Quantitative evaluation on the elastic property of oil-bearing mudstone/shale from a Chinese continental basin

Abstract

This study aims at quantitatively evaluating the impact of material compositions on the elastic property (static Young's modulus) of oil-bearing mudstone and shale (MS). Six samples (two mudstone and four shale) from a Chinese continental basin (Bohai Bay basin) were investigated under different hydrostatic triaxial compression conditions. The primary findings of this study include the following: (a) the elastic property of MS rocks are sensitive to the hydrostatic confinement condition. In response, the MS Young's modulus gradually increases with increasing confining stress. (b) The mineralogical compositions impacting the MS Young's modulus primarily include quartz, plagioclase, calcite and clay. Overall, the total content of siliceous (calcareous) minerals has a positive (negative) effect on Young's modulus. Clay also contributes to the decrease of Young's modulus. (c) Due to its relatively low stiffness and strength, organic matter has a substantially negative impact on Young's modulus. (d) MS reservoirs that contain a high siliceous mineral content will be favorable to hydraulic fracturing. Finally, an empirical model evaluating MS Young's modulus was established by coupling Young's modulus with material compositions; the model shows a good fit with the experimental results. Thus, the MS Young's modulus is comprehensively affected by multiple constituents found in MS rocks and can be expressed as a function of material composition.