可变形天然裂缝动态宽度流-固耦合计算模型

Calculation Model of Hydro-mechanical Coupling for Dynamic Width of Deformable Natural Fracture

彭浩 李黔 高佳佳 尹虎 陈一凡

PENGHao LIQian GAOJiajia YINHu CHENYifan

中国石油集团川庆钻探工程有限公司川西钻探公司, 四川 成都 610051 西南石油大学石油与天然气工程学院, 四川 成都 610500

Chuanxi Drilling Company, Chuanqing Drilling Engineering Company Limited, CNPC, Chengdu, Sichuan 610051, China Petroleum Engineering School, Southwest Petroleum University, Chengdu, Sichuan 610500, China

针对当前的天然裂缝宽度预测模型没有考虑裂缝在缝内流动净压力作用下变形的问题,开展了可变形天然裂缝动态宽度流-固耦合计算模型研究。首先,根据天然裂缝的变形控制方程和缝内流动净压力方程建立流-固耦合漏失动力学模型,得到漏失速率和漏失前端侵入速度的控制方程;然后,运用自适应搜索法求取天然裂缝等效平均宽度,结合体积等效原则求得天然裂缝初始宽度,联合初始宽度和漏失速率的几何控制方程建立天然裂缝形态系数的求解方法;最后,基于漏失前端侵入速度的几何控制方程进行天然裂缝形态约束求解得到法向刚度,进而得到天然裂缝动态宽度流-固耦合计算模型。建立的可变形天然裂缝动态宽度流-固耦合计算模型,经验证其计算结果与现场测量数据吻合较好,仅需钻井液性能、井漏现场测量的漏失速率序列及漏失体积序列,就能进行天然裂缝动态宽度预测,便于现场应用。

Aiming at the fact that existing models for calculating the dynamic width of natural fractures fail to consider the compression deformation of the fracture under the net flow pressure in the fracture,the model of hydro-mechanical coupling for dynamic width of natural fracture is studied.Firstly,according to the deformation law of natural fracture wall and the net flow pressure equation in the fracture,a hydro-mechanical coupling leakage dynamic model is established,by which the geometric control equations of the leakage rate and the invasion velocity of the leakage front distance are obtained;then,the self-adaptive search method is used to calculate the equivalent average width of the natural fracture,and the initial width of the natural fracture is obtained based on the volume equivalent principle.The solution method of the natural fracture shape coefficient is established by combining the geometric control equations of leakage rate and the initial width;finally,according to the geometric governing equation of the invasion velocity of the leakage front distance,the natural fracture shape constraint is solved to obtain the normal stiffness,and then the model of hydro-mechanical coupling for dynamic width of natural fracture is obtained.The model of hydro-mechanical coupling for dynamic width of natural fracture has been verified on-site and the calculation results are in good agreement with the on-site measured data.Only the drilling fluid performance,the lost circulation rate sequence and the lost volume sequence measured on-site are needed to predict the dynamic width of natural fractures,which is convenient for on-site application.

10.11885/j.issn.1674-5086.2020.10.28.02