Novel shale oil and gas reservoir brittleness determination method

Abstract

The invention discloses a novel shale oil and gas reservoir brittleness determination method, which comprises the following steps of shale oil and gas reservoir brittleness classification analysis: determining brittleness index characteristics of different types of shale oil and gas reservoirs by taking a brittleness index as a reference; reservoir brittleness function construction: constructing a reservoir brittleness function according to rock mechanical response characteristics of different types of shale reservoirs; rock mechanics analysis and brittleness function parameter determination: determining related parameters in brittleness functions of different types of shale oil and gas reservoirs according to specific oil and gas reservoir rock mechanics parameter experiments; and calculating a shale oil and gas reservoir brittleness data body: calculating the reservoir brittleness by applying the brittleness function and the shale reservoir rock mechanical parameter data body. The method can overcome the defects that an existing brittleness index method is poor in adaptability and low in precision to the brittleness technology of the shale oil and gas reservoir under the special geological conditions in China, meanwhile, the defect that the method is not suitable for the brittleness technology of the continental facies shale oil and gas reservoir is overcome, and a new method is provided for accurately determining the brittleness of different types of shale oil and gas reservoirs.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development engineering, and in particular to a new method for determining the brittleness of shale oil and gas reservoirs. Background Art

[0002] As a very important oil and gas replacement resource, shale oil and gas has huge resources, but shale oil and gas must be fractured to obtain industrial production capacity. Therefore, the brittleness of shale oil and gas reservoirs is an important indicator parameter for evaluating the quality of shale reservoirs, and it is also one of the important bases for the design and optimization of shale oil and gas reservoir fracturing construction plans. Therefore, the accurate prediction or determination of shale brittleness is of great significance to the exploration and development of shale oil and gas.

[0003] The method currently commonly used for shale brittleness evaluation is mainly the brittleness index formula proposed by American reservoir physicist Gateway in 2008. This formula uses Young's modulus and Poisson's ratio to characterize the brittleness of rocks, and has played an important role in the development of shale oil and gas in North America. Domestic shale oil and gas development currently directly draws on this technology, and has achieved certain results in the development of marine shale gas. However, for the more widely distributed terrestrial and marine-terrestrial transitional shale oil and gas reservoirs, the application effect of this technology is not ideal. Therefore, it is very necessary to invent a new technology that can accurately determine the brittleness of shale oil and gas reservoirs to provide support for shale oil and gas development. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a new method for determining the brittleness of shale oil and gas reservoirs, which can overcome the defects of the current brittleness index method in poor adaptability and low accuracy to the brittleness technology of shale oil and gas reservoirs under China's special geological conditions, and at the same time overcome the disadvantage that this method is not suitable for the brittleness technology of terrestrial shale oil and gas reservoirs, and provides a new method for accurately determining the brittleness of different types of shale oil and gas reservoirs.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A new method for determining the brittleness of shale oil and gas reservoirs comprises the following steps:

[0007] S1. Classification and analysis of brittleness of shale oil and gas reservoirs: Using the brittleness index as a reference, determine the brittleness index characteristics of different types of shale oil and gas reservoirs;

[0008] S2. Construction of reservoir brittleness function: Construct reservoir brittleness function according to the rock mechanical response characteristics of different types of shale reservoirs;

[0009] S3. Rock mechanics analysis and brittleness function parameter determination: Determine the relevant parameters in the brittleness function of different types of shale oil and gas reservoirs based on the rock mechanics parameter experiments of specific oil and gas reservoirs;

[0010] S4. Calculation of shale oil and gas reservoir brittleness data body: Apply brittleness function and shale reservoir rock mechanics parameter data body to obtain reservoir brittleness.

[0011] Furthermore, in step S1, the brittleness of different types of shale oil and gas reservoirs is analyzed with reference to the brittleness index, and the brittleness index characteristics of marine shale reservoirs and non-marine shale reservoirs are analyzed respectively to determine the differences in rock mechanical properties between marine shale reservoirs, non-marine shale reservoirs and surrounding rocks.

[0012] Furthermore, step S1 includes the following sub-steps:

[0013] The reservoir brittleness index is calculated based on the well logging curves of the drilled wells using the brittleness index calculation formula:

[0014]

[0015]

[0016]

[0017] Where: BI is the brittleness index of shale gas reservoir, unit is %; E is the static Young's modulus, E min is the minimum static Young's modulus, E max is the maximum value of the static Young's modulus, in MPa; σ is the static Poisson's ratio, σ min is the minimum static Poisson’s ratio, σ max is the maximum value of static Poisson's ratio, in MPa;

[0018] The reservoir category is determined according to the fracturing effect of the target oil and gas wells, and the shale oil and gas reservoirs are divided into brittleness index increased type, brittleness index decreased type, and intermediate brittleness index. The reservoir with a larger brittleness index, better fracturing effect and better brittleness is an increased brittleness index reservoir; the reservoir with a smaller brittleness index, better fracturing effect and better brittleness is a reduced brittleness index reservoir; the reservoir with a moderate brittleness index, better fracturing effect and better brittleness is an intermediate brittleness index reservoir.

[0019] Furthermore, in step S2, in marine shale reservoirs, the more brittle minerals there are, the better the brittleness. Taking the brittleness parameter as a variable, the brittleness parameter is an augmenting variable in the reservoir brittleness function. In non-marine shale reservoirs, the reservoir brittleness is best when the brittle minerals are moderate, so the brittleness parameter is an intermediate variable in the reservoir brittleness function.

[0020] Furthermore, step S2 includes the following sub-steps:

[0021] According to the brittleness classification result of shale oil and gas reservoirs in step S1, a brittleness function with a brittleness index as a direct variable is constructed for different types of reservoirs;

[0022] For the enlarged shale oil and gas reservoir, the brittleness function expression is:

[0023]

[0024] For intermediate shale oil and gas reservoirs, the brittleness function expression is:

[0025]

[0026] For the reduced shale oil and gas reservoir, the brittleness function expression is:

[0027]

[0028] In the above formula, f1 is the steepness of the curve, f2 is the value corresponding to F(BI)=50, c is the mean value of the variable, and σ is the variance.

[0029] Furthermore, in step S3, rock mechanical parameters are first tested on the core of the known well, and then the parameters in the brittleness function are determined by curve fitting or regression technology.

[0030] Furthermore, step S3 includes the following sub-steps:

[0031] Conduct rock mechanics analysis and measurement, and draw a brittleness and brittleness index relationship curve by measuring the drilled core;

[0032] The relevant function parameters in equations (4), (5) and (6) are obtained according to the response curves, thereby determining the regional brittleness function and using it to calculate the reservoir brittleness at any point in the region.

[0033] Furthermore, in step S4, prestack inversion is first performed to obtain the isotropic rock mechanical parameter data volume in the compressibility function, and then the brittleness of the reservoir is calculated using the brittleness function to obtain the shale reservoir brittleness data volume.

[0034] Furthermore, the isotropic rock mechanics parameter data volumes in the compressibility function obtained through prestack inversion include Young's modulus and Poisson's ratio data volumes.

[0035] Furthermore, in step S4, the Young's modulus and Poisson's ratio data bodies obtained by prestack inversion are combined with equations (1), (2), and (3) to obtain the brittleness index BI data body, and then according to the shale oil and gas reservoir type, the corresponding reservoir brittleness function is selected in equations (4), (5), and (6) to calculate the reservoir brittleness data body.

[0036] The beneficial effects of the present invention are:

[0037] The shale oil and gas reservoir brittleness determination method of the present invention takes into account the differences in brittle rock mechanical characteristics of different types of shale reservoirs, constructs brittleness expression functions of different types of shale oil and gas reservoirs, and establishes a new rock brittleness calculation method and process, which overcomes the shortcomings of traditional technology that is only suitable for marine shale oil and gas reservoirs and has low accuracy in brittleness calculation of non-marine shale oil and gas reservoirs, greatly improves the prediction accuracy of shale oil and gas reservoir brittleness, and achieves good results in shale oil and gas reservoir TOC brittleness prediction, shale oil and gas reservoir brittleness evaluation and construction plan design. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart of a method for determining brittleness of shale oil and gas reservoirs according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation methods of the present invention are now described. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the embodiments described are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0040] like Figure 1 As shown, this embodiment provides a new method for determining the brittleness of shale oil and gas reservoirs, comprising the following steps:

[0041] S1. Classification and analysis of brittleness of shale oil and gas reservoirs: Using the brittleness index as a reference, determine the brittleness index characteristics of different types of shale oil and gas reservoirs;

[0042] S2. Construction of reservoir brittleness function: Construct reservoir brittleness function according to the rock mechanical response characteristics of different types of shale reservoirs;

[0043] S3. Rock mechanics analysis and brittleness function parameter determination: Determine the relevant parameters in the brittleness function of different types of shale oil and gas reservoirs based on the rock mechanics parameter experiments of specific oil and gas reservoirs;

[0044] S4. Calculation of shale oil and gas reservoir brittleness data body: Apply brittleness function and shale reservoir rock mechanics parameter data body to obtain reservoir brittleness.

[0045] Preferably, the method for determining the brittleness of shale oil and gas reservoirs is specifically implemented as follows:

[0046] 1) Classification and analysis of brittleness of shale oil and gas reservoirs

[0047] At present, shale oil and gas reservoirs can be divided into three categories according to their geological classification, namely marine shale oil and gas reservoirs, continental oil and gas reservoirs and marine-continental transitional phase oil and gas reservoirs. The conventional brittleness index calculation method is mainly for marine shale oil and gas reservoirs. For marine oil and gas reservoirs, the larger the brittleness index, the better the brittleness, but it is not applicable to the other two categories.

[0048] Therefore, this embodiment uses the brittleness index as a reference to analyze the brittleness of different types of shale oil and gas reservoirs, analyzes the brittleness index characteristics of marine shale reservoirs and non-marine shale reservoirs, and determines the differences in rock mechanical properties between marine shale reservoirs, non-marine shale reservoirs and surrounding rocks.

[0049] Specifically, the reservoir brittleness index is first calculated based on the well logging curve of the drilled well using the brittleness index calculation formula:

[0050]

[0051]

[0052]

[0053] Where: BI is the brittleness index of shale gas reservoir, unit is %; E is the static Young's modulus, E min is the minimum static Young's modulus, E max is the maximum value of the static Young's modulus, in MPa; σ is the static Poisson's ratio, σ min is the minimum static Poisson’s ratio, σ max is the maximum static Poisson's ratio, and the unit is MPa.

[0054] Then, the reservoir category is determined according to the fracturing effect of the target oil and gas wells, and the shale oil and gas reservoirs are divided into brittleness index increased type, brittleness index decreased type, and intermediate brittleness index type. The reservoir with a larger brittleness index, better fracturing effect, and better brittleness is an increased brittleness index reservoir; the reservoir with a smaller brittleness index, better fracturing effect, and better brittleness is a reduced brittleness index reservoir; the reservoir with a moderate brittleness index, better fracturing effect, and better brittleness is an intermediate brittleness index reservoir.

[0055] 2) Construction of reservoir brittleness function

[0056] In marine shale reservoirs, the more brittle minerals there are, the better the brittleness. Taking the brittleness parameter as a variable, the brittleness parameter is an increasing variable in the reservoir brittleness function. In non-marine shale reservoirs, the reservoir brittleness is best when the brittle minerals are moderate, so the brittleness parameter is an intermediate variable in the reservoir brittleness function.

[0057] Therefore, this step constructs a brittleness function with the brittleness index as a direct variable for different types of reservoirs based on the brittleness classification results of shale oil and gas reservoirs in the previous step.

[0058] For the enlarged shale oil and gas reservoir, the brittleness function expression is:

[0059]

[0060] For intermediate shale oil and gas reservoirs, the brittleness function expression is:

[0061]

[0062] For the reduced shale oil and gas reservoir, the brittleness function expression is:

[0063]

[0064] In the above formula, f1 is the steepness of the curve, f2 is the value corresponding to F(BI)=50, c is the mean value of the variable, and σ is the variance.

[0065] 3) Rock mechanics analysis and brittleness function parameter determination

[0066] In this step, rock mechanical parameters are first tested on the cores of known wells, and then the parameters in the brittleness function are determined by curve fitting or regression technology.

[0067] Specifically, rock mechanics analysis and measurement are first carried out, and the relationship curve between brittleness and brittleness index is drawn by measuring the drilled core. Then, the relevant function parameters in equations (4), (5), and (6) are obtained according to the response curve, so as to determine the regional brittleness function and use it to calculate the reservoir brittleness at any point in the area.

[0068] 4) Calculation of brittle data volume of shale oil and gas reservoirs

[0069] For different types of shale oil and gas reservoirs, the brittleness of the reservoir needs to be determined using formulas (4), (5), and (6). The relevant function parameters such as f1, f2, c, and σ have been determined in step 3). In this step, only the brittleness index BI needs to be obtained to apply functions (4), (5), and (6) to obtain the reservoir brittleness. The brittleness index BI needs to be obtained by applying formulas (1), (2), and (3). There are two variables in formulas (1), (2), and (3), namely E-static Young's modulus and σ-static Poisson's ratio. The calculation of these two quantities requires the application of seismic prestack inversion.

[0070] Therefore, in this step, prestack inversion is first performed to obtain the isotropic rock mechanical parameter data volume in the compressibility function, and then the brittleness function is applied to calculate the reservoir brittleness to obtain the shale reservoir brittleness data volume. Among them, the isotropic rock mechanical parameter data volume in the compressibility function includes the Young's modulus and Poisson's ratio data volume.

[0071] Finally, the Young's modulus and Poisson's ratio data obtained by prestack inversion are combined with equations (1), (2), and (3) to obtain the brittleness index BI data body. Then, according to the type of shale oil and gas reservoir, the corresponding reservoir brittleness function is selected in equations (4), (5), and (6) to calculate the reservoir brittleness data body.

[0072] It should be noted that, for the aforementioned method embodiments, for the sake of simplicity of description, they are expressed as a series of action combinations, but those skilled in the art should be aware that the present application is not limited by the order of the actions described, because according to the present application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present application.

Claims

1. A new method for determining the brittleness of shale oil and gas reservoirs, characterized in that: The following steps are involved: S1. Classification and analysis of brittleness of shale oil and gas reservoirs: Using the brittleness index as a reference, determine the brittleness index characteristics of different types of shale oil and gas reservoirs; S2. Construction of reservoir brittleness function: Construct reservoir brittleness function according to the rock mechanical response characteristics of different types of shale reservoirs; S3. Rock mechanics analysis and brittleness function parameter determination: Determine the relevant parameters in the brittleness function of different types of shale oil and gas reservoirs based on the rock mechanics parameter experiments of specific oil and gas reservoirs; S4. Calculation of shale oil and gas reservoir brittleness data body: Apply brittleness function and shale reservoir rock mechanics parameter data body to obtain reservoir brittleness.

2. The new method for determining brittleness of shale oil and gas reservoirs according to claim 1 is characterized in that: In step S1, the brittleness of different types of shale oil and gas reservoirs is analyzed with reference to the brittleness index, and the brittleness index characteristics of marine shale reservoirs and non-marine shale reservoirs are analyzed respectively to determine the differences in rock mechanical properties between marine shale reservoirs, non-marine shale reservoirs and surrounding rocks.

3. The new method for determining brittleness of shale oil and gas reservoirs according to claim 1 is characterized in that: Step S1 includes the following sub-steps: The reservoir brittleness index is calculated based on the well logging curves of the drilled wells using the brittleness index calculation formula: Where: BI is the brittleness index of shale gas reservoir, unit is %; E is the static Young's modulus, E min is the minimum static Young's modulus, E max is the maximum value of the static Young's modulus, in MPa; σ is the static Poisson's ratio, σ min is the minimum static Poisson’s ratio, σ max is the maximum value of static Poisson's ratio, in MPa; The reservoir category is determined according to the fracturing effect of the target oil and gas wells, and the shale oil and gas reservoirs are divided into brittleness index increased type, brittleness index decreased type, and intermediate brittleness index. The reservoir with a larger brittleness index, better fracturing effect and better brittleness is an increased brittleness index reservoir; the reservoir with a smaller brittleness index, better fracturing effect and better brittleness is a reduced brittleness index reservoir; the reservoir with a moderate brittleness index, better fracturing effect and better brittleness is an intermediate brittleness index reservoir.

4. The new method for determining brittleness of shale oil and gas reservoirs according to claim 3 is characterized in that: In step S2, in marine shale reservoirs, the more brittle minerals there are, the better the brittleness. Taking the brittleness parameter as a variable, the brittleness parameter is an increasing variable in the reservoir brittleness function. In non-marine shale reservoirs, the reservoir brittleness is best when the brittle minerals are moderate, so the brittleness parameter is an intermediate variable in the reservoir brittleness function.

5. The new method for determining brittleness of shale oil and gas reservoirs according to claim 3 is characterized in that: Step S2 includes the following sub-steps: According to the brittleness classification result of shale oil and gas reservoirs in step S1, a brittleness function with a brittleness index as a direct variable is constructed for different types of reservoirs; For the enlarged shale oil and gas reservoir, the brittleness function expression is: For intermediate shale oil and gas reservoirs, the brittleness function expression is: For the reduced shale oil and gas reservoir, the brittleness function expression is: In the above formula, f1 is the steepness of the curve, f2 is the value corresponding to F(BI)=50, c is the mean value of the variable, and σ is the variance.

6. The new method for determining brittleness of shale oil and gas reservoirs according to claim 5 is characterized in that: In step S3, rock mechanical parameters are first tested on the core of the known well, and then the parameters in the brittleness function are determined by curve fitting or regression technology.

7. The new method for determining brittleness of shale oil and gas reservoirs according to claim 5 is characterized in that: Step S3 includes the following sub-steps: Conduct rock mechanics analysis and measurement, and draw a brittleness and brittleness index relationship curve by measuring the drilled core; The relevant function parameters in equations (4), (5) and (6) are obtained according to the response curves, thereby determining the regional brittleness function and using it to calculate the reservoir brittleness at any point in the region.

8. The new method for determining brittleness of shale oil and gas reservoirs according to claim 7 is characterized in that: In step S4, pre-stack inversion is first performed to obtain the isotropic rock mechanical parameter data volume in the compressibility function, and then the brittleness of the reservoir is calculated using the brittleness function to obtain the shale reservoir brittleness data volume.

9. The new method for determining brittleness of shale oil and gas reservoirs according to claim 8, characterized in that: The isotropic rock mechanical parameter data volumes in the compressibility function obtained through prestack inversion include Young's modulus and Poisson's ratio data volumes.

10. The new method for determining brittleness of shale oil and gas reservoirs according to claim 9, characterized in that: In step S4, the Young's modulus and Poisson's ratio data bodies obtained by prestack inversion are combined with equations (1), (2), and (3) to obtain the brittleness index BI data body. Then, according to the type of shale oil and gas reservoir, the corresponding reservoir brittleness function is selected in equations (4), (5), and (6) to calculate the reservoir brittleness data body.

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