Since the mid 1990's a number of sour, carbonate oil fields have been discovered in the South of Oman. During this time it became apparent that due to the high initial pressures and the high H2S (up to 10 mol%) and CO2 content (up to 25 mol%) of the light crude, the full field development of these carbonate stringers by a miscible gas injection method would be very capital intensive.

Because of the risk on capital and the related subsurface uncertainties, it was decided in the early 2000's to take a phased approach to the development of these fields. This was excuted via the installation of Early Depletion Facilities (EDF) and of a connection to an existing production station 40 km away, capital expenditure was limited and thus the risk of the development minimised. The EDF comprised of 4 manifolds, a remote gathering station, a 69km trunkline and installation of a new separation train and gas injector compressor at the existing station. These facilities were brought on stream in 2004. At that time the end of the EDF production phase was predicted to be 2013, however with the continuous discovery of further fields and delay of the full field development by a new production station, the EDF system has still been in full utilization until present day.

Thus, the EDF will be operational for almost 2 decades. During this time very significant oil revenue income has been generated, while key subsurface data for understanding the connectivity and the behaviour of the fields has been accomplished.

In this paper, the EDF system and the challenges in installation and operation will be discussed. The related information obtained regarding the depletion behaviour of the fields will be shown in some field examples. Field S showed a much higher depletion than anticipated, which resulted in STOIIP reduction and subsequent well location optimisation had to be carried out; field D production behaviour has been much better than expected, however connectivity was found to be an issue; field G alternatively, showed mixed reservoir performance.

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