Development of methane hydrate production method

Abstract

− 90 − Synthesiology Vol.5 No.2（2012） depressurization, thermal stimulation and inhibitor injection [5]. The depressurization method decreases the reservoir pressure below the equilibrium pressure of methane hydrate formation at the reservoir temperature. This method appears to be a cost-effective solution for producing natural gas from methane-hydrate-bearing layers [6]. On the basis of numerical simulations of gas productivity, this method is considered to be predictable and effective for producing gas from the reservoirs consisting of alternating layers of sand and mud. However, hydrate dissociation is a very complex process of coupling heat and mass transfers with the kinetics of hydrate dissociation. Therefore, to understand the dissociation process of methane hydrate existing within the pore spaces of sandy sediments, dissociation experiments on methane-hydrate-bearing cores in a laboratory would be useful [7]-[10]. The performance of gas production strongly depends on the size and permeability of the samples. Heat transfer is a predominant factor in dissociation experiments on methane-hydrate-bearing cores performed in a laboratory (of the order of a few centimetres), whereas mass transfer dominates the dissociation process in an actual reservoir field (of the order of a few 100 m). This difference in the dominant factors between core-scale experiments and field-scale production is responsible for the difference in gas production behaviours. To overcome this problem and to establish gas production conditions at a reservoir field, it is necessary to conduct methane hydrate sedimentary core production experiments on a larger scale. Thus, AIST recently developed and introduced a large-scale apparatus for methane hydrate laborator y production tests, which can conduct gas production experiments under conditions similar to those at actual natural methane hydrate reservoir fields. In this paper, I first present an overview of the Methane Hydrate Research and Development Program [11]. Then I describe the problems in conducting research issues such as methane hydrate production experiments at a laboratory scale, actual field production tests and numerical prediction of productivity, and finally, I report the advantage and certification of a large-scale reactor developed recently to overcome such problems.