Method for evaluating reservoir types of fractured-vuggy carbonate rocks after acid fracturing

Abstract

The invention discloses a reservoir type evaluation method after fracture-cavity type carbonate rock acid fracturing, and belongs to the technical field of carbonate rock reservoir type evaluation, and the method comprises the steps: determining the well bottom reservoir type and the development degree and effectiveness of an oil-gas well drilling fracture-cavity body, and obtaining the well bottom pressure curve form of oil-gas well acid fracturing construction; judging whether acid fracturing is communicated with the fracture-cavity body or not according to the oil-gas well acid fracturing construction bottom hole pressure curve form, and determining the volume of the communicated fracture-cavity body and the distance between the communicated fracture-cavity body and the oil-gas well; and drawing a pilot production curve, and determining the type of a reservoir body for acid fracturing communication and the number of fracture-cavity bodies participating in liquid supply. By combining seismic reflection data before acid fracturing, drilling leakage data, an acid fracturing bottom pressure curve, an acid etching fracture conductivity curve, a pilot production curve after acid fracturing and the like, whether a fracture cavity exists or not, the volume of a karst cave, the position of the fracture cavity and the like are comprehensively determined, the field operability is high, and the interpretation result is reliable.

Description

Technical Field

[0001] The invention belongs to the technical field of carbonate reservoir type evaluation, and in particular relates to a method for evaluating the reservoir type of fracture-cavity carbonate rocks after acid fracturing. Background Art

[0002] The geological structural conditions of carbonate oil and gas reservoirs are extremely complex, the oil and gas reservoirs are scattered, and the macroscopic distribution has strong uncertainty and unevenness. For example, as a major type of carbonate, fracture-cavity carbonate has a large number of caves and natural fractures in the reservoir, and is highly heterogeneous. Exploration and development practices have shown that caves are storage spaces for oil and gas resources, while natural fractures are the main seepage channels for oil and gas. Therefore, clarifying the fracture-cavity types and their parameters in the reservoir has important guiding significance for the efficient development of fracture-cavity carbonate reservoirs. Related invention patent 1-"Method and device for determining the type of carbonate reservoir" (patent application publication number: CN110792436A) determines the bottom hole pressure difference by obtaining the first pressure value of the reservoir to be tested before acid fracturing and the second bottom hole pressure value after acid fracturing, and then obtains the first acid fluid parameters injected into the reservoir and the second acid fluid parameters discharged, and determines the reservoir type in combination with the production situation after acid fracturing.

[0003] Related invention patent 2 - "A method for classifying carbonate reservoirs and a method for establishing a reservoir identification map" (patent application publication number: CN114444559A) classifies reservoirs by analyzing logging data, core analysis data, pore throat median radius data and oil test data, and then calculates reservoir structure parameters for the coring section of each reservoir type, normalizes the parameters and establishes an intersection map with porosity, thereby obtaining a reservoir type identification map.

[0004] Related invention patent 3 - "Evaluation method of fracture-cavity carbonate reservoir based on seismic-well logging calibration" (patent application publication number: CN105093333A) performs borehole collapse correction, multi-well standardization and consistency processing on the logging curve, loads the processed logging and seismic data for well-seismic calibration, extracts sub-waves suitable for the target layer, and performs post-stack deterministic inversion and post-stack geostatistical inversion. By statistically analyzing the relationship between the wave impedance of each well and the porosity of the reservoir evaluation parameter, a preliminary multi-well impedance and porosity map is obtained, and the relationship between the porosity and acoustic wave time difference and density of the well leakage and empty well sections of some wells is statistically analyzed to correct the multi-well impedance.

[0005] The above patents do not establish detailed evaluation methods for fracture-cavity carbonate reservoir types. In addition, they are basically based on geological or engineering parameters, and fail to combine geological and engineering parameters to evaluate reservoirs. Currently, there are few reports on fracture-cavity carbonate reservoir type evaluation and fracture-cavity parameter interpretation methods. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for evaluating the reservoir type of fracture-cavity carbonate rocks after acid fracturing, which is used to solve the problem of lack of fracture-cavity carbonate reservoir type evaluation and fracture-cavity parameter interpretation methods.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for evaluating reservoir types of fracture-cavity carbonate rocks after acid fracturing, comprising the following steps:

[0009] Determine the bottom hole reservoir type and the development degree and effectiveness of the fracture-cavity bodies encountered in the oil and gas wells, and obtain the bottom hole pressure curve shape of the oil and gas well acid fracturing operation;

[0010] According to the bottom hole pressure curve of the oil and gas well acid fracturing construction, determine whether the acid fracturing has connected the fracture and cave, and determine the volume of the connected fracture and cave and its distance from the oil and gas well;

[0011] Draw a test production curve and determine the type of reservoir body connected by acid fracturing and the number of fractures and caves involved in fluid supply.

[0012] Preferably, the type of bottom hole reservoir and the degree of development and effectiveness of fracture-cavity bodies encountered by the oil and gas well are determined in combination with seismic reflection type, logging interpretation, and drilling leakage.

[0013] Preferably, the method for determining the bottom hole reservoir type and the development degree and effectiveness of the fracture-cavity body encountered by the oil and gas well is:

[0014] Determine the development degree of formation fractures and caves based on the seismic reflection type of the formation encountered by the oil and gas well;

[0015] The effectiveness of drilling into the fracture-cavity body is determined based on the degree of leakage in the target layer.

[0016] Preferably, when determining the development degree, if the seismic reflection type is "beaded", the formation fracture-cavity body is developed, and if the seismic reflection type is weak reflection or chaotic reflection, the formation fracture-cavity body is underdeveloped.

[0017] Preferably, when determining the effectiveness of drilling into fracture-cavity bodies, if there is a continuous strong leakage when drilling into the target layer, it means that a large fracture-cavity body has been drilled; if there is a small amount of intermittent leakage and the leakage rate is low, it means that the scale of the fracture-cavity body drilled into the oil and gas well is limited; if no leakage occurs, it means that no fracture-cavity body has been drilled at the bottom of the well.

[0018] Preferably, the method of obtaining the shape of the bottom hole pressure curve of the acid fracturing construction of the oil and gas well is specifically to comprehensively consider the parameters such as the acid fracturing surface construction curve, the acid fracturing pipe string structure, the acid fracturing liquid friction resistance, etc., and calculate the bottom hole pressure curve of the acid fracturing construction.

[0019] Preferably, the specific method for judging whether the acid fracturing connects the fracture-cavity body and determining the volume of the connecting fracture-cavity body is:

[0020]

[0021] Where: V is the volume of the fracture cavity; N inj B is the surface volume of water injected after acid fracturing to connect the fractured cave; w B is the volume coefficient of injected water when the formation pressure rises to the current formation pressure; oi is the volume coefficient of crude oil under the original formation pressure; ΔP is the total pressure increase in the fracture cavity; C o is the compression coefficient of crude oil; C w The compressibility coefficient of bound water; C p is the effective compression coefficient of rock; S oi is the initial crude oil saturation; S wi is the bound water saturation.

[0022] Preferably, if the bottom hole pressure drops significantly during the construction process, it means that the acid fracturing fractures have connected the fracture-cavity body. With the further injection of the acid fracturing liquid, if the bottom hole pressure starts to rise, it means that the fracture-cavity body is small in size and the bottom hole pressure wave has affected the entire fracture-cavity body. The volume of the fracture-cavity body connected by acid fracturing is calculated according to formula (1). If the bottom hole pressure continues to drop after the fracture-cavity body is connected by acid fracturing and does not rise again, it means that the bottom hole pressure wave has not affected the entire fracture-cavity body. The lower limit of the volume of the fracture-cavity body connected by acid fracturing is calculated according to formula (1).

[0023] Preferably, the distance between the communicating fracture-cavity body and the oil and gas well is determined by: an inflection point appears on the curve when the conductivity decreases with increasing fracture length, and the position of the inflection point is the position of the communicating fracture-cavity body.

[0024] Preferably, the method for determining the type of reservoir body for acid fracturing communication and the number of fracture-cavity bodies involved in fluid supply according to the test production curve is:

[0025] The relationship between the cumulative production and cumulative pressure drop of the target oil and gas wells was plotted, and compared with the characteristic curves of cumulative liquid production and cumulative pressure drop of three types of reservoirs obtained by laboratory simulation, namely cave type, cave + fracture-pore type, and fracture-pore type, so as to determine the reservoir type of acid-fracture communication and the number of fracture-cavity bodies involved in fluid supply.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention discloses a method for evaluating the reservoir type of fracture-cavity carbonate rock after acid fracturing. By determining the bottom hole reservoir type and the development degree and effectiveness of the fracture-cavity body encountered by the oil and gas well and obtaining the shape of the bottom hole pressure curve of the oil and gas well acid fracturing construction, it is judged whether the fracture-cavity body is connected by acid fracturing, and the volume of the connected fracture-cavity body and its distance from the oil and gas well are determined; the test production curve after acid fracturing is determined, and the existence of fractures and caves, the volume of the caves, the location of the fractures and caves, etc. are comprehensively determined by combining the seismic reflection data and drilling leakage data before acid fracturing, the bottom hole pressure curve of acid fracturing and the conductivity curve of the acid-etched fractures, the test production curve after acid fracturing, etc., the field operability is high, and the various data before, during and after acid fracturing are fully combined. The data acquisition is not difficult, and the existence of fractures and caves, the volume of the caves, the location of the fractures and caves, etc. can be determined through comprehensive analysis. The field operability is high and the interpretation result is reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of the method of the present invention.

[0029] Figure 2 This is a typical bottom hole pressure curve of the fracture-cavity body during the acid fracturing process.

[0030] Figure 3 It is a seismic reflection map.

[0031] Figure 4 It is the conductivity curve of acid-etched cracks;

[0032] Figure 5 It is a curve chart showing the corresponding relationship between the test production characteristics and reservoir space types obtained in the laboratory.

[0033] Figure 6 It is the cumulative production-cumulative pressure drop curve obtained on site. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0035] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0036] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0037] The geological structural conditions of my country's carbonate oil and gas reservoirs are extremely complex, the oil and gas reservoirs are scattered, and the macroscopic distribution has strong uncertainty and unevenness. For example, as a major type of carbonate, fracture-cavity carbonate has a large number of caves and natural fractures developed in the reservoir, and has strong heterogeneity. Exploration and development practice shows that caves are the storage space of oil and gas resources, while natural fractures are the main seepage channels of oil and gas. Therefore, clarifying the fracture-cavity types and their parameters in the reservoir has important guiding significance for the efficient development of fracture-cavity carbonate reservoirs. In addition, most carbonate oil and gas wells have low natural productivity after completion, and acid fracturing is often required to increase the production of oil and gas wells. Therefore, the present invention aims to provide a method for evaluating the reservoir type of fracture-cavity carbonate rocks after acid fracturing, which is used to fill the gaps in related fields at home and abroad.

[0038] See also Figure 1 The technical solution adopted by the present invention to solve the above technical problems includes the following steps:

[0039] S1: Determine the bottom hole reservoir type and the development degree and effectiveness of the fracture-cavity bodies encountered by the oil and gas wells and obtain the bottom hole pressure curve shape of the oil and gas wells during acid fracturing operation;

[0040] S2. Judging whether the acid fracturing has connected the fracture-cavity body according to the bottom hole pressure curve of the oil and gas well acid fracturing construction, and determining the volume of the connected fracture-cavity body and its distance from the oil and gas well;

[0041] S3. Combined with the test production curve, further determine the reservoir type of acid-fracture communication and the number of fractures and caves involved in fluid supply.

[0042] As a preferred solution, in step S1, the type of reservoir at the bottom of the well and the development degree and effectiveness of the fracture-cavity body encountered by the oil and gas well are preliminarily determined by combining the seismic reflection type, logging interpretation, drilling leakage and other data;

[0043] As a preferred solution, the method for preliminarily judging the bottom hole reservoir type and the development degree and effectiveness of the fracture-cavity body encountered by the oil and gas well in step S1 is:

[0044] Determine the development degree of formation fractures and caves based on the seismic reflection type of the formation encountered by the oil and gas well;

[0045] The effectiveness of drilling into the fracture-cavity body is determined based on the degree of leakage in the target layer.

[0046] Further preferably, when determining the development degree, if the seismic reflection type is "beaded", the formation fracture-cavity body is developed; if the seismic reflection type is weak reflection or chaotic reflection, the formation fracture-cavity body is underdeveloped.

[0047] Further preferably, when determining the effectiveness of drilling into fracture-cavity bodies, if there is a continuous strong leakage when drilling into the target layer, it means that a large fracture-cavity body has been drilled; if there is an intermittent small leakage and the leakage rate is low, it means that the scale of the fracture-cavity body drilled into the oil and gas well is limited; if no leakage occurs, it means that no fracture-cavity body has been drilled at the bottom of the well.

[0048] As a preferred solution, the method for determining whether the fracture-cavity body is connected by acid fracturing and the volume of the connected fracture-cavity body in step S2 is:

[0049] The bottom hole pressure curve of acid fracturing construction is calculated by comprehensively considering parameters such as the acid fracturing surface construction curve, the acid fracturing string structure, and the friction resistance of the acid fracturing liquid. If the bottom hole pressure drops significantly during the construction process, it means that the acid fracturing fractures have connected the fracture-cavity body. With the further injection of the acid fracturing liquid, if the bottom hole pressure starts to rise, it means that the fracture-cavity body is small and the bottom hole pressure wave has affected the entire fracture-cavity body. The volume of the fracture-cavity body connected by acid fracturing can be calculated according to formula (1). If the bottom hole pressure continues to drop after the fracture-cavity body is connected by acid fracturing and does not rise again, it means that the bottom hole pressure wave has not affected the entire fracture-cavity body. At this time, the lower limit of the volume of the fracture-cavity body connected by acid fracturing can be calculated according to formula (1).

[0050]

[0051] Where: V is the volume of the fracture cavity, m 3 ; N inj is the surface volume of water injected after acid fracturing the fractured cave, m 3 ; B w B is the volume coefficient of injected water when the formation pressure rises to the current formation pressure; oi is the crude oil volume coefficient at the original formation pressure, MPa -1 ; ΔP—total pressure rise value in the fracture cavity, MPa; C o is the compressibility coefficient of crude oil, MPa -1 ; C w Compression coefficient of bound water, MPa -1 ; Cp is the effective compression coefficient of rock, MPa -1 ; S oi is the initial crude oil saturation; S wi is the bound water saturation.

[0052] As a preferred solution, the method for determining the distance between the communicating fracture-cavity body and the oil and gas well in step S2 is:

[0053] Generally speaking, as the length of the crack increases, the crack width becomes narrower and the fracture conductivity gradually decreases. When the artificial crack connects the fracture-cavity body, the permeability of the formation improves, which is equivalent to the width of the crack becoming larger. The conductivity of the acid-etched crack will increase, that is, an inflection point appears on the curve in the process where the conductivity decreases with the increase of the crack length (the downward slope of the curve decreases or even increases). The position of the inflection point is the location of the connected fracture-cavity body.

[0054] As a preferred solution, the method for determining the reservoir type of the acid-fracture connection and the number of fracture-cavity bodies involved in the fluid supply according to the test production curve in step S3 is:

[0055] The relationship between the cumulative production and cumulative pressure drop of the target oil and gas wells was plotted, and compared with the characteristic curves of cumulative liquid production and cumulative pressure drop of three types of reservoirs obtained by laboratory simulation, namely cave type, cave + fracture-pore type, and fracture-pore type, so as to determine the reservoir type of acid-fracture communication and the number of fracture-cavity bodies involved in fluid supply.

[0056] [Example 1]

[0057] A method for evaluating reservoir types of fracture-cavity carbonate rocks after acid fracturing, specifically comprising the following steps:

[0058] S1. Combine seismic reflection type, logging interpretation, drilling and leakage data to preliminarily determine the bottom reservoir type and the development degree and effectiveness of the fractures and caves encountered by the oil and gas wells;

[0059] 1) The seismic reflection type of the formation encountered by the oil and gas well is "beaded", indicating that the formation fractures and caves are well developed. If the seismic reflection type is weak reflection or chaotic reflection, it means that the formation fractures and caves are underdeveloped;

[0060] 2) If there is a continuous and strong leakage when drilling into the target layer, it means that a large fracture-cavity body has been drilled; if there is a small amount of intermittent leakage and the leakage rate is low, it means that the scale of the fracture-cavity body encountered by the oil and gas well is limited; if there is no leakage, it means that no fracture-cavity body has been drilled at the bottom of the well.

[0061] S2. Judging whether the acid fracturing has connected the fracture-cavity body according to the bottom hole pressure curve of the oil and gas well acid fracturing construction, and determining the volume of the connected fracture-cavity body and its distance from the oil and gas well;

[0062] S3. Combined with the characteristics of the test production curve, further determine the reservoir type of acid-fracture communication and the number of fractures and caves involved in fluid supply.

[0063] [Example 2]

[0064] A method for evaluating reservoir types of fracture-cavity carbonate rocks after acid fracturing, specifically comprising the following steps:

[0065] S1. Combine seismic reflection type, logging interpretation, drilling and leakage data to preliminarily determine the bottom reservoir type and the development degree and effectiveness of the fractures and caves encountered by the oil and gas wells;

[0066] 1) The seismic reflection type of the formation encountered by the oil and gas well is "beaded", indicating that the formation fractures and caves are well developed. If the seismic reflection type is weak reflection or chaotic reflection, it means that the formation fractures and caves are underdeveloped;

[0067] 2) If there is a continuous and strong leakage when drilling into the target layer, it means that a large fracture-cavity body has been drilled; if there is a small amount of intermittent leakage and the leakage rate is low, it means that the scale of the fracture-cavity body encountered by the oil and gas well is limited; if there is no leakage, it means that no fracture-cavity body has been drilled at the bottom of the well.

[0068] S2. Judging whether the acid fracturing has connected the fracture-cavity body according to the bottom hole pressure curve of the oil and gas well acid fracturing construction, and determining the volume of the connected fracture-cavity body and its distance from the oil and gas well;

[0069] The method for judging whether the fracture-cavity body is connected by acid fracturing and determining the volume of the fracture-cavity body is as follows:

[0070] The bottom hole pressure curve of acid fracturing construction is calculated by comprehensively considering parameters such as the acid fracturing surface construction curve, the acid fracturing string structure, and the friction resistance of the acid fracturing liquid. If the bottom hole pressure drops significantly during the construction process, it means that the acid fracturing fractures have connected the fracture-cavity body. With the further injection of the acid fracturing liquid, if the bottom hole pressure starts to rise, it means that the fracture-cavity body is small and the bottom hole pressure wave has affected the entire fracture-cavity body. The volume of the fracture-cavity body connected by acid fracturing can be calculated according to formula (1). If the bottom hole pressure continues to drop after the fracture-cavity body is connected by acid fracturing and does not rise again, it means that the bottom hole pressure wave has not affected the entire fracture-cavity body. At this time, the lower limit of the volume of the fracture-cavity body connected by acid fracturing can be calculated according to formula (1).

[0071]

[0072] Where: V is the volume of the fracture cavity, m 3 ; N inj is the surface volume of water injected after acid fracturing the fractured cave, m 3 ; B w B is the volume coefficient of injected water when the formation pressure rises to the current formation pressure; oi is the crude oil volume coefficient at the original formation pressure, MPa -1; ΔP—total pressure rise value in the fracture cavity, MPa; C o is the compressibility coefficient of crude oil, MPa -1 ; C w Compression coefficient of bound water, MPa -1 ; C p is the effective compression coefficient of rock, MPa -1 ; S oi is the initial crude oil saturation; S wi is the bound water saturation.

[0073] S3. Combined with the characteristics of the test production curve, further determine the reservoir type of acid-fracture communication and the number of fractures and caves involved in fluid supply.

[0074] [Example 3]

[0075] A method for evaluating reservoir types of fracture-cavity carbonate rocks after acid fracturing, specifically comprising the following steps:

[0076] S1. Combine seismic reflection type, logging interpretation, drilling and leakage data to preliminarily determine the bottom reservoir type and the development degree and effectiveness of the fractures and caves encountered by the oil and gas wells;

[0077] 1) The seismic reflection type of the formation encountered by the oil and gas well is "beaded", indicating that the formation fractures and caves are well developed. If the seismic reflection type is weak reflection or chaotic reflection, it means that the formation fractures and caves are underdeveloped;

[0078] 2) If there is a continuous and strong leakage when drilling into the target layer, it means that a large fracture-cavity body has been drilled; if there is a small amount of intermittent leakage and the leakage rate is low, it means that the scale of the fracture-cavity body encountered by the oil and gas well is limited; if there is no leakage, it means that no fracture-cavity body has been drilled at the bottom of the well.

[0079] S2. Judging whether the acid fracturing has connected the fracture-cavity body according to the bottom hole pressure curve of the oil and gas well acid fracturing construction, and determining the volume of the connected fracture-cavity body and its distance from the oil and gas well;

[0080] The method for judging whether the fracture-cavity body is connected by acid fracturing and determining the volume of the fracture-cavity body is as follows:

[0081] The bottom hole pressure curve of acid fracturing construction is calculated by comprehensively considering parameters such as the acid fracturing surface construction curve, the acid fracturing string structure, and the friction resistance of the acid fracturing liquid. If the bottom hole pressure drops significantly during the construction process, it means that the acid fracturing fractures have connected the fracture-cavity body. With the further injection of the acid fracturing liquid, if the bottom hole pressure starts to rise, it means that the fracture-cavity body is small and the bottom hole pressure wave has affected the entire fracture-cavity body. The volume of the fracture-cavity body connected by acid fracturing can be calculated according to formula (1). If the bottom hole pressure continues to drop after the fracture-cavity body is connected by acid fracturing and does not rise again, it means that the bottom hole pressure wave has not affected the entire fracture-cavity body. At this time, the lower limit of the volume of the fracture-cavity body connected by acid fracturing can be calculated according to formula (1).

[0082]

[0083] Where: V is the volume of the fracture cavity, m 3 ; N inj is the surface volume of water injected after acid fracturing the fractured cave, m 3 ; B w B is the volume coefficient of injected water when the formation pressure rises to the current formation pressure; oi is the crude oil volume coefficient at the original formation pressure, MPa -1 ; ΔP—total pressure rise value in the fracture cavity, MPa; C o is the compressibility coefficient of crude oil, MPa -1 ; C w Compression coefficient of bound water, MPa -1 ; C p is the effective compression coefficient of rock, MPa -1 ; S oi is the initial crude oil saturation; S wi is the bound water saturation.

[0084] The method for determining the distance between the communicating fracture-cavity body and the oil and gas well is as follows:

[0085] Generally speaking, as the length of the crack increases, the crack width becomes narrower and the fracture conductivity gradually decreases. When the artificial crack connects the fracture-cavity body, the permeability of the formation improves, which is equivalent to the width of the crack becoming larger. The conductivity of the acid-etched crack will increase, that is, an inflection point appears on the curve in the process where the conductivity decreases with the increase of the crack length (the downward slope of the curve decreases or even increases). The position of the inflection point is the location of the connected fracture-cavity body.

[0086] S3. Combined with the characteristics of the test production curve, further determine the reservoir type of acid-fracture communication and the number of fractures and caves involved in fluid supply.

[0087] [Example 4]

[0088] A method for evaluating reservoir types of fracture-cavity carbonate rocks after acid fracturing, specifically comprising the following steps:

[0089] S1. Combine seismic reflection type, logging interpretation, drilling and leakage data to preliminarily determine the bottom reservoir type and the development degree and effectiveness of the fractures and caves encountered by the oil and gas wells;

[0090] 1) The seismic reflection type of the formation encountered by the oil and gas well is "beaded", indicating that the formation fractures and caves are well developed. If the seismic reflection type is weak reflection or chaotic reflection, it means that the formation fractures and caves are underdeveloped;

[0091] 2) If there is a continuous and strong leakage when drilling into the target layer, it means that a large fracture-cavity body has been drilled; if there is a small amount of intermittent leakage and the leakage rate is low, it means that the scale of the fracture-cavity body encountered by the oil and gas well is limited; if there is no leakage, it means that no fracture-cavity body has been drilled at the bottom of the well.

[0092] S2. Judging whether the acid fracturing has connected the fracture-cavity body according to the bottom hole pressure curve of the oil and gas well acid fracturing construction, and determining the volume of the connected fracture-cavity body and its distance from the oil and gas well;

[0093] The method for judging whether the fracture-cavity body is connected by acid fracturing and determining the volume of the fracture-cavity body is as follows:

[0094] The bottom hole pressure curve of acid fracturing construction is calculated by comprehensively considering parameters such as the acid fracturing surface construction curve, the acid fracturing string structure, and the friction resistance of the acid fracturing liquid. If the bottom hole pressure drops significantly during the construction process, it means that the acid fracturing fractures have connected the fracture-cavity body. With the further injection of the acid fracturing liquid, if the bottom hole pressure starts to rise, it means that the fracture-cavity body is small and the bottom hole pressure wave has affected the entire fracture-cavity body. The volume of the fracture-cavity body connected by acid fracturing can be calculated according to formula (1). If the bottom hole pressure continues to drop after the fracture-cavity body is connected by acid fracturing and does not rise again, it means that the bottom hole pressure wave has not affected the entire fracture-cavity body. At this time, the lower limit of the volume of the fracture-cavity body connected by acid fracturing can be calculated according to formula (1).

[0095]

[0096] Where: V is the volume of the fracture cavity, m 3 ; N inj is the surface volume of water injected after acid fracturing the fractured cave, m 3 ; B w B is the volume coefficient of injected water when the formation pressure rises to the current formation pressure; oi is the crude oil volume coefficient at the original formation pressure, MPa -1 ; ΔP—total pressure rise value in the fracture cavity, MPa; C o is the compressibility coefficient of crude oil, MPa -1 ; C w Compression coefficient of bound water, MPa -1 ; C p is the effective compression coefficient of rock, MPa -1 ; S oi is the initial crude oil saturation; S wi is the bound water saturation.

[0097] The method for determining the distance between the communicating fracture-cavity body and the oil and gas well is as follows:

[0098] Generally speaking, as the length of the crack increases, the crack width becomes narrower and the fracture conductivity gradually decreases. When the artificial crack connects the fracture-cavity body, the permeability of the formation improves, which is equivalent to the width of the crack becoming larger. The conductivity of the acid-etched crack will increase, that is, an inflection point appears on the curve in the process where the conductivity decreases with the increase of the crack length (the downward slope of the curve decreases or even increases). The position of the inflection point is the location of the connected fracture-cavity body.

[0099] S3. Combined with the characteristics of the test production curve, further determine the reservoir type of acid-fracture communication and the number of fractures and caves involved in fluid supply.

[0100] The method for determining the type of reservoir body for acid fracturing communication and the number of fractures and caves involved in fluid supply based on the test production curve is as follows:

[0101] The relationship between the cumulative production and cumulative pressure drop of the target oil and gas wells was plotted, and compared with the characteristic curves of cumulative liquid production and cumulative pressure drop of three types of reservoirs obtained by laboratory simulation, namely cave type, cave + fracture-pore type, and fracture-pore type, so as to determine the reservoir type of acid-fracture communication and the number of fracture-cavity bodies involved in fluid supply.

[0102] The present invention is further described in detail below with reference to specific examples.

[0103] The target reservoir is an Ordovician carbonate oil reservoir with a burial depth of about 6500m, a reservoir thickness of 60m, an average porosity of 8%, and an average permeability of 10mD.

[0104] Step S1:

[0105] The seismic reflection map of the target reservoir is shown in Figure 3 ,from Figure 3 It can be seen that there are many "beads" in the reservoir, indicating that the reservoir has a lot of fractures and caves. During the drilling of Well W in the target reservoir, continuous leakage occurred, with a cumulative leakage of 895m 3 This indicates that a large fracture-cavity body was encountered during the drilling process. Combining seismic reflection and drilling leakage, it is preliminarily determined that the reservoir has a large number of fracture-cavity bodies.

[0106] Step S2:

[0107] In order to improve the single well production capacity of Well W, acid fracturing was adopted. During the acid fracturing construction of the well, the bottom hole pressure curve was calculated based on the ground construction curve, acid fracturing pipe string structure, acid fracturing liquid friction and other parameters. Figure 2 The bottom hole pressure dropped significantly during the construction process, and with the further injection of fracturing fluid, the bottom hole pressure began to rise, indicating that the size of the fracture-cavity body is limited and the bottom hole pressure wave has spread to the entire fracture-cavity body. Therefore, formula (1) is used to calculate the volume of the fracture-cavity body of the acid fracturing communication. The specific parameter value is: N inj450m3, B w 1.06, B oi is 1.16, ΔP is 5MPa, C o 0.0007MPa-1, C w 0.0006MPa-1, C p 0.00125MPa-1, S oi 0.85, S wi is 0.15, so:

[0108]

[0109] The conductivity curve of acid-etched cracks after acid fracturing is shown in Figure 4 .from Figure 4 It can be seen that as the length of the crack gradually increases, the conductivity of the acid-etched crack gradually decreases. When and only when the crack length reaches about 45m, the slope of the curve increases slightly, indicating that the location of this point is the location of the cave, which is about 45m away from the wellbore.

[0110] Step S3:

[0111] The characteristic curves of cumulative liquid production and cumulative pressure drop of three types of reservoirs, cave type, cave + fracture-hole type, and fracture-hole type, obtained by laboratory simulation are shown in Figure 5 , and the relationship between the cumulative production and cumulative pressure drop during the well production test is shown in Figure 6 .contrast Figure 5 and Figure 6 It can be seen that there is a fracture-cavity body unit supplying liquid during the production process, that is, only one fracture-cavity body unit is connected during the acid fracturing process, which is consistent with the result obtained in step S2.

[0112] In summary, the target reservoir has a large number of fracture-cavity bodies and is a fracture-cavity carbonate reservoir, but only one fracture-cavity unit was connected during the acid fracturing process.

[0113] The present invention combines seismic reflection data and drilling loss data before acid fracturing, acid fracturing bottom hole pressure curve and acid-etched fracture conductivity curve, test production curve after acid fracturing, etc., to comprehensively determine whether fractures and caves exist, the volume of caves, the location of fractures and caves, etc., with high on-site operability and reliable interpretation results.

[0114] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for evaluating reservoir type of fracture-cavity carbonate rock after acid fracturing, characterized in that: The following steps are involved: Determine the bottom hole reservoir type and the development degree and effectiveness of the fracture-cavity bodies encountered in the oil and gas wells, and obtain the bottom hole pressure curve shape of the oil and gas well acid fracturing operation; According to the bottom hole pressure curve of the oil and gas well acid fracturing construction, determine whether the acid fracturing has connected the fracture and cave, and determine the volume of the connected fracture and cave and its distance from the oil and gas well; Draw a test production curve and determine the type of reservoir body connected by acid fracturing and the number of fractures and caves involved in fluid supply.

2. The method for evaluating reservoir type of fracture-cavity carbonate rock after acid fracturing according to claim 1, characterized in that: Combined with seismic reflection type, logging interpretation, and drilling leakage, the bottom hole reservoir type and the development degree and effectiveness of the fractures and caves encountered by the oil and gas wells are determined.

3. The method for evaluating reservoir type of fracture-cavity carbonate rock after acid fracturing according to claim 2, characterized in that: The method for determining the bottom hole reservoir type and the development degree and effectiveness of the fracture-cavity body encountered by the oil and gas well is as follows: Determine the development degree of formation fractures and caves based on the seismic reflection type of the formation encountered by the oil and gas well; The effectiveness of drilling into the fracture-cavity body is determined based on the degree of leakage in the target layer.

4. The method for evaluating reservoir type of fracture-cavity carbonate rock after acid fracturing according to claim 3 is characterized in that: When determining the development degree, if the seismic reflection type is "beaded", the formation fracture-cavity body is developed; if the seismic reflection type is weak reflection or chaotic reflection, the formation fracture-cavity body is underdeveloped.

5. The method for evaluating reservoir type of fracture-cavity carbonate rock after acid fracturing according to claim 3 is characterized in that: When determining the effectiveness of drilling into fractures and caves, if there is a continuous strong loss when drilling into the target layer, it means that a large fracture and cave has been drilled; if there is a small amount of intermittent loss and the loss rate is low, it means that the scale of the fracture and cave encountered by the oil and gas well is limited; if no loss occurs, it means that no fracture and cave has been drilled at the bottom of the well.

6. The method for evaluating reservoir type of fracture-cavity carbonate rock after acid fracturing according to claim 1, characterized in that: The method of obtaining the bottom hole pressure curve of the oil and gas well acid fracturing construction specifically comprises comprehensively analyzing the parameters such as the acid fracturing surface construction curve, the acid fracturing pipe string structure, and the acid fracturing liquid friction resistance, and calculating the bottom hole pressure curve of the acid fracturing construction.

7. The method for evaluating reservoir type of fracture-cavity carbonate rock after acid fracturing according to claim 1, characterized in that: The specific method for judging whether the fracture-cavity body is connected by acid fracturing and determining the volume of the fracture-cavity body is: Where: V is the volume of the fracture cavity; N inj B is the surface volume of water injected after acid fracturing to connect the fractured cave; w B is the volume coefficient of injected water when the formation pressure rises to the current formation pressure; oi is the volume coefficient of crude oil under the original formation pressure; ΔP is the total pressure increase in the fracture cavity; C o is the compression coefficient of crude oil; C w The compressibility coefficient of bound water; C p is the effective compression coefficient of rock; S oi is the initial crude oil saturation; S wi is the bound water saturation.

8. The method for evaluating reservoir type of fracture-cavity carbonate rock after acid fracturing according to claim 7, characterized in that: If the bottom hole pressure drops significantly during the construction process, it means that the acid fracturing fractures have connected the fracture-cavity body. With the further injection of acid fracturing liquid, if the bottom hole pressure starts to rise, it means that the fracture-cavity body is small and the bottom hole pressure wave has affected the entire fracture-cavity body. The volume of the fracture-cavity body connected by acid fracturing is calculated according to formula (1). If the bottom hole pressure continues to drop after the fracture-cavity body is connected by acid fracturing and does not rise again, it means that the bottom hole pressure wave has not affected the entire fracture-cavity body. The lower limit of the volume of the fracture-cavity body connected by acid fracturing is calculated according to formula (1).

9. The method for evaluating reservoir type of fracture-cavity carbonate rock after acid fracturing according to claim 1, characterized in that: The distance between the communicating fracture-cavity body and the oil and gas well is determined as follows: an inflection point appears on the curve when the conductivity decreases with increasing fracture length, and the position of the inflection point is the position of the communicating fracture-cavity body.

10. The method for evaluating reservoir type of fracture-cavity carbonate rock after acid fracturing according to claim 1, characterized in that: The method for determining the type of reservoir body for acid fracturing communication and the number of fractures and caves involved in fluid supply based on the test production curve is as follows: The relationship between the cumulative production and cumulative pressure drop of the target oil and gas wells was plotted, and compared with the characteristic curves of cumulative liquid production and cumulative pressure drop of three types of reservoirs obtained by laboratory simulation, namely cave type, cave + fracture-pore type, and fracture-pore type, so as to determine the reservoir type of acid-fracture communication and the number of fracture-cavity bodies involved in fluid supply.

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