Reservoir evaluation method based on in-fracture net pressure, medium and equipment

Abstract

The invention relates to the technical field of reservoir structure recognition, in particular to a reservoir evaluation method based on in-fracture net pressure, a medium and equipment. The method comprises the steps that the stress difference between the maximum principal stress and the minimum principal stress of a to-be-evaluated area is calculated; the net pressure in the natural crack of the to-be-evaluated area is obtained; dividing a well productivity evaluation range, and determining an in-seam static pressure range corresponding to the well productivity evaluation range; and determining well productivity evaluation of the to-be-evaluated region based on the net pressure in the natural crack of the to-be-evaluated region. According to the method, the development strength of the fractures of the fracture-cavity reservoir is researched by applying the net pressure in the fractures, and the problems that a common fracture density research method is insufficient in reservoir description precision, the development strength of the fractures of the reservoir cannot be accurately determined, the yield of a reservoir well cannot be predicted, and follow-up well position adjustment and deployment are not facilitated are solved. According to the method, researchers can establish clearer regional geological knowledge, and a basis is provided for well location deployment of oil-gas exploration.

Description

Technical Field

[0001] The present invention relates to the technical field of reservoir structure identification, and in particular to a reservoir evaluation method, medium and device based on net pressure in fractures. Background Art

[0002] Large carbonate sedimentary layers are widely distributed in the Early Cambrian - Middle Ordovician. The long-term low geothermal environment has enabled the Lower Cambrian source rocks to form condensate oil and natural gas. A large number of mudstones in the Late Ordovician serve as reservoir-cap rocks, thus forming a complete source-reservoir-cap combination, providing favorable conditions for the formation of large oil and gas fields. Exploration in the past decade has shown that the carbonate rocks of the Middle and Lower Ordovician and the Cambrian carbonate rocks are key areas for oil and gas exploration. Affected by multiple tectonic movements, two sets of main strike-slip faults and several secondary faults have been formed. Due to sea-level changes, the strata have undergone severe erosion and collapse. Carbonate fault-controlled karst reservoirs are widely developed in the ultra-deep Ordovician, and the formed cave-fracture system has the characteristics of strong heterogeneity and local connectivity, creating favorable conditions for oil and gas migration and accumulation. Therefore, accurately depicting the internal structure of these fault-controlled karst conduction systems is of great significance for oil and gas exploration.

[0003] Reservoir research is of great significance in the development process of fracture-cavity reservoirs, and it has great guiding effects on well productivity evaluation, reservoir water control and water prevention, and development potential evaluation. Fracture-cavity reservoirs have strong heterogeneity and rapid lateral changes. The main seepage channels of the reservoir space are fractures, and the characterization of fractures is of great significance for the static connectivity characterization of units. Different seismic attributes have differences in the characterization of fractures. How to select reasonable seismic attributes and threshold values is the key to the characterization of fracture development intensity. However, common fracture development intensity descriptions such as the seismic fracture density method often have insufficient accuracy in reservoir characterization, cannot accurately determine the development strength of reservoir fractures, cannot predict the well production of reservoirs, and are not conducive to subsequent adjustment and deployment.

[0004] Therefore, there is an urgent need for a reservoir evaluation method, medium and device based on net pressure in fractures. Summary of the Invention

[0005] To avoid the above problems existing in the prior art, the purpose of the present invention is to provide a reservoir evaluation method, medium and device based on net pressure in fractures.

[0006] To achieve the above purpose, the present invention provides the following technical solution: A reservoir evaluation method based on net pressure in fractures, comprising the following steps:

[0007] S1: Calculate the stress difference between the maximum principal stress and the minimum principal stress in the area to be evaluated;

[0008] S2: Obtain the net pressure in natural fractures in the area to be evaluated;

[0009] S3: Based on the cumulative well production of the previously drilled wells, divide the well productivity evaluation grades and determine the corresponding in - fracture static pressure ranges for each well productivity evaluation grade;

[0010] S4: Compare the net pressure in the natural fractures of the area to be evaluated with the in - fracture static pressure ranges corresponding to different well productivity evaluation grades, determine the corresponding well productivity evaluation grade of the net pressure in the natural fractures of the area to be evaluated, and evaluate the well productivity of the reservoir in the area to be evaluated.

[0011] The present invention is further configured such that step S1 specifically includes the following steps:

[0012] S11: According to the deformation geometric equations in the rectangular coordinate system, confirm the strain components based on the thin - plate theory;

[0013] S12: Establish the physical constitutive relationship and calculate the maximum principal stress and the minimum principal stress;

[0014] S13: Obtain the stress difference between the maximum principal stress and the minimum principal stress in the area to be evaluated.

[0015] The present invention is further configured such that step S11 is specifically: the deformation geometric equations in the rectangular coordinate system:

[0016]

[0017]

[0018] u z = w(3)

[0019] It is known from the thin - plate theory that

[0020]

[0021]

[0022] Define the curvature deformation components:

[0023]

[0024] Therefore, the strain components can be written as:

[0025] ε x =-zκ x ε y =-zκ y γ xy =-2zκ xy (7)

[0026] where ε x ε y ε z are the strains in the x, y, and z directions respectively, and γxy , γ xz , γ yz are the shear strains on the xy-plane, xz-plane, and yz-plane respectively; u x , u y , u z are the displacements in the x, y, and z directions respectively; z represents the thickness of the surface formation; κ x , κ y , κ xy represent the curvatures in the x, y, and xy directions respectively.

[0027] The present invention is further configured such that step S12 is specifically, according to Hooke's law in general form,

[0028]

[0029]

[0030]

[0031] Its inverse relationship is:

[0032] σ x = 2Gε x + λθ, τ xy = Gγ xy (11)

[0033] σ y = 2Gε y + λθ, τ yz = Gγ yz (12)

[0034] σ z = 2Gε z + λθ, τ xz = Gγ xz (13)

[0035] θ = ε kk (14)

[0036] where λ is the Lame constant, G is the shear modulus, and E is the Young's modulus; ε kk is the volume strain; σ x , σ y , σ z are the stresses in the x, y, and z directions respectively, and τ xy , τ xz , τ yz are the shear stresses on the xy-plane, xz-plane, and yz-plane respectively;

[0037] Substituting formulas (8)-(10) into (11)-(12), we can obtain

[0038]

[0039] Furthermore,[[]]

[0040]

[0041]

[0042] According to the reflection principle of seismic waves, the time on the post-stack time section represents the two-way travel time. Therefore, the formation thickness t = 2z. Substituting it into the above formula, the stress component on the formation surface represented by the curvature component is obtained:

[0043]

[0044]

[0045] It can be seen from the above formula that when the formation surface is convex upward, the curvature is greater than zero, which exactly corresponds to the tensile stress on the convex formation surface, and the tensile stress is positive. In order to conform to the symbols of geomechanics, the symbol convention of positive compressive stress and negative tensile stress is adopted here. A curvature less than zero indicates that the formation is convex upward.

[0046] Calculate its maximum principal stress and minimum principal stress according to formula (17):

[0047]

[0048] where σ max is the maximum principal stress, and σ min is the minimum principal stress.

[0049] The present invention is further configured such that step S2 is specifically to calculate the net pressure in the natural fracture by the following formula:

[0050]

[0051] where P f represents the static pressure in the fracture, and v represents the Poisson's ratio of the rock.

[0052] The present invention is further configured such that step S3 is specifically to divide the well productivity evaluation range into four grades based on the cumulative well production of the previously drilled wells, including high-quality high-yield reservoir bodies, high-quality reservoir areas, ordinary reservoir areas, and karst cave underdeveloped areas, and confirm the corresponding net pressure range in the fractures of each area.

[0053] The present invention is further configured such that the division of the well productivity evaluation range is specifically as follows: the cumulative well production of the previously drilled wells is sorted from large to small. The top 5% before sorting is the high-quality and high-yield reservoir body, 5% to 20% is the high-quality reservoir area, 20% to 50% is the ordinary reservoir area, and after 50% is the area where karst caves are underdeveloped.

[0054] It should be noted that the well productivity evaluation range does not include the endpoint value of this range.

[0055] The present invention further includes an electronic device, which includes:

[0056] a memory storing executable instructions;

[0057] a processor that runs the executable instructions in the memory to implement the above-mentioned reservoir evaluation method based on the net pressure in the fracture.

[0058] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, it implements the above-mentioned reservoir evaluation method based on the net pressure in the fracture.

[0059] In summary, the beneficial effects of the above technical solutions of the present invention are as follows:

[0060] 1. The present invention predicts and evaluates the reservoir production based on the net pressure in the fracture, and preferably uses seismic attributes to predict the fracture distribution. The net pressure in the fracture is used to study the fracture development intensity of the fracture-vug reservoir, making up for the problems of the common reservoir fracture density research method, such as insufficient accuracy in reservoir characterization, inability to accurately determine the reservoir connection channels, inability to accurately determine the strength of reservoir fracture development, inability to predict the well production of the reservoir, and being unfavorable for subsequent well location adjustment and deployment. The present invention helps researchers establish a clearer regional geological understanding, improve the judgment and prediction of the reservoir, and provide a basis for the well location deployment of oil and gas exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0062] Figure 1 It is a flowchart of a reservoir evaluation method based on the net pressure in the fracture according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0063] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Based on the embodiments in the present invention, other similar embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0064] In addition, the directional terms mentioned in the following embodiments, such as "up", "down", "left", "right", etc., are only references to the directions in the accompanying drawings. Therefore, the directional terms used are for illustration rather than to limit the present invention.

[0065] The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments.

[0066] Embodiment 1:

[0067] As Figure 1 shown, it is a preferred embodiment of the present invention. A reservoir evaluation method based on the net pressure in the seam includes the following steps:

[0068] S1: Calculate the stress difference between the maximum principal stress and the minimum principal stress in the area to be evaluated;

[0069] S11: Confirm the strain components according to the deformation geometric equation in the rectangular coordinate system by the thin plate theory;

[0070] Establish the deformation geometric equation in the rectangular coordinate system:

[0071]

[0072]

[0073] u z = w (3)

[0074] It can be known from the thin plate theory that

[0075]

[0076]

[0077] Define the curvature deformation components:

[0078]

[0079] Therefore, the strain components can be written as:

[0080] ε x = -zκ x ,ε y = -zκ y ,γ xy = -2zκ xy (7)

[0081] Among them, ε x , ε y , ε z are the strains in the x, y, and z directions respectively, and γ xy , γ xz , γ yz are the shear strains in the xy plane, xz plane, and yz plane respectively; u x , u y , u z are the displacements in the x, y, and z directions respectively; z represents the thickness of the surface formation.

[0082] S12: Establish a physical constitutive relationship and calculate the maximum principal stress and the minimum principal stress;

[0083] According to Hooke's law in general form,

[0084]

[0085]

[0086]

[0087] Its inverse relationship is:

[0088] σ x = 2Gε x + λθ, τ xy = Gγ xy (11)

[0089] σ y = 2Gε y + λθ, τ yz = Gγ yz (12)

[0090] σ z = 2Gε z + λθ, τ xz = Gγ xz (13)

[0091] θ = ε kk (14)

[0092] Among them, λ is the Lame constant, G is the shear modulus, and E is the Young's modulus; ε kk is the volume strain; σ x , σ y , σ z are the stresses in the x, y, and z directions respectively, and τ xy , τ xz , τ yzShear stresses on the xy plane, xz plane, and yz plane, respectively;

[0093] Substituting formulas (8)-(10) into (11)-(12), we can obtain

[0094]

[0095] Furthermore,

[0096]

[0097]

[0098] According to the reflection principle of seismic waves, the time on the post-stack time section represents the two-way travel time. Therefore, the formation thickness t = 2z. Substituting it into the above formula, the stress components on the formation surface represented by the curvature components are obtained:

[0099]

[0100]

[0101] As can be seen from the above formula, when the formation surface is convex upward, the curvature is greater than zero, which exactly corresponds to the tensile stress on the convex formation surface, and the tensile stress is positive. In order to conform to the symbols of geomechanics, the symbol convention of positive for compressive stress and negative for tensile stress is adopted here. A curvature less than zero indicates that the formation is convex upward.

[0102] Calculate its maximum principal stress and minimum principal stress according to formula (17):

[0103]

[0104] where σ max is the maximum principal stress, and σ min is the minimum principal stress.

[0105] S13: Obtain the stress difference between the maximum principal stress and the minimum principal stress in the area to be evaluated.

[0106] S2: Obtain the net pressure inside the natural fractures in the area to be evaluated;

[0107] Specifically, step S2 is to calculate the net pressure inside the natural fractures through the following formula:

[0108]

[0109] where P f represents the static pressure inside the fracture, and v represents the Poisson's ratio of the rock.

[0110] S3: Based on the cumulative well production of the previously drilled wells, divide the well productivity evaluation grades and determine the range of static pressure inside the fractures corresponding to the well productivity evaluation grades;

[0111] Step S3 specifically is as follows: Based on the cumulative well production of the previously drilled wells, the well productivity evaluation range is divided into four grades, including high-quality high-production reservoirs, high-quality reservoir areas, ordinary reservoir areas, and areas with underdeveloped karst caves, and the corresponding in-fracture static pressure ranges for each area are confirmed.

[0112] The specific division of the well productivity evaluation range is as follows: Sort the cumulative well production of the previously drilled wells from large to small. The top five percent are high-quality high-production reservoirs, five percent to twenty percent are high-quality reservoir areas, twenty percent to fifty percent are ordinary reservoir areas, and after fifty percent are areas with underdeveloped karst caves.

[0113] S4: Determine the well productivity evaluation of the area to be evaluated based on the net in-fracture pressure of the natural fractures in the area to be evaluated. Compare the net in-fracture pressure of the natural fractures in the area to be evaluated with the corresponding in-fracture static pressure ranges of different well productivity evaluation grades, determine the corresponding well productivity evaluation grade of the net in-fracture pressure of the natural fractures in the area to be evaluated, and evaluate the well productivity of the reservoir in the area to be evaluated.

[0114] Embodiment 2:

[0115] An electronic device, the electronic device includes:

[0116] A memory storing executable instructions;

[0117] A processor, the processor runs the executable instructions in the memory to implement the above-mentioned reservoir evaluation method based on the net in-fracture pressure.

[0118] Embodiment 3:

[0119] A computer-readable storage medium, the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, it implements the above-mentioned reservoir evaluation method based on the net in-fracture pressure.

[0120] The above are only the preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, several improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A reservoir evaluation method based on the net pressure in the fracture, characterized in that, It includes the following steps: S1: Calculate the stress difference between the maximum principal stress and the minimum principal stress in the area to be evaluated; S2: Obtain the net pressure inside the natural fractures in the area to be evaluated; S3: Based on the cumulative well production of the previously drilled wells, divide the well productivity evaluation grades, and determine the corresponding range of static pressure inside the fractures for each well productivity evaluation grade; S4: Compare the net pressure inside the natural fractures in the area to be evaluated with the corresponding ranges of static pressure inside the fractures for different well productivity evaluation grades, determine the corresponding well productivity evaluation grade of the net pressure inside the natural fractures in the area to be evaluated, and evaluate the well productivity of the reservoir in the area to be evaluated.

2. The reservoir evaluation method based on the net pressure in the fracture according to claim 1, wherein Step S1 specifically includes the following steps: S11: According to the deformation geometric equation in the rectangular coordinate system, confirm the strain components by the thin plate theory; S12: Establish the physical constitutive relationship and calculate the maximum principal stress and the minimum principal stress; S13: Obtain the stress difference between the maximum principal stress and the minimum principal stress in the area to be evaluated.

3. The reservoir evaluation method based on in-seam net pressure according to claim 2, characterized in that Specifically, for step S11, establish the deformation geometric equation in the rectangular coordinate system: u z = w(3) As known from the thin plate theory, Define the curvature deformation components: Therefore, the strain components can be written as: ε x = -zκ x ,ε y = -zκ y ,γ xy = -2zκ xy (7) where ε x , ε y , ε z are strains in the x, y, and z directions respectively, and γ xy , γ xz , γ yz are shear strains in the xy, xz, and yz planes respectively; u x , u y , u z are displacements in the x, y, and z directions respectively; z represents the thickness of the surface formation, and κ x , κ y , κ xy represent curvatures in the x, y, and xy directions respectively.

4. The reservoir evaluation method based on the net pressure in the fracture according to claim 3, characterized in that, Specifically, for step S12, according to Hooke's law in general form, Its inverse relationship is: σ x = 2Gε x + λθ,τ xy = Gγ xy (11) σ y = 2Gε y + λθ,τ yz = Gγ yz (12) σ z = 2Gε z + λθ,τ xz = Gγ xz (13) θ = ε kk (14) where λ is the Lame constant, G is the shear modulus, and E is the Young's modulus; ε kk is the volume strain; σ x and σ y and σ z are the stresses in the x, y, and z directions, respectively, and τ xy and τ xz and τ yz are the shear stresses on the xy, xz, and yz planes, respectively; Substitute formulas (8)-(10) into (11)-(12), and we can get Furthermore, According to the reflection principle of seismic waves, the time on the post-stack time section represents the two-way travel time. Therefore, the formation thickness t = 2z. Substitute it into the above formula to obtain the stress components on the formation surface represented by the curvature components: As can be seen from the above formula, when the formation surface is convex upward, the curvature is greater than zero, which exactly corresponds to the tensile stress on the convex formation surface, and the tensile stress is positive; Calculate its maximum principal stress and minimum principal stress according to formula (17): Among them, σ max is the maximum principal stress, and σ min is the minimum principal stress.

5. The reservoir evaluation method based on the net pressure in the fracture according to claim 4, characterized in that, Specifically, for step S2, calculate the net pressure inside the natural fractures through the following formula: Among them, P f represents the static pressure in the seam, and v represents the Poisson's ratio of the rock.

6. The reservoir evaluation method based on the net pressure in the fracture according to claim 1, characterized in that Specifically, for step S3, based on the cumulative well production of the previously drilled wells, divide the well productivity evaluation range into four grades, including high-quality high-yield reservoir bodies, high-quality reservoir areas, ordinary reservoir areas, and areas with underdeveloped karst caves, and confirm the corresponding ranges of static pressure inside the fractures for each area.

7. A reservoir evaluation method based on the net pressure in the fracture according to claim 6, characterized in that The specific division of the well productivity evaluation range is as follows: Sort the cumulative well production of the previously drilled wells from large to small. The top 5% are high-quality high-yield reservoir bodies, 5% to 20% are high-quality reservoir areas, 20% to 50% are ordinary reservoir areas, and after 50% are areas with underdeveloped karst caves.

8. An electronic device, characterized in that, The electronic device includes: A memory storing executable instructions; A processor that runs the executable instructions in the memory to implement a reservoir evaluation method according to any one of claims 1-7.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, which when executed by a processor implements a reservoir evaluation method according to any one of claims 1-7.

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