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Research Themes - Carbonate Reservoirs

Theme leaders: Rachel Wood & Patrick Corbett

The ECOSSE carbonate reservoirs research theme is establishing a major centre of excellence in understanding and managing carbonate reservoirs (now containing some 60% of the world’s proven oil and gas reserves) and aquifers (a primary source of potable water in many arid areas).


Carbonate Deposition and Diagenesis of the Thamama Group

The Lower Cretaceous Thamama Group represents an extensive, carbonate ramp system that hosts many complex, stacked reservoirs both onshore and offshore throughout the Arabian Gulf. Various techniques have been applied using bounding sequence stratigraphic surfaces to correlate the Thamama throughout the whole of the southeastern Arabian Gulf oil province, but many have proved inadequate in the prediction of reservoir flow behavior and oil recovery. As in many carbonate fields, the main challenges in building a reservoir model are establishing valid criteria for field-wide correlation, an adequate understanding of lateral heterogeneity, and the relative roles of depositional and diagenetic processes in determining reservoir quality.

In collaboration with Dr. Tony Dickson (University of Cambridge), we are re-appraising the sequence stratigraphy and diagenesis of a major offshore field in U.A.E. using both wireline log and core data. We have established a revised paragenetic sequence based on separated component stable isotopic analysis, and are evaluating the preferential role of diagenesis in the evolution of porosity and permeability.

Peter Cox (ECOSSE Ph.D) student is extending this work in the Lekhwair Formation to onshore U.A.E. and outcrop Oman.

Natural CO2 leakage in Italy: Neotectonic settings in Carbonates

One of the most important uncertainties for CO2 storage is the geological integrity of potential underground sites to retain fluid, low viscosity, and buoyant CO2 for sufficiently long time periods. One way to reduce this uncertainty is the study of natural analogues, to gain insight into the processes by which CO2 is either retained deep in the subsurface, or is actively leaking. Italy is an especially suitable location, as it provides numerous accessible examples of both small and large CO2 leakage sites in a variety of tectonic settings. These include areas of active faulting, and breach of natural mudrock seals. Jen Roberts (ECOSSE PhD student) is investigating the critical parameters controlling CO2 retention, or leakage flux, in relation to regional carbonate geological setting and local case studies providing evidence of rock mineralogy.

Modelling of Carbonate Systems

Problems encountered in carbonates are due to the inherent heterogeneity and complexity of these systems combined with sparse sampling of data constraining reservoir geometries and properties. Heterogeneity in carbonates is caused by highly variable in situ biological growth and sedimentation processes, as well as subsequent alteration by diagenetic overprinting. The latter often occurs along fluid migration pathways, in turn determined by depositional architecture.

My research in this area has three main aims: 1) to quantify the range of possible geologies incorporating full uncertainty; 2) to enable interpolation between field analogues, and 3) to constrain the range of pore-size distribution and permeabilities that might be found within any given carbonate lithology.

Forward modelling in 3-D has remained of limited utility until recently as both knowledge of complex geological processes in carbonates and computational power have proved insufficient. However, such methods and software are being developed by Jon Hill (former Ph.D. student, Edinburgh), and these modelling packages incorporate known physical and chemical processes that control deposition, redistribution and diagenesis to simulate realistic 3-D geologies.


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