Aberdeen-based Industry Technology Facilitator (ITF) is launching four joint-industry research projects that aim to improve understanding of carbonate reservoirs.
The four projects represent a total investment of more than £1.5million pounds. The sum is modest but the leverage through improved understanding could be enormous.
Carbonate reservoirs already make a substantial contribution to global hydrocarbon supply – they include many of the big Middle Eastern fields – and their relative importance is likely to increase in the future, as they account for a large proportion of the world’s remaining reserves.
However, carbonate reservoirs present different challenges to their sandstone counterparts, where recovery factors are generally higher, and a better understanding is required if we are to maximise production from them.
According to ITF senior technology analyst Colin Sanderson, carbonate reservoirs are more heterogeneous than sandstone ones, and this heterogeneity can occur at the micron/pore space scale through rock grain and texture to heterogeneity measured in terms of kilometres.
This is a result of a number of factors including the chemical and biological origin of the material and its depositional environment, as well as the subsequent geological processes, such as compaction, and faulting and fracture formation. Carbonates are also readily susceptible to chemical change following deposition, which increases their complexity.”
Sanderson said: “Techniques used to characterise sandstone reservoirs are currently applied to carbonate reservoirs, although it is recognised that their properties are very different. For example, reliable porosity and permeability data is a basic requirement for reservoir characterisation.
“This information is generally gathered from cores and logging tools – a reasonable approach in sandstone reservoirs, but the more heterogeneous nature of carbonate reservoirs make scaling up from a core more problematic. Additional tools and technology are required to improve our understanding of the rock properties and fabric, and these four projects go some way to addressing that.”
The first of the four projects will be led by Dr Fiona Whitaker from the University of Bristol, and is named Integrated Reaction Transport Modelling of Dolomite Evolution.
Dolomites typically represent distinct units within a reservoir and can act as barriers or conduits for fluid flow, but their distribution and quality is difficult to predict.
The project will integrate numerical modelling of fluid flow and reactions with existing observational data, to aid prediction of reservoir quality in partially dolomitised limestones.
The results of this study could significantly increase production from mature fields by targeting infill drilling, as well as helping to focus exploration and aid early identification of targets.
ECOSSE (the Edinburgh Collaborative of Subsurface Science and Engineering) combines expertise from the School of GeoSciences at the University of Edinburgh, the Institute of Petroleum Engineering at Heriot-Watt University, the British Geological Survey, and the Scottish Universities Environmental Research Centre.
It is undertaking a project titled Role of Microporosity and Wettability on Fluid Flow in Carbonates, which will be managed by Dr Rachel Wood at Edinburgh University.
It will use new 3D pore models to enable modelling of the microscopic transport physics of multiphase flow in complex carbonates.
Two previously separate approaches will be linked to develop a method that allows quantification of the impact of microporosity in multiphase flow, and explore how this interacts with the wettability of the multiscale pore system.
At the University of Aberdeen researchers will be working on a project named The Influence of Carbonate Depositional and Diagenetic Facies on the Petrophysical Properties of Fault Damage Zones, led by Dr Dave Healy.
It will quantify key petrophysical properties of faulted carbonate reservoirs, such as seismic velocities and porosity. A key output will be a quantitative understanding of how extrinsic damage around faults combines with intrinsic lithological variation of different carbonate facies, and their expression in petrophysical attributes.
Last but not least, the fourth project will be undertaken at the University of Manchester and is titled Integrated Structural, Sedimentological and Diagenetic Evaluation of Hydrothermal Dolomite, Cretaceous-Eocene, Hamman Faraun Fault Block, Gulf of Suez.
This study, led by Dr Cathy Hollis, involves integration of classical field techniques, quantitative surveying, petrographical and geochemical methodologies and modelling. Geological outcrops such as the Hamman Fauran Fault block provide a crucial source of data for subsurface modelling.
It will aid calculation of in-place hydrocarbon volumes and well planning, and deliver data for scenario modelling in mature fields.