页岩诱导性裂缝漏失压力动力学模型  

A dynamic model for the leakage pressure of induced fractures in shale reservoirs

作　　者：翟晓鹏[1,2] 鞠鹏飞 谢志涛[3] 楼一珊[1] 张艳[1,2] 

机构地区：[1]长江大学油气钻井技术国家工程实验室防漏堵漏技术研究室 [2]长江大学西部研究院 [3]中国石油新疆油田公司工程技术研究院

出　　处：《天然气工业》2018年第3期81-86,共6页Natural Gas Industry

基　　金：国家科技重大专项"砂泥岩互层开发井防砂优化技术"(编号:2016ZX05025-002-003);克拉玛依市科技合作交流基金项目(编号:2017HZ003A)

摘　　要：现有的诱导裂缝漏失压力模型只能判断裂缝是否开裂,无法分析裂缝开裂后裂缝宽度变化对漏失压力的影响。为此,首先建立了诱导裂缝在有效内压下裂缝宽度变化的计算方法 ;然后结合井底流体稳态扩散方程,在考虑漏失速度系数、裂缝宽度、流体黏度、井眼半径等影响因素的基础上,建立了流体在裂隙中稳态扩散的漏失压力动力学模型;最后以四川盆地焦石坝页岩气田的岩石力学性质及现场监测漏失速度为参数,计算了漏失压力的动态变化情况。结果表明:(1)井筒液柱压力与地层压力作用下的正压差是引发诱导性裂缝漏失的主要原因,现场施工中见漏就堵人为造成裂缝扩大的方法不可取;(2)诱导性裂缝漏失压力随时间改变而发生动态变化,裂缝宽度和漏失速度随漏失压力增加而增大;(3)存在着发生严重漏失的裂缝宽度临界值,漏失压差保持不变时,裂缝宽度与漏失速度呈幂指数变化关系。结论认为,现场应用效果证明了该模型的可行性,对于页岩诱导裂缝漏失可以采用控制漏失压力的方式来减小裂缝宽度,进而达到控制漏失的效果。The current leakage pressure model used for induced fractures can only identify whether fractures are created or not, but can- not analyze the influence of the change of fracture width on the leakage pressure. In this paper, a method for calculating the change of induced fracture width under the effective inner pressure was firstly developed. Then, based on the steady state diffusion equation of bottom hole fluid, a dynamic model for calculating the leakage pressure in the steady state diffusion of fluid in cracks was established considering the influential factors, including loss rate coefficient, fracture width, fluid viscosity and wellbore radius. Finally, the rock me- chanic property and loss rate monitored on site in the Jiaoshiba Shale Gas Field, Sichuan Basin, were taken as the parameters to calculate the dynamic change of leakage pressure. And the following research results were obtained. First, the positive pressure difference under the effect of wellbore fluid column pressure and formation pressure is the main reason for the pressure leakage of induced fractures, and it is inadvisable to block the leakage as soon as it is discovered on site, for it can increase the fracture width artificially. Second, the leak- age pressure of induced fractures changes dynamically over the time, and fracture width and loss rate increase with the increase of leak- age pressure. Third, there is a critical fracture width corresponding to the serious leakage. If the leakage pressure difference is constant, there is a power exponent relationship between the fracture width and the loss rate. Field application effect proves the feasibility of this model. It is concluded that the fracture width can be decreased by controlling the leakage pressure so as to control the pressure leakage of induced fractures in shale reservoirs.

关 键 词：页岩气 钻井 钻井流体 诱导裂缝 漏失 漏失压力 裂缝宽度临界值 漏失量 

分 类 号：TE21[石油与天然气工程—油气井工程]