压后返排支撑剂回流模型研究(英文)

Proppant Mechanical Model for Postfrac Flowback Procedures

支撑剂回流是压后返排工艺中一个重要的评价标准。在分析了支撑剂运移回流的物理过程基础上,对于裂缝闭合前后支撑剂不同的受力情况,建立了支撑剂回流力学模型。计算结果表明:裂缝闭合前,沉降在裂缝底部的支撑剂不易发生回流,悬浮在裂缝上部的支撑剂较易发生回流。裂缝闭合后,闭合应力开始作用在支撑剂上,颗粒之间胶结更加紧密,发生回流需要的临界流速也变得更大。破胶压裂液粘度直接影响支撑剂回流效果,粘度越大,返排临界流速越小,支撑剂回流越容易发生。裂缝闭合前采用小流速返排,裂缝闭合后增大返排流速,同时尽可能降低破胶压裂液粘度,即可使压裂液得以尽快返排,同时保证了尽可能多的支撑剂停留在裂缝中,该模型丰富和完善了压裂返排支撑剂回流理论。

It is well known that proppant back flow is a key evaluation standard for postfrac flowback procedures. Based on the analysis of the course of proppant flowback, proppant mechanical model is established after considering different stress situations before and after fracture closure. The results show that deposited proppants are carried difficultly and suspended proppant are carried easily before fracture closure. The cementations of particles become closer after fracture closure and critical velocity become bigger. Fracturing fluid viscosity for gel breaking directly affects flowback procedure, critical velocity increase with viscosity decreasing. Adopted low velocity before fracture closure and high velocity after fracture closure, decreased fracturing fluid viscosity for gel breaking as much as possible cannot only carry fracturing fluid away from formation as soon as possible, but guarantee keeping proppant in fracturing as much as possible. These results enrich and perfect posffrac proppant flowback theories.