Investigation of shale imbibition capability and the influencing factors based on a convenient method

A shale gas reservoir is commonly characterized by nano-scale pores and throats, high clay contents, and strong heterogeneity in permeability and porosity. Such tight structure can prevent a large proportion of fracturing fluid from flowing back after the hydraulic fracturing operations. It remains challenging to quantitatively analyze the water imbibition capability of shale as the rock sample size and shape are not unified when water imbibition behavior is experimentally investigated. In this study, a new method is proposed to evaluate the water imbibition capability of shale using the ratio of the imbibition area to the mass of the rock sample to normalize the size and shape of the sample. More specifically, the experimental shale samples were collected from three different shale gas reservoirs (Sichuan Changning Block, Yunnan Zhaotong Block, Chongqing Pengshui Block) to verify the proposed method and evaluate the influencing factors of shale imbibition capability. Imbibition experiments were then conducted to analyze the influence of four factors, including matrix porosity, fracture size, clay, and rock sample size, on the water imbibition capability of shale. The results show that the proposed method can characterize the maximum imbibition capability and imbibition rate and avoid errors in the measured porosity. In addition, the rank of factors affecting the imbibition capability was found to be fracture size, porosity, clay content, and sample size.