No abstract

No abstract

No 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.

Summary High quality 3D seismic data over a large UAE field combined with high-end geophysical techniques resulted in spectacular porosity detail from seismic data over this carbonate field. By using special post stack filtering techniques to improve data continuity and discontinuity, two optimal data sets were generated. One data volume was optimized for structure and stratigraphic interpretation and the other for event mapping and quantitative seismic attribute analysis. A multi-attribute calibration method was used to estimate the porosity from the seismic data. Attributes used include seismic and geologic or interpretative attributes. The result was a porosity prediction that was 20% improved over the traditional single attribute approach, as measured on hidden well data. The predicted porosity volume provided high quality detail of reservoir heterogeneity and was very useful in understanding flood front advance in the platform interior and flow patterns in the clinoforms. In addition, the seismic porosity volume provides a means to place future wells to tap by-passed oil and to optimize the location of planned injector and producer zones. Introduction Seismic data is often used as a means to estimate rock properties between well controls. A typical method is to calibrate seismic attribute information with rock properties, such as porosity, from well log information. The seismic attribute data can then be transformed using the calibration function into an estimate of rock properties. In our study a multi-attribute neural network calibration is used to produce a 3D volume of rock property predictions from the seismic data (Hampson 2001).This seismic-scale rock property volume is then used to place new wells in favorable locations or in building geologic models for reserve estimation and/or reservoir simulation. Geologic Setting The study field is located in Abu Dhabi within the United Arab Emirates. The field is positioned over a low relief doubly plunging anticline that is oriented N-NE. The reservoir interval is comprised of a low relief, prograding carbonate platform. The main producing interval is in the Lower Cretaceous. The complex stratal architecture is driven largely by the longer-term (second-order) accommodation history. The field is characterized by significantly different stratal geometries that are clearly imaged by the enhanced 3D seismic. The northern part of the field is characterized by strong basinward progradation that occurs in the late highstand and falling-stage systems tracts. Clinoforms exhibit spatial variability in geometry, composition and texture that significantly impact reservoir geometry and quality. The southern part of the field is characterized by aggradational platform facies that show variations in stacking patterns and composition keyed to position in the sequence-stratigraphic hierarchy. Most notably, strong aggradation during the highstand sequence set, coupled with proliferation of rudist "reef" builders, resulted in development of a complex system of moderate relief, higher-energy rudistid shoals (moderate to high reservoir quality). These shoals are separated by low relief, restricted lagoonal "ponds" that are filled largely with low-energy, mud-prone facies (low reservoir quality).