A multi-scale pore-fracture space damage weight evaluation method for fractured oil and gas reservoirs

Abstract

The present invention provides a method for evaluating the weight of multi-scale pore-fracture space damage in fractured oil and gas reservoirs, which belongs to the technical field of reservoir protection in fractured oil and gas reservoirs. The present invention drills a long core and divides it into segments, artificially creates fractures, and then connects them in series to simulate the pore-fracture space of fractured oil and gas reservoirs with developed fractures. The treated long core is subjected to working fluid dynamic damage and permeability test, and the working fluid damage and fluid multi-scale mass transfer and output process in fractured oil and gas reservoirs are simulated. The degree of damage to the multi-scale pore-fracture space in fractured oil and gas reservoirs is accurately evaluated, and the matrix calculation base block and the weight of fracture damage of different scales are used to make the reservoir protection material added by the working fluid more targeted. The present invention can effectively solve the problems faced by the current evaluation of working fluid damage in fractured oil and gas reservoirs, and is of great significance to the optimization of the working fluid system in fractured oil and gas reservoirs.

Description

Technical Field

[0001] The invention relates to the technical field of fractured oil and gas reservoir reservoir protection, and in particular to a method for evaluating the weight of multi-scale pore space damage in fractured oil and gas reservoirs. Background Art

[0002] Fractured oil and gas reservoirs have great development potential due to their huge geological reserves. The most notable feature of fractured reservoirs is the development of natural fractures, which makes the oil and gas production process more complicated and poses a high risk of damage. Once damage occurs, the degree of damage is generally high. Therefore, accurately evaluating the degree of damage to the working fluid in fractured oil and gas reservoirs and clarifying the weight of pore space damage are of great significance to the economic and efficient development of fractured oil and gas reservoirs.

[0003] Due to the development of natural fractures in fractured oil and gas reservoirs, the working fluid operation and oil and gas production process are very complicated, and the traditional reservoir damage evaluation method is difficult to evaluate the pore space damage weight. At present, the commonly used reservoir damage evaluation methods are mostly based on the industry standard SY / T6540-2002 "Indoor Evaluation Method for Damage to Reservoirs by Drilling Fluid and Completion Fluid", which stipulates the basic method of static / dynamic simulation evaluation experiment of working fluid damage, but this method cannot clearly determine the proportion of matrix and fracture in the whole damage process. The Chinese inventions with publication numbers CN109946436A and CN109946437A proposed reservoir working fluid damage evaluation methods that can evaluate the weight of matrix and fracture damage, but both methods only calculated the degree of matrix pore throat damage and fracture damage, and could not clearly indicate how much role the matrix and fracture played in the working fluid damage process and how much proportion each accounted for, that is, they could not determine the multi-scale pore space damage weight of fractured oil and gas reservoirs. In fractured oil and gas reservoirs, natural fractures and induced fractures coexist. When working fluid damage occurs, the working fluid enters the deep reservoir along the seepage channel of induced fractures-natural fractures-matrix pore throats, reducing the seepage capacity of the reservoir. Oil and gas production also flows through the matrix storage space to fractures of different scales and then flows into the wellbore. Therefore, a working fluid damage evaluation method is formed that can simulate the development of multi-scale fractures in fractured oil and gas reservoirs, the process of oil and gas production and working fluid damage, and evaluate the weight of multi-scale pore space damage in fractured oil and gas reservoirs. It is of great significance for the optimization of the working fluid system for reservoir protection in fractured oil and gas reservoirs. Summary of the invention

[0004] In order to solve at least one of the above problems, the present invention proposes a method for evaluating the weight of multi-scale pore and fracture space damage in fractured oil and gas reservoirs. This method divides long cores, creates artificial fractures, and then connects them in series to simulate the pore and fracture space of fractured oil and gas reservoirs with developed fractures. The treated long cores are subjected to working fluid dynamic damage and permeability tests to simulate the working fluid damage and multi-scale mass transfer and production process of fluids in fractured oil and gas reservoirs, accurately evaluate the degree of damage to fractured oil and gas reservoirs, and calculate the weight of damage to base blocks and fractures of different scales through matrices, which is of great significance to the optimization of the formula of working fluids for protecting reservoirs and efficient development of fractured oil and gas reservoirs.

[0005] The technical solution adopted by the present invention to solve the above problem is: a method for evaluating the weight of multi-scale pore-fracture space damage in fractured oil and gas reservoirs, comprising the following steps:

[0006] S1. Determine the number of core plungers M to be drilled according to the number of simulated reservoir fracture scales N, and drill a corresponding number of core plungers from reservoir rock blocks where macroscopic fractures have not been seen and dry them for standby use, wherein the number of core plungers M is greater than the number of fracture scales N, such as M=N+1, M=N+2. The drying temperature and time can be selected and adjusted according to needs or actual conditions, such as drying at 60°C for 48 hours; the core drilling method is selected according to the drilling method. When evaluating the damage of the working fluid in a vertical well, choose to drill the core column parallel to the bedding plane; when evaluating the damage of the working fluid in a horizontal well, choose to drill the core column perpendicular to the bedding plane.

[0007] S2. For each core plug, the core plug is divided into N+1 sections, wherein one section of the core plug is not processed to simulate the base block, and the remaining sections of the core plug are fractured respectively and each section of the core plug corresponds to a fracture of a certain scale. The core plugs of each section (N+1 sections) are connected in series in the order of gradual change of the fracture opening (increasing or decreasing) to form a multi-scale pore fracture core plug A. i .

[0008] A i represents the i-th multi-scale pore core plug; preferably, each core plug is divided into N+1 sections of equal scale.

[0009] S3. Determine the permeability K0 (A) of each section of the multi-scale pore core plug before damage. ij ), A ij represents the jth core plug in the i-th multi-scale pore core plug, K0(A ij ) represents the permeability of the jth section of the ith core before core damage.

[0010] S4. The permeability K0 (A) of each multi-scale pore core before plug damage was determined by forward displacement. i ), K0(A i) represents the permeability of the i-th multi-scale pore core before the plug damage.

[0011] S5. Reversely circulate the working fluid to be evaluated through each multi-scale pore core plunger to simulate the multi-scale fracture damage process.

[0012] S6, positively displace the multi-scale pore core plugs of S5 with a certain backflow pressure difference until the flow rate is stable;

[0013] S7. Forward displacement is used to measure the permeability of each multi-scale pore core plug after damage, and the permeability of each section of the multi-scale pore core plug after damage. K1(A i ) represents the permeability of the i-th multi-scale pore core after plug damage, K1(A ij ) represents the permeability of the jth section of the i-th multi-scale pore core plug after damage.

[0014] S8. Calculate the degree of damage of the working fluid of each multi-scale pore core plug and the degree of damage of the working fluid of each section of the core plug in each multi-scale pore core plug:

[0015]

[0016]

[0017] Where: R A It is the overall working fluid damage degree of the multi-scale pore core plunger, dimensionless quantity; is the degree of damage of the working fluid in the i-th multi-scale pore core plunger, dimensionless; is the degree of working fluid damage in the jth core plug in the ith multi-scale pore core plug, a dimensionless quantity.

[0018] S9, calculate the damage weights of the foundation block and cracks of different scales;

[0019]

[0020] Where: T1 is the damage weight of the base block of the multi-scale pore core plug, which is dimensionless; T2 is the damage weight of the first scale crack of the multi-scale pore core plug, which is dimensionless; T N+1 It is the damage degree of the Nth scale crack in the multi-scale pore core plug, a dimensionless quantity.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) This paper provides a new idea for the damage evaluation experiment of working fluid in fractured oil and gas reservoirs, which can provide reference for other types of damage evaluation experimental methods involving matrix and fractures.

[0023] (2) It can evaluate the damage weights of the matrix and fracture cores of different scales, and optimize the formulation of the reservoir protection working fluid according to the measured damage weights of the matrix and fracture cores of different scales, so as to select reservoir protection materials and adjust the formulation of the reservoir protection working fluid in a more targeted manner.

[0024] Instruction Manual

[0025] Figure 1 Schematic diagram of the core structure of multi-scale pore space;

[0026] In the figure, 1 is the original long matrix core plug, 2 is the matrix core plug, 3 is the natural fracture core plug, and 4 is the induced fracture core plug. DETAILED DESCRIPTION

[0027] In order to facilitate those skilled in the art to better understand the present invention, the present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0028] Example 1

[0029] This embodiment involves operations such as measuring permeability and reverse circulation of the working fluid to be evaluated. Various existing experimental devices can achieve this measurement function, such as the experimental devices disclosed in CN109946436A and CN109946437A. The specific devices and their operations will not be described in detail here.

[0030] This embodiment involves forward displacement and reverse circulation of the core plunger, wherein the forward displacement refers to the displacement of a multi-scale pore core plunger composed of multiple sections of core plungers with the end of the core plunger with a smaller fracture opening as the inlet end, and the reverse displacement is in the opposite direction. For a single-section core plunger, the permeability can be tested with any end as the inlet end.

[0031] This embodiment uses a typical sandstone rock sample from a block in the Tarim Basin as an experimental rock sample. There are two types of reservoir fracture scales, namely natural fractures and induced fractures. The water quality of the formation water used in this embodiment is shown in Table 1. The liquid level to be evaluated used in this embodiment is the drilling fluid SR2PE used on site in the block, which comes from Sinopec Petroleum Engineering Technology Research Institute Co., Ltd.

[0032] Table 1 Formation water quality table

[0033] <![CDATA[Na + (mg / L)]]> <![CDATA[Cl - (mg / L)]]> Total mineralization (mg / L) 10000 10000 20000

[0034] The calculation of the hole and crack space damage weight in this embodiment specifically includes the following steps:

[0035] Step 1: Drill three long core plugs (each 15 cm long) vertically from the bedding plane of the reservoir rock blocks without macro fractures and dry them at 60°C for 48 hours.

[0036] Step 2: Divide the long core plug in step (1) into three equal-sized sections (each 5 cm long), where the three sections of the first long core plug are marked as A 11 , A 12 , A 13 The three sections of the second long core plug are marked as A 21 , A 22 , A 23 The three sections of the third long core plug are marked as A 31 , A 32 , A 33 .

[0037] The core plug A 11 , A 21 , A 31 Without any treatment, it is used as the base core plug section; 12 , A 22 , A 32 Cut along the central axis to create a through fracture as a natural fracture core plug section. The natural fracture core seam width is (0-50 μm). 13 , A 23 , A 33 Cut along the central axis to create a through crack and pad the wire mesh to open the crack, which is used as a core plug section for induced fractures with a wider crack width (>50μm).

[0038] Step 3: Determine the permeability of each core plug before damage: After applying a certain confining pressure to each core plug section, select any end as the inlet section and use formation water for displacement. Determine the permeability of each core plug section A 11 , A 12 , A 13 , A 21 , A 22 , A 23 , A 31 , A 32 , A 33 Permeability before damage K 0( A 11) , K 0( A 12) , K 0( A 13) , K 0( A 21) , K 0( A 22) , K 0( A 23) , K 0( A 31) , K 0( A 32) , K 0( A33) , the specific test results are shown in Table 2.

[0039] Table 2 Permeability of each section of core before plug damage

[0040] serial number <![CDATA[K 0( A 11) ]]> <![CDATA[K 0( A 12) ]]> <![CDATA[K 0( A 13) ]]> Permeability (mD) 1.011 292.302 1082.073 serial number <![CDATA[K 0( A 21) ]]> <![CDATA[K 0( A 22) ]]> <![CDATA[K 0( A 33) ]]> Permeability (mD) 2.069 135.989 1330.551 serial number <![CDATA[K 0( A 31) ]]> <![CDATA[K 0( A 32) ]]> <![CDATA[K 0( A 33) ]]> Permeability (mD) 3.747 371.615 1217.488

[0041] Step 4: Determine the permeability of each multi-scale pore core plug before damage: 11 , A 12 , A 13 The multi-scale pore-fracture core plug A1 was combined in series to simulate the core plugs with different pore-fracture spaces. The permeability K before damage was measured by forward displacement of formation water. 0( A 1) ; The core plug A 21 , A 22 , A 23 The multi-scale pore core plug A2 was assembled in series, and its permeability K before damage was measured by forward displacement of formation water. 0( A 2) , core plug A 31 , A 32 , A 33 The multi-scale pore core plug A3 was assembled in series, and the permeability K before damage was measured by forward displacement of formation water. 0( A 3) , the test results are shown in Table 3.

[0042] Table 3 Permeability of cores with various multi-scale pores and fractures before plug damage

[0043] serial number <![CDATA[K 0( A 1) ]]> <![CDATA[K 0( A 2) ]]> <![CDATA[K 0( A 3) ]]> Permeability (mD) 3.405 7.115 16.201

[0044] Step 5: Place the multi-scale pore core plugs A1, A2, and A3 in the holder respectively, and reversely circulate the working fluid SR2PE to be evaluated under simulated formation working conditions to simulate the process of multi-scale fractures being damaged by the working fluid to be evaluated. The reverse circulation time is 1 hour.

[0045] Step 6: The multi-scale pore core plugs A1, A2, and A3 in step (5) are respectively forwardly displaced at a constant backflow pressure difference (3.5 MPa) until the flow rate is stable, and the displacing fluid is formation water.

[0046] Step 7: Determine the permeability K of the multi-scale pore core plugs A1, A2, and A3 after damage in step (6) by forward displacement of formation water 1( A 1) , K 1( A 2) , K 1( A 3); Each multi-scale pore core plug A1, A2, A3 is disassembled to determine the permeability K of each section of the core plug after damage 1( A 11) , K 1( A 12) , K 1( A 13) , K 1( A 21) , K 1( A 22) , K 1( A 23) , K 1( A 31) , K 1( A 32) , K 1( A 33) , the test results are shown in Table 4 and Table 5.

[0047] Table 4 Permeability of cores with multi-scale pores and fractures after plug damage

[0048] serial number <![CDATA[K 1( A 1) ]]> <![CDATA[K 1( A 2) ]]> <![CDATA[K 1( A 3) ]]> Permeability (mD) 0.608 1.604 1.221

[0049] Table 5 Permeability of each section of core after plunger damage

[0050] serial number <![CDATA[K 1( A 11) ]]> <![CDATA[K 1( A 12) ]]> <![CDATA[K 1( A 13) ]]> Permeability (mD) 0.242 123.539 1031.576 serial number <![CDATA[K 1( A 21) ]]> <![CDATA[K 1( A 22) ]]> <![CDATA[K 1( A 33) ]]> Permeability (mD) 0.697 107.651 1210.197 serial number <![CDATA[K 1( A 31) ]]> <![CDATA[K 1( A 32) ]]> <![CDATA[K 1( A 33) ]]> Permeability (mD) 0.411 170.857 1091.148

[0051] Step 8: Convert the K 0( A 11) , K 0( A 12) , K 0( A 13) , K 0( A 21) , K 0( A 22) , K 0( A 23) , K 0( A 31) , K 0( A 32) , K 0( A 33) , K 0( A 1) , K 0( A 2) , K 0( A 3) , K 1( A 1) , K 1( A 11) , K 1( A 12) , K 1( A 13) , K 1( A2) , K 1( A 3) , K 1( A 21) , K 1( A 22) 、K1 ( A 23) , K 1( A 31) , K 1( A 32) , K 1( A 33) Substituting the data into the following equation, we can obtain the degree of working fluid damage of each multi-scale pore core plug and the degree of working fluid damage of each section of the core plug in each multi-scale pore core plug. The specific results are shown in Table 6.

[0052]

[0053]

[0054] Where: R A1 is the overall working fluid damage degree of multi-scale pore core plug A1, dimensionless quantity; R A2 R is the overall working fluid damage degree of the multi-scale pore core plug A2, dimensionless quantity; A3 R is the overall working fluid damage degree of the multi-scale pore core plug A3, dimensionless quantity; A11 is the damage degree of the working fluid in the matrix of the multi-scale pore core plug A1, dimensionless quantity; R A12 is the degree of damage of the working fluid in the natural fractures of the multi-scale pore core plug A1, dimensionless quantity; R A13 R is the damage degree of the induced fracture working fluid in the multi-scale pore core plug A1 with a wider fracture width, a dimensionless quantity; A21 R is the damage degree of working fluid in the core plug A2 of multi-scale pores and fractures, dimensionless quantity; A22 is the degree of damage of the working fluid in the natural fractures of the multi-scale pore core plug A2, dimensionless quantity; R A23 R is the damage degree of the induced fracture working fluid in the multi-scale pore core plug A2 with a wider fracture width, a dimensionless quantity; A31 R is the damage degree of working fluid in the core plug A3 of multi-scale pores and fractures, dimensionless quantity; A32 is the degree of damage of the working fluid in the natural fractures of the multi-scale pore core plug A3, dimensionless quantity; R A33 It is the damage degree of the induced fracture working fluid in the multi-scale pore core plug A3 with a wider fracture width, a dimensionless quantity.

[0055] Table 6 Damage degree of core plungers in each section and core plungers in series

[0056] serial number <![CDATA[R A11 ]]> <![CDATA[R A12 ]]> <![CDATA[R A13 ]]> <![CDATA[R A1 ]]> Damage degree (%) 76.05 57.73 4.67 82.16 serial number <![CDATA[R A21 ]]> <![CDATA[R A22 ]]> <![CDATA[R A23 ]]> <![CDATA[R A2 ]]> Damage degree (%) 66.29 60.42 9.04 85.05 serial number <![CDATA[R A31 ]]> <![CDATA[R A32 ]]> <![CDATA[R A33 ]]> <![CDATA[R A3 ]]> Damage degree (%) 89.02 54.02 10.39 92.46

[0057] Step 9: Replace R in step (8) A11 , R A12 , R A13 , R A21 , R A22 , R A23 , R A31 , R A32 , R A33 , R A1 , R A2 , R A3 Substitute the following matrix to obtain the damage weights of the base block and cracks of different scales;

[0058]

[0059] Where: T1 is the damage weight of the base block of the multi-scale pore-fracture core plug, which is a dimensionless quantity; T2 is the damage weight of the natural fracture of the multi-scale pore-fracture core plug, which is a dimensionless quantity; T3 is the damage weight of the induced fracture with a wider width of the multi-scale pore-fracture core plug, which is a dimensionless quantity; the normalized calculation results are shown in Table 7.

[0060] Table 7 Damage weights of foundation blocks and cracks of different scales

[0061] serial number <![CDATA[T1]]> <![CDATA[T2]]> <![CDATA[T3]]> Damage weight (%) 18.90 29.90 51.20

[0062] It can be seen from Table 7 that T3 is the largest in the reservoir of this embodiment, that is, the drilling fluid SR2PE used on site in this block has the largest weight on the damage to the induced fractures. Therefore, it is necessary to specifically add reservoir protection materials that can temporarily plug the induced fractures, such as calcite particles with a particle size of 50 to 100 μm, to effectively temporarily plug the induced fractures to prevent the working fluid from damaging the natural fractures and matrix, and comprehensively protect the multi-scale fracture reservoir.

[0063] The above specific implementation scheme has been combined with the accompanying drawings to describe the method of the present invention in detail, but the present invention is not limited to the above specific implementation scheme. The above specific implementation scheme is merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can flexibly change the experimental conditions, analysis methods and objects as long as they do not exceed the scope of the main purpose of the present invention, and all of these belong to the protection scope of the present invention.

Claims

1. A multi-scale pore-fracture space damage weight evaluation method for fractured oil and gas reservoirs, characterized in that: The following steps are involved: S1. Determine the number of core plugs M to be drilled according to the number of simulated reservoir fracture scales N, and drill core plugs from reservoir rock blocks where no macro fractures are found and dry them for standby use, where M≥N+1; S2. For each core plunger, the core plunger is divided into N+1 sections, and fractures are respectively formed in the N sections of the core plungers, and each section of the core plunger corresponds to a fracture of a certain scale; the core plungers of each section are connected in series in the order of gradually changing fracture apertures to form a multi-scale pore and fracture core plunger; S3. Determine the permeability K0 (A) of each section of the multi-scale pore core plug before damage. ij ), K0(A ij ) represents the permeability of the jth core plug in the i-th multi-scale pore core plug before damage; S4. The permeability K0 (A) of each multi-scale pore core before plug damage was determined by forward displacement. i ), K0(A i ) represents the permeability of the i-th multi-scale pore core before the plug damage; S5. Reversely circulate the working fluid to be evaluated through each multi-scale pore core plunger to simulate the multi-scale fracture damage process; S6, forward displacement of each multi-scale pore core plug of S5 with a constant backflow pressure difference until the flow rate is stable; S7. The permeability K1 (A) of each multi-scale pore core after plug damage was measured by forward displacement. i ); Determine the permeability K1 (A) of each section of the core plug after damage in each multi-scale pore core plug ij ); K1(A i ) represents the permeability of the i-th multi-scale pore core after plug damage, K1(A ij ) represents the permeability of the jth section of the core plug after damage in the i-th multi-scale pore-fracture core plug; S8. Calculate the degree of damage of the working fluid of each multi-scale pore core plug and the degree of damage of the working fluid of each section of the core plug in each multi-scale pore core plug: Where: is the degree of damage of the working fluid in the i-th multi-scale pore core plunger, dimensionless; is the degree of damage of the working fluid in the jth section of the core plug in the i-th multi-scale pore core plug, a dimensionless quantity; S9, calculate the damage weights of the foundation block and cracks of different scales; Where: T1 is the damage weight of the base block of the multi-scale pore core plug, which is dimensionless; T2 is the damage weight of the first scale crack in the multi-scale pore core plug, which is dimensionless; T N+1 It is the damage degree of the Nth scale crack in the multi-scale pore core plug, a dimensionless quantity.

2. The multi-scale pore-fracture space damage weight evaluation method for fractured oil and gas reservoirs according to claim 1 is characterized in that: In step S2, the core plunger is evenly divided into N+1 sections of equal size.

3. The multi-scale pore-fracture space damage weight evaluation method for fractured oil and gas reservoirs according to claim 1 is characterized in that The method of drilling the core plunger in step S1 is: when evaluating the damage of the working fluid in a vertical well, the core plunger is selected to be drilled parallel to the bedding plane; when evaluating the damage of the working fluid in a horizontal well, the core plunger is selected to be drilled perpendicular to the bedding plane.

4. The multi-scale pore-fracture space damage weight evaluation method for fractured oil and gas reservoirs according to claim 1, characterized in that: The multi-scale pore-fracture core plug consists of a base block section, a natural fracture section, and an induced fracture section.

Images