Impact of Reservoir Heterogeneity on Gas Recovery and Water Cresting, Columbus Basin Gas Fields, Offshore Trinidad

Richard P. Sech¹, Matthew D. Jackson¹, Gary J. Hampson¹, Richard J. Dixon², Dirk Bodnar², and Paulo R. Ballin^2
1 Imperial College, London, United Kingdom
² BP Trinidad and Tobago, N/A,

The Columbus Basin, offshore East Trinidad contains several major gas discoveries, each of which present unique development challenges. Reservoir sands are of Pliocene to Pleistocene age and were deposited in deltaic to shoreface-shelf environments. These sands form laterally extensive, vertically stacked, sheets which possess excellent reservoir properties. The association of some reservoirs with an aquifer raises concern over the potential for water influx and a subsequent decline in recovery. The aim of this project is to improve prediction of how depositional heterogeneity may influence ultimate gas recovery and water encroachment from a reservoir with a bottom-water aquifer.

Analogous sandstone units exposed in the Kenilworth Member, Book Cliffs, Utah, U.S.A., can be used to constrain reservoir architecture. The nature of these outcrops and the use of novel modeling techniques, allows for the construction of a 3-D geologic model which is conditioned to robust, high resolution, stratigraphic data. By simulating directly upon the adaptive geologic grid, which enables increased facies definition, realistic flow dynamics can be observed and the effect of facies distribution assessed. Initial studies have aimed to capture the controls upon distortion of the gas-water interface, focussing specifically on the phenomenon of water cresting associated with horizontal wells. It has been shown that the presence of depositional heterogeneity impacts the propagation of pressure drawdown from the horizontal well out into the reservoir and, as a result, the water crest behaviour may in some instances be affected.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005