纤维强制裂缝转向规律实验及现场试验

Experimental study on the fiber-based diverting fracturing technology of artificial fractures and its field application

可降解纤维可以强制人工裂缝发生转向,促进复杂缝网的形成,目前还不清楚纤维强制裂缝转向规律。通过纤维滤失暂堵能力实验,评价纤维转向剂对人工裂缝的暂堵转向作用,分析纤维转向剂对不同裂缝宽度、不同流速时裂缝暂堵规律,确定形成暂堵的临界纤维质量分数。根据降解性能评价实验,纤维在少量水存在的情况下降解率能够达到85%以上,并在暂堵后依靠储层温度恢复而实现自动降解;根据真三轴压裂物模实验,验证纤维转向剂在裂缝存在条件下形成暂堵强制裂缝转向的可靠性,得出裂缝发生转向的水平主应力差上限为7.5 MPa,两次压裂产生裂缝间夹角与水平主应力差呈负相关关系。85口井次的现场纤维转向酸压工艺试验表明,转向压力最高达到40.0 MPa,增产效果明显。该研究结果对理解纤维暂堵裂缝转向机理与指导现场压裂施工设计具有指导意义。

Degradable fiber has a number of advantages such as being suitable for high temperature formation,high blocking strength,automatically complete degradation at the formation temperature,small damage to the formation permeability.Via this technology,artificial fracture could be forced to divert in a new direction,and thus it will promote the generation of fracture network further.But currently the diversion rule of fiber-assisted fracturing is not clear.By evaluating fiber's temporary block capability in the laboratory,we systematically evaluate the diversion action of this clean plugging agent on artificial fractures,and obtain the law of temporary block at different fracture widths and flow rates.The critical fiber concentration(mass fraction)is also obtained.This will provide a fundamental principle for diverting fracturing design and its application.The results of degradation capability experiment show that the degradation rate could be up to 85% when fiber contacts to small amount of water.The reliability of diverting fracture generation with this technology could be verified by true triaxial fracturing test,and the law of temporary block is further explored.The upper limit of horizontal principle stress difference is7.5 MPa when artificial fracture can be diverted.The smaller the horizontal principle stress difference is,the bigger the angle between the first fracture and the diverted fracture is.This technique has been successfully applied to total 85 wells in the oilfield.The maximum diverting pressure is up to 40.0MPa after fiber fluid is injected to the down hole.This investigation will be significant for understanding the mechanisms of fiber assisted diverting fracturing and guiding its design scheme in the filed application.