Abstract

Reservoir Engineering and Geological data gathered from 22 years of production from the Fateh Ilam reservoir and from almost 200 wells cannot be reconciled using existing reservoir and geological models. Prior to building a full field model to evaluate further development of the waterflood and potential for future infill drilling, a better understanding of the reservoir is required.

Recent re-characterization of the reservoir is described and results are summarized from a fully integrated reservoir study that showed the Ilam to be both complex and heterogeneous. Examination of the core and log data revealed orientable fractures that, following detailed analysis, were seen to be crudely related to lithology. The study also shows that the wide range of pressure transient characteristics and anomalous production and waterflood behavior observed in the Ilam can be explained using a simplified model consistent with these findings.

Introduction

Commercial hydrocarbons in the Ilam Formation (equivalent to the Halul Formation of Abu Dhabi) were discovered offshore Dubai by the exploratory well A-1 in June 1966 (Fig. 1). Fateh Field, as it was named, has been continuously developed from that time until the present. Although commercial hydrocarbons have been discovered at three deeper horizons the Ilam Formation remains an important reservoir in Fateh Field. To date almost 200 wells (Fig. 2) have been drilled on the field with virtually all the wells penetrating the Ilam Formation. Production from the Ilam Formation commended in September 1969 and current studies are aimed at evaluating the development of a full field waterflood scheme.

The Upper Cretaceous, Ilam Formation, in Fateh Field comprises a sequence of variable dominantly muddy limestones approximately 260 feet thick overlain by the Aruma/Fiqa shales and underlain by the Laffan Formation (Fig. 3). The sediments are considered to have been deposited on a shallow water, mud dominated cabonate ramp with environments ranging from high energy tidal to deeper low energy subtidal marine. Periodic movements of the underlying Cambrian Hormuz Salt led to the development of the Fateh structure and at key geological times influenced the sedimentation of the Fateh area (Fig. 4). A number of reservoir mapping projects have subdivided the Ilam Formation into an increasingly greater number of correlatable layers. The most recent project 5 forming the basis for the current reservoir model, divides the Ilam reservoir into four layers (Fig. 5). The layering scheme is based upon lithological changes and porosity indications seen on wireline logs.

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