低渗透煤层气有限导流垂直裂缝井压力动态分析  

Pressure Transient Analysis of Finite-Conductivity Vertical Fractured Wells in Low Permeability Coalbed Methane Reservoirs

作　　者：张先敏[1] 孙贝贝 冯其红[1] 张纪远[1] 

机构地区：[1]中国石油大学(华东)石油工程学院,山东青岛266580

出　　处：《力学季刊》2017年第1期144-151,共8页Chinese Quarterly of Mechanics

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)

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.As a typical tight porous media, coal rocks have been proved to have a threshold pressure gradient. According to bilinear flow mechanics of low permeability coalbed methane finite-conductivity vertical fractured wells, a new bilinear flow mathematical model for vertical fractured wells was established in consideration of the threshold pressure gradient and wellbore storage effect. Then from the numerical solutions of dimensionless bottomhole pressure, the influences of various parameters such as the threshold pressure gradient, fractured conductivity coefficient and adsorption coefficient on typical curves of vertical fractured wells were studied. By analyzing these typical bilinear flow curves, several conclusions were obtained. A typical bilinear flow curve could be divided into five characteristic stages： the early fillup stage, bilinear flow stage, coalbed linear flow stage, transition flow stage and coalbed boundary linear flow stage. Starting from the coalbed linear flow stage, the curves take on an obvious upward trend due to the threshold pressure gradient effect with a bigger threshold pressure gradient leading to an earlier upward trend. Furthermore, a straight line with the unit slope instead of the 1/2 slope appears for the coalbed boundary linear flow stage. All these results show the effect of threshold pressure gradient on the bilinear flow of coalbed methane finite-conductivity vertical fractured wells in low permeability reservoirs, and could be used to guide the practical coalbed methane well testing.

关 键 词：煤层气 有限导流 垂直裂缝井 启动压力梯度 压力动态分析 

分 类 号：TE373[石油与天然气工程—油气田开发工程]