A method for system decomposition of skin factor of fracture type buried hill reservoir

Abstract

The present application relates to a kind of fracture type buried hill reservoir skin coefficient system decomposition method, comprising: step A.Combined with the calculation method of various types of dynamic and static skin coefficient of fracture type buried hill reservoir characteristics constitutes total skin;Step B.Based on the test data of test well, total skin coefficient of test well is obtained using pressure recovery well test interpretation method;Step C.According to the well condition of test well, the main dynamic and static skin coefficient constituting total skin coefficient of test well is determined;Step D.The method of step A is used to calculate the skin coefficient type determined in step C, to realize the skin decomposition of test well, and to clarify the composition of various skin coefficients of test well.The present application can accurately obtain the size of various skin coefficients of test well in fracture type buried hill reservoir, and provide guidance for further stimulation operation.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field exploration and development technology, specifically a method for systematically decomposing the skin coefficient of fractured buried hill reservoirs. Background Technology

[0002] The skin coefficient is a crucial parameter for evaluating the degree of damage to oil and gas reservoirs and plays a vital role in assessing reservoir completeness. The skin coefficient obtained from formation testing is the sum of the true skin coefficient reflecting the reservoir damage degree and various pseudo-skin coefficients caused by different factors during drilling and completion. Only the true damage skin coefficient can be eliminated through interventions. If the total skin coefficient is used as the evaluation basis in the reservoir damage degree assessment process, it will inevitably lead to a deviation in the assessment of the true reservoir damage degree, resulting in weak targeting of production enhancement measures and thus affecting their effectiveness. Therefore, it is necessary to systematically decompose the skin coefficient, clarify its composition, and thereby identify the main controlling factors of reservoir damage through skin coefficient analysis, determine the degree of reservoir damage, and provide a reliable basis for predicting and implementing reservoir stimulation effects.

[0003] While numerous studies exist on skin decomposition, they fail to fully address the needs of skin decomposition in fractured buried hill reservoirs. Current skin coefficient decomposition methods often lack a comprehensive range of skin coefficients and rarely consider the impact of fractured reservoirs on skin decomposition. When calculating stress-sensitive skin coefficients (pressure-sensitive skin coefficients), most formulas focus on the decrease in permeability of the sandstone reservoir matrix. However, the primary flow pathway in fractured buried hill reservoirs is fractures, where matrix permeability is extremely low. Furthermore, fractures can improve formation flow capacity, generating a negative skin effect, which is rarely mentioned in fracture skin coefficients.

[0004] Currently, the calculation methods for skin decomposition factors, including partially opened skin coefficient, well deviation skin coefficient, non-Darcy flow skin coefficient, phase change skin coefficient, perforation skin coefficient, impermeable straight boundary skin coefficient, isobaric straight boundary skin coefficient, anisotropic skin coefficient, variable production skin coefficient, stress-sensitive skin coefficient, and reservoir damage skin coefficient, are relatively mature. However, when performing skin decomposition on fractured buried hill reservoirs, the differences between the calculation of non-Darcy flow skin coefficient and stress-sensitive skin coefficient and conventional methods cannot be ignored.

[0005] Additional crack skin factor needs to be considered.

[0006] Therefore, a comprehensive approach should be taken into account and integrated with various reservoir damage causes to calculate the skin coefficient, and combined with the characteristics of fractured buried hill reservoirs, to complete a systematic decomposition method for the skin coefficient of fractured buried hill reservoirs. Summary of the Invention

[0007] This invention provides a systematic decomposition method for the skin coefficient of fractured buried hill reservoirs, which can accurately obtain the skin coefficient caused by various damage factors in fractured buried hill reservoirs.

[0008] This invention discloses a method for systematically decomposing the skin coefficient of fractured buried hill reservoirs, comprising the following steps:

[0009] A. A method for calculating the skin coefficient by comprehensively considering various damage factors in conjunction with the characteristics of fractured buried hill reservoirs;

[0010] B. Obtain test data from the test wells;

[0011] C. Determine the types of skin coefficients to be decomposed in the test well based on the data from step B;

[0012] D. Calculate the skin coefficient types determined in step C using the method in step A, and complete the skin decomposition of the test well.

[0013] The skin coefficient described in this invention characterizes the nature and severity of the skin effect in a well. The skin effect refers to the phenomenon where changes in the permeability of the formation near the well, caused by factors such as mud intrusion during drilling, imperfect perforation opening, well workover, acidizing and fracturing measures, water sensitivity, and rate sensitivity, result in an additional pressure drop in this area when crude oil flows from the oil layer into the wellbore, forming a very thin, annular "skin zone" around the wellbore. The well testing described in this invention refers to measuring the physical parameters of the formation around the wellbore using various downhole instruments, such as acoustic waves, resistivity, neutron density, and natural gamma ray intensity. Interpretation using well logging technology enables lithological identification, reservoir segmentation, determination of oil, gas, and water layers, and evaluation of reservoir parameters. The test data includes completion, logging, and well testing data.

[0014] This invention systematically decomposes the skin coefficient of fractured buried hill reservoirs, comprehensively considering various reservoir damage factors.

[0015] By analyzing the resulting skin coefficient and combining it with the characteristics of fractured buried hill reservoirs, we can obtain accurate skin coefficients for each component, identify the main controlling factors of reservoir damage, determine the degree of reservoir damage, and provide a reliable basis for predicting reservoir stimulation effects and practical applications.

[0016] Existing technologies for skin decomposition of fractured reservoirs are limited and incomplete. This invention, however, combines the stress-sensitive skin coefficient and fracture skin coefficient studied based on the characteristics of fractured reservoirs, enabling more accurate skin decomposition of fractured buried hill reservoirs.

[0017] Furthermore, the skin coefficients caused by the various damage factors mentioned in step A include non-Darcy permeability skin coefficient, stress-sensitive skin coefficient, fracture skin coefficient, well deviation skin coefficient, phase change skin coefficient, anisotropic skin coefficient, impermeable straight boundary skin coefficient, isobaric straight boundary skin coefficient, variable production skin coefficient, and reservoir damage skin coefficient.

[0018] The non-Darcy skin coefficient is the skin coefficient resulting from turbulence around the wellbore as fluid accumulates near the wellbore when the well is producing at a high rate. Calculation formula: In the formula, D is the non-Darcy flow coefficient, which can be expressed as: Since the bedrock in fractured buried hill reservoirs has virtually no flow capacity, and fractures serve as the primary flow channels, the above model needs to be modified based on fracture development characteristics. The modified model is as follows: In the formula, For crack permeability, ; For crack porosity; Where is the crack width, in meters; Let the crack length be in meters (m). f is the fracture density, fracturing / m; h is the reservoir thickness, m; The relative density of the gas; For gas viscosity, ; For bottom hole flowing pressure, .

[0019] The stress-sensitive skin coefficient is a dimensionless quantity representing the additional pressure drop caused by the decrease in formation permeability due to a reduction in formation pressure. Based on the distribution of the formation pressure field at any given moment during the production process of a single well, the stress-sensitive skin coefficient can be calculated. : In the formula, The original permeability of the reservoir is expressed in mD. The reservoir's current permeability is given by r (mD); the pressure relief radius is given by r (m). Let be the radius of the wellbore, in meters (m).

[0020] The fracture skin coefficient refers to the negative skin effect resulting from fractures improving formation flowability. Using the equivalent resistance method, the additional pressure drop in the wellbore caused by the presence of fractures as fluid flow can be calculated, and the fracture skin coefficient can be obtained, which can be expressed as:

[0021] ;in: In the formula: The crack surface coefficient; To test the production of the well, ; The dynamic viscosity of the fluid. ; The volume coefficient of the fluid; Where is the permeability of the test well, mD; h is the thickness of the test layer, m; The additional pressure drop around the wellbore caused by the fracture, in MPa; The flow pressure difference generated by pure fracture flow. ; The flow pressure difference generated by the homogeneous reservoir ; denoted as , where is the fracture length (m); and A is the area of ​​the fractured rock sample. ; b is the crack porosity; b is the crack width, in cm. Let be the radius of the homogeneous layer, in meters. Let the boundary radius be m; denoted as matrix permeability, mD.

[0022] The well inclination skin coefficient is the skin coefficient caused by the negative skin effect resulting from the increased contact area between the well and the formation when the well has an inclination angle. Cinco et al. (1975) provided a method for calculating the well inclination skin coefficient. The computational model is as follows: In the formula, — Well inclination angle, h is the reservoir thickness, in meters. The well diameter is in meters (m). Let md be the horizontal permeability. Let md be the vertical permeability.

[0023] The phase change skin coefficient The skin coefficient is the result of changes in fluid flow capacity caused by changes in relative permeability. For oil wells, when the well is producing under high pressure differential, the pressure around the wellbore can drop below the hydrocarbon bubble point pressure, resulting in gas blockage. For condensate gas wells, when producing below the dew point pressure, condensate oil precipitates around the wellbore, obstructing gas flow. Both phenomena are due to the influence of relative permeability.

[0024] The phase change skin factor for oil wells can be expressed as: ;

[0025] For condensate gas wells, the phase change skin coefficient can be expressed as: ;

[0026] In the formula, Let be the outer radius of the two-phase region, in meters. The oil phase saturation in the two-phase region; and For penetration rate, md; For single-phase oil phase saturation, The well diameter is in meters (m). This refers to the gas phase saturation in the two-phase region. This represents the gas phase saturation in the single-phase region.

[0027] The anisotropic skin coefficient refers to the skin coefficient that reflects the impact of permeability anisotropy on oil production during reservoir formation, influenced by factors such as sedimentation, diagenesis, and tectonics. It can be written as: ; For anisotropy coefficients, the coefficients are: for isotropic... ,have For anisotropy ,have That is, the epidermal coefficient produced by anisotropy is negative.

[0028] The skin factor of the impermeable straight boundary is the skin factor that affects the surface of the test well due to the boundary effect when an impermeable boundary exists in the formation. It can be written as: ;

[0029] In the formula, The boundary distance is m; Formation porosity; The viscosity of the fluid. ; The combined compressibility coefficient of the formation and the fluids within it. ; The permeability of the strata, .

[0030] The skin factor of the constant-pressure straight boundary is the skin factor that affects the surface of the test well due to the boundary effect when a constant-pressure boundary exists in the formation. It can be written as: In the formula, The boundary distance is m; It represents the pressure conductivity coefficient.

[0031] The variable production rate coefficient is the skin coefficient caused by the fluctuation of flow patterns near the wellbore due to changes in oil well production, resulting in additional resistance near the wellbore. Variable production rate skin coefficient Calculation formula: ;

[0032] In the formula, For production, ; The production time is in hours (h).

[0033] For a fixed output ;when hour, That is, when output increases from small to large, the variable output produces a negative skin coefficient; when hour, That is, when the output changes from large to small, the change in output produces a positive skin coefficient.

[0034] The reservoir damage skin coefficient reflects the true degree of reservoir damage and is only a part of the total skin coefficient. From the total skin coefficient The remainder after deducting various other skin coefficients.

[0035] ;

[0036] Furthermore, the test well mentioned in step B is an oil well or a gas well, and the test data includes well completion, logging, and well testing data.

[0037] Furthermore, in step C, the skin coefficient types to be decomposed for the test well are determined based on the data from step B. This means that the test well does not need to calculate all types of skin coefficients, and the skin coefficients to be calculated for the test well are determined based on the data.

[0038] Furthermore, step D, which involves using the method in step A to calculate the skin coefficient types determined in step C and completing the skin decomposition of the test well, refers to substituting the test well parameters into the corresponding skin coefficient calculation method in step A.

[0039] The beneficial effects of this invention include:

[0040] 1. Be able to identify reservoir damage factors and correctly understand reservoir damage mechanisms.

[0041] 2. Obtain the actual damaged surface of the reservoir to determine the extent of reservoir damage.

[0042] 3. Obtain the skin coefficient of each reservoir damage factor in the accurate test well, identify the main controlling factors of reservoir damage, and provide a reliable basis for reservoir stimulation effect prediction and practice. Attached Figure Description

[0043] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0044] Figure 1 This is a flowchart of a method for systematically decomposing the skin coefficient of fractured buried hill reservoirs according to the present invention;

[0045] Figure 2 This is a logic block diagram of a systematic decomposition method for the skin coefficient of fractured buried hill reservoirs according to the present invention. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The components of the embodiments of this application described and shown in the figures here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0047] like Figure 1 and Figure 2 As shown, the present invention provides a method for systematic decomposition of the skin coefficient of fractured buried hill reservoirs, comprising the following steps:

[0048] A. A method for calculating the skin coefficient by comprehensively considering various damage factors in conjunction with the characteristics of fractured buried hill reservoirs;

[0049] B. Obtain test data from the test wells;

[0050] C. Determine the types of skin coefficients that need to be decomposed in the test well based on the data from step B;

[0051] D. Calculate the skin coefficient types determined in step C using the method in step A, and complete the skin decomposition of the test well;

[0052] This invention systematically decomposes the skin coefficient of fractured buried hill reservoirs, comprehensively considers the skin coefficient caused by various reservoir damage factors, and combines the characteristics of fractured buried hill reservoirs to obtain accurate skin coefficients for each component, identify the main controlling factors of reservoir damage, determine the degree of reservoir damage, and provide a reliable basis for predicting and implementing reservoir stimulation effects.

[0053] Existing technologies for skin decomposition of fractured reservoirs are limited and incomplete. This invention, however, combines the stress-sensitive skin coefficient and fracture skin coefficient studied based on the characteristics of fractured reservoirs, enabling more accurate skin decomposition of fractured buried hill reservoirs.

[0054] In step A, the skin coefficient characterizes the nature and severity of the skin effect in a well. The skin effect refers to the phenomenon where changes in the permeability of the formation near the well, caused by factors such as mud intrusion during drilling, imperfect perforation opening, well workover, acidizing pressure measures, water sensitivity, and rate sensitivity, result in an additional pressure drop in this area when crude oil flows from the oil layer into the wellbore, forming a very thin, annular "skin zone" around the wellbore. The skin coefficients caused by the various damaging factors include partial well deviation skin coefficient, non-Darcy flow skin coefficient, phase change skin coefficient, impermeable straight boundary skin coefficient, constant pressure straight boundary skin coefficient, anisotropic skin coefficient, variable production skin coefficient, stress-sensitive skin coefficient, fracture skin coefficient, and reservoir damage skin coefficient.

[0055] The non-Darcy skin coefficient is the skin coefficient generated by turbulence around the wellbore when the fluid accumulates near the wellbore during high-yield production. Calculation formula:

[0056] (1);

[0057] In the formula, D is the non-Darcy flow coefficient, which can be expressed as:

[0058] (2);

[0059] Since the bedrock in fractured buried hill reservoirs has virtually no flow capacity, and fractures serve as the primary flow channels, the above model needs to be modified based on fracture development characteristics. The modified model is as follows: (3);

[0060] In the formula, For crack permeability, ; For crack porosity; Where is the crack width, in meters; Let the crack length be in meters (m). f is the fracture density, fracturing / m; h is the reservoir thickness, m; The relative density of the gas; For gas viscosity, ; For bottom hole flowing pressure, .

[0061] The stress-sensitive skin coefficient is a dimensionless quantity representing the additional pressure drop caused by the decrease in formation permeability due to a reduction in formation pressure. Based on the distribution of the formation pressure field at any given moment during a single well's production process, the stress-sensitive skin coefficient can be calculated. : (4);

[0062] In the formula, The original permeability of the reservoir is expressed in mD. The reservoir's current permeability is given by r (mD); the pressure relief radius is given by r (m). Let be the radius of the wellbore, in meters (m).

[0063] The fracture skin coefficient refers to the negative skin effect resulting from fractures improving the formation's flow capacity. (5); where: ;

[0064] In the formula: The crack surface coefficient; To test the production of the well, ; The dynamic viscosity of the fluid. ; The volume coefficient of the fluid; Where is the permeability of the test well, mD; h is the thickness of the test layer, m; The additional pressure drop around the wellbore caused by the fracture, in MPa; The flow pressure difference generated by pure fracture flow. ; The flow pressure difference generated by the homogeneous reservoir ; denoted as , where is the fracture length (m); and A is the area of ​​the fractured rock sample. ; b is the crack porosity; b is the crack width, in cm. Let be the radius of the homogeneous layer, in meters. Let the boundary radius be m; denoted as matrix permeability, mD.

[0065] The well inclination skin coefficient is the skin coefficient caused by the negative skin effect resulting from the increased contact area between the well and the formation when the well has an inclination angle. Cinco et al. (1975) provided a method for calculating the well inclination skin coefficient. The computational model is as follows: (6);

[0066] In the formula, — Well inclination angle, h is the reservoir thickness, in meters. The well diameter is in meters (m). Let md be the horizontal permeability. Let md be the vertical permeability.

[0067] The phase change skin coefficient The skin coefficient is the result of changes in fluid flow capacity caused by changes in relative permeability. For oil wells, when the well is producing under high pressure differential, the pressure around the wellbore can drop below the hydrocarbon bubble point pressure, resulting in gas blockage. For condensate gas wells, when producing below the dew point pressure, condensate oil precipitates around the wellbore, obstructing gas flow. Both phenomena are due to the influence of relative permeability.

[0068] The phase change skin factor for oil wells can be expressed as: (7); For condensate gas wells, the phase change skin coefficient can be expressed as: (8);

[0069] In the formula, Let be the outer radius of the two-phase region, in meters. The oil phase saturation in the two-phase region; and For penetration rate, md; For single-phase oil phase saturation, The well diameter is in meters (m). This refers to the gas phase saturation in the two-phase region. This represents the gas phase saturation in the single-phase region.

[0070] The anisotropic skin coefficient refers to the skin coefficient that reflects the impact of permeability anisotropy on oil production during reservoir formation, influenced by factors such as sedimentation, diagenesis, and tectonics. It can be written as: (9);

[0071] For anisotropy coefficients, the coefficients are: for isotropic... ,have For anisotropy ,have That is, the epidermal coefficient produced by anisotropy is negative.

[0072] The skin factor of the impermeable straight boundary is the skin factor that affects the surface of the test well due to the boundary effect when an impermeable boundary exists in the formation. It can be written as: (10);

[0073] In the formula, The boundary distance is m; Formation porosity; The viscosity of the fluid. ; The combined compressibility coefficient of the formation and the fluids within it. ; The permeability of the strata, .

[0074] The skin factor of the constant-pressure straight boundary is the skin factor that affects the surface of the test well due to the boundary effect when a constant-pressure boundary exists in the formation. It can be written as: (11);

[0075] In the formula, L is the boundary distance (m); χ is the pressure conductivity coefficient. The variable production coefficient is the skin coefficient caused by the fluctuation of flow patterns near the wellbore due to changes in oil well production, resulting in additional resistance near the wellbore. Variable production skin coefficient Calculation formula: (12);

[0076] In the formula, For production, ; The production time is in hours (h).

[0077] For a fixed output ;when hour, That is, when output increases from small to large, the variable output produces a negative skin coefficient; when hour, That is, when the output changes from large to small, the change in output produces a positive skin coefficient.

[0078] The reservoir damage skin coefficient reflects the true degree of reservoir damage and is only a part of the total skin coefficient. From the total skin coefficient The remainder after deducting various other skin coefficients.

[0079] ;

[0080] When the test well is an oil well, the total skin factor S is calculated as follows: (14);

[0081] When the test well is a gas well, according to the pressure distribution equation for pseudo-steady flow in an infinite formation, the expression for the total skin coefficient S can be obtained as follows: (15);

[0082] Wherein the pseudo-pressure expression is: ;

[0083] In the formula, K is the permeability of the formation. h is the thickness of the stratum, in meters. The original formation pressure, ;

[0084] For bottom hole flowing pressure, q represents the oil well production. μ is the viscosity of the fluid, mPa·s; B is the volume coefficient of the fluid; t is the production time, h; The porosity of the reservoir; The combined compressibility coefficient of the formation and the fluids within it. ; Let be the radius of the wellbore, in meters (m). The temperature under standard conditions is specified as follows: ; The pressure under standard conditions is specified as ; For gas well production, ; is the gas layer temperature, K; Z is the gas deviation factor.

[0085] The test well mentioned in step B is an oil well or a gas well, and the test data includes completion, logging, and well testing data. The total skin factor can be obtained from the pressure recovery well test data.

[0086] Step C, which determines the types of skin factors to be decomposed for the test well based on the data from Step B, clarifies that the test well does not need to calculate all types of skin factors. The skin factors to be calculated for the test well are determined based on the data. For example, if the completion data shows that the test interval includes the entire reservoir interval, then there is no need to consider the partially opened skin factor; if no boundary is detected in the test data, then there is no need to calculate the boundary and shape skin factors.

[0087] Step D describes using the method in step A to calculate the skin coefficient types determined in step C, thus completing the skin decomposition of the test well. This refers to substituting the test well parameters into the corresponding skin coefficient calculation method in step A.

[0088] The following description, based on test data from a gas well, further illustrates the present invention:

[0089] The method for systematically decomposing the skin coefficient of fractured buried hill reservoirs according to the present invention comprises the following steps:

[0090] A. Consider decomposing the total skin factor into well deviation skin factor, non-Darcy seepage skin factor, phase change skin factor, impermeable straight boundary skin factor, isobaric straight boundary skin factor, anisotropic skin factor, variable production skin factor, stress-sensitive skin factor, fracture skin factor, and reservoir damage skin factor.

[0091] B. The buried hill gas well was completed using open-hole technology. The test layer ranged from 3509m to 3566m, encompassing the entire reservoir section. The main flow channels in this reservoir were fractures, with a fracture density of only 1 fracture / m. The pressure recovery curve showed no detected boundaries.

[0092] According to the well's testing procedure, the skin coefficient at quasi-stability under different testing regimes was calculated based on formula (15) and the superposition principle. Table 1 shows the calculation results of the skin coefficient under different testing regimes. The results are shown in the table below. It can be seen that the production is relatively stable. In addition, the skin coefficient interpreted based on the pressure recovery test is 28.82, and the results are not significantly different.

[0093] Table 1. Calculation results of epidermal coefficient under different testing regimes.

[0094] C. Based on the test data, it can be determined that the skin coefficients for variable production rate, boundary, and shape can be disregarded. Therefore, the total skin coefficient of this well mainly consists of the well deviation skin coefficient, stress-sensitive skin coefficient, non-Darcy flow skin coefficient, fracture skin coefficient, and reservoir damage skin coefficient.

[0095] D. The following section will proceed with the decomposition of the epidermis.

[0096] (1) Well inclination skin coefficient

[0097] The average well inclination angle of the test section of the well is calculated to be 1.35° based on the logging data. According to formula (6), the well inclination skin coefficient is -0.001, which can be ignored.

[0098] (2) Crack skin coefficient

[0099] The primary target layer of this well is a bedrock buried hill reservoir, which can be divided into a weathering and dissolution fracture zone and an internal fracture zone from top to bottom. Based on conventional and imaging logging data, numerous fractures were identified, indicating a high-density fracture network structure with localized dissolution cavities.

[0100] Based on the reservoir section determined by the well logging interpretation data and the calculated fracture parameters, the permeability of the fracture system and the homogeneous system were calculated to obtain the production pressure difference during the fixed production process of each model. The pressure drop difference between the two models was substituted into the skin calculation formula (5) to obtain the fracture skin coefficient. The results are shown in Table 2.

[0101]

[0102] Table 2 Calculation results of fracture skin in test section of test well.

[0103] (3) Non-Darcy flow skin coefficient

[0104] Based on imaging logging data, relevant parameters such as fracture width and density can be interpreted, and the results are shown in Table 3. Combining the production output under different testing regimes during stable production, the non-Darcy flow skin coefficient under different operating regimes can be calculated using equation (1).

[0105]

[0106] Table 3. Calculation results of non-Darcy flow skin coefficient under different testing regimes in test wells.

[0107] (4) Stress-sensitive skin coefficient

[0108] Pressure sensitivity coefficient While these factors can be obtained experimentally, a calculation method without experiments is presented below. When production is constant, the total skin coefficient, well inclination skin coefficient, fracture skin coefficient, non-Darcy flow skin coefficient, and reservoir damage skin coefficient are all constant values, while the stress-sensitive skin coefficient is a value that varies over time. Based on the characteristics of these skin coefficients, the well inclination skin coefficient, fracture skin coefficient, non-Darcy flow skin coefficient, and reservoir damage skin coefficient can be considered as a whole, with their additional pressure reduced to a constant value. Under a given production time under a specific testing operating regime, the stress-sensitive coefficient can be calculated based on a single-well simulation model, and its magnitude can be obtained through interpolation.

[0109] With a 9.53mm nozzle, the total skin coefficient was 28.88 after 14.4 hours of production, and the production pressure differential was 24.22. Based on different stress sensitivity coefficients, the production pressure difference at a given time can be obtained using the stress sensitivity model without considering other skin coefficients. The pressure sensitivity coefficient can be calculated as 0.146 by plotting the intersection curve based on the actual production pressure difference and skin coefficient of the well.

[0110] Based on the calculated stress sensitivity coefficient, the stress sensitivity skin coefficient was calculated using equation (4). The reservoir damage skin coefficient (contamination skin coefficient) is the total skin coefficient minus the well deviation, fracture, non-Darcy flow, and stress sensitivity skin coefficient. The total skin coefficient under each production regime during the initial operation was decomposed, and the results are shown in Table 4. Due to the presence of water production during the initial operation using a 5.56mm nozzle, which may be due to contaminated liquid backflow, the contamination skin coefficient is relatively large.

[0111]

[0112] Table 4. Decomposition Results of Skin Coefficient in Test Wells

[0113] The decomposition results show that the skin coefficients of the well are relatively large for stress-sensitive skin coefficient, non-Darcy flow skin coefficient, and contaminated skin coefficient.

[0114] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0115] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A systematic decomposition method for the skin coefficient of fractured buried hill reservoirs, characterized by the following steps: A. A method for calculating the skin coefficient by comprehensively considering various damage factors in conjunction with the characteristics of fractured buried hill reservoirs; The skin coefficients caused by various factors mentioned in step A include non-Darcy permeability skin coefficient, stress-sensitive skin coefficient, fracture skin coefficient, well deviation skin coefficient, phase change skin coefficient, anisotropic skin coefficient, impermeable straight boundary skin coefficient, isobaric straight boundary skin coefficient, variable production skin coefficient, and reservoir damage skin coefficient. The non-Darcy flow skin factor is a skin factor generated by the turbulence phenomenon around the wellbore when the gas well produces at a high rate, and the non-Darcy flow skin factor The calculation formula is: where D is the non-Darcy flow coefficient. Because the base rock has no flow capacity basically in the fractured buried hill reservoir, the fracture is the main flow channel, so the non-Darcy flow coefficient is calculated according to the fracture development characteristics, and the calculation model is as follows: ; wherein, is the fracture permeability, ; is the fracture porosity; is the fracture width, m; is the fracture length, m; is the fracture density, strip / m; h is the reservoir thickness, m; is the gas relative density; is the gas viscosity, ; is the bottom hole flowing pressure, ; The stress-sensitive skin factor is a dimensionless quantity of additional pressure drop caused by the decrease of formation permeability due to the decrease of formation pressure, and the stress-sensitive skin factor can be obtained according to the distribution of stress field and seepage field in the process of single well production: ; wherein, is the original permeability of the reservoir, ; k is the current permeability of the reservoir, ; r is the pressure relief radius, m; is the wellbore radius, m; B. Based on the test data of the test well, the total skin factor of the test well is obtained by using the pressure recovery data well test interpretation method; The reservoir damage skin coefficient reflects the true degree of damage to the reservoir and is a part of the total skin coefficient. The reservoir damage skin coefficient is the part remaining after deducting other skin coefficients from the total skin coefficient. C. Determine the types of skin coefficients to be decomposed in the test well based on the data from step B; D. Calculate the skin coefficient types determined in step C using the method in step A, and complete the skin decomposition of the test well.

2. The method for systematically decomposing the skin coefficient of fractured buried hill reservoirs as described in claim 1, characterized in that: the fracture skin coefficient is the negative skin effect generated by fractures improving the flow capacity of the formation. Based on the equivalent resistance method, the additional pressure drop caused by the presence of fractures on the wellbore as a fluid flow can be calculated, and thus the fracture skin coefficient can be obtained, expressed as: ; In the formula: denoted as the fracture skin factor; q represents the production rate of the test well. ; The dynamic viscosity of the fluid. is the volume coefficient of the fluid; k is the permeability of the test well. h is the thickness of the test layer, in meters. The additional pressure drop caused by the fracture around the wellbore. ; The flow pressure difference generated by pure fracture flow. ; The flow pressure difference generated by the homogeneous reservoir L is the fracture length, in meters; A is the area of ​​the fractured rock sample. ; b is the crack porosity; b is the crack width, in cm. Let be the radius of the homogeneous layer, in meters. Let the boundary radius be m; For matrix permeability, .

3. The method for systematic decomposition of skin coefficient of fractured buried hill reservoir as described in claim 1, characterized in that: the test well in step B is an oil well or a gas well, and the test data is well test data.

4. The method for systematically decomposing the skin coefficient of fractured buried hill reservoirs as described in claim 1, characterized in that: in step C, the skin coefficient types to be decomposed for the test well based on the data in step B are determined so that the test well does not need to calculate all the skin coefficients, and the skin coefficients to be calculated for the test well are determined based on the data.

5. The method for systematic decomposition of skin coefficients in fractured buried hill reservoirs as described in claim 1, characterized in that: step D, which uses the method of step A to calculate the types of skin coefficients determined in step C to complete the skin decomposition of the test well, refers to substituting the test well parameters into the corresponding skin coefficient calculation method in step A.

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