Description, Modeling and Uncertainty Analysis for the Future Development of a Giant Brown Field Carbonate Reservoir, Oman

Volker C. Vahrenkamp¹ and Fahud Studies Team^2
1 Petroleum Development Oman, Muscat, Oman
² Petroleum Development Oman & Shell International EP, Muscat, Oman

Following 40 years of production and the drilling of some 380 wells a next development phase is envisaged for one of the giant carbonate reservoirs of Oman, which requires enormous investments while still carrying significant risks. The study presents a case history of integrated reservoir description, static modelling and dynamic simulation using experimental design techniques. It has led to a significantly improved assessment of how individual subsurface uncertainties impact the economics of various development scenarios thus guiding additional data gathering, studies activities and ultimately selection of robust development options. The reservoir is contained in Albian to Turonian high porosity, low permeability fractured carbonates. It is composed of three third-order sequences, is up to 450 m thick and covers an area of more than 50 km2. Depositional environments range from intra-shelf basins with carbonate source rocks to shallow water rudist banks. Lateral and vertical heterogeneity in depositional facies, pore types, karst and fracture distribution are key complications to predict reservoir behaviour. An extensive and integrated study program based on existing and newly acquired data from 3D seismic, cores, logs, outcrop analogues and production analysis has given rise to new/refined depositional, stratigraphic, diagenetic and structural models, which are recombined with reservoir data to guide the construction of static reservoir models. However, numerical ranges of basic modelling parameters remain significant. Using experimental design techniques during dynamic simulation and historical production data allows constraining of some uncertainties (i.e. matrix kv/kh, fracture porosity, imbibition Pc). Others such as matrix k/phi, fracture density, etc. remain unconstrained from historical data but exert significant impact on production forecasts and hence project economics.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005