Geothermal phenomena in the context of gravity-driven basinal flow of groundwater

Abstract

Gravity-driven groundwater flow systems function in topographic basins as subsurface conveyor belts. They pick up and move fluids, gases, solutes, colloids, particulate matter and heat from loading sites in recharge areas and/or on their way to the discharge areas and can deliver them "en route" or in discharge regions. Gravitational flow systems of various horizontal and vertical extents are organized into hierarchically nested complex patterns controlled by the configuration of the water table's relief and modified by the rock framework's heterogeneities of permeability. The systems are ubiquitous and act simultaneously on broad ranges of the spatial and temporal scales of measurement. Their universal geologic agency is manifest by numerous different, even disparate, natural processes and phenomena. Several of these are associated with geothermal heat flow. The understanding of geothermal phenomena in the context of basinal flow systems requires, therefore, an intimate familiarity with the overarching "Theory of regional groundwater flow" which, in turn, comprises two component theories: "The hydraulics of basin-scale groundwater flow systems" and "The geologic agency of basin-scale groundwater flow-systems". The paper's outline is based on this conceptual structure. The paper presents examples for geothermal effects of groundwater flow by means of the first theoretical models and some case studies of thermal springs and wells, and petroleum accumulations. The final section reflects the author's conviction that geothermal studies cannot be complete without consideration and understanding of the area's groundwater flow regime.

Hybrid numerical modelling of fluid and heat transport between the overpressured and gravitational flow systems of the Pannonian Basin

“…Geothermal systems are commonly grouped as conventional and non-conventional systems according to the heat conveyance mechanism. Conventional geothermal systems have a natural heat source, the reservoirs have high porosity and permeability, and natural groundwater flow systems convey the heat (Tóth, 2015). Non-conventional systems have a natural heat source but the reservoirs are either engineered and/or the fluids are artificially circulated.…”

Locating Geothermal Resources: Insights from 3D Stress and Flow Models at the Upper Rhine Graben Scale

“…Regionally moving groundwater is the basic and common cause of a wide variety of natural processes and phenomena that makes the gravity-driven groundwater flow a key process [19,44]. The key reason for the geological scale effects of the groundwater flow is that the flow systems are ubiquitous and active over large spectra of time and space.…”

“…These anomalies are mainly located in the western part of the URG [18]. Recalling that thermal anomalies are mostly affected by the regional groundwater circulation [19], the high potential of the URG for thermal anomalies is widely interpreted as a signature of the regional-scale fluid migrations hosted by the numerous fault zones cutting through the rock mass (multiscale fracturecontrolled systems, [20]). Arguing that the fault zones are critically stressed and mostly under shearing conditions, Baillieux et al [21] estimated that the regional fluid migrations could be responsible for up to 75-85% of the thermal anomalies in the URG.…”