Multi-scale coupled reservoir fracturing fracture transformation effect evaluation method

Abstract

The invention discloses a multi-scale coupled reservoir fracturing fracture transformation effect evaluation method, and relates to the technical field of applied geophysics, and the method comprises the following steps: S1, obtaining array acoustic logging data before fracturing and array acoustic logging data after fracturing; s2, determining the height of a near-wellbore fracturing crack; and S3, according to the height of the near-wellbore fracturing fracture, fracturing fracture volume expansion is carried out, and the fracturing fracture volume expansion form is obtained. According to the method, the problem of comprehensive evaluation of the fracturing fracture in the existing reservoir fracturing transformation effect evaluation can be solved, the multi-scale coupled reservoir fracturing fracture transformation effect evaluation is realized by comprehensively utilizing the longitudinal wave tomography technology and the volume fracturing fracture extension simulation, and the evaluation range of the reservoir fracturing fracture transformation effect can be effectively expanded.

Description

Technical Field

[0001] The invention relates to the field of applied geophysical technology, and in particular to a multi-scale coupled reservoir fracture reconstruction effect evaluation method. Background Art

[0002] In recent years, with the continuous deepening of offshore exploration and development, low-permeability reservoirs have become a key area for increasing oil and gas reserves and production in my country. Industrial oil and gas flows can only be obtained through fracturing. Therefore, fracturing is an inevitable way to assist the exploration and development of low-permeability reservoirs. The effect of fracturing in low-permeability reservoirs and whether the expected effect of fracturing construction is achieved have become a difficult problem in the exploration and development of low-permeability reservoirs.

[0003] At present, the traditional reservoir fracturing effect evaluation technologies mainly include well temperature method, radioactive tracer method, optical fiber method, anisotropy analysis method and radial tomography method, but the above methods can only evaluate the height of the fracture, but cannot evaluate the radial extension characteristics of the fracture, and the detection range is limited. It cannot evaluate the reservoir fracturing effect at a distance from the well, and cannot achieve an overall evaluation of the fracture transformation. Although the microseismic method can evaluate information such as the length, height and width of the fracture, and has a large detection range, it can fully display the effect of the fracture transformation, but due to the limited space for offshore fracturing operations, it is still difficult to implement microseismic technology at sea. Using fracturing construction data to simulate the expansion of hydraulic fracturing volume fracturing fractures is also a means of fracture evaluation. The commonly used methods are mainly displacement discontinuity method, finite element method and extended finite element method. The above methods are mainly based on logging and geological data to establish geological models, and then use fracturing construction data to use different numerical simulation methods to simulate the expansion of hydraulic fractures. Although the scale of hydraulic fractures can be fully evaluated, the fracture information comes from numerical simulation, which is too theoretical and has poor evaluation effect.

[0004] In view of the shortcomings of the prior art, the present invention proposes a reservoir fracturing transformation effect evaluation method based on multi-scale coupling of well logging and fracturing construction data. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a multi-scale coupled reservoir fracturing transformation effect evaluation method.

[0006] The technical solution of the present invention is: a multi-scale coupled reservoir fracturing transformation effect evaluation method comprises the following steps:

[0007] S1, obtaining array acoustic logging data before fracturing and array acoustic logging data after fracturing;

[0008] S2, determining the height of the fracture near the wellbore according to the array acoustic logging data before and after the fracturing;

[0009] S3. Expand the volume of the hydraulic fracture according to the height of the hydraulic fracture near the wellbore to obtain the volume expansion shape of the hydraulic fracture.

[0010] Furthermore, S1 includes the following sub-steps:

[0011] S11, acquiring array acoustic logging data before fracturing and array acoustic logging data after fracturing;

[0012] S12, processing the array acoustic logging data before fracturing and the array acoustic logging data after fracturing to obtain a relative radial velocity profile of the longitudinal wave of the formation before fracturing and a relative radial velocity profile of the longitudinal wave of the formation after fracturing;

[0013] S13, taking the difference between the relative radial velocity profile of the longitudinal wave of the formation after fracturing and the relative radial velocity profile of the longitudinal wave of the formation before fracturing as the difference of the relative radial velocity profile before and after fracturing;

[0014] S14. According to the difference in relative radial velocity profiles before and after fracturing, the height of the fracture near the wellbore is obtained.

[0015] Furthermore, in S12, the calculation formula for processing the array acoustic logging data before fracturing and the array acoustic logging data after fracturing is:

[0016] Δv′ p =(v p0 -v pd ) / v p0 ×100%;

[0017] In the formula, v p0 represents the original formation P-wave velocity, v pd Indicates the longitudinal wave velocity at a certain radial depth on the absolute velocity profile, Δv′ p Indicates relative speed change.

[0018] Furthermore, S2 includes the following sub-steps:

[0019] S21. Construct a rock mechanics mathematical model and solve it using the displacement discontinuity method;

[0020] S22. Construct a nonlinear fluid mechanics model and solve it using the finite difference method;

[0021] S23, coupling the solved rock mechanics mathematical model and the nonlinear fluid mechanics model to obtain a coupled model;

[0022] S24, using the height of the hydraulic fracture near the wellbore to constrain, and expanding the volume of the hydraulic fracture according to the coupling model;

[0023] S25. When the difference between the pressure obtained after the hydraulic fracture volume expansion and the actual pressure is the smallest, the hydraulic fracture volume expansion shape is obtained.

[0024] Furthermore, in S21, the calculation formula for solving the rock mechanics mathematical model using the displacement discontinuity method is:

[0025]

[0026] In the formula, represents the normal stress of element i, represents the tangential stress of element i, Indicates that the normal displacement is discontinuous, Indicates that the displacement in the shear direction is discontinuous, G ij represents the three-dimensional correction factor, The elastic influence coefficient matrix represents the influence of normal stress on element i due to shear displacement discontinuity on element j under plane strain conditions, represents the normal stress at single element i due to the opening displacement discontinuity of element j, The elastic influence coefficient matrix represents the influence of normal stress on element i due to shear displacement discontinuity on element j under plane strain conditions, It represents the shear stress of element i due to the discontinuity of the opening displacement of element j, and N represents the normal direction.

[0027] Furthermore, in S24, the calculation formula for the expansion of the hydraulic fracture volume is:

[0028]

[0029] In the formula, K Ⅰ Stress intensity factor indicating that the expansion mode is opening, K Ⅱ represents the stress intensity factor when the propagation mode is shear, and θ represents the deflection angle in the polar coordinate system where the origin is located in the shear shortening of the crack.

[0030] Furthermore, the stress intensity factor K of the expansion mode is the opening Ⅰ The calculation formula is:

[0031]

[0032] Where E represents Young's modulus, D n represents the normal displacement discontinuity, v represents the Poisson’s ratio, and a represents half the length of the plane element;

[0033] The stress intensity factor K for the shear mode of expansion is Ⅱ The calculation formula is:

[0034]

[0035] Where D s Indicates that the displacement in the shear direction is discontinuous.

[0036] Furthermore, in S24, the overall material balance expression when the fracturing crack volume expansion is performed is:

[0037]

[0038] Where N f Indicates the number of cracks, L i (t) represents the total crack length of the i-th crack at that time, q l (s, t) represents the volume loss rate per unit length of the crack, h represents the crack height, w represents the crack width, Q T (t) represents the total flow rate during the crack expansion time, s represents the distance along the crack, and t represents the time taken to travel the distance along the crack.

[0039] The beneficial effects of the present invention are:

[0040] (1) Based on the fact that fracturing causes formation rocks to break and generate a large number of cracks, the present invention evaluates the height of the hydraulic fracture near the wellbore by comparing the difference in radial velocity profiles before and after fracturing. On this basis, based on the fracturing construction data, the hydraulic fracture height near the wellbore is used as a constraint, and the displacement discontinuity method and the finite difference method are used to simulate the expansion of hydraulic fractures, thereby realizing the evaluation of the reservoir hydraulic fracture transformation effect under multi-scale coupling;

[0041] (2) The present invention can solve the problem of all-round evaluation of hydraulic fractures in the current evaluation of reservoir hydraulic fracture transformation effects. By comprehensively utilizing longitudinal wave tomography technology and volume hydraulic fracture expansion simulation, multi-scale coupled reservoir hydraulic fracture transformation effect evaluation can be achieved, which can effectively improve the evaluation range of reservoir hydraulic fracture transformation effects;

[0042] (3) The present invention has good application effect and high applicability, and at the same time provides a new idea for the evaluation of fracturing effects of unconventional reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a flow chart of the multi-scale coupled reservoir fracturing stimulation effect evaluation method;

[0044] Figure 2 This is the result diagram of the accuracy verification of the fracture volume expansion model of the offshore fracture well X1;

[0045] Figure 3 Three-dimensional imaging of multi-scale coupled fracturing fracture transformation morphology. DETAILED DESCRIPTION

[0046] The embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0047] like Figure 1 As shown, the present invention provides a multi-scale coupled reservoir fracturing transformation effect evaluation method, comprising the following steps:

[0048] S1, obtaining array acoustic logging data before fracturing and array acoustic logging data after fracturing;

[0049] S2, determining the height of the fracture near the wellbore according to the array acoustic logging data before and after the fracturing;

[0050] S3. Expand the volume of the hydraulic fracture according to the height of the hydraulic fracture near the wellbore to obtain the volume expansion shape of the hydraulic fracture.

[0051] The present invention collects array acoustic logging data and fracturing construction data before and after fracturing in the depth interval of interest; uses longitudinal wave travel time tomography technology to process array acoustic wave data before and after fracturing to evaluate the height of the near-wellbore fracturing; based on the fracturing construction data, the near-wellbore fracturing height is used as a constraint to simulate the volume expansion of the fracturing crack; based on the near-wellbore fracturing evaluation results, combined with the far-well fracturing morphology and wellbore trajectory information, a multi-scale coupled three-dimensional imaging map of the fracturing transformation morphology is obtained; the simulation results of the reservoir fracturing transformation morphology are compared with the actual fracturing construction curve to verify the accuracy of the model.

[0052] In this embodiment of the present invention, S1 includes the following sub-steps:

[0053] S11, acquiring array acoustic logging data before fracturing and array acoustic logging data after fracturing;

[0054] S12, processing the array acoustic logging data before fracturing and the array acoustic logging data after fracturing to obtain a relative radial velocity profile of the longitudinal wave of the formation before fracturing and a relative radial velocity profile of the longitudinal wave of the formation after fracturing;

[0055] S13, taking the difference between the relative radial velocity profile of the longitudinal wave of the formation after fracturing and the relative radial velocity profile of the longitudinal wave of the formation before fracturing as the difference of the relative radial velocity profile before and after fracturing;

[0056] S14. According to the difference in relative radial velocity profiles before and after fracturing, the height of the fracture near the wellbore is obtained.

[0057] In the embodiment of the present invention, in S12, the calculation formula for processing the array acoustic logging data before fracturing and the array acoustic logging data after fracturing is:

[0058] Δv′ p =(v p0-v pd ) / v p0 ×100%;

[0059] In the formula, v p0 represents the original formation P-wave velocity, v pd Indicates the longitudinal wave velocity at a certain radial depth on the absolute velocity profile, Δv′ p Indicates relative speed change.

[0060] In this embodiment of the present invention, S2 includes the following sub-steps:

[0061] S21. Construct a rock mechanics mathematical model and solve it using the displacement discontinuity method;

[0062] S22. Construct a nonlinear fluid mechanics model and solve it using the finite difference method;

[0063] S23, coupling the solved rock mechanics mathematical model and the nonlinear fluid mechanics model to obtain a coupled model;

[0064] S24, using the height of the hydraulic fracture near the wellbore to constrain, and expanding the volume of the hydraulic fracture according to the coupling model;

[0065] S25. When the difference between the pressure obtained after the hydraulic fracture volume expansion and the actual pressure is the smallest, the hydraulic fracture volume expansion shape is obtained.

[0066] In the embodiment of the present invention, the travel time of the acoustic wave propagating to the first receiver in the array acoustic wave monopole full wave is calculated, and it is defined as the reference travel time TT rf , the formula is as follows:

[0067]

[0068] Wherein, v(z) is the formation P-wave velocity curve extracted by array acoustic wave processing; the upper and lower limits of the integral are the depth positions of the sound source s and the first receiver R1, respectively; TTf is the propagation time of the P-wave in the fluid in the well.

[0069] Compare the reference travel time with the measured travel time. For formations with no radial changes in v(z), the reference travel time is consistent with the measured travel time. When the sound speed increases radially, the measured travel time is the time it takes for the ray to enter the formation from shallow to deep and then refract back. Since v(z) is the velocity at the maximum penetration depth, the reference travel time calculated by the above formula is smaller than the measured travel time, that is, the measured travel time lags behind the reference travel time. In order to more intuitively display the changes in the longitudinal wave velocity of the formation near the well wall, a velocity model is established. By continuously updating the velocity model, the reference travel time is made to coincide with or be close to the measured travel time. The velocity model at this time is the absolute velocity profile required.

[0070] In the embodiment of the present invention, in S21, the calculation formula for solving the rock mechanics mathematical model using the displacement discontinuity method is:

[0071]

[0072] In the formula, represents the normal stress of element i, represents the tangential stress of element i, Indicates that the normal displacement is discontinuous, Indicates that the displacement in the shear direction is discontinuous, G ij represents the three-dimensional correction factor, The elastic influence coefficient matrix represents the influence of normal stress on element i due to shear displacement discontinuity on element j under plane strain conditions, represents the normal stress at single element i due to the opening displacement discontinuity of element j, The elastic influence coefficient matrix represents the influence of normal stress on element i due to shear displacement discontinuity on element j under plane strain conditions, It represents the shear stress of element i due to the discontinuity of the opening displacement of element j, and N represents the normal direction.

[0073] 3D correction factor G ij The calculation formula is:

[0074]

[0075] Among them, d ij represents the distance between the centers of unit i and unit j, h represents the crack height, and α and β are constants determined empirically.

[0076] In an embodiment of the present invention, in S24, crack expansion is a process in which the length gradually increases. At each time step, fluid is injected into the crack to increase the pressure inside the crack, the crack width, and the stress intensity factor before expansion. When the intensity factor at the crack tip reaches the critical point of the material strength, the front end of the crack will move forward a certain distance. In this expansion process, it is necessary to determine the critical conditions, expansion direction, and expansion speed of the crack expansion. When the crack expands, it is necessary to determine the expansion direction. When the crack expansion direction is non-planar, the expansion is usually controlled by the opening mode and shear mode loads. The calculation formula for the volume expansion of the hydraulic fracture is:

[0077]

[0078] In the formula, K Ⅰ Stress intensity factor indicating that the expansion mode is opening, K Ⅱrepresents the stress intensity factor when the propagation mode is shear, and θ represents the deflection angle in the polar coordinate system where the origin is located in the shear shortening of the crack.

[0079] In the embodiment of the present invention, when K I >0 and K II = 0, the expansion of the plane crack should proceed along θ = 0°. I = 0 and K II ≠0, a pure shear mode occurs, resulting in a maximum bending fracture direction along θ = ±70.5°. The stress intensity factor K for the expansion mode is the opening Ⅰ The calculation formula is:

[0080]

[0081] Where E represents Young's modulus, D n represents the normal displacement discontinuity, v represents the Poisson’s ratio, and a represents half the length of the plane element;

[0082] Stress intensity factor K for shear expansion mode Ⅱ The calculation formula is:

[0083]

[0084] Where D s Indicates that the displacement in the shear direction is discontinuous.

[0085] In the embodiment of the present invention, in S24, since the fracturing fluid is a non-Newtonian fluid, the flow of the fluid in the fracture should be considered during the fracture expansion process. For the propagation of a single fracture, only the fluid flow in the fracture needs to be considered. For multiple fractures, the fluid flow in the fracture, the fluid flow in the horizontal wellbore, and the total material balance of all fractures need to be considered. The entire fluid flow system must satisfy the law of conservation of matter, that is, the total volume of fluid pumped during injection is equal to the volume of fluid retained in multiple fractures and the volume lost to the surrounding porous medium. The overall material balance expression when performing fracturing fracture volume expansion is:

[0086]

[0087] Where N f Indicates the number of cracks, L i (t) represents the total crack length of the i-th crack at that time, q l (s, t) represents the volume loss rate per unit length of the crack, h represents the crack height, w represents the crack width, Q T (t) represents the total flow rate during the crack expansion time, s represents the distance along the crack, and t represents the time taken to travel the distance along the crack.

[0088] The reservoir fracture reconstruction effect evaluation method of the present invention is further described by means of specific examples.

[0089] Figure 2 This is the result of the accuracy verification of the fracturing fracture volume expansion model of the offshore fracturing well X1. According to the actual fracturing construction data fitting, the bottom hole pressure calculated by the fracturing fracture volume expansion model of this well is in good agreement with the actual bottom hole pressure curve, indicating that the model is highly accurate and can reflect the actual fracturing situation. Combined with the information of the far well fracturing fracture morphology and wellbore trajectory, a multi-scale coupled three-dimensional imaging of the fracturing fracture transformation morphology is formed, such as Figure 3 As shown, the simulation results show that the average fracture height of the three clusters of fractures is about 10.62m, the average fracture width is 3.85mm, and the fractures can be effectively supported. The average half-fracture length of the fractures is about 153.76m, and the fracture efficiency is relatively high, indicating that the fractures have good horizontal extension in the formation. The average fracture conductivity is relatively high, about 782.59mD.m, indicating that the reservoir can be well utilized. Overall, the fracturing effect of this well is relatively good. This well had no production capacity before fracturing, and after fracturing, it produced 19.5 cubic meters of oil per day and 1589 cubic meters of gas per day. Combined with the production information, the evaluation of the fracturing effect by the above method is further verified, and finally the correctness and effectiveness of the multi-scale coupled reservoir fracturing transformation effect evaluation method proposed in the present invention are explained.

[0090] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A multi-scale coupled reservoir fracturing transformation effect evaluation method, characterized in that: The following steps are involved: S1, obtaining array acoustic logging data before fracturing and array acoustic logging data after fracturing; S2, determining the height of the fracture near the wellbore according to the array acoustic logging data before and after the fracturing; S3. Expand the volume of the hydraulic fracture according to the height of the hydraulic fracture near the wellbore to obtain the volume expansion shape of the hydraulic fracture.

2. The multi-scale coupled reservoir fracturing transformation effect evaluation method according to claim 1, characterized in that: The S1 comprises the following sub-steps: S11, acquiring array acoustic logging data before fracturing and array acoustic logging data after fracturing; S12, processing the array acoustic logging data before fracturing and the array acoustic logging data after fracturing to obtain a relative radial velocity profile of the longitudinal wave of the formation before fracturing and a relative radial velocity profile of the longitudinal wave of the formation after fracturing; S13, taking the difference between the relative radial velocity profile of the longitudinal wave of the formation after fracturing and the relative radial velocity profile of the longitudinal wave of the formation before fracturing as the difference of the relative radial velocity profile before and after fracturing; S14. According to the difference in relative radial velocity profiles before and after fracturing, the height of the fracture near the wellbore is obtained.

3. The multi-scale coupled reservoir fracturing reconstruction effect evaluation method according to claim 2, characterized in that: In S12, the calculation formula for processing the array acoustic logging data before fracturing and the array acoustic logging data after fracturing is: Δv′ p =(v p0 -v pd ) / v p0 ×100%; In the formula, v p0 represents the original formation P-wave velocity, v pd Indicates the longitudinal wave velocity at a certain radial depth on the absolute velocity profile, Δv′ p Indicates relative speed change.

4. The multi-scale coupled reservoir fracturing reconstruction effect evaluation method according to claim 1, characterized in that: The S2 comprises the following sub-steps: S21. Construct a rock mechanics mathematical model and solve it using the displacement discontinuity method; S22. Construct a nonlinear fluid mechanics model and solve it using the finite difference method; S23, coupling the solved rock mechanics mathematical model and the nonlinear fluid mechanics model to obtain a coupled model; S24, using the height of the hydraulic fracture near the wellbore to constrain, and expanding the volume of the hydraulic fracture according to the coupling model; S25. When the difference between the pressure obtained after the hydraulic fracture volume expansion and the actual pressure is the smallest, the hydraulic fracture volume expansion shape is obtained.

5. The multi-scale coupled reservoir fracturing reconstruction effect evaluation method according to claim 4, characterized in that: In S21, the calculation formula for solving the rock mechanics mathematical model using the displacement discontinuity method is: In the formula, represents the normal stress of element i, represents the tangential stress of element i, Indicates that the normal displacement is discontinuous, Indicates that the displacement in the shear direction is discontinuous, G ij represents the three-dimensional correction factor, The elastic influence coefficient matrix represents the influence of normal stress on element i due to shear displacement discontinuity on element j under plane strain conditions, represents the normal stress at single element i due to the opening displacement discontinuity of element j, The elastic influence coefficient matrix represents the influence of normal stress on element i due to shear displacement discontinuity on element j under plane strain conditions, It represents the shear stress of element i due to the discontinuity of the opening displacement of element j, and N represents the normal direction.

6. The multi-scale coupled reservoir fracturing reconstruction effect evaluation method according to claim 4, characterized in that: In S24, the calculation formula for the expansion of the hydraulic fracture volume is: In the formula, K Ⅰ Stress intensity factor indicating that the expansion mode is opening, K Ⅱ represents the stress intensity factor when the propagation mode is shear, and θ represents the deflection angle in the polar coordinate system where the origin is located in the shear shortening of the crack.

7. The multi-scale coupled reservoir fracturing reconstruction effect evaluation method according to claim 6, characterized in that: The expansion mode is the stress intensity factor K of the opening Ⅰ The calculation formula is: Where E represents Young's modulus, D n represents the normal displacement discontinuity, v represents the Poisson’s ratio, and a represents half the length of the plane element; The stress intensity factor K for the shear mode of expansion is Ⅱ The calculation formula is: Where D s Indicates that the displacement in the shear direction is discontinuous.

8. The multi-scale coupled reservoir fracturing reconstruction effect evaluation method according to claim 4, characterized in that: In S24, the overall material balance expression when the hydraulic fracture volume expansion is performed is: Where N f Indicates the number of cracks, L i (t) represents the total crack length of the i-th crack at that time, q l (s, t) represents the volume loss rate per unit length of the crack, h represents the crack height, w represents the crack width, Q T (t) represents the total flow rate during the crack expansion time, s represents the distance along the crack, and t represents the time taken to travel the distance along the crack.

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