Method for calculating shale oil volume fracturing reconstruction space permeability

Abstract

The present application belongs to the technical field of oil reservoir development, and relates to a method for calculating the permeability of a shale oil volume fracturing reconstruction space. The method comprises the following steps: step 1, drawing a curve of daily oil production and production time in a logarithmic coordinate system to identify the flow mode of shale oil in different production stages; step 2, calculating the production time of shale oil in different flow stages; step 3, using microseismic monitoring data to identify the fracture geometry after volume fracturing; step 4, calculating the intersegment distance between fracturing segments of different volume fracturing geometries; and step 5, calculating the permeability of the volume fracturing reconstruction space. The method realizes accurate calculation of the permeability of a shale oil volume fracturing reconstruction space, improves the understanding of fracturing and reservoir properties, objectively and accurately evaluates the fracturing effect, provides a basis for evaluation of the flow capacity of a complex space after shale oil volume fracturing reconstruction, and fills the gap in the prior art.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil reservoir development, and relates to a shale oil volume fracturing reconstruction space permeability calculation method. BACKGROUND

[0002] With the in-depth theoretical research and rapid development of shale gas exploration and development, shale oil has also become another new hotspot of oil and gas development and an important source of oil and gas supply. Shale oil reservoirs belong to ultra-low permeability tight reservoirs, which generally have no natural productivity or low productivity, and need to be reconstructed by volume fracturing and other "artificial permeability" technical means to realize effective development of shale oil. Due to the influence of the brittleness characteristics and natural fracture development of shale oil reservoirs, the hydraulic fracturing cracks are no longer the traditional double-wing symmetrical cracks, but are very easy to form a complex crack network system. During the volume fracturing process, there are complex mechanical behaviors such as shearing, breaking and slipping, and a large number of secondary cracks exist at the same time as the tensile main cracks, and form a complex network system with micro-cracks, increase the reconstruction volume, and communicate the flow field.

[0003] Due to the complex crack network system formed after volume fracturing, the permeability of the fracturing reconstruction space formed by the main cracks and secondary cracks and micro-cracks after reconstruction is not clear, and the reconstruction effect cannot be quantitatively evaluated, so it is necessary to evaluate the flow capacity of the reconstruction space, improve the understanding of the fracturing and reservoir properties, and objectively and accurately evaluate the fracturing effect, which has a guiding role in the aspects of improving the understanding of the fracturing and reservoir properties and objectively and accurately evaluating the fracturing effect. SUMMARY

[0004] The main purpose of the present application is to provide a shale oil volume fracturing reconstruction space permeability calculation method, which realizes accurate calculation of the shale oil volume fracturing reconstruction space permeability, improves the understanding of the fracturing and reservoir properties, objectively and accurately evaluates the fracturing effect, provides a basis for evaluation of the flow capacity of the complex space after shale oil volume fracturing reconstruction, and fills the gap in the prior art.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] The present application provides a shale oil volume fracturing reconstruction space permeability calculation method, which comprises the following steps:

[0007] Step 1, draw a relationship curve of daily oil production and production time in a logarithmic coordinate system, and identify the flow mode of shale oil in different production stages;

[0008] Step 2, calculate the production time of shale oil in different flow stages;

[0009] Step 3, use microseismic monitoring data to identify the crack geometry after volume fracturing;

[0010] Step 4, calculate the inter-stage distance between the fracturing stages of different volume fracturing geometries;

[0011] Step 5, calculate the permeability of the volume fracturing reconstruction space.

[0012] To achieve the above object, the application can also adopt the following technical scheme:

[0013] In step 1, in the relationship curve between daily oil production and production time, the flow mode of shale oil is divided into: formation linear flow mode, elliptical flow mode and pseudo-steady flow mode.

[0014] Further, the flow mode of shale oil is divided by the change of the curve slope k of the relationship curve between daily oil production and production time: when k=-0.5, the shale oil is in the formation linear flow mode in the reconstruction space, when-0.5<k<1, the shale oil is in the elliptical flow mode in the reconstruction space, and when k=1, the shale oil is in the pseudo-steady flow mode in the reconstruction space.

[0015] In step 2, the time when the line segment of k=-0.5 ends is the formation linear flow end time t1, and the time when the straight line segment of k=1 starts is the pseudo-steady flow start time t2, and the difference between t2 and t1 is the production time of elliptical flow.

[0016] In step 3, the interpretation result of microseismic monitoring data is analyzed according to the following formula to identify the fracture geometry:

[0017]

[0018]

[0019]

[0020] In the formula, L is the length of the horizontal well section, N is the number of fracturing stages of the horizontal well, w e is the fracture zone width of microseismic monitoring, a, a1, b, b1 are undetermined coefficients.

[0021] Further, when a≤w e ≤b, the volume fracturing reconstruction space is in a complex fracture network form; when 0≤w e ≤a, the volume fracturing reconstruction space is in a segmented fracturing fracture network.

[0022] In step 4, on the basis of step 3, the inter-stage distance between the fracturing stages of different volume fracturing geometries is calculated,

[0023] When the fracture geometry is a complex fracture network:

[0024] L s =L

[0025] When the fracture geometry is a segmented fracture network:

[0026]

[0027] wherein L s is the intersegment spacing between the fractures.

[0028] In step 5, the permeability of the volume fracturing reconstruction space is calculated, and the formula is:

[0029]

[0030] wherein k eff is the permeability of the volume fracturing reconstruction space, t1 is the end time of linear flow of the formation, μ is the oil viscosity of the formation, is the core porosity, c t is the comprehensive compression coefficient of the formation, L s is the intersegment spacing between the fractures.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] The method of the present application realizes the accurate calculation of the permeability of the volume fracturing reconstruction space of shale oil, improves the understanding of the fracturing and the reservoir properties, objectively and accurately evaluates the fracturing effect, provides the basis for the evaluation of the flow capacity of the complex space after the volume fracturing reconstruction of shale oil, and fills the blank of the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0033] The drawings accompanying the specification of the present application serve to provide a further understanding of the present application, and the schematic embodiments of the present application and the description thereof serve to explain the present application, and do not constitute an improper limitation on the present application.

[0034] Figure 1 The flow chart of the method for calculating the permeability of the volume fracturing reconstruction space of shale oil according to one specific embodiment of the present application is shown in the figure;

[0035] Figure 2 The schematic diagram of the fracture geometry after the volume fracturing of shale oil according to one specific embodiment of the present application is shown in the figure;

[0036] Figure 3 The flow mode identification diagram of shale oil in different production according to one specific embodiment of the present application is shown in the figure;

[0037] Figure 4 The microseismic monitoring result diagram according to one specific embodiment of the present application is shown in the figure;

[0038] Figure 5 The different fracture segment bandwidth diagram obtained by the microseismic monitoring according to one specific embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0039] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0040] It is also important to note that the terms used herein are not intended to limit the particular embodiments of the present application to the preferred embodiments described. Rather, the terms are used only to describe specific embodiments of the present application. As used herein, unless the context clearly indicates otherwise, the singular forms "a," "an," and "the" are intended to include the plural forms as well, e.g., the singular "a" is intended to include the plural references "a" or "an," unless the context clearly indicates otherwise. Furthermore, it is to be understood that the terms "comprise" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0041] In order to enable a person skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific embodiments.

[0042] As shown in Figure 1 , Figure 1 is a flow chart of the shale oil volume fracturing reconstruction space permeability calculation method described in the present embodiment.

[0043] In step 101, a curve of daily oil production and production time in a logarithmic coordinate system is drawn, and the flow mode of shale oil in different production stages is identified. In the example, three flow modes are identified by the change of the slope of the curve, which are ① formation linear flow mode, ② elliptical flow, and ③ pseudo-steady flow. When the production time is 50 days to 150 days, the slope of the straight line segment is k=-0.5, and the shale oil is in the formation linear flow mode in the reconstruction space; when the production time is 150 days to 2500 days, -0.5<k<1, and the shale oil is in the elliptical flow in the reconstruction space; and when the production time exceeds 2500 days, k=1, and the shale oil is in the pseudo-steady flow.

[0044] In step 102, the production time of shale oil in different flow stages is calculated on the basis of step 101. The time when the line segment with k=-0.5 ends is the linear flow end time t1, and the time when the straight line segment with k=1 starts is the pseudo-steady flow start time t2. In the example, the linear flow end time t1 is 150 days, and the pseudo-steady flow start time t2 is 2500 days.

[0045] In step 103, on the basis of step 102, the geometry of the fractures after volume fracturing is identified by using microseismic monitoring data, and the interpretation result of the microseismic monitoring data is analyzed according to the following formula to identify the fracture geometry:

[0046]

[0047]

[0048]

[0049] In the formula, L is the length of the horizontal well section, N is the number of the horizontal well fracturing section, w e is the fracture bandwidth of microseismic monitoring, a, a1, b, b1 are undetermined coefficients.

[0050] When a≤w e ≤b, the volume fracturing reconstruction space is in the complex fracture network form;

[0051] When 0≤w e ≤a, the volume fracturing reconstruction space is in the segmented fracturing fracture network.

[0052] In the example, the length of the horizontal well section is 942m, the number of the fracturing section is 21 sections, and according to the bandwidth of different fracturing sections monitored by microseismic, the average bandwidth w e of fracturing is calculated as 41.4m. a=22.4m, b=44.9m are calculated, and according to 22.4<w e <44.9, it is judged that the complex fracture network is formed after the multi-section fracturing of the horizontal well in the example.

[0053] In step 104, the section spacing between the fracturing sections of different volume fracturing geometric forms is calculated,

[0054] When the fracture geometric form is a complex fracture network:

[0055] L s =L

[0056] When the fracture geometric form is a segmented fracture network:

[0057]

[0058] In the formula, L s is the section spacing between the fracturing sections.

[0059] On the basis of step 103, the complex fracture network is formed after the volume fracturing, and therefore the section spacing between the fracturing sections of the complex fracture network is the length of the horizontal well section, 942m.

[0060] In step 105, on the basis of step 104, the permeability of the volume fracturing reconstruction space is calculated by using the following formula:

[0061]

[0062] In the formula, k eff is the permeability of the volume fracturing reconstruction space, t1 is the end time of the linear flow of the formation, μ is the oil viscosity of the formation, is the core porosity, c t is the comprehensive compression coefficient of the formation, and L sThe distance between the fractured fractures is the intersegment distance.

[0063] The distance between the fractured fractures is 942 meters, the crude oil viscosity is 0.8 mPa.s, the matrix porosity is 7%, and the formation comprehensive compressibility is 5*10 -6 kpa -1 The formation linear flow time is 150 days, and the permeability of the fracturing reconstruction space is calculated as 9.7 md.

[0064] As can be seen from the above, the method described in the embodiment realizes accurate calculation of the permeability of the shale oil volume fracturing reconstruction space, improves the understanding of the fracturing and the reservoir properties, objectively and accurately evaluates the fracturing effect, and provides a basis for evaluation of the flow capacity of the complex space after the shale oil volume fracturing reconstruction.

[0065] The above embodiment is a preferred embodiment of the present application, but the embodiments of the present application are not limited to the above embodiment, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and all are included in the protection scope of the present application.

Claims

1. A method for calculating the spatial permeability of shale oil volume fracturing, characterized in that: It includes the following steps: Step 1: Plot the relationship curve of daily oil production and production time in a logarithmic coordinate system, and identify the flow patterns of shale oil in different production stages; Step 2: Calculate the production time of shale oil in different flow stages; Step 3: Use microseismic monitoring data to identify the fracture geometry after volume fracturing; Step 4: Calculate the segment spacing between fracturing segments with different volume fracturing geometries; Step 5: Calculate the permeability of the volume fracturing reformed space; In Step 1, in the relationship curve of daily oil production and production time, the flow patterns of shale oil are divided into: formation linear flow pattern, elliptical flow pattern, and pseudo-steady state flow pattern; the flow patterns of shale oil are divided by the change of the curve slope k of the relationship curve of daily oil production and production time: when k = -0.5, the shale oil is in the formation linear flow pattern in the reformed space, when -0.5 < k < 1, the shale oil is in the elliptical flow pattern in the reformed space, and when k = 1, the shale oil is in the pseudo-steady state flow pattern in the reformed space; In Step 2, the time when the line segment with k = -0.5 ends is the end time t1 of the formation linear flow, the time when the straight line segment with k = 1 starts is the start time t2 of the pseudo-steady state flow, and the difference between t2 and t1 is the production time of the elliptical flow; In Step 3, analyze the interpretation results of microseismic monitoring data according to the following formula to identify the fracture geometry: Where L is the length of the horizontal well section, N is the number of horizontal well fracturing stages, and w e is the crack bandwidth of microseismic monitoring, a, a1, b, b1 are unknown coefficients; when a≤w e When ≤b, the volume fracturing stimulation space is a complex fracture network; when 0≤w e When ≤a, the volume fracturing stimulation space is a segmented fracture network; In Step 4, based on Step 3, calculate the segment spacing between fracturing segments with different volume fracturing geometries, When the fracture geometry is a complex fracture network: L s =L [[ID= Where, L s is the interval between fracturing stages; ​ Where k eff is the permeability of the volume fracturing reconstruction space, t1 is the end time of the formation linear flow, μ is the formation oil viscosity, is the core porosity, c t is the comprehensive compression coefficient of the formation, L s is the interval between fractures.

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