A Feasibility Study of Using Geothermal Energy to Enhance Natural Gas Production from Offshore Gas Hydrate Reservoirs by CO₂ Swapping

Abstract

The energy industry faces a significant challenge in extracting natural gas from offshore natural gas hydrate (NGH) reservoirs, primarily due to the low productivity of wells and the high operational costs involved. The present study offers an assessment of the feasibility of utilizing geothermal energy to augment the production of natural gas from offshore gas hydrate reservoirs through the implementation of the methane-CO 2 swapping technique. The present study expands the research scope of the authors beyond their previous publication, which exclusively examined the generation of methane from marine gas hydrates. Specifically, the current investigation explores the feasibility of utilizing the void spaces created by the extracted methane in the hydrate reservoir for carbon dioxide storage. Analytical models were employed to forecast the heat transfer from a geothermal zone to an NGH reservoir. A study was conducted utilizing data obtained from a reservoir situated in the Shenhu region of the Northern South China Sea. The findings of the model indicate that the implementation of geothermal heating can lead to a substantial enhancement in the productivity of wells located in heated reservoirs during CO 2 swapping procedures. The nonlinear relationship between the temperature of the heated reservoir and the rate of fold increase has been observed. It is anticipated that the fold of increase will surpass 5 when the gas hydrate reservoir undergoes a temperature rise from 6°C to 16°C. The mathematical models utilized in this study did not incorporate the impact of heat convection resulting from CO 2 flow into the gas reservoir. This factor has the potential to enhance well productivity. The mathematical models' deviation assumptions may cause over-prediction of well productivity in geothermalstimulated reservoirs. Additional research is required to examine the impacts of temperature drawdown, heat convection resulting from depressurization, heat-induced gas pressure increment, and the presence of free gas in the formation containing hydrates. The process of CH 4 -CO 2 swapping, which has been investigated, involves the utilization of geothermal stimulation. This method is highly encouraging as it enables the efficient injection of CO 2 into gas hydrate reservoirs, resulting in the permanent sequestration of CO 2 in a solid state. Additional research is warranted to examine the rate of mass transfer of CO 2 within reservoirs of gas hydrates. KEYWORDSGas hydrate; CO 2 -swapping; geothermal stimulation; well productivity; feasibility study Nomenclature c Specific heat of reservoir rock, J/kg-°C C p Heat capacity of the fluid inside the wellbore, J/kg-°C d c Inner diameter of insulation-cement sheath, ft d p Inner diameter of pipe, ft

Comprehensive Review and Perspectives of CO2 Hydrate Storage in Subseafloor Saline Sediments: Formation, Stability, and Optimization Strategies

“…By strategically placing heat sources in specific locations within the sediments, researchers can harness geothermal energy to induce localized heating. 254,255 This minimizes the need for external energy inputs and aligns with sustainable practices. Utilizing geothermal gradients provides a cost-effective and energy-efficient alternative, demonstrating the potential for harnessing naturally occurring thermal resources to optimize CO 2 hydrate formation and stability in subseafloor saline sediments.…”

“…In contrast to controlled heating methods, utilizing geothermal gradients for localized heating offers a unique and environmentally friendly strategy. , This approach capitalizes on the natural temperature gradients in subseafloor environments. By strategically placing heat sources in specific locations within the sediments, researchers can harness geothermal energy to induce localized heating. , This minimizes the need for external energy inputs and aligns with sustainable practices. Utilizing geothermal gradients provides a cost-effective and energy-efficient alternative, demonstrating the potential for harnessing naturally occurring thermal resources to optimize CO 2 hydrate formation and stability in subseafloor saline sediments. , Researchers exploring thermal manipulation strategies can benefit from considering both controlled heating methods and the innovative use of geothermal gradients to advance CO 2 hydrate.…”