Characteristics of high-permeability zones using core analysis, and production logging data

Abstract

Carbonate reservoirs are heterogeneous in nature and sometimes they contain natural fractures. Zones with extremely high permeability are commonly found in these reservoirs. These zones are a subject of concern for reservoir engineers, as they lead to early water breakthrough in oil producers and uneven sweep around water injectors. These zones cause many problems to production engineers during acid or other chemical placement. We conducted a study to identify and characterize high permeability zones using conventional petrophysical tests in conjunction with production logs (flow meter measurements). High permeability zones were identified and characterized using core data and production logging. These zones were found at the top of the formations examined, with a thickness up to 10 ft and they contributed more than 50% of the total well production. These zones had permeability greater than 20 Darcies and are sandwiched with two layers of low permeability (a few micro-darcies). The two low-permeability layers act as a barrier that minimizes cross-flow. Calliper log of the open hole indicated that hole enlargement and wash-out occurred at depths where these zones are located. Based on production data, it is evident that the flow profile was dominated by high flow from these zones. The mineralogy of super-k zones was mainly dolomite. The use of Amaefule et al.'s approach allows for a more precise definition of reservoir zonation. Excellent agreement was obtained between the cumulative distribution of reservoir quality index (RQI) and flow zone indicator (FZI) with well flow profile data for wells without natural fractures, whereas, no agreement was obtained for wells with significant natural fractures.