页岩油储集层压后焖井时间优化方法

Shut-in time optimization after fracturing in shale oil reservoirs

建立了考虑毛管压力、渗透压、膜效应以及弹性能的压裂-焖井-生产多过程多相流模型,提出了以产能最大化为目标的页岩油水平井分段多簇压裂后焖井时间优化方法,采用现场生产数据和商业软件验证了该模型的准确性。基于该模型和方法,根据现场压裂压力数据反演裂缝参数,建立物理模型,模拟了压裂、焖井以及生产阶段储集层孔隙压力、含油饱和度的变化动态,并研究了7种因素对最优焖井时间的影响规律,通过开展正交实验明确了最优焖井时间的主控因素。研究表明,随着焖井时间增加,累计产量增量先快速增加后趋于某一稳定值,变化拐点对应的焖井时间为最优焖井时间。最优焖井时间与基质渗透率、孔隙度、毛管压力倍数及裂缝长度呈非线性负相关,与膜效率、注入液体总量呈非线性正相关,与排量呈近线性正相关。对最优焖井时间的影响程度从大到小依次为注入液体总量、毛管压力倍数、基质渗透率、孔隙度、膜效率、压裂液矿化度和排量。

A multi-process(fracturing,shut-in and production)multi-phase flow model was derived considering the osmotic pressure,membrane effect,elastic energy and capillary force,to determine the optimal shut-in time after multi-cluster staged hydraulic fracturing in shale reservoirs for the maximum production.The accuracy of the model was verified by using production data and commercial software.Based on this model and method,a physical model was made based on the inversion of fracture parameters from fracturing pressure data,to simulate the dynamic changes of pore pressure and oil saturation during fracturing,soaking and production,examine effects of 7 factors on the optimal shut-in time,and find out the main factors affecting the optimal shut-in time through orthogonal experiments.With the increase of shut-in time,the increment of cumulative production increases rapidly first and then tended to a stable value,and the shut-in time corresponding to the inflection point of the change was the optimal shut-in time.The optimal shut-in time has a nonlinear negative correlation with matrix permeability,porosity,capillary pressure multiple and fracture length,a nonlinear positive correlation with the membrane efficiency and total volume of injected fluid,and a nearly linear positive correlation with displacement.The seven factors in descending order of influence degree on optimal shut-in time are total volume of injected fluid,capillary force multiple,matrix permeability,porosity,membrane efficiency,salinity of fracturing fluid,fracturing fluid displacement.