Method for establishing permeability model of fracturing zone

Abstract

The present invention provides a method for establishing a permeability model of a fracturing transformation area, and the method comprises: step 1, determining the shape and range of the fracturing transformation area by analyzing and processing the original microseismic point map; step 2, calculating the distribution density of microseismic points in each fracturing transformation area according to the division result of the fracturing transformation area; step 3, verifying the rationality of the division method of the fracturing transformation area; step 4, inverting and obtaining the permeability of each fracturing transformation area. The method for establishing a permeability model of a fracturing transformation area innovatively proposes to divide the fracturing transformation area by using the distribution law of isobars around horizontal wells, effectively processes the distribution of microseismic points scientifically and accurately, and establishes a corresponding permeability model, which provides a key technical means for studying the seepage law of such oil reservoirs in the future.

Description

Technical Field

[0001] The invention relates to the technical field of oil field development, and in particular to a method for establishing a permeability model of a fracturing transformation zone. Background Art

[0002] Layered conglomerate reservoirs are low-porosity and ultra-low-permeability reservoirs with insufficient natural energy, low natural production capacity, and rapid production capacity decline, requiring fracturing and production. During the fracturing development process, microcracks will form in the reservoir. The area where microcracks develop is called the fracturing transformation zone, and its range and seepage characteristics directly determine the production capacity of this type of reservoir. Therefore, establishing a permeability model for the fracturing transformation zone is of great significance for guiding the development of this type of reservoir.

[0003] Microseismic monitoring is an important means to understand the effect of reservoir fracturing development. The collected microseismic signals can be used to analyze the underground state and predict the spatial distribution of cracks. Since the distribution of microseismic points in the reservoir is disorderly, although many studies have been conducted by predecessors, there is still no reasonable explanation for the distribution law of microseismic points, making it difficult to analyze the impact of microseismic points on seepage laws.

[0004] In the Chinese patent application with application number: 201610810941.0, a method and device for reconstructing a fracture network based on microseismicity is involved, which belongs to the field of oil extraction technology. The fracture network reconstruction method includes: preliminary processing of the data of microseismic monitoring points during hydraulic fracturing; taking the starting point of each fracturing section as the starting point, iteratively reconstructing the fracture network N of each fracturing section; calculating the permeability k of each fracture section in the fracture network N; merging the fracture network N of all fracturing sections, establishing a discrete fracture grid model and performing production numerical simulation, and performing production history fitting between the obtained production numerical simulation value and the actual production value; obtaining the cumulative distribution function of the pressure value of all points in the reservoir, taking its inflection point as the boundary pressure of the reservoir transformation volume and drawing a contour map, and obtaining the shape and range of the reservoir transformation volume generated by this fracturing. First of all, the premise of realizing the reconstruction of the fracture network in this patent is to use seismic wave data inversion to obtain parameters such as rock cracking point, fracture time and fracture energy, which is not suitable for the situation where incomplete microseismic data is provided on site. Secondly, the patent does not give a reasonable explanation for the distribution of microseismic points around vertical fractures. Although the shape and range of the fracturing transformation zone are determined by fitting the discrete fracture network model, the distribution of microseismic points is not effectively used to simplify the solution to the division of the fracturing transformation zone, making the division process very complicated. Finally, the fracturing network in the patent contains many fracturing segments. The merging of fracturing segments for iterative correction of permeability increases the amount of trial calculations, and the fracturing network is difficult to represent in numerical simulation software, which increases the complexity of permeability correction. In summary, the patent has a narrow scope of application, a complex operation process, and a large amount of calculation, so it is not easy to be promoted.

[0005] In the Chinese patent application with application number: 201710006652.X, a method for calculating the volume area of ​​tight reservoir fracturing transformation is involved, which includes the following steps: establishing a non-planar turning extension model of multiple hydraulic fractures in the process of horizontal well fracturing in tight reservoirs, a formation stress field change model, a reservoir pressure field change model, and a natural fracture destruction criterion, obtaining geological parameters, horizontal well fracturing construction parameters, and total fracturing time, assigning initial values ​​of fracture filtration loss, initial values ​​of fracture half-length, initial values ​​of fracture pressure, initial fracture extension turning angle, initial permeability, and initial values ​​of fracturing time, solving each model, and calculating the coordinate data of the natural fracture destruction point; using the spatial numerical integration method, respectively calculating the volume of the tensile destruction transformation area and the shear destruction transformation area in the reservoir, and defining the spatial union of the two as the overall transformation volume area. First of all, when there are natural fractures in the reservoir and all basic parameters are known, the patent can be used to calculate the fracturing transformation volume area, otherwise the patent will no longer be applicable. Secondly, the patent takes into account multiple physical change processes during staged fracturing of horizontal wells. The mutual coupling between the physical change processes not only increases the complexity of the calculation, but also puts forward higher requirements on the accuracy of the basic parameters, otherwise it will affect the calculation accuracy of the fracturing transformation volume area. Finally, the patent does not give a reasonable explanation for the distribution law of microseismic points around vertical fractures. Therefore, the patent has a small scope of application, a complex calculation process, and is difficult to promote.

[0006] To this end, we invented a new method for establishing a permeability model for the fracturing transformation area to solve the above technical problems. Summary of the invention

[0007] The purpose of the present invention is to provide a method for establishing a permeability model for a fracturing transformation zone, which utilizes the distribution law of isobars around horizontal wells to realize the division of fracturing transformation zones, and completes the establishment of a permeability model according to the distribution density of microseismic points in the fracturing transformation zone.

[0008] The purpose of the present invention can be achieved through the following technical measures: a method for establishing a permeability model of a fracturing transformation zone, the method for establishing a permeability model of a fracturing transformation zone comprising: step 1, determining the shape and range of the fracturing transformation zone by analyzing and processing an original microseismic point map; step 2, calculating the distribution density of microseismic points in each fracturing transformation zone according to the division result of the fracturing transformation zone; step 3, verifying the rationality of the fracturing transformation zone division method; step 4, inverting to obtain the permeability of each fracturing transformation zone.

[0009] The purpose of the present invention can also be achieved by the following technical measures:

[0010] In step 1, the main fracture is regarded as a horizontal well, and the isobars distributed around the horizontal well are used to divide the fracturing transformation zone, i.e., the elliptical ring. According to the change law of the distribution density of microseismic points, the microseismic points are reasonably wrapped inside the elliptical ring; the shape of each transformation zone gradually changes from ellipse to circle from the inside to the outside; the closer the fracturing transformation zone is to the main fracture, the stronger the seepage capacity is. As it extends to the periphery of the reservoir, the seepage capacity of the fracturing transformation zone weakens until it becomes a pure matrix zone.

[0011] In step 2, according to the division result of the hydraulic fracturing zone, the distribution density of microseismic points in each hydraulic fracturing zone is calculated, and the distribution density is proportional to the seepage capacity formed by the microcracks in the hydraulic fracturing zone.

[0012] In step 2, first, the number of microseismic points T in each elliptical ring, i.e., the internal fracturing zone, is calculated. i ; Next, calculate the area S of each elliptical ring i ; Finally, the distribution density ρ of the microseismic points in each elliptical ring is obtained i =T i / S i .

[0013] In step 3, taking the fracturing zone closest to the main fracture, i.e., zone 1, as the benchmark, the permeability of the microcracks formed in each fracturing zone and the multiple of the area of ​​each fracturing zone compared to the fracturing zone 1 are calculated in turn, i.e., K i ' / K1'=ρ i / ρ1 and S i / S1;

[0014] Where: K i '——permeability of microcracks formed in zone i of fracturing transformation, i=1, 2, 3, 4, 5; K1'——permeability of microcracks formed in zone 1 of fracturing transformation; ρ i ——distribution density of microseismic points in fracturing zone i; ρ1——distribution density of microseismic points in fracturing zone 1; S i ——the area of ​​fracturing zone i; S1——the area of ​​fracturing zone 1;

[0015] Then, the permeability increase factor K of the microcracks formed in the fracturing zone is fitted. i ' / K1' increases with the area of ​​the fracturing transformation area i / S1, and the permeability K of microcracks formed in each fracturing zone i The relationship between ' and K1' is given by the relation To express;

[0016] K i '——permeability of microcracks formed in zone i after fracturing;

[0017] Because the overall permeability of the fractured zone is equal to the sum of the permeability of microcracks and the matrix permeability, that is, K i =K i '+K m , then the permeability of each fracturing zone is:

[0018]

[0019] Where: K i ——permeability of zone i after fracturing transformation; K1'——permeability of microcracks formed in zone 1 after fracturing transformation; S i ——the area of ​​fracturing zone i; S1——the area of ​​fracturing zone 1; K m ——Matrix permeability.

[0020] In step 4, a numerical simulation model is established according to the actual situation of the reservoir and the division results of the fracturing zone, and the permeability of each fracturing zone is obtained by inversion using the historical production data of the reservoir.

[0021] The method for establishing the permeability model of the fracturing transformation zone in the present invention is based on the characteristics of simulated horizontal well development in which vertical long fractures are formed by fracturing of vertical wells. It innovatively proposes to divide the fracturing transformation zone by using the distribution law of isobars around horizontal wells. It effectively processes the distribution of microseismic points in a scientific and accurate manner and establishes a corresponding permeability model, which provides a key technical means for future research on the seepage law of such oil reservoirs.

[0022] The present invention provides a set of technical methods, which can make up for the shortcomings of the existing technology and describe the vertical well fracturing transformation zone more scientifically and accurately; divide the scope of the fracturing transformation zone according to the isobars distributed around the horizontal well, and realize the accurate description of the fracturing transformation zone; by calculating the distribution density of microseismic points in each fracturing transformation zone, the quantitative characterization of the seepage capacity of the fracturing transformation zone is realized; a simple, specific and operable technical method and implementation steps are given for establishing a permeability model of the fracturing transformation zone; it is not only suitable for the development of layered conglomerate oil reservoirs, but also can provide a reference for the research of other low-porosity and low-permeability oil reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of a fracturing transformation zone in a specific embodiment of the present invention;

[0024] Figure 2 It is a schematic diagram of the verification result of the method for dividing the fracturing transformation area in a specific embodiment of the present invention;

[0025] Figure 3 It is a schematic diagram of a single well numerical model in a specific embodiment of the present invention;

[0026] Figure 4 It is a schematic diagram of the daily fluid production fitting result in a specific embodiment of the present invention;

[0027] Figure 5 It is a schematic diagram of the fitting result of the cumulative production liquid in a specific embodiment of the present invention;

[0028] Figure 6 The present invention is a flowchart of a specific embodiment of the method for establishing a permeability model of a hydraulic fracturing zone. DETAILED DESCRIPTION

[0029] In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings.

[0030] like Figure 6 As shown, Figure 6 The present invention is a flow chart of the method for establishing a permeability model for a hydraulic fracturing zone.

[0031] Step 101, determine the shape and range of the fracturing stimulation area.

[0032] By analyzing and processing the original microseismic point map, the shape and scope of the fracturing transformation area are determined. Figure 1 As shown in the figure, extending from the main fracture to the periphery of the reservoir, the distribution of microseismic points (each microseismic point represents a tiny fracture) changes from dense to sparse, that is, the seepage capacity changes from strong to weak. After observation and experiment, the main fracture is regarded as a horizontal well, and the isobars distributed around the horizontal well are used to divide the fracturing transformation area (elliptical ring). According to the change law of the distribution density of microseismic points, the microseismic points can be reasonably wrapped inside the elliptical ring. From the inside to the outside, the shape of each transformation area changes from ellipse to circle. The closer the fracturing transformation area is to the main fracture, the stronger the seepage capacity is. As it extends to the periphery of the reservoir, the seepage capacity of the fracturing transformation area becomes weaker until it becomes a pure matrix area.

[0033] Step 102, calculating the distribution density of microseismic points in each hydraulic fracturing zone.

[0034] According to the division results of the fracturing transformation area, the distribution density of microseismic points in each fracturing transformation area is calculated. The distribution density is proportional to the seepage capacity of the microcracks formed in the fracturing transformation area. First, the number of microseismic points inside each elliptical ring (i.e., fracturing transformation area) is calculated. i ; Next, calculate the area S of each elliptical ring i ; Finally, the distribution density ρ of the microseismic points in each elliptical ring is obtained i =T i / S i The specific calculation results are shown in Appendix 1.

[0035] Table 1 Calculation results of relevant parameters

[0036]

[0037]

[0038] Step 103, verifying the rationality of the method for dividing the fracturing transformation area.

[0039] As shown in Appendix 1, taking the fracturing zone (Zone 1) closest to the main fracture as the benchmark, the permeability of the microcracks formed in each fracturing zone and the multiple of the area of ​​each fracturing zone compared to the fracturing zone 1 are calculated in turn, that is, K is calculated. i ' / K1'=ρ i / ρ1 and S i / S1. Then fit the permeability increase factor K of microcracks formed in the fracturing transformation area i ' / K1' increases with the area of ​​the fracturing transformation area i / S1 change trend (see attached Figure 3 ), it can be seen that the error R 2 is very close to 1, indicating that this method of dividing the fracturing zone is very reasonable, and the permeability K of the microcracks in each fracturing zone is i The relationship between ' and K1' can be expressed by the relation Because the overall permeability of the fracturing zone is equal to the sum of the permeability of microcracks and the matrix permeability, that is, K i =K i '+K m , then the permeability of each fracturing zone is:

[0040]

[0041] Step 104, inverting to obtain the permeability of each fractured zone.

[0042] According to the actual situation of the reservoir and the results of the division of the fracturing zone, a numerical simulation model was established, and the permeability of each fracturing zone was obtained by inversion using the historical production data of the reservoir. This result reflects the seepage characteristics of the real reservoir.

[0043] In a specific embodiment of the present invention, the Figure 1 As an example, the main fracture and fracturing transformation area in the vertical fracture are shown in Appendix 2, and the fracturing transformation area division is shown in Appendix Figure 1 .

[0044] Table 2 Vertical main crack parameters

[0045]

[0046] First, using the matrix parameters in Appendix 3, a single well numerical model is established along the extension direction of the main fracture. Figure 3 shown.

[0047] Table 3 Matrix parameters

[0048]

[0049] Then, 10 parameter combination schemes were designed for the three factors of main fracture conductivity, permeability of fracturing zone 1, and main fracture compression coefficient. The permeability of fracturing zones 2 to 5 can be calculated according to the fitting formula (1). The scheme design list is shown in Appendix 4.

[0050] Table 4 Design list

[0051]

[0052] Finally, the results of these 10 solutions are used to fit the historical production data of the reservoir, and the following is obtained: Figure 4 The daily fluid fitting results are shown in the attached Figure 5 The cumulative fluid production fitting results are shown in the figure. It can be seen that Scheme 8 has the best fitting effect, that is, the main fracture conductivity obtained by inversion is 14D·cm, and the main fracture compression coefficient is 0.001MPa -1 , the permeability of fracturing zone 1 is K1=1.95mD, and the permeability of the remaining fracturing zones can be calculated by formula (1).

Claims

1. A method for establishing a permeability model for a fracturing transformation area, characterized in that: The method for establishing the permeability model of the fracturing transformation area includes: Step 1, determining the shape and range of the fracturing zone by analyzing and processing the original microseismic point map; Step 2, according to the division result of the hydraulic fracturing zone, calculating the distribution density of microseismic points in each hydraulic fracturing zone; Step 3, verifying the rationality of the fracturing transformation area division method; Step 4, inverting to obtain the permeability of each fracturing zone; In step 1, the main fracture is regarded as a horizontal well, and the isobars distributed around the horizontal well are used to divide the fracturing transformation area, i.e., the elliptical ring. According to the change law of the distribution density of microseismic points, the microseismic points are reasonably wrapped inside the elliptical ring; the shape of each transformation area changes from ellipse to circle from the inside to the outside; the closer the fracturing transformation area is to the main fracture, the stronger the seepage capacity is. As it extends to the periphery of the reservoir, the seepage capacity of the fracturing transformation area becomes weaker until it becomes a pure matrix area; In step 3, taking the fracturing zone closest to the main fracture, i.e., zone 1, as the benchmark, the permeability of the microcracks formed in each fracturing zone and the multiple of the area of ​​each fracturing zone compared to the fracturing zone 1 are calculated in turn, i.e., K i ' / K1'=ρ i / ρ1 and S i / S1; Where: K i '——permeability of microcracks formed in zone i of fracturing transformation, i=1, 2, 3, 4, 5; K1'——permeability of microcracks formed in zone 1 of fracturing transformation; ρ i ——distribution density of microseismic points in fracturing zone i; ρ1——distribution density of microseismic points in fracturing zone 1; S i ——the area of ​​fracturing zone i; S1——the area of ​​fracturing zone 1; Then, the permeability increase factor K of microcracks in the fracturing zone is fitted. i ' / K1' increases with the area of ​​the fracturing transformation area i / S1, and the permeability K of microcracks formed in each fracturing zone i The relationship between ' and K1' is given by the relation To express; K i '——permeability of microcracks formed in zone i during fracturing transformation; Because the overall permeability of the fractured zone is equal to the sum of the permeability of microcracks and the matrix permeability, that is, K i =K i '+K m , then the permeability of each fracturing zone is: Where: K i ——permeability of zone i after fracturing transformation; K1'——permeability of microcracks formed in zone 1 after fracturing transformation; S i ——the area of ​​fracturing zone i; S1——the area of ​​fracturing zone 1; K m ——Matrix permeability.

2. The method for establishing a permeability model of a fracturing zone according to claim 1, characterized in that: In step 2, according to the division result of the hydraulic fracturing zone, the distribution density of microseismic points in each hydraulic fracturing zone is calculated, and the distribution density is proportional to the seepage capacity formed by the microcracks in the hydraulic fracturing zone.

3. The method for establishing a permeability model of a fracturing transformation zone according to claim 2, characterized in that: In step 2, first, the number of microseismic points T in each elliptical ring, i.e., the internal fracturing zone, is calculated. i ; Next, calculate the area S of each elliptical ring i ; Finally, the distribution density ρ of the microseismic points in each elliptical ring is obtained i =T i / S i .

4. The method for establishing a permeability model of a fracturing zone according to claim 1, characterized in that: In step 4, a numerical simulation model is established according to the actual situation of the reservoir and the division results of the fracturing zone, and the permeability of each fracturing zone is obtained by inversion using the historical production data of the reservoir.

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