九龙山致密气田压后支撑剂回流机理研究

四川九龙山气田为低孔、低渗致密砂岩气藏,储层的孔隙度和渗透率极低,但储层微裂缝较为发育。该区气井进行压裂作业后,出现了支撑剂回流的现象,支撑剂回流导致压裂支撑缝长、缝宽变小,同时也会导致导流能力下降。以单颗粒支撑剂受力分析方法为基础,研究了压裂气井支撑剂回流机理,推导了该区支撑剂发生返排的临界流速;结合改造研究区气藏的施工数据,分析了影响支撑剂回流临界流速的因素,临界流速会随着支撑剂的密度和粒径的增加而增加,而压裂液的黏度降低将会明显增大临界流速;结合工程流体力学和气藏工程原理,建立返排油嘴临界尺寸与返排临界速度的关系,通过井口控制油嘴尺寸来控制压裂液返排速度,形成了一套支撑剂回流控制技术,为现场施工控制压裂液返排提供指导。

Study on proppant flowback mechanism of Kowloon Tight Gas Field after fracturing

The Kowloon Tight Gas Field is a low porosity and tight sandstone gas reservoir. The porosity and permeability are extremely low, whereas micro-fractures are well-developed. There emerges a phenomenon that proppant flows back to the wellbores after hydraulic fracturing, which results in the reducing of fracture length and width, and also causes a decline in conductivity capacity. In this paper, the proppant flowback mechanism is investigated based on force analysis of single particle proppant, and the critical velocity causing the flowback is deduced. The factors affecting proppant flowback are analyzed by combining construction data of the gas reservoir. The critical velocity increases with the increasing of proppant density and particle size, and the reducing of fracturing fluid viscosity leads to an apparent increase in critical velocity. The relationship between critical flowback velocity and choke size is established based on engineering fluid mechanics and gas reservoir engineering principles. The flowback velocity can be controlled by wellhead choke size, and a set of control technology for proppant flowback is established, which can provide guidance for field application.