An Integrated Approach for Characterization of Fractured Reservoirs

E. L. Majer, J. E. Peterson, T. M. Daley, A. Datta-Gupta, D. W. Vasco, J. C. S. Long, J. H. Queen, W. D. Rlzer, and P. S. D'Onfro

High resolution (1 to 10 kHz) crosswell and single well seismic surveys and a series of interference tests were performed in a fractured limestone formation at Conoco's Borehole Test Facility. Two inverse approaches for constructing fracture flow models were applied to the interference test data. The first approach creates equivalent discontinuum models that conceptualize the fracture system as a partially filled Iattice of (constant aperture) conductors which are locally connected or disconnected to reproduce the observed fluid flow behaviors The second approach creates variable aperture lattice models that represent the fracture system as a fully connected network composed of conductors of varying apertures. Both approaches successfully reproduced the transient pressure behavior at the pumping and observation wells and indicated a preferential fracture flow path between two wells aligned in an east-northeast direction, the dominant direction of fracturing mapped in the area.

Crosswell and single well seismic experiments were performed before and after air injection designed to displace water from the fracture flow path and increase seismic visibility. The crosswell experiments showed that replacement of water with a gas (in this case air) produces significant changes in the seismic signal. The single well reflection surveys were able to precisely locate the position of the fracture flow path indicated by inverse modelling of the interference tests. To validate the results of the field experiments, we drilled and cored a slant well that intersected the fracture flow path at the target depth.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California