CN113153264A - Anisotropy-considered early water production data analysis method and system for coal-bed gas well - Google Patents
Anisotropy-considered early water production data analysis method and system for coal-bed gas well Download PDFInfo
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Abstract
The invention discloses an anisotropy-considered method and system for analyzing early water production data of a coal-bed gas well, which comprises the following steps: obtaining known coal bed physical parameters and single-phase water stage production historical data of a coal bed gas well; homogeneous permeability k assuming conversion of a heterogeneous coal seam to a homogeneous coal seami(ii) a Carrying out linearization treatment on the coal-bed gas well water production equation considering anisotropy, and calculating the values of independent variable X and dependent variable Y in the linearization equation; putting the X, Y value in the step into the same rectangular coordinate system, and obtaining the permeability k according to the inverse calculation of the slope of the linear relation; k and k areiComparing, and if the relative error of the two is within 1%, considering kiIs correct; otherwise, continue to assume homogeneous permeability ki(ii) a Calculating the permeability k of the coal bed face in the cleat direction according to the intercept and the slope in the linear equation of the water production of the coal bed gas well considering the anisotropyxAnd coalPermeability k in the direction of layer end cleavagey。
Description
Technical Field
The invention relates to the field of oil and gas field development engineering, in particular to an anisotropy-considered early water production data analysis method and system for a coal bed gas well, which are used for unconventional oil and gas reservoir development.
Background
The production data analysis method is a method for analyzing actual production data of an oil (gas) well through a mathematical model so as to reversely solve reservoir parameters, and the used mathematical model is generally obtained through derivation based on an oil (gas) reservoir internal fluid seepage equation, boundary conditions and the like. The production data analysis method can reduce the seepage state of reservoir fluid as much as possible theoretically, has clear physical significance and theoretical background, and is practically based on the actual production data of the oil (gas) well, including yield data, pressure data, production time and the like, so that the method interpretation result has considerable reliability and practicability. In view of this, the production data analysis method has both theoretical background and practicability, is simple and convenient to apply, has reliable results, and is beneficial to quickly determining the key parameters of the reservoir in the oil (gas) reservoir site.
The coal seam generally develops a cleat system, cleats are natural fractures which generally develop in the coal seam, and cleats generally appear in two groups which are perpendicular or vertical to each other and are divided into a face cleat and an end cleat. The permeability of gas and coal-rock gas in a cleat system shows extremely strong heterogeneity, and a large number of investigations show that, as shown in table 1, the permeability in the surface cleat direction in coal-rock is always greater than that in the end cleat direction.
In the experimental evaluation of coal rock permeability anisotropy by Wangya, the permeability of a test sample collected from a Shanxi Hancheng mining area with active coal bed methane exploration and development in China is determined in the direction of face-cutting and end-cutting, and the result shows that: the permeability of the coal rock has obvious anisotropy, and the ratio of the permeability in the surface cleat direction to the permeability in the end cleat direction can reach 5.1-9.0; in a coal cleat compression experiment and permeability numerical simulation of the Friedel-crafts sea, surface cleats and end cleats of samples collected from Chengchuang mines, high-level hope cloud mines, Lu-Anyu mines and Lu-Anwuyang mines are measured under a microscope, and the initial width of the surface cleats is larger than the initial width of the end cleats, so that the permeability of the surface cleats is larger than that of the end cleats; in the coal bed gas productivity prediction based on the coal rock cleat orthogonal anisotropy, a sample is taken from an Ordos basin, the cleat opening of a coal reservoir simulation parameter surface is larger than the end cleat opening, and the ratio of the permeability is about 3.6; in the research of reasonable arrangement of coal seam extraction drill holes based on gas permeability anisotropy in Zengchunling, the permeability of a coal body in a parallel bedding direction is about 2.6 times of the permeability of a coal body in a vertical bedding direction, and further the anisotropic permeability difference of gas in a coal seam is caused.
Therefore, the trends of the face cutting and the end cutting in the coal seam are nearly orthogonal, and the permeability ratio of the face cutting and the end cutting is between 1.2 and 9.0, so that the remarkable permeability heterogeneity is shown.
TABLE 1 ratio of the face-to-face cleat and toe-cleat permeabilities of different coal mine areas
The production of a conventional coal bed gas well can go through an early drainage stage, the well bottom pressure of the early drainage stage is higher than the critical desorption pressure in a coal bed, no gas phase or a small amount of free gas phase exists in the coal rock cutting process, and the flow mechanism is a single-phase water flow. And (3) gradually reducing the bottom hole pressure along with the further production, once the bottom hole pressure is smaller than the critical desorption pressure, desorbing the adsorbed gas and entering a cutting system, and generating gas-water two-phase flow in the coal rock. According to the production characteristics of the coal-bed gas well, namely a single-phase drainage stage at the early production stage (time span of several months to several years) and a gas-water two-phase flow stage at the middle and later production stages (time span of several years to ten years), the existing coal-bed gas well production data analysis method can be divided into a single-phase water stage analysis method and a gas-water two-phase flow analysis method, wherein most researches belong to a gas-water two-phase flow analysis method.
The existing coal bed gas well 'single-phase water phase' analysis method can be subdivided into two types, one type uses the production data analysis method of conventional oil reservoirs and gas reservoirs for reference, replaces oil phases and gas phases with water phases, and still assumes that the reservoir has the characteristic of isotropic permeability; the other method considers the rock mechanical property and the low permeability characteristic of the coal rock, and considers the stress sensitivity effect and the pressure propagation distance on the basis of the first method, but the method does not consider the influence of anisotropy on the fluid permeability in the reservoir.
In general, most of the existing methods for analyzing production data of coal-bed gas wells aim at the stage of gas-water two-phase flow of the coal bed, and a small amount of methods for analyzing production data aim at the stage of single-phase water of the coal bed do not consider the influence of heterogeneity on single-phase water seepage in the coal bed. Moreover, the yield data of the coal bed gas-water two-phase flow stage is influenced by various factors such as profit sensitivity, matrix shrinkage and gas-water two-phase flow, so that the difficulty of inverting the formation parameters according to the two-phase flow data is high, and the reliability is questionable. In contrast, single phase water stage production data is only affected by stress sensitivity (higher geostress coal seam), permeability itself, and it is naturally superior to explain the permeability of the coal seam based on single phase water stage production data. In view of the above, the early water production data analysis method considering the coal bed anisotropy provided by the invention is of great significance.
Disclosure of Invention
In order to solve the problems and requirements, the method for analyzing the early water production data of the coal-bed gas well considering the anisotropy is provided, and the technical purpose can be achieved due to the adoption of the following technical characteristics, and other technical effects are brought.
The invention provides an anisotropic early water production data analysis method of a coal-bed gas well, which is characterized by comprising the following steps:
s10: obtaining a known coal bed physical parameter (P)e，φ，CtH) production history (t, Q (t), P) of single-phase water stage of coal-bed gas wellw(t)); wherein, PeIs the original bottom pressure, phi is the porosity of the coal bed, CtThe comprehensive compression coefficient of the coal bed is shown, and h is the thickness of the reservoir; t is the production time, Q (t) is the water production history, Pw(t) bottom hole pressure history;
s20: suppose notHomogeneous permeability k when transforming a homogeneous coal seam into a homogeneous coal seami；
S30: the water production equation of the coal-bed gas well considering the anisotropy is subjected to linearization treatment to obtain the following results:
wherein the content of the first and second substances,
wherein r iseRepresents the distance of the coal seam boundary from the bottom of the well, m; the permeability of coal bed gas is low, the production initial stage is accompanied with the transmission process of pressure wave, a 'dynamic boundary' exists, and the distance r between the coal bed boundary and the bottom of the welleThe expression of (a) is:
wherein t represents the production time, d; phi represents the porosity of the coal bed, and has no dimension; ctRepresents the overall compression factor, MPa-1；
Wherein mu represents the viscosity of coal bed water, mpa.S; r iswRepresents the wellbore radius, m; k represents the homogeneous permeability, mD, when converting a heterogeneous coal seam to a homogeneous coal seam; beta represents the heterogeneity intensity of the coal bed without dimension;
the parameters obtained in the above step S10 are substituted
Obtaining the value of Y at a certain production moment;
the parameters obtained in the above step S10 are substituted
Obtaining the value of X at a certain production moment;
s30: putting the X, Y value in the step S20 into the same coordinate system, and performing a linear equation according to a coal-bed gas well water production equation considering anisotropy to obtain the homogeneous permeability k when the heterogeneous coal bed is converted into the homogeneous coal bed;
s40: the homogeneous permeability k obtained in step S40 when the heterogeneous coal seam is converted into a homogeneous coal seam and the homogeneous permeability k obtained in step S20 when the heterogeneous coal seam is assumed to be converted into a homogeneous coal seamiComparing, and if the relative error epsilon of the two is within 1%, considering that the calculated homogeneous permeability when the assumed heterogeneous coal seam is converted into the homogeneous coal seam is correct; otherwise, go to S20 to continue assuming a homogeneous permeability k when the heterogeneous coal seam is converted to a homogeneous coal seami；
S50: calculating the permeability k of the coal bed face in the cleat direction according to the intercept and the slope in the linear equation of the water production of the coal bed gas well considering the anisotropyxAnd coal seam end cleat direction permeability ky。
In addition, the method for analyzing the early water production data of the coal-bed gas well considering the anisotropy can also have the following technical characteristics:
in one example of the invention, the initial value of homogeneous permeability when converting a heterogeneous coal seam to a homogeneous coal seam is the critical coal-bed gas well permeability or permeability explained by the well logging, well testing method.
According to a second aspect of the invention, a coal-bed gas well early water production data analysis system considering coal-bed anisotropy comprises:
a first input unit for inputting the known coal bed property parameter (P)e，φ，CtH) production history (t, Q (t), P) of single-phase water stage of coal-bed gas wellw(t)) parameter input; wherein, PeIs the original bottom pressure, phi is the porosity of the coal bed, CtThe comprehensive compression coefficient of the coal bed is shown, and h is the thickness of the reservoir; t is the production time, Q (t) is the water production history, Pw(t) bottom hole pressure history;
a second input unit for converting the homogeneous permeability k of the assumed heterogeneous coal seam into a homogeneous coal seamiInputting a value; the first calculation unit is used for obtaining the following result after carrying out linearization treatment on the coal-bed gas well water production equation considering anisotropy:
wherein the content of the first and second substances,
wherein r iseRepresents the distance of the coal seam boundary from the bottom of the well, m; the permeability of coal bed gas is low, the production initial stage is accompanied with the transmission process of pressure wave, a 'dynamic boundary' exists, and the distance r between the coal bed boundary and the bottom of the welleThe expression of (a) is:
wherein t represents the production time, d; phi represents the porosity of the coal bed, and has no dimension; ctRepresents the overall compression factor, MPa-1；
Wherein mu represents the viscosity of coal bed water, mpa.S; r iswRepresents the wellbore radius, m; k represents the homogeneous permeability, mD, when converting a heterogeneous coal seam to a homogeneous coal seam; beta represents the heterogeneity intensity of the coal bed without dimension;
bringing in the parameters obtained by the first input unit
Calculating to obtain the value of Y at a certain production moment;
bringing in the parameters obtained by the first input unit
Calculating to obtain the value of X at a certain production moment;
the second calculation unit is used for putting the X, Y value obtained by the first calculation unit into the same coordinate system, and performing a linearization equation according to a coal-bed gas well water production equation considering anisotropy to obtain the homogeneous permeability k when the heterogeneous coal bed is converted into the homogeneous coal bed;
a determination unit for determining whether the received signal is a signalThe homogeneous permeability k when the heterogeneous coal seam obtained by the second input unit is converted into a homogeneous coal seam and the homogeneous permeability k when the assumed heterogeneous coal seam obtained by the first input unit is converted into a homogeneous coal seamiComparing, and if the relative error epsilon of the two is within 1%, considering that the calculated homogeneous permeability when the assumed heterogeneous coal seam is converted into the homogeneous coal seam is correct; otherwise, the coal seam is transferred to a second input unit, and the homogeneous permeability k when the heterogeneous coal seam is converted into the homogeneous coal seam is continuously assumedi；
A third calculation unit for calculating the permeability k of the coal bed face in the cleat direction according to the intercept and the slope in the linear equation of the water production of the coal bed gas well considering the anisotropyxAnd coal seam end cleat direction permeability ky。
In one example of the invention, the initial value of homogeneous permeability when converting a heterogeneous coal seam to a homogeneous coal seam is the critical coal-bed gas well permeability or permeability explained by the well logging, well testing method.
The following description of the preferred embodiments for carrying out the present invention will be made in detail with reference to the accompanying drawings so that the features and advantages of the present invention can be easily understood.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments of the present invention will be briefly described below. Wherein the drawings are only for purposes of illustrating some embodiments of the invention and are not to be construed as limiting the invention to all embodiments thereof.
FIG. 1 is a flow chart of a method for analyzing early water production data of a coalbed methane well in consideration of anisotropy according to an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of specific embodiments of the present invention.
According to the first aspect of the invention, the method for analyzing the early water production data of the coal-bed gas well considering the anisotropy comprises the following steps:
s10: obtaining a known coal bed physical parameter (P)e，φ，CtH) production history (t, Q (t), P) of single-phase water stage of coal-bed gas wellw(t)); wherein, PeIs the original bottom pressure, phi is the porosity of the coal bed, CtThe comprehensive compression coefficient of the coal bed is shown, and h is the thickness of the reservoir; t is the production time, Q (t) is the water production history, Pw(t) bottom hole pressure history;
s20: homogeneous permeability k assuming conversion of a heterogeneous coal seam to a homogeneous coal seami(ii) a Preferably, the initial value of the homogeneous permeability when the heterogeneous coal seam is converted into the homogeneous coal seam is the permeability of a critical coal-bed gas well or the permeability explained by a well logging and testing method;
s30: the water production equation of the coal-bed gas well considering the anisotropy is subjected to linearization treatment to obtain the following results:
wherein the content of the first and second substances,
the parameters obtained in the above step S10 are substituted
Obtaining the value of Y at a certain production moment;
the parameters obtained in the above step S10 are substituted
Obtaining the value of X at a certain production moment;
the water production equation expression of the coal-bed gas well considering anisotropy is as follows:
wherein mu represents the viscosity of coal bed water, mpa.S; r iseRepresents the distance of the coal seam boundary from the bottom of the well, m; r iswRepresents the wellbore radius, m; k represents the homogeneous permeability, mD, when converting a heterogeneous coal seam to a homogeneous coal seam; beta represents the heterogeneity intensity of the coal bed without dimension;
wherein the content of the first and second substances,
in the formula, kxRepresenting the permeability of the coal seam face in the cutting direction, mD; k is a radical ofyRepresenting the permeability of the coal seam end in the cleat direction, mD;
wherein the content of the first and second substances,
wherein t represents the production time, d; phi represents the porosity of the coal bed, and has no dimension; ctRepresents the overall compression factor, MPa-1；
Ct＝Cf+Cw
Wherein C isfRepresents the compression coefficient of coal rock, MPa-1；CwRepresents the formation water compressibility factor, MPa-1；
From the linearization of the anisotropic coalbed methane well water production equation, X, Y is a function of production time, and k is a function of
The water production equation of the single-mouth coal-bed gas well is related to the permeability of the coal bed, and the single-mouth coal-bed gas well can be considered not to change along with time, so that the linear relation of the anisotropic coal-bed gas well water production equation to a linearization equation is established; moreover, the linear relationship has a slope of k and an intercept of
Can be used for explaining the heterogeneity of the obtained coal bed.
S30: putting the X, Y values of different production moments in the step S20 into the same rectangular coordinate system, and performing a linear equation according to a coal-bed gas well water production equation considering anisotropy to obtain the homogeneous permeability k when the heterogeneous coal bed is converted into the homogeneous coal bed; that is, the slope and intercept are obtained according to the linear relationship interpretation, and the k value is obtained.
S40: the homogeneous permeability k obtained in step S40 when the heterogeneous coal seam is converted into a homogeneous coal seam and the homogeneous permeability k obtained in step S20 when the heterogeneous coal seam is assumed to be converted into a homogeneous coal seamiComparing, and if the relative error epsilon of the two is within 1%, considering that the calculated homogeneous permeability when the assumed heterogeneous coal seam is converted into the homogeneous coal seam is correct; otherwise, go to S20 to continue assuming a homogeneous permeability k when the heterogeneous coal seam is converted to a homogeneous coal seami；
Wherein epsilon | ki-k∣/ki；
S50: calculating the permeability k of the coal bed face in the cleat direction according to the intercept and the slope in the linear equation of the water production of the coal bed gas well considering the anisotropyxAnd coal seam end cleat direction permeability ky；
Specifically, firstly, a linearization equation is carried out by an anisotropic coal-bed gas well water production equation:
determining the strength of heterogeneity beta of the coal seam, i.e.
Wherein b represents the intercept obtained by the linear relationship, with no dimension;
then respectively obtaining permeability k of coal layer in the coal seam face in the cleat direction according to intercept b and slope k values of linear relation in formulaxAnd coal seam end cleat direction permeability kyI.e. by
kx＝k×β
That is, when using this method, input parameters are requiredThe number includes production time t, water production history Q (t), bottom hole pressure history Pw(t), original base pressure PePorosity of coal bed, phi, comprehensive compressibility of coal bed, CtReservoir thickness h. The parameter obtained by the method is the permeability k of the coal bed surface in the cleat directionxPermeability k in the coal seam end cutting directiony。
The method is a reliable and accurate key reservoir parameter obtaining mode by combining a production data analysis method and oil (gas) well production data back-solving reservoir parameters, is obviously different from a conventional oil and gas reservoir, is a coal bed universal development and cleat system (including face cleat and end cleat), has nearly orthogonal trend in the coal beds of the conventional oil and gas reservoir and has larger difference of permeability, so that the coal bed has extremely strong anisotropic characteristic; the invention focuses on the influence of the heterogeneity on the fluid output of the reservoir, simultaneously considers that the influence factor of the productivity of the coal-bed gas well in the early production stage (single-phase water stage) is relatively single, and provides the method for analyzing the early water production data of the coal-bed gas well in consideration of the anisotropy, wherein the permeability in the coal-bed secant and end-secant directions can be reversely obtained according to the early water production, the production time and the bottom hole flow pressure of the coal-bed gas well. The method firstly carries out 'linearization' treatment on a water production equation under the influence of anisotropy, and can quickly determine the permeability anisotropy characteristic of the coal seam by combining the provided iteration and fitting method. At present, coal bed anisotropy is generally evaluated through indoor experimental research, the accuracy of an evaluation result depends on whether a core is representative or not and the number of experiments, and the obtained data has large uncertainty.
The analysis method is simple and convenient to apply, on one hand, reservoir information is directly extracted from actual production data based on seepage mechanics, the reliability of the explained heterogeneous characteristics is high, on the other hand, the steps of field coring and experiment operation of experiments are omitted, and the cost can be effectively controlled; the method can quickly, reliably and economically obtain the heterogeneity of the permeability of the coal bed, and lays a theoretical foundation for the efficient development of the coal bed gas well.
According to a second aspect of the invention, a coal-bed gas well early water production data analysis system considering coal-bed anisotropy comprises:
a first input unit for inputting the known coal bed property parameter (P)e，φ，CtH) production history (t, Q (t), P) of single-phase water stage of coal-bed gas wellw(t)) parameter input; wherein, PeIs the original bottom pressure, phi is the porosity of the coal bed, CtThe comprehensive compression coefficient of the coal bed is shown, and h is the thickness of the reservoir; t is the production time, Q (t) is the water production history, Pw(t) bottom hole pressure history;
a second input unit for converting the homogeneous permeability k of the assumed heterogeneous coal seam into a homogeneous coal seamiInputting a value; preferably, the initial value of homogeneous permeability when converting the heterogeneous coal seam into a homogeneous coal seam is a critical coal seam gas well permeability or a permeability explained by a logging, well testing method.
The first calculation unit is used for obtaining the following result after carrying out linearization treatment on the coal-bed gas well water production equation considering anisotropy:
wherein the content of the first and second substances,
bringing in the parameters obtained by the first input unit
Calculating to obtain the value of Y at a certain production moment;
bringing in the parameters obtained by the first input unit
Calculating to obtain the value of X at a certain production moment;
the water production equation expression of the coal-bed gas well considering anisotropy is as follows:
wherein Q represents water production, m3D; h represents reservoir thickness, m; peRepresenting the pressure at the coal seam boundary, since the present invention is directed to single phase water phase production data, PeIs the original coal bed pressure, MPa; pwThe pressure at the bottom of the coal bed gas well is represented as MPa; mu represents the viscosity of coal bed water, mpa.S; r iseRepresents the distance of the coal seam boundary from the bottom of the well, m; r iswRepresents the wellbore radius, m; k represents the homogeneous permeability, mD, when converting a heterogeneous coal seam to a homogeneous coal seam; beta represents the heterogeneity intensity of the coal bed without dimension;
wherein the content of the first and second substances,
in the formula, kxRepresenting the permeability of the coal seam face in the cutting direction, mD; k is a radical ofyRepresenting the permeability of the coal seam end in the cleat direction, mD;
wherein the content of the first and second substances,
wherein t represents the production time, d; phi represents the porosity of the coal bed, and has no dimension; ctRepresents the overall compression factor, MPa-1；
The second calculation unit is used for putting the X, Y values at different production moments obtained by the first calculation unit into the same rectangular coordinate system, and performing a linearization equation according to a coal-bed gas well water production equation considering anisotropy to obtain the homogeneous permeability k when the heterogeneous coal bed is converted into the homogeneous coal bed; that is, the slope and intercept are obtained according to the linear relationship interpretation, and the k value is obtained.
A judging unit for converting the homogeneous permeability k obtained by the second input unit when the heterogeneous coal seam is converted into a homogeneous coal seam and the homogeneous permeability k obtained by the first input unit when the assumed heterogeneous coal seam is converted into a homogeneous coal seamiComparing, and if the relative error epsilon of the two is within 1%, considering that the calculated homogeneous permeability when the assumed heterogeneous coal seam is converted into the homogeneous coal seam is correct; otherwise, the coal seam is transferred to a second input unit, and the homogeneous permeability k when the heterogeneous coal seam is converted into the homogeneous coal seam is continuously assumedi；
A third calculation unit for calculating the permeability k of the coal bed face in the cleat direction according to the intercept and the slope in the linear equation of the water production of the coal bed gas well considering the anisotropyxAnd coal seam end cleat direction permeability ky；
Specifically, firstly, a linearization equation is carried out by an anisotropic coal-bed gas well water production equation:
determining the strength of heterogeneity beta of the coal seam, i.e.
Wherein b represents the intercept obtained by the linear relationship, with no dimension;
then respectively obtaining permeability k of coal layer in the coal seam face in the cleat direction according to intercept b and slope k values of linear relation in formulaxAnd coal seam end cleat direction permeability kyI.e. by
kx＝k×β
The analysis system is simple and convenient to apply, on one hand, reservoir information is directly extracted from actual production data based on seepage mechanics, the reliability of the explained heterogeneous characteristics is high, on the other hand, the steps of field coring and experiment operation of experiments are omitted, and the cost can be effectively controlled; and the system can rapidly, reliably and economically acquire the heterogeneity of the permeability of the coal bed, and lays a theoretical foundation for the efficient development of the coal bed gas well.
While the exemplary embodiment of the method for analyzing early water production data of a coal-bed gas well considering anisotropy of the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that various modifications and changes can be made to the specific embodiments and various combinations of the technical features and structures of the present invention without departing from the concept of the present invention, and the scope of the present invention is defined by the appended claims.
Claims (4)
1. An anisotropic early water production data analysis method for a coal-bed gas well is characterized by comprising the following steps:
s10: obtaining a known coal bed physical parameter (P)e，φ，CtH) production history (t, Q (t), P) of single-phase water stage of coal-bed gas wellw(t)); wherein, PeIs the original bottom pressure, phi is the porosity of the coal bed, CtThe comprehensive compression coefficient of the coal bed is shown, and h is the thickness of the reservoir; t is the production time, Q (t) is the water production history, Pw(t) bottom hole pressure history;
s20: homogeneous permeability k assuming conversion of a heterogeneous coal seam to a homogeneous coal seami；
S30: the water production equation of the coal-bed gas well considering the anisotropy is subjected to linearization treatment to obtain the following results:
wherein the content of the first and second substances,
wherein r iseRepresents the distance of the coal seam boundary from the bottom of the well, m; the permeability of coal bed gas is low, the production initial stage is accompanied with the transmission process of pressure wave, a 'dynamic boundary' exists, and the distance r between the coal bed boundary and the bottom of the welleThe expression of (a) is:
wherein t represents the production time, d; phi represents the porosity of the coal bed, and has no dimension; ctRepresents the overall compression factor, MPa-1；
Wherein mu represents the viscosity of coal bed water, mpa.S; r iswRepresents the wellbore radius, m; k represents the homogeneous permeability, mD, when converting a heterogeneous coal seam to a homogeneous coal seam; beta represents the heterogeneity intensity of the coal bed without dimension;
the parameters obtained in the above step S10 are substituted
Obtaining the value of Y at a certain production moment;
the parameters obtained in the above step S10 are substituted
Obtaining the value of X at a certain production moment;
s30: putting the X, Y values of different production moments in the step S20 into the same rectangular coordinate system, and performing a linear equation according to a coal-bed gas well water production equation considering anisotropy to obtain the homogeneous permeability k when the heterogeneous coal bed is converted into the homogeneous coal bed;
s40: the homogeneous permeability k obtained in step S40 when the heterogeneous coal seam is converted into a homogeneous coal seam and the homogeneous permeability k obtained in step S20 when the heterogeneous coal seam is assumed to be converted into a homogeneous coal seamiComparing, and if the relative error epsilon of the two is within 1%, considering that the calculated homogeneous permeability when the assumed heterogeneous coal seam is converted into the homogeneous coal seam is correct; otherwise, go to S20 to continue assuming a homogeneous permeability k when the heterogeneous coal seam is converted to a homogeneous coal seami；
S50: calculating the permeability k of the coal bed face in the cleat direction according to the intercept and the slope in the linear equation of the water production of the coal bed gas well considering the anisotropyxAnd coal seam end cleat direction permeability ky。
2. The method for analyzing early water production data of a coalbed methane well considering anisotropy as recited in claim 1, wherein the initial value of homogeneous permeability when the heterogeneous coal seam is converted into the homogeneous coal seam is critical coalbed methane well permeability or permeability explained by a well logging and well testing method.
3. A coal bed gas well early water production data analysis system considering coal bed anisotropy is characterized by comprising:
a first input unit for inputting the known coal bed property parameter (P)e，φ，CtH) production history (t, Q (t), P) of single-phase water stage of coal-bed gas wellw(t)) parameter input; wherein, PeIs the original bottom pressure, phi is the porosity of the coal bed, CtThe comprehensive compression coefficient of the coal bed is shown, and h is the thickness of the reservoir; t is the production time, Q (t) is the water production history, Pw(t) bottom hole pressure history;
a second input unit for converting the homogeneous permeability k of the assumed heterogeneous coal seam into a homogeneous coal seamiInputting a value;
the first calculation unit is used for obtaining the following result after carrying out linearization treatment on the coal-bed gas well water production equation considering anisotropy:
wherein the content of the first and second substances,
wherein r iseRepresents the distance of the coal seam boundary from the bottom of the well, m; the permeability of coal bed gas is low, the production initial stage is accompanied with the transmission process of pressure wave, a 'dynamic boundary' exists, and the distance r between the coal bed boundary and the bottom of the welleThe expression of (a) is:
wherein t represents the production time, d; phi represents the porosity of the coal bed, and has no dimension; ctRepresents the overall compression factor, MPa-1；
Wherein mu represents the viscosity of coal bed water, mpa.S; r iswRepresents the wellbore radius, m; k represents the homogeneous permeability, mD, when converting a heterogeneous coal seam to a homogeneous coal seam; beta represents the heterogeneity intensity of the coal bed without dimension;
bringing in the parameters obtained by the first input unit
Calculating to obtain the value of Y at a certain production moment;
bringing in the parameters obtained by the first input unit
Calculating to obtain the value of X at a certain production moment;
the second calculation unit is used for putting the X, Y values at different production moments obtained by the first calculation unit into the same rectangular coordinate system, and performing a linearization equation according to a coal-bed gas well water production equation considering anisotropy to obtain the homogeneous permeability k when the heterogeneous coal bed is converted into the homogeneous coal bed;
a judging unit for converting the homogeneous permeability k obtained by the second input unit when the heterogeneous coal seam is converted into a homogeneous coal seam and the homogeneous permeability k obtained by the first input unit when the assumed heterogeneous coal seam is converted into a homogeneous coal seamiComparing, and if the relative error epsilon of the two is within 1%, considering that the calculated homogeneous permeability when the assumed heterogeneous coal seam is converted into the homogeneous coal seam is correct; otherwise, the coal seam is transferred to a second input unit, and the homogeneous permeability k when the heterogeneous coal seam is converted into the homogeneous coal seam is continuously assumedi；
A third calculation unit for calculating the permeability k of the coal bed face in the cleat direction according to the intercept and the slope in the linear equation of the water production of the coal bed gas well considering the anisotropyxAnd coal seam end cleat direction permeability ky。
4. The system for analyzing the early water production data of the coal-bed gas well considering the anisotropy of the coal bed as recited in claim 1,
the initial value of the homogeneous permeability when the heterogeneous coal seam is converted into the homogeneous coal seam is the permeability of a critical coal-bed gas well or the permeability explained by a well logging and testing method.
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