Fully Coupled Thermo-Hydro-Mechanical Modeling of Mud Loss in Deep Fractured Gas Reservoirs

Summary To address persistent lost circulation challenges in deep fractured gas reservoirs that impede hydrocarbon recovery, we present a mud loss model for fractured gas reservoirs with gas/liquid two-phase flow. The model adopts the discrete fracture network (DFN) approach, accounting for the distinct physical properties of mud and gas, as well as the dynamic evolution of formation mechanical and fluid properties under thermo-hydro-mechanical (THM) coupling. A numerical solver was developed using COMSOL Multiphysics®, integrating partial differential equations (PDEs), built-in physical fields, and custom function sets. Model validation was performed through comparison with fractured medium seepage experiments and existing finite element models, confirming its accuracy. Further analysis quantified critical modeling limitations, revealing that single-phase flow assumptions underestimate mud loss rates by 79.2%, while neglecting stress and temperature field couplings introduces additional errors of 65.0% and 8.9%, respectively. The study also elucidates the evolution of matrix and fracture permeability during mud loss and evaluates the influence of reservoir geological conditions and operational parameters. By analyzing the correlation between mud loss rate and key factors, a new statistical correlation between leakage pressure difference and mud loss rate was established, providing a more efficient method for leakage pressure prediction in fractured gas reservoirs. These findings offer critical insights for lost circulation diagnosis and the design of effective plugging strategies in such reservoirs.