Couples, Gary D.¹, J.M. Questiaux¹, N. Ruby¹
(1) Heriot-Watt University, Edinburgh, Scotland, United Kingdom

ABSTRACT: Reservoir Management of Fractured Carbonate Fields

Carbonate successions host some of the largest hydrocarbon fields of the world. Many (most?) of these fields exhibit behaviours related to the presence of natural fractures, and devising successful management strategies for such reservoirs has often proven elusive. This paper will demonstrate the value (in reservoir management) of incorporating knowledge about the typical distributions of fractures in layered carbonate rocks that have been folded. In addition to ubiquitous arays of “background” small-scale fractures (which can be readily upscaled), a common feature in such fields is the occurrence of fracture corridors – in outcrop studies, these prove to be zones ranging in width from less than a metre to tens of metres, limited above and below by mechanical-unit boundaries (bedding-plane slip surfaces), and with bed-parallel lengths of a km or more – where deformation is concentrated during the folding process. The intense fracturing of the corridors can also be upscaled and represented adequately in straightforward, simple (single-porosity system) reservoir models. When conditioned to specific cases, these reservoir models produce flow performance that is nearly identical to the actual production history of the example fields. We have explored the flow behaviour of such models to derive guidelines for well placement, well type (horizontal/vertical), and completion/operation strategies (including injection schemes). Simple changes in operation practice can alter the recovery from 8% to more than 34% of the oil in place. Economic analysis helps to identify the best management options.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.