Multi-gas co-production from deep-water shallow hydrates and underlying free gas: A numerical study of coupled production dynamics and secondary hydrate formation

Abstract

The co-occurrence of marine gas hydrates, shallow gas, and deep oil and gas has been widely recognized, offering favorable conditions for integrated resource development. This study aims to explore the coupled production dynamics of shallow gas hydrates and underlying free gas to support the industrialization of marine natural gas hydrate resources. A productivity prediction model for the combined extraction of hydrate and underlying gas is developed, integrating multi-physics coupling mechanisms. Using logging data from two test wells in the Qiongdongnan Basin, a short-term physical model is constructed to simulate and predict production performance. Results show that: (1) The average wellhead gas production rate increases significantly with a linear relationship to the production pressure differential; (2) pressure propagation differs notably between hydrate and free gas layers, with a distinct low-temperature zone forming near the wellbore in the hydrate-bearing layer; (3) free gas migration results in a high-saturation gas zone near the hydrate-gas interface, and elevated pressure differentials can trigger secondary hydrate formation; and (4) during short-term testing, hydrate decomposition is limited, with most gas production sourced from the underlying gas layer. By adjusting production pressure or controlling wellbore temperature, hydrate decomposition and reformation can be balanced to optimize recovery efficiency. This study highlights a novel multi-gas co-production approach and provides a theoretical basis for sustainable deepwater hydrate development.

Keywords

Natural gas hydrate / Combustible ice / Unconventional energy / Clean Energy / Underlying free gas / Deep-water shallow hydrate / Multi-gas joint-development / Deep oil and gas / Numerical simulation

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