Comprehensive evaluation method for coal rock reservoir of deep coal bed gas

Abstract

The invention discloses a comprehensive evaluation method for a deep coal bed gas reservoir, and the method comprises the following specific steps: S100, classifying gas wells according to the effects of produced wells in a research area, and dividing the gas wells into three types of gas wells I, II and III; s200, in combination with gas well classification standards, carrying out classification evaluation on three types of gas wells I, II and III, including coal rock type, coal rank, coal body structure, coal seam thickness, coal seam physical property, coal seam gas-bearing property, coal seam roof and floor research and the like; and S300, establishing a coal rock reservoir comprehensive evaluation classification standard table according to classification evaluation, evaluating the reservoir quality of the undeveloped target area of the research area, and guiding coal bed gas development. By establishing the comprehensive evaluation method for the deep coal-bed gas reservoir, the method has good guiding significance for efficient development of the deep coal-bed gas, the actual reservoir characteristics of the deep coal-bed gas can be reflected, the requirement for the quality of the geological comprehensive evaluation reservoir is met, a favorable area is preferably selected for comprehensive evaluation of the deep coal-bed gas reservoir, and efficient development is achieved.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane exploration and development technology, specifically to a comprehensive evaluation method for deep coalbed methane coal-rock reservoirs. Background Technology

[0002] my country possesses vast deep coalbed methane resources with promising development prospects. However, due to the strong heterogeneity of deep coalbed methane reservoirs and the development of interbedded rock within the coal seams, evaluating high-quality reservoirs is challenging, resulting in low production rates at deployed coalbed methane wells and failing to meet the requirements for efficient coalbed methane development. Therefore, accurate and effective evaluation of favorable deep coalbed methane reservoirs is fundamental to efficient development and provides a scientific basis for the deployment of efficient deep coalbed methane development.

[0003] For example, the invention patent with patent number CN201910669207.0 discloses an evaluation method for high-yield coalbed methane reservoirs, belonging to the field of coalbed methane exploration and development technology. This invention, through the selection and acquisition of evaluation parameters, performs a primary evaluation of the coal reservoir fracture development characteristic parameters, effective stress parameters, and gas content parameters obtained in step two, referring to evaluation standards. A secondary evaluation is then performed based on the results of the primary evaluation according to the evaluation scoring standards, obtaining fracture development characteristic scores, effective stress scores, and gas content scores respectively. The evaluation result scores are calculated according to formulas, and finally, the calculated evaluation result scores are evaluated according to the evaluation result standards to obtain the coalbed methane reservoir evaluation result. This evaluation method for high-yield coalbed methane reservoirs targets high-yield coalbed methane wells, simplifies evaluation parameters, optimizes the method of obtaining evaluation parameters, proposes evaluation standards, establishes an evaluation method, and classifies the evaluation results.

[0004] Although this method for evaluating high-yield coalbed methane reservoirs simplifies evaluation parameters, optimizes the acquisition of these parameters, proposes evaluation standards, establishes evaluation methods, and classifies evaluation results, it is primarily used to evaluate engineering parameters and cannot reflect the actual characteristics of deep coalbed methane reservoirs. It fails to meet the requirements of comprehensive geological evaluation of reservoir quality, making it difficult to achieve predetermined goals in the comprehensive evaluation of deep coalbed methane reservoirs to select favorable areas and realize efficient development of coalbed methane wells; further improvement is needed. Summary of the Invention

[0005] The purpose of this invention is to provide a comprehensive evaluation method for deep coalbed methane coal-rock reservoirs. This method aims to address the shortcomings of existing methods, which primarily evaluate engineering parameters but fail to reflect the actual reservoir characteristics of deep coalbed methane. These methods cannot adequately assess the quality of the reservoir through comprehensive geological evaluation, hindering the achievement of predetermined goals in selecting favorable areas and realizing efficient development of coalbed methane wells. Further improvements are needed to address these issues.

[0006] This invention is implemented as follows: a comprehensive evaluation method for deep coalbed methane coal-rock reservoirs, the specific steps of which are as follows:

[0007] S100. Based on the performance of the producing wells in the study area, the gas wells are classified into three categories: I, II, and III.

[0008] S200, in conjunction with the gas well classification standards, conducts classification evaluations of gas wells of categories I, II and III, including coal and rock type, coal rank, coal body structure, coal seam thickness, coal seam physical properties, coal seam gas content, and research on the roof and floor of the coal seam;

[0009] S300. Establish a comprehensive evaluation and classification standard table for coal and rock reservoirs based on classification and evaluation, evaluate the quality of undeveloped target areas in the study area, and guide coalbed methane development.

[0010] Preferably, the classification of gas wells in S100 refers to the classification based on the stable daily gas production standards of vertical and horizontal wells, into three categories: I, II, and III.

[0011] Preferably, the stable daily gas production standards for the three types of gas wells (I, II, and III) refer to: a stable daily gas production of at least 50,000 cubic meters for a Class I horizontal well and at least 20,000 cubic meters for a Class I vertical well; a stable daily gas production of at least 20,000 to 50,000 cubic meters for a Class II horizontal well and at least 10,000 to 20,000 cubic meters for a Class II vertical well; and a stable daily gas production of at least 20,000 cubic meters for a Class III horizontal well and at least 10,000 cubic meters for a Class III vertical well.

[0012] Preferably, the coal and rock types in S200 are divided into bright coal, semi-bright coal, semi-dark coal, and dark coal. The favorable reservoir coal and rock types corresponding to Class I gas wells are bright coal and semi-bright coal, the favorable reservoir coal and rock types corresponding to Class II gas wells are semi-bright coal and semi-dark coal, and the reservoir coal and rock types corresponding to Class III gas wells are semi-dark coal and dark coal.

[0013] Preferably, the coal rank in S200 is divided into high-rank coal, medium-rank coal, mature low-rank coal, and low-rank coal. The favorable reservoir coal rank corresponding to Class I gas wells is high-rank coal, the favorable reservoir coal rank corresponding to Class II gas wells is medium-rank coal, and the reservoir coal rank corresponding to Class III gas wells is mature low-rank coal and low-rank coal.

[0014] Preferably, the coal body structure in S200 is divided into primary structure coal, fractured coal, granular coal, and mylonite. The favorable reservoir coal body structure corresponding to Class I gas wells is mainly primary structure coal and fractured coal, with a small amount of granular coal. The favorable reservoir coal body structure corresponding to Class II gas wells is mainly granular coal, with a small amount of fractured coal and mylonite. The reservoir coal body structure corresponding to Class III gas wells is mainly mylonite, with a small amount of fractured coal and granular coal.

[0015] Preferably, the coal seam thickness in S200 refers to the thickness of the favorable primary structural coal or fractured coal reservoir corresponding to Class I gas wells being greater than 10 meters, the thickness of the favorable primary structural coal or fractured coal reservoir corresponding to Class II gas wells being 6-10 meters, and the thickness of the favorable primary structural coal or fractured coal reservoir corresponding to Class III gas wells being less than 6 meters.

[0016] Preferably, the coal seam properties in S200 refer to the favorable reservoir porosity of Class I gas wells being above 4.5%, the favorable reservoir porosity of Class II gas wells being 3.5-4.5%, and the favorable reservoir porosity of Class III gas wells being less than 3.5%.

[0017] Preferably, the gas content of the coal seam in S200 refers to the favorable reservoir coal seam gas content of Class I gas wells being greater than 22 cubic meters per ton, the favorable reservoir coal seam gas content of Class II gas wells being 16-22 cubic meters per ton, and the favorable reservoir coal seam gas content of Class III gas wells being less than 16 cubic meters per ton.

[0018] Preferably, the top and bottom plates of the coal seam in S200 refer to the top and bottom plates of the favorable reservoir coal seam corresponding to Class I gas wells, which are limestone or mudstone with a thickness greater than 7 meters; the top and bottom plates of the favorable reservoir coal seam corresponding to Class II gas wells, which are limestone or mudstone with a thickness of 5-7 meters; and the top and bottom plates of the favorable reservoir coal seam corresponding to Class III gas wells, which are mudstone or sandstone with a mudstone thickness of less than 5 meters.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. This invention establishes a comprehensive evaluation method for deep coalbed methane reservoirs based on coal rock type, coal rank, coal body structure, coal seam thickness, coal seam physical properties, coal seam gas content, and the top and bottom plates of the coal seam. This method has significant guiding significance for the efficient development of deep coalbed methane. It can reflect the actual reservoir characteristics of deep coalbed methane, meet the requirements of comprehensive geological evaluation of reservoir quality, and help to select favorable areas in the comprehensive evaluation of deep coalbed methane reservoirs and achieve efficient development of coalbed methane wells.

[0021] 2. This invention improves the accuracy of deep coalbed methane reservoir evaluation by establishing a comprehensive evaluation method for deep coalbed methane reservoirs based on coal rock type, coal rank, coal body structure, coal seam thickness, coal seam physical properties, coal seam gas content, and the top and bottom plates of the coal seam. It also solves the problem of low production and low efficiency in well deployment caused by unreasonable reservoir evaluation. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the comprehensive evaluation method for deep coalbed methane and coal-rock reservoirs according to the present invention.

[0023] Figure 2 This is the comprehensive evaluation and classification standard table for coal and rock reservoirs of the present invention. Detailed Implementation

[0024] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0025] The following description, in conjunction with the accompanying drawings and specific embodiments, provides further details:

[0026] Example 1

[0027] like Figure 1 and Figure 2 As shown, a comprehensive evaluation method for deep coalbed methane coal-rock reservoirs is presented. The specific steps of this comprehensive evaluation method for deep coalbed methane coal-rock reservoirs are as follows:

[0028] S100. Based on the performance of the producing wells in the study area, the gas wells are classified into three categories: I, II, and III.

[0029] In S100, gas wells are classified according to the standard of stable daily gas production of vertical and horizontal wells, and are divided into three categories: I, II, and III.

[0030] The stable daily gas production standards for Class I, II, and III gas wells are as follows: Class I horizontal wells have an initial stable daily gas production of ≥50,000 cubic meters; Class I vertical wells have an initial stable daily gas production of ≥20,000 cubic meters; Class II horizontal wells have an initial stable daily gas production of 20,000 to 50,000 cubic meters; Class II vertical wells have an initial stable daily gas production of 10,000 to 20,000 cubic meters; Class III horizontal wells have an initial stable daily gas production of <20,000 cubic meters; and Class III vertical wells have an initial stable daily gas production of <10,000 cubic meters.

[0031] S200, in conjunction with the gas well classification standards, conducts classification evaluations of gas wells of categories I, II and III, including coal and rock type, coal rank, coal body structure, coal seam thickness, coal seam physical properties, coal seam gas content, and research on the roof and floor of the coal seam;

[0032] In S200, the coal and rock types are divided into bright coal, semi-bright coal, semi-dull coal, and dark coal. The favorable reservoir coal and rock types corresponding to Class I gas wells are bright coal and semi-bright coal, the favorable reservoir coal and rock types corresponding to Class II gas wells are semi-bright coal and semi-dull coal, and the reservoir coal and rock types corresponding to Class III gas wells are semi-dull coal and dark coal.

[0033] In S200, coal ranks are divided into high-rank coal, medium-rank coal, mature low-rank coal, and low-rank coal. The favorable reservoir coal rank corresponding to Class I gas wells is high-rank coal, the favorable reservoir coal rank corresponding to Class II gas wells is medium-rank coal, and the reservoir coal rank corresponding to Class III gas wells is mature low-rank coal and low-rank coal.

[0034] The coal body structure in S200 is divided into primary structure coal, fractured coal, granular coal, and mylonite. The favorable reservoir coal body structure corresponding to Class I gas wells is mainly primary structure coal and fractured coal, with a small amount of granular coal. The favorable reservoir coal body structure corresponding to Class II gas wells is mainly granular coal, with a small amount of fractured coal and mylonite. The reservoir coal body structure corresponding to Class III gas wells is mainly mylonite, with a small amount of fractured coal and granular coal.

[0035] In S200, the coal seam thickness refers to the thickness of favorable primary structural coal or fractured coal reservoirs corresponding to Class I gas wells, which is greater than 10 meters; Class II gas wells, which are 6-10 meters thick; and Class III gas wells, which are less than 6 meters thick.

[0036] In S200, the coal seam properties refer to the favorable reservoir porosity of Class I gas wells being above 4.5%, Class II gas wells being 3.5-4.5%, and Class III gas wells being less than 3.5%.

[0037] In S200, the gas content of coal seams refers to the favorable reservoir coal seam gas content of Class I gas wells being greater than 22 cubic meters per ton, Class II gas wells being 16-22 cubic meters per ton, and Class III gas wells being less than 16 cubic meters per ton.

[0038] In S200, the top and bottom plates of the coal seam refer to the favorable reservoir coal seam top and bottom plates corresponding to Class I gas wells, which are limestone or mudstone with a thickness greater than 7 meters; the favorable reservoir coal seam top and bottom plates corresponding to Class II gas wells, which are limestone or mudstone with a thickness of 5-7 meters; and the favorable reservoir coal seam top and bottom plates corresponding to Class III gas wells, which are mudstone or sandstone with a mudstone thickness of less than 5 meters.

[0039] S300. Establish a comprehensive evaluation and classification standard table for coal and rock reservoirs based on classification and evaluation, evaluate the quality of undeveloped target areas in the study area, and guide coalbed methane development.

[0040] Example 2

[0041] like Figure 1 and Figure 2 As shown, a comprehensive evaluation method for deep coalbed methane coal-rock reservoirs is presented. The specific steps of this comprehensive evaluation method for deep coalbed methane coal-rock reservoirs are as follows:

[0042] Based on the production status of the wells already in operation in the target area, gas wells are divided into three categories. The stable daily gas production standards for categories I, II, and III are as follows: Category I horizontal wells have an initial stable daily gas production of ≥50,000 cubic meters, and Category I vertical wells have an initial stable daily gas production of ≥20,000 cubic meters; Category II horizontal wells have an initial stable daily gas production of 20,000 to 50,000 cubic meters, and Category II vertical wells have an initial stable daily gas production of 10,000 to 20,000 cubic meters; Category III horizontal wells have an initial stable daily gas production of <20,000 cubic meters, and Category III vertical wells have an initial stable daily gas production of <10,000 cubic meters.

[0043] Based on the analysis of logging data, the coal rock type, coal rank, coal body structure, coal seam thickness, coal seam physical properties, coal seam gas content, and lithology and thickness of the roof and floor of Class I gas wells were analyzed. Among them, the favorable reservoir coal rock types of Class I wells are bright coal and semi-bright coal, the coal rank is high-rank coal and medium-rank coal, the coal body structure is mainly primary structure coal or fractured coal, the thickness of favorable primary structure coal or fractured coal reservoirs is greater than 10 meters, the porosity of favorable reservoirs is greater than 4.5%, the gas content is greater than 22 cubic meters / ton, and the roof and floor lithology is mainly limestone or mudstone, with the thickness of limestone and mudstone greater than 7 meters.

[0044] Based on the analysis of logging data, the coal rock type, coal rank, coal body structure, coal seam thickness, coal seam physical properties, coal seam gas content, and lithology and thickness of the roof and floor of Class II gas wells were analyzed. Among them, the favorable reservoir coal rock type of Class II wells is semi-bright coal and semi-dull coal, the coal rank is medium-rank coal, the coal body structure is mainly composed of granular coal, with a small amount of fractured coal and mylonite, the thickness of favorable primary structure coal or fractured coal reservoir is 6-10 meters, the porosity of favorable reservoir is 3.5-4.5%, the gas content is 16-22 cubic meters / ton, and the roof and floor lithology is mainly limestone or mudstone, with the thickness of limestone and mudstone being 5-7 meters.

[0045] Based on the analysis of logging data, the coal rock type, coal rank, coal body structure, coal seam thickness, coal seam physical properties, coal seam gas content, and lithology and thickness of the roof and floor of Class III gas wells were analyzed. Among them, the favorable reservoir coal rock type of Class III wells is semi-obscure coal and obscure coal, the coal rank is mature low-rank or low-rank coal, the coal body structure is mainly mylonite, containing a small amount of fractured coal and granular coal, the thickness of favorable primary structure coal or fractured coal reservoir is less than 6 meters, the porosity of favorable reservoir is less than 3.5%, the gas content is less than 16 cubic meters / ton, and the roof and floor lithology is mainly limestone or mudstone, with the thickness of limestone and mudstone less than 5 meters.

[0046] Based on the gas well classification standards, a comprehensive evaluation and classification standard for deep coalbed methane reservoirs is established, dividing deep coalbed methane reservoirs into three categories: I, II, and III.

[0047] Based on the comprehensive evaluation and classification standard table of coal and rock reservoirs, the reservoir types in the undeveloped area were analyzed and evaluated. Two development wells were deployed in the Class I reservoir area. Among them, the horizontal well Y1H initially achieved a stable daily gas production of 80,000 cubic meters, and accumulated a gas production of 23 million cubic meters after one year of production. The vertical well S1 initially achieved a stable daily gas production of 23,000 cubic meters, and accumulated a gas production of 5.8 million cubic meters after 280 days of production. The well sites deployed in favorable areas through multi-parameter comprehensive evaluation showed good production results.

[0048] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A comprehensive evaluation method for deep coalbed methane coal-rock reservoirs, characterized in that, The specific steps of this comprehensive evaluation method for deep coalbed methane coal-rock reservoirs are as follows: S100. Based on the performance of the producing wells in the study area, the gas wells are classified into three categories: I, II, and III. S200, in conjunction with the gas well classification standards, conducts classification evaluations of gas wells of categories I, II and III, including coal and rock type, coal rank, coal body structure, coal seam thickness, coal seam physical properties, coal seam gas content, and research on the roof and floor of the coal seam; S300. Establish a comprehensive evaluation and classification standard table for coal and rock reservoirs based on classification and evaluation, evaluate the quality of undeveloped target areas in the study area, and guide coalbed methane development.

2. The comprehensive evaluation method for deep coalbed methane coal-rock reservoirs according to claim 1, characterized in that, The classification of gas wells in S100 refers to the classification based on the stable daily gas production standards of vertical and horizontal wells, which are divided into three categories: I, II, and III.

3. The comprehensive evaluation method for deep coalbed methane coal-rock reservoirs according to claim 2, characterized in that, The stable daily gas production standards for the three types of gas wells (I, II, and III) are as follows: for Class I horizontal wells, the initial stable daily gas production is greater than or equal to 50,000 cubic meters; for Class I vertical wells, the initial stable daily gas production is greater than or equal to 20,000 cubic meters; for Class II horizontal wells, the initial stable daily gas production is 20,000 to 50,000 cubic meters; for Class II vertical wells, the initial stable daily gas production is 10,000 to 20,000 cubic meters; for Class III horizontal wells, the initial stable daily gas production is less than 20,000 cubic meters; and for Class III vertical wells, the initial stable daily gas production is less than 10,000 cubic meters.

4. The comprehensive evaluation method for deep coalbed methane coal-rock reservoirs according to claim 1, characterized in that, The coal and rock types in S200 are divided into bright coal, semi-bright coal, semi-dark coal, and dark coal. The favorable reservoir coal and rock types corresponding to Class I gas wells are bright coal and semi-bright coal, the favorable reservoir coal and rock types corresponding to Class II gas wells are semi-bright coal and semi-dark coal, and the reservoir coal and rock types corresponding to Class III gas wells are semi-dark coal and dark coal.

5. The comprehensive evaluation method for deep coalbed methane coal-rock reservoirs according to claim 1, characterized in that, The coal rank in S200 is divided into high-rank coal, medium-rank coal, mature low-rank coal, and low-rank coal. The favorable reservoir coal rank corresponding to Class I gas wells is high-rank coal, the favorable reservoir coal rank corresponding to Class II gas wells is medium-rank coal, and the reservoir coal rank corresponding to Class III gas wells is mature low-rank coal and low-rank coal.

6. The comprehensive evaluation method for deep coalbed methane coal-rock reservoirs according to claim 1, characterized in that, The coal body structure in S200 is divided into primary structure coal, fractured coal, granular coal, and mylonite. The favorable reservoir coal body structure corresponding to Class I gas wells is mainly primary structure coal and fractured coal, with a small amount of granular coal. The favorable reservoir coal body structure corresponding to Class II gas wells is mainly granular coal, with a small amount of fractured coal and mylonite. The reservoir coal body structure corresponding to Class III gas wells is mainly mylonite, with a small amount of fractured coal and granular coal.

7. The comprehensive evaluation method for deep coalbed methane coal-rock reservoirs according to claim 1, characterized in that, The coal seam thickness in S200 refers to the thickness of favorable primary structural coal or fractured coal reservoirs corresponding to Class I gas wells being greater than 10 meters, Class II gas wells being 6-10 meters, and Class III gas wells being less than 6 meters.

8. The comprehensive evaluation method for deep coalbed methane coal-rock reservoirs according to claim 1, characterized in that, The coal seam properties in S200 refer to the favorable reservoir porosity of Class I gas wells being above 4.5%, Class II gas wells being 3.5-4.5%, and Class III gas wells being less than 3.5%.

9. The comprehensive evaluation method for deep coalbed methane coal-rock reservoirs according to claim 1, characterized in that, The gas content of coal seams in S200 refers to the favorable reservoir coal seam gas content of Class I gas wells being greater than 22 cubic meters per ton, the favorable reservoir coal seam gas content of Class II gas wells being 16-22 cubic meters per ton, and the favorable reservoir coal seam gas content of Class III gas wells being less than 16 cubic meters per ton.

10. The comprehensive evaluation method for deep coalbed methane coal-rock reservoirs according to claim 1, characterized in that, The coal seam top and bottom plates in S200 refer to the following: for Class I gas wells, the favorable reservoir coal seam top and bottom plates are limestone or mudstone with a thickness greater than 7 meters; for Class II gas wells, the favorable reservoir coal seam top and bottom plates are limestone or mudstone with a thickness of 5-7 meters; and for Class III gas wells, the favorable reservoir coal seam top and bottom plates are mudstone or sandstone with a mudstone thickness less than 5 meters.

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