基于停泵压力降落曲线分析的压后裂缝参数反演

An approach to estimate hydraulic fracture parameters with the pressure falloff data of main treatment

在主压裂停泵压降分析中,目前没有任何模型可以定量地计算出包括天然裂缝在内的裂缝总面积。而在小型压裂和微注测试分析中,Liu-Economides模型已经可以对包括天然裂缝在内的裂缝系统进行模拟,并给出了所涉及到的相关参数的解析解,包括天然裂缝和水力裂缝的面积。借鉴Liu-Economides模型,提出了一套针对主压裂停泵后的压降分析方法,从而评价天然裂缝和水力裂缝参数。利用该方法在四川盆地某页岩气水平井F井的实际压裂施工中进行了压力分析与应用。结果表明:该F井的28段现场压裂数据中有15段由于压后停泵测压时间不足,没有出现特征线段,无法进行裂缝参数的计算。利用模型对13段有效数据进行裂缝参数分析,发现提高缝内净压力,页岩气储层压裂裂缝复杂性会显著增加。同时,由于天然裂缝开启比例的增加,主裂缝长度也会发生显著降低。研究可以为压裂施工现场压后效果的实时评价提供理论依据与技术支撑,从而提高后续压裂施工的针对性与有效性。

Currently,no method is available to quantitatively estimate surface areas of hydraulic fracture and natural fracture with the pressure falloff data after pumping of the main treatment. While,Liu and Ehlig-Economides developed a comprehensive global DFIT(diagnostic fracture injection test)model that accounts for the behaviors of the natural fracture,from which surface areas of both hydraulic fracture and natural fracture can be determined.To estimate surface areas of both hydraulic and natural fractures,we attempt to extend the Liu-Economides model to the pressure falloff analysis of the main hydraulic fracture treatment. We compare the main treatment pressure falloff analysis to the DFIT,and illustrate the data section that could be used for fracture surface area estimation. Analytical solutions of hydraulic and natural fracture surface areas are provided. A field case of a horizontal well with 28 stages is presented as an example to determine the fracture areas for all stages that their fracture closure trends are observed. The analysis result shows that 15 out of 28 stages have no indication of fracture closure trend because of their short shut-in time,fracture surface areas therefore cannot be determined in those stages.For the rest 13 stages,we find a positive relationship between net pressure and the fracture complexity,and a negative relationship between natural fracture area and the hydraulic fracture half-length. The study could support the post treatment evaluation and provide more insight on the hydraulic fracture design.