Evaluation of factors affecting productivity of low-permeability coalbed methane reservoirs

Du Zhimin; Fu Yu; Wu Yong

doi:10.11743/ogg20070412

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Evaluation of factors affecting productivity of low-permeability coalbed methane reservoirs
Vol. 28, Issue 4, Pages: 516-519(2007)
Online First：25 August 2007，

Published：2007
DOI： 10.11743/ogg20070412
稿件说明：

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DOI：

Du Zhimin, Fu Yu, Wu Yong. Evaluation of factors affecting productivity of low-permeability coalbed methane reservoirs[J]. 2007, 28(4): 516-519. DOI： 10.11743/ogg20070412.

摘要

采用数值模拟方法

从煤层气的流动机理入手

利用 Langmuir 等温吸附方程描述煤层气从煤表面的解吸过程

用Fick定律描述煤层气在煤基质和微孔隙中的扩散

综合考虑了煤层气的解吸、扩散和渗流3个过程

建立了煤层气储层数学模型

推导数值模型并进行了模拟计算。计算结果表明:裂缝半长越长产能越高

当裂缝半长增加100m后

裂缝半长对产能的影响较小;裂缝的导流能力越大产能越高

当裂缝导流能力超过20μm

·cm后

产能增加不明显;分子扩散系数对产能影响较小

而割理的渗透率对产能影响较大;对于不同的煤层气井在投产时

应合理优选压裂缝半长和导流能力。

Abstract

Beginning with flow mechanism of coal methane

a mathematical model for coalbed methane reservoirs is established by utilizing the Langmuir isothermal adsorption equation to describe the desorption of methane from coal surface and the Fick's law to delineate the diffusion of methane in coal matrix and micropores.The calculated results of this model show that the productivity steps up with the increase of fracture half length and flow conductivity.However

when the fracture half length is increased to 100m and the fracture flow conductivity is beyond 20 μm

·cm

their effects upon the productivity becomes less evident.Molecular diffusion coefficient has no big influence over the productivity

while the permeability of cleaps

on the contrary

is closely connected with productivity changes.A rational selection of fracture half length and flow conductivity is strongly recommended when put a coalbed methane gas well into production.