A study has been initiated to determine the best development scheme to recover oil and gas from two oil rim reservoirs off shore Abu Dhabi utilizing horizontal wells. One pilot horizontal well has already been drilled in the lower reservoir and few more are planned. Due to uncertainties in the fluid contacts and reservoir characteristics, a vertical pilot hole had to be drilled and cored to decide on the optimum location of the horizontal hole. A detailed core study was conducted to study the main rock types and lithofacies of this reservoir and a sector model was constructed to study the effect of different reservoir parameters on the performance of the horizontal well. PVT data from the gas cap and the oil rim will be used to construct an EOS that will be used in the full field compositional model. The results from this model and the performance of the pilot horizontal wells along with ongoing detailed geological study will help in determining the optimum development plan for these reservoirs.

This paper presents a case study drawn from a full field simulation study on an oil rim in a field offshore Abu Dhabi. Initially the reservoir contained a large gas cap underlain by a thin saturated oil rim. The gas production from the gas cap started in 1976. In 1989, about 22% of the gas from the gas cap had been produced. The reservoir pressure had dropped by more than 1100 psi. Then gas injection from a deeper reservoir into the gas cap started and the reservoir was slowly repressurised. However, a moderately active aquifer encroached and flooded part of the oil rim. The oil was pushed up dip. The main objective of the study was to propose a full field development scheme for the oil rim. Meanwhile, the opportunity was taken to optimize the condensate recovery. A multidisciplinary reservoir characterisation study was carried out on the formation. Based on this study, seven rock types were defined and a reservoir-layering scheme was developed. A full field compositional simulation model was built and history matched. The history match included the match of six oil producers, which experienced water and/or free gas production. The Gas Cap CGR history was also successfully matched. Finally, the history-matched model was used for recommending a development scenario. Few oil producer concepts were tested. Several development scenarios were compared. One of the scenarios was assuming gas cap depletion after year 2005 while the other scenarios were assuming partial or full recycling at different rates. Introduction The development of an oil rim in a heterogeneous formation is a challenge in itself. In this study, the task has been made even more difficult by the production history of the gas cap, Figure 1. Between 1977 and 1989, the Gas Cap was produced without pressure support. In 1989, about 22% of the gas from the gas cap had been produced. The reservoir pressure had dropped by more than 1100 psi. In 1989, gas injection from a deeper reservoir into the gas cap started and the reservoir was slowly repressurised. However, a moderately active aquifer encroached and flooded part of the oil rim. The oil was pushed up dip.