG+μQ+αC)m=(G.sup.Td+C.sup.Tξ)  (6)

wherein, G is relation matrix between reflection coefficients m and seismic data d; μ and α are constraint coefficients and can be given with corresponding constant values according to the target characteristic; ξ=ln EI(t)/ln EI(t.sub.0) provides an elastic impedance model constraint for inversion, EI(t) is an elastic impedance value at a moment t, and t.sub.0 is initial moment;

[0037] ξ=Cm, C is the integral matrix;

[00006]$Q=\mathrm{diag}\left(\frac{1}{{\left(1+m_1^2/{\sigma }_m^2\right)}^2},\frac{1}{{\left(1+m_2^2/{\sigma }_m^2\right)}^2},\mathrm{.Math.},\frac{1}{{\left(1+m_n^2/{\sigma }_m^2\right)}^2}\right),$

σ.sub.m is the parameter of the Cauchy distribution model obeyed by the target parameters.

[0038] The reflection coefficient m can be obtained by solving Formula (6) by using the iterative reweighted least square method, and then the elastic impedance is obtained by using the trace integration idea:

EI=EI(t.sub.0)exp[2∫.sub.t.sub.0.sup.tm(τ)dτ]  (7)

[0039] Step two, extracting reservoir elastic parameters based on the elastic impedance inversion data volume; and establishing the functional relationship between the Young's modulus and the elastic impedance:

[00007]$\begin{array}{cc}\left[\begin{array}{ccc}\ln \left(\frac{\mathrm{EI}\left({\theta }_1,t_1\right)}{{\mathrm{EI}}_0}\right)& \ln \left(\frac{\mathrm{EI}\left({\theta }_2,t_1\right)}{{\mathrm{EI}}_0}\right)& \ln \left(\frac{\mathrm{EI}\left({\theta }_3,t_1\right)}{{\mathrm{EI}}_0}\right)\\ \ln \left(\frac{\mathrm{EI}\left({\theta }_1,t_2\right)}{{\mathrm{EI}}_0}\right)& \ln \left(\frac{\mathrm{EI}\left({\theta }_2,t_2\right)}{{\mathrm{EI}}_0}\right)& \ln \left(\frac{\mathrm{EI}\left({\theta }_3,t_2\right)}{{\mathrm{EI}}_0}\right)\\ \mathrm{.Math.}& \mathrm{.Math.}& \mathrm{.Math.}\\ \ln \left(\frac{\mathrm{EI}\left({\theta }_1,t_n\right)}{{\mathrm{EI}}_0}\right)& \ln \left(\frac{\mathrm{EI}\left({\theta }_2,t_n\right)}{{\mathrm{EI}}_0}\right)& \ln \left(\frac{\mathrm{EI}\left({\theta }_3,t_n\right)}{{\mathrm{EI}}_0}\right)\end{array}\right]\hspace{1em}\left[\begin{array}{c}a\left({\theta }_1\right)\\ a\left({\theta }_2\right)\\ a\left({\theta }_3\right)\end{array}\right]=\left[\begin{array}{c}\ln \left(\frac{E\left(t_1\right)}{E_0}\right)\\ \ln \left(\frac{E\left(t_2\right)}{E_0}\right)\\ \mathrm{.Math.}\\ \ln \left(\frac{E\left(t_n\right)}{E_0}\right)\end{array}\right]& \left(8\right)\end{array}$

wherein EI(θ.sub.i,t) represents the elastic impedance value at a t t.sub.j.sup.th moment when an incident angle is θ.sub.i; the elastic impedance inversion data volume of the near-well seismic channel and the measured value of the Young's modulus from the well log are substituted into Formula (8) to fit a reasonable coefficient vector [a(θ.sub.1) a(θ.sub.2) a(θ.sub.3)].sup.T, and then the elastic impedance inversion data volume of the target working area and the fitted coefficient vector are substituted into Formula (8) to obtain the Young's modulus data volume of the target working area. For Poisson's ratio σ, rock density ρ and velocity V in the target working area are extracted with the same steps.

[0040] Step S304, determining an effective pressure of the deep shale reservoir according to a pore pressure and an overlying formation pressure of the deep shale reservoir.

[0041] In some embodiments, the effective pressure is determined as follows.

[0042] Firstly, the overlying formation pressure is calculated:

P=∫.sub.t.sub.0.sup.tρ(t)V(t)gdt  (9)

wherein, g is gravitational acceleration in the unit of m/s.sup.2; ρ(t) is measured rock density in the unit of kg/m.sup.3; V(t) is measured rock velocity in the unit of m/s; and t is time depth of the deep shale reservoir, and t.sub.0 is time depth of a reference datum plane.

[0043] Then, the hydrostatic pressure P.sub.0 is calculated:

P.sub.0=ρ.sub.wgH  (10)

wherein, H is formation buried depth in the unit of m; and ρ.sub.w is the formation water density in the unit of kg/m.sup.3.

[0044] Next, the pore pressure P.sub.p is estimated using the Eaton's method:

[00008]$\begin{array}{cc}{P}_p=P-\left(P-P_0\right){\left(\frac{\Delta t_n}{\Delta t_s}\right)}^c& \left(11\right)\end{array}$

wherein, c is the Eaton coefficient, an applicable constant value is selected according to the characteristics of the working area, and c=3 is generally applicable to under-compaction overpressure; Δt.sub.s=1/V is measured interval transit time in the unit of μs/m; and Δt.sub.n is normal compaction interval transit time in the unit of μs/m and can be calculated by Formula (12):

Δt.sub.n,=Δt.sub.m+(Δt.sub.ml−Δt.sub.m)e.sup.−aH  (12)

wherein, Δt.sub.m is interval transit time of a rock matrix in the unit of μs/m, and Δt.sub.m can be estimated according to mineral well logging data and a rock physical modeling theory; Δt.sub.m is interval transit time of the surface or seabed in the unit of μs/m; H is formation buried depth in the unit of m; and the constant a is a regional index and can be given empirically.

[0045] Finally, Formulas (9)-(12) are integrated, and the inverted rock density and velocity data volume in the working area are substituted to estimate the effective pressure Pe=P−P of the formation in the working area.

[0046] Step S306, adjusting the Rickman brittleness index to obtain the brittleness index of the deep shale reservoir according to an exponential relationship of the brittleness index with the effective pressure of the deep shale reservoir.

[0047] In some embodiments, according to Formula (5), a brittleness index of the deep shale reservoir is obtained, thereby achieving a deep reservoir brittleness evaluation in the working area.

[0048] FIG. 4a shows the seismic prediction result of the Rickman brittleness index of a horizon slice of the deep shale reservoir in the working area, and FIG. 4b shows the prediction result of the brittleness index considering the effective pressure in the working area.

[0049] In the figures, the buried depth of Area {circle around (1)} is greater than that of Area {circle around (2)}, and the brittleness of Area {circle around (2)} should be stronger than that of Area {circle around (1)}. The analysis and prediction results show that the brittleness index considering the effective pressure proposed by the application is more reasonable for the deep shale reservoir.

[0050] The embodiment of the application also provides a computer device, such as a smart phone, a tablet computer, a notebook computer, a desktop computer, a rack server, a blade server, a tower server or a cabinet server (comprising an independent server or a server cluster formed by a plurality of servers), and the like which can execute programs. As shown in FIG. 5, the computer device 50 of the present embodiment includes at least, but is not limited to a memory 51 and a processor 52 communicatively connected to each other via a system bus. It should be noted, however, that it should be understood that not all illustrated components may be required and that more or fewer components may be implemented instead.

[0051] In this embodiment, the memory 51 (i.e., readable storage medium) includes flash memory, hard disk, multimedia card, card-type memory (e.g., SD or DX memory, etc.), random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), magnetic memory, magnetic disk, optical disk, etc. In some embodiments, the memory 51 may be an internal storage unit of the computer device 50, such as a hard disk or memory of the computer device 50. In other embodiments, the memory 51 may also be an external storage device of the computer device 50, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) card, a Flash Card, etc., provided on the computer device 50. Of course, the memory 51 may also comprise both the internal storage unit and the external storage device of the computer device 50. In this embodiment, the memory 51 is typically used to store an operating system and various types of application software installed on the computer device 50, such as program codes for deep shale reservoir brittleness evaluation, etc. In addition, the memory 51 may also be used to temporarily store various types of data that have been or are to be output.

[0052] The processor 52 may be, in some embodiments, a central processing unit (CPU), a controller, a microcontroller, a microprocessor, or other data processing chip. The processor 52 is typically used to control the overall operation of the computer device 50. In this embodiment, the processor 52 is configured to run program codes or process data stored in the memory 51, such as a brittleness evaluation program for a deep shale reservoir, to implement the steps of the method for evaluating brittleness of the deep shale reservoir.

[0053] This embodiment also provides a computer-readable storage medium, such as flash memory, hard disk, multimedia card, card-type memory (e.g., SD or DX memory, etc.), random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), magnetic storage, magnetic disk, optical disk, server, App application mall or the like which has stored thereon a computer program, and the computer program, when executed by a processor, performs a corresponding function. The computer readable storage medium of the embodiment is used for storing a brittleness evaluation program for a deep shale reservoir which, when executed by a processor, realizes a method for evaluating brittleness of the deep shale reservoir.

[0054] It should be noted that the terms “including”, comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element defined by the phrase “comprises a . . . ” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0055] The above-mentioned embodiments of the present application are by way of illustration only and do not represent advantages or disadvantages of the embodiments.

[0056] From the above description of the embodiments, it will be clear to a person skilled in the art that the above-described embodiment method can be implemented by means of software plus a necessary general-purpose hardware platform, but in many cases the former is a better embodiment. Based on this understanding, the technical solution of the present application, in essence or in part contributing to the prior art, may be embodied in the form of a software product stored in a storage medium (e.g., ROM/RAM, diskette, optical disk) that includes instructions for causing a terminal (which may be a cell phone, computer, server, air conditioner, network device, etc.) to perform the methods described in the various embodiments of the present application.

[0057] Embodiments of the present application have been described above with reference to the accompanying drawings, but the present application is not limited to the specific embodiments described above, which are merely illustrative and not restrictive, and those skilled in the art, from the enlightenment of this application, may make many forms falling within the protection of this application without departing from the spirit and claimed scope of the invention.