The detection and quantification of horizontal-permeability anisotropy play a vital role in optimally placing geothermal wells in geothermal reservoirs and thereby maximizing the geothermal-energy recovery from a given geothermal-reservoir area. However, the study of permeability anisotropy within the horizontal plane has received less attention and often permeability anisotropy is neglected in view of simplification.
Our study show that the horizontal permeability anisotropy has been observed in nearly all geothermal doublets that have been tested so far in the Netherlands. The main objective of this work is to study the impacts of horizontal permeability anisotropy inferred from pressure-interference tests on geothermal-doublets performance.
A theoretical relation between the measured directional permeability and the elements of the permeability tensor are presented. In a case study, horizontal anisotropy has been detected and quantified using a pressure-transient analysis, interference test, and the knowledge of the reservoir geometry gained from the geological study. In addition, this work uses a detailed three-dimensional thermal reservoir simulator of a reservoir in the West Netherlands Basin to demonstrate the importance of considering permeability anisotropy in predicting the lifecycle, which is determined by the cold-temperature breakthrough of an existing doublet and in optimally designing the second doublet in the same licensed area.
It has been established that the areal permeability anisotropy plays an important role in the energy sweep efficiency and doublets placement. A correct arrangement between the permeability anisotropy direction and the placement of the wells leads to longer breakthrough time and increasing the heat sweep efficiency.
This work shows that the knowledge gained from the interference test and/or other experiments about the presence, direction, and scale of anisotropy can be used to adjust the reservoir model that can be further used to design and optimize geothermal doublets.