Volume 39: Energy Transitions toward Carbon Neutrality: Part II

Factors Controlling Stress Sensitivity of Shale Oil Reservoirs: Mineral Composition and Mechanical Properties Shuai Zhao, Shenglai Yang ,Yun Luo,Li You,Yubo Liu,Huiying Guo

Abstract

Shale oil reservoirs are dense and characterized by ultra-low porosity and ultra-low permeability, which are usually developed effectively by horizontal wells and large-scale volume fracturing. However, with the continuous advancement of the development process, the formation pressure decreases, and the stress sensitivity problem brought about by the force compression of the effective seepage channels in shale becomes a key factor restricting the development effect. In this paper, two shale cores with different lithologies from Xinjiang Oilfield in China are used as research objects to conduct stress sensitivity simulation experiments under simulated reservoir in-situ conditions. Meanwhile, the whole rock XRD analysis and nanoindentation mechanical property test are combined to investigate the influence of shale mineral composition and mechanical properties on stress sensitivity. The experimental results show that mudstone shale has higher clay mineral content, and its elastic modulus and hardness are lower than that of sandy shale with high brittle mineral content. In addition, the maximum permeability loss rate of both shales exceeds 50%, which indicates that the stress sensitivity is stronger, among which the mudstone shale has stronger stress sensitivity. In addition, the stress sensitivities of the two shales with different lithologies also show some differences, with mudstone shale having a higher clay mineral content, a lower modulus of elasticity, a higher plasticity, and a harder crack recovery after stress recovery, and its stress sensitivity is higher than that of sandy shale with a higher content of brittle minerals. The stress sensitivity experiments carried out in this paper under in situ conditions in shale reservoirs clarified the control law of mineral composition and mechanical properties on stress sensitivity, which can provide more accurate data reference for the optimization of production system in shale reservoirs.

Keywords shale oil, stress sensitive, mineral compos-ition，mechanical property, in situ condition