页岩气井井筒完整性若干研究进展

在页岩气开发工程中遭遇了井筒完整性问题,主要包括页岩气井水泥环密封失效引起的环空带压问题和页岩气井压裂过程中的套管变形问题。基于目前已有的相关研究成果,总结分析了页岩气井井筒完整性失效问题的相关研究进展情况。随着国内外学者对页岩气井压裂过程中套管变形研究的逐渐深入,认为页岩气井套管变形的主要影响因素包括压裂过程中的温度应力、储层非对称压裂、固井质量差及断层或裂缝滑动等。其中,压裂过程中断层或裂缝滑动造成的页岩气井套管剪切变形机理已经受到越来越多的研究人员关注,并提出可以通过提高套管强度和固井质量、避开断层或裂缝滑动区域来有效降低套管变形的技术对策。页岩气井水泥环密封失效主要由套管内压变化和套管偏心引起的水泥环屈服破坏、界面裂缝引起的窜流等问题造成的,通过采用膨胀水泥、柔性水泥及环空预应力等技术措施可有效减小水泥环密封失效的风险。通过优化设计页岩气井的特殊水泥浆体系,对于有效提高页岩气井水泥环密封完整性具有重要意义。考虑到水泥浆固井密封能力的局限性,还可以附加考虑在井眼环空局部采用机械密封方法达到密封完整性要求。关于页岩气井井筒完整性的研究结果,对于通过体积压裂完井的其它非常规油气井工程相关设计控制也具有重要的参考意义。

Progresses in shale gas well integrity research

The sustainable annular pressure (SCP) caused by sealing failure of cement sheath and the casing deformation during hydraulic fracturing,are the major well problems integrity encountered in shale gas development.Based on the existing research results,we focus on summarizing and analyzing the progresses in research of factors contributing to failure of shale gas well integrity.With the progress in researches about casing deformation during hydraulic fracturing in shale gas wells worldwide,we know that the major influential factors include temperature,stress,asymmetric fracturing in the reservoir,poor cementing and the slip of faults or natural fractures.Among them,the shear deformation mechanism of the casing in shale gas well caused by the slip of faults or natural fractures during fracturing has attracted more and more attention among the researchers.It is proposed that the casing deformation can be effectively reduced by increasing the casing strength and the cementing performance,or avoiding the areas with fault or natural fracture slips.Besides,the sealing failure of cement sheath in shale gas wells is mainly caused by yield failure of cement sheath out of pressure variation within the casing or eccentricity of casing and channeling through interface cracks.The sealing failure of cement sheath can be effectively reduced by applying expansive cement,flexible cement or annular pre-stressing techniques,while the optimization of special cement slurry system in shale gas wells is particularly important for improving the sealing integrity of cement sheath.Given the limitation of the cement sheath sealing ability,additional mechanical sealing methods can also be used to meet the requirements of sealing integrity for certain well annulus areas.The research results about the shale gas well integrity are also of referential value to the design and control of other unconventional oil & gas wells to be completed through volume-fracturing.