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P2:THE GAS HYDRATE PETROLEUM SYSTEM

发布时间:2014-07-28

Timothy S. COLLETT

U.S. Geological Survey, Denver Federal Center, Colorado 80225, U.S.A

The study of gas hydrates in nature has been ongoing for over 40 years. Significant strides have been made in our understanding of the occurrence, distribution, and characteristics of marine and permafrost associated gas hydrates; but our knowledge related to the role that gas hydrates may play as an energy resource, as a geologic hazard, and as a possible agent in climate change is still incomplete. More work is needed to integrate our gas hydrate related research efforts and to further our understanding of gas hydrates in nature.
Numerous field studies, have shown that the amount of gas stored as gas hydrates in the world greatly exceeds the volume of known conventional gas resources. Gas hydrate research in recent years has focused on: (1) documenting the geologic parameters that control the occurrence and stability of gas hydrates in nature, (2) assessing the volume of natural gas stored within various gas hydrate accumulations, (3) analyzing the production response and characteristics of gas hydrates, (4) identifying and predicting natural and induced environmental and climate impacts of natural gas hydrates, and (5) analyzing the effects of gas hydrate on drilling safety.

The concept of a gas hydrate petroleum system, similar to that guides conventional oil and gas exploration, has been developed to systematically assess the geologic controls on the occurrence of gas hydrate in nature. In a gas hydrate petroleum system, the individual factors that contribute to the formation of gas hydrate can be identified and assessed; the most important include (1) gas hydrate pressure-temperature stability conditions, (2) gas source, (3) gas migration, (4) availability of water, and (5) suitable host sediment or “reservoir”.

Research coring and seismic programs carried out by the Ocean Drilling Program (ODP) and Integrated Ocean Drilling Program (IODP), starting with the ODP Leg 164 drilling of the Blake Ridge in the Atlantic Ocean in 1995, have contributed greatly to our understanding of the geologic factors that make up the various components of known gas hydrate petroleum systems. For the most part gas hydrate research expeditions carried out by the ODP and IODP provided the foundation for our scientific understanding of gas hydrates.
Recognizing the importance of gas hydrate research and the need for a coordinated effort, the U.S. Congress enacted the Methane Hydrate Research and Development Act of 2000. This Act called for the Secretary of Energy to begin a methane hydrate research and development program in consultation with other U.S. federal agencies. At the same time a new gas hydrate research program had been launched in Japan by the Ministry of International Trade and Industry to develop plans for a gas hydrate exploratory drilling project in the Nankai Trough. Since this early start we have seen other countries including China, India, Canada, and the Republic of Korea establish large gas hydrate research and development programs. These national led efforts have also included the investment in a long list of important scientific research drilling expeditions and production test studies that have provided a wealth of information on the occurrence of gas hydrate in nature.

Over the last 10 years, national led gas hydrate research programs, along with industry interest have led to the development and execution of major gas hydrate production field test programs. Two of the most important production field testing programs have been conducted at the Mallik site in the Mackenzie River Delta of Canada and in the Eileen gas hydrate accumulation on the North Slope of Alaska. Most recently we have also seen the completion of the world’s first marine gas hydrate production test in the Nankai Trough in the offshore of Japan. Industry interest in gas hydrates has also included important projects that have dealt with the assessment of geologic hazards associated with the presence of hydrates.

Our understanding of how gas hydrates occur and behave in nature is still growing and evolving – we do not yet know if gas hydrates can be economically produced, nor do we know fully the role of hydrates as an agent of climate change or as a geologic hazard. But it is known for certain that international cooperative projects have contributed greatly to our understanding of hydrates in nature and will continue to be a critical source of the information to advance our understanding of gas hydrates.