Written by R. Trice
Published by the Society of Petroleum Engineers
Sourced from the SPE Middle East Oil and Gas Show and Conference, 12-15 March, Kingdom of Bahrain, 2005.
Copyright: 2005. Society of Petroleum Engineers
This paper is a summary of ongoing work to establish the impact of karst on optimising oil production from carbonate reservoirs. The paper is based on a review of 44 Middle East carbonate reservoirs and is intended to convey preliminary findings. Key observations from this review are that karst reservoirs in the Middle East form one end-member of a continuum that includes, a) conventional layered reservoirs, b) fractured reservoirs, and c) karst reservoirs. It is also evident that many Middle East reservoirs are hybrid reservoirs having static and dynamic characteristics of all three end-members. In such instances the key challenge is to differentiate any karst components that may impact on achieving optimum oil production. Attempting to differentiate the karst contribution is complicated by the frequent occurrence of permeable tectonic fractures and faults. These lineaments contribute to permeability and production characteristics of many of the studied reservoirs, but because their characteristic flow properties are similar to that produced by karst drainage networks, karst drainage has the potential to be unrecognised. In an attempt to identify and isolate karst drainage system contribution to production, a first pass ‘quick look’ method has been developed by which carbonate reservoirs/fields can be ranked with the objective of assessing the degree that karst influences are present. The quick look method is intended to identify karst products, or the potential for karst products to be present, from which steps can then be undertaken to establish whether a karst drainage system impacts optimum oil productivity.