Method and system for evaluating compressibility of fractured tight sandstone gas reservoir

Abstract

The invention discloses a method for evaluating compressibility of a fractured tight sandstone gas reservoir. The method comprises the following steps: collecting basic parameter indexes of a to-be-evaluated well in a reservoir position; according to the basic parameter indexes of the reservoir horizon, various compressibility influence factor indexes of the reservoir horizon are calculated respectively, and various compressibility influence factors comprise a geomechanical compressibility factor, a logging compressibility factor, a reservoir physical property compressibility factor, a natural fracture compressibility factor, a fracture compressibility factor and a logging compressibility factor; and quantitatively evaluating the comprehensive compressibility index according to each compressibility influence index of the reservoir horizon. According to the method, all the characteristics influencing the compressibility of the breaking-joint-type tight sandstone are comprehensively considered, and the problem of quantitative and accurate evaluation of the breaking-joint-type tight sandstone gas reservoir dessert is effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas fracturing, and in particular to a method and system for evaluating the compressibility of fractured tight sandstone gas reservoirs. Background Art

[0002] Tight sandstone gas reservoirs need to be hydraulically fractured to obtain production. Compressibility refers to the ease of rock fracture under hydraulic fracturing. The evaluation result of the compressibility index is closely related to the engineering feasibility. High-quality compressible reservoirs are often called "sweet spots" and are important evaluation indicators for well and layer selection and process evaluation in hydraulic fracturing. Accurately predicting and evaluating compressibility is very important.

[0003] Currently, the evaluation of compressibility focuses on shale reservoirs or carbonate rock reservoirs. The evaluation of the compressibility of shale reservoirs mainly considers the brittleness index and the ability to form complex fracture networks, and tends to the characteristics of the shale matrix. The evaluation of the compressibility of carbonate rock reservoirs mainly considers the deep transformation of the reservoir, including long-distance communication of fractures / caves, etc., and tends to the extension characteristics of carbonate rocks. Tight sandstone, especially fractured tight sandstone, has the dual characteristics of natural fractures and tight reservoirs. It is difficult to fracture the reservoir without communicating with natural fractures, and low-yield and low-efficiency wells are often formed. Therefore, the focus of the evaluation of the compressibility of fractured tight sandstone is to fracture the reservoir and at the same time aim to communicate with natural fractures.

[0004] Since the focus of the evaluation of the compressibility of fractured tight sandstone is different from that of shale and carbonate rocks, its evaluation indicators and methods are also different from the two. The currently widely used methods for evaluating the compressibility of shale or carbonate rocks are not applicable to fractured tight sandstone, and there is no mature method for evaluating the compressibility of fractured tight sandstone in the prior art. Empirical estimation is mainly used, and the evaluation accuracy is low.

[0005] Therefore, the prior art needs to provide an evaluation method that can accurately evaluate the compressibility of fractured tight sandstone. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for evaluating the compressibility of a fractured tight sandstone gas reservoir, so as to provide an important parameter basis for the design optimization of single-well layer selection, segment cluster optimization, fracturing scheme, etc.

[0007] To solve the above technical problems, an embodiment of the present invention provides a method for evaluating the compressibility of fractured tight sandstone gas reservoirs, including: collecting the basic parameter indicators of the target well in the reservoir layer; calculating the indicators of various compressibility influencing factors of the reservoir layer according to the basic parameter indicators of the reservoir layer, where the various compressibility influencing factors include geomechanical compressibility factor, logging compressibility factor, reservoir physical property compressibility factor, natural fracture compressibility factor, fracture compressibility factor, and mud logging compressibility factor; quantitatively evaluating the comprehensive compressibility index according to the above-mentioned various compressibility influencing indicators of the reservoir layer.

[0008] Preferably, in the process of calculating the comprehensive compressibility index, it includes: determining the weights of various compressibility influencing factors; calculating the comprehensive compressibility index representing the compressibility difficulty of the current reservoir layer according to the indicators of various compressibility influencing factors and the corresponding weights, where the comprehensive compressibility index is calculated using the following expression:

[0009]

[0010] where f represents the comprehensive compressibility index of the current reservoir layer, i represents the serial number of the compressibility influencing factor, f i represents the index of the i-th compressibility influencing factor, and T i represents the weight of the i-th compressibility influencing factor.

[0011] Preferably, according to the actual data of the basic parameters of the target well in the reservoir layer collected, the grey relational analysis method is used to calculate the weights of various compressibility influencing factors.

[0012] Preferably, in the process of calculating the geomechanical compressibility factor of the reservoir layer, it includes: calculating the degree to which the compressibility of the current reservoir layer is affected by stress according to the reservoir burial depth index, horizontal minimum principal stress index, and horizontal maximum principal stress index of the reservoir layer, and recording it as the geomechanical compressibility factor, where the geomechanical compressibility factor is calculated using the following expression:

[0013] f 1 =12σ h / Z+0.13(σ H -σ h )

[0014] where f 1 represents the geomechanical compressibility factor of the current reservoir layer, Z represents the reservoir burial depth index of the current reservoir layer, σ H represents the horizontal maximum principal stress index of the current reservoir layer, and σ h represents the horizontal minimum principal stress index of the current reservoir layer.

[0015] Preferably, in the process of calculating the log compressibility factor of the reservoir layer, it includes: calculating the degree to which the compressibility of the current reservoir layer is affected by logging according to the longitudinal wave velocity index, shear wave velocity index, compensated acoustic travel time index, and natural gamma index of the reservoir layer, and recording it as the log compressibility factor, where the log compressibility factor is calculated using the following expression:

[0016] f 2 =3.27V P / V s +1.87AC / GR

[0017] Wherein, f 2 represents the log compressibility factor of the current reservoir layer, V P represents the longitudinal wave velocity index of the current reservoir layer, V s represents the shear wave velocity index of the current reservoir layer, AC represents the compensated acoustic travel time index of the current reservoir layer, and GR represents the natural gamma index of the current reservoir layer.

[0018] Preferably, in the process of calculating the reservoir physical property compressibility factor of the reservoir layer, it includes: calculating the degree to which the compressibility of the current reservoir layer is affected by the reservoir physical properties according to the reservoir porosity index and permeability index of the reservoir layer, and recording it as the reservoir physical property compressibility factor, where the reservoir physical property compressibility factor is calculated using the following expression:

[0019] f 3 =1.3φ+0.9K

[0020] Wherein, f 3 represents the reservoir physical property compressibility factor of the current reservoir layer, φ represents the reservoir porosity index of the current reservoir layer, and K represents the permeability index of the current reservoir layer.

[0021] Preferably, in the process of calculating the natural fracture compressibility factor of the reservoir layer, it includes: calculating the degree to which the compressibility of the current reservoir layer is affected by natural fractures according to the natural fracture dip angle index and natural fracture density index of the reservoir layer, and recording it as the natural fracture compressibility factor, where the natural fracture compressibility factor is calculated using the following expression:

[0022] f 4 =0.21c θ +45c β

[0023] Wherein, f 4 represents the natural fracture compressibility factor of the current reservoir layer, c θ represents the natural fracture dip angle index of the current reservoir layer, c β represents the natural fracture density index of the current reservoir layer.

[0024] Preferably, in the process of calculating the fracture compressibility factor of the reservoir layer, it includes: calculating the degree to which the compressibility of the current reservoir layer is affected by fractures based on the reservoir fracture length and reservoir fracture distance of the reservoir layer, denoted as the fracture compressibility factor, where the fracture compressibility factor is calculated using the following expression:

[0025] f 5 = 0.185L / S

[0026] where, f 5 represents the fracture compressibility factor of the current reservoir layer, L represents the reservoir fracture length of the current reservoir layer, and S represents the reservoir fracture distance of the current reservoir layer.

[0027] Preferably, in the process of calculating the logging compressibility factor of the reservoir layer, it includes: calculating the degree to which the compressibility of the current reservoir layer is affected by logging based on the reservoir mud loss and reservoir mud density of the reservoir layer, denoted as the logging compressibility factor, where the logging compressibility factor is calculated using the following expression:

[0028] f 6 = 0.018M V ×ρ m

[0029] where, f 6 represents the logging compressibility factor of the current reservoir layer, M V represents the reservoir mud loss of the current reservoir layer, and ρ m represents the reservoir mud density of the current reservoir layer.

[0030] On the other hand, an embodiment of the present invention provides a system for evaluating the compressibility of fractured tight sandstone gas reservoirs, including: a data collection module configured to collect the basic parameter indicators of the well to be evaluated at the reservoir layer; an influencing factor index calculation module configured to calculate the various compressibility influencing factor indicators of the reservoir layer according to the basic parameter indicators of the reservoir layer, where the various compressibility influencing factors include a geomechanics compressibility factor, a logging compressibility factor, a reservoir physical property compressibility factor, a natural fracture compressibility factor, a fracture compressibility factor, and a logging compressibility factor; and a compressibility quantitative evaluation module configured to quantitatively evaluate the comprehensive compressibility index according to the various compressibility influencing indicators of the reservoir layer.

[0031] Compared with the prior art, one or more of the above embodiments may have the following advantages or beneficial effects:

[0032] The present invention provides a method and system for evaluating the compressibility of fractured tight sandstone gas reservoirs. The method and system are based on six evaluation factors including the stress factor, logging factor, physical property factor, fracture factor, fault-fracture factor, and logging factor of the reservoir of the well to be evaluated, and combined with the parameter distribution range of the block, to conduct the compressibility evaluation of the influence of single factors. Finally, the comprehensive compressibility evaluation index of the reservoir is calculated by combining the influence weights of each factor. The present invention comprehensively considers the characteristics of various aspects (geomechanics, fault-fractures, logging, physical properties, natural fractures) that affect the compressibility of fractured tight sandstone, and effectively solves the problem of quantitative and accurate evaluation of sweet spots in fractured tight sandstone gas reservoirs.

[0033] Other features and advantages of the present invention will be described in the following specification, and in part will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained by the structures specifically pointed out in the specification, claims, and drawings. Brief Description of the Drawings

[0034] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention. In the drawings:

[0035] Figure 1 It is a schematic diagram of the steps of the method for evaluating the compressibility of fractured tight sandstone gas reservoirs according to the embodiment of the present application.

[0036] Figure 2 It is a block diagram of the modules of the system for evaluating the compressibility of fractured tight sandstone gas reservoirs according to the embodiment of the present application. Detailed Embodiments

[0037] The following will combine the drawings and embodiments to detail the implementation manners of the present invention, so as to fully understand how the present invention uses technical means to solve technical problems and achieve the realization process of technical effects and implement accordingly. It should be noted that as long as there is no conflict, the various embodiments in the present invention and the various features in each embodiment can be combined with each other, and the formed technical solutions are all within the protection scope of the present invention.

[0038] In addition, the steps shown in the flowchart of the drawings can be executed in a computer system such as a set of computer-executable instructions. And although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0039] The terms used herein are merely for describing specific embodiments and are not intended to limit the exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms "a" and "an" used herein are also intended to include the plural. It should also be understood that the terms "comprises" and / or "comprising" specify the presence of the stated features, integers, steps, operations, units and / or components, and do not preclude the presence or addition of one or more other features, integers, steps, operations, units, components and / or their combinations.

[0040] Tight sandstone gas reservoirs need to be hydraulically fractured to obtain production. Compressibility refers to the ease of rock fracture under hydraulic fracturing. The evaluation results of the compressibility index are closely related to engineering feasibility. High-quality compressible reservoirs are often referred to as "sweet spots" and are important evaluation indicators for well and layer selection and process evaluation in hydraulic fracturing. Accurately predicting and evaluating compressibility is very important.

[0041] Currently, the evaluation of compressibility focuses on shale reservoirs or carbonate reservoirs. The evaluation of the compressibility of shale reservoirs mainly considers the brittleness index and the ability to form complex fracture networks, and tends to focus on the characteristics of the shale matrix. The evaluation of the compressibility of carbonate reservoirs mainly considers the deep transformation of the reservoir, including the long-distance communication of fractures / caves, etc., and tends to focus on the extension characteristics of carbonate rocks. Tight sandstone, especially faulted tight sandstone, has the dual characteristics of natural fractures and tight reservoirs. It is difficult to fracture the reservoir without communicating with natural fractures, and it often results in low-yield and low-efficiency wells. Therefore, the focus of the compressibility evaluation of faulted tight sandstone is to fracture the reservoir and at the same time aim to communicate with natural fractures.

[0042] Since the focus of the compressibility evaluation of faulted tight sandstone is different from that of shale and carbonate rocks, its evaluation indicators and methods are also different from the two. The currently widely used methods for evaluating the compressibility of shale or carbonate rocks are not applicable to faulted tight sandstone, and there is no mature method for evaluating the compressibility of faulted tight sandstone in the prior art. Empirical estimation is mainly used, and the evaluation accuracy is low.

[0043] To solve the above technical problems, the embodiments of the present application propose a method and system for evaluating the compressibility of fractured tight sandstone gas reservoirs. Based on six evaluation factors, namely, stress factor, logging factor, physical property factor, fracture factor, fault fracture factor, and mud logging factor, of the reservoir of the well to be calculated, the compressibility evaluation of single-factor influence is carried out, and finally the comprehensive compressibility evaluation index of the reservoir of each layer is calculated by combining the weights of each factor. Thus, it provides an important parameter basis for the design optimization of single-well layer selection, segment cluster optimization, fracturing scheme, etc.

[0044] Example 1

[0045] Figure 1Schematic diagram of the steps of the method for evaluating the compressibility of fractured tight sandstone gas reservoirs according to the embodiments of the present application. The following describes the specific step flow of the method for evaluating the compressibility of fractured tight sandstone gas reservoirs (also referred to as the "compressibility evaluation method") described in the embodiments of the present invention.

[0046] As Figure 1 shown, in step S110, the basic parameter indicators of the well to be evaluated at the reservoir layer are collected. In step S110, in the step of collecting the basic parameters of the reservoir layer, according to the actual data of the basic parameters of the reservoir layer collected in the embodiments of the present invention, each basic parameter indicator corresponding to the reservoir layer in the well to be evaluated is calculated.

[0047] Among them, in the embodiments of the present invention, the basic parameters include reservoir burial depth Z, longitudinal wave velocity V P , shear wave velocity V s , minimum horizontal principal stress σ h , maximum horizontal principal stress σ H , compensated acoustic travel time AC, natural gamma GR, porosity φ, permeability K, natural fracture dip angle c θ , natural fracture density c β , fracture length L, fracture surface distance S, mud loss volume M V , density of lost mud ρ m .

[0048] In one embodiment, the vertical depth of the middle part of the reservoir in the reservoir layer is used as the reservoir burial depth (indicator) Z of the current layer.

[0049] In one embodiment, all the minimum horizontal principal stress data and all the maximum horizontal principal stress data sets of the reservoir layer can be obtained through the wellbore trajectory data in the drilling and completion report, so as to obtain the minimum horizontal principal stress (indicator) σ of the reservoir layer to be evaluated in the well to be evaluated by calculating the average value of the minimum horizontal principal stress data h , and the maximum horizontal principal stress (indicator) σ of the reservoir layer to be evaluated in the well to be evaluated is obtained by calculating the average value of the maximum horizontal principal stress data H .

[0050] In one embodiment, the longitudinal wave velocity (indicator) V of the current reservoir layer P , shear wave velocity (indicator) V s , compensated acoustic travel time (indicator) AC, and natural gamma (indicator) GR are all calculated by taking the average value of all the actual data of the direct reading parameters of the logging-while-drilling instrument in the reservoir section of the well to be evaluated.

[0051] In one embodiment, the porosity (index) φ of the current reservoir layer is the weighted average of all porosity data in the reservoir section by thickness. Additionally, it can also be obtained through laboratory core porosity tests, or calculated from well logging data. The permeability (index) K of the current reservoir layer is the average of the permeability data of all thicknesses in the reservoir section. Additionally, the permeability can also be obtained through permeability tests after reservoir coring, or calculated from conventional well logging data.

[0052] In one embodiment, the dip angle (index) c of natural fractures in the current reservoir layer θ is the average of the dip angles of all natural fractures in the target layer section, and the natural fracture density (index) c β is the geometric mean of the densities of all natural fractures in the target layer section. Additionally, both the dip angle index and the density index of natural fractures in the reservoir layer can be obtained through acoustic far detection, core observation, or downhole imaging logging data.

[0053] In one embodiment, both the fracture length L and the fracture surface distance S of the current reservoir layer can be obtained from 3D seismic interpretation data.

[0054] In one embodiment, the mud loss volume M V and the density ρ of the lost mud m of the current reservoir layer can both be obtained from the logging data in the drilling and completion report.

[0055] Thus, after collecting and calculating the actual data, it proceeds to step S120.

[0056] Reference Figure 1 , in step S120, according to the various basic parameter indexes of the reservoir layer collected in step S110, the indexes of various factors affecting the compressibility of the reservoir layer are calculated respectively. The indexes of various factors affecting compressibility are evaluation indexes for the degree of influence of the reservoir compressibility from different factor aspects. In the embodiments of the present invention, the various factors affecting compressibility include: geomechanical compressibility factor, logging compressibility factor, reservoir physical property compressibility factor, natural fracture compressibility factor, fracture compressibility factor, and logging compressibility factor.

[0057] Furthermore, in the process of calculating the geomechanical compressibility factor of the reservoir layer, it includes: calculating the degree to which the compressibility of the current reservoir layer is affected by stress based on the reservoir burial depth index, horizontal minimum principal stress index, and horizontal maximum principal stress index of the reservoir layer, denoted as the geomechanical compressibility factor.

[0058] In one embodiment, first calculate the ratio of the horizontal minimum principal stress index to the reservoir burial depth index, denoted as the first ratio; then calculate the difference between the horizontal maximum principal stress index and the horizontal minimum principal stress index, and thus obtain the geomechanical compressibility factor by calculating the weighted sum of the first ratio and the horizontal principal stress difference. Among them, the geomechanical compressibility factor is calculated using the following expression:

[0059] f 1 =12σ h / Z + 0.13(σ H -σ h ) (1)

[0060] Among them, f 1 represents the geomechanical compressibility factor of the current reservoir layer, dimensionless; Z represents the reservoir burial depth index of the current reservoir layer, with the unit of m; σ H represents the horizontal maximum principal stress index of the current reservoir layer, with the unit of MPa; σ h represents the horizontal minimum principal stress index of the current reservoir layer, with the unit of MPa.

[0061] Furthermore, in the process of calculating the log compressibility factor of the reservoir layer, it includes: calculating the degree to which the compressibility of the current reservoir layer is affected by logging according to the longitudinal wave velocity index, shear wave velocity index, compensated acoustic travel time index, and natural gamma index of the reservoir layer, denoted as the log compressibility factor.

[0062] In one embodiment, first calculate the ratio of the longitudinal wave velocity index to the shear wave velocity index, denoted as the second ratio; then calculate the ratio of the compensated acoustic travel time index to the natural gamma index, denoted as the third ratio, and thus obtain the log compressibility factor by calculating the weighted sum of the second ratio and the third ratio. Among them, the log compressibility factor is calculated using the following expression:

[0063] f 2 =3.27V P / V s +1.87AC / GR (2)

[0064] Among them, f 2 represents the log compressibility factor of the current reservoir layer, dimensionless; V P represents the longitudinal wave velocity index of the current reservoir layer, with the unit of km / s; V s represents the shear wave velocity index of the current reservoir layer, with the unit of km / s; AC represents the compensated acoustic travel time index of the current reservoir layer, with the unit of μs / ft; GR represents the natural gamma index of the current reservoir layer, with the unit of API.

[0065] Further, in the process of calculating the reservoir physical property compressibility factor of the reservoir layer, it includes: calculating, based on the reservoir porosity index and permeability index of the reservoir layer, the degree to which the compressibility of the current reservoir layer is affected by the reservoir physical properties, denoted as the reservoir physical property compressibility factor.

[0066] In one embodiment, the reservoir physical property compressibility factor is obtained by calculating the weighted sum of the reservoir porosity index and the permeability index. Among them, the reservoir physical property compressibility factor is calculated using the following expression:

[0067] f 3 =1.3φ + 0.9K (3)

[0068] Among them, f 3 represents the reservoir physical property compressibility factor of the current reservoir layer, dimensionless; φ represents the reservoir porosity index of the current reservoir layer, with the unit of %; K represents the permeability index of the current reservoir layer, with the unit of mD.

[0069] Further, in the process of calculating the natural fracture compressibility factor of the reservoir layer, it includes: calculating, based on the natural fracture dip angle index and natural fracture density index of the reservoir layer, the degree to which the compressibility of the current reservoir layer is affected by the natural fractures, denoted as the natural fracture compressibility factor.

[0070] In one embodiment, the natural fracture compressibility factor is obtained by calculating the weighted sum of the natural fracture dip angle index and the natural fracture density index. Among them, the natural fracture compressibility factor is calculated using the following expression:

[0071] f 4 =0.21c θ + 45c β (4)

[0072] Among them, f 4 represents the natural fracture compressibility factor of the current reservoir layer, dimensionless; c θ represents the natural fracture dip angle index of the current reservoir layer, with the unit of °; c β represents the natural fracture density index of the current reservoir layer, with the unit of fractures per meter.

[0073] Further, in the process of calculating the fracture compressibility factor of the reservoir layer, it includes: calculating, based on the reservoir fracture length and reservoir fracture distance of the reservoir layer, the degree to which the compressibility of the current reservoir layer is affected by the fractures, denoted as the fracture compressibility factor.

[0074] In one embodiment, first calculate the ratio of the reservoir fracture length to the reservoir fracture distance, denoted as the fourth ratio; then multiply the fourth ratio by the first preset coefficient to obtain the fracture compressibility factor. Among them, the fracture compressibility factor is calculated using the following expression:

[0075] f 5 = 0.185 L / S (5)

[0076] where f 5 represents the fracture compressibility factor of the current reservoir layer, dimensionless; L represents the reservoir fracture length of the current reservoir layer, with the unit of m; S represents the reservoir fracture distance of the current reservoir layer, with the unit of m. In the embodiment of the present invention, the first preset coefficient is 0.185.

[0077] Furthermore, in the process of calculating the logging compressibility factor of the reservoir layer, it includes: calculating the degree of influence of logging on the compressibility of the current reservoir layer based on the mud loss volume and mud density of the reservoir layer, denoted as the logging compressibility factor.

[0078] In one embodiment, multiplying the mud loss volume of the reservoir layer, the mud density of the reservoir layer, and the second preset coefficient to obtain the logging compressibility factor. Among them, the logging compressibility factor is calculated using the following expression:

[0079] f 6 = 0.018 M V × ρ m (6)

[0080] where f 6 represents the logging compressibility factor of the current reservoir layer, dimensionless; M V represents the mud loss volume of the reservoir layer of the current reservoir layer, with the unit of m 3 ; ρ m represents the mud density of the reservoir layer of the current reservoir layer, with the unit of g / cm 3 . In the embodiment of the present invention, the first preset coefficient is 0.018.

[0081] In this way, the embodiment of the present invention uses the above expressions (1) to (6) to calculate the indexes of various compressibility influencing factors of the reservoir layer of the well to be evaluated, so as to characterize the influence degree of the actual data of different factors of the current reservoir layer on compressibility, and thus enter step S130.

[0082] Step S130 quantitatively evaluates the comprehensive compressibility index of the current reservoir layer according to the various compressibility influencing indexes of the reservoir layer.

[0083] In one embodiment, according to the various compressibility influencing indexes of the reservoir layer, a weighted average algorithm is used to quantitatively evaluate the comprehensive compressibility index of the current reservoir layer.

[0084] Specifically, first determine the weights of various compressibility influencing factors; using the weighted average method, calculate the comprehensive compressibility index representing the compressibility difficulty of the current reservoir layer according to the indicators and corresponding weights of various compressibility influencing factors.

[0085] In one embodiment, the weights of various compressibility influencing factors can be calculated by using the grey correlation method according to the actual data of the basic parameters of the well to be evaluated in the reservoir layer. For example, the weights of the geomechanics compressibility factor, logging compressibility factor, reservoir physical property compressibility factor, natural fracture compressibility factor, fault compressibility factor, and mud logging compressibility factor are 13.01%, 11.58%, 9.49%, 27.32%, 20.48%, and 18.12% respectively.

[0086] In one embodiment, the comprehensive compressibility index can be calculated using the following expression:

[0087]

[0088] where f represents the comprehensive compressibility index of the current reservoir layer, i represents the serial number of the compressibility influencing factor, f i represents the index of the i-th compressibility influencing factor, and T i represents the weight of the i-th compressibility influencing factor.

[0089] Example 2

[0090] Based on the compressibility evaluation method described in Embodiment 1, in an embodiment of the present invention, a well Y to be evaluated in a fractured tight sandstone in the Sichuan Basin is taken as an example for compressibility evaluation.

[0091] Step A: Collect the basic parameters of the reservoir of Well Y, with the burial depth Z being 4725 m, the horizontal minimum principal stress σ h being 94.3 MPa, the horizontal maximum principal stress σ H being 131.5 MPa, the longitudinal wave velocity V p being km / s, the shear wave velocity V s being km / m, the compensated acoustic wave transit time AC being 61.1 μs / ft, the natural gamma ray GR being 121.1 API, the porosity φ being 3.8%, the permeability K being 0.045 mD, the dip angle c θ of the natural fracture being 34°, the density c β of the natural fracture being 0.16 fractures / m, the fracture length L being 1453 m, the cross-section distance S being 25 m, the mud loss amount M V being 322 m 3 and the density ρ m of the lost mud being 1.64 g / cm 3 .

[0092] Step B: The burial depth H of the reservoir is 4,725 m, and the horizontal minimum principal stress σ h is 94.3 MPa, and the horizontal maximum principal stress σ H is 131.5 MPa. Calculate the compressibility score f 1 affected by stress according to Expression (1) to be 6.83.

[0093] Step C: The longitudinal wave velocity V p of the reservoir is 5.14 km / s, the shear wave velocity V s is 3.27 km / m, the compensated acoustic travel time AC is 61.1 μs / ft, and the natural gamma ray GR is 121.1 API. Calculate the compressibility factor score f 2 affected by well logging according to Expression (2) to be 6.08.

[0094] Step D: The porosity φ of the reservoir is 3.8%, and the permeability K is 0.045 mD. Calculate the compressibility score f 3 of the reservoir physical properties according to Expression (3) to be 4.98.

[0095] Step E: The dip angle c θ of the natural fractures in the reservoir is 34°, and the natural fracture density c β is 0.16 fractures / m. Calculate the compressibility score f 4 affected by the fracture factor according to Expression (4) to be 14.34.

[0096] Step F: The fracture length L of the reservoir is 1,453 m, and the section distance S is 25 m. Calculate the compressibility score f 5 affected by the fracture according to Expression (5) to be 10.75.

[0097] Step G: The mud loss volume M V of the reservoir is 322 m 3 , and the density ρ m of the lost mud is 1.64 g / cm 3 . Calculate the compressibility score f 6 of the mud logging factor according to Expression (6) to be 9.51.

[0098] Step H: Based on the compressibility scores f 1 ~f 6 of the six factors obtained in Steps A - G, which are 6.83, 6.08, 4.98, 14.34, 10.75, and 9.51 respectively, and the weights corresponding to these six factors are 13.01%, 11.58%, 9.49%, 27.32%, 20.48%, and 18.12% in sequence. Calculate the comprehensive reservoir compressibility index f of Well Y to be 9.91 according to Expression (7).

[0099] At present, this design method has been applied on-site 18 times in a deep fracture-type tight sandstone in the Sichuan Basin. The accuracy rate of the compressibility evaluation is 91.82%. Compared with the previous empirical prediction method, the accuracy rate has increased by 35.7%, and the application effect is remarkable.

[0100] Example 3

[0101] Based on the compressibility evaluation method described in the above-mentioned Example 1 or Example 2, the present invention also provides a system for evaluating the compressibility of fractured tight sandstone gas reservoirs (also referred to as the "compressibility evaluation system").

[0102] Figure 2 It is a module block diagram of the system for evaluating the compressibility of fractured tight sandstone gas reservoirs in the embodiments of this application. As Figure 2 shown, the quantitative evaluation system described in the embodiments of the present invention includes: a data collection module 21, an influencing factor index calculation module 22, and a compressibility quantitative evaluation module 23.

[0103] Specifically, the data collection module 21 is implemented according to the method described in the above step S110, and is configured to collect the basic parameter indexes of the target well in the reservoir layer; the influencing factor index calculation module 22 is implemented according to the method described in the above step S120, and is configured to calculate each compressibility influencing factor index of the reservoir layer according to the basic parameter indexes of the reservoir layer. Among them, each compressibility influencing factor includes a geomechanical compressibility factor, a logging compressibility factor, a reservoir physical property compressibility factor, a natural fracture compressibility factor, a fracture compressibility factor, and a mud logging compressibility factor; the compressibility quantitative evaluation module 23 is implemented according to the method described in the above step S130, and is configured to quantitatively evaluate the comprehensive compressibility index according to the above-mentioned various compressibility influencing indexes of the reservoir layer.

[0104] The present invention discloses a method and a system for evaluating the compressibility of fractured tight sandstone gas reservoirs. Based on six evaluation factors including the stress factor, logging factor, physical property factor, fracture factor, fracture and seam factor, and mud logging factor of the reservoir of the target well, combined with the parameter distribution range of the block, the compressibility evaluation of single-factor influence is carried out, and finally the reservoir comprehensive compressibility evaluation index is calculated by combining the influence weights of each factor. The present invention comprehensively considers the characteristics of various aspects (geomechanics, fracture and seam, logging, physical properties, natural fractures) affecting the compressibility of fractured tight sandstone, and effectively solves the problem of accurate quantitative evaluation of sweet spots in fractured tight sandstone gas reservoirs.

[0105] As described above, it is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

[0106] In the description of the present invention, unless otherwise specified, the meaning of "a plurality of" is two or more; the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention. In addition, terms such as "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0107] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0108] It should be understood that the embodiments disclosed by the present invention are not limited to the specific structures, processing steps or materials disclosed herein, but should extend to equivalent alternatives of these features understood by those of ordinary skill in the relevant art. It should also be understood that the terms used herein are only for the purpose of describing specific embodiments and do not mean to limit.

[0109] The "one embodiment" or "embodiment" mentioned in the specification means that the specific features, structures or characteristics described in connection with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment" or "embodiment" appearing throughout the specification do not necessarily all refer to the same embodiment.

[0110] Although the embodiments disclosed by the present invention are as above, the content described is only the embodiment adopted for the convenience of understanding the present invention and is not used to limit the present invention. Any person skilled in the art within the technical field to which the present invention pertains can make any modifications and changes in the form of implementation and details without departing from the spirit and scope disclosed by the present invention. However, the patent protection scope of the present invention must still be subject to the scope defined by the appended claims.

Claims

1. A method for evaluating the compressibility of fractured tight sandstone gas reservoirs, characterized in that, it includes: Collecting the basic parameter indicators of the reservoir layer of the well to be evaluated; According to the basic parameter indicators of the reservoir layer, calculating the indicators of various compressibility influencing factors of the reservoir layer respectively, where each compressibility influencing factor includes a geomechanical compressibility factor, a logging compressibility factor, a reservoir physical property compressibility factor, a natural fracture compressibility factor, a fracture compressibility factor, and a mud logging compressibility factor; Quantitatively evaluating the comprehensive compressibility index according to the above-mentioned various compressibility influencing indicators of the reservoir layer.

2. The method according to claim 1, characterized in that, In the process of calculating the comprehensive compressibility index, it includes: Determining the weights of various compressibility influencing factors; Calculating the comprehensive compressibility index representing the compressibility difficulty of the current reservoir layer according to the indicators and corresponding weights of various compressibility influencing factors, where the comprehensive compressibility index is calculated using the following expression: Among them, f represents the comprehensive compressibility index of the current reservoir layer position, i represents the serial number of the compressibility influencing factors, and f i represents the index of the i-th compressibility influencing factor, and T i represents the weight of the i-th compressibility influencing factor.

3. The method according to claim 2, characterized in that, According to the actual data of the basic parameters of the reservoir layer of the well to be evaluated collected, using the grey correlation method to calculate the weights of various compressibility influencing factors.

4. The method according to any one of claims 1 to 3, characterized in that, In the process of calculating the geomechanical compressibility factor of the reservoir layer, it includes: According to the reservoir burial depth index, horizontal minimum principal stress index, and horizontal maximum principal stress index of the reservoir layer, calculating the degree to which the compressibility of the current reservoir layer is affected by stress, denoted as the geomechanical compressibility factor, where the geomechanical compressibility factor is calculated using the following expression: f 1 = 12σ h / Z + 0.13(σ H - σ h ) Among them, f 1 represents the geomechanical compressibility factor of the current reservoir layer, Z represents the reservoir burial depth index of the current reservoir layer, and σ H represents the horizontal maximum principal stress index of the current reservoir layer, and σ h represents the horizontal minimum principal stress index of the current reservoir layer.

5. The method according to any one of claims 1 to 4, characterized in that, In the process of calculating the logging compressibility factor of the reservoir layer, it includes: According to the longitudinal wave velocity index, transverse wave velocity index, compensated acoustic travel time index, and natural gamma index of the reservoir layer, calculating the degree to which the compressibility of the current reservoir layer is affected by logging, denoted as the logging compressibility factor, where the logging compressibility factor is calculated using the following expression: f 2 = 3.27 V P / V s + 1.87 AC / GR Among them, f 2 represents the logging compressibility factor of the current reservoir layer, V P represents the longitudinal wave velocity index of the current reservoir layer, V s represents the shear wave velocity index of the current reservoir layer, AC represents the compensated acoustic travel time index of the current reservoir layer, and GR represents the natural gamma index of the current reservoir layer.

6. The method according to any one of claims 1 to 5, characterized in that, In the process of calculating the reservoir physical property compressibility factor of the reservoir layer, it includes: According to the reservoir porosity index and permeability index of the reservoir layer, calculating the degree to which the compressibility of the current reservoir layer is affected by reservoir physical properties, denoted as the reservoir physical property compressibility factor, where the reservoir physical property compressibility factor is calculated using the following expression: f 3 = 1.3φ + 0.9K Among them, f 3 represents the compressibility factor of reservoir physical properties of the current reservoir layer, φ represents the reservoir porosity index of the current reservoir layer, and K represents the permeability index of the current reservoir layer.

7. The method according to any one of claims 1 to 6, characterized in that, In the process of calculating the natural fracture compressibility factor of the reservoir layer, it includes: According to the natural fracture dip angle index and natural fracture density index of the reservoir layer, calculating the degree to which the compressibility of the current reservoir layer is affected by natural fractures, denoted as the natural fracture compressibility factor, where the natural fracture compressibility factor is calculated using the following expression: f 4 = 0.21c θ + 45c β Among them, f 4 represents the compressibility factor of natural fractures at the current reservoir layer position, c θ represents the dip angle index of natural fractures at the current reservoir layer position, c β represents the density index of natural fractures at the current reservoir layer position.

8. The method according to any one of claims 1 to 7, characterized in that, In the process of calculating the fracture compressibility factor of the reservoir layer, it includes: According to the reservoir fracture length and reservoir fracture distance of the reservoir layer, the degree to which the compressibility of the current reservoir layer is affected by fractures is calculated and denoted as the fracture compressibility factor. Among them, the fracture compressibility factor is calculated using the following expression: f 5 = 0.185 L / S Among them, f 5 represents the fracture compressibility factor of the current reservoir layer, L represents the reservoir fracture length of the current reservoir layer, and S represents the reservoir fracture distance of the current reservoir layer.

9. The method according to any one of claims 1 to 8, characterized in that, in the process of calculating the logging compressibility factor of the reservoir layer, it includes: According to the reservoir mud loss amount and reservoir mud density of the reservoir layer, the degree to which the compressibility of the current reservoir layer is affected by logging is calculated and denoted as the logging compressibility factor. Among them, the logging compressibility factor is calculated using the following expression: f 6 = 0.018M V × ρ m Among them, f 6 represents the logging compressibility factor of the current reservoir layer, M V represents the mud loss volume of the reservoir in the current reservoir layer, ρ m represents the mud density of the reservoir in the current reservoir layer.

10. A system for evaluating the compressibility of fractured tight sandstone gas reservoirs, characterized in that, comprising: a data collection module configured to collect the basic parameter indicators of the well to be evaluated at the reservoir layer; an influencing factor index calculation module configured to calculate the various compressibility influencing factor indicators of the reservoir layer according to the basic parameter indicators of the reservoir layer, wherein the various compressibility influencing factors include the geomechanical compressibility factor, the logging compressibility factor, the reservoir physical property compressibility factor, the natural fracture compressibility factor, the fracture compressibility factor, and the logging compressibility factor; a compressibility quantitative evaluation module configured to quantitatively evaluate the comprehensive compressibility index according to the various compressibility influencing indicators of the reservoir layer.

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