--> Reservoir Permeability In Difficult Carbonate Reservoirs

Pacific Section AAPG, SPE and SEPM Joint Technical Conference

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Reservoir Permeability In Difficult Carbonate Reservoirs

Abstract

Carbonate reservoirs can be complex and difficult to understand from conventional logs. Low porosity from density/neutron logs in the 3-4% range is not unusual in many dense carbonates and is quite typical in some. Even in these low-porosity conditions, secondary enhancement features can have a dramatically positive impact on production. An adequate description of these characteristics is needed to determine completion candidates. Nuclear magnetic resonance responses have been proposed as a method that can measure and predict the results of these alterations. One analysis method of this data is the Bray-Smith permeability equation. This paper examines the application of the Bray-Smith permeability equation for determining the productive capacity of these carbonate reservoirs. This calculation uses relaxation (T2) NMR responses to provide direct permeability without any external inputs. There is no need to adjust for rock type and the equation corrects for any rock texture differences. Responses from the Atoka Lime, the Atoka Wash, and the Mississippian carbonate reservoir types are included. Some produce from only primary porosity, others have secondary porosity development in the form of vugs or fractures. The Bray-Smith equation compares favorably to core results (where available) and to actual production results in every case.