A method for evaluating reservoir types after acid fracturing of a fracture-vug carbonate rock

Abstract

The application discloses a kind of fracture-cave type carbonate rock reservoir type evaluation method after acid fracturing, belong to carbonate reservoir type evaluation technical field, comprising: determining well bottom reservoir type and the development degree and effectiveness of oil and gas well drilling fracture-cave and obtain the well bottom pressure curve form of oil and gas well acid fracturing construction;According to the well bottom pressure curve form of oil and gas well acid fracturing construction, whether acid fracturing is communicated fracture-cave is judged, and the volume of communicated fracture-cave and its distance from oil and gas well are determined;Draw test curve, and determine the reservoir type of acid fracturing communication and the number of fracture-cave participating in liquid supply.Combining seismic reflection data and drilling leakage data before acid fracturing, acid fracturing well bottom pressure curve and acid etching fracture conductivity curve, test curve after acid fracturing, etc., whether fracture-cave exists and the volume of cave, the position of fracture-cave, etc.are comprehensively determined, and the interpretation result is reliable.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbonate reservoir type evaluation, and particularly relates to a fracture-cave type carbonate reservoir type evaluation method after acid fracturing. BACKGROUND

[0002] The geological structure condition of carbonate oil and gas reservoir is extremely complex, the oil and gas reservoirs are scattered, and the macroscopic distribution has strong uncertainty and non-uniformity. For example, as a main type of carbonate, the fracture-cave type carbonate has a large number of solution caves and natural fractures in the reservoir, and has strong heterogeneity. The exploration and development practice shows that the solution cave is the reservoir space of oil and gas resources, and the natural fracture is the main seepage channel of oil and gas, so it is of important guiding significance to determine the fracture-cave type and its parameters in the reservoir for efficient development of the fracture-cave type carbonate reservoir. Related invention patent 1 - "determination method and device of carbonate reservoir type" (patent application publication number: CN110792436A) determines the bottom hole pressure difference by obtaining the first pressure value before acid fracturing and the second bottom hole pressure value after acid fracturing of the measured reservoir, then obtains the first acid liquid parameter injected into the reservoir and the second acid liquid parameter returned and discharged, and determines the reservoir type in combination with the production situation after acid fracturing.

[0003] Related invention patent 2 - "carbonate reservoir classification method and reservoir identification chart establishment method" (patent application publication number: CN114444559A) classifies the reservoirs through the analysis of logging data, core analysis data, pore throat median radius data and oil test data, calculates the reservoir structure parameters for each cored well section of each reservoir type, and establishes the crossplot of the normalized parameters and porosity, and further obtains the reservoir type identification chart.

[0004] Related invention patent 3 - "fracture-cave type carbonate reservoir evaluation method based on seismic-logging calibration" (patent application publication number: CN105093333A) performs wellbore collapse correction, multi-well standardization and consistency processing on the logging curve, loads the processed logging and seismic data to perform well-seismic calibration, extracts a wavelet suitable for the target layer, and performs post-stack deterministic inversion and post-stack geostatistical inversion, preliminarily obtains a multi-well impedance and porosity chart by statistically analyzing the relationship between the well impedance and the reservoir evaluation parameter porosity, and corrects the multi-well impedance by statistically analyzing the relationship between the porosity and the acoustic time difference and the density of the well leakage and the empty well section.

[0005] The above patents do not establish a detailed evaluation method for the fracture-cave type carbonate reservoir, in addition, the evaluation is basically based on geological or engineering parameters on one side, and the geological and engineering parameters are not combined to evaluate the reservoir. At present, there are few reports on the fracture-cave type carbonate reservoir type evaluation and fracture-cave parameter interpretation method. SUMMARY

[0006] In order to overcome the above-mentioned defects of the prior art, the purpose of the present application is to provide a fracture-cave carbonate reservoir type evaluation method after acid fracturing, which is used to solve the problems of fracture-cave carbonate reservoir type evaluation and fracture-cave parameter interpretation method.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] A fracture-cave carbonate reservoir type evaluation method after acid fracturing, comprising the following steps:

[0009] determining the bottom hole reservoir type, the development degree and effectiveness of the fracture-cave body drilled by the oil and gas well, and obtaining the bottom hole pressure curve shape of the oil and gas well during acid fracturing operation;

[0010] judging whether the acid fracturing communicates the fracture-cave body according to the bottom hole pressure curve shape of the oil and gas well during acid fracturing operation, and determining the volume of the communicated fracture-cave body and the distance from the oil and gas well;

[0011] drawing a test production curve, and determining the reservoir type communicated by the acid fracturing and the number of fracture-cave bodies participating in liquid supply.

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

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

[0014] determining the development degree of the fracture-cave body of the stratum according to the seismic reflection type of the stratum drilled by the oil and gas well;

[0015] determining the effectiveness of the fracture-cave body drilled according to the loss degree of the drilled target layer.

[0016] Preferably, when determining the development degree, if the seismic reflection type is "bead-like", the fracture-cave body of the stratum is developed, and if the seismic reflection type is weak reflection or chaotic reflection, the fracture-cave body of the stratum is underdeveloped.

[0017] Preferably, when determining the effectiveness of the fracture-cave body drilled, if there is strong and continuous loss in the drilled target layer, it means that a large fracture-cave body has been drilled; if there is intermittent and small loss, and the loss speed is small, it means that the scale of the fracture-cave body drilled by the oil and gas well is limited; if there is no loss, it means that the fracture-cave body has not been drilled at the bottom hole.

[0018] Preferably, the obtaining of the bottom hole pressure curve shape of the oil and gas well during acid fracturing operation specifically comprises comprehensively calculating the acid fracturing ground operation curve, acid fracturing pipe column structure, acid fracturing liquid friction and other parameters, and calculating the bottom hole pressure curve of the acid fracturing operation.

[0019] Preferably, the specific method for determining whether acid pressure connects to the cavity and for determining the volume of the cavity is as follows:

[0020]

[0021] In the formula: V is the volume of the slit; N inj B is the ground volume of water injected after acid fracturing of the joint cavity; w B is the injection water volume factor when the formation pressure increases to the current formation pressure; oi C is the crude oil volume factor under the original formation pressure; ΔP is the total pressure increase within the fracture cavity; C o C is the compressibility coefficient of crude oil. w The compressibility coefficient of bound water; C p S is the effective compressibility coefficient of the rock; oi S represents the initial crude oil saturation. wi To constrain water saturation.

[0022] Preferably, if the bottom pressure drops significantly during construction, it indicates that the acid-pumped fracture has connected the fracture cavity. If the bottom pressure starts to rise as the acid-pumped liquid is further injected, it indicates that the fracture cavity is small and the bottom pressure wave has affected the entire fracture cavity. The volume of the acid-pumped fracture cavity is calculated according to formula (1). If the bottom pressure continues to drop after the acid-pumped fracture cavity is connected and does not rise, it indicates that the bottom pressure wave has not affected the entire fracture cavity. The lower limit of the volume of the acid-pumped fracture cavity is calculated according to formula (1).

[0023] Preferably, the method for determining the distance between the connecting fracture and the oil and gas well is as follows: when the conductivity on the curve decreases as the fracture length increases, an inflection point appears, and the location of the inflection point is the location of the connecting fracture.

[0024] Preferably, the method for determining the reservoir type and the number of fractured cavities involved in the fluid supply based on the trial production curve is as follows:

[0025] Plot the relationship between cumulative production and cumulative pressure drop of the target oil and gas well, and compare it with the cumulative production and cumulative pressure drop characteristic curves of three types of reservoirs—cavity type, cavity + fracture-cavity type, and fracture-cavity type—obtained from laboratory simulations, so as to determine the type of reservoir with acid fracturing 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] This invention discloses a method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing. By determining the bottom-hole reservoir type and the development and effectiveness of fractured-vuggy bodies encountered in oil and gas wells, and obtaining the bottom-hole pressure curve morphology during acid fracturing, it is possible to determine whether acid fracturing connects to the fractured-vuggy bodies, and to determine the volume of the connecting fractured-vuggy bodies and their distance from the oil and gas well. The method also determines the post-acid fracturing production curve, combining pre-acid fracturing seismic reflection data, drilling loss data, bottom-hole pressure curves from acid fracturing, fracture conductivity curves from acid etching, and post-acid fracturing production curves to comprehensively determine the existence, volume, and location of fractures and vuggies. This method has high field operability, fully integrates various data before, during, and after acid fracturing, and data acquisition is not difficult. The existence, volume, and location of fractures and vuggies can be determined through comprehensive analysis, resulting in reliable interpretation of the results. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method of the present invention.

[0029] Figure 2 This is a typical bottom-hole pressure curve diagram for connecting the fractured cavity during acid fracturing.

[0030] Figure 3 It is an earthquake reflection map.

[0031] Figure 4 This is a graph showing the conductivity of acid-etched cracks;

[0032] Figure 5 It is a graph showing the correspondence between the characteristics of the trial mining obtained in the laboratory and the type of reservoir space.

[0033] Figure 6 It is a cumulative production-cumulative pressure drop curve obtained on-site. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort 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, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0036] The present invention will now be described in further detail with reference to the accompanying drawings:

[0037] The geological structure of carbonate oil and gas reservoirs in my country is extremely complex, with scattered reservoirs exhibiting significant uncertainty and heterogeneity in their macroscopic distribution. For example, fractured-vuggy carbonate reservoirs, a major type, are characterized by numerous caverns and natural fractures, exhibiting strong heterogeneity. Exploration and development practices have shown that caverns serve as storage spaces for oil and gas resources, while natural fractures act as the primary seepage channels. Therefore, clearly defining the types and parameters of fractures and caverns in reservoirs is crucial for the efficient development of fractured-vuggy carbonate reservoirs. Furthermore, most carbonate oil and gas wells have low natural production capacity upon completion, often requiring acid fracturing to improve well production. Therefore, this invention aims to provide a method for evaluating the reservoir type of fractured-vuggy carbonate rocks after acid fracturing, filling a gap in related fields both domestically and internationally.

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

[0039] S1: Determine the bottom-hole reservoir type and the development degree and effectiveness of fractured cavities encountered in oil and gas well drilling, and obtain the bottom-hole pressure curve shape of acid fracturing operations in oil and gas wells;

[0040] S2. Based on the bottom pressure curve shape of the acid fracturing operation of the oil and gas well, determine whether the acid fracturing connects to the fractured cavity, and determine the volume of the connecting fractured cavity and its distance from the oil and gas well.

[0041] S3. Based on the trial production curve, further determine the type of reservoir with acid fracturing and the number of fractured cavities involved in the liquid supply.

[0042] As a preferred option, in step S1, data such as seismic reflection type, well logging interpretation, and well leakage are combined to make a preliminary judgment on the bottom-hole reservoir type and the development degree and effectiveness of the fractured cavity encountered in the oil and gas well.

[0043] As a preferred option, the method for initially determining the bottom-hole reservoir type and the development degree and effectiveness of fractured cavities encountered in oil and gas wells in step S1 is as follows:

[0044] The degree of formation fracture and cavity development is determined based on the seismic reflection type of the formation encountered by oil and gas wells.

[0045] The effectiveness of the drilled cavity is determined based on the degree of leakage in the target layer.

[0046] More preferably, when determining the degree of development, if the seismic reflection type is "beaded", then the stratum fracture-cavity is developed; if the seismic reflection type is weak reflection or chaotic reflection, then the stratum fracture-cavity is underdeveloped.

[0047] More preferably, when determining the validity of drilling into a fractured cavity, if there is a continuous and strong leakage in the target layer, it indicates that a large fractured cavity has been encountered; if there is intermittent and small leakage, and the leakage rate is low, it indicates that the scale of the fractured cavity encountered in the oil and gas well is limited; if no leakage occurs, it indicates that no fractured cavity has been encountered at the bottom of the well.

[0048] As a preferred embodiment, the method for determining whether acid fracturing connects to the fracture cavity and for determining the volume of the fracture cavity in step S2 is as follows:

[0049] Based on the combined parameters of the acid fracturing surface construction curve, acid fracturing string structure, and acid fracturing fluid friction, the bottom pressure curve of the acid fracturing construction well is calculated: If the bottom pressure drops significantly during the construction process, it indicates that the acid fracturing fracture has connected the fracture cavity. If the bottom pressure starts to rise as the acid fracturing fluid is further injected, it indicates that the fracture cavity is small in scale and the bottom pressure wave has affected the entire fracture cavity. The volume of the acid fracturing fracture cavity can be calculated according to formula (1). If the bottom pressure continues to drop after the acid fracturing fracture cavity is connected and does not rise, it indicates that the bottom pressure wave has not affected the entire fracture cavity. At this time, the lower limit of the volume of the acid fracturing fracture cavity can be calculated according to formula (1).

[0050]

[0051] In the formula: V is the volume of the slit, m 3 N inj The volume of water injected into the ground after acid fracturing of the joint cavity is expressed in m. 3 B w B is the injection water volume factor when the formation pressure increases to the current formation pressure; oi The crude oil volume coefficient under the original formation pressure, in MPa -1 ΔP—The total pressure increase within the cavity, in MPa; C o The compressibility coefficient of crude oil is expressed in MPa. -1 C w The compressibility of bound water, in MPa -1 Cp The effective compressibility coefficient of the rock is expressed in MPa. -1 S oi S represents the initial crude oil saturation. wi To constrain water saturation.

[0052] As a preferred option, the method for determining the distance between the fractured cavity and the oil / gas well in step S2 is as follows:

[0053] Generally, as the length of a fracture increases, the width of the fracture narrows, and the conductivity of the fracture gradually decreases. When an artificial fracture connects to a cavity, the permeability of the formation improves, which is equivalent to the fracture width increasing. The conductivity of the acid-etched fracture will increase. That is, in the process of the conductivity decreasing with the increase of the fracture length, there will be an inflection point (the slope of the curve decreases or even increases). The location of the inflection point is the location of the cavity that is connected.

[0054] As a preferred embodiment, the method for determining the reservoir type and the number of fractured cavities involved in the fluid supply based on the trial production curve in step S3 is as follows:

[0055] Plot the relationship between cumulative production and cumulative pressure drop of the target oil and gas well, and compare it with the cumulative production and cumulative pressure drop characteristic curves of three types of reservoirs—cavity type, cavity + fracture-cavity type, and fracture-cavity type—obtained from laboratory simulations, so as to determine the type of reservoir with acid fracturing and the number of fracture-cavity bodies involved in fluid supply.

[0056]

Example 1

[0057] A method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing, specifically including the following steps:

[0058] S1. Based on data such as seismic reflection type, well logging interpretation, and well leakage, a preliminary judgment is made on the bottom-hole reservoir type and the development degree and effectiveness of the fractured cavities encountered in oil and gas wells.

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

[0060] 2) If there is a continuous and strong leakage in the target layer, it indicates that a large fractured cavity has been encountered; if there is intermittent and small leakage, and the leakage rate is low, it indicates that the scale of the fractured cavity encountered in the oil and gas well is limited; if no leakage occurs, it indicates that no fractured cavity has been encountered at the bottom of the well.

[0061] S2. Based on the bottom pressure curve shape of the acid fracturing operation of the oil and gas well, determine whether the acid fracturing connects to the fractured cavity, and determine the volume of the connecting fractured cavity and its distance from the oil and gas well.

[0062] S3. Based on the characteristics of the trial production curve, further determine the type of reservoir with acid fracturing and the number of fractured cavities involved in the liquid supply.

[0063]

Example 2

[0064] A method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing, specifically including the following steps:

[0065] S1. Based on data such as seismic reflection type, well logging interpretation, and well leakage, a preliminary judgment is made on the bottom-hole reservoir type and the development degree and effectiveness of the fractured cavities encountered in oil and gas wells.

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

[0067] 2) If there is a continuous and strong leakage in the target layer, it indicates that a large fractured cavity has been encountered; if there is intermittent and small leakage, and the leakage rate is low, it indicates that the scale of the fractured cavity encountered in the oil and gas well is limited; if no leakage occurs, it indicates that no fractured cavity has been encountered at the bottom of the well.

[0068] S2. Based on the bottom pressure curve shape of the acid fracturing operation of the oil and gas well, determine whether the acid fracturing connects to the fractured cavity, and determine the volume of the connecting fractured cavity and its distance from the oil and gas well.

[0069] The methods for determining whether acid fracturing connects to the fracture cavity and for determining the volume of the fracture cavity are as follows:

[0070] Based on the combined parameters of the acid fracturing surface construction curve, acid fracturing string structure, and acid fracturing fluid friction, the bottom pressure curve of the acid fracturing construction well is calculated: If the bottom pressure drops significantly during the construction process, it indicates that the acid fracturing fracture has connected the fracture cavity. If the bottom pressure starts to rise as the acid fracturing fluid is further injected, it indicates that the fracture cavity is small in scale and the bottom pressure wave has affected the entire fracture cavity. The volume of the acid fracturing fracture cavity can be calculated according to formula (1). If the bottom pressure continues to drop after the acid fracturing fracture cavity is connected and does not rise, it indicates that the bottom pressure wave has not affected the entire fracture cavity. At this time, the lower limit of the volume of the acid fracturing fracture cavity can be calculated according to formula (1).

[0071]

[0072] In the formula: V is the volume of the slit, m 3 N inj The volume of water injected into the ground after acid fracturing of the joint cavity is expressed in m. 3 B w B is the injection water volume factor when the formation pressure increases to the current formation pressure; oi The crude oil volume coefficient under the original formation pressure, in MPa -1ΔP—The total pressure increase within the cavity, in MPa; C o The compressibility coefficient of crude oil is expressed in MPa. -1 C w The compressibility of bound water, in MPa -1 C p The effective compressibility coefficient of the rock is expressed in MPa. -1 S oi S represents the initial crude oil saturation. wi To constrain water saturation.

[0073] S3. Based on the characteristics of the trial production curve, further determine the type of reservoir with acid fracturing and the number of fractured cavities involved in the liquid supply.

[0074]

Example 3

[0075] A method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing, specifically including the following steps:

[0076] S1. Based on data such as seismic reflection type, well logging interpretation, and well leakage, a preliminary judgment is made on the bottom-hole reservoir type and the development degree and effectiveness of the fractured cavities encountered in oil and gas wells.

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

[0078] 2) If there is a continuous and strong leakage in the target layer, it indicates that a large fractured cavity has been encountered; if there is intermittent and small leakage, and the leakage rate is low, it indicates that the scale of the fractured cavity encountered in the oil and gas well is limited; if no leakage occurs, it indicates that no fractured cavity has been encountered at the bottom of the well.

[0079] S2. Based on the bottom pressure curve shape of the acid fracturing operation of the oil and gas well, determine whether the acid fracturing connects to the fractured cavity, and determine the volume of the connecting fractured cavity and its distance from the oil and gas well.

[0080] The methods for determining whether acid fracturing connects to the fracture cavity and for determining the volume of the fracture cavity are as follows:

[0081] Based on the combined parameters of the acid fracturing surface construction curve, acid fracturing string structure, and acid fracturing fluid friction, the bottom pressure curve of the acid fracturing construction well is calculated: If the bottom pressure drops significantly during the construction process, it indicates that the acid fracturing fracture has connected the fracture cavity. If the bottom pressure starts to rise as the acid fracturing fluid is further injected, it indicates that the fracture cavity is small in scale and the bottom pressure wave has affected the entire fracture cavity. The volume of the acid fracturing fracture cavity can be calculated according to formula (1). If the bottom pressure continues to drop after the acid fracturing fracture cavity is connected and does not rise, it indicates that the bottom pressure wave has not affected the entire fracture cavity. At this time, the lower limit of the volume of the acid fracturing fracture cavity can be calculated according to formula (1).

[0082]

[0083] In the formula: V is the volume of the slit, m 3 N inj The volume of water injected into the ground after acid fracturing of the joint cavity is expressed in m. 3 B w B is the injection water volume factor when the formation pressure increases to the current formation pressure; oi The crude oil volume coefficient under the original formation pressure, in MPa -1 ΔP—The total pressure increase within the cavity, in MPa; C o The compressibility coefficient of crude oil is expressed in MPa. -1 C w The compressibility of bound water, in MPa -1 C p The effective compressibility coefficient of the rock is expressed in MPa. -1 S oi S represents the initial crude oil saturation. wi To constrain water saturation.

[0084] The method for determining the distance between the connecting fracture and the oil / gas well is as follows:

[0085] Generally, as the length of a fracture increases, the width of the fracture narrows, and the conductivity of the fracture gradually decreases. When an artificial fracture connects to a cavity, the permeability of the formation improves, which is equivalent to the fracture width increasing. The conductivity of the acid-etched fracture will increase. That is, in the process of the conductivity decreasing with the increase of the fracture length, there will be an inflection point (the slope of the curve decreases or even increases). The location of the inflection point is the location of the cavity that is connected.

[0086] S3. Based on the characteristics of the trial production curve, further determine the type of reservoir with acid fracturing and the number of fractured cavities involved in the liquid supply.

[0087]

Example 4

[0088] A method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing, specifically including the following steps:

[0089] S1. Based on data such as seismic reflection type, well logging interpretation, and well leakage, a preliminary judgment is made on the bottom-hole reservoir type and the development degree and effectiveness of the fractured cavities encountered in oil and gas wells.

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

[0091] 2) If there is a continuous and strong leakage in the target layer, it indicates that a large fractured cavity has been encountered; if there is intermittent and small leakage, and the leakage rate is low, it indicates that the scale of the fractured cavity encountered in the oil and gas well is limited; if no leakage occurs, it indicates that no fractured cavity has been encountered at the bottom of the well.

[0092] S2. Based on the bottom pressure curve shape of the acid fracturing operation of the oil and gas well, determine whether the acid fracturing connects to the fractured cavity, and determine the volume of the connecting fractured cavity and its distance from the oil and gas well.

[0093] The methods for determining whether acid fracturing connects to the fracture cavity and for determining the volume of the fracture cavity are as follows:

[0094] Based on the combined parameters of the acid fracturing surface construction curve, acid fracturing string structure, and acid fracturing fluid friction, the bottom pressure curve of the acid fracturing construction well is calculated: If the bottom pressure drops significantly during the construction process, it indicates that the acid fracturing fracture has connected the fracture cavity. If the bottom pressure starts to rise as the acid fracturing fluid is further injected, it indicates that the fracture cavity is small in scale and the bottom pressure wave has affected the entire fracture cavity. The volume of the acid fracturing fracture cavity can be calculated according to formula (1). If the bottom pressure continues to drop after the acid fracturing fracture cavity is connected and does not rise, it indicates that the bottom pressure wave has not affected the entire fracture cavity. At this time, the lower limit of the volume of the acid fracturing fracture cavity can be calculated according to formula (1).

[0095]

[0096] In the formula: V is the volume of the slit, m 3 N inj The volume of water injected into the ground after acid fracturing of the joint cavity is expressed in m. 3 B w B is the injection water volume factor when the formation pressure increases to the current formation pressure; oi The crude oil volume coefficient under the original formation pressure, in MPa -1 ΔP—The total pressure increase within the cavity, in MPa; C o The compressibility coefficient of crude oil is expressed in MPa. -1 C w The compressibility of bound water, in MPa -1 C p The effective compressibility coefficient of the rock is expressed in MPa. -1 S oi S represents the initial crude oil saturation. wi To constrain water saturation.

[0097] The method for determining the distance between the connecting fracture and the oil / gas well is as follows:

[0098] Generally, as the length of a fracture increases, the width of the fracture narrows, and the conductivity of the fracture gradually decreases. When an artificial fracture connects to a cavity, the permeability of the formation improves, which is equivalent to the fracture width increasing. The conductivity of the acid-etched fracture will increase. That is, in the process of the conductivity decreasing with the increase of the fracture length, there will be an inflection point (the slope of the curve decreases or even increases). The location of the inflection point is the location of the cavity that is connected.

[0099] S3. Based on the characteristics of the trial production curve, further determine the type of reservoir with acid fracturing and the number of fractured cavities involved in the liquid supply.

[0100] The method for determining the reservoir type and the number of fractured cavities involved in the fluid supply based on the trial production curve is as follows:

[0101] Plot the relationship between cumulative production and cumulative pressure drop of the target oil and gas well, and compare it with the cumulative production and cumulative pressure drop characteristic curves of three types of reservoirs—cavity type, cavity + fracture-cavity type, and fracture-cavity type—obtained from laboratory simulations, so as to determine the type of reservoir with acid fracturing and the number of fracture-cavity bodies involved in fluid supply.

[0102] The invention will now be described in further detail 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] See the seismic reflection map of the target reservoir. Figure 3 ,from Figure 3 The study revealed numerous "beaded" formations within the reservoir, indicating well-developed fractured-vuggy structures. During drilling of well W in the target reservoir, continuous leakage occurred, with a cumulative loss of 895 m³. 3 This indicates that a large fractured cavity was encountered during drilling. Based on seismic reflections and drilling losses, it is preliminarily determined that the reservoir contains numerous fractured cavities.

[0106] Step S2:

[0107] To improve the single-well productivity of Well W, acid fracturing was employed as a production enhancement method. During the acid fracturing operation, the bottom hole pressure curve was calculated based on parameters such as the surface construction curve, the acid fracturing string structure, and the frictional resistance of the acid fracturing fluid. Figure 2 They exhibit the same trend. During the construction process, the bottom hole pressure dropped significantly, and with further injection of fracturing fluid, the bottom hole pressure began to rise, indicating that the fractured cavity was of limited size and the bottom hole pressure wave had affected the entire fractured cavity. Therefore, formula (1) was used to calculate the volume of the acid fracturing channel to the fractured cavity, with the specific parameter value being: N inj450m3, B w 1.06, B oi =1.16, ΔP = 5MPa, C o 0.0007MPa-1, C w 0.0006MPa-1, C p 0.00125MPa-1, S oi 0.85, S wi Since it is 0.15, therefore:

[0108]

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

[0110] Step S3:

[0111] The characteristic curves of cumulative production and cumulative pressure drop of three types of reservoirs obtained from laboratory simulations are shown below. Figure 5 The relationship between cumulative production and cumulative pressure drop during the well's trial production process is shown in the graph below. Figure 6 .contrast Figure 5 and Figure 6 It can be seen that there is a single crevice unit supplying liquid during the production process, meaning that only one crevice unit is connected during the acid pressing 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, making it a fracture-cavity carbonate reservoir, but only one fracture-cavity unit was connected during acid fracturing.

[0113] This invention combines pre-fracturing seismic reflection data and drilling leakage data, fracturing bottom pressure curves and acid-etched fracture conductivity curves, post-fracturing test production curves, etc., to comprehensively determine the existence of fractures and cavities, the volume of the cavities, the location of the fractures and cavities, etc. It has high operability in the field and the interpretation results are reliable.

[0114] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing, characterized in that, Includes the following steps: By combining seismic reflection type, well logging interpretation, and well leakage, the bottom reservoir type and the development degree and effectiveness of fractured cavities encountered in oil and gas wells are determined, and the bottom pressure curve morphology of acid fracturing operations in oil and gas wells is obtained. Based on the bottom pressure curve shape during acid fracturing of oil and gas wells, determine whether acid fracturing connects to the fractured cavity, and determine the volume of the connecting cavity and its distance from the oil and gas well. Plot the trial production curve and determine the type of reservoir with acid fracturing and the number of fractured cavities involved in the fluid supply. The specific method for determining whether acid fracturing connects to the cavity and for determining the volume of the cavity is as follows: （1） In the formula: The volume of the slit hole; The ground volume of water injected after acid fracturing of the joint cavity; This is the volume factor of injected water when the formation pressure increases to the current formation pressure; The crude oil volume coefficient under the original formation pressure; This represents the total pressure increase within the cavity; The compressibility coefficient of crude oil; The compressibility of bound water; The effective compressibility coefficient of the rock; The initial crude oil saturation; To bind water saturation; If the bottom pressure drops significantly during construction, it indicates that the acid-pumped fracture has connected the fracture cavity. If the bottom pressure starts to rise as the acid-pumped liquid is further injected, it indicates that the fracture cavity is small and the bottom pressure wave has affected the entire fracture cavity. The volume of the acid-pumped fracture cavity is calculated according to formula (1). If the bottom pressure continues to drop after the acid-pumped fracture cavity is connected and does not rise, it indicates that the bottom pressure wave has not affected the entire fracture cavity. The lower limit of the volume of the acid-pumped fracture cavity is calculated according to formula (1).

2. The method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing according to claim 1, characterized in that, The method for determining the bottom-hole reservoir type and the development degree and effectiveness of fractured and cavitary formations encountered in oil and gas wells is as follows: The degree of formation fracture and cavity development is determined based on the seismic reflection type of the formation encountered by oil and gas wells. The effectiveness of the drilled cavity is determined based on the degree of leakage in the target layer.

3. The method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing according to claim 2, characterized in that, When determining the degree of development, if the earthquake reflection type is "beaded", then the strata fractures and cavities are developed; if the earthquake reflection type is weak reflection or chaotic reflection, then the strata fractures and cavities are underdeveloped.

4. The method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing according to claim 2, characterized in that, When determining the validity of a drilled fractured cavity, if there is a continuous and strong leakage in the target layer, it indicates that a large fractured cavity has been encountered; if there is intermittent and small leakage at a low rate, it indicates that the scale of the fractured cavity encountered in the oil and gas well is limited; if no leakage occurs, it indicates that no fractured cavity has been encountered at the bottom of the well.

5. The method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing according to claim 1, characterized in that, The specific method for obtaining the bottom pressure curve shape of the acid fracturing operation of oil and gas wells involves comprehensively considering parameters such as the surface construction curve of acid fracturing, the structure of the acid fracturing tubing, and the frictional resistance of the acid fracturing fluid to calculate the bottom pressure curve of the acid fracturing operation.

6. The method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing according to claim 1, characterized in that, The method for determining the distance between the connecting fracture and the oil and gas well is as follows: when the conductivity on the curve decreases as the fracture length increases, an inflection point appears, and the location of the inflection point is the location of the connecting fracture.

7. The method for evaluating the type of fractured-vuggy carbonate reservoirs after acid fracturing according to claim 1, characterized in that, The method for determining the reservoir type and the number of fractured cavities involved in the fluid supply based on the trial production curve is as follows: Plot the relationship between cumulative production and cumulative pressure drop of the target oil and gas well, and compare it with the cumulative production and cumulative pressure drop characteristic curves of three types of reservoirs—cavity type, cavity + fracture-cavity type, and fracture-cavity type—obtained from laboratory simulations, so as to determine the type of reservoir with acid fracturing and the number of fracture-cavity bodies involved in fluid supply.

Images