Numerical assessment of gas production potential via depressurization: Impact of production interval and bottom hole pressure at site NGHP-01-10D of the Krishna-Godavari Basin hydrate reservoir

Abstract

The National Gas Hydrate Program expeditions (NGHP-01 and -02) have conclusively proven the presence of hydrate deposits on the eastern coast of India. The novelty of the present study lies in its investigation of the richest gas hydrate deposit (hydrate saturation [Sh] > 0.75), NGHP-01-10D, in the Krishna-Godavari (KG) Basin, India. The study presents a first look at the long-term gas production viability using a single vertical well, subjected to variations in production interval and bottom hole pressure. Specifically, we compared the gas production at bottom hole pressures of 3–6 MPa and production intervals of 20–40 m. The results indicate production rates that are technically feasible but lower than commercially acceptable standards. Increasing the bottom hole pressure drawdown from 6 MPa to 3 MPa increased the gas production from 1297 m³/d to 4902 m³/d (i.e., more than tripling the average daily gas production). Meanwhile, while expanding the production interval from 20 m to 40 m led to an increase in gas production, it also resulted in higher water production. As a result, the average gas-to-water ratio (R_GW) decreased from 9.5 to 5.3 with the expansion of the production interval, thereby highlighting the need to optimize the interval length. Furthermore, the spatial evolution of certain thermodynamic parameters, including pressure, temperature, and phase saturation (methane, water, and hydrate), underscores the critical role of heat transfer from the UB. Our study findings offer valuable insights for long-term production forecasting, the delineation of phase evolution patterns, and the identification of potential flow barriers that may impede deliverability.