Considerable progress has been made in geothermal technology during the past decade of research and development activity, especially in exploration methodology and reservoir development technology. There are still some remaining technical problems and economic impediments to greater development of geothermal resources. Major uncertainties in evaluating the economics of a geothermal system include estimating reservoir characteristics, drilling costs, and long-term performance of power conversion equipment. Further improvements are needed to make geothermal technology economically competitive, particularly in the areas of resource (reservoir) potential assessment, exploration techniques, improved drilling techniques, reservoir handling techniques, and hot dry rock energy extraction R&D.
Resource (Reservoir) Potential Assessment: The economic utilisation of geothermal energy is extremely complex because geothermal systems are site-specific. The nature and quality of the resource vary from reservoir to reeorvoir. improved rooorvoir modelling hao been undertaken to avoid costly confirmation drilling and geoscientific studies for prediction of precise reservoir production capacity.
Exploration Techniques: Because of the relative scarcity of commercial geothermal systems, rapid low-cost reconnaissance techniques are usually employed first. When the search has been narrowed, more precise and somewhat more expensive techniques are used to define the resource potential. Because high geothermal temperature gradients are a prerequisite for any type of geothermal system, the initial exploration effort concentrates on defining such anomalous areas. Then, emphasis shifts to an evaluation of the permeability and hydrology of the area. Geothermal energy is a relatively new type of resource, and appropriate exploration rationales or programmes are the source of much debate and controversy. New exploration technologies for characterising fractured reservoirs are being investigated that locate the fractured area, evaluate the reservoirs, and predict reservoir response to production and injection. Improvement of exploration methods is likely to continue for decades.
Improved Drilling Techniques: Drilling for geothermal energy is similar to drilling for gae and oil; but there are issues specific to geothermal, such as high temperature circumstances, hard rock penetration, cementing procedures, casing design, circulating drilling mud oyotemo, wellhead equipment, and well completion. Rock penetration mechanics, advanced borehole instrumentation for operation over 250°C, and new drilling and coring technologies are research areas being supported world-wide.
Reservoir Handling Techniques: The basic task of the reservoir engineer is the prediction of the long-term behaviour of the well and reservoir. The optimum development of the reservoir requires a decision on the number and geometrical pattern of production and injection wells, the rate nf production, and the optimum development plan. Sub-surface injection of spent cold water involves the analysis of fluid migration, prediction of thermal and chemical effects, and optimisation of injection well placement and reservoir operations. Studies of these reservoir handing techniques are being conducted for the optimum development of the reservoir.
Fluid Properties: The quality of the extracted geothermal fluid3 or brine can have a significant impact on energy costs. The dissolved solids and gases present in geothermal waters can cause precipitation, scaling, erosion or corrosion of materials and equipment, affect heat recovery rates, and Increase maintenance costs. Efforts are underway lu increase the understanding of chemically complex geothermal brines and to develop better methods for coping with them.
Hot Dry Rock Energy Extraction R&D: The economic extraction of energy from hot dry rock systems lies in the future, pending solution of key problems including (1) design and creation of artificial fractures, (2) mapping and measurements of the fractures created, and (3) evaluation and improvement of artificial reservoirs.
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