We have investigated the role of high-frequency cycles (HFCs) in carbonates during water flooding. These are normally sub-seismic and therefore below grid resolution and must be upscaled, both in terms of single- and multiphase flow behaviour, to predict time to water breakthrough, recovery factors, and the habitat of remaining oil properly. Particularly the latter could be important when designing appropriate enhanced oil recovery schemes that target the remaining oil. The importance of selecting a high vertical resolution grid has been demonstrated for HFCs with continuous petrophysical log gradients and discontinuities, and the consequence these high permeability ranges have on waterflood velocity has been presented: capturing all of a continuous gradient requires increasing the vertical resolution so as to predict a fast enough water front, and a realistic distribution of the residual oil within the HFCs. In addition, the importance of selective diagenesis has been investigated by considering the effect of early-stage diagenesis at the top of HFCs in end-member Greenhouse and Icehouse climates. HFCs are very common in carbonates, even if they are nested within larger-scale heterogeneous geobodies, and the value of this investigation is in its application to real reservoir models.@en

Porosity and permeability of carbonate sediments evolve markedly with burial depth, reflecting the combined effects of mechanical compaction, chemical compaction, dissolution and cementation. While trends in porosity change with depth can be qualified, the evolution of permeability remains problematic. Here, we create a theoretical series of 2D images of major pore-occluding and pore enhancing diagenetic processes linked to their depth of occurrence. These images were then used to create 3D pore architecture models using Markov Chain Monte Carlo simulation, from which pore network were extracted to obtain multiphase fluid flow properties. The modelled porosity and permeability evolution from three different diagenetic pathways display several tipping points where the decrease in permeability is significantly larger than the associated drop in porosity. Such diagenetic pathway models can provide constraints on the predicted behaviour of carbonates during burial and/or uplift scenarios.@en

Carbonate reservoirs have petrophysical property distributions largely controlled by a combination of the depositional, diagenetic, and structural (burial/uplift) histories of the reservoir itself and also of the basins that contain them. Carbonates are very prone to diagenetic alteration; porosity and permeability can be strongly affected by the thermal state, fluid-pressure and pore fluid chemistry through their geological history. We use a novel workflow, adapted from basin modelling, to investigate how the burial/uplift history of an offshore carbonate reservoir and its basin, taken as a system, can have controlled the fluid and heat movement within, into and out of the reservoir. The reservoir rock properties and diagenetic history are assessed, as is the local and regional geological evolution for potential contributory factors to the diagenesis. A model of the potential basin system is developed, observed reservoir diagenetic history being added to the normal basin modelling constraints. This model provides good estimates of geometry and property evolution, and of fluid transport, through geological time. Since fluid and heat fluxes are important in the diagenetic evolution of the carbonate pore system, these results are complemented by simulating the movement of heat and brine in the reservoir using finite element-finite volume simulations. These simulations capture the complex geological structures, especially fault-fracture systems, and better represent the flow physics and chemistry that control reservoir diagenesis. Results from these simulations will later be returned to the basin model to improve the calibration of the timing, depth, and rates of diagenetic events. This new workflow is applied to a Lower Eocene offshore carbonate reservoir with a complex diagenetic history which seems to have a strong basin evolution influence. Importantly this workflow is generic and can be applied to any carbonate reservoir to enhance the link between geological models at the basin scale and reservoir scale models.@en

Basin modelling tools are widely used to predict reservoir charging but, unfortunately, their application to carbonate reservoirs is far from straightforward. For carbonates, the relationships between porosity/ effective stress/depth, must be addressed before a reliable basin model can be produced. We propose using a synthetic diagenesis approach, where Pore Architecture Models (PAMs) are used to generate representative porosity values for the different diagenetic (backstripped) stages that are recognised from cores or thin sections. The synthetic diagenesis approach is then used to inform more conventional basin modelling. The viability of this method is the topic of this contribution.@en