New Frontiers in 3D Seismic Characterization of Carbonate Reservoirs: Example from a Supergiant Field in Abu Dhabi

Abstract

High-effort 3D seismic data collected by ADCO in onshore Abu Dhabi are some of the highest quality data ever collected over a carbonate reservoir. These data provide the opportunity to test the limits of high-end seismic technologies in carbonates and to demonstrate the value of seismic for integrated carbonate reservoir characterization. Seismic data were integrated with other subsurface data to develop a new, sequence stratigraphic based reservoir framework. The Lower Cretaceous (Aptian) reservoir records a large-scale transgressive-regressive depositional cycle that, in turn, is divided into six (6) depositional sequences. Reservoir architecture and quality vary predictably within the sequence framework and correspond closely to variations in seismic properties. Sequence-stratigraphic surfaces define the 3D distribution of flow barriers and flow units within the reservoir and are used to guide framework and rock property distributions in 3D reservoir models. Quantitative seismic information on reservoir architecture and porosity variations provides a new understanding of reservoir heterogeneity and the underlying geologic controls. Multi-attribute volume interpretation and co-rendering techniques help to visualize geologic and reservoir variations and provide a volume-based framework for reservoir evaluation. In the southern field area, 3D seismic data reveal a complex mosaic of tidal channels, high-energy rudist shoals, and inter-shoal ponds in detail comparable to Landsat images of modern carbonate environments. These geologic features have different geometries and reservoir properties that impact reservoir sweep and conformance. Seismic imaging of these features provides a 3D framework to integrate production and geoscience data, evaluate reservoir performance and constrain reservoir models. In the northern field area, seismic images of prograding slope clinoforms reveal systematic variations in architecture and reservoir quality that are tied closely to the sequence stratigraphic framework. A pattern gas flood has been implemented in the clinoforms to add pressure support and improve recovery. Seismic detection of clinoforms and their internal porosity variations allows for 3D visualization of reservoir and well-pair connectivity that will assist in gas flood management. Together, the sequence-based reservoir framework and 3D seismic provide an integrated platform for addressing a range of production and performance issues. Applications of these results include:3D seismic visualization as a tool for optimizing well placement, identifying by-passed reservoirs and evaluating reservoir connectivity,integration of quantitative, volume-based seismic information into reservoir models,maximizing recovery through full integration of all subsurface data, andenhanced communication among geoscientists and engineers leading to improved reservoir management practices. Introduction The stratigraphic and diagenetic complexities inherent in carbonate reservoirs require the most accurate reservoir descriptions and models possible to optimize recovery. 3D seismic data provide the only continuous source of information on reservoir properties in the subsurface, and acquisition of 3D seismic has become a standard best practice for carbonate reservoir evaluation. With increasingly more 3D seismic available over carbonate fields, the challenge is to maximize the value of the seismic for characterization of carbonate reservoir architecture and rock properties1–2.