Application of a Coupled Thermo-Hydro-Mechanical-Chemical Simulation to a North Sea Hydrocarbon Chalk Reservoir

Water weakening effect in the chalk reservoir causes additional compaction due to the interaction between the rock and injected water. To consider the impact of the coupled interactions on the fluid transport (e.g., production) and reservoir deformation due to the seawater injection into the chalk reservoirs, in this study, a wrapper is developed in Matlab that combines Eclipse 100 reservoir simulator and Visage geomechanics simulator to capture the induced alteration of mechanical and petrophysical properties of chalk.

Here, we utilize the history-matched reservoir model of the Halfdan sector model to investigate the impact of the temperature-dependent fluid-rock interactions induced by sulfate adsorption on the surface of calcite grains on the deformation behavior of the reservoir during waterflooding. Our sector-scale simulation results show that while considering the geomechanics model has a considerable impact on calculated reservoir pressure and recovery, the impact on history matched data due to water weakening is not significant when yield stress and bulk modulus are expressed as functions of temperature and sulfate concentration for the Halfdan model.

We argue that the minor contribution of the water weakening effect at in situ conditions is due to 1) the relatively high initial water saturation in the water flooded section of the reservoir and 2) the low initial temperature (70 ˚C) of Halfdan reservoir, especially towards the northern part of the Danish North Sea.