Permeability Of Geothermal Reservoirs Research Articles

Particle blockage mechanism of a weakly consolidated sandstone geothermal reservoir during tailwater recharge

Weakly consolidated sandstone geothermal reservoirs (WCSGR) are widely distributed, highly developed and utilized, with tremendous potential to meet enormous energy needs. However, this kind of geothermal reservoir (GR) suffer from permeability damage during tailwater recharge, primarily due to particle blockage (PB). The exact impact of PB on the permeability of GRs during tailwater recharge remains unclear. Therefore, an experimental study investigating PB in WCSGR tailwater recharge was conducted, considering the comprehensive effects of multiple factors. The study aimed to understand the mechanism of PB and its effect on GR permeability by observing the migration of fluorescent particles in sandstone core. Through analysis of microsphere migration/blockage properties, theoretical calculations, and empirical criteria, the PB mechanism during tailwater recharge in weakly consolidated sandstone was revealed. A physical model of particle movement was developed to explain the permeability attenuation phenomena in the experimental cores, describing the occurrence and development process of PB in real recharge operations. Finally, the theoretical computation were integrated with the experimental findings, and the chemical and dynamic conditions of geothermal tailwater recharge in the WCSGR were optimized. This study provides theoretical guidance for further numerical simulations and field tests.

Investigating high permeable zones in non-volcanic geothermal systems using lineament analysis and fault fracture density (FFD): northern Konawe Regency, Indonesia

Indonesia has high geothermal potential comprising 40% of the world’s potential geothermal energy, volcanic and non-volcanic systems. Volcanic systems have witnessed more exploration activities for geothermal resources compared to non-volcanic systems. A high potential non-volcanic system in Indonesia is located in the northern part of Konawe, Southeast Sulawesi. Previous research had identified surface temperature anomaly (high temperature) and some surface manifestations for this area, specifically in the northeast part of Wawolesea. However, the source of surface manifestations and permeable zones as an implication of a good reservoir are still unknown. Therefore, this research aims to investigate the permeable zones and geothermal potential in the non-volcanic geothermal system of north Wawolesea by applying lineaments analysis and the fault fracture density (FFD) method. A total of 1694 major and minor lineaments were manually delineated using ArcGIS based on Digital Elevation Model Nasional (DEMNAS). FFD map and rose diagrams displayed the orientation of all lineaments and structures with the major lineaments trending NNE–SSW, whereas the minor lineaments showed irregular distribution and orientation. Field measurements also show the same azimuth orientation for the mapped fractures. Five zones were characterized by high FFD values (2.81–4.54 km/km2). One of the extensively fractured zones (Zone C) is located between Meluhu and Lembo, covering an area of around 19.39 km2. This area is interpreted to be highly permeable and suggestive of a recharge area that contributes to surface manifestation in the Wawolesea. Therefore, the area between Meluhu and Lembo in the northern part of Konawe shows high geothermal potential due to its planar morphology and high FFD values. This study allows an improved understanding of how fracture geometry, distribution and density control the permeability in geothermal reservoirs.

Geothermal Exploration by Seismoelectric Survey

In the following, we present the first successful case in geothermal exploration history that utilizes seismoelectric survey methods. Through rigorous research, we developed a novel seismoelectric surveying system that includes the design of proprietary specialized instruments to acquire, process, and interpret the seismoelectric signal (SES) in order to measure relative permeability in geothermal reservoirs. The system is based, on the principles of subsurface seismic wave propagation, its disturbance of the electric double layer in water saturation zones and the seismoelectric signal (SES) generated by this interaction. Theoretically, our system is designed on the Helmholtz-Smoluchowski equation (defines steady state streaming potential-1859). Our method involves generating, recording, processing in interpreting the seismoelectric signals (SES). This technique has been applied in over 300 surveys worldwide in both groundwater and petroleum reservoirs. Its ability to detect fractures has delivered a water source in areas lacking conventional porous media. The system’s portability permits us carry out studies in difficult to reach areas. Results demonstrate that it is effective in locating geothermal reservoirs, groundwater as well as hydrocarbons. This seismoelectric survey system is more economical, more accurate, and more efficient and correlates better to well log data in comparison to other geophysical techniques.

The role of fluid chemistry on permeability evolution in granite: Applications to natural and anthropogenic systems

Efforts to maintain and enhance reservoir permeability in geothermal systems can contribute to sourcing more sustainable energy, and hence to lowering CO2 emissions. The evolution of permeability in geothermal reservoirs is strongly affected by interactions between the host rock and the fluids flowing through the rock's permeable pathways. Precipitation of secondary mineral phases, the products of fluid-rock interactions, within the fracture network can significantly reduce the permeability of the overall system, whereas mineral dissolution can enhance reservoir permeability. The coupling between these two competing processes dictates the long-term productivity and lifetime of geothermal reservoirs. In this study, we simulate the conditions within a geothermal system from induced fracturing to the final precipitation stage. We performed batch and flow-through experiments on cores of the Carnmenellis granite, a target unit for geothermal energy recovery in Cornwall (UK), to understand the role of mineral dissolution and precipitation in controlling the permeability evolution of the system. The physico-chemical properties of the cores were monitored after each reaction-phase using ICP-OES, SEM, hydrostatic permeability measurements, and X-ray Computed Tomography. Results show that permeability evolution is strongly dependent on fluid chemistry. Undersaturated alkaline fluids dissolve the most abundant mineral phases in granite (quartz and feldspars), creating cavities along the main fractures and generating pressure-independent permeability in the core. Conversely, supersaturated alkaline fluids, resulting from extended periods of fluid-rock interactions, promote the precipitation of clay minerals, and decrease the permeability of the system. These results suggest that chemical dissolution during geothermal operations could generate permeable pathways that are less sensitive to effective stress and will remain open at higher pressures. Similarly, maintaining the circulation of undersaturated fluids through these granitic reservoirs can prevent the precipitation of pore-clogging mineral phases and preserve reservoir permeability in granite-hosted geothermal systems.

Saturated heating and quenching of three crustal rocks and implications for thermal stimulation of permeability in geothermal reservoirs

Thermal stimulation is a reservoir enhancement technique that relies on the generation of permeable fractures by thermal gradients. Replication of thermal stimulation in a controlled laboratory environment provides insight to the physical changes that may be expected at the field scale and assist in stimulation optimization. We present a new methodology designed to replicate thermal stimulation in such an environment. We developed an apparatus to allow rocks to be heated to 375°C at up to 35MPa confining pressure and rapidly quenched with cold water to ambient temperature while maintaining system pressure. To test our methodology, we characterized three rocks that represent a range of geothermal developments and laboratory based investigations: Lanhélin Granodiorite (granite) from Brittany, France, Allandale Rhyolite from the Lyttelton Volcano, New Zealand and Halswell Basalt also from the Lyttelton Volcano. Our characterization consists of profiling microstructure, porosity, density, dynamic elastic moduli and permeability prior to thermal stressing. Results indicate that we have increased porosity, decreased density, attenuated elastic moduli and significantly enhanced the permeability of the rocks. Rapidly cooled and slowly cooled samples are presented with the rapidly cooled samples showing an increase in permeability. The results are compared to similar studies previously carried out under dry conditions and implications discussed for geothermal operations.

A parallel computing tool for large-scale simulation of massive fluid injection in thermo-poro-mechanical systems

Massive fluid injections into the earth’s upper crust are commonly used to stimulate permeability in geothermal reservoirs, enhance recovery in oil reservoirs, store carbon dioxide and so forth. Currently used models for reservoir simulation are limited to small perturbations and/or hydraulic aspects that are insufficient to describe the complex thermal-hydraulic-mechanical behaviour of natural geomaterials. Comprehensive approaches, which take into account the non-linear mechanical deformations of rock masses, fluid flow in percolating pore spaces, and changes of temperature due to heat transfer, are necessary to predict the behaviour of deep geo-materials subjected to high pressure and temperature changes. In this paper, we introduce a thermodynamically consistent poromechanics formulation which includes coupled thermal, hydraulic and mechanical processes. Moreover, we propose a numerical integration strategy based on massively parallel computing. The proposed formulations and numerical integration are validated using analytical solutions of simple multi-physics problems. As a representative application, we investigate the massive injection of fluids within deep formation to mimic the conditions of reservoir stimulation. The model showed, for instance, the effects of initial pre-existing stress fields on the orientations of stimulation-induced failures.