Nelson Rodrigues

A hydro-thermo-mechanical numerical model for HDR geothermal reservoir evaluation

A two-dimensional numerical model of coupled fluid flow, heat transfer and rock mechanics in naturally fractured rock is developed. The model is applicable to assessments of hot dry rock (HDR) geothermal reservoir characterisation experiments, and to the study of hydraulic stimulations and the heat extraction potential of HDR reservoirs. Modelling assumptions are based on the characteristics of the experimental HDR reservoir in the Carnmenellis granite in Cornwall, S. W. England. In particular, the model assumes that fluid flow is horizontal and is confined to the most hydraulically conductive fractures in two orthogonal and vertical fracture sets. The mathematical model representing the hydro-mechanical interactions that are induced during reservoir creation is described. Furthermore, the solution method for calculating thermally induced stresses and strains in the reservoir due to heat extraction is discussed. The resultant numerical model, HOTGRID, is used to investigate the effects of stress perturbations on the fluid flow distribution in an HDR geothermal reservoir.

Uranium accumulation by aquatic plants from uranium-contaminated water in Central Portugal

Several species of plants have developed a tolerance to metal that enables them to survive in metal contaminated and polluted sites. Some of these aquatic plants have been reported to accumulate significant amounts of specific trace elements and are, therefore, useful for phytofiltration. This work focuses the potential of aquatic plants for the phytofiltration of uranium (U) from contaminated water. We observed that Callitriche stagnalis, Lemna minor, and Fontinalis antipyretica, which grow in the uraniferous geochemical province of Central Portugal, have been able to accumulate significant amounts of U. The highest concentration of U was found in Callitriche stagnalis (1948.41 mg/kg DW), Fontinalis antipyretica (234.79 mg/kg DW), and Lemna minor (52.98 mg/kg DW). These results indicate their potential for the phytofiltration of U through constructed treatment wetlands or by introducing these plants into natural water bodies in the uraniferous province of Central Portugal.

Modelling of a european prototype hdr reservoir

Abstract The European Hot Dry Rock Geothermal Energy Project, located in the Rhine graben at Soultz-sous-Forets, Alsace, France, is entering a new phase in its development. Over the next few years the existing HDR system will be developed to form an operational Scientific Prototype HDR System. This paper provides an introduction to the collaborative reservoir modelling studies undertaken as part of the European Programme. In particular the paper addresses the general methodology adopted in the reservoir design process and focuses on one of the preliminary objectives of the study, assessment of the minimum HDR doublet separation required to meet the thermal performance objectives during circulation. Two “preliminary reservoir designs” are adopted as starting points for the study, the first based on exploitation of large scale planar fractures, the second on the development of a modular (multi-cell) system based on 3 cells supporting 51/s production each. Estimates were obtained using models based on both idealised geometry and empirical observations of reservoir circulation at the Camborne School of Mines (CSM) HDR project. The results indicate that a wellbore separation of around 400m would be required for the multi-cell system to achieve the required thermal performance of 10% thermal drawdown, or less, during 10 years circulation at 151/s production. Whereas, the wellbore separation required for the single fracture design would be in excess of 650m.

Uranium accumulator plants from the centre of Portugal — their potential to phytoremediation

The strategies of metal tolerance developed by several plants that enable them to survive in contaminated and polluted sites allow that some of them may accumulate significant concentration of a specific element. The work presented here is part of a larger on going study about the uraniferous geochemical province of Central Portugal, and it focus only in a preliminary description of results obtained with aquatic plants that show potential for phytoremediation. We have observed that Apium nodiflorum, Callitriche stagnalis, Lemna minor and Fontinalis antipyretica accumulate significant amounts of uranium, whereas Oenanthe crocata inhibit the uranium uptake.

Modelling tracer tests in the Rosemanowes HDR reservoir

Tracer tests from the Rosemanowes (Cornwall, UK) Phase 2B reservoir (1985 to 1991) are fitted to a model with adjustable parameters. The model is a weighted sum of three similar residence time density functions. The objective was to test if components from the decomposition of surface to surface tracer tests could be correlated to different flowing zones into the production well. The results revealed that a surface to surface tracer test is insufficient to distinguish between individual flow zones. Each flow zone is itself a combination of fluid with short, medium and long residence times inside the reservoir. The analysis also revealed that changes in the reservoir during circulation affected mainly the long residence time flow paths inside the reservoir, thus indicating a continuous evolution of the Rosemanowes reservoir during its circulation. This has implications for the thermal performance of the reservoir.