UNDERSTANDING THE ROLE OF MICROPORES IN FLUID FLOW WITHIN CARBONATE RESERVOIRS

Understanding the pore system and petrophysical properties of subsurface reservoir rocks is vital for accurate prediction of fluid flow behaviour and therefore hydrocarbon recovery. This can be a particularly complex task in carbonate hosted reservoirs as the pore systems are inherently multi-scale, often incorporating four relevant orders of magnitude of pore size variation.

In some of the largest known carbonate hosted hydrocarbon reservoirs, a significant percentage of the total porosity and potential storage capacity is found as microporosity between the faces of micrite crystals. Understanding the properties of these microporous carbonates is further complicated by the small micropore dimensions (diameter <10microns) and we have only a rudimentary understanding of the contribution of this pore type to multiphase flow.

Here, a flexible, object-based rock reconstruction methodology has been developed to enable fluid flow modelling in heterogeneous, microporous carbonates. The reconstruction produces realistic models of micritic fabrics as observable from SEM image analysis, in order to accurately represent the pore space properties relevant to fluid flow. Multiphase and lattice-Boltzmann flow simulations performed on extracted pore networks are used to understand the flow properties of different types of microporous fabrics. This enables quantification of the relative influences of micropores, macropores and their interaction on macro-scale fluid flow. Consideration of different wettability distributions within the models allows these effects to be quantified as well. Results show that micropores can have a significant impact on flow and sweep characteristics in the modelled fabrics.

Such models and flow simulations will ultimately allow full quantification of how, and under what conditions, micropores contribute to flow under different geological fabric scenarios, thus leading to a more accurate prediction of the petrophysical properties of microporous carbonates.