A method for dividing rock mechanics layers of deep tight sandstone reservoirs

Abstract

The present invention discloses a method for dividing rock mechanics layers of deep tight sandstone reservoirs. The method comprises the following steps: S1, calculating dynamic rock mechanics parameters, namely dynamic Young's modulus and dynamic Poisson's ratio, through logging; S2, converting dynamic and static rock mechanics parameters to obtain static Young's modulus and static Poisson's ratio; S3, constructing a discriminant index model for rock mechanics layers; S4, dividing rock mechanics layers. The present invention calculates through dynamic rock mechanics parameters, establishes a dynamic-static conversion model for rock mechanics parameters of the target horizon, constructs a discriminant index model for rock mechanics layers, and divides rock mechanics layers by setting different threshold values D of the discriminant index for rock mechanics layers. The present invention patent proposes a method for dividing rock mechanics layers of deep tight sandstone reservoirs, which has high practical value, and the division process is simple and clear, and the recognition result has practical value for the exploration and development of oil and gas in oil and gas-bearing basins.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration and development in oil and gas bearing basins, and particularly relates to a method for dividing rock mechanical layers of deep tight sandstone reservoirs. Background Art

[0002] A rock mechanical layer refers to a set of rock layers with similar rock mechanical properties or similar rock mechanical behaviors. The accurate characterization of rock mechanical layers is the key to the effective application of geomechanical modeling of deep tight sandstone reservoirs, and determines the accuracy of fracture prediction and in-situ stress modeling of deep tight sandstone reservoirs. Usually, qualitative geological observation methods and semi-quantitative rock mechanics experimental methods are used to characterize the rock mechanical layers of deep tight sandstone reservoirs. These two methods require a large number of cores and field samples, are time-consuming and laborious, and it is difficult to accurately divide the rock mechanical layers of deep tight sandstone reservoirs, which restricts the exploration and development of deep tight sandstone reservoirs. Therefore, how to establish a reasonable method for dividing rock mechanical layers is an actual problem faced in reservoir geomechanics. Summary of the Invention

[0003] The purpose of the present invention is to propose a method for dividing rock mechanical layers of deep tight sandstone reservoirs, which can quantitatively divide the rock mechanical layers of deep tight sandstone reservoirs, aiming at the above-mentioned deficiencies of the prior art.

[0004] A method for dividing rock mechanical layers of deep tight sandstone reservoirs according to the present invention includes the following steps:

[0005] S1, calculating dynamic rock mechanical parameters, dynamic Young's modulus and dynamic Poisson's ratio by well logging;

[0006] S2, converting dynamic and static rock mechanical parameters to obtain static Young's modulus and static Poisson's ratio ;

[0007] S3, constructing a discriminant index model for rock mechanical layers:

[0008] Construct a new discriminant index F (F1, F2... Fm) for rock mechanical layers corresponding to each logging point of a single well, where m is the number of logging points, and the relevant calculation formula is as follows:

[0009]

[0010] Wherein, is the discriminant index of the rock mechanical layer at the i-th logging point; is the static Young's modulus at the i-th logging point, in GPa; is the static Young's modulus at the (i + 1)-th logging point, in GPa; is the static Poisson's ratio of the i-th measurement point; is the static Poisson's ratio of the (i + 1)-th measurement point;

[0011] S4, Rock mechanics layer division

[0012] According to the distribution interval of the rock mechanics layer discrimination index F, set the threshold value of the rock mechanics layer discrimination index as D1. Starting from the data point F1, it is set as the rock mechanics layer. For the data point F2, if the value of F2 is less than D1, F2 and F1 are classified into the same rock mechanics layer, otherwise they are classified into different rock mechanics layers, and the rock mechanics layer division of the data point F2 is completed; for the data point F3, if the value of F3 is less than D1, F3 and the upper part are classified into the same rock mechanics layer, and the rock mechanics layer division of the data point F3 is completed; sequentially complete the rock mechanics layer division of F1, F2... Fm; for the threshold value D1 of the rock mechanics layer discrimination index, use the degree of development of structural fractures in the divided rock mechanics layer section to conduct an accuracy test of the rock mechanics layer division. If there are obvious differences in the degree of development of structural fractures in the divided rock mechanics layer section, the threshold value D1 of the rock mechanics layer discrimination index can be adjusted down to D2, and according to the above method, complete the rock mechanics layer division under the threshold value D2 of the rock mechanics layer discrimination index, and use the above method to conduct an accuracy test of the rock mechanics layer division; if there is a similar degree of development of structural fractures in the divided rock mechanics layer section, then complete the rock mechanics layer division of the target horizon. If there are obvious differences in the degree of development of structural fractures in the divided rock mechanics layer section, continue to adjust the threshold value D2 of the rock mechanics layer discrimination index down to D3... Dn (Dn > 0) until there is a similar degree of development of structural fractures in the divided rock mechanics layer section, and complete the rock mechanics layer division of the target horizon.

[0013] Furthermore, the degree of fracture development is characterized by fracture density, fracture aperture, fracture length, and fracture porosity.

[0014] Furthermore, D1 takes the middle value of the distribution interval of the rock mechanics layer discrimination index F.

[0015] Furthermore, in step S1, use the array acoustic logging data to calculate the dynamic rock mechanics parameters. The rock mechanics parameters include Young's modulus and Poisson's ratio; calculate the dynamic rock mechanics parameters based on the array acoustic logging data, and the relevant calculation formulas are as follows:

[0016]

[0017]

[0018] In the formula, is the dynamic Young's modulus, GPa; is the dynamic Poisson's ratio, dimensionless; is the rock density, kg / m 3 ; and are the shear wave travel time and the compressional wave travel time respectively, in μs / ft.

[0019] Furthermore, in step S2, triaxial rock mechanics experiments are carried out on core samples of the target horizon to obtain the static rock mechanics parameters of each core sample. The static rock mechanics parameters of multiple core samples in the target horizon are linearly fitted with their corresponding depth dynamic rock mechanics parameters to obtain the dynamic-static conversion model of rock mechanics parameters for the tight sandstone reservoir in the target horizon. The relevant calculation formulas are as follows:

[0020]

[0021]

[0022] In the formula, is the static Young's modulus, in GPa; is the static Poisson's ratio, dimensionless; a and c are coefficients; b and d are constants.

[0023] The beneficial effects of the present invention are as follows: calculating through dynamic rock mechanics parameters; establishing a dynamic-static conversion model of rock mechanics parameters for the target horizon; constructing a discriminant index model for rock mechanics layers; and dividing rock mechanics layers by setting different discriminant index thresholds D for rock mechanics layers. The present invention patent proposes a method for dividing rock mechanics layers of deep tight sandstone reservoirs, which has high practical value, and the division process is simple and clear, and the identification result has practical value for the exploration and development of oil and gas in oil and gas bearing basins. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flow chart of a method for dividing rock mechanics layers of deep tight sandstone reservoirs.

[0025] Figure 2 is a graph of the division results of rock mechanics layers with different discriminant index thresholds for Well X8. DETAILED DESCRIPTION OF THE INVENTION

[0026] The following are specific embodiments of the present invention in combination with the drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0027] This invention patent takes Well X8 in the Bozie Block of the Tarim Oilfield as an example to illustrate the specific implementation process of the present invention.

[0028] The first step is to calculate the dynamic rock mechanics parameters of the target horizon of Well X8 using the following formula;

[0029]

[0030]

[0031] Step 2: Perform linear fitting on the static rock mechanical parameters of multiple core samples at the target horizon and their corresponding dynamic rock mechanical parameters at the corresponding depths, and use the following formula to determine the static rock mechanical parameters of the target horizon of Well X8:

[0032]

[0033]

[0034] Step 3: Use the formula to calculate the rock mechanical layer discrimination index ( Figure 2 ) of the target horizon of Well X8;

[0035] The relevant calculation formulas are as follows:

[0036]

[0037] In formula (5), is the rock mechanical layer discrimination index of the i-th measurement point; is the static Young's modulus of the i-th measurement point, in GPa; is the static Young's modulus of the (i + 1)-th measurement point, in GPa; is the static Poisson's ratio of the i-th measurement point; is the static Poisson's ratio of the (i + 1)-th measurement point;

[0038] Step 4: On the basis of determining the rock mechanical layer discrimination index of the target horizon of Well X8, set the threshold D of the rock mechanical layer discrimination index to 0.2. Starting from data point F1, initially set it as a rock mechanical layer. For the next data point F2, if the value of F2 is less than 0.2, classify F2 and F1 into the same rock mechanical layer; otherwise, classify them into different rock mechanical layers, and complete the rock mechanical layer classification of data point F2. For the next data point F3, if the value of F3 is less than 0.1, classify F3 and the upper data point into the same rock mechanical layer; otherwise, classify them into different rock mechanical layers, and complete the rock mechanical layer classification of data point F3. In this way, successively complete the rock mechanical layer classification of F1, F2...F600. Analyze the fracture development degree within the divided rock mechanical layer segments, and it is considered that there are obvious differences in the fracture development degree. Set the threshold D of the rock mechanical layer discrimination index to 0.1, and according to the above rock mechanical layer classification method, complete the rock mechanical layer classification when the threshold D of the rock mechanical layer discrimination index is 0.1. Analyze the fracture development degree within the divided rock mechanical layer segments, and it is considered that there are similar fracture development degrees within the divided rock mechanical layer segments, and complete the rock mechanical layer classification of the target horizon of Well X8 ( Figure 2 ).

[0039] Wherever not covered above, the prior art shall apply.

[0040] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration purposes and not for limiting the scope of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways of substitution, but will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention should all be included within the protection scope of the present invention.

Claims

1. A method for dividing rock mechanics layers of deep tight sandstone reservoirs, characterized in that: It includes the following steps: S1, Logging calculation of dynamic rock mechanics parameters, dynamic Young's modulus , dynamic Poisson's ratio ; S2, converting the dynamic and static rock mechanical parameters to obtain the static Young's modulus , the static Poisson's ratio ; S3. Construct a discrimination index model for rock mechanics layers: Construct a new discrimination index F (F1, F2... Fm) for rock mechanics layers corresponding to each logging point of a single well, where m is the number of logging points. The relevant calculation formulas are as follows: wherein, is the rock mechanics layer discrimination index of the i-th measurement point; is the static Young's modulus of the i-th measurement point, in GPa; is the static Young's modulus of the (i + 1)-th measurement point, in GPa; is the static Poisson's ratio of the i-th measurement point; is the static Poisson's ratio of the (i + 1)-th measurement point; S4. Rock mechanics layer division According to the distribution interval of the discrimination index F for rock mechanics layers, set the discrimination index threshold for rock mechanics layers as D1. Starting from the data point F1, it is set as a rock mechanics layer. For the data point F2, if the value of F2 is less than D1, F2 and F1 are classified into the same rock mechanics layer; otherwise, they are classified into different rock mechanics layers, and the division of the rock mechanics layer for the data point F2 is completed. For the data point F3, if the value of F3 is less than D1, F3 and the upper part are classified into the same rock mechanics layer, and the division of the rock mechanics layer for the data point F3 is completed. Sequentially complete the division of the rock mechanics layers of F1, F2... Fm. For the discrimination index threshold D1 of the rock mechanics layer, use the degree of development of structural fractures within the divided rock mechanics layer segment to conduct an accuracy test for the division of the rock mechanics layer. If there are obvious differences in the degree of development of structural fractures within the divided rock mechanics layer segment, the discrimination index threshold D1 of the rock mechanics layer can be adjusted down to D2, and according to the above method, complete the division of the rock mechanics layer under the discrimination index threshold D2 of the rock mechanics layer, and use the above method to conduct an accuracy test for the division of the rock mechanics layer. If there is a similar degree of development of structural fractures within the divided rock mechanics layer segment, the division of the rock mechanics layer of the target horizon is completed. If there are obvious differences in the degree of development of structural fractures within the divided rock mechanics layer segment, continue to adjust the discrimination index threshold D2 down to D3... Dn, Dn > 0, until there is a similar degree of development of structural fractures within the divided rock mechanics layer segment, and complete the division of the rock mechanics layer of the target horizon.

2. The method for dividing rock mechanical layers of a deep tight sandstone reservoir according to claim 1, wherein: The degree of fracture development is characterized by fracture density, fracture aperture, fracture length, and fracture porosity.

3. The method for dividing rock mechanics layers of a deep tight sandstone reservoir according to claim 1, wherein: D1 takes the median value of the distribution interval of the discrimination index F for rock mechanics layers.

4. A method for dividing the rock mechanics layers of a deep and tight sandstone reservoir as described in claim 1, characterized in that: In step S1, use the array acoustic logging data to calculate the dynamic rock mechanics parameters. The rock mechanics parameters include Young's modulus and Poisson's ratio. Calculate the dynamic rock mechanics parameters based on the array acoustic logging data. The relevant calculation formulas are as follows: In the formula, is the dynamic Young's modulus, in GPa; is the dynamic Poisson's ratio, dimensionless; is the rock density, in kg / m 3 ; and are the shear wave slowness and the compressional wave slowness, respectively, in μs / ft.

5. A method for dividing rock mechanics layers of a deep and tight sandstone reservoir according to claim 1, characterized in that: In step S2, conduct a triaxial rock mechanics experiment on the core samples of the target horizon to obtain the static rock mechanics parameters of each core sample. Linearly fit the static rock mechanics parameters of multiple core samples in the target horizon with their corresponding dynamic rock mechanics parameters at the same depth to obtain a conversion model between the static and dynamic rock mechanics parameters of the tight sandstone reservoir in the target horizon. The relevant calculation formulas are as follows: In the formula, is the static Young's modulus, in GPa; is the static Poisson's ratio, dimensionless; a and c are coefficients; b and d are constants.

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