A method, system and device for calculating unconventional reservoir brittleness indicator curve

Abstract

The present invention proposes a method, system, and apparatus for calculating an unconventional reservoir brittleness indicator curve. The method comprises: determining the shale content based on a well logging data curve and reservoir rock physical parameter information; and determining the brittleness indicator curve based on the shale content and well logging porosity. The method, system, and apparatus for calculating an unconventional reservoir brittleness indicator curve of the present invention, based on conventional P-wave logging, density logging, and porosity logging information, integrates rock physical analysis to construct a brittleness indicator curve calculation formula, and implements brittleness indicator parameter calculation and evaluation under conventional logging conditions. This method does not rely on S-wave logging information and is not affected by human factors. It is a highly applicable and accurate brittleness index extraction method. Conducting shale gas reservoir brittleness evaluation based on this method will effectively improve the accuracy of shale gas reservoir fracturing evaluation and reduce the risks of exploration and development.

Description

Technical Field

[0001] The present invention belongs to the field of petroleum geophysical exploration, and in particular relates to a method, system and equipment for calculating an unconventional reservoir brittleness indicator curve. Background Art

[0002] With the continuous deepening of exploration, conventional reservoir exploration has gradually entered the development stage. In order to find new reserve growth points, unconventional exploration has received increasing attention, especially shale gas exploration. Shale gas resources are vast worldwide and equally abundant in my country, especially in the Sichuan Basin and the Tarim Basin. The main task of shale gas exploration is to find the target "sweet spot". The evaluation of shale gas reservoirs is mainly carried out from three aspects: the source rock quality (TOC content), reservoir properties (porosity and saturation), and rock fracturing ability (brittleness index). TOC content determines the hydrocarbon generation capacity of shale, while the brittleness index determines the fracturing ability of shale. Because shale itself has relatively low porosity and permeability, shale reservoirs need to be fractured during the production process to obtain better oil and gas migration pathways and increase the shale gas constant. Given the quality of source rocks, the brittleness index of shale determines the feasibility and production efficiency of exploration and development. Therefore, it is crucial to conduct brittleness assessments tailored to the characteristics of my country's shale gas reservoirs. This allows for the identification of favorable areas for shale fracturing and targeted deployment of exploration wells, thereby increasing shale gas production. Currently, conventional brittleness assessment methods primarily include brittleness index calculations based on P- and S-wave information and brittleness index calculations based on mineral composition. The first P- and S-wave-based prediction method primarily uses P- and S-wave parameters to calculate elastic parameters such as Young's modulus or Poisson's ratio, then establishes a relationship between these elastic parameters and the brittleness index. This method, however, is characterized by its high data requirements, requiring P- and S-wave logging data for well logging and prestack seismic gathers for seismic analysis. The mineral composition-based brittleness index calculation method characterizes brittleness by calculating the proportion of brittle minerals. However, this method is not widely applicable across regions and requires separate mineral type and content calculations for different regions and even different formations. Its application is subject to significant human influence and lacks a theoretical foundation in rock physics.

[0003] In response to the problems existing in conventional brittleness index evaluation methods for shale gas exploration, the present invention proposes a brittleness index calculation method and device. This method combines the advantages of current brittleness index evaluation methods while overcoming the high data requirements and serious human influence of conventional methods. It realizes brittleness index evaluation based on conventional logging data and improves the accuracy of shale gas exploration. This method is based on conventional P-wave logging, density logging, and porosity logging information, integrates rock physics analysis, constructs a brittleness indicator curve calculation formula, and realizes the calculation and evaluation of brittleness indicator parameters under conventional logging conditions. This method does not rely on S-wave logging information and is not affected by human factors. It is a brittleness index extraction method with strong applicability and high accuracy. Carrying out shale gas reservoir brittleness evaluation based on this method will effectively improve the accuracy of shale gas reservoir fracturing evaluation and reduce the risk of exploration and development. Summary of the Invention

[0004] In response to the above problems, the present invention proposes a method for calculating the brittleness indicator curve of unconventional reservoirs, the method comprising:

[0005] Determine the shale content based on the well logging data curve and reservoir rock physical parameter information;

[0006] The brittleness indicator curve is determined based on the mud content and logging porosity.

[0007] Furthermore, the logging data curve includes compressional wave velocity, density and porosity;

[0008] The reservoir rock physical parameters include the longitudinal wave velocity of the rock matrix, the density of the rock matrix; the longitudinal wave velocity of the saturated fluid in the pores, the density of the saturated fluid in the pores; the longitudinal wave velocity of the clay and the density of the clay.

[0009] Furthermore, the mud content is expressed as:

[0010]

[0011] Where Vsh represents the mud content, ρ ma represents the density of the rock matrix, Vp represents the P-wave velocity, ρ represents the density, Vpma represents the P-wave velocity of the rock matrix, φ represents the porosity, Vpfl represents the P-wave velocity of the saturated fluid in the pores, ρ fl represents the density of the saturated fluid in the pores, ρ sh represents the density of clay, and Vpsh represents the longitudinal wave velocity of clay.

[0012] Furthermore, a brittleness index is determined according to the shale content and the logging porosity, and the logging data curve and reservoir rock physical parameter information are substituted into the brittleness index to obtain a brittleness indication curve.

[0013] Furthermore, the brittleness index is expressed as:

[0014]

[0015] Where BI represents the brittleness index and φ represents the porosity.

[0016] The present invention also provides a calculation system for an unconventional reservoir brittleness indicator curve, the system comprising: a first determination unit and a curve determination unit,

[0017] The first determining unit is used to determine the shale content according to the well logging data curve and reservoir rock physical parameter information;

[0018] The curve determining unit is in communication with the first determining unit and is used to determine a brittleness indication curve according to the mud content and the logging porosity.

[0019] Furthermore, the logging data curve includes compressional wave velocity, density and porosity;

[0020] The reservoir rock physical parameters include the longitudinal wave velocity of the rock matrix, the density of the rock matrix; the longitudinal wave velocity of the saturated fluid in the pores, the density of the saturated fluid in the pores; the longitudinal wave velocity of the clay and the density of the clay.

[0021] Furthermore, the mud content is expressed as:

[0022]

[0023] Where Vsh represents the mud content, ρ ma represents the density of the rock matrix, Vp represents the P-wave velocity, ρ represents the density, Vpma represents the P-wave velocity of the rock matrix, φ represents the porosity, Vpfl represents the P-wave velocity of the saturated fluid in the pores, ρ fl represents the density of the saturated fluid in the pores, ρ sh represents the density of clay, and Vpsh represents the longitudinal wave velocity of clay.

[0024] Furthermore, the curve determination unit is used to determine the brittleness indication curve according to the mud content and the well logging porosity, including:

[0025] The brittleness index is determined according to the shale content and the logging porosity, and the logging data curve and the reservoir rock physical parameter information are substituted into the brittleness index to obtain a brittleness indication curve.

[0026] Furthermore, the brittleness index is expressed as:

[0027]

[0028] Where BI represents the brittleness index and φ represents the porosity.

[0029] The present invention also provides a device for calculating an unconventional reservoir brittleness indicator curve, the device comprising at least one processor and at least one memory, the memory being electrically connected to the processor, wherein:

[0030] The memory stores instructions that can be executed by the at least one processor. The instructions are executed by the at least one processor to enable the at least one processor to perform the above-mentioned method for calculating the unconventional reservoir brittleness indicator curve.

[0031] The unconventional reservoir brittleness indicator curve calculation method, system and equipment of the present invention are based on conventional longitudinal wave logging, density logging and porosity logging information, integrated with rock physical analysis, to construct a brittleness indicator curve calculation formula, and realize the calculation and evaluation of brittleness indicator parameters under conventional logging conditions. This method does not rely on shear wave logging information and is not affected by human factors. It is a brittleness index extraction method with strong applicability and high accuracy. Conducting shale gas reservoir brittleness evaluation based on this method will effectively improve the accuracy of shale gas reservoir fracturing evaluation and reduce the risk of exploration and development.

[0032] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 A schematic diagram of a flow chart of a method for calculating an unconventional reservoir brittleness indicator curve in an embodiment of the present invention is shown;

[0035] Figure 2 A schematic diagram of the structure of the unconventional reservoir brittleness indicator curve calculation system in an embodiment of the present invention is shown;

[0036] Figure 3 A comparison diagram of the brittleness indication curve obtained by calculation and the oil test conclusion in an embodiment of the present invention is shown;

[0037] Figure 4 The diagram shows a distribution diagram of favorable shale gas reservoirs predicted based on the brittleness indicator curve in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0039] The present invention provides a method for calculating the brittleness indicator curve of unconventional reservoirs. Figure 1 The following is a flow chart of a method for calculating an unconventional reservoir brittleness indicator curve in an embodiment of the present invention. Figure 1 The method includes determining the shale content according to the well logging data curve and the reservoir rock physical parameter information; and determining the brittleness indicator curve according to the shale content and the well logging porosity.

[0040] Specifically, the logging data curve includes P-wave velocity, density and porosity; the reservoir rock physical parameters include the P-wave velocity of the rock matrix, the density of the rock matrix; the P-wave velocity of the saturated fluid in the pores, the density of the saturated fluid in the pores; the P-wave velocity of clay and the density of clay.

[0041] Specifically, the mud content is expressed as:

[0042]

[0043] Where Vsh represents the mud content, ρ ma represents the density of the rock matrix, Vp represents the P-wave velocity, ρ represents the density, Vpma represents the P-wave velocity of the rock matrix, φ represents the porosity, Vpfl represents the P-wave velocity of the saturated fluid in the pores, ρ fl represents the density of the saturated fluid in the pores, ρ sh represents the density of clay, and Vpsh represents the longitudinal wave velocity of clay.

[0044] Specifically, in an embodiment of the present invention, a brittleness index is determined based on the shale content and the logging porosity, and the logging data curve and reservoir rock physical parameter information are substituted into the brittleness index to obtain a brittleness indication curve.

[0045] Specifically, the brittleness index is expressed as:

[0046]

[0047] Where BI represents the brittleness index and φ represents the porosity.

[0048] The embodiment of the present invention further describes in detail the calculation method of the unconventional reservoir brittleness indicator curve with reference to the accompanying drawings:

[0049] Step 101: Obtain compressional wave velocity, density, and porosity logging curve data:

[0050] Specifically, the P-wave velocity, density, and porosity logging curve data of the wells drilled in the study area are obtained. In the embodiment of the present invention, the logging curve data is within the scope of conventional logging data acquisition and does not limit the method of obtaining the logging data.

[0051] Step 102: Input reservoir rock physical parameter information:

[0052] In the embodiment of the present invention, the input reservoir rock physical parameters include the P-wave velocity and density of the rock matrix; the P-wave velocity and density of the saturated fluid in the pores; and the P-wave velocity and density of the clay. In the embodiment of the present invention, the rock matrix is ​​selected as quartz, and the saturated fluid in the pores is selected as natural gas, that is, the input rock physical parameters are the P-wave velocity and density of quartz, and the P-wave velocity and density of natural gas. In the embodiment of the present invention, the selection of the rock matrix and the saturated fluid in the pores is an adaptive choice. Without departing from the technical concept of the present invention, changes only in the types of the rock matrix and the saturated fluid in the pores are also within the scope of protection of the present invention.

[0053] Step 103: Determine the shale content based on the well logging data curve and reservoir rock physical parameter information, and determine the brittleness indicator curve based on the shale content and the well logging porosity:

[0054] In the embodiment of the present invention, according to rock physics theory, the calculation formula of the longitudinal wave velocity of the logging data curve is:

[0055]

[0056] Where Vp is the P-wave velocity in m / s, φ is the porosity, dimensionless, Vsh is the shale content, dimensionless, Vpma is the P-wave velocity of the rock matrix, in m / s, Vpsh is the P-wave velocity of the clay, in m / s, and Vpfl is the P-wave velocity of the saturated fluid in the pores, in m / s.

[0057] The density calculation formula of the logging data curve is:

[0058] ρ=(1-φ-Vsh)ρ ma +Vshρ sh +φρ fl (2)

[0059] Where ρ represents the density of the shale reservoir, in g / cm 3 , ρ ma Indicates the density of the rock matrix (quartz) in g / cm3 , ρ sh Indicates the density of clay in g / cm 3 , ρ fl Indicates the density of natural gas saturated in the pores, in g / cm 3 ;

[0060] According to formula (1) and formula (2), the calculation formula of mud content Vsh can be derived as follows:

[0061]

[0062] According to the brittleness index calculation formula:

[0063]

[0064] Where BI represents the brittleness index, φ represents the porosity, and Vsh represents the shale content;

[0065] Substituting the clay content calculation formula into the brittleness index formula, the final brittleness index calculation formula can be obtained as shown below:

[0066]

[0067] According to the brittleness index calculation formula, the obtained P-wave velocity, density, porosity logging curves and reservoir rock physical parameter information are substituted into it to calculate the brittleness indicator curve;

[0068] Figure 3 The figure shows the comparison between the brittleness indication curve calculated in the embodiment of the present invention and the oil test conclusion. Figure 3 The left curve in the middle is the calculated brittleness indicator curve, and the right is the test interpretation conclusion. The asterisk area in the figure is the actual drilling test area. The actual drilling results confirm that this area is a high-yield gas layer, and the corresponding shale rock is well fracturable. After fracturing treatment, the connected pores in this area are greatly increased, and the oil and gas migration is smooth. The test results show high gas production. The core sampling analysis confirms that the shale brittleness index in this area is large (greater than 30), which is significantly different from the overlying and underlying strata. Comparing the calculated brittleness indicator curve with the test interpretation conclusion, it can be seen that when the brittleness indicator curve value is greater than 30, it corresponds to the distribution range of the effective gas layer (dark area), and when the brittleness indicator curve value is less than or equal to 30, it corresponds to the distribution range of the invalid reservoir (light area). The analysis results show that the brittleness indicator curve calculated based on the method proposed in this application can accurately identify the distribution range of the effective shale gas reservoir, effectively reducing the risk of shale gas exploration.

[0069] Step 104: Predict the distribution range of favorable shale gas reservoirs based on the brittleness indicator curve:

[0070] During the implementation process, the brittleness indicator curve data body of the work area is calculated based on the brittleness indicator curve constructed in step 103, and then based on the conclusion that the brittleness index determined by core analysis is greater than 30, it is determined to be an effective reservoir, and the prediction of shale gas effective reservoirs within the work area is carried out. Figure 4 This is a distribution map of favorable shale gas reservoirs predicted based on the brittleness indicator curve in the embodiment. The dark area in the figure corresponds to the range where the brittleness indicator curve value is greater than 30, and the light area corresponds to the range where the brittleness indicator curve value is less than or equal to 30. The drilled well-1 in the figure is a high-yield gas well at the depth of the target layer. The predicted brittleness indicator curve value at the corresponding well point reaches about 90, confirming that the predicted brittleness indicator curve is consistent with the drilling conclusion. According to the distribution law of the predicted brittleness indicator curve plane map, it is judged that the area belongs to fluvial phase deposition. The prediction result is consistent with the understanding of petroleum geological deposition in this area, further confirming the effectiveness of this method. The prediction results of the embodiment show that the brittleness indicator curve constructed by this method can effectively indicate the distribution law of the brittleness index of shale gas reservoirs, and is a reliable technical means for predicting shale gas reservoirs.

[0071] In an embodiment of the present invention, a system for calculating the brittleness indicator curve of an unconventional reservoir is also provided. Figure 2 The schematic diagram of the structure of the unconventional reservoir brittleness indicator curve calculation system in the embodiment of the present invention is shown. The system includes: a first determination unit and a curve determination unit.

[0072] The first determining unit is used to determine the shale content according to the well logging data curve and reservoir rock physical parameter information;

[0073] The curve determining unit is in communication with the first determining unit and is used to determine a brittleness indication curve according to the mud content and the logging porosity.

[0074] Specifically, the logging data curve includes compressional wave velocity, density and porosity;

[0075] The reservoir rock physical parameters include the longitudinal wave velocity of the rock matrix, the density of the rock matrix; the longitudinal wave velocity of the saturated fluid in the pores, the density of the saturated fluid in the pores; the longitudinal wave velocity of the clay and the density of the clay.

[0076] Specifically, the curve determination unit is used to determine the brittleness indication curve according to the mud content and the well logging porosity, including:

[0077] The brittleness index is determined according to the shale content and the logging porosity, and the logging data curve and the reservoir rock physical parameter information are substituted into the brittleness index to obtain a brittleness indication curve.

[0078] The unconventional reservoir brittleness indicator curve calculation method, system, and equipment of the present invention combine the advantages of current brittleness index evaluation methods while overcoming the high data requirements and severe human influence of conventional methods. This method realizes brittleness index evaluation based on conventional logging data, thereby improving the accuracy of shale gas exploration. Based on conventional P-wave logging, density logging, and porosity logging information, this method integrates rock physics analysis to construct a brittleness indicator curve calculation formula, realizing the calculation and evaluation of brittleness indicator parameters under conventional logging conditions. This method does not rely on S-wave logging information and is not affected by human factors. It is a highly applicable and accurate brittleness index extraction method. Conducting shale gas reservoir brittleness evaluation based on this method will effectively improve the accuracy of shale gas reservoir fracturing evaluation and reduce the risk of exploration and development.

[0079] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the brittleness indicator curve of unconventional reservoirs, characterized in that: The method comprises: Determine the shale content based on the well logging data curve and reservoir rock physical parameter information; Determine the brittleness indicator curve based on the mud content and logging porosity; The logging data curve includes compressional wave velocity, density and porosity; The reservoir rock physical parameters include the longitudinal wave velocity of the rock matrix, the density of the rock matrix; the longitudinal wave velocity of the saturated fluid in the pores, the density of the saturated fluid in the pores; the longitudinal wave velocity of the clay and the density of the clay; The mud content is expressed as: in, Vsh Indicates the mud content, ρ ma represents the density of the rock matrix, Vp represents the longitudinal wave velocity, ρ represents density, Vpma represents the longitudinal wave velocity of the rock matrix, φ represents the porosity, Vpfl represents the longitudinal wave velocity of the saturated fluid in the pores, ρ fl represents the density of the saturated fluid in the pores, ρ sh represents the density of clay, Vpsh represents the longitudinal wave velocity of clay; Determine a brittleness index based on the shale content and the logging porosity, and substitute the logging data curve and reservoir rock physical parameter information into the brittleness index to obtain a brittleness indication curve; The brittleness index is expressed as: Among them, BI represents the brittleness index, φ Indicates porosity.

2. A calculation system for unconventional reservoir brittleness indicator curves, characterized in that: The system includes: a first determination unit and a curve determination unit, The first determining unit is used to determine the shale content according to the well logging data curve and reservoir rock physical parameter information; a curve determining unit, in communication with the first determining unit, configured to determine a brittleness indication curve according to mud content and logging porosity; The logging data curve includes compressional wave velocity, density and porosity; The reservoir rock physical parameters include the longitudinal wave velocity of the rock matrix, the density of the rock matrix; the longitudinal wave velocity of the saturated fluid in the pores, the density of the saturated fluid in the pores; the longitudinal wave velocity of the clay and the density of the clay; The mud content is expressed as: in, Vsh Indicates the mud content, ρ ma represents the density of the rock matrix, Vp represents the longitudinal wave velocity, ρ represents density, Vpma represents the longitudinal wave velocity of the rock matrix, φ represents the porosity, Vpfl represents the longitudinal wave velocity of the saturated fluid in the pores, ρ fl represents the density of the saturated fluid in the pores, ρ sh represents the density of clay, Vpsh represents the longitudinal wave velocity of clay; The curve determination unit is used to determine the brittleness indication curve based on the mud content and logging porosity, including: Determine a brittleness index based on the shale content and the logging porosity, and substitute the logging data curve and reservoir rock physical parameter information into the brittleness index to obtain a brittleness indication curve; The brittleness index is expressed as: Among them, BI represents the brittleness index, φ Indicates porosity.

3. An unconventional reservoir brittleness indicator curve calculation device, characterized in that: The device includes at least one processor and at least one memory, wherein the memory is electrically connected to the processor, The memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the method of claim 1.

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