Modelling of Carbonate Systems: pore to reservoir

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 (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.

Much data from carbonate reservoirs are collected via wireline logs rather than more costly coring. Accurate derivation of geological information therefore becomes a challenge. To this end, David Price (Ph.D student, Edinburgh) is developing statistical interpretation methods to reconstruct carbonate heterogeneity from image-log data using X-Ray tomogram data.

Work is underway in collaboration with Kejian Wu (Heriot-Watt University) to understand the role of microporosity in the multiphase flow of fluids in carbonate micropores. We are using methods that reconstruct 3D, multiscale pore networks and their characteristics to quantify these properties. In addition, with PDRA Cees van der Land we are exploring new rock-typing methods from first principles.

Publications:

• HILL, J., TETZLAFF, D., CURTIS, A., and WOOD, R. 2009. Modelling Carbonate Supersaturation on carbonate platforms via residence time. Computers and Geology, 35: 1862-1874.
  
• PRICE, D., CURTIS, A. and WOOD, R. 2008. Statistical correlation between geophysical logs and extracted core. Geophysics 73: E97-E106.