Triaxial Hydraulic-Mechanical-Chemical Coupled Experiments for Hydrocarbon Production in Unconventional Shale Reservoirs

Abstract Unconventional oil and gas play a key role in the global transition to clean energy. Advances in horizontal drilling and hydraulic fracturing have enabled substantial hydrocarbon extraction from shale formations. However, the initial high production rates from these formations are not sustained over time, leading to a significantly lower recovery rates compared to conventional reservoirs. Hydrocarbon production in shale formations is governed by complex, multi-physical coupled mechanisms, including fluid diffusion in the tight matrix, multiphase flow in fractures, and stress dependent interactions between matrix and fracture. To address these challenges, we developed a high pressure ‘quad-pore’ triaxial cell and an in situ experimental protocol to simulate the live oil production scenarios. Under fully in-situ conditions, we saturated Wolfcamp shale with live oil, induced fractures, and conducted soaking, pressure drawdown, long term production, and stress dependent permeability evaluation. Through multiple tests, we found that shale gas production is mainly driven by pressure drawdown, long term production, and fracturing, while oil production was mainly produced during the long-term production and pressure drawdown. Soaking enhances hydrocarbon production through imbibition. Complex, branched fractures with larger surface areas are more effective in producing shale gas. As pressure decreases, the produced hydrocarbons becomes heavier, with higher concentrations of intermediate-chain and longer-chain hydrocarbons. Heavier oil dominates in the late production stage. The bubble point marks a critical threshold, beyond which a large amount of oil and gas are produced. These findings promote the development of a better strategy for unconventional oil and gas production and contribute to achieving important economic, energy security, and environmental benefits.