Fracture Propagation and Permeability Change under Poro-thermoelastic Loads & Silica Reactivity in Enhanced Geothermal Systems

Technical Report · Thu Oct 01 04:00:00 EDT 2009

DOI:https://doi.org/10.2172/1021468· OSTI ID:1021468

Ghassemi, Ahmad ^[1]

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1. TEES

Geothermal energy is recovered by circulating water through heat exchange areas within a hot rock mass. Geothermal reservoir rock masses generally consist of igneous and metamorphic rocks that have low matrix permeability. Therefore, cracks and fractures play a significant role in extraction of geothermal energy by providing the major pathways for fluid flow and heat exchange. Therefore, knowledge of the conditions leading to formation of fractures and fracture networks is of paramount importance. Furthermore, in the absence of natural fractures or adequate connectivity, artificial fractures are created in the reservoir using hydraulic fracturing. Multiple fractures are preferred because of the large size necessary when using only a single fracture. Although the basic idea is rather simple, hydraulic fracturing is a complex process involving interactions of high pressure fluid injections with a stressed hot rock mass, mechanical interaction of induced fractures with existing natural fractures, and the spatial and temporal variations of in-situ stress. As a result, it is necessary to develop tools that can be used to study these interactions as an integral part of a comprehensive approach to geothermal reservoir development, particularly enhanced geothermal systems. In response to this need we have developed advanced poro-thermo-chemo-mechanical fracture models for rock fracture research in support of EGS design. The fracture propagation models are based on a regular displacement discontinuity formulation. The fracture propagation studies include modeling interaction of induced fractures. In addition to the fracture propagation studies, two-dimensional solution algorithms have been developed and used to estimate the impact of pro-thermo-chemical processes on fracture permeability and reservoir pressure. Fracture permeability variation is studied using a coupled thermo-chemical model with quartz reaction kinetics. The model is applied to study quartz precipitation/dissolution, as well as the variation in fracture aperture and pressure. Also, a three-dimensional model of injection/extraction has been developed to consider the impact poro- and thermoelastic stresses on fracture slip and injection pressure. These investigations shed light on the processes involved in the observed phenomenon of injection pressure variation (e.g., in Coso), and allow the assessment of the potential of thermal and chemical stimulation strategies.

• Research Organization: Texas Emgineering Experiment Station, Texas A&M University
• Sponsoring Organization: USDOE; USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE EE Office of Geothermal Technologies (EE-2C)
• DOE Contract Number: FG36-06GO16059
• OSTI ID: 1021468
• Report Number(s): TAMU-RM-DOE09-F
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
ALGORITHMS
APERTURES
Boundary element
DESIGN
Enhanced geothermal systems
FLUID FLOW
FLUID INJECTION
FRACTURES
Fracture Initiation
Fracture Permeability
Fracture deformation
Fracture slip
GEOTHERMAL ENERGY
GEOTHERMAL SYSTEMS
Geothermal
HYDRAULIC FRACTURING
Heat transport
Induced seismicity
METAMORPHIC ROCKS
Natural fracture
Naturally Fractured Reservoir
PERMEABILITY
Poroelasticity
QUARTZ
REACTION KINETICS
RESERVOIR PRESSURE
RESERVOIR ROCK
SILICA
SLIP
STIMULATION
STRESSES
Silica Precipitation
Thermoelasticity