Influence of Flow Properties on Gas Productivity in Gas-Hydrate Reservoirs: What Can We Learn from Offshore Production Tests?

Abstract

Gas hydrates are expected to be an energy resource in this century. Many countries, such as the United States, China, India, and Japan, have explored potential reservoirs and promising production methods. During the past decade, Japan has conducted the world’s first offshore production test in the eastern Nankai Trough, followed by China in the South China Sea. These offshore production tests have demonstrated that gas can be produced continuously from hydrate-bearing sand or silt-rich sediments. However, production tests in the eastern Nankai Trough have shown that gas production declines for a few days and then remains constant at a constant pressure in the bottom hole for at least a period of 4 days. This result is different from predicted behaviors by numerical simulations, showing a gradual increase in the gas production rate with time. The discrepancy between actual data and numerical simulations indicates that numerical simulators overestimate the response as a result of the lack of a proper system description in the models. Numerical simulation can reproduce the tendency of gas production stagnation by considering hydrate reformation in the reservoir. However, hydrate reformation is not expected to occur during the early stages of tests. Recent experimental and numerical studies have shown that sediment compaction and particle crushing by high effective stress, migration of fines leading to the formation of a skin, and changes in relative permeability are induced by depressurization during gas production. These phenomena result in dynamic permeability changes that can lead to gas production stagnation in the early stages.

Geological Reservoir Characterization of a Gas Hydrate Prospect Associated with the Hydrate-01 Stratigraphic Test Well, Alaska North Slope

“…The Japan Research and Development Consortium for Pore Filling Hydrate in Sand (MH21-S), as organized by the Ministry of Economy, Trade and Industry, Japan (METI), has conducted several production tests by applying the depressurization method at offshore sites in Japan on the margins of the Nankai Trough, − at onshore permafrost regions at the Mallik site in Canada, , and at the Iġnik Sikumi site on the Alaska North Slope (Figure ). Valuable data related to dynamic reservoir performance, as well as static reservoir properties derived from geological and geophysical data, were obtained from these production tests.…”

Energy Transition and Climate Mitigation Require Increased Effort on Methane Hydrate Research

“…To date, only short-term production tests have been performed onshore in Alaska , and Canada , and offshore in Japan , and China, , which have produced encouraging results. Reservoir response modeling ,− suggests that gas production from methane hydrates increased during the first several years, which is in contrast to production from other resources, such as shale gas. , With the exclusion of the Arctic/Antarctic methane hydrate accumulations and with oceanic methane hydrates representing 99% of the total global methane hydrate resource, , the U.S. Department of Energy, Gulf of Mexico methane hydrate program is focused on the need for offshore reservoir characterization of coarse-grained methane hydrate reservoirs. , …”

Recent Advances in Methods of Gas Recovery from Hydrate-Bearing Sediments: A Review

“…The above key challenges are rooted in the existing research gaps on the strong multiphysics coupling relationship of thermal–hydraulic–mechanical–chemical (THMC) aspects in HBS during gas recovery (shown in Figure ). However, the multifield relationship is in the weak coupling stage, which simplifies the nonlinearity degree of HBS and makes the NGH development idealized. ,,, Moreover, given the unconsolidated nature of HBS, a complexly disturbed situation near the wellbore, vertical and horizontal heterogeneities of HBS, and weak coupling of THMC could be determined as the leading causes for the discrepancy in production behavior predicted by the THMC model and actual monitoring in the field. , The powerful interactions among THMC can be described as follows briefly: interactions between chemical and hydraulic fields The NGH dissociation/formation and water–ice phase transition under certain P – T are guaranteed to change the fluid flow parameters (e.g., porosity, the permeability of HBS). However, the variations in the pressure of HBS, in turn, affect their transition rate. interactions between chemical and thermal fields NGH formation/dissociation are exothermic/endothermic reactions, and ice formation and ice ablation are exothermic/endothermic reactions, respectively, directly determining the temporal and spatial distribution of the thermal field in HBS.…”

“…140,386,396,397 Moreover, given the unconsolidated nature of HBS, a complexly disturbed situation near the wellbore, vertical and horizontal heterogeneities of HBS, and weak coupling of THMC could be determined as the leading causes for the discrepancy in production behavior predicted by the THMC model and actual monitoring in the field. 398,399 The powerful interactions among THMC can be described as follows briefly:…”