非均质底水油藏水平井合理生产压差实验研究

Experimental study on reasonable drawdown pressure in horizontal wells in heterogeneous reservoir with bottom water

利用底水油藏水平井小尺度离散化物理模拟装置,研究不同生产压差以及不同含水阶段变生产压差对水平井采出程度和含水率等开发指标的影响。结果表明:原油黏度较高时,较小压差下中低含水阶段单位含水率上升所对应的采出程度随生产压差的增大而增大;较大压差下进入中高含水阶段含水率随采出程度的增加上升幅度减缓。原油黏度较低时,在中低含水阶段,单位含水上升所对应的采出程度随生产压差的增大而减小,在含水率达80%左右出现明显拐点。利用基尼系数定量描述不同压差下各渗透率条带的采出程度差异度。基尼系数越大,各渗透率条带采出程度差异越大,基尼系数与综合采出程度呈"负相关"关系。原油黏度较大时,较大生产压差可将"单一指进"变为"多指进"而提高综合采出程度;在高含水阶段过分放大压差,底水驱替效果变差。原油黏度较小时,较低生产压差在中低含水阶段可获得较好的开采效果;在中高含水阶段放大生产压差可提高底水驱替效率。对于I类普通稠油,水驱有效系数与变压时含水率呈幂函数关系,较低含水率阶段增大生产压差能获得较好的开采效果。

The impacts of different drawdown pressures at different water cut stages on development indices such as the recovery percent of reserves and water cut were studied using a small-scale discretized physical simulation device for horizontal wells in bottom water reservoir.The results indicate that when oil viscosity is high and drawdown pressure is low,the recovery percent of reserves increases with the increasing of drawdown pressure in mid-low water cut phase corresponding to unit increasing of water cut;under high drawdown pressure and at mid-high water cut stage,the increasing amplitude of water cut mitigates along with the increasing of the recovery percent of reserves.When oil viscosity is low and water cut is mid-low,the recovery percent of reserves decreases with the increasing of drawdown pressure,corresponding to unit increasing of water cut,and there appears an apparent inflection point at water cut around 80%.Gini coefficient is used to quantitatively describe the differences of recovery percent of reserves among different permeability zones with different drawdown pressures.The bigger the Gini coefficient is,the greater the differences of recovery percent of reserves among different permeability zones are.The Gini coefficient is in negative correlation with the integrated recovery percent of reserves.When oil viscosity is high,larger drawdown pressures can turn 'single fingering'into 'multiple fingering',thus improving integrated recovery percent of reserves;if drawdown pressure is too high at high water cut stage,the displacement efficiency by bottom water becomes poor.When oil viscosity is low,lower drawdown pressure can bring about satisfactory recovery response at mid-low water cut stage;increasing drawdown pressure can improve displacement efficiency by bottom water at mid-high water cut stage.For conventional heavy oil,there exists a power function relationship between the effective coefficient of water flooding and the water cut at pressure variation,and good recovery response can be achieved by increasing drawdown pressure at low water cut stage.