Project

Geothermal reservoir

Goal: Geothermal reservoir characterization and modeling.
Geothermal resource assessment.

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Project log

Michel Garcia
added a research item
For a few years, deep geothermal energy is getting a new and tremendous interest worldwide as an effective alternative clean and renewable energy. The use of deep geothermal energy tends to be considered possible almost everywhere to produce electricity or for direct use of heat. Nevertheless, the risks due to subsurface uncertainties or related to drilling remain an obstacle to large-scale deployment. For lack of effective solutions to mitigate the risks, risk pooling and insurance systems are sought as a substitute. They can facilitate project financing but should not be enough for scale-up. We are convinced that exploration is the key to success. It has to be revisited as a whole, associated with meaningful phenomenological studies and relevant resource and risk assessment methodologies in a decision-making process at all stages. It must be a multidisciplinary and collaborative approach with the highest expertise in geoscience. It has to be routinely implemented by committed companies, highly specialized and trained, outside of a research framework. Exploration data must be cost-effective and primarily intended to conceive and test hypotheses, that are likely to confirm or not the potential of deep geothermal resources, and anticipate the risks. This is the purpose of the presented solution.
Michel Garcia
added a research item
New exploration studies were carried out during summer 2012 to better characterize and assess the geothermal resource of the Hot Spring Valley area on Akutan Island, Alaska. These studies included geological mapping and the implementation and interpretation of magnetotelluric (resistivity) and gravity surveys. In previous studies, several conceptual models of the Akutan geothermal field were proposed, primarily based on surface observations. They all consider the same hydrothermal fluid upflow area from a high-temperature deep source, followed by a shallower and lower temperature sub-horizontal flow (“outflow”) farther from the heat source. The models differ one another regarding the outflow paths. Fluid flows in the geothermal system at equilibrium are supposed to be strong enough to rule the temperature field. We propose a numerical approach, using the Tough2 reservoir simulator, to quantify the impact of regional flow and heat transport on the temperature field. The already established conceptual models, the aerial images and all available gravity, 3D resistivity and well data are used to build simplified structural and geological models, including the preferential outflow paths, and to define relevant flow and temperature boundary conditions. The numerical flow and temperature solutions are compared with spatial trends derived from the temperature data. The latter come from direct measurements, in the two wells and in surface fluids, but also from interpreted geochemical data. For each conceptual model, the flow properties, attached to rock types, and the flow and temperature boundary conditions are considered as model calibration parameters. Playing with these calibration parameters, it can be quantitatively studied their impact on the temperature spatial trend. The comparison with the temperature data then allows to identify and validate the numerical models, hence the conceptual models, that are most likely to explain and predict the temperature field. These numerical models also provide useful information about the regional flow velocity field, which is consequential to reservoir production performances. Using the most appropriate numerical temperature model, a suitable geostatistical method is finally used to estimate a temperature field that honors the observed temperature data and reproduces the numerically simulated spatial trends.
Michel Garcia
added a research item
As part of the GEOTREF research project, a cost-effective approach, relying on innovative software tools, is proposed to carry out prefeasibility studies prior drilling based on numerical conceptual models associated with phenomenological modelling and well layout optimization. The numerical conceptual models are intended to be 3D structural, geological and geothermal numerical models that integrate at best all understanding, interpretations and data about the geothermal reservoir. They are defined at a scale where relevant boundary conditions can be specified, including recharge, basal heat flux and heat sources. Scenarios are used to formalize the uncertainty about numerical conceptual models, whether it is related to data values or interpretations, model assumptions or simplifications, or geothermal reservoir model components. Each scenario determines a numerical conceptual model as a possible representation of the actual geothermal reservoir. Phenomenological modelling is carried out by numerically simulating the geothermal systems corresponding to various scenarios. Results provide information to determine and understand the structural, geological and geothermal conditions that should be met to explain the presence of a geothermal resource. The geothermal potential of hot scenarios is then assessed by seeking optimal production and injection well locations that maximize the production of electrical power from the available geothermal energy.
Michel Garcia
added a research item
Objectives/Scope: The development and management of geothermal reservoirs is complicated and expensive, the maximum potential geothermal energy recovery is highly depending on the optimal well location. Within the framework of a multidisciplinary research platform for the exploration and development of high geothermal energy in fractured reservoirs, a method has been developed to optimise well layouts (location and depth) based on geothermal reservoir production performance criteria (objective functions). Objective functions such as available thermal exergy, electrical power output, leftover energy rate and simplified net present value are proposed in this paper to be used as performance criteria for locating the optimal well layouts. Methods, Procedures, Process: The optimisation method uses the principle of superposition as proxy-based method to simulate the production of a well layout by summing the effects of individual injection and production wells of the layout simulated separately. Using this method, the computation time required to search for an optimal well layout design is significantly reduced. The well layouts are defined based on a number of injection and production wells to be selected among many possible well locations and depths. They are all simulated using the principle of superposition and ranked according to the selected objective function. The optimal well layout is the one maximising the objective function. Results, Observations, Conclusions: Data from an actual case study are used to evaluate the method. The four objective functions are tested using reservoir simulations and sensitivity analysis based on various production parameters. The results show that the proxy-based method can simulate the performances of well layouts with sufficient accuracy, the discrepancy between proxy-based simulations and full simulations increasing with production rate. More important, the method proves to be consistent by preserving the ranks of the top one hundred well layouts under all high, medium and low production/injection rates. Preserving the ranks is the required condition that makes the proposed method reliable for seeking optimal well layouts in geothermal reservoirs. The choice of an objective function does not drastically change the areas that are recognised as good or bad for production or injection wells. Novel/Additive Information: Provided relevant data are available as input to the most comprehensive objective functions (i.e., electrical power output, simplified net present value), this study concludes that the proposed method is highly reliable to be used for the search of optimum well layouts in geothermal reservoirs in a relatively short computation time.
Michel Garcia
added a project goal
Geothermal reservoir characterization and modeling.
Geothermal resource assessment.