Multiphase Transient Flow in Wellbore during Shallow Hydrate Reservoir Drilling in Deep Water

During shallow hydrate reservoir drilling in deepwater, hydrates in the reservoir and drilling cuttings decompose under specific temperatures and pressures. This process impacts the temperature of the reservoir and wellbore as well as the concentration of cuttings, leading to intricate gas-liquid-solid multiphase dynamics in the wellbore. These dynamics can cause significant errors in the predicted wellbore pressure, which may lead to blowout accidents. This paper examines the effects of hydrate decomposition on the reservoir temperature field, considering the migration of cuttings and the decomposition of hydrate in both the cuttings and the reservoir. A multiphase flow model was developed for drilling in deepwater shallow hydrate formations, and its accuracy was validated using experimental data. The study also demonstrates the influence of the wellhead backpressure, drilling fluid density, drilling fluid inlet temperature, and rate of penetration (ROP) on the hydrate decomposition rate, void fraction, mud pit gain, and bottom-hole pressure. The simulation results indicate that applying wellhead pressure, increasing drilling fluid density, reducing the inlet temperature of drilling fluids, and lowering ROP can effectively inhibit hydrate decomposition, reduce void fraction, and help maintain bottom-hole pressure.