Mechanical strength and seismic property measurements of hydrate-bearing sediments (HBS) during hydrate formation and loading tests (OTC 19559)

Authors: Seiji Nakagawa (speaker), Timothy J. Kneafsey, and George J. Moridis

Venue: 2008 Offshore Technology Conference, Houston, Texas, May 5-8, 2008 http://www.spe.org and http://www.smenet.org [external sites]

Abstract: An on-going effort on conducting laboratory triaxial compression tests on synthetic methane hydrate-bearing sediment cores is presented. Methane hydrate is formed within a sand pack inside a test cell under controlled temperature and confining stress, and triaxial compression tests are performed while monitoring seismic properties. A unique aspect of the experiment is that the formation and dissociation of hydrate in a sediment core, and the failure of the sample during loading tests, can be monitored in real time using both seismic waves and x-ray CT imaging. For this purpose, a specially designed triaxial (geomechanical) test cell was built. This cell allows for conducting seismic wave measurements on a sediment core using compressional and shear (torsion) waves. Concurrently, CT images can be obtained through an x-ray-transparent cell wall. These are used to determine the porosity distribution within a sample owing to both original sand packing and formation of hydrate in the pore space. For interpreting the results from both seismic measurements and geomechanical tests, characterization of sample heterogeneity can be critically important. In this paper, the basic functions of the test cell are presented, with the results of preliminary experiments using non-hydrate bearing sandpack and sandstone core. These measurements confirmed that (1) clear x-ray images of gas-fluid boundaries within a sediment/rock core can be obtained through a thick aluminum test cell wall, (2) the test cell functions correctly during loading tests, and (3) both compressional and shear waves can be measured during a loading test. Further experiments using methane-hydrate-bearing samples will be presented at the conference.

Related NETL Project
This presentation is related to the NETL project ESD05-048, “Laboratory Studies in Support of Characterization of Recoverable Resources from Methane Hydrate Deposits.” The overall objective of this proposal is to continue in Fiscal Year 2006 the current studies on the characterization and analysis of recoverable resources from gas hydrate deposits. The research will enhance the National Energy Technology Laboratory (NETL)-funded programs on Natural Gas Hydrate research and development by bringing new laboratory measurements and evaluation techniques to bear on the difficult problems of characterization and gas recovery from methane hydrate deposits.

Project Contacts
NETL – Robert Vagnetti (Robert.Vagnetti@netl.doe.gov or 304-285-1334)
LBNL – Timothy J. Kneafsey (tjkneafsey@lbl.gov or 510-486-4414)