特高含水期水驱特征曲线拐点时机判别新方法

A new method for determining the inflection point of water drive characteristic curve in extra high water cut period

水驱特征曲线在中、高含水开发阶段得到广泛应用。然而,油田进入特高含水开发期后,水驱特征曲线会发生上翘,出现拐点。针对这一现象,通过室内124组高注入倍数(1 000倍孔隙体积)水驱油实验,明确了水驱特征曲线出现拐点的根本原因是水相渗透率急剧增加,并指出水驱特征曲线出现拐点是客观存在的。同时,由于水驱特征曲线的累积效应,使得拐点在发生之后才能被发现,存在严重的滞后性,造成对拐点时机的误判。为了消除水驱特征曲线的累积效应对拐点出现滞后性的影响,从甲型水驱特征曲线入手,推导出了含油率与累积产油量在半对数坐标上的关系式,应用该关系式,消除了累积效应的影响,可准确判断水驱特征曲线拐点时机,及时制定开发技术对策,为矿场改善开发效果奠定基础,更好地指导油田开发生产实践。

Water drive characteristic curve is widely used in the middle-high water cut development stage. However,when oilfield entered extra high water cut period,the water drive characteristic curve will slope upward and an inflection point will occur. Focusing on this phenomenon and according to124 water flooding experiments with high multiple injection(1 000 pore volume),it was found that the fundamental reason for the upward water drive characteristic curve is due to the sharp increase in water permeability,and it was pointed out that the inflection point is an objective existence for the water drive characteristic curve. At the same time,affected by the cumulative effect of water drive characteristic curve,the inflection point can only be found after its appearance,resulting in a delayed estimation on its occurring time. In order to eliminate the influence of the cumulative effect of water flooding characteristic curve on the inflection point estimation,a lgfo-Np formula was derived starting from the first water drive characteristic curve. The cumulative impact of water drive characteristic curve can be overcome by application of this formula to estimate the accurate occurring time of the inflection point.The new method can help to make technical development strategies in time,which lay the foundation for the field to improve the development effect of oilfield production and to guide the practice better.