Reservoir Simulation for Play-based Development of Low Enthalpy Geothermal Resources

Abstract

As implementation of deep geothermal energy projects in the Netherlands increases, reservoir simulation for these geothermal systems stands to play a key role in understanding how these systems will behave and how large scale projects can be optimised to save cost and reduce risk. In this thesis, an extensive simulation study has been conducted using a new Operator based linearisation simulator (DARTS) on a geological model of the Delft Sandstone Member within the West Netherlands Basin (a prolific geothermal reservoir). The first section of the study outlines the construction of a representative geological model of the Delft Sandstone in Petrel using core, well log and seismic data.
The model is quality checked by comparing derived model values with both values recorded in the literature and data from well tests. Following this, a sensitivity and uncertainty study was conducted which examines the effect of changing a wide range of model values and inputs on the thermal
performance of production wells. A well placement study was then implemented, examining how well configuration, orientation and distance can affect well performance. Finally, a considerable section of the thesis investigates the role of non-reservoir lithologies in geothermal reservoir simulation and how the heat transfer from these lithologies can be accounted for utilising multi-scale
upscaling. The findings of the uncertainty and sensitivity analysis suggest that the primary uncertainty for simulation in the Delft Sandstone is the porosity and intrinsically linked permeability, with the value and spatial distribution of these properties having the largest effect on thermal performance of wells (10’s of years difference in thermal breakthrough). From the well placement study, it was found that different well configurations performed variably according to local reservoir conditions (especially reservoir dip) and that optimum configuration should be decided on a case-by-case basis. It was also found that both well separation/interference and orientation have a key role in controlling the thermal productivity of wells. Finally, the section on non-reservoir lithologies finds that firstly, thermal recharge of injected water from these rocks can have a very large effect on thermal breakthrough time (10’s of years for low N/G reservoir) and must not be ignored in geothermal simulations and secondly,
of the three multi-scale upscaling methods implemented to more efficiently simulate conductive heat flux from the non-reservoir rocks, only multiple sub-region upscaling shows significant promise in terms of accurately accounting for heat flux and significantly reducing the number of grid cells. However, the quality of the solution for this method is still strongly linked to fluid flow rate, with higher rates resulting in better solutions.