考虑井壁稳定及增产效果的页岩气水平井段方位优化方法

An optimal method of horizontal interval azimuth for a shale gas well considering wellbore stability and stimulation effects

针对页岩气水平井钻井过程中常见的井壁失稳垮塌问题,为提高井壁稳定性和为后期压裂增产提供良好的条件,分析了层理面产状和地应力类型对井壁稳定性的影响,并对压裂缝与水平井段夹角,以及与水平气井产量之间的关系进行了研究,进而提出了通过对水平井段方位的优化来提高井壁稳定性和改善压裂增产效果的技术思路:利用川南地区页岩气井的测井、地应力及岩石力学资料,通过页岩层理面破坏模型及本体破坏模型分析计算出不同方位角下的井壁坍塌压力,找出井壁稳定性最好时井眼与层理面产状和地应力类型之间的关系;通过对压裂缝延伸方向的分析,得出了压裂缝的一般延伸规律;利用产能公式计算裂缝与水平井段呈不同夹角时的产量,以此获得了裂缝与水平井段夹角影响压裂效果的规律。还以川南地区的W201-H3井为例,充分考虑页岩气井壁稳定及增产效果,提出了有针对性的水平井段方位优化设计,使该井能在保持良好井壁稳定性的前提下获得良好的增产效果。

Horizontal well drilling is one of the key technologies for shale gas development.An analysis was conducted of the impact of bedding plane occurrence and in-situ stress type on wellbore stability to solve many common problems such as wellbore collapse,stimulation improvement in late fracturing,etc.in the drilling of a horizontal shale gas well.A study was also made on the intersection angle between a fracture and a horizontal interval and the relationship between fractures and horizontal gas well production.Then,we proposed a method to improve wellbore stability and stimulation effects of fracturing through an optimization of horizontal interval azimuths.More specifically,we used the shale bedding plane damage model and rock mass damage model to analyze and calculate wellbore collapse pressures at different azimuths based on the logging,in-situ stress and rock mechanic data of shale gas wells in southern Sichuan Basin.Subsequently,we worked out the relationship between wellbore and bedding plane occurrence and in-situ stress while the wellbore had the best stability.Moreover,we got the general law of fracture extension by analyzing fracture trend and obtained the law of the impact of intersection angles between fractures and horizontal intervals on fracturing effects by using the productivity formula to calculate the production at different intersection angles between fractures and horizontal intervals.In a case study of Well W201-H3 in southern Sichuan Basin,we fully considered the wellbore stability of this shale gas well and stimulation effects and put forward a pertinent and optimal design for the horizontal interval azimuth to realize a better stimulation effect in stable wellbore.