异常高压气藏早期动态储量计算方法的建立

Reserve Estimate Method of the Abnormally Pressured Gas Reservoir in the Early Stage of Field Development

针对传统虚拟储量校正法在计算异常高压气藏动态储量时难以确定压降曲线拐点位置的问题,引入了压力校正项的概念。通过分析典型异常高压气藏压力校正项与气藏压力系数的关系,发现压力校正项以压力系数等于1.2为界,分为异常高压段和正常压力段两个生产阶段;且异常高压段的压力校正项与压力系数存在着近似的直线关系,从而确定了压降曲线拐点位置;在此基础上建立了新的虚拟储量校正方程。实例应用表明,该方法与容积法计算结果的相对误差仅为1.75%,可以用于异常高压气藏的早期储量计算。

Two lines with distinct slopes can be observed in the p /z vs. cumulative production plots for the abnormally pressured gas reservoirs,the reserve estimates should base on the second-slope line which states the normally pressured portion of the gas reservoir. For this reason the accurate estimate of gas reserves can be hardly obtained in the early stages of field development. To address this problem,an alternative method which bases only on the early data( i. e. the first-slope line) has been developed. After the collection of the data from the public documents,the plot of the correction factor( CeΔp) of the abnormally pressured gas reservoirs was drawn as the function of the pressure coefficient( α). It was clearly observed that the correction factor changed linearly along with the pressure coefficient when α > 1. 2 and stayed almost constant when α≤1. 2. This evidently proved that the abnormally pressured portion and the normally pressured portion transformed when the pressure coefficient equaled 1. 2,thus the inflection point should be also set at the condition of α = 1. 2. With the accurate determination of the inflection point,the correction function was then established. The field example showed a relative error of 1. 75% of this method compared to the volumetric method,which proves that this method is both effective and applicable for the reserve estimate in the early stage of field development.