Dissociation behavior of Methane Hydrate presumed by NMR log analysis

Abstract:

This study has been conducted with the aim of comprehending dissociation behavior of MH. The production test was operated in the Daini-Atsumi knoll in the eastern Nankai Trough, Japan. We corresponded the NMR log data acquired from the three wells, which drilled before the test (AT1-MC) and after the test (AT1-LWD1 and AT1-LWD2). NMR log measures T2 relaxation time, and calculates porosity and permeability. We especially focused on the T2 distribution.

It is assumed that MH occupied larger pore space in the sandy sediment because the T2 distribution in the MH bearing layer has no peak in the longer time zone at the AT1-MC. However, T2 peak appeared over 33ms zone at the AT1-LWD1 and AT1-LWD2. This phenomenon is observed in the thin MH bearing layers rather than thick one. On the other hand, nothing T2 peak appeared over the 33ms zone in the thick MH bearing layer, but T2 distribution shifts to longer relaxation time in the short time interval. Hence, it is assumed that the MH was dissociated from the contact faces with the grain. In terms of the thermal conductivity, near the grain-grain contact faces are more dissociable than the MH-grain contact; however both of dissociation zones are essentially MH-grain contact faces. Nothing or few MH was observed in the muddy layer at the coring campaign near these wells. Abovementioned, NMR logging detected various changes on the T2 distribution. It seems to indicate the dissociation of MH. And these data gets into alignment with other log data and monitoring data, which are resistivity and temperature measurement. However, as this logging data acquired from each location, there is possibility that the initial condition was originally distinct.

This research was conducted as a part of the MH21 research, and the authors would like to express their sincere appreciation to MH21 and the Ministry of Economy, Trade and Industry for providing the permission to disclose this research.