Khazzan field, situated in Block 61 in northern Oman, contains hydrocarbons at several deep levels, including the Barik, Miqrat, Amin and Buah formations. The Barik and Amin reservoirs are being developed in the southern portion of the block to produce 1 bcf/d of gas by end 2017. The development, jointly owned by Oman Oil Company (40%) and BP (60% and operator), will cost over 16 billion US$ and will include a central processing facility and surface facilities for about 300 wells. Most of the wells will be 1000m long horizontal wells, completed using multiple hydraulic fracturing techniques. The two other reservoirs, Miqrat and Buah, contain high H2S levels; these will not be developed at this phase due to high subsurface uncertainties and the cost to process the sour development.

This paper presents a case study of an evolving reservoir description of a large, tight gas reservoir, the Barik Formation. It is rare to embark on a major “greenfield” reservoir development of a tight gas reservoir with limited static and almost no dynamic data. The reservoir description is essential to the successful evaluation and management of the inherent subsurface uncertainty at this stage in the field development. Building an associated appraisal plan and being flexible to new understanding is required to make the development a success. The reservoir description is guiding the ongoing appraisal activities in an attempt to reduce the risk and increase the overall project value.

This paper presents the evolution of the reservoir description over the last 6 years of BP activity in Block 61 in the Sultanate of Oman. It reviews three stages of reservoir description: Pre-Appraisal, Mid-Appraisal, and Development. The pre-appraisal description was built using the pre-bid data package and published literature to support the commercial access decisions. The Mid Appraisal description provided a health-check for development readiness and appraisal plan revision. Finally, the Development description is presented in a 3D geo-cellular model which is based on the summary of the appraisal activities and supporting field development learnings. The paper discusses these descriptions and the benefits of the changing description, explanation of the advantages of front end loading at the early appraisal stage and how this has led us to our current state

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