含启动压力梯度油藏的两相渗流分析

/ ANALYSIS OF TWO\|PHASE FLUID FLOW IN LOW PERMEABILITY RESERVOIR WITH THE THRESHOLD PRESSURE GRADIENT

在低渗透油藏中存在着启动压力梯度。根据ＢｕｃｋｌｙＬｅｖｅｒｅｔ不混溶两相渗流驱替理论，考虑启动压力梯度的影响，对水驱油两相渗流进行了分析，得到了含启动压力梯度油藏中线性水驱、径向水驱、垂直裂缝井水驱和水平井油水两相渗流的解析解公式。对于含启动压力梯度的油藏，两相渗流的效果受相渗曲线、注入速率、油水相启动压力梯度和重力的影响。启动压力梯度的存在，不仅增大了原油的开采难度，而且降低了原油的最终采收率。增大注入速率可以减少启动压力梯度对两相渗流的不利影响，提高原油的最终采收率。因此，开发低渗透油藏，应采用小井距、大流量、大压差的注水开发方案。对于倾斜地层，应尽可能采用从高位井注入。

xperiments show that there is threshold pressure gradient (TPG) in low permeability reservoir. Based on the Buckley\|Leverett fractional flow theory, the linear two\|phase fluid flow of oil displaced by water are analyzed with consideration of the effects of TPG. The analytical solutions of two\|phase flow in a vertical well,a vertically fractured well or a horizontal well are derived. For two\|phase fluid flow in reservoirs with TPG, oil production is influenced not only by relative permeability curves, but also by TPG of oil and water, injection rate and gravity. The existence of TPG makes the production more difficult, and decreases the ultimate recovery factor.Increasing injection rate can decrease the effects of TPG and improve the ultimate recovery factor. The big injection rate and big pressure drop should be used in the development of reservoir with TPG. Moreover, for the slant zones, the gravity action should be utilized. Water is injected from relatively high location, and oil is produced from the low position. The analytical solutions in this paper are certified as correct by some experiments in laboratories and some oilfields.\=