Coal rock variable skeleton porosity calculation method

Abstract

The present application provides a coal rock variable skeleton porosity calculation method, and belongs to the technical field of petroleum, natural gas geology and exploration and development engineering. The present application uses a coal rock skeleton density formula to calculate the skeleton density value of a coal rock experimental sample; according to a coal rock volume physical model, a target function is established to calculate the skeleton density value of each mineral; a logging parameter sensitive to the change of the coal rock industrial component is optimized, a multiple regression interpretation model between each mineral and the sensitive logging parameter is established, and the volume content of each mineral component is calculated; 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; and the coal rock variable skeleton porosity is calculated according to the coal rock variable skeleton density curve. The present application fully considers the change of the coal rock skeleton caused by the change of the content of the coal rock industrial component, and has high calculation precision and good application effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of petroleum, natural gas geology and exploration and development engineering, and particularly relates to a coal rock variable framework porosity calculation method. BACKGROUND

[0002] Due to the influence of factors such as the change of coal rock industrial component content and cleat development, when the conventional porosity model is used to calculate the porosity of the coal rock reservoir, the calculation accuracy of the porosity of the coal rock reservoir is low, the error is large, and the obtained porosity calculation result cannot meet the requirement of fine reservoir evaluation.

[0003] For some areas, the deep coal rock gas resource reserves are very rich, which are different from the traditional coalbed methane. More than 80% of the coal rock in these areas is buried at a depth of 2000-3500m, and belongs to deep coal rock reservoir. The porosity of this type of reservoir is large, the storage space is mainly medium and large pores, and the coal rock gas mainly exists in the pore space in the form of free gas. Therefore, the calculation accuracy of the porosity parameter of the coal rock gas reservoir plays a crucial role in the evaluation of the coal rock gas reservoir. Due to the complexity of the composition of the coal rock reservoir, if the conventional porosity model is used to calculate the porosity without considering the influence of the change of the content of the coal rock industrial component, the calculation error of the porosity will inevitably increase, and the free gas content cannot be accurately evaluated.

[0004] In order to establish a high-precision coal rock gas reservoir evaluation model and improve the evaluation accuracy of the coal rock gas reservoir, it is necessary to consider the influence of the change of the content of the coal rock industrial component when calculating the porosity. In view of the change of the content of the coal rock industrial component, a variable framework porosity model is established, so that the porosity calculation accuracy is higher and the real situation of the coal rock reservoir can be better reflected.

[0005] At present, the most commonly used method for calculating the porosity of the coal rock reservoir is to analyze the porosity based on the coal core experiment, establish a density-porosity or acoustic travel time-porosity crossplot, determine the coal rock density or acoustic travel time framework value, and then calculate the porosity. This method uses a fixed coal rock framework and does not consider the influence of the change of the content of the coal rock industrial component on the coal rock framework, which leads to low accuracy and poor application effect of the above calculation method. SUMMARY

[0006] In order to solve the problems in the prior art, the present application provides a coal rock variable skeleton porosity calculation method, which is based on a coal rock volume physical model, determines the coal rock variable skeleton porosity from logging curves, calculates the skeleton density value of a coal rock experimental sample by using a coal rock skeleton density formula, establishes an objective function according to the coal rock volume physical model, calculates the skeleton density value of each mineral, optimizes logging parameters sensitive to the change of the coal rock industrial component, establishes a multiple regression interpretation model between each mineral and the sensitive logging parameters, calculates the volume content of each mineral component, constructs a coal rock variable skeleton density curve 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, and calculates the coal rock variable skeleton porosity according to the coal rock variable skeleton density curve.The present application fully considers the change of the coal rock skeleton caused by the change of the content of the coal rock industrial component, has high calculation precision and good application effect.

[0007] The present application provides a coal rock variable skeleton porosity calculation method, which is based on a coal rock volume physical model, determines the coal rock variable skeleton porosity from logging curves.

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

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

[0010] Step 102: Calculate the skeleton density value of a coal rock experimental sample by using a coal rock skeleton density formula;

[0011] Step 103: Calculate the skeleton density value of each mineral according to the coal rock volume physical model by establishing an objective function with the constraint condition that the density value of each mineral component is greater than zero;

[0012] Step 104: Calculate the volume content of each mineral component by optimizing logging parameters sensitive to the change of the coal rock industrial component and establishing a multiple regression interpretation model between each mineral and the sensitive logging parameters;

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

[0014] Step 106: Calculate the coal rock variable skeleton porosity according to the coal rock variable skeleton density curve.

[0015] Preferably, the industrial components of the 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 multiple regression interpretation model between fixed carbon, ash and volatile matter and sensitive logging parameters is established, and the volume content of fixed carbon, ash and volatile matter is calculated.

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

[0018]

[0019] In the formula:

[0020] ρ m is the calculated skeleton density data of the coal rock experimental sample points, with the unit of g / cm 3 ;

[0021] DEN is the logging density data corresponding to the coal rock experimental sample points, with the unit of g / cm 3 ;

[0022] is the effective porosity of coal rock;

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

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

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

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

[0027] In the formula:

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

[0029] V Aad is the volume content of ash;

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

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

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

[0033]

[0034] wherein:

[0035] f (x) is the objective function of the constrained optimization solution;

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

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

[0038] p 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 volatile matter volume content, in %;

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

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

[0044] n is the total number of experimental sample points of coal rock;

[0045] The constraint condition is determined based on the following formula:

[0046] p Aad > 0, p FC > 0, p Vda > 0 (4)

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

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

[0052] In the formula:

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

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

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

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

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

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

[0059]

[0060] In the formula:

[0061] DEN mb is the coal rock variable matrix density data, in 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 volatile volume content, in %;

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

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

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

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

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

[0070]

[0071] In the formula:

[0072] is the coal rock variable framework porosity, unit: %;

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

[0074] DEN mb is the coal rock variable framework density data, unit: g / cm 3 ;

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

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

[0077] Compared with the prior art, the present application has the following beneficial effects:

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

[0079] Figure 1 is the flowchart of the coal rock variable framework porosity calculation method of an embodiment of the present application;

[0080] Figure 2 is the coal rock volume physical model diagram of an embodiment of the present application;

[0081] Figure 3 is the experimental analysis ash content and calculated ash content volume content correlation diagram of an embodiment of the present application;

[0082] Figure 4 is the comparison diagram of the calculation results of the coal rock variable framework porosity calculation method and the traditional coal rock porosity calculation method of an embodiment of the present application;

[0083] Figure 5 is the actual application effect diagram of an embodiment of the present application. DETAILED DESCRIPTION

[0084] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0085] The application provides a coal rock variable skeleton porosity calculation method, which is determined based on a coal rock volume physical model and well logging curves.

[0086] According to one specific embodiment of the application, the coal rock variable skeleton porosity is determined based on a coal rock volume physical model and well logging curves, and specifically includes the following steps:

[0087] Step 101: Obtain coal quality analysis data of a target reservoir, including moisture and mineral components in coal rock, mineral component volume content data, 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: Calculate the skeleton density value of a coal rock experimental sample by using a coal rock skeleton density formula.

[0089] Step 103: According to a coal rock volume physical model, establish a target function, and calculate the mineral skeleton density value by taking the density value of each mineral component as a constraint condition.

[0090] Step 104: Preferentially select a well logging parameter sensitive to coal rock industrial component changes, establish a multiple regression interpretation model between each mineral and the sensitive well logging parameter, and calculate the volume content of each mineral component.

[0091] Step 105: According to the coal rock volume physical model, construct a coal rock variable skeleton density curve by using the mineral skeleton density data calculated in step 103 and the volume content of each mineral component calculated in step 104.

[0092] Step 106: Calculate the coal rock variable skeleton porosity according to the coal rock variable skeleton density curve.

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

[0094] According to one specific embodiment of the application, in step 103, the mineral skeleton density values of the fixed carbon, ash, and volatile matter are calculated by taking the density values of the fixed carbon, ash, and volatile matter as constraint conditions; and in step 104, a multiple regression interpretation model between the fixed carbon, ash, and volatile matter and the sensitive well logging parameter is established, and the volume content of the fixed carbon, ash, and volatile matter is calculated.

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

[0096]

[0097] In the formula,

[0098] p m The calculated coal rock experimental sample point skeleton density data is g / cm 3 ;

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

[0100] The coal rock effective porosity is

[0101] V f The fluid density data is g / cm 3 ;

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

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

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

[0105] In the formula:

[0106] V m The total coal rock skeleton volume is

[0107] V Aad The ash volume content is

[0108] V Fc The fixed carbon volume content is

[0109] V Vda The volatile matter volume content is

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

[0111]

[0112] In the formula:

[0113] f (x) The objective function of the constraint optimization solution is

[0114] p Aad The ash skeleton density is g / cm 3 ;

[0115] p FC The fixed carbon skeleton density is g / cm 3;

[0116] p Vda is the volatile matter skeleton density, unit: g / cm 3 ;

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

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

[0119] V Vda is the volatile matter volume content, unit: %;

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

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

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

[0123] The constraint condition is determined based on the following formula:

[0124] p Aad > 0, p FC > 0, p Vaa > 0 (4)

[0125] According to one specific embodiment of the present application, in the 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] In the formula:

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

[0133] V Fc is the fixed carbon volume content, unit: %;

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

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

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

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

[0138]

[0139] In the formula:

[0140] DEN mb is the coal rock variable matrix density data, unit is g / cm 3 ;

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

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

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

[0144] ρ Aad is the ash matrix density, unit is g / cm 3 ;

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

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

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

[0148] According to one specific embodiment of the present application, in the step 106, the coal rock variable matrix porosity curve is determined based on the following formula:

[0149]

[0150] In the formula:

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

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

[0153] DEN mb is the variable skeleton density data of coal rock, unit: g / cm 3 ;

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

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

[0156] Example 1

[0157] Figure 1 is a flow chart of the method for calculating the variable skeleton porosity of coal rock according to the embodiment of the present application, as shown in the figure, the method comprises the following steps: Figure 1

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

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

[0161]

[0162] In the formula:

[0163] ρ m is the calculated skeleton density data of the coal rock experimental sample point, unit: g / cm 3 ;

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

[0165] is the effective porosity of coal rock;

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

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

[0168] Step 103, according to the coal rock volume physical model, a target function is established to calculate the mineral skeleton density values of fixed carbon, ash and volatile matter, with the constraint condition that the density values of fixed carbon, ash and volatile matter are greater than zero.

[0169] According to the industrial analysis method of coal, coal rock can be divided into four parts: fixed carbon, ash, volatile matter and moisture. According to the composition, a coal rock volume physical model is established, as shown in FIG. 1. Since the moisture adheres to the inner surface of the coal rock reservoir space and is not part of the coal rock skeleton, it is considered that the skeleton volume of the coal rock is composed of three parts: fixed carbon, ash and volatile matter. The coal rock volume physical model is determined based on the following formula: Figure 2

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

[0171] In the formula:

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

[0173] V Aad is the volume content of ash;

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

[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 considered that the logging density data is the sum of the contribution values of the fixed carbon skeleton density, ash skeleton density and volatile matter skeleton density of the coal rock. Therefore, by applying the optimization mathematical method, according to the principle of nonlinear weighted least squares method and error theory, a target function and constraint conditions are established, and the optimal solution of the target function is obtained under the constraint conditions, that is, when the target function value reaches the minimum value, the theoretical response value of the coal rock skeleton density ( ) reaches the best fitting with the corresponding input density logging response value, ρ Aad , ρ FC , ρ Vda , which are the fixed carbon skeleton density, ash skeleton density and volatile matter skeleton density obtained by constraint optimization, are considered as the most reasonable fixed carbon skeleton density, ash skeleton density and volatile matter skeleton density.

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

[0178]

[0179] wherein:

[0180] f (x) is the objective function of the constrained optimization solution;

[0181] p Aad is the ash skeleton density, unit g / cm 3 ;

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

[0183] p Vda is the volatile skeleton density, unit g / cm 3 ;

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

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

[0186] V Vda is the volatile volume content, unit %;

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

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

[0189] The constraint condition is determined based on the following formula:

[0190] p Aad > 0, p FC > 0, p Vda > 0 (4)

[0191] Step 104, the multi-element regression interpretation model between the fixed carbon, ash, volatile and the sensitive logging parameter which is preferably sensitive to the change of the coal rock industrial component is established, and the volume content of the fixed carbon, ash and volatile is calculated.

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

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

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

[0195] Figure 3 It is the experimental analysis of the ash and the calculation of the ash volume content correlation schematic diagram provided by the optional embodiment of the application, as Figure 3 shown, the formula calculation result has high correlation with the experimental analysis data, and the calculation result is accurate.

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

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

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

[0199] V Fc fixed carbon volume content, unit: %; V Aad ash volume content, unit: %.

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

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

[0202] V Vda volatile matter volume content, unit: %; V Aad ash volume content, unit: %.

[0203] Step 105, combine the mineral skeleton density values of fixed carbon, ash, and volatile matter and the calculated volume content of fixed carbon, ash, and volatile matter, and use the coal rock volume physical model to construct the coal rock variable skeleton density curve.

[0204] Due to the complex structure of coal rock reservoir and the easy expansion, the acoustic travel time is difficult to reliably reflect the porosity of coal rock reservoir, and it is also difficult to accurately calculate the porosity of coal rock reservoir by using the hydrogen index affected by moisture, fracture water and other places in coal rock. Therefore, the density logging curve data is the preferred logging curve data for calculating the porosity of coal rock reservoir. Therefore, for the target work area, based on the coal rock volume physical model, the mineral skeleton density of fixed carbon, ash, and volatile matter obtained by constraint optimization solving and the volume content of fixed carbon, ash, and volatile matter calculated by modeling are substituted into formula (8) to construct the coal rock variable skeleton density curve.

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

[0206]

[0207] In the formula, DEN mb is the coal rock variable skeleton density data, with the unit of g / cm 3 ; V Aad is the ash volume content, with the unit of %; V Fc is the fixed carbon volume content, with the unit of %; V Vda is the volatile matter volume content, with the unit of %; p Aad is the ash skeleton density, with the unit of g / cm 3 ; p FC is the fixed carbon skeleton density, with the unit of g / cm 3 ; p Vda is the volatile matter skeleton density, with the unit of g / cm 3 ; and j is the number of variable skeleton density curve data points.

[0208] Step 106, use the existing porosity model to calculate the coal rock variable skeleton porosity in combination with the coal rock variable skeleton density curve.

[0209] Substitute the coal rock reservoir density (DEN) curve data of the target work area measured by the logging instrument and the constructed coal rock variable skeleton density data into formula (9), and calculate point by point according to the sampling points of the logging instrument, to finally realize the continuous calculation of the coal rock variable skeleton porosity. Through comparison and analysis with the experimental analysis of coal rock porosity, the calculation result of this method is more accurate.

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

[0211]

[0212] In the formula: is coal rock variable skeleton porosity, unit: %; DEN is density logging data, unit: g / cm 3 ; DEN mb is coal rock variable skeleton density data, unit: g / cm 3 ; p f is fluid density data, unit: g / cm 3 ; k is the number of coal rock variable skeleton porosity curve data points.

[0213] Figure 4 is a comparison diagram of the calculation results of the coal rock variable skeleton porosity calculation method and the traditional coal rock porosity calculation method provided by the optional embodiment of the present application, as shown in Figure 4 , the porosity calculated by the coal rock variable skeleton porosity calculation method can be obtained, and the porosity calculated by the traditional coal rock porosity calculation method is compared and analyzed, the calculation result of the method is more accurate and more accurate.

[0214] Figure 5 is a schematic diagram of the actual application effect provided by the optional embodiment of the present application, as shown in Figure 5 , in Figure 5 , the first track in the figure is a natural gamma curve (GR), the second track is a depth track, the third track is a lithology profile, the fourth track is a drilling core, the fifth track is a deep and shallow lateral resistivity curve (RT, RI), the sixth track is a three-porosity curve (AC, DEN, CNL), the seventh track is a calculated ash content curve (circular point is the experimental analysis of ash content), the eighth track is a calculated volatile content curve (circular point is the experimental analysis of volatile content), the ninth track is a calculated fixed carbon content curve (circular point is the experimental analysis of fixed carbon content), the tenth track is a calculated variable skeleton density curve, the eleventh track is a calculated variable skeleton porosity curve (circular point is the experimental analysis of porosity), and the twelfth track is a porosity curve calculated by a traditional porosity model (circular point is the experimental analysis of porosity). In the figure, the porosity calculated by the traditional porosity model has a low degree of coincidence with the coal rock experimental analysis porosity, and has a large calculation error. By using the coal rock variable skeleton porosity calculation method, the calculated variable skeleton porosity has a high degree of coincidence with the experimental analysis porosity, and has a small calculation error, thereby verifying the reliability of the method.

[0215] In conclusion, the present application provides a method for determining coal rock variable framework porosity from logging curves based on a coal rock volume physical model. The method comprises: obtaining coal quality analysis data of the target reservoir, including coal rock industrial component (fixed carbon, ash, moisture and volatile matter) volume content data, coal rock logging data (natural gamma, density), and coal rock experimental analysis porosity; using a coal rock framework density formula to calculate the framework density value of the coal rock experimental sample; according to the coal rock volume physical model, establishing a target function with the constraint condition that the density values of fixed carbon, ash and volatile matter are greater than zero, to calculate the mineral framework density values of fixed carbon, ash and volatile matter; preferably selecting logging parameters sensitive to changes in coal rock industrial components, establishing a multiple regression interpretation model between fixed carbon, ash, volatile matter and sensitive logging parameters, to calculate the volume content of fixed carbon, ash and volatile matter; combining the mineral framework density values of fixed carbon, ash and volatile matter and the already calculated volume content of fixed carbon, ash and volatile matter, using the coal rock volume physical model to construct a coal rock variable framework density curve; using an existing porosity model in combination with the coal rock variable framework density curve to finally realize the calculation of coal rock variable framework porosity, which has a significantly better calculation accuracy than traditional technologies and improves the calculation accuracy of coal rock reservoir porosity.

[0216] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall fall within the protection scope of the present application.

Claims

1. A method for calculating coal rock variable framework porosity, characterized in that, Based on the coal rock volume physical model, the coal rock variable framework porosity is determined according to the logging curve, and specifically includes the following steps: Step 101, obtaining coal quality analysis data of the target reservoir, including moisture and mineral composition in the coal rock, mineral composition volume content data, coal rock logging data, and coal rock experimental analysis porosity; the coal rock logging data includes natural gamma data and density data; Step 102, calculating the framework density value of the coal rock experimental sample by using the coal rock framework density formula; Step 103, according to the coal rock volume physical model, establishing a target function, taking the density value of each mineral component being greater than zero as a constraint condition, and calculating the mineral framework density value; Step 104, preferably selecting a logging parameter sensitive to the change of the coal rock industrial component, establishing a multiple regression interpretation model between each mineral and the sensitive logging parameter, and calculating the volume content of each mineral component; Step 105, according to the coal rock volume physical model, using the mineral framework density data calculated in step 103 and the volume content of each mineral component calculated in step 104, constructing a coal rock variable framework density curve; Step 106, calculating the coal rock variable framework porosity according to the coal rock variable framework density curve; In the step 103, the target function is determined based on the following formula: The constraint condition is determined based on the following formula: In the formula: f (x) to constrain the objective function of the optimization solution; Ash skeleton density in g / cm 3 ; To fix the carbon skeleton density in g / cm 3 ; Volatile skeleton density in g / cm3 3 ; Ash content in vol. %, unit %; Fixed carbon volume content, in %; VOC is the volatile content in volume, in %; Density data of the coal rock experimental sample points, in g / cm 3 ; Coal rock experimental sample point serial number; n Total number of coal rock experimental samples.

2. The method of calculating coal matrix reconfiguration porosity according to claim 1, characterized in that, The industrial components of the coal rock include fixed carbon, ash and volatile matter.

3. The method of calculating coal matrix reconfiguration porosity according to claim 2, characterized in that, In step 103, the mineral framework density values of the fixed carbon, ash and volatile matter are calculated with the constraint condition that the density values of the fixed carbon, ash and volatile matter are greater than zero; in step 104, the multiple regression interpretation model between the fixed carbon, ash and volatile matter and the sensitive logging parameter is established, and the volume content of the fixed carbon, ash and volatile matter is calculated.

4. The method of calculating coal matrix reconfiguration porosity according to claim 1, characterized in that, In the step 102, the coal rock experimental sample point framework density data is determined based on the following formula: In the formula: The calculated coal rock experimental sample point skeleton density data is in g / cm 3 ; Density data of the coal rock experimental sample points, in g / cm 3 ; φe is effective porosity of coal rock; Fluid density data in g / cm 3 ; Assign a serial number to the coal rock experimental sample.

5. The method of calculating coal matrix reconfiguration porosity according to claim 1, wherein, In the step 103, the coal rock volume physical model is determined based on the following formula: In the formula: Vtotal is the total volume of the coal matrix skeleton; Ash content is the volume content; Fixed carbon volume content; VOC is the volume content of volatile components.

6. The method of calculating coal matrix reconfiguration porosity according to claim 1, wherein, In the step 104, the ash volume content is determined based on the following formula: The fixed carbon volume content is determined based on the following formula: The volatile matter volume content is determined based on the following formula: In the formula: Ash volume content in %; Fixed carbon volume content, in %; VOC is the volatile content in volume, in %; Natural gamma ray log data, API; Density data of the coal rock experimental sample points, g / cm 3 .

7. The method of calculating coal matrix reconfiguration porosity according to claim 1, characterized in that, In the step 105, the variable framework density curve is determined based on the following formula: In the formula: Coal matrix density data, in g / cm 3 ; Ash volume content in %; Fixed carbon volume content, in %; VOC is the volatile content in volume, in %; Ash skeleton density in g / cm 3 ; To fix the carbon skeleton density in g / cm 3 ; Volatile skeleton density in g / cm3 3 ; j represents the skeleton density curve data point number.

8. The method of calculating coal matrix reconfiguration porosity according to claim 1, wherein, In the step 106, the coal rock variable framework porosity curve is determined based on the following formula: In the formula: is the coal rock variable framework porosity, in %; Density log data in g / cm 3 ; Coal density data, in g / cm 3 ; For fluid density data, units are g / cm 3 ; The number of coal rock variable skeleton porosity curve data points.

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