川西低渗透气藏采用气体钻井技术钻进时,致密砂岩井段井下垮塌频繁,为给制定防塌技术措施提供依据,在分析非达西渗流、储层敏感性对孔隙压力影响,计算气层产气时径向拖曳力的基础上,分析了径向拖曳力影响下井周的有效应力场,利用川西X3井实钻数据分析了气体钻井井壁垮塌的机理,并与摩尔库伦准则和拉伸破坏模型相结合,提出了适用于川西低渗透气藏气体钻井的井壁稳定性评价方法.川西低渗透气藏气体钻井井壁垮塌机理为:低渗透储层中高速非达西渗流和气体产出时产生的径向拖曳力使坍塌压力升高,井壁稳定性变差,同时在径向拖曳力作用下先发生拉伸破坏,随后地层压力降低进而发生剪切破坏,出现垮塌.利用低渗透气藏气体钻井井壁稳定性评价方法评价了X3井低渗透储层的井壁稳定性,评价结果与实钻情况相符,说明采用该评价方法可以评价川西低渗透气藏气体钻井时的井壁稳定性,能够为川西低渗透气藏气体钻井制定防塌技术措施提供指导.%In gas drilling through low permeability gas reservoirs in Western Sichuan, borehole collapse occurs frequently in the tight sandstone sections. To develop a protocol for anti-collapse technical measures during gas drilling of such as in the kinds of gas reservoirs found in western Sichuan, effective stress around the wellbore under the influence of radial drag force has been analyzed based on the analysis of non-Darcy seepage and reservoir sensitivity on pore pressure, and radial drag force during gas production. The wellbore collapse mechanism of gas drilling was analyzed by using practical drilling data of Well X3 in Western Sichuan. Then a wellbore stability evaluation method during gas drilling through low permeability gas reservoirs in western Sichuan was proposed in combination with Mohr-Coulomb criterion and tensile failure model. Results showed that the high-speed non-Darcy seepage and the radial drag force generated during gas production in low permeability reservoir will increase the borehole collapse pressure, so damage borehole stability. Tensile failure occurs first under radial drag force, and then shear failure happens due to the decrease of formation pressure. Those rock failures result in wellbore collapse. Wellbore stability of Well X3 in the low permeability reservoir was evaluated using this method, and the results were consistent with the practical drilling situations. It demonstrated that this method could be used to evaluate wellbore stability during gas drilling in low permeability gas reservoir in western Sichuan, and it would provide a protocol and recommended best practices for the development of anti-collapse measures during gas drilling in low permeability gas reservoir in Western Sichuan.
展开▼
