Sequence Stratigraphy in a Carbonate Prograding Margin; Implications for Dynamic Flow Modeling and Field Development

Abstract

Abstract This paper concerns a super-giant carbonate oil field in Abu Dhabi, UAE (first oil production in1962). Remaining reserves are mostly located in Lower Cretaceous carbonate build-up and prograding basin-margin deposits of the Shuaiba Formation. The principal challenges to maintain future production are pressure decline and uneven water advance. A key to understanding dynamic flow behavior is the spatial distribution of flow barriers, facies, diagenesis and faulting / fracturing in the prograding clinoform domain. The static model needs to accurately capture these heterogeneities by combining interpolation of reservoir parameters from wells with structural and sedimentological trends extracted from 3D seismic data. A comprehensive work program was initiated to understand the depositional evolution of the reservoirs using a sequence stratigraphic approach. The application of high-resolution sequence stratigraphy (recognition of 3rd and 4th order sequences) associated with detailed seismic interpretation of the clinoform domain represents a new approach rarely successful in carbonate reservoirs. Low permeability carbonate mudstone facies associated with transgression in the clinoform domain create local vertical barriers to fluid flow. The progradational clinoform topsets contain the best reservoir facies with a thickness distribution systematically related to position within the clinoform. Sequences of 3rd and 4th order have been interpreted to generate a seismically constrained stratigraphic framework. High quality 3D seismic combined with a thorough description of stratigraphic architecture provides a new approach to populating the reservoir model with reservoir facies (former lithostratigraphic units) honoring the depositional shapes from seismic interpretation. Combining the stratigraphic surfaces of the clinoforms with the lithological surfaces as property boundaries derived from the progradational geometries represents a new approach to reservoir modeling. The current pressure maintenance scheme is through peripheral water injection, with some pattern injection in the lower parts of the clinoforms. The preferred flow paths of injected fluids are strongly controlled by the geometry of clinoforms, and an understanding of this enables more accurate prediction of the pressure fronts and future water / gas breakthrough. Development optimization plans currently being evaluated will incorporate the reservoir property trends derived from the spatial distribution of stratigraphic sequences (3rd and 4th order). The location of proposed simulation and production pilot patterns has been based a facies interpolation methodology within a sequence stratigraphic framework.