The objective of this paper is to present an integrated approach to quantify subsurface uncertainties and to share the assessments that have been applied in the subsurface studies of a new offshore oil field development in United Arab Emirates. A methodology was developed to review and rank the various subsurface uncertainties. Seismic and geological tools were used to assess uncertainties of static parameters, while integration of all uncertainties was made in the dynamic simulation model. New approaches were implemented to address two important parameters: Critical Water Saturation and Permeability. Critical Water Saturation uncertainty was derived by history matching production test data using a Saturation-Versus-Height model coupled with a Fractional Flow equation. For estimating uncertainty on Permeability, correlations with core derived fracture densities were developed. Uncertainty on the Critical Water Saturation was found to have the highest impact on oil recovery. This uncertainty is related to an observation already made for other carbonate reservoirs where perforated intervals are sometimes producing at very low water-cut in spite of high water saturations interpreted from the logs. This uncertainty review allowed updating the Dynamic Model with more robust P50 estimates of its parameters. The updated model was used to define a new base case development well scheme and production profile. The study was important in maturing the development studies further. It was used in particular not only for updating the Dynamic Model, but also for defining future studies, preparing a data acquisition plan, and identifying mitigation actions to reduce the subsurface risks.

A green field offshore Abu Dhabi is planned to be developed with slanted-horizontal wells (single and dual drains) and an optimized five spot water injection scheme. Three major carbonate reservoirs (2 Jurassic & 1 Cretaceous) will be targeted. Challenges appear in the field development plan due to the high heterogeneous nature of the carbonate reservoirs and fault /fracture network uncertainty. The main challenges are the early water breakthrough mitigation and well drain accessibility. This will be overcomed by utilizing Inflow Control Devices (ICD) coupled with Sliding Sleeve (SSD) to ensure uniform water front displacement across all reservoir layers and control water breakthrough, and Multi-Lateral Tie Back Systems (MLTBS) to allow Coil Tubing (CT) access to the well upper horizontal drains. This paper describes the workflow that was used to evaluate the benefits of ICD-SSD & MLTBS using sector models, and presents some results. The sector models cover representative areas of the studied reservoirs. History match using the available dynamic & static data acquired during field appraisal was conducted to calibrate the sector models. The data included well test data (Flowing & Build-up tests), zonal contribution from production logging, and MDT reservoir pressures, where available. Faults / fracture network uncertainty was addressed using "what-if" scenarios. The study confirmed the potential significant increase in oil recovery by using ICD equipped with SSD. MLTBS providing CT accessibility to the upper drain of the dual lateral wells was shown to positively impact well productivity and oil recovery.