低渗透疏松油藏注水井试井分析

Well Test Analysis of Water Injection Wells in Low-permeability Unconsolidated Oil Reservoirs

低渗透疏松油藏由于渗透率较低,存在一定的启动压力梯度,且由于储层岩石胶结疏松,存在中等-较强的应力敏感性,导致原油渗流速度很慢,难以获得充足资料对储层做出合理的解释,油井试井效果难以取得满意的效果,而低渗透油藏注水井试井可以很好地解决这个难题。综合考虑流度比、启动压力梯度、应力敏感性等的影响,建立了低渗透疏松油藏注水井低速非达西渗流有效井径试井的数学模型。由于所建模型具有强非线性,采用稳定的有限差分格式利用Newton-Raphson迭代法求得数值解,进一步研究了压力动态特征及其影响因素,绘制了用于实际资料拟合分析的典型试井曲线。

Low-permeability unconsolidated reservoirs have a threshold pressure gradient to a certain extent due to low permeability. In addition, the reservoir rock shows medium to strong stress sensitivity because of the unconsolidated cementation, resulting in low oil flow velocity. Therefore, it is difficult to obtain sufficient information to make a reasonable interpretation. Water-injection well test is a good way to solve this problem. Based on analysis of the mobility ratio, the effects of stress sensitivity and threshold pressure gradient, a mathematical model for waler-injection well test in low-permeability unconsolidated reservoirs was established. Since this model has strong nonlinearity, stable finite-difference scheme and Newton-Raphson iteration method were adopted to obtain the arithmetic solution. The pressure performance and influencing factors were also evaluated, and the typical well testing curves for analysis of real datawere plotted.