缝洞型碳酸盐岩储气库地应力变化特征及力学完整性研究

Mechanism investigation on in-situ stress characteristics and mechanical integrity of fracture-cavity carbonate underground gas storage reservoir

缝洞型碳酸盐岩储层非均质性极强,储集空间结构和渗流关系复杂,为地应力分析、注采参数选择、力学完整性评价带来了诸多挑战。因此,为进一步明确缝洞型碳酸盐岩储气库运行过程中的地应力变化、保证储气库运行过程中的力学完整性、提高上限压力,建立机理模型,分析缝洞型碳酸盐岩储气库应力分布特征及四维地应力变化规律,同时评价不同介质力学完整性。结果表明:①缝洞型碳酸盐岩储层相较于均质储层在缝洞处应力集中较为明显,尤其溶洞边界易出现应力的极小值;②缝洞处孔隙压力及应力变化更为剧烈,储气库运行过程中溶洞边界更易发生剪切或张拉破坏;③在采气过程中,溶洞边界沿最小主应力方向更易发生剪切破坏,注气过程中,溶洞边界沿最大主应力方向更易发生张拉破坏;④缝洞型储层整体相较于均质储层更易在注气过程发生张拉或剪切破坏,采气过程缝洞型储层整体较为安全,但洞周围更易发生剪切破坏。研究成果可为缝洞型碳酸盐岩储气库地应力分析和力学完整性评价工作提供理论及方法支撑。

Fracture-cavity carbonate reservoirs are highly heterogeneous,presenting complex relationships between reservoir pore space and seepage flow.These complexities pose significant challenges for in-situ stress analysis,selection of injection and production parameters,and evaluations of mechanical integrity.In order to further clarify the variation of in-situ stress during the operation of fracture-cavity carbonate underground gas storage(UGS),ensure the mechanical integrity during the operation of UGS and increase the upper limit pressure,the model was developed to analyze the stress distribution in fracture-cavity carbonate gas storage and to monitor the variations in fourdimensional in-situ stress.This model also assesses the mechanical integrity across different pore spaces.The findings reveal that:①Stress concentration is more pronounced in fracture-cavity carbonate reservoirs than in homogeneous ones,with the lowest stress levels often occurring at cavity boundaries.②Pore pressure and stress fluctuations are more severe in fracture-cavity environments,increasing the likelihood of shear or tensile failures at cavity boundaries during UGS operations.③During gas production,shear failure tends to occur along the direction of minimum principal stress,whereas tensile failure is more probable along the direction of maximum principal stress during gas injection.④Compared to homogeneous reservoirs,fracture-cavity reservoirs are more prone to tension or shear failures during gas injection but are generally safer during gas production,though shear failures around cavities are more likely.These results provide valuable theoretical and methodological insights for in-situ stress analysis and mechanical integrity assessments of fracture-cavity carbonate UGS.