The influence of facies heterogeneity on the doublet performance in low-enthalpy geothermal sedimentary reservoirs

R.A Crooijmans,C.J.L Willems,H.M Nick,D.F Bruhn

doi:10.1016/j.geothermics.2016.06.004

R.A Crooijmans, C.J.L Willems + Show 2 more

Open Access

https://doi.org/10.1016/j.geothermics.2016.06.004

Copy DOI

Abstract

A three-dimensional model is used to study the influence of facies heterogeneity on energy production under different operational conditions of low-enthalpy geothermal doublet systems. Process-based facies modelling is utilised for the Nieuwerkerk sedimentary formation in the West Netherlands Basin to construct realistic reservoir models honouring geological heterogeneity. A finite element based reservoir simulator is used to model the fluid flow and heat transfer over time. A series of simulations is carried out to examine the effects of reservoir heterogeneity (Net-to-Gross ratio, N/G) on the life time and the energy recovery rate for different discharge rates and the production temperature (Tmin) above which the doublet is working. With respect to the results, we propose a design model to estimate the life time and energy recovery rate of the geothermal doublet. The life time is estimated as a function of N/G, Tmin and discharge rate, while the design model for the energy recovery rate is only a function of N/G and Tmin. Both life time and recovery show a positive relation with an increasing N/G. Further our results suggest that neglecting details of process-based facies modelling may lead to significant errors in predicting the life time of low-enthalpy geothermal systems for N/G values below 70%.

Highlights

Geothermal energy production from deep geological formations has been growing in the Netherlands since the first doublets were realised in 2007
For example, porosity, initial temperature, permeability and heat capacity that lead to different geothermal performance indicators such as the life time of the doublet, recovery and the daily energy production
When applying the base case conditions for the dynamic simulation of different realisations of model Type I the following features were observed: (i) the net-to-gross ratio (N/G) has noticeable impact on the life time of the doublet especially for low N/G values (Fig. 2); (ii) decreasing N/G results in decreasing the life time, which is more pronounced for realisations with N/G smaller than 40%; and (iii) the cumulative energy production shows the same results as the recovery (Fig. 3), but the recovery increases slightly faster at N/G values larger than 60%

Summary

Introduction

Geothermal energy production from deep geological formations has been growing in the Netherlands since the first doublets were realised in 2007 (van Heekeren, 2015). The main targets are sedimentary fluvial reservoirs at depths between 2 and 2.5 km with a temperature between 70 and 90 ◦C (Bonté et al, 2012). These are so-called low-enthalpy reservoirs, which are mainly used for heating of buildings in the horticultural sector. The sedimentary fluvial reservoirs have different characteristics from conventional geothermal in magmatic settings Such characteristics are, for example, porosity, initial temperature, permeability and heat capacity that lead to different geothermal performance indicators such as the life time of the doublet (how long the doublet can produce economically), recovery (produced energy compared to the total amount of available energy) and the daily energy production. The focus of this study is on the performance of such a system where the life time and the recovery are dependent on both human and physical controlled parameters

Methods

Results

Discussion

Conclusion