摘要
对油气井压裂改造时,向井眼内注入大量流体,井筒周围应力场重新分布,主要通过积分形式求解,过程繁杂,且对应力场的影响因素分析较少.利用拉氏变换,以流固耦合控制方程和应力平衡方程等为基础,结合注入流体诱导应力场的积分形式解,在定压条件下推导内、外边界拉氏变换解;利用Stephfest拉氏数值反演方法对变换解进行数值求解.数值模拟结果表明,切向应力场在最小水平主应力方向上变化较大,距离井壁越近,注入流体诱导的切向应力场值越大,随着距离增加,其值变小;在一定条件下(如地应力差较小),切向应力场发生反转,使得压裂裂缝转向.切向应力场与注入时间、流体黏度和地层渗透率等因素有关:延长注入时间、增加注入体积、较低的液体黏度和较高地层渗透率有利于使切向应力场增加,诱导切向应力场发生反转,有利于人工裂缝转向.
During the process of hydraulic fracturing treatment,large amounts of fracturing fluid are pumped into the wellbore,resulting to stress field redistribution near the wellbore.At present,the main method for solving the problem is the integral solution form of stress field,but its solving process is very complex,and the corresponding impact factors is rarely studied.In this paper,by using the Laplace transform,on the basis of fluid-solid coupling control equation,stress equilibrium equation and other equations in the elasticity theory,combined with the integral solution form of stress field,the Laplace transform solution of stress field at the constant pressure of internal and inner boundary is derived,and the numerical solutions are obtained by inversion Laplace transform.The results show that the change of tangential stress field in the minimum horizontal stress direction is larger than that in other direction.The closer the distance from the wellbore,the greater the fluid-induced shear stress field is.With the distance increasing,its value becomes smaller and smaller.Under certain conditions(such as small insitu stress difference),the stress field may be reversal,which makes hydraulic fracture reorientation possible.Tangential stress field is related with injection time,fluid viscosity and formation permeability.Greater injection time,larger fluid volume,lower viscosity liquid and higher formation permeability is in favor of increasing the tangential stress field,which will make the stress field reversal and help reorientate the artificial fractures.Our results have been compared with the results in the existing literature,and oil field applications demonstrate the correctness of the mathematical model again.
出处
《东北石油大学学报》
CAS
北大核心
2015年第2期85-93,10,共9页
Journal of Northeast Petroleum University
基金
国家重点基础研究发展计划项目(2015CB250903)
国家自然科学基金重大项目(51490652)
中国石油天然气股份有限公司科学研究与技术开发项目(2010E-2105)
关键词
拉氏变换
注入流体
诱导应力场
数学模型
切向应力
径向应力
Laplace transform
injected fluid
induced stress field
mathematical model
tangential stress
radial stress
