Reservoir characterization and prediction modeling have long been among the more challenging tasks in geothermal reservoir engineering. The main reason is the presence of fractures and faults, which control the mass and heat transport in the subsurface. Nowadays, with a substantial increase in data due to advances in computer power and measuring equipment, the oil and gas as well as the geothermal industries are presented with some of today’s most complex data science problems.
Modeling of geothermal reservoirs poses significant difficulties for nonlinear solvers in reservoir simulation. This research focuses on designing novel numerical algorithms to overcome these nonlinear difficulties. These difficulties arise from the strong coupling between the mass and energy conservation equations. This strong coupling results in an apparent "negative compressibility" for blocks that have both liquid and steam phases.
Wellhead measurements of enthalpy and mass flow rate are routine monitoring procedures in geothermal fields. Due to wellbore heat loss, measurement of surface enthalpy can only provide incomplete information about the wellbore and the reservoir, especially during the early testing phases of a development. Measurement of enthalpy downhole would allow for better understanding of the reservoir condition and so would be of great practical significance.
Accurate modeling of fracture flow behavior is important for tight reservoirs, such as shale gas and geothermal systems, where faults and fractures are the main conduits for flow. In enhanced geothermal systems (EGS), hydraulic fracturing is used to increase permeability by creating new fractures or inducing slip on preexisting fractures (McClure and Horne, 2011). If appropriate investments in research and development are made, EGS has a potential of having up to 100 GWe of generating capacity in the next 50 years (Tester et al., 2006).
In order to assess whether particle tracers can provide more useful information about future thermal behavior of reservoirs than existing solute tracers, models were developed for both solute tracers and particle tracers. Three existing solute tracer types were modeled: conservative solute tracers (CSTs), reactive solute tracers with temperature dependent reaction kinetics (RSTs), and sorbing solute tracers that sorb reversibly to fracture walls (SSTs).
This study aimed to estimate the connectivity of fracture networks using direct current resistivity measurements. In these surveys, a direct current is sent into the ground through electrodes and the voltage differences between them are recorded. The input current and measured voltage difference give information about the subsurface resistivity, which can then be used to infer fracture locations. Other geophysical surveys used commonly to find hidden geothermal resources are self-potential and magnetotelluric surveys. Garg et al.
In Enhanced Geothermal Systems (EGS), hydraulic stimulation is carried out by injecting water at high pressure into low permeability, typically crystalline rock. In most cases, the fluid injection causes slip on the preexisting fractures, enhancing their permeability and increasing well productivity. The simplest EGS arrangement is a two well doublet in which cool water is injected by an injector well, it heats up as it moves through the rock, and then is produced by a second well.
Project Technology Type: EGS Component R&D › Reservoir Characterization
Awardee: Stanford University
Location: Stanford, CA