低渗透煤层气有限导流垂直裂缝井压力动态分析

发布时间：2019-04-25 20:39

【摘要】：作为典型的致密多孔介质,煤岩储层已被证实存在启动压力梯度.根据煤层气垂直裂缝井的双线性流动机制,综合考虑启动压力梯度和井筒储存效应的影响,建立了一个新的低渗透煤层气有限导流垂直裂缝井双线性流动数学模型,采用Laplace变换和Stehfest数值反演方法对数学模型进行了求解,并分析了无因次启动压力梯度等参数对无因次井底压力及其导数曲线的影响规律.分析结果表明:典型的低渗透煤层气垂直裂缝井双线性流动曲线可划分为早期续流段、双线性流段、煤层线性流段、过渡流段和煤层边界线性流段5个特征阶段,其中由于启动压力梯度存在的影响,无因次井底压力及其导数曲线自煤层线性流段开始出现明显上翘,且启动压力梯度值越大,曲线上翘趋势越明显;此外,煤层边界线性流段呈现为单位斜率的直线,而非1/2斜率的线性流段直线.这些结果表现出启动压力梯度对低渗透煤层气垂直裂缝井双线性流动的影响,可用于指导现场煤层气井试井分析.
[Abstract]:As a typical compact porous medium, the coal-rock reservoir has been proved to have a start-up pressure gradient. According to the bilinear flow mechanism of coalbed methane vertical fracture well and considering the influence of starting pressure gradient and wellbore storage effect, a new bilinear flow mathematical model of vertical fracture well with low permeability coalbed methane finite conductivity is established. The mathematical model is solved by Laplace transform and Stehfest numerical inversion method, and the influence of dimensionless starting pressure gradient and other parameters on dimensionless bottom hole pressure and its derivative curves is analyzed. The analysis results show that the typical bilinear flow curve of vertical fracture well of low permeability coalbed methane can be divided into five characteristic stages: early continuous flow section, bilinear flow section, linear flow section of coal seam, transition flow section and linear flow section of coal seam boundary. Because of the influence of the start-up pressure gradient, the dimensionless bottom-hole pressure and its derivative curve began to appear obvious upwarping from the linear flow section of the coal seam, and the larger the start-up pressure gradient value, the more obvious the upwarping trend of the curve was. In addition, the linear flow section at the boundary of coal seam presents a straight line with unit slope, but not a linear flow segment with 1 / 2 slope. These results show the influence of starting pressure gradient on bilinear flow of low permeability coalbed methane vertical fracture wells, which can be used to guide well testing analysis of coal seam gas wells in situ.
【作者单位】：中国石油大学(华东)石油工程学院;
【基金】：国家自然科学基金(11302265) 中央高校基本科研业务费专项基金资助项目(14CX02046A)
【分类号】：TE373

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