Calculation method of coal rock variable skeleton porosity

Abstract

The invention provides a coal rock variable skeleton porosity calculation method, and belongs to the technical field of petroleum and natural gas geology and exploration and development engineering. The method comprises the following steps: calculating a skeleton density value of a coal rock experimental sample by utilizing a coal rock skeleton density formula; according to the coal rock volume physical model, an objective function is established, and the density value of each mineral skeleton is calculated; preferably selecting logging parameters sensitive to the change of the industrial components of the coal rock, establishing a multiple regression interpretation model between each mineral and the sensitive logging parameters, and calculating the volume content of each mineral component; according to the coal rock volume physical model, constructing a coal rock variable skeleton density curve by utilizing the density data of each mineral skeleton and the volume content of each mineral component; and calculating the coal rock variable skeleton porosity according to the coal rock variable skeleton density curve. The method fully considers the change of the coal rock skeleton caused by the change of the coal rock industrial component content, and is high in calculation precision and good in application effect.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum and natural gas geology and exploration and development engineering, and in particular to a method for calculating the porosity of coal rock skeleton. Background Art

[0002] Due to the influence of factors such as changes in the content of industrial components in coal and rock and the development of cleats, when the conventional porosity model is used to calculate the porosity of coal and rock reservoirs, the calculation accuracy of the porosity of coal and rock reservoirs is low and the error is large. The porosity calculation results obtained cannot meet the requirements of fine reservoir evaluation.

[0003] For some areas, deep coal-rock gas resources are very rich. Different from the traditional coal-bed methane, more than 80% of the coal in these areas is buried at a depth of 2000-3500m, which belongs to deep-buried coal-rock reservoirs. This type of reservoir has a large porosity, and the storage space is mainly medium and large pores. Coal-rock gas is mainly free gas in the pore space. Therefore, the calculation accuracy of the porosity parameters of coal-rock gas reservoirs plays a vital role in the evaluation of coal-rock gas reservoirs. Due to the complex composition of coal-rock reservoirs, at this time, if the conventional porosity model is used for porosity calculation without considering the influence of changes in coal-rock component content, it will inevitably lead to an increase in porosity calculation errors and the free gas content cannot be accurately evaluated.

[0004] In order to establish a high-precision coal-rock gas reservoir evaluation model to improve the evaluation accuracy of coal-rock gas reservoirs, it is necessary to consider the influence of changes in the content of coal-rock industrial components when calculating porosity. In view of the changes in the content of coal-rock industrial components, a variable skeleton porosity model is established to make the porosity calculation more accurate and better reflect the real situation of coal-rock reservoirs.

[0005] At present, the most commonly used method for calculating the porosity of coal rock reservoirs is to analyze the porosity based on coal core experiments, establish density-porosity or sonic transit time-porosity cross-plots, determine the coal rock density or sonic transit time skeleton value, and then calculate the porosity. This method uses a fixed coal rock skeleton and does not consider the impact of changes in the content of coal rock industrial components on the coal rock skeleton, resulting in low accuracy and poor application effect of the above calculation method. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention provides a method for calculating the variable skeleton porosity of coal rock. Based on the coal rock volume physical model, the variable skeleton porosity of coal rock is determined by the logging curve, and the skeleton density value of the coal rock experimental sample is calculated by using the coal rock skeleton density formula; according to the coal rock volume physical model, an objective function is established to calculate the skeleton density value of each mineral; the logging parameters that are sensitive to the changes in the industrial components of coal rock are selected, and a multivariate regression interpretation model between each mineral and the sensitive logging parameters is established to calculate the volume content of each mineral component; according to the coal rock volume physical model, the coal rock variable skeleton density curve is constructed by using the skeleton density data of each mineral and the volume content of each mineral component; according to the coal rock volume physical model, the coal rock variable skeleton density curve is calculated. The present invention fully considers that the changes in the content of the coal rock industrial components lead to changes in the coal rock skeleton, and has high calculation accuracy and good application effect.

[0007] The present invention provides a method for calculating coal-rock skeleton porosity. The method is based on a coal-rock volume physical model and determines the coal-rock skeleton porosity from a well logging curve.

[0008] Preferably, based on the coal rock volume physical model, determining the coal rock variable skeleton porosity from the logging curve specifically includes the following steps:

[0009] Step 101, obtaining coal quality analysis data of the target reservoir, including water content and mineral components in coal rock, volume content data of mineral components, coal rock logging data, and coal rock experimental analysis porosity; coal rock logging data includes natural gamma data and density data; water content and mineral components are collectively referred to as industrial components;

[0010] Step 102, using the coal rock skeleton density formula, calculate the skeleton density value of the coal rock test sample;

[0011] Step 103, establishing an objective function based on the coal rock volume physical model, taking the density value of each mineral component greater than zero as a constraint condition, and calculating the density value of each mineral skeleton;

[0012] Step 104, selecting well logging parameters that are sensitive to changes in coal and rock industry components, establishing a multivariate regression interpretation model between each mineral and the sensitive well logging parameters, and calculating the volume content of each mineral component;

[0013] Step 105, constructing a coal rock variable skeleton density curve according to the coal rock volume physical model using the skeleton density data of each mineral calculated in step 103 and the volume content of each mineral component calculated in step 104;

[0014] Step 106, calculating the coal-rock transformed skeleton porosity according to the coal-rock transformed skeleton density curve.

[0015] Preferably, the industrial components of coal rock include fixed carbon, ash and volatile matter.

[0016] Preferably, in step 103, the mineral skeleton density values ​​of fixed carbon, ash and volatile matter are calculated with the constraint that the density values ​​of fixed carbon, ash and volatile matter are greater than zero; in step 104, a multivariate regression interpretation model between fixed carbon, ash and volatile matter and sensitive logging parameters is established to calculate the volume content of fixed carbon, ash and volatile matter.

[0017] Preferably, in step 102, the skeleton density data of the coal rock experimental sample points is determined based on the following formula:

[0018]

[0019] Where:

[0020] ρ m The calculated coal rock sample point skeleton density data, in g / cm 3 ;

[0021] DEN is the well logging density data corresponding to the coal rock experimental sample point, in g / cm 3 ;

[0022] is the effective porosity of coal rock;

[0023] ρ f is the fluid density data, in g / cm 3 ;

[0024] i is the serial number of the coal rock experimental sample point.

[0025] Preferably, the coal rock volume physical model in step 103 is determined based on the following formula:

[0026] V m =V Aad +V Fc +V Vda (2)

[0027] Where:

[0028] V m is the total volume of coal rock skeleton;

[0029] V Aad is the ash volume content;

[0030] V Fc is the fixed carbon volume content;

[0031] V Vda is the volume content of volatile matter.

[0032] Preferably, the objective function in step 103 is determined based on the following formula:

[0033]

[0034] Where:

[0035] f (x) The objective function to be solved for constrained optimization;

[0036] ρ Aad is the ash skeleton density, in g / cm 3 ;

[0037] ρ FC is the fixed carbon skeleton density, in g / cm 3 ;

[0038] ρ Cda is the volatile matter skeleton density, in g / cm 3 ;

[0039] V Aad is the ash volume content, in %;

[0040] V Fc is the fixed carbon volume content, in %;

[0041] V Vda is the volume content of volatile matter, in %;

[0042] DEN is the well logging density data corresponding to the coal rock experimental sample point, in g / cm 3 ;

[0043] i is the serial number of the coal rock experimental sample point;

[0044] n is the total number of coal and rock experimental samples;

[0045] The constraints are determined based on the following formula:

[0046] ρ Aad >0,ρ FC >0,ρ Vda >0 (4)

[0047] Preferably, in step 104, the ash volume content is determined based on the following formula:

[0048] V Aad =GR*0.027+DEN*12.528-14.697 (5) The fixed carbon volume content is determined based on the following formula:

[0049] V Fc =V Aad *(-4.725)+77.367 (6)

[0050] The volatile matter volume content is determined based on the following formula:

[0051] V Vda =V Aad *3.555+21.342 (7)

[0052] Where:

[0053] V Aad is the ash volume content, in %;

[0054] V Fc is the fixed carbon volume content, in %;

[0055] V Vda is the volume content of volatile matter, in %;

[0056] GR is the natural gamma logging data, API;

[0057] DEN is the well logging density data corresponding to the coal rock experimental sample point, g / cm 3 .

[0058] Preferably, in step 105, the variable skeleton density curve is determined based on the following formula:

[0059]

[0060] Where:

[0061] DEN mb Coal rock skeleton density data, unit is g / cm 3 ;

[0062] V Aad is the ash volume content, in %;

[0063] V Fc is the fixed carbon volume content, in %;

[0064] V Vda is the volume content of volatile matter, in %;

[0065] ρ Aad is the ash skeleton density, in g / cm 3 ;

[0066] ρ FC is the fixed carbon skeleton density, in g / cm 3 ;

[0067] ρ Vda is the volatile matter skeleton density, in g / cm 3 ;

[0068] j represents the data point number of the variable skeleton density curve.

[0069] Preferably, in step 106, the coal rock skeleton porosity curve is determined based on the following formula:

[0070]

[0071] Where:

[0072] is the coal rock matrix porosity, in %;

[0073] DEN is the density logging data, the unit is g / cm 3 ;

[0074] DEN mb Coal rock skeleton density data, unit is g / cm 3 ;

[0075] ρ f is the fluid density data, in g / cm 3 ;

[0076] k is the number of data points of the coal rock skeleton porosity curve.

[0077] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0078] When calculating the variable skeleton porosity of coal rock, the present invention fully considers the change of coal rock skeleton caused by the change of industrial component content of coal rock, and has high calculation accuracy and good application effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 A flow chart of a method for calculating coal rock skeleton porosity according to an embodiment of the present invention;

[0080] Figure 2 A physical model diagram of coal rock volume according to an embodiment of the present invention;

[0081] Figure 3 A schematic diagram of the correlation between the experimental analysis of ash content and the calculated ash volume content according to an embodiment of the present invention;

[0082] Figure 4 A schematic diagram comparing the calculation results of a coal rock variable skeleton porosity calculation method according to an embodiment of the present invention and a traditional coal rock porosity calculation method;

[0083] Figure 5 The figure is a schematic diagram of the practical application effect of an embodiment of the present invention. DETAILED DESCRIPTION

[0084] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings.

[0085] The present invention provides a method for calculating coal-rock skeleton porosity. The method is based on a coal-rock volume physical model and determines the coal-rock skeleton porosity from a well logging curve.

[0086] According to a specific embodiment of the present invention, based on the coal rock volume physical model, determining the coal rock variable skeleton porosity from the logging curve specifically includes the following steps:

[0087] Step 101, obtaining coal quality analysis data of the target reservoir, including water content and mineral components in coal rock, volume content data of mineral components, coal rock logging data, and coal rock experimental analysis porosity; the coal rock logging data includes natural gamma data and density data;

[0088] Step 102, using the coal rock skeleton density formula, calculate the skeleton density value of the coal rock test sample;

[0089] Step 103, establishing an objective function based on the coal rock volume physical model, taking the density value of each mineral component greater than zero as a constraint condition, and calculating the density value of each mineral skeleton;

[0090] Step 104, selecting well logging parameters that are sensitive to changes in coal and rock industry components, establishing a multivariate regression interpretation model between each mineral and the sensitive well logging parameters, and calculating the volume content of each mineral component;

[0091] Step 105, constructing a coal rock variable skeleton density curve according to the coal rock volume physical model using the skeleton density data of each mineral calculated in step 103 and the volume content of each mineral component calculated in step 104;

[0092] Step 106, calculating the coal-rock transformed skeleton porosity according to the coal-rock transformed skeleton density curve.

[0093] According to a specific embodiment of the present invention, the industrial components of coal rock include fixed carbon, ash and volatile matter.

[0094] According to a specific embodiment of the present invention, in step 103, the mineral skeleton density values ​​of fixed carbon, ash and volatile matter are calculated with the constraint that the density values ​​of fixed carbon, ash and volatile matter are greater than zero; in step 104, a multivariate regression interpretation model between fixed carbon, ash and volatile matter and sensitive logging parameters is established to calculate the volume content of fixed carbon, ash and volatile matter.

[0095] According to a specific embodiment of the present invention, in step 102, the skeleton density data of the coal rock experimental sample point is determined based on the following formula:

[0096]

[0097] Where:

[0098] ρ m The calculated coal rock sample point skeleton density data, in g / cm 3 ;

[0099] DEN is the well logging density data corresponding to the coal rock experimental sample point, in g / cm 3 ;

[0100] is the effective porosity of coal rock;

[0101] V f is the fluid density data, in g / cm 3 ;

[0102] i is the serial number of the coal rock experimental sample point.

[0103] According to a specific embodiment of the present invention, the coal rock volume physical model in step 103 is determined based on the following formula:

[0104] V m =V Aad +V Fc +V Vda (2)

[0105] Where:

[0106] V m is the total volume of coal rock skeleton;

[0107] V Aad is the ash volume content;

[0108] V Fc is the fixed carbon volume content;

[0109] V Vda is the volume content of volatile matter.

[0110] According to a specific embodiment of the present invention, the objective function in step 103 is determined based on the following formula:

[0111]

[0112] Where:

[0113] f (x) The objective function to be solved for constrained optimization;

[0114] ρ Aad is the ash skeleton density, in g / cm 3 ;

[0115] ρ FC is the fixed carbon skeleton density, in g / cm3 ;

[0116] ρ Vda is the volatile matter skeleton density, in g / cm 3 ;

[0117] V Aad is the ash volume content, in %;

[0118] V Fc is the fixed carbon volume content, in %;

[0119] V Vda is the volume content of volatile matter, in %;

[0120] DEN is the well logging density data corresponding to the coal rock experimental sample point, in g / cm 3 ;

[0121] i is the serial number of the coal rock experimental sample point;

[0122] n is the total number of coal and rock experimental samples;

[0123] The constraints are determined based on the following formula:

[0124] ρ Aad >0,ρ FC >0,ρ Vaa >0 (4)

[0125] According to a specific embodiment of the present invention, in step 104, the ash volume content is determined based on the following formula:

[0126] V Aad =GR*0.027+DEN*12.528-14.697 (5)

[0127] The fixed carbon volume content is determined based on the following formula:

[0128] V Fc =V Aad *(-4.725)+77.367 (6)

[0129] The volatile matter volume content is determined based on the following formula:

[0130] V Vda =V Aad *3.555+21.342 (7)

[0131] Where:

[0132] V Aad is the ash volume content, in %;

[0133] V Fcis the fixed carbon volume content, in %;

[0134] V Vda is the volume content of volatile matter, in %;

[0135] GR is the natural gamma logging data, API;

[0136] DEN is the well logging density data corresponding to the coal rock experimental sample point, g / cm 3 .

[0137] According to a specific embodiment of the present invention, in step 105, the variable skeleton density curve is determined based on the following formula:

[0138]

[0139] Where:

[0140] DEN mb Coal rock skeleton density data, unit is g / cm 3 ;

[0141] V Aad is the ash volume content, in %;

[0142] V Fc is the fixed carbon volume content, in %;

[0143] V Vda is the volume content of volatile matter, in %;

[0144] ρ Aad is the ash skeleton density, in g / cm 3 ;

[0145] ρ FC is the fixed carbon skeleton density, in g / cm 3 ;

[0146] ρ Vda is the volatile matter skeleton density, in g / cm 3 ;

[0147] j represents the data point number of the variable skeleton density curve.

[0148] According to a specific embodiment of the present invention, in step 106, the coal rock skeleton porosity curve is determined based on the following formula:

[0149]

[0150] Where:

[0151] is the coal rock matrix porosity, in %;

[0152] DEN is the density logging data, the unit is g / cm 3 ;

[0153] DEN mb Coal rock skeleton density data, unit is g / cm 3 ;

[0154] ρ f is the fluid density data, in g / cm 3 ;

[0155] k is the number of data points of the coal rock skeleton porosity curve.

[0156] Example 1

[0157] Figure 1 is a flow chart of a method for calculating coal rock skeleton porosity according to an embodiment of the present invention. Figure 1 As shown, the method comprises the following steps:

[0158] Step 101, obtaining coal quality analysis data of the target reservoir, including volume content data of industrial components of coal rock (fixed carbon, ash, moisture and volatile matter), coal rock logging data (natural gamma, density), and coal rock experimental analysis porosity.

[0159] The volume content data of fixed carbon, ash, moisture and volatile matter in the coal rock reservoir of the target work area are obtained from the coal rock industrial component analysis experiment, the natural gamma (GR) curve data and density (DEN) curve data of the coal rock reservoir in the target work area are measured by logging instruments, and the experimental analysis porosity of the coal rock reservoir in the target work area is obtained from the physical property analysis experiment.

[0160] Step 102: Calculate the skeleton density value of the coal rock test sample using the coal rock skeleton density formula.

[0161]

[0162] Where:

[0163] ρ m The calculated coal rock sample point skeleton density data, in g / cm 3 ;

[0164] DEN is the well logging density data corresponding to the coal rock experimental sample point, in g / cm 3 ;

[0165] is the effective porosity of coal rock;

[0166] ρ f is the fluid density data, in g / cm 3 ;

[0167] i is the serial number of the coal rock experimental sample point.

[0168] Step 103: According to the coal rock volume physical model, an objective function is established, and the mineral skeleton density values ​​of fixed carbon, ash and volatile matter are calculated with the density values ​​of fixed carbon, ash and volatile matter being greater than zero as a constraint condition.

[0169] According to the industrial analysis method of coal, coal rock can be divided into four parts: fixed carbon, ash, volatile matter and water. According to the composition, the volume physical model of coal rock is established, such as Figure 2 As shown in the figure, since the water is attached to the inner surface of the coal rock storage space and is not part of the coal rock skeleton, it is believed that the coal rock skeleton volume is composed of three parts: fixed carbon, ash and volatile matter. The coal rock volume physical model is determined based on the following formula:

[0170] V m =V Aad +V Fc +V Vda (2)

[0171] Where:

[0172] V m is the total volume of coal rock skeleton;

[0173] V Aad is the ash volume content;

[0174] V Fc is the fixed carbon volume content;

[0175] V Vda is the volume content of volatile matter.

[0176] According to the generalized inversion theory in geophysics, the optimization method is applied to the calculation of the skeleton density values ​​of ash, volatile matter, and fixed carbon. It is believed that the logging density data is the sum of the contribution values ​​of the three parts of the fixed carbon skeleton density, ash skeleton density, and volatile skeleton density of coal rock. Therefore, the optimization mathematical method is applied, according to the principle of nonlinear weighted least squares method and error theory, to establish the objective function and constraint conditions, and to find the optimal solution of the objective function under the constraint conditions, that is, when the objective function value reaches the minimum value, the theoretical response value of the coal rock skeleton density ( ) and the corresponding input density logging response value to achieve the best fit, ρ Aad , FC , Vda That is, the fixed carbon skeleton density, ash skeleton density and volatile matter skeleton density obtained by constrained optimization solution, and the constrained optimization solution value is taken as the most reasonable fixed carbon skeleton density, ash skeleton density and volatile matter skeleton density.

[0177] The objective function is determined based on the following formula:

[0178]

[0179] Where:

[0180] f (x) The objective function to be solved for constrained optimization;

[0181] ρ Aad is the ash skeleton density, in g / cm 3 ;

[0182] ρ FC is the fixed carbon skeleton density, in g / cm 3 ;

[0183] ρ Vda is the volatile matter skeleton density, in g / cm 3 ;

[0184] V Aad is the ash volume content, in %;

[0185] V Fc is the fixed carbon volume content, in %;

[0186] V Vda is the volume content of volatile matter, in %;

[0187] DEN is the well logging density data corresponding to the coal rock experimental sample point, in g / cm 3 ;

[0188] i is the serial number of the coal rock experimental sample point;

[0189] The constraints are determined based on the following formula:

[0190] ρ Aad >0,ρ FC >0,ρ Vda >0 (4)

[0191] Step 104: Optimize the logging parameters that are more sensitive to the changes in coal and rock industrial components, establish a multivariate regression interpretation model between fixed carbon, ash, volatile matter and sensitive logging parameters, and calculate the volume content of fixed carbon, ash and volatile matter.

[0192] Since fixed carbon, volatile matter and ash have good linear correlation, in the well logging interpretation evaluation of fixed carbon, ash and volatile volume content, the correlation between the well logging curve data and ash is first analyzed, and the well logging curve data that is more sensitive to the change of ash content is selected, and a multivariate regression interpretation model between ash and sensitive well logging curves is established. For the target work area, the natural gamma (GR) curve data and density (DEN) curve data are selected, and a multivariate regression interpretation model between ash and natural gamma (GR) and density (DEN) is established. The ash volume content is determined based on the following formula:

[0193] V Aad =GR*0.027+DEN*12.528-14.697 (5)

[0194] Where: V Aad is the ash volume content, in %; GR is the natural gamma logging data, API; DEN is the density logging data, g / cm 3 .

[0195] Figure 3 Schematic diagram of the correlation between the experimental analysis of ash and the calculated ash volume content provided by an optional embodiment of the present invention, such as Figure 3 As shown, the calculation results of this formula have a high correlation with the experimental analysis data and are accurate.

[0196] After obtaining the ash content, the linear correlation between fixed carbon, volatile matter and ash is used to further establish a fixed carbon and volatile matter volume content model to calculate the fixed carbon and volatile matter volume content of coal rock in the target work area.

[0197] The fixed carbon volume content is determined based on the following formula:

[0198] V Fc =V Aad *(-4.725)+77.367 (6)

[0199] Where: V Fc V is the fixed carbon volume content, in %; Aad is the ash volume content, in %.

[0200] The volatile matter volume content is determined based on the following formula:

[0201] V Vda =V Aad *3.555+21.342 (7)

[0202] Where: V Vda V is the volume content of volatile matter, in %; Aad is the ash volume content, in %.

[0203] Step 105: Combining the mineral skeleton density values ​​of fixed carbon, ash, and volatile matter with the calculated volume contents of fixed carbon, ash, and volatile matter, and using the coal rock volume physical model, a coal rock variable skeleton density curve is constructed.

[0204] Due to the complex structure of coal reservoirs and their easy expansion, the acoustic time difference is difficult to reliably reflect the porosity of coal reservoirs. In addition, the coal is affected by water, fracture water and other hydrogen indexes, so it is difficult to use it to accurately calculate the porosity of coal reservoirs. Therefore, density logging curve data is the preferred logging curve data for calculating the porosity of coal reservoirs. Therefore, for the target work area, according to the coal volume physical model, the mineral skeleton density of fixed carbon, ash, and volatile matter obtained by constrained optimization and the volume content of fixed carbon, ash, and volatile matter calculated by modeling are substituted into formula (8) to construct the coal variable skeleton density curve.

[0205] The variable skeleton density curve is determined based on the following formula:

[0206]

[0207] Where: DEN mb Coal rock skeleton density data, unit is g / cm 3 ; V Aad V is the ash volume content, in %; Fc V is the fixed carbon volume content, in %; Vda is the volume content of volatile matter, in %; ρ Aad is the ash skeleton density, in g / cm 3 ρ FC is the fixed carbon skeleton density, in g / cm 3 ρ Vda is the volatile matter skeleton density, in g / cm 3 ; j is the number of data points of the variable skeleton density curve.

[0208] Step 106: Calculate the coal-rock skeleton porosity by using the existing porosity model in combination with the coal-rock skeleton density curve.

[0209] Substitute the coal reservoir density (DEN) curve data of the target work area measured by the logging instrument and the constructed coal-rock skeleton density data into formula (9), and perform point-by-point calculation according to the sampling points of the logging instrument, and finally realize the continuous calculation of the coal-rock skeleton porosity. By comparing and analyzing the coal-rock porosity with the experimental analysis, the calculation results of this method are more accurate and precise.

[0210] The coal rock skeleton porosity curve is determined based on the following formula:

[0211]

[0212] Where: is the coal rock skeleton porosity, in %; DEN is the density logging data, in g / cm 3 ;DEN mb Coal rock skeleton density data, unit is g / cm 3 ρ f is the fluid density data, in g / cm 3 ; k is the number of data points of the coal rock skeleton porosity curve.

[0213] Figure 4 : is a schematic diagram comparing the calculation results of the coal rock variable skeleton porosity calculation method provided by an optional embodiment of the present invention and the traditional coal rock porosity calculation method, such as Figure 4 As shown, the porosity calculated by the coal rock variable skeleton porosity calculation method can be obtained. By comparing and analyzing the porosity calculated by the traditional coal rock porosity calculation method, the calculation results of this method are more precise and accurate.

[0214] Figure 5 is a schematic diagram of the actual application effect provided by an optional embodiment of the present invention, such as Figure 5 As shown, Figure 5 In the figure, the first track is the natural gamma curve (GR), the second track is the depth track, the third track is the lithology profile, the fourth track is the drilling core, the fifth track is the deep and shallow lateral resistivity curve (RT, RI), the sixth track is the three porosity curves (AC, DEN, CNL), the seventh track is the calculated ash content curve (the circle is the experimental analysis ash content), the eighth track is the calculated volatile content curve (the circle is the experimental analysis volatile content), the ninth track is the calculated fixed carbon content curve (the circle is the experimental analysis fixed carbon content), the tenth track is the calculated variable skeleton density curve, the eleventh track is the calculated variable skeleton porosity curve (the circle is the experimental analysis porosity), and the twelfth track is the porosity curve calculated by the traditional porosity model (the circle is the experimental analysis porosity). In the figure, the porosity calculated by the traditional porosity model is less consistent with the experimental analysis porosity of coal and rock, and the calculation error is large. By adopting the coal rock variable skeleton porosity calculation method, the calculated variable skeleton porosity is highly consistent with the experimental analysis porosity and the calculation error is small, which verifies the reliability of this method.

[0215] In summary, the present invention provides a calculation method for determining the variable skeleton porosity of coal rock from logging curves based on the coal rock volume physical model. The method includes: obtaining coal quality analysis data of the target reservoir, including volume content data of industrial components of coal rock (fixed carbon, ash, moisture and volatile matter), coal rock logging data (natural gamma, density), and coal rock experimental analysis porosity; using the coal rock skeleton density formula to calculate the skeleton density value of the coal rock experimental sample; according to the coal rock volume physical model, establishing an objective function, with the density value of fixed carbon, ash and volatile matter greater than zero as a constraint condition, calculating the mineral skeleton density value of fixed carbon, ash and volatile matter; preferably selecting logging data that is more sensitive to changes in industrial components of coal rock. Parameters, a multivariate regression interpretation model between fixed carbon, ash, volatile matter and sensitive logging parameters was established, and the volume content of fixed carbon, ash and volatile matter was calculated; the coal rock volume physical model was used to construct the coal rock variable skeleton density curve by combining the mineral skeleton density values ​​of fixed carbon, ash and volatile matter and the calculated volume content of fixed carbon, ash and volatile matter; the existing porosity model was used in combination with the coal rock variable skeleton density curve to finally realize the calculation of the coal rock variable skeleton porosity. The calculation accuracy is significantly better than that of traditional technology, which improves the calculation accuracy of the coal rock reservoir porosity.

[0216] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for calculating the porosity of coal rock skeleton, characterized in that: Based on the coal rock volume physical model, the coal rock variable skeleton porosity is determined by the logging curve.

2. The method for calculating the coal rock skeleton porosity according to claim 1, characterized in that: Based on the coal rock volume physical model, the determination of coal rock variable skeleton porosity from the well logging curve specifically includes the following steps: Step 101, obtaining coal quality analysis data of the target reservoir, including water content and mineral components in coal rock, volume content data of mineral components, coal rock logging data, and coal rock experimental analysis porosity; the coal rock logging data includes natural gamma data and density data; Step 102, using the coal rock skeleton density formula, calculate the skeleton density value of the coal rock test sample; Step 103, establishing an objective function based on the coal rock volume physical model, taking the density value of each mineral component greater than zero as a constraint condition, and calculating the density value of each mineral skeleton; Step 104, optimizing the logging parameters that are sensitive to the changes in coal and rock industrial components, establishing a multivariate regression interpretation model between each mineral and the sensitive logging parameters, and calculating the volume content of each mineral component; Step 105, constructing a coal rock variable skeleton density curve according to the coal rock volume physical model using the skeleton density data of each mineral calculated in step 103 and the volume content of each mineral component calculated in step 104; Step 106, calculating the coal-rock transformed skeleton porosity according to the coal-rock transformed skeleton density curve.

3. The method for calculating the coal rock skeleton porosity according to claim 2, characterized in that: The industrial components of coal rock include fixed carbon, ash and volatile matter.

4. The method for calculating the coal rock skeleton porosity according to claim 3, characterized in that: In step 103, the mineral skeleton density values ​​of fixed carbon, ash and volatile matter are calculated with the constraint that the density values ​​of fixed carbon, ash and volatile matter are greater than zero; in step 104, a multivariate regression interpretation model between fixed carbon, ash and volatile matter and sensitive logging parameters is established to calculate the volume content of fixed carbon, ash and volatile matter.

5. The method for calculating the coal rock skeleton porosity according to claim 2, characterized in that: In step 102, the skeleton density data of the coal rock experimental sample points are determined based on the following formula: Where: ρ m The calculated coal rock sample point skeleton density data, in g / cm 3 ; DEN is the well logging density data corresponding to the coal rock experimental sample point, in g / cm 3 ; is the effective porosity of coal rock; ρ f is the fluid density data, in g / cm 3 ; i is the serial number of the coal rock experimental sample point.

6. The method for calculating the coal rock skeleton porosity according to claim 2, characterized in that: The coal rock volume physical model in step 103 is determined based on the following formula: V m =V Aad +V Fc +V Vda (2) Where: V m is the total volume of coal rock skeleton; V Aad is the ash volume content; V Fc is the fixed carbon volume content; V Vda is the volume content of volatile matter.

7. The method for calculating the coal rock skeleton porosity according to claim 2, characterized in that: The objective function in step 103 is determined based on the following formula: The constraints are determined based on the following formula: r Aad >0,ρ FC >0,ρ Vda >0 (4) Where: f (x) The objective function to be solved for constrained optimization; ρ Aad is the ash skeleton density, in g / cm 3 ; ρ FC is the fixed carbon skeleton density, in g / cm 3 ; ρ Vda is the volatile matter skeleton density, in g / cm 3 ; V Aad is the ash volume content, in %; V Fc is the fixed carbon volume content, in %; V Vda is the volume content of volatile matter, in %; DEN is the well logging density data corresponding to the coal rock experimental sample point, in g / cm 3 ; i is the serial number of the coal rock experimental sample point; n is the total number of coal rock experimental samples.

8. The method for calculating the coal rock skeleton porosity according to claim 2, characterized in that: In step 104, the ash volume content is determined based on the following formula: V Aad =GR*0.027+DEN*12.528-14.697 (5) The fixed carbon volume content is determined based on the following formula: V Fc =V Aad *(-4.725)+77.367 (6) The volatile matter volume content is determined based on the following formula: V Vda =V Aad *3.555+21.342 (7) Where: V Aad is the ash volume content, in %; V Fc is the fixed carbon volume content, in %; V Vda is the volume content of volatile matter, in %; GR is the natural gamma logging data, API; DEN is the well logging density data corresponding to the coal rock experimental sample point, g / cm 3 .

9. The method for calculating the coal rock skeleton porosity according to claim 2, characterized in that: In step 105, the variable skeleton density curve is determined based on the following formula: Where: DEN mb Coal rock skeleton density data, unit is g / cm 3 ; V Aad is the ash volume content, in %; V Fc is the fixed carbon volume content, in %; V Vda is the volume content of volatile matter, in %; ρ Aad is the ash skeleton density, in g / cm 3 ; ρ FC is the fixed carbon skeleton density, in g / cm 3 ; ρ Vda is the volatile matter skeleton density, in g / cm 3 ; j represents the data point number of the variable skeleton density curve.

10. The method for calculating coal rock skeleton porosity according to claim 2, characterized in that: In step 106, the coal-rock skeleton porosity curve is determined based on the following formula: Where: is the coal rock matrix porosity, in %; DEN is the density logging data, the unit is g / cm 3 ; DEN mb Coal rock skeleton density data, unit is g / cm 3 ; ρ f is the fluid density data, in g / cm 3 ; k is the number of data points of the coal rock skeleton porosity curve.

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