Effects of shale swelling on shale mechanics during shale–liquid interaction

Abstract

An essential feature of shale is swelling induced by shale–liquid interactions. Shale swelling is an important inducing factor for shale damage that affects shale mechanics. A better understanding of the effects of shale swelling on shale mechanics is crucial for drilling and fracturing design. Therefore, the effects of shale swelling on shale damage and shale mechanics were investigated. The results demonstrated that an increase in shale swelling increases shale damage, thus negatively affecting shale mechanics. The compressive strength decreases rapidly with increasing shale swelling. Moreover, the decrease in the elastic modulus is controlled by shale swelling. The elastic modulus of shale reduces by 17.9% when shale swelling is 0.4%, compared to only 3.1% when shale swelling is 0.2%. The effects of shale swelling on the elastic modulus are affected by quartz content and confining pressure. Shale can maintain a high elastic modulus at high quartz content during shale swelling. The correlations of shale swelling and elastic modulus under different quartz contents were established. Based on these research results, a possible reason for casing deformation in the Weirong shale gas field was discussed.