低渗透油藏CO_2驱试井曲线特征分析

根据低渗透油藏CO2驱流体分布,将渗流区划分为CO2区、CO2-原油过渡区和未波及原油区,考虑过渡区内流体物性参数幂律变化,建立变性质CO2驱三区复合油藏模型,应用Laplace变换及Stehfest数值反演,求得井底压力解,绘制典型试井曲线,研究试井曲线变化特征及其影响因素。结果表明,过渡区流体流度、储容系数变化幂律指数和CO2区与过渡区交界面流度比、储容比分别影响CO2区与过渡区间的过渡段以及过渡区径向流直线段斜率;储容系数变化幂律指数、交界面储容比越大,过渡区与原油区间的过渡段开始时间越早,过渡段峰值越小;增大过渡区半径,压力波在过渡区内传播时间增加,过渡区径向流直线段延长,过渡区向原油区过渡段曲线右移,CO2注入压力降低。

Characteristics analysis of well testing curve of CO2 flooding in low permeability reservoir

On the basis of fluid distribution of carbon dioxide flooding in low permeability reservoir, the flowing areas are divided into CO₂ region, CO₂-oil transition region and oil unswept region. Considering the power law variation of fluid physical parameters in the transition region, we establish a varied property carbon dioxide flooding three-zone composite reservoir well testing model, and obtain the solution of bottom hole pressure by applying Laplace transform and Stehfest numerical inversion. In this way, the characteristics of variation of the well testing curve and influential factors are investigated. The results show that the slope of curves representing the transition section between the CO₂ region and transition region and radial flow of the transition region is mainly affected by the power law exponent of mobility and storativity and mobility and storativity ratio in the CO₂-transition region interface. The larger the storativity power law exponent and storativity ratio at the CO₂-transition region interface is, the earlier the transition section between miscible region and oil unswept region begins, the lower the peak is. When the radius of the transition region is increased, the line of radius flow in the transition region becomes longer, the transition curve from the transition to oil unswept region shifts right, and CO₂ injection pressure decreases.