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International Journal of Geophysics
Volume 2012, Article ID 148919, 13 pages
http://dx.doi.org/10.1155/2012/148919
Research Article

Characterization of Fractured Reservoirs Using a Combination of Downhole Pressure and Self-Potential Transient Data

GSJ, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 7, Tsukuba, Ibaraki 305-8567, Japan

Received 1 July 2011; Revised 11 October 2011; Accepted 8 November 2011

Academic Editor: Laurence Jouniaux

Copyright © 2012 Yuji Nishi and Tsuneo Ishido. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

In order to appraise the utility of self-potential (SP) measurements to characterize fractured reservoirs, we carried out continuous SP monitoring using multi Ag-AgCl electrodes installed within two open holes at the Kamaishi Mine, Japan. The observed ratio of SP change to pressure change associated with fluid flow showed different behaviors between intact host rock and fractured rock regions. Characteristic behavior peculiar to fractured reservoirs, which is predicted from numerical simulations of electrokinetic phenomena in MINC (multiple interacting continua) double-porosity media, was observed near the fractures. Semilog plots of the ratio of SP change to pressure change observed in one of the two wells show obvious transition from intermediate time increasing to late time stable trends, which indicate that the time required for pressure equilibration between the fracture and matrix regions is about 800 seconds. Fracture spacing was estimated to be a few meters assuming several micro-darcies (10-18 m2) of the matrix region permeability, which is consistent with geological and hydrological observations.