基于现场套管损伤分析的套管围压确定方法

Method for Determining Casing Confining Pressure Based on Field Casing Damage Analysis

利用油层套管作为压裂通道进行大排量高泵压储层改造是页岩油气、致密油气效益开发不可或缺的手段。为了准确分析套管压裂过程中套管强度的安全性,需要准确确定套管的围压载荷。针对油层套管完井情况复杂、准确确定围压载荷难度高的实际情况,利用现场压裂施工数据,通过对事故井油套安全性反演的方法确定了特定段套管围压载荷系数。分析结果显示,从技套管鞋处至油套水泥返高处,该段油层套管围压载荷系数(MPa/100m)在0.97~1.04之间,与清水液柱压力系数相当。根据研究结果并考虑地层压力对水泥环的作用受时间因素影响,在计算已固井段压裂工况下套管的安全性时,套管围压载荷选取清水液柱压力而非地层压力,计算结果会更具有实际指导意义。

Reservoir stimulation with large pump rate and high pump pressure by using production casing as injection channel is an indispensable means for the cost-effective development of shale and tight oil and gas.In order to accurately analyze the strength safety of casing during fracturing process,it is necessary to accurately determine the confining pressure load of casing.In view of the complicated situation of wells completed with production casing and the great difficulty in accurately determining the confining pressure load,field fracturing data are used to determine the confining pressure load factor of a specific section of casing by conducting inversion for the safety of production casing in wells with accidents.The analysis results show that the confining pressure load factor(MPa/100m)of the casing in the section from intermediate casing shoe to the cement top in production casing is 0.97-1.04,which is equivalent to the pressure factor of fresh water column.Based on the study findings and considering that the effect of formation pressure on cement sheath is affected by time factor,fresh water column pressure rather than formation pressure is selected as the casing confining pressure in calculating the safety of casing under the fracturing conditions of cemented well section,which will yield a calculation result with more practical guiding significance.