A method for determining the lower limit of porosity in fractured pore carbonate reservoirs

Abstract

The present application provides a method for determining the lower limit of the porosity of a fractured pore carbonate reservoir. Two types of porosity (fracture porosity and matrix porosity) in carbonate rocks are described in their respective regression modes, and respective calculation formulas are obtained. The two types of porosity of the test oil layer are calculated using the test oil data and well logging curves widely available in the oil field. A highly operational reservoir and dry layer boundary demarcation method is proposed through the compilation of a scatter plot. At the same time, the lower limits of the two types of porosity are determined, providing a basis for the evaluation of fractured pore carbonate reservoirs.

Description

Technical Field

[0001] The invention belongs to the technical field of carbonate oil and gas reservoir evaluation, and in particular relates to a method for determining the lower limit of porosity of fracture pore type carbonate reservoir. Background Art

[0002] Fracture-pore carbonate rocks refer to carbonate rocks with both fractures and matrix pores. The ratio of fracture volume and matrix pore volume to the total volume of the rock is called fracture porosity and matrix porosity, respectively. In fracture-pore carbonate rocks, fractures are both storage spaces and conducting media for pore communication. Both fractures and porosity in this type of carbonate rock are of great significance to oil and gas reservoirs.

[0003] Experiments show that the matrix porosity of carbonate oil and gas reservoirs is generally between 3% and 12%, while the fracture porosity is generally between 0.005% and 0.5%. Although the fracture porosity is low, due to the dual role of fractures in oil and gas reservoirs, a slight change in fracture porosity can have a significant impact on the storage capacity of fracture-pore carbonate rocks.

[0004] Patent CN104806232B proposes a method for obtaining the lower limit of the porosity of carbonate reservoirs, which uses experimental analysis to obtain parameters such as porosity, throat radius, and water saturation, and then establishes the correlation between porosity and throat radius and water saturation, and infers the lower limit of the porosity of oil and gas reservoirs based on the principle of phase permeability. This method essentially only obtains the lower limit of "total porosity" (the sum of mass porosity and fracture porosity), but has not yet obtained the lower limits of matrix porosity and fracture porosity; and because the fracture porosity is of a low order of magnitude (compared to matrix porosity), the general lower limit of "total porosity" cannot reflect the lower limit of fracture porosity. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for determining the lower limit of porosity of fractured pore carbonate reservoirs, which overcomes the above problems or at least partially solves the above problems.

[0006] In order to solve the above technical problems, the present invention provides a method for determining the lower limit of porosity of fractured pore type carbonate reservoir, characterized in that the method comprises the steps of:

[0007] Divide the oil-testing intervals in the target area into reservoir and dry layers;

[0008] Acquiring basic data of the target area;

[0009] Calculating the fracture porosity value and matrix porosity value of the oil testing layer section;

[0010] Draw a scatter plot of the fracture porosity values ​​and the matrix porosity values;

[0011] distinguishing data of the reservoir and the dry layer in the scatter plot;

[0012] The lower limit value of fracture porosity and the lower limit value of matrix porosity are determined according to the data of the reservoir and the dry layer.

[0013] Preferably, the calculation of the fracture porosity value and the matrix porosity value of the oil testing layer section further comprises:

[0014] Calculating the fracture porosity of the fractures in the target area based on the basic data;

[0015] Obtaining a fracture porosity logging calculation formula according to the basic data and the fracture porosity;

[0016] Calculating the matrix porosity of the core in the target area according to the basic data;

[0017] A matrix porosity logging calculation formula is obtained according to the basic data and the matrix porosity.

[0018] Preferably, the step of acquiring the basic data of the target area comprises the following steps:

[0019] Acquiring core data of the target area;

[0020] Acquiring logging curve data of the target area;

[0021] Acquire oil testing data of the target area.

[0022] Preferably, the calculating the fracture porosity of the fractures in the target area according to the basic data comprises the steps of:

[0023] Acquiring core data of the target area;

[0024] identifying carbonate cores in the target area based on the core data;

[0025] Selecting a core section with developed fractures in the carbonate rock core;

[0026] measuring crack density, crack length and crack width of the cracks;

[0027] Calculating an average crack length of the cracks according to the crack lengths;

[0028] Calculating an average crack width of the crack according to the crack width;

[0029] Calculating the product of the crack density, the average length of the cracks and the average width of the cracks;

[0030] The product value is taken as the fracture porosity.

[0031] Preferably, the step of obtaining the fracture porosity logging calculation formula according to the basic data and the fracture porosity comprises the following steps:

[0032] Acquire a density curve of cracks in the target area;

[0033] Obtaining an acoustic time difference logging curve of the fracture;

[0034] Obtaining a natural gamma curve of the crack;

[0035] Obtaining a caliper logging curve of the fracture;

[0036] Obtaining the fracture porosity of the fracture;

[0037] At the same time, multiple regression is performed on the density curve, the acoustic time difference logging curve, the natural gamma curve, the caliper logging curve and the fracture porosity;

[0038] The multivariate regression result is used as the fracture porosity logging calculation formula.

[0039] Preferably, the step of calculating the matrix porosity of the core in the target area according to the basic data comprises the following steps:

[0040] Acquiring core data of the target area;

[0041] identifying carbonate cores in the target area based on the core data;

[0042] Selecting a core section in the carbonate rock core where fractures are not developed;

[0043] obtaining a plug sample from the core section;

[0044] performing a core porosity test on the plunger sample;

[0045] The matrix porosity of the core is obtained according to the test results.

[0046] Preferably, the step of obtaining the matrix porosity logging calculation formula according to the basic data and the matrix porosity comprises the following steps:

[0047] Acquire acoustic time difference logging curve data of the core in the target area;

[0048] Obtaining the matrix porosity of the core;

[0049] Performing exponential regression on the acoustic time difference logging curve data and the matrix porosity;

[0050] The exponential regression result is used as the matrix porosity logging calculation formula.

[0051] Preferably, the step of drawing a scatter plot of the fracture porosity values ​​and the matrix porosity values ​​comprises the steps of:

[0052] A rectangular coordinate system is established with fracture porosity as the ordinate and matrix porosity as the abscissa;

[0053] Obtaining all the fracture porosity values ​​and the matrix porosity values;

[0054] Arrange all the fracture porosity values ​​correspondingly on the rectangular coordinate system;

[0055] Arrange all the matrix porosity values ​​correspondingly on the rectangular coordinate system;

[0056] A scatter plot of the fracture porosity values ​​and the matrix porosity values ​​is obtained in the rectangular coordinate system.

[0057] Preferably, the step of distinguishing the data of the reservoir and the dry layer in the scatter plot comprises the steps of:

[0058] Obtaining the scatter plot;

[0059] representing the data of the reservoir in the scatter plot using a first marker;

[0060] Using a second marker to represent the data of the dry layer in the scatter plot;

[0061] Using a first scale to mark the fracture porosity values ​​in the reservoir and the dry layer;

[0062] A second scale is used to mark the matrix porosity values ​​in the reservoir layer and the dry layer.

[0063] Preferably, the step of determining the lower limit value of fracture porosity and the lower limit value of matrix porosity according to the data of the reservoir and the dry layer comprises the following steps:

[0064] Obtaining a first fracture porosity value and a first matrix porosity value corresponding to the reservoir;

[0065] Obtaining a second fracture porosity value and a second matrix porosity value corresponding to the dry layer;

[0066] Plotting the first fracture porosity value, the second fracture porosity value, the first matrix porosity value, and the second matrix porosity value in the same coordinate system;

[0067] Obtaining a first boundary transition zone between the first fracture porosity value and the second fracture porosity value;

[0068] The middle value of the first dividing line transition zone is used as the lower limit value of the fracture porosity;

[0069] Obtaining a second boundary transition zone between the first matrix porosity value and the second matrix porosity value;

[0070] The middle value of the second dividing line transition zone is taken as the lower limit value of the matrix porosity.

[0071] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: the present application provides a method for determining the lower limit of the porosity of a fractured pore type carbonate reservoir, which describes the two types of porosity (fracture porosity and matrix porosity) in carbonate rocks in a respective regression manner, and obtains respective calculation formulas; and uses the oil test data and well logging curves widely available in oil fields to calculate the two types of porosity of the test oil layer; and then proposes a highly operational reservoir and dry layer boundary demarcation method through the compilation of a scatter plot; and at the same time determines the lower limits of the two types of porosity, providing a basis for the evaluation of fractured pore type carbonate reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. 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 creative work.

[0073] Figure 1 It is a flow chart of a method for determining the lower limit of porosity of a fractured pore carbonate reservoir provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0074] The present invention will be described in detail below in conjunction with specific implementations and examples, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific implementations and examples are used to illustrate the present invention, rather than to limit the present invention.

[0075] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. In the event of a conflict, the present specification takes precedence.

[0076] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0077] like Figure 1 In an embodiment of the present application, the present invention provides a method for determining the lower limit of porosity of a fractured pore carbonate reservoir, the method comprising the steps of:

[0078] S1: Divide the oil-testing intervals in the target area into reservoir and dry layers;

[0079] In the embodiment of the present application, the test oil layer segment data can be divided into two categories according to the "Petroleum and Natural Gas Industry Standard of the People's Republic of China SY6293-2008 Exploration and Testing Work Specifications". One category is the reservoir, including oil layers, gas layers, water layers, water-bearing oil layers, oil-water layers, oil-bearing water layers, low-yield oil and gas layers, etc., whose daily liquid production is higher than the dry layer standard; the second category is the dry layer, whose daily liquid production is lower than the dry layer standard.

[0080] In the embodiment of the present application, the benefit of dividing the oil testing layer section in the target area into reservoir and dry layer is to classify the data in a targeted manner to prepare for subsequent steps.

[0081] S2: Acquire basic data of the target area;

[0082] In the embodiment of the present application, obtaining the basic data of the target area in step S2 includes the following steps:

[0083] Acquiring core data of the target area;

[0084] Acquiring logging curve data of the target area;

[0085] Acquire oil testing data of the target area.

[0086] In an embodiment of the present application, the method for obtaining the core data of the target area is: during the drilling process (that is, the process in which the drill bit drills through the formation and grinds the rock), a cylindrical rock sample is taken out from the hole using an annular core drill bit when approaching the target layer. This sample is the core sample.

[0087] In an embodiment of the present application, the method for obtaining the logging curve data of the target area is: by utilizing physical principles such as electricity, magnetism, and sound, various logging instruments are lowered into the well using logging cables, and ground testing instruments continuously record various changing parameters along the wellbore with depth, thereby obtaining logging curve data.

[0088] In an embodiment of the present application, the method for obtaining the oil test data of the target area is: underground perforating the target layer, then testing the oil, gas and water production, and obtaining data such as bottom hole pressure and physical properties of oil, gas and water, and directly determining the oil layer, gas layer and water layer based on this.

[0089] In the embodiment of the present application, the benefit of acquiring the basic data of the target area is to obtain a large number of original production data samples, which provide a source for the data analysis of the present method.

[0090] S3: Calculate the fracture porosity value and matrix porosity value of the test oil layer section;

[0091] In the embodiment of the present application, the calculation of the fracture porosity value and the matrix porosity value of the oil testing layer section in step S3 includes the following steps:

[0092] Calculating the fracture porosity of the fractures in the target area based on the basic data;

[0093] Obtaining a fracture porosity logging calculation formula according to the basic data and the fracture porosity;

[0094] Calculating the matrix porosity of the core in the target area according to the basic data;

[0095] A matrix porosity logging calculation formula is obtained according to the basic data and the matrix porosity.

[0096] In an embodiment of the present application, the calculating the fracture porosity of the fractures in the target area according to the basic data comprises the steps of:

[0097] Acquiring core data of the target area;

[0098] identifying carbonate cores in the target area based on the core data;

[0099] Selecting a core section with developed fractures in the carbonate rock core;

[0100] measuring crack density, crack length and crack width of the cracks;

[0101] Calculating an average crack length of the cracks according to the crack lengths;

[0102] Calculating an average crack width of the crack according to the crack width;

[0103] Calculating the product of the crack density, the average length of the cracks and the average width of the cracks;

[0104] The product value is taken as the fracture porosity.

[0105] In the embodiment of the present application, the carbonate core in the target area is identified by core data (rock color, mineral characteristics, degree of bubbling when dropping hydrochloric acid, etc.) (the identification method is specifically described in "Petroleum and Natural Gas Industry Standard SY / T5336-2006 Core Analysis Method of the People's Republic of China"), and then the core section with developed cracks in the carbonate core is selected, and the well number and depth of the core section are recorded; then the crack density (that is, the number of cracks within 1m2), crack length (unit m) and crack width (unit m) of the core cracks are measured and recorded, and the average crack length and average crack width are calculated according to the crack length and width, respectively, and the fracture porosity is calculated according to the formula fracture porosity = fracture density × average crack length × average fracture width.

[0106] In the embodiment of the present application, the fractures measured and recorded in this step refer to unfilled fractures. Some fractures in the core will be filled with minerals such as calcite, dolomite, and quartz. Since the filled fractures have no oil and gas reservoir significance, these filled fractures are not included in this measurement record. In addition, in order to improve the regression effect below, it is necessary to select as many cores as possible for measurement.

[0107] In the embodiment of the present application, the fracture porosity logging calculation formula is expressed as:

[0108] F=(0.33×DEN+1.51×AC-0.36×CAL-0.47) / 100,

[0109] Where, F is the fracture porosity (unit: %), DEN is the density logging value (unit: g / cm3), AC acoustic logging value (unit: us / m), and CAL is the caliper logging value (unit: cm);

[0110] The matrix porosity logging calculation formula is:

[0111] B=0.00028e 0.1784×AC ;

[0112] Wherein, B is the matrix porosity (unit: %), and AC is the acoustic logging value (unit: us / m).

[0113] In the embodiment of the present application, the benefit of calculating the fracture porosity of the fractures in the target area based on the basic data is to obtain intuitive, reliable and quantitative fracture porosity development conditions.

[0114] In an embodiment of the present application, the step of obtaining a fracture porosity logging calculation formula according to the basic data and the fracture porosity comprises the following steps:

[0115] Acquire a density curve of cracks in the target area;

[0116] Obtaining an acoustic time difference logging curve of the fracture;

[0117] Obtaining a natural gamma curve of the crack;

[0118] Obtaining a caliper logging curve of the fracture;

[0119] Obtaining the fracture porosity of the fracture;

[0120] At the same time, multiple regression is performed on the density curve, the acoustic time difference logging curve, the natural gamma curve, the caliper logging curve and the fracture porosity;

[0121] The multivariate regression result is used as the fracture porosity logging calculation formula.

[0122] It is known that the appearance of fractures in the core makes the logging curve data of this depth section have corresponding response characteristics, specifically:

[0123] ① Cracks reduce rock density, so the density curve (which can reflect rock density) of the crack development section decreases;

[0124] ② The acoustic time difference logging curve reflects the speed of sound waves propagating in rocks. Due to the development of fractures, the speed of sound waves propagating in rocks slows down and the acoustic time difference increases.

[0125] ③ The existence of cracks (the present invention refers to unfilled cracks) causes mud to invade during the drilling process, and the natural gamma curve will increase due to the increase in mud content (invaded mud), so the natural gamma will increase;

[0126] ④ When there are many cracks, the formation is prone to collapse in the crack area, which will affect the drilling wellbore, and the wellbore logging curve reflecting the wellbore will increase.

[0127] In an embodiment of the present application, a multivariate regression can be performed based on the above-mentioned curve sensitive to fracture development and using Excel software, that is, a multivariate regression is performed on the fracture porosity calculated in step S2 and the above-mentioned density curve, the acoustic time difference logging curve, the natural gamma curve and the caliper logging curve, and the regression result is the fracture porosity logging calculation formula.

[0128] In the embodiment of the present application, the fracture porosity logging calculation formula is expressed as:

[0129] F=(0.33×DEN+1.51×AC-0.36×CAL-0.47) / 100,

[0130] Where, F is the fracture porosity (unit: %), DEN is the density logging value (unit: g / cm3), AC acoustic logging value (unit: us / m), and CAL is the caliper logging value (unit: cm);

[0131] In the embodiment of the present application, the advantage of obtaining the fracture porosity logging calculation formula based on the basic data and the fracture porosity is that the fracture porosity can be calculated using the drilling logging curve data, and oil and gas drilling usually has logging curves, so a large amount of fracture porosity data can be obtained.

[0132] In an embodiment of the present application, the step of calculating the matrix porosity of the core in the target area according to the basic data includes the following steps:

[0133] Acquiring core data of the target area;

[0134] identifying carbonate cores in the target area based on the core data;

[0135] Selecting a core section in the carbonate rock core where fractures are not developed;

[0136] obtaining a plug sample from the core section;

[0137] performing a core porosity test on the plunger sample;

[0138] The matrix porosity of the core is obtained according to the test results.

[0139] In the embodiment of the present application, the carbonate core in the target area is identified by core data (rock color, mineral characteristics, degree of bubbling when dropping hydrochloric acid, etc.) (the identification method is specifically described in the "Petroleum and Natural Gas Industry Standard SY / T5336-2006 Core Analysis Method of the People's Republic of China"), and then the core section with undeveloped fractures in the carbonate core is selected, and the well number and depth of the core section are recorded; then a plunger sample is taken from the core, and a core porosity test is carried out to obtain the matrix porosity of the core.

[0140] In the embodiment of the present application, the principle of obtaining the matrix porosity of the core according to the core porosity test result is as follows: the core is washed, dried and weighed, and then weighed after desaturation with formation water. The difference between the two is divided by the formation water density to obtain the pore volume. The pore volume divided by the rock volume is the porosity. The benefit of calculating the matrix porosity of the core in the target area according to the basic data is to obtain quantitative pore data that is commonly used in the industry.

[0141] In an embodiment of the present application, the step of obtaining a matrix porosity logging calculation formula according to the basic data and the matrix porosity includes the following steps:

[0142] Acquire acoustic time difference logging curve data of the core in the target area;

[0143] Obtaining the matrix porosity of the core;

[0144] Performing exponential regression on the acoustic time difference logging curve data and the matrix porosity;

[0145] The exponential regression result is used as the matrix porosity logging calculation formula.

[0146] It is known that the sonic transit time is very sensitive to matrix porosity, so the most commonly used method is to use sonic transit time logging curve data to reflect the porosity of the core.

[0147] In the embodiment of the present application, the sonic time difference logging curve data in step S3 and the matrix porosity of the core in step S4 are subjected to exponential regression, and the regression result is used as the matrix porosity logging calculation formula.

[0148] In the embodiment of the present application, the matrix porosity logging calculation formula is expressed as:

[0149] B=0.00028e 0.1784×AC ,

[0150] Wherein, B is the matrix porosity (unit: %), and AC is the acoustic logging value (unit: us / m).

[0151] In the embodiment of the present application, the advantage of obtaining the matrix porosity logging calculation formula based on the basic data and the matrix porosity is that the fracture porosity can be calculated using the drilling logging curve data, and oil and gas drilling usually has logging curves, so a large amount of fracture porosity data can be obtained.

[0152] S4: drawing a scatter plot of the fracture porosity value and the matrix porosity value;

[0153] In the embodiment of the present application, drawing a scatter plot of the fracture porosity value and the matrix porosity value in step S4 includes the steps of:

[0154] A rectangular coordinate system is established with fracture porosity as the ordinate and matrix porosity as the abscissa;

[0155] Obtaining all the fracture porosity values ​​and the matrix porosity values;

[0156] Arrange all the fracture porosity values ​​correspondingly on the rectangular coordinate system;

[0157] Arrange all the matrix porosity values ​​correspondingly on the rectangular coordinate system;

[0158] A scatter plot of the fracture porosity values ​​and the matrix porosity values ​​is obtained in the rectangular coordinate system.

[0159] In the embodiment of the present application, a rectangular coordinate system is established in the Excel software with the fracture porosity as the ordinate and the matrix porosity as the abscissa, and then the fracture porosity values ​​and the matrix porosity values ​​calculated in step S3 are arranged correspondingly on the rectangular coordinate system, and then a scatter plot is made in the rectangular coordinate system.

[0160] In the embodiment of the present application, the benefit of drawing a scatter plot of the fracture porosity value and the matrix porosity value is to obtain an intuitive distribution of the two data, laying a foundation for determining the lower limit value.

[0161] S5: Distinguishing data of the reservoir and the dry layer in the scatter plot;

[0162] In the embodiment of the present application, distinguishing the data of the reservoir and the dry layer in the scatter plot in step S5 includes the steps of:

[0163] Obtaining the scatter plot;

[0164] representing the data of the reservoir in the scatter plot using a first marker;

[0165] Using a second marker to represent the data of the dry layer in the scatter plot;

[0166] Using a first scale to mark the fracture porosity values ​​in the reservoir and the dry layer;

[0167] A second scale is used to mark the matrix porosity values ​​in the reservoir layer and the dry layer.

[0168] In the embodiment of the present application, different marks are used in the scatter plot to distinguish the two groups of data, the reservoir and the dry layer, in the scatter plot. For example, red can be used to represent the data of the reservoir, and yellow can be used to represent the data of the dry layer. Furthermore, since the fracture porosity is between 0.001% and 0.7%, a logarithmic scale is used to mark the fracture porosity values ​​in the reservoir and the dry layer; and since the matrix porosity is between 1% and 14%, a normal scale is used to mark the matrix porosity values ​​in the reservoir and the dry layer.

[0169] In the embodiment of the present application, the advantage of distinguishing the data of the reservoir and the dry layer in the scatter plot is that the matrix porosity and fracture porosity of the reservoir and the dry layer are intuitively visible, and the lower limit value is easy to obtain.

[0170] S6: determining a fracture porosity lower limit value and a matrix porosity lower limit value according to the data of the reservoir and the dry layer;

[0171] In the embodiment of the present application, determining the fracture porosity lower limit value and the matrix porosity lower limit value according to the data of the reservoir and the dry layer in step S6 includes the following steps:

[0172] Obtaining a first fracture porosity value and a first matrix porosity value corresponding to the reservoir;

[0173] Obtaining a second fracture porosity value and a second matrix porosity value corresponding to the dry layer;

[0174] Plotting the first fracture porosity value, the second fracture porosity value, the first matrix porosity value, and the second matrix porosity value in the same coordinate system;

[0175] Obtaining a first boundary transition zone between the first fracture porosity value and the second fracture porosity value;

[0176] The middle value of the first dividing line transition zone is taken as the lower limit value of the fracture porosity.

[0177] Obtaining a second boundary transition zone between the first matrix porosity value and the second matrix porosity value;

[0178] The middle value of the second dividing line transition zone is taken as the lower limit value of the matrix porosity.

[0179] In the embodiment of the present application, since the fracture porosity values ​​corresponding to the reservoir and the dry layer are plotted in the same coordinate system, theoretically, the fracture porosity value corresponding to the boundary between the two is the fracture porosity lower limit. However, in actual operation, due to the oil testing process, the randomness of sampling, the test error of the above steps, etc., the reservoir and the dry layer have a certain degree of intersection, and the boundary between the two is not very obvious. Therefore, the middle value of the transition zone between the reservoir and the dry layer is selected as the fracture porosity lower limit. In this embodiment, the fracture porosity lower limit is 0.011%.

[0180] In the embodiment of the present application, since the matrix porosity values ​​corresponding to the reservoir and the dry layer are plotted in the same coordinate system, theoretically, the matrix porosity value corresponding to the boundary between the two is the lower limit of the matrix porosity. However, in actual operation, due to the oil testing process, the randomness of sampling, the test error of the above steps, etc., the reservoir and the dry layer have a certain degree of intersection, and the boundary between the two is not very obvious. Therefore, the middle value of the transition zone between the reservoir and the dry layer is selected as the lower limit of the matrix porosity. In this embodiment, the lower limit of the matrix porosity is 2.4%.

[0181] In the embodiment of the present application, the advantage of determining the lower limit values ​​of fracture porosity and matrix porosity based on the data of the reservoir and the dry layer is that by adopting this division method, the lower limit values ​​of reservoir matrix porosity and fracture porosity are directly obtained.

[0182] The present application provides a method for determining the lower limit of the porosity of a fractured pore carbonate reservoir. The method uses two types of porosity (fracture porosity and matrix porosity) in carbonate rocks to describe their respective regression methods, and obtains their respective calculation formulas; and uses the oil test data and well logging curves widely available in oil fields to calculate the two types of porosity of the test oil layer; and then proposes a highly operational reservoir and dry layer boundary demarcation method through the compilation of a scatter plot; and at the same time, determines the lower limits of the two types of porosity, providing a basis for the evaluation of fractured pore carbonate reservoirs.

[0183] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the process, method, article or device including the elements. The above is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. The various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied for herein.

[0184] In short, the above is only a preferred embodiment of the technical solution of the present invention, and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining the lower limit of porosity of fractured pore carbonate reservoirs, characterized in that: The method comprises the steps of: Divide the oil-testing intervals in the target area into reservoir and dry layers; Acquiring basic data of the target area; Calculating the fracture porosity value and matrix porosity value of the oil testing layer section; Draw a scatter plot of the fracture porosity values ​​and the matrix porosity values; distinguishing data of the reservoir and the dry layer in the scatter plot; Determining the lower limit value of fracture porosity and the lower limit value of matrix porosity according to the data of the reservoir and the dry layer; Wherein, the calculation of the fracture porosity value and matrix porosity value of the oil testing layer section further includes: Calculating the fracture porosity of the fractures in the target area based on the basic data; Obtaining a fracture porosity logging calculation formula according to the basic data and the fracture porosity; Calculating the matrix porosity of the core in the target area according to the basic data; Obtaining a matrix porosity logging calculation formula according to the basic data and the matrix porosity; The method of obtaining the fracture porosity logging calculation formula according to the basic data and the fracture porosity comprises the following steps: Acquire a density curve of cracks in the target area; Obtaining an acoustic time difference logging curve of the fracture; Obtaining a natural gamma curve of the crack; Obtaining a caliper logging curve of the fracture; Obtaining the fracture porosity of the fracture; At the same time, multiple regression is performed on the density curve, the acoustic time difference logging curve, the natural gamma curve, the caliper logging curve and the fracture porosity; Using the multivariate regression result as the fracture porosity logging calculation formula; The method of obtaining the matrix porosity logging calculation formula according to the basic data and the matrix porosity comprises the following steps: Acquire acoustic time difference logging curve data of the core in the target area; Obtaining the matrix porosity of the core; Performing exponential regression on the acoustic time difference logging curve data and the matrix porosity; Using the exponential regression result as the matrix porosity logging calculation formula; The step of drawing a scatter plot of the fracture porosity values ​​and the matrix porosity values ​​comprises the following steps: A rectangular coordinate system is established with fracture porosity as the ordinate and matrix porosity as the abscissa; Obtaining all the fracture porosity values ​​and the matrix porosity values; Arrange all the fracture porosity values ​​correspondingly on the rectangular coordinate system; Arrange all the matrix porosity values ​​correspondingly on the rectangular coordinate system; Obtaining a scatter plot of the fracture porosity values ​​and the matrix porosity values ​​in the rectangular coordinate system; The method of determining the lower limit value of fracture porosity and the lower limit value of matrix porosity according to the data of the reservoir and the dry layer comprises the following steps: Obtaining a first fracture porosity value and a first matrix porosity value corresponding to the reservoir; Obtaining a second fracture porosity value and a second matrix porosity value corresponding to the dry layer; Plotting the first fracture porosity value, the second fracture porosity value, the first matrix porosity value, and the second matrix porosity value in the same coordinate system; Obtaining a first boundary transition zone between the first fracture porosity value and the second fracture porosity value; The middle value of the first dividing line transition zone is used as the lower limit value of the fracture porosity; Obtaining a second boundary transition zone between the first matrix porosity value and the second matrix porosity value; The middle value of the second dividing line transition zone is taken as the lower limit value of the matrix porosity; The first dividing line transition zone and the second dividing line transition zone are formed because the reservoir and the dry layer have a certain degree of intersection and the boundary between the reservoir and the dry layer is not obvious.

2. The method for determining the lower limit of porosity of fractured pore carbonate reservoir according to claim 1, characterized in that: The obtaining of the basic data of the target area comprises the steps of: Acquiring core data of the target area; Acquiring logging curve data of the target area; Acquire oil testing data of the target area.

3. The method for determining the lower limit of porosity of fractured pore carbonate reservoir according to claim 1, characterized in that: The calculating of the fracture porosity of the fractures in the target area according to the basic data comprises the steps of: Acquiring core data of the target area; identifying carbonate cores in the target area based on the core data; Selecting a core section with developed fractures in the carbonate rock core; measuring crack density, crack length and crack width of the cracks; Calculating an average crack length of the cracks according to the crack lengths; Calculating an average crack width of the crack according to the crack width; Calculating the product of the crack density, the average length of the cracks and the average width of the cracks; The product value is taken as the fracture porosity.

4. The method for determining the lower limit of porosity of fractured pore carbonate reservoir according to claim 1, characterized in that: The step of calculating the matrix porosity of the core in the target area according to the basic data comprises the following steps: Acquiring core data of the target area; identifying carbonate cores in the target area based on the core data; Selecting a core section in the carbonate rock core where fractures are not developed; obtaining a plug sample from the core section; performing a core porosity test on the plunger sample; The matrix porosity of the core is obtained according to the test results.

5. The method for determining the lower limit of porosity of fractured pore carbonate reservoir according to claim 1, characterized in that: The step of distinguishing the data of the reservoir and the dry layer in the scatter plot comprises the following steps: Obtaining the scatter plot; representing the data of the reservoir in the scatter plot using a first marker; Using a second marker to represent the data of the dry layer in the scatter plot; Using a first scale to mark the fracture porosity values ​​in the reservoir and the dry layer, wherein the first scale is a logarithmic scale; A second scale is used to mark the matrix porosity values ​​in the reservoir and the dry layer, and the second scale is a normal scale.

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