线性组合边界中煤层气井的不稳定压力数值分析

NUMERICAL ANALYSIS OF TRANSIENT PRESSURE FOR COAL-BED GAS WELLS WITH M IXED LINEAR BOUNDARIES 1)

文章建立并求解了不同线性组合边界条件下的煤层气井不定常渗流模型,得到了井底压力和压力导数的理论曲线,以及压力场分布图。在不稳定流动的早期,压力和压力导数曲线都是斜率为1的直线段。当流体流动进入稳定流动状态时,在压力导数曲线上出现一个值为0.5的水平直线段。在理论曲线的晚期,理论曲线与边界性质存在密切关系。对于全封闭煤层气藏,所有压力和压力导数曲线是斜率为1的直线段。对于存在定压边界煤层气藏,压力双对数曲线的晚期是水平直线段,压力导数双对数曲线的晚期都是急剧下掉的曲线。但是混合边界的压力导数存在上翘现象,上翘程度和早晚与封闭边界的数目多少以及距离大小有关。压力场中,在靠近封闭边界的等压线垂直于边界,在靠近定压边界的等压线平行于边界。在邻近定压和封闭边界交合处,定压边界起主导作用。所得到的理论曲线可以直接应用于煤层气田的试井测试资料分析,压力场分布图对了解煤层气藏的开发状况有积极的意义。

A new transient percolation model is developed and solved under different conditions of mixed linear boundaries for coal-bed gas wells. The theoretical curves of bottom-hole pressure and pressure derivative, and the distribution map of pressure fields are obtained. The curves of the pressure and pressure derivative are all straight line with the slope equal to 1 in the early stage of the transient percolation. When fluid flow enters into stable state, the curve of pressure derivative is a horizontal line with value of 0. 5. In the late stage, the theoretical curves are correlated with the boundary features closely. As for a closed coal-bed gas reservoir, all the curves of pressure and pressure derivative are straight line with the slope equal to 1. As for the coal-bed gas reservoirs with constant pressure boundary, the log-log pressure curves are horizontal lines and the log-log pressure derivative curves are falling rapidly in the late stage. But the log-log pressure derivative curves are lifting for the reservoirs with mixed boundary. The lifting level and time are related with the amount and distance of the closed boundaries. In the pressure field, the pressure contours near the closed boundary are vertical to the boundary, and the pressure contours near the constant pressure boundary are parallel to the boundary. In the region near the cross of the constant pressure boundary and the closed boundary, the pressure contours are mainly controlled by the constant pressure boundary. The derived theoretical curves can be directly used to analyze the well testing data of coal-bed gas fields. The distribution map of pressure fields is very helpful to understand the production performance of coal-bed gas reservoirs.