Numerical Study on the Impact of Deep-Water Shallow Gas Reservoir Production with Overlying Natural Gas Hydrate Layer on Wellhead Stability

Abstracts The results of the on-site geological exploration of Block XX-1 in the South China Sea indicate the existence of a geological composition of deep-water shallow gas overlying hydrate layer. Prior studies have not sufficiently considered the impact of shallow gas on the overlying hydrate layer, as well as its effects on wellhead stability. In this paper, a wellhead-hydrate-shallow gas analysis model considering the shallow gas extraction process is constructed, the study analyzes the effect on the overlying hydrate layer as the shallow gas is extracted to obtain the effect on wellhead stability. The results indicate that the production of shallow gas reservoir leads to the decomposition of the overlying hydrate layer. During the production of shallow gas reservoir with overlying hydrate layer, hydrate decomposition causes greater formation subsidence compared to scenarios without overlying hydrate layer. The subsidence is primarily concentrated in the wellhead region and gradually decreases outward. Factors such as production pressure, reservoir thickness, reservoir depth, and production well sections significantly influence formation subsidence, thereby impacting wellhead stability. These findings provide important guidance for the safe development of shallow gas reservoir containing overlying hydrate layer.