Method for determining recovery factor of deep coal bed methane wells
Abstract
A method for determining a recovery factor of a deep coal bed methane (CBM) well includes steps of: (1) collecting an original formation pressure and pressure-volume-temperature (PVT) experimental data of the CBM well, and establishing a relationship table between pressure and deviation factor; (2) obtaining isothermal adsorption experimental data, an original adsorbed gas content and an original free gas content for the deep coal rock; (3) according to the isothermal adsorption experimental data, determining Langmuir's pressure and Langmuir's volume; (4) determining an abandoned formation pressure in CBM well exploitation; (5) obtaining a deviation factor at the original formation pressure and a deviation factor at the abandoned formation pressure; and (6) according to the original formation pressure, the original adsorbed gas content, the original free gas content, the Langmuir's pressure, the abandoned formation pressure, the above deviation factors, the recovery factor of the CBM well is calculated.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1 . A method for determining a recovery factor of a deep coal bed methane (CBM) well, the method comprising steps of:
(step 1) collecting an original formation pressure P i and pressure-volume-temperature (PVT) experimental data of the CBM well, obtaining deviation factors corresponding to different pressures at a formation temperature of CBM, and establishing a relationship table between the pressures and the deviation factors; (step 2) obtaining isothermal adsorption experimental data, an adsorbed gas content G 0ad and a free gas content G 0f at the original formation pressure and an original temperature for deep coal rock; (step 3) according to the isothermal adsorption experimental data, determining Langmuir's pressure P L and Langmuir's volume V L ; (step 4) according to a depth of burial of the CBM well, determining an abandoned formation pressure P ab in CBM well exploitation; (step 5) according to the relationship table between the pressures and the deviation factors in the (step 1), obtaining a deviation factor Z i at the original formation pressure P i and a deviation factor Z ab at the abandoned formation pressure P ab ; and (step 6) according to the original formation pressure P i in the (step 1), the adsorbed gas content G 0ad and the free gas content G 0f at the original formation pressure and the original temperature in the (step 2), the Langmuir's pressure P L in the (step 3), the abandoned formation pressure P ab in the (step 4), and the deviation factor Z i at the original formation pressure P i and the deviation factor Z ab at the abandoned formation pressure P ab in the (step 5), by a model of
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0
f
×
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1
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Z
i
P
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+
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,
calculating the recovery factor of the CBM well.
2 . The method according to claim 1 , wherein the (step 3) specifically comprises:
taking
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and
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,
wherein
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according to adsorbed gas volumes V g(1) , V g(2) , . . . , V g(n) corresponding to different pressures P (1) , P (2) , . . . , P (n) at the formation temperature of the CBM, obtaining a series of observation points (y (i) , x (i) ); and
obtaining a line equation by performing linear fitting on the observation points, wherein the Langmuir's volume V L is equal to a reciprocal of an intercept of the line equation, and the Langmuir's pressure P L is equal to a slope of the line equation divided by the intercept of the line equation.
3 . The method according to claim 1 , wherein in the (step 4), the abandoned formation pressure P ab in CBM well exploitation is determined by analog method or empirical formula method.
4 . The method according to claim 1 , wherein in the (step 5), according to the relationship table between the pressures and the deviation factors in the (step 1), the deviation factor Z i at the original formation pressure P i and the deviation factor Z ab at the abandoned formation pressure P ab are obtained by interpolation method;
or according to the relationship table between the pressures and the deviation factors in the (step 1), a fitted function relationship Z=f(P) between the deviation factors and the pressures is established by taking the deviation factors as a dependent variable and the pressures as an independent variable, and then by the fitted function relationship, obtaining the deviation factor Z i =f(P i ) at the original formation pressure P i , and the deviation factor Z ab =f(P ab ) at the abandoned formation pressure P ab .Join the waitlist — get patent alerts
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