Submission #7

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Fri, 05/22/2015 - 10:55
Numerical simulation of two phase compositional high energy geothermal systems in fractured reservoirs
PhD Thesis
Geothermal energy is a carbon-free steady energy source with low environmental impact. In countries with a favorable geological context, high temperature geothermal energy can make a significant contribution to power production. On the French territory, it is already an attractive option in volcanic islands context compared to importing fossil fuel. Today, about 5 pourcents of yearly electricity consumption of Guadeloupe already comes from geothermal energy and it is essential for achieving energetic and environmental targets, according to which the overseas territories should produce 50 pourcents of their electricity consumption from renewable resources by 2020 and achieve their energy autonomy in 2030. As for other parts of the world, the geothermal development potential of the Caribbean islands is high and several industrial projects are in preparation or already underway, in French overseas territories (Guadeloupe, Martinique) as well as in nearby islands (Dominica, Montserrat).

Numerical modeling has become essential in all phases of geothermal operations. It is used in the exploration phases to assess the geothermal potential, validate conceptual hypothesis and help well siting. Field development and resource management need quantitative estimation to prevent resource exhaustion and achieve its sustainable exploitation (production/injection scenarios). Finally numerical modeling is also helpful in studying exploitation related industrial risks such as the interaction with shallow water levels (drinking water resources, hydrothermal vents or eruption).

The objective of the PhD is to develop a numerical model to simulate the flow of the liquid and steam compositional phases coupled with energy conservation and thermal equilibrium in geothermal systems (Coumou 2008). The model will take into account the flow in the discrete fault network acting as major heat and mass transfer corridors coupled with the flow in the surrounding three dimensional porous media (the matrix). Different formulations of the model will be investigated in order to take into account the liquid and gas appearance and disapearance due to thermodynamical equilibrium including sub and supercritical regimes and compositional effects.

To deal with complex geometry involved by the fault network, we will focus on the asymptotic class of models (Martin et al 2005) representing faults as interfaces of codimension one in the 3D matrix domain. Both pressure continuous and pressure discontinuous models at the matrix fault interfaces will be investigated.
The spatial discretization will be based on the gradient scheme framework including a large class of conforming and non conforming discretizations. We will in particular focus on a recently introduced finite volume method called Vertex Approximate Gradient (VAG scheme (Brenner et al 2014) which is very efficient on mainly tetrahedral meshes thanks to its essentially nodal feature.
High order MUSCL type discretizations of the transport will also be investigated to obtain an accurate description of the compositions in the reservoir.

The model, its discretization and solution algorithms will be assessed in collaboration with BRGM on different test cases with main target the Bouillante geothermal field located in the West Indies in Guadeloupe and operated by a subsidiary company of BRGM.
Tue, 09/01/2015
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