Abstract

Ratawi Limestone is a fairly low permeability reservoir in the Umm Gudair field of Kuwait. Production history shows low liquid rate and fast pressure depletion around the wellbore. To understand the causatives for flow restriction, this study captures systematically different pore types, their relationship, distribution, connectivity and their impact on reservoir fluid flow behavior. It is observed that pores are not related to any depositional surface and are rather formed due to mesogenetic corrosion of highly micritized, tight carbonate rock bodies. Primary pores are almost completely destroyed during the process of shallow burial diagenesis. Separate vug pores are both fabric as well as nonfabric selective type and are the main contributor of pore volume within an overall pervasive (micritic) matrix pore dominated system of wackestone and packstone. Five porefacies are created on the basis of capillarity within a wider range of pore throat size variation. Type 1 is represented by macropores, Type 2 and 5 are mesopore and rests are micropore dominated. Each porefacies is assigned a linear equation on core calibrated porosity- permeability transform. The resultant permeability shows about 20% less value compared to permeabilities of corresponding intergranular Lucia class 2 pore type. This gap is specially pronounced within the reservoir rocks with high porosity and intermediate permeability values. Seven years of production history of this reservoir shows low rate of production with rapid pressure depletion around wellbore within a few months of production. Logical option to improve production is to increase the reservoir contact using horizontal multilaterals along with reduced well spacing and aggressive pressure support through water injection.

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