Method for evaluating tectonic fractures of continental facies shale oil reservoir based on lithofacies constraint

Abstract

A lithofacies constraint-based tectonic fracture evaluation method for a continental facies shale oil reservoir belongs to the field of petroleum geology science, and comprises the following steps: (1) carrying out continental facies shale lithofacies type division on a research area; (2) on the basis of the lithofacies type division of the research area in the step (1), extracting characteristic parameters which influence the development of the tectonic fracture, wherein the characteristic parameters comprise a continental facies shale brittleness index I, a rock structure index S and a rock mechanical layer thickness H; (3) analyzing the sensitivity of different characteristic parameters in the step (2) to the development strength response of the tectonic fracture; (4) analyzing combination modes of brittleness indexes, rock structure indexes and rock mechanical layer thickness indexes of different types of lithofacies; and (5) establishing a quantitative evaluation index of continental facies shale oil reservoir structure fractures based on lithofacies, and calculating fracture development indexes Fj of different types of lithofacies. The method can be applied to evaluation of continental facies shale oil reservoir structure fractures, and provides technical support for reasonable development of continental facies shale oil reservoirs in China.

Description

Technical Field

[0001] The invention belongs to the field of petroleum geology, and in particular is a method for evaluating structural fractures of continental shale oil reservoirs based on lithofacies constraints. Background Art

[0002] In recent years, as continental shale oil wells have achieved high production one after another, shale oil has become a more realistic exploration breakthrough target and resource succession area for major domestic oil fields.

[0003] Compared with conventional sandstone and tight sandstone reservoirs, shale reservoirs have poor matrix properties, and the oil and gas permeability in the reservoir mainly depends on the development of natural fractures. However, at this stage, the quantitative evaluation of natural fractures in shale oil reservoirs still needs in-depth research and the establishment of accurate evaluation methods.

[0004] Structural fractures are the dominant type of natural fractures in shale oil reservoirs. Due to the limitations of the amount of core data and the accuracy of logging data, the identification and evaluation of structural fractures in shale oil reservoirs are very difficult. Therefore, there is an urgent need for a new parameter system and method that can be applied to the quantitative evaluation of structural fractures in continental shale oil reservoirs.

[0005] The lithofacies of continental shale is an intrinsic factor in the development of tectonic fractures. The rock structure, mineral composition, rock mechanical layer thickness, etc. of shales of different lithofacies types are different, resulting in significant differences in mechanical properties and failure mechanisms, which in turn lead to differences in the development patterns of tectonic fractures in different types of lithofacies. Therefore, quantitatively predicting and evaluating the development degree and distribution law of tectonic fractures based on the rock structure, mineral composition, rock mechanical layer thickness and their combination patterns of different lithofacies of continental shale oil reservoirs can provide a reliable geological basis and reference for the exploration and development of continental shale oil reservoirs. Summary of the invention

[0006] The purpose of the present invention is to provide a method for evaluating structural fractures in continental shale oil reservoirs based on lithofacies constraints, which can quantitatively predict and evaluate the development degree and distribution law of structural fractures, and provide a reliable geological basis and reference for the exploration and development of continental shale oil reservoirs.

[0007] The technical solution to achieve the above object is: a method for evaluating structural fractures in continental shale oil reservoirs based on lithofacies constraints, characterized in that it comprises the following steps:

[0008] (1) Classify the continental shale lithofacies types in the study area;

[0009] (2) Based on the classification of lithofacies in the study area in step (1), characteristic parameters affecting the development of structural fractures are extracted: continental shale brittleness index I, rock structure index S, and rock mechanical layer thickness H;

[0010] (3) Analyze the sensitivity of different characteristic parameters in step (2) to the intensity response of structural fracture development;

[0011] (4) Based on the lithology types and characteristic parameters determined in step (1) and step (2), further analyzing the combination patterns of brittleness index, rock structure index, and rock mechanical layer thickness index of different types of lithofacies;

[0012] (5) Establish a quantitative evaluation index for structural fractures in continental shale oil reservoirs based on lithofacies, and calculate the fracture development index F for different types of lithofacies j .

[0013] Furthermore, in step (1), the terrestrial shale lithofacies types are divided based on the regional geological background, diagenetic evolution characteristics and core data.

[0014] Furthermore, the method for determining the lithofacies type in step (1) is based on core observation and XRD whole-rock mineral diffraction data, and according to the brittleness of the minerals, quartz, feldspar, and pyrite are determined to be strongly brittle minerals, dolomite and calcite are weakly brittle minerals, and clay minerals are plastic minerals, and a three-end member lithofacies division chart is established based on this to determine the lithofacies;

[0015] At the same time, the complex sedimentary structure in the continental shale is also taken into consideration when performing lithofacies division in step (1). The primary sedimentary structure of the rock is divided into laminar, layered, and massive structures according to the degree of bedding development.

[0016] Furthermore, the thickness of individual laminar layers is <1 mm, the thickness of individual layered layers is greater than 1 mm and less than <1 cm, and the massive layered structure is not developed.

[0017] Furthermore, in step (2), the rock brittleness index I of a certain sample point is i It is calculated using XRD whole-rock mineral composition measurement data, and the calculation formula is:

[0018] In the formula, I i represents the brittleness index of the i-th sample point; Represents the weight of quartz mineral at the sample point, in g; Represents the weight of feldspar mineral at the sample point, in g; Represents the weight of carbonate minerals at the sample point, in g; A i Represents the total weight of minerals at the sample point, in g;

[0019] The rock structure index S of a certain sample point i It refers to the number of weak planes of mechanical properties of rock per unit length, and the calculation formula is:

[0020] S i =N i / T i

[0021] In the formula, S i Represents the rock structure index of the i-th sample point; N i Represents the mechanical property weak surface of the i-th sample point; N i represents the rock thickness of the i-th sample point, in m;

[0022] The rock mechanical layer thickness index H at a certain sample point i Obtained through actual measurement, the unit is m.

[0023] Furthermore, the sensitivity of different characteristic parameters to the intensity response of structural fracture development in step (3) is specifically to make an intersection diagram of the brittleness index I, rock structure index S, and rock mechanical layer thickness H with the structural fracture development density, and determine the sensitivity coefficient R of the continental shale oil reservoir brittleness index I, rock structure index S, and rock mechanical layer thickness H to the intensity response of structural fracture development. I , R S , R H .

[0024] Furthermore, the characteristic parameter combination mode in step (4) is determined by performing normalization processing after determining the brittleness index, rock structure index, and rock mechanical layer thickness of different types of lithofacies:

[0025]

[0026] In the formula, is the brittleness index of the jth lithofacies, I j is the average brittleness index of the jth lithofacies, I min is the minimum brittleness index, I max is the maximum brittleness index.

[0027]

[0028] In the formula, is the rock structure index of the jth lithofacies, S j is the average rock texture index of the jth lithofacies, S min is the minimum rock structure index, S max is the maximum rock structure index.

[0029]

[0030] In the formula, is the rock mechanical layer thickness index of the jth lithofacies, H j is the average rock mechanical layer thickness index of the jth lithofacies (cm), Hmin is the minimum rock mechanical layer thickness index (cm), H max is the maximum rock mechanical layer thickness index (cm).

[0031] Furthermore, the fracture development index F of different types of lithofacies in step (5) j Calculated according to formula (1);

[0032]

[0033] Beneficial effects of the present invention:

[0034] The present invention innovatively proposes a quantitative evaluation method for structural fractures in continental shale oil reservoirs based on lithofacies constraints. Compared with traditional methods, this method improves the evaluation accuracy of structural fractures in continental shale reservoirs and provides a feasible new idea for the evaluation of structural fractures in continental shale oil reservoirs. This method can be applied to the evaluation of structural fractures in continental shale oil reservoirs and provide technical support for the rational development of continental shale oil reservoirs in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the process of the present invention;

[0036] Figure 2 It is the intersection diagram of brittleness index I and structural fracture line density;

[0037] Figure 3 It is the intersection diagram of rock structure index S and structural fracture line density;

[0038] Figure 4 It is the intersection diagram of rock mechanical layer thickness index H and structural fracture line density;

[0039] Figure 5 It is a diagram of the normalized processing results of brittleness index, rock structure index and rock mechanical layer thickness;

[0040] Figure 6 is the crack development index F j Graph of calculation results. DETAILED DESCRIPTION

[0041] The method for evaluating structural fractures of continental shale oil reservoirs based on lithofacies constraints is characterized by comprising the following steps:

[0042] (1) Based on the regional geological background, diagenetic evolution characteristics and core data, the continental shale lithofacies types in the study area were divided;

[0043] (2) Based on the classification of lithofacies in the study area in step (1), characteristic parameters affecting the development of structural fractures are extracted: continental shale brittleness index I, rock structure index S, and rock mechanical layer thickness H;

[0044] (3) Analyze the sensitivity of different characteristic parameters in step (2) to the intensity response of structural fracture development;

[0045] (4) On the basis of the lithology types and characteristic parameters determined in steps (1) and (2), further analyzing the combination patterns of brittleness index, rock structure index, and rock mechanical layer thickness index of different types of lithofacies;

[0046] (5) Establish a quantitative evaluation index for structural fractures in continental shale oil reservoirs based on lithofacies, and calculate the fracture development index F for different types of lithofacies j .

[0047] The method for determining the lithofacies type in step (1) is based on core observation and XRD whole-rock mineral diffraction data. According to the brittleness of the minerals, quartz, feldspar, and pyrite are determined to be strongly brittle minerals, dolomite and calcite are weakly brittle minerals, and clay minerals are plastic minerals. Based on this, a three-end-member lithofacies division chart is established to determine the lithofacies. This division method takes into account the composition of the minerals in the rock and is related to the brittleness of the rock.

[0048] At the same time, the complex sedimentary structure in the continental shale is also taken into account when performing lithofacies division in step (1). The primary sedimentary structure of the rock is divided into laminar (single bedding thickness <1 mm), layered (<1 mm single bedding thickness <1 cm), and massive (laminated structure is not developed) according to the degree of bedding development.

[0049] The rock brittleness index I of a certain sample point in step (2) is i It is calculated using XRD whole-rock mineral composition measurement data, and the calculation formula is:

[0050]

[0051] In the formula, I i represents the brittleness index of the i-th sample point; Represents the weight of quartz mineral at the sample point, in g; Represents the weight of feldspar mineral at the sample point, in g; Represents the weight of carbonate minerals at the sample point, in g; A i Represents the total weight of minerals at the sample point, in g;

[0052] The rock structure index S of a certain sample point i It refers to the number of weak planes of mechanical properties of rock per unit length, and the calculation formula is:

[0053] S i =N i / T i

[0054] In the formula, S i Represents the rock structure index of the i-th sample point; N i Represents the mechanical property weak surface of the i-th sample point; N i represents the rock thickness of the i-th sample point, in m;

[0055] The rock mechanical layer thickness index H at a certain sample point i Obtained through actual measurement, the unit is m.

[0056] The sensitivity of different characteristic parameters to the intensity response of structural fracture development in step (3) is specifically to make an intersection diagram of the brittleness index I, the rock structure index S, and the rock mechanical layer thickness H with the structural fracture development density, and determine the sensitivity coefficient R of the continental shale oil reservoir brittleness index I, the rock structure index S, and the rock mechanical layer thickness H to the intensity response of structural fracture development. I , R S , R H .

[0057] The characteristic parameter combination mode in step (4) is specifically determined by performing normalization processing after determining the brittleness index, rock structure index, and rock mechanical layer thickness of different types of lithofacies:

[0058]

[0059] In the formula, is the brittleness index of the jth lithofacies, I j is the average brittleness index of the jth lithofacies, I min is the minimum brittleness index, I max is the maximum brittleness index.

[0060]

[0061] In the formula, is the rock structure index of the jth lithofacies, S j is the average rock texture index of the jth lithofacies, S min is the minimum rock structure index, S max is the maximum rock structure index.

[0062]

[0063] In the formula, is the rock mechanical layer thickness index of the jth lithofacies, H j is the average rock mechanical layer thickness index of the jth lithofacies (cm), H min is the minimum rock mechanical layer thickness index (cm), H maxis the maximum rock mechanical layer thickness index (cm).

[0064] The fracture development index F of different types of lithofacies in step (5) j Calculated according to formula (1);

[0065]

[0066] The embodiments of the present invention are described in detail below through specific examples.

[0067] This method was used to evaluate structural fractures in a major shale oil formation in eastern my country. Based on the regional geological background, diagenetic evolution characteristics and core data, the main lithofacies types in the area can be divided into five types: dolomitic shale, siliceous shale, limestone shale, mixed shale and mudstone.

[0068] The rock structure index S of each data point is calculated based on different lithofacies types, the brittleness index I of different lithofacies is calculated using the mineral composition of the whole rock, and the rock thickness H of different lithofacies is determined.

[0069] After determining the above parameters, make intersection diagrams with the density of structural fracture development to determine the sensitivity index of the above parameters, as shown in (Attachment Figure 2 , Attachment Figure 3 , Attachment Figure 4 ), and their sensitivity coefficients are R I =0.4520, R S =0.3910, R H =0.5212.

[0070] After the sensitivity parameters are determined, the corresponding parameters are normalized (see Appendix Figure 5 ), and calculate the crack development index F j The calculation results are as follows (Attachment Figure 6 ). The calculated parameters are compared with the measured fracture density of the core, and the results show that the distribution of the two has a good correspondence.

Claims

1. A method for evaluating structural fractures in continental shale oil reservoirs based on lithofacies constraints, characterized in that: The following steps are involved: (1) Classify the continental shale lithofacies types in the study area; (2) Based on the classification of lithofacies in the study area in step (1), characteristic parameters affecting the development of structural fractures are extracted: continental shale brittleness index I, rock structure index S, and rock mechanical layer thickness H; (3) Analyze the sensitivity of different characteristic parameters in step (2) to the intensity response of structural fracture development; (4) Based on the lithology types and characteristic parameters determined in step (1) and step (2), further analyzing the combination patterns of brittleness index, rock structure index, and rock mechanical layer thickness index of different types of lithofacies; (5) Establish a quantitative evaluation index for structural fractures in continental shale oil reservoirs based on lithofacies, and calculate the fracture development index F for different types of lithofacies j .

2. The method for evaluating structural fractures of continental shale oil reservoirs based on lithofacies constraints according to claim 1, characterized in that: Step (1) is to classify the continental shale lithofacies types based on the regional geological background, diagenetic evolution characteristics and core data.

3. The method for evaluating structural fractures of continental shale oil reservoirs based on lithofacies constraints according to claim 2, characterized in that: The method for determining the lithofacies type in step (1) is based on core observation and XRD whole-rock mineral diffraction data, and according to the brittleness of the minerals, quartz, feldspar, and pyrite are determined to be strongly brittle minerals, dolomite and calcite are weakly brittle minerals, and clay minerals are plastic minerals, and a three-end member lithofacies division chart is established based on this to determine the lithofacies; At the same time, the complex sedimentary structure in the continental shale is also taken into consideration when performing lithofacies division in step (1). The primary sedimentary structure of the rock is divided into laminar, layered, and massive structures according to the degree of bedding development.

4. The method for evaluating structural fractures of continental shale oil reservoirs based on lithofacies constraints according to claim 3, characterized in that: The thickness of individual laminar layers is less than 1 mm, the thickness of individual layered layers is greater than 1 mm and less than 1 cm, and the massive layered structure is not developed.

5. The method for evaluating structural fractures of continental shale oil reservoirs based on lithofacies constraints according to claim 2, characterized in that: In the step (2), the rock brittleness index I of a certain sample point is i It is calculated using XRD whole-rock mineral composition measurement data, and the calculation formula is: In the formula, I i represents the brittleness index of the i-th sample point; Represents the weight of quartz mineral at the sample point, in g; Represents the weight of feldspar mineral at the sample point, in g; Represents the weight of carbonate minerals at the sample point, in g; A i Represents the total weight of minerals at the sample point, in g; The rock structure index S of a certain sample point i It refers to the number of weak planes of mechanical properties of rock per unit length, and the calculation formula is: S i =N i / T i In the formula, S i Represents the rock structure index of the i-th sample point; N i Represents the mechanical property weak surface of the i-th sample point; N i represents the rock thickness of the i-th sample point, in m; The rock mechanical layer thickness index H at a certain sample point i Obtained through actual measurement, the unit is m.

6. The method for evaluating structural fractures of continental shale oil reservoirs based on lithofacies constraints according to claim 2, characterized in that: The sensitivity of different characteristic parameters to the intensity response of structural fracture development in step (3) is specifically to make an intersection diagram of the brittleness index I, the rock structure index S, and the rock mechanical layer thickness H with the structural fracture development density, and determine the sensitivity coefficient R of the continental shale oil reservoir brittleness index I, the rock structure index S, and the rock mechanical layer thickness H to the intensity response of structural fracture development. I , R S , R H .

7. The method for evaluating structural fractures of continental shale oil reservoirs based on lithofacies constraints according to claim 6, characterized in that: The characteristic parameter combination mode in step (4) is specifically determined by performing normalization processing after determining the brittleness index, rock structure index, and rock mechanical layer thickness of different types of lithofacies: In the formula, is the brittleness index of the jth lithofacies, I j is the average brittleness index of the jth lithofacies, I min is the minimum brittleness index, I max is the maximum brittleness index. In the formula, is the rock structure index of the jth lithofacies, S j is the average rock texture index of the jth lithofacies, S min is the minimum rock structure index, S max is the maximum rock structure index. In the formula, is the rock mechanical layer thickness index of the jth lithofacies, H j is the average rock mechanical layer thickness index of the jth lithofacies (cm), H min is the minimum rock mechanical layer thickness index (cm), H max is the maximum rock mechanical layer thickness index (cm).

8. The method for evaluating structural fractures of continental shale oil reservoirs based on lithofacies constraints according to claim 7, characterized in that: The fracture development index F of different types of lithofacies in step (5) j Calculated according to formula (1);

Images