Gas Hydrates- Geohazard? Resource? Integrated and cooperative research will help us better understand both

Abstract

The literature on gas hydrates, ice-like substances composed of natural gas and water that form at high pressures and low temperatures, will often contain two key words “geohazard’ and “energy resource.” Clearly gas hydrate studies easily relate to both. Advances in geohazard studies help scientists working on the energy development questions and vice versa. For example, geohazard assessments helped identify the seismic signature of high saturation gas hydrate sands of interest to energy production and modeling gas hydrate reservoir responses to production methods has allowed for modeling soil response to gas hydrate dissociation that translate to wellbore stress at conventional oil and gas fields. The phenomena than underlies some of the geohazard concerns and the reservoir response to production are shared. In the typical marine environment any rapid disassociation of gas hydrates from the ice-like solids back to natural gas and water will cause changes in the geomechanical properties of the sediments. Changes in geomechanical properties in the often-weak sediments on deepwater marine slopes could initiate slope instability, or within the foundation, cause stress and loads to the conventional oil and gas deepwater production wellbore. Purposefully disassociating the gas hydrate to produce the natural gas will also precipitate these same geomechanical instabilities in the target sediments, producing solids as well as gas and water that will need to be handled by the production system. Much of natural gas hydrate applied research is directed at understanding natural gas hydrate geohazards or the operational hazards and constraints related to oil and gas exploration and production activities through the gas hydrate stability zone and is the focus of oil and gas companies working in deepwater at locations where a gas hydrate focus is warranted. Producing natural gas from gas hydrates, however, is the key aim that underlies most gas hydrate research and these efforts are largely government funded. Gas hydrates, had long been recognized as chemical engineering issue inside pipelines in the cold high latitudes. When widespread natural gas hydrate systems were discovered around the globe in the late 1970s and early 1980s- a time coincident with when the leading world economies were wracked by the oil shock and energy insecurity, the promise of gas hydrates as an energy resource was quickly taken up by public policy/energy policy sectors and by marine geology researchers around the world. The energy potential of gas hydrates could be huge, but the distribution of gas hydrate was uncertain and untested. One could easily imagine the roles reversed but it is national governments that are driving applied research in gas hydrate energy resources and oil and gas companies that are driving applied research for gas hydrate geohazards. The impetus for the resource research by governments was because of insecurity of natural gas resources, heighted by general energy insecurity in countries like Japan and Korea where gas hydrate hydrocarbon systems were discovered in their respective Exclusive Economic Zones. The United States enacted the Methane Hydrate Development Act of 2000 primarily to “…develop methane hydrate as a source of energy.” Other countries with active national methane hydrate development programs include China, New Zealand, and India. Oil and gas companies, on the other hand, may have a handful of strategists and futurists looking at gas hydrate as an energy resource, but they have not moved forward to produce gas hydrates to date. So far, oil and gas companies have actively only looked at geohazard issues related to gas hydrate presence in exploration and appraisal well drilling and post discovery for the site characterization of an oil and gas development. At most deepwater oil and gas exploration and development sites, gas hydrates have not been present and/or not recognized within the gas hydrate stability zone which is surprising since these are basins with robust, active, and exploitable petroleum systems. The message “that gas hydrates are not widespread even in hydrocarbon charged basins”, has rightly tempered and focused the expectations of gas hydrate resource researchers in a positive way- they have employed a petroleum systems approach to gas hydrate identification and prospecting and this has led to better-planned and more successful gas hydrate field investigation programs. The common absence, or perceived absence, of gas hydrate within the stability zone, however, can also lead to complacency about gas hydrate hazards in the oil and gas industry. Some gas hydrate signatures are easy to see, therefore avoid, but others are far more subtle. It is gas hydrates that are subtle or difficult to detect within the first few hundred meters that can present significant risks and constraints to oil and gas development. Recent initial and successful marine production tests were completed in Japan and China. Japan targeted production from thin high saturation gas hydrate sands. In China fine grained clays were targeted for the production test. Clearly, there is a promising path forward for energy production from gas hydrates. The positive loop linking advances in understanding gas hydrate geohazards to advances in gas hydrate energy understanding and vice versa is illustrated with examples from around the world and key gaps relevant to both areas of study are addressed.

AAPG Datapages/Search and Discovery Article #90348 © 2019 AAPG Asia Pacific Region Geosciences Technology Workshop, Gas Hydrates – From Potential Geohazard to Carbon-Efficient Fuel?, Auckland, New Zealand, April 15-17, 2019