Towards Commercial Gas Production from Hydrate Deposits

Hydrate occurrence in Europe: Risks, rewards, and legal frameworks

In January of this year (2020), a major scientific study ('the Minshull report') announced that gas hydrate reservoirs were found in many offshore areas across Europe. The European Commission is now considering a policy view to commercialize the development and extraction of methane gas from European offshore areas. Affirmation from the European Commission that offshore methane hydrates are too useful and too valuable to forego development could initiate a global response to adopt offshore methane hydrates as a new source of natural gas for heating, for electrical power supplies, and for potential new revenues. The upside? The potential rewards from offshore methane hydrates are multi-fold. Coastal states are surrounded in methane hydrate resources that if responsibly developed could enable vast amounts of methane (natural gas) to be produced for decades or centuries beyond the timelines of conventional natural gas assets. There are also massive volumes of fresh water trapped in hydrates that could aid in fighting droughts and desertification. The downside? There are novel foreseeable risks that might result from those commercial methane hydrate activities. The climate change risks and geo-physical hazards from offshore methane hydrates are quite distinct from both conventional and unconventional hydrocarbons. There are new challenges to achieving safety and sustainability. In review, this paper both welcomes the discovery and confirmation of offshore methane hydrates in European waters and also raises concerns that more research is required on the optimal policy strategies for the known and foreseeable risks to best enable safe and sustainable policy choices.

The Rule of Carrying Cuttings in Horizontal Well Drilling of Marine Natural Gas Hydrate

Horizontal well drilling is a highly effective way to develop marine gas hydrate. During the drilling of horizontal wells in the marine gas hydrate layer, hydrate particles and cutting particles will migrate with the drilling fluid in the horizontal annulus. The gravity of cuttings is easy to deposit in the horizontal section, leading to the accumulation of cuttings. Then, a cuttings bed will be formed, which is not beneficial to bring up cuttings and results in the decrease of wellbore purification ability. Then the extended capability of the horizontal well will be restricted and the friction torque of the drilling tool will increase, which may cause blockage of the wellbore in severe cases. Therefore, this paper establishes geometric models of different hole enlargement ways: right-angle expansion, 45-degree angle expansion, and arc expanding. The critical velocity of carrying rock plates are obtained by EDEM and FLUENT coupling simulation in different hydrate abundance, different hydrate-cuttings particle sizes and different drilling fluid density. Then, the effects of hole enlargement way, particle size, hydrate abundance and drilling fluid density on rock carrying capacity are analyzed by utilizing an orthogonal test method. Simulation results show that: the critical flow velocity required for carrying cuttings increases with the increase of the particle size of the hydrate-cuttings particle when the hydrate abundance is constant. The critical flow velocity decreases with the increase of drilling fluid density, the critical flow velocity carrying cuttings decreases with the increase of hydrate abundance when the density of the drilling fluid is constant. Orthogonal test method was used to evaluate the influence of various factors on rock carrying capacity: hydrate-cuttings particle size > hole enlargement way > hydrate abundance > drilling fluid density. This study provides an early technical support for the construction parameter optimization and well safety control of horizontal well exploitation models in a marine natural gas hydrate reservoir.