Multi-well strategy for gas production by depressurization from methane hydrate-bearing sediments

Abstract

Abstract Hydrate-bearing sediments are a potential source of energy. Depressurization is the preferred production method in mechanically stable and highly permeable sandy reservoirs. The goal of this study is to develop closed-form analytical solutions for multi-well depressurization strategies and to explore the synergistic interactions among wells. The key variables are the aquitard and sediment permeabilities, the reservoir layer and aquitard thicknesses, and water pressures in the far-field, at phase transformation and at the wells. These variables combine to define two governing dimensionless ratios (for permeability and fluid pressure), and a characteristic length scale λsed. Proposed solutions show that synergistic multi-well strategies dissociate a larger hydrate volume than an equal number of individual wells working independently. The optimal distance between wells increases: (1) with the length scale λsed, (2) for tighter aquitards, (3) for lower well pressure and when the original water pressure of the reservoir is close to the dissociation pressure, and (4) when both the aquitard and the reservoir are thick. Implications extend to both vertical and horizontal wells. The proposed closed-form solutions expedite design and economic analyses and allow the fast comparison of potential production scenarios.