A Reservoir Engineering Study of the Margham Field, Dubai, U.A.E.

SPE Members

Abstract

A reservoir study of the Margham field in Dubai, United Arab Emirates was performed. The main objectives of the study were to combine and evaluate all current production and geologic data to better understand historic reservoir performance and develop reservoir management plans for future field depletion and development. To realize this objective a number of simulation tools were developed to help better understand the condensate recovery mechanisms occurring at Margham. This paper concentrates on the development and application of a full-field computer model of the Margham reservoir.

Due to the complexity of the Margham reservoir special procedures were required to describe the reservoir geology, represent the field's structure, and model gas condensate phase behavior. A successful match of two and one half years of pressure and production data was achieved using a single porosity simulator. Preliminary results from a strip model indicated the dual porosity mechanism to be inappropriate. However specific areas with extensive, sometimes unmapped faults appear to behave in a manner similar to a dual porosity system. These small areas were adequately modeled with porosity system. These small areas were adequately modeled with the single porosity model by implementing pore volume reductions to represent areas of low sweep efficiency. An aquifer was included in the reservoir description in order to match the field pressure history. Predictions of future field performance emphasized increasing condensate recovery by optimizing current field operations, understanding the benefits of continued gas cycling versus immediate full or partial release of produced gas, and the need for additional infill wells. This paper includes a comparison of actual performance versus the model predicted response during the year following the completion of the study.

Introduction

The Margham reservoir was discovered in Dubai, U.A.E. in 1982. It is one of the more complex reservoirs operated by ARCO. It is an overpressured, highly fractured and faulted, carbonate containing a retrograde gas condensate fluid with approximately 6.0% CO2 content. The original reservoir pressure was 7272 psia and the original dew point pressure equaled 6934 psia. The average reservoir temperature is 280 degrees F. Gas condensate is produced from the porous and fractured intervals of the Shuaiba, Kharaib, and Lekhwair Formations within the Thamama limestone. In order to support the reservoir pressure and thus minimize retrograde condensation within the reservoir, all produced dry gas is reinjected into the reservoir. The current injection plan can best be described as crestal. At the time of this study there were a total of 14 wells 5 injectors and 9 producers. The three highest rate injectors, M-1, 6 and 10B are all on or near the crest while M-3 is a low rate flank injector in the north and M-13 is a recent high rate injector drilled on the southern flank. Production began in late 1984 while the full pressure maintenance program commenced in early 1985. water pressure maintenance program commenced in early 1985. water production is limited to condensed vapor except at M-2 where production is limited to condensed vapor except at M-2 where significant quantities of saline formation water are produced.

Production performance has been characterized by poor volumetric Production performance has been characterized by poor volumetric conformance of the dry injection gas. Significant dry gas breakthrough from injectors to producers first occurred in late 1985 at which time less than 5% of the original reservoir fluid had been displaced with dry gas. Wells M-4, 9, 11 and 12 all observed breakthrough within the first nine months of production. Breakthrough can easily be identified by rapid decreases in condensate yield (or alternately increases in GOR). As of January 1987, 15.7% of all gas produced to date was recycle gas.

The retrograde fluid phase behavior, structurally complex geology, and hostile production environment make optimization of Margham's production operations a formidable task. In June, 1986 it was production operations a formidable task. In June, 1986 it was decided to perform a complete reservoir study of the field to better evaluate current and future operations. The objective of this study was to combine and evaluate all current production and geologic data in order to obtain a tool that could be used to study and evaluate the future development of the field. The multi-disciplinary study team consisted of members from ARCO Oil and Gas Co.'s research and technical service center, ARCO International Oil and Gas Co's reservoir engineering staff, and ARCO Dubai's operations staff.

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