变形介质储层压力恢复试井曲线特征

Pressure buildup behavior in deformable medium formation

针对深层高压、致密低渗和裂缝性油气藏介质变形对储层物性影响显著的特点,建立了变形介质储层压力恢复试井理论模型。定义了表征渗透率变化的拟压力函数对方程进行拟线性化处理,并利用数值方法计算得到了变形介质储层不稳定试井典型曲线,对比分析了介质变形对典型曲线特征的影响。变形介质储层压降试井和压力恢复试井曲线特征明显不同。径向流阶段,压降试井和压力恢复试井导数值均高于0.5;压力降落试井压力导数曲线随生产时间逐渐上升,且渗透率模量越大,压力曲线与压力导数曲线的距离越小;压力恢复试井压力导数曲线随关井时间逐渐下落,且渗透率模量越大,压力曲线与压力导数曲线的距离越大。生产时间越长,压降曲线与压力恢复曲线差别越明显,叠加原理不再适用于变形介质储层。

Based on the fact that formation properties of deep high pressure reservoirs, low permeability tight reservoirs, and naturally fractured reservoirs are trend to be affected by the variation of effective stress, a buildup test model is established for deformable medium reservoir. By defining a pseudo function, the formulations of the model are linearized partially, and numerical method is used to solve the problems. Typical curves of pressure transient tests are obtained and analyzed on double logarithm plots. Both pressure curves and pressure derivative curves of deformable medium formation are significantly different between drawdown and buildup cases. During radial flow period, the pressure derivative curves of drawdown test goes upwards gradually with the duration of production, and the greater is the permeability modulus, the shorter is the distance between the pressure curves and the pressure derivative curves. While as for buildup test, the pressure derivative curves goes downwards gradually with duration of shut in, and the greater is the permeability modulus, the greater is the distance between the pressure curves and the pressure derivative curves. The difference between pressure drawdown and pressure buildup curves becomes more obvious as production time increasing. Thus, the principle of superposition cannot be used to pressure buildup analysis in deformable formation.