稠油非线性渗流启动压力梯度实验研究

Experimental study on start-up pressure gradient for nonlinear flow of heavy oil

稠油中胶质、沥青质等高分子混合物决定其特殊的结构特性,表现出非线性渗流的特点。启动压力梯度是研究非线性渗流的重要环节。以实际某油田为例,对比分析目前国内外常用的几种测量启动压力梯度的方法,选择出最佳实验方法,通过实验研究不同渗透率条件下启动压力梯度存在的临界黏度并绘制版图,最后研究目标油田全流度范围内启动压力梯度与流度的关系。实验结果表明:微流量驱替法是较为实用的测量启动压力梯度的方法;目标油田启动压力梯度存在的临界黏度随渗透率的增加而增大,且增大的幅度逐渐趋于平缓;流度较小时,随流度的增加启动压力梯度下降较快,随着流度的不断增加,启动压力梯度下降幅度减缓。

Heavy oil has a special structural property due to the high molecular mixtures of colloid and asphaltene in it, and thus shows a feature of nonlinear fow. The start-up pressure gradient is a key indicator to study the nonlinear fow. Taking an oilfeld as an example, some common measuring methods in China and abroad were compared and analyzed, and the optimal experimental method was selected to defne the critical viscosity for the existence of start-up pressure gradient at different permeabilities. Typical curves were prepared. Finally, the relationship between the start-up pressure gradient and the mobility within the full mobility range of the oilfeld was diagnosed. The experimental results show that the micro-fow displacement method is a practical method for measuring the start-up pressure gradient. The critical viscosity at which the start-up pressure gradient exists in the oilfeld increases with the increase of perme-ability, but at a gradually-gentle rate. When the mobility is small, the start-up pressure gradient drops fast with the increase of mobility, and as the mobility increases steadily, the decline rate of start-up pressure gradient slackens.