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As one of the methods to extract geothermal energy, downhole coaxial heat exchanger is widely concerned because of its high heat extraction rate and no need of re injection. However, there are few studies on the extraction of open-loop heat from a single deep geothermal shaft, and there is a lack of detailed inlet and outlet transient temperature data. In this study, the downhole coaxial open-loop heat collector is improved, and the slotted liner at the bottom of the well is used to form a free open space to improve the heat exchange. Using the improved experimental device design, the field thermal recovery test was carried out in deep geothermal well of Shengli Oilfield, Dongying, China. According to the field test results, the control equation was established, and the influence of parameters on the thermal recovery rate was studied. It is found that the improved heat output is greater than the reported value of the downhole heat exchanger with the traditional structure. After about eight days, the heat extraction rate reached a gradually stable stage. After 15 days of continuous operation, the heat output is stable at 200 kW, and the water temperature at the water outlet is 34.6 °C. [ABSTRACT FROM AUTHOR]

Geothermal energy is a renewable energy that has not been utilised as solar, wind, and biomass energy because of the cost of exploration, cost of implementation, and possible environmental concerns such as enhancing the chances of earthquakes, and tremors.The remote sensing technique and Surface Energy Balance model was proposed to determine the absorbed terrestrial radiation and other salient parameters. Forty years remote sensing dataset (1980–2019), was obtained from the MERRA-2 for three hundred and two (302) locations across Nigeria. The acquired thermal parameters were processed using known models. The heat catchment with the highest magnitude of 330.244 W/m2 are found in Nembe, Okirika, Yenagoa (Niger-Delta basin); 334.198 W/m2 in Ozubulu, Oguta, Obolo (Anambra basin); 332.877 W/m2 in Okitipupa, Atijere (Dahomey basin); 318.021 W/m2 in Eban, Mokwa (Bida basin); 318.682 W/m2 in Kumaganum, Gashua, Geidam (Chad basin); 321.050 W/m2 in Kuchi, Gwandi, Gwadabawa (Sokoto basin); 289.247 W/m2 in Gombe, Potiskum, Kafarati (Upper Benue basin); 312.964 W/m2 in Lokoja, Otukpa (Mid-Benue basin); and 338.962 W/m2 Malumfashi, Kano (Basement Complex). Likely geothermal wells were listed within the research. It is recommended that more ground measurements should be carried out in the basement complexes and sedimentary basins of Nigeria. [ABSTRACT FROM AUTHOR]

Geothermal energy is a new renewable and clean energy source with low cost and wide distribution. In the process of production and reinjection of geothermal well system (mainly including facilities such as wellbore, downhole casing, wellhead device and surface pipe sink), due to various factors such as temperature, pressure, pH, flow velocity, degree of supersaturation, and presence of other salts and ions interfering in solution, precipitation is easily formed, resulting in the phenomenon of scaling in geothermal well system. This phenomenon can seriously affect the normal production operation of the geothermal well system, reduce the service life of the equipment, and cause a series of problems such as energy waste and economic loss. This paper presents a review of recent research progress on scaling and scale inhibition in geothermal well systems. The mechanism of scaling in geothermal well systems, as well as the main technical means of scale inhibition and removal currently adopted were introduced. The future research directions of scale inhibition and descaling in geothermal well systems are also presented. [ABSTRACT FROM AUTHOR]

Knowledge of fluid flow temperature along the wellbore can be useful for a realistic calculation of the total heat production in geothermal wells. Therefore, wellbore modeling is an important part of the characterization of geothermal wells and predicting their future behavior. This study describes the dynamic transport of transient heat and fluid dynamic transport inside a geothermal well and also heat loss in the surrounding rocks. The objective of this investigation is to accurately predict temperature and pressure variations within the producing well GPK2 of the geothermal site Soultz-sous-Forêts. The temperature effect of possible leakage zones in the reservoir section of the production casing was also considered. A single-phase flow modeling was carried out using Comsol software. Our study highlights that the properties of the flow (well flow rates for steady and unsteady flow), of the fluid (density, viscosity, chemical composition), and the well (diameter, length, thermal properties of environments) are parameters, which directly influence the pressure and temperature profiles of the well. A sensitivity study has been carried out to demonstrate the role that these parameters play in the heat transport occurring in this well. According to our simulated results, during the flow of hot water in GPK2 well the production temperature of water decreases by dozen degrees of its downhole temperature. It is also shown that the leakage zone affects the temperature, decreasing it at least by 1–2°C. [ABSTRACT FROM AUTHOR]

This paper reports a comprehensive survey of well drilling time and cost. The models include both specific correlations on various well types and generalised correlations for rough estimation. The models are derived from robust multivariable regression to minimise the residuals. Africa has the highest construction cost component in well drilling and the United States has the lowest. Data in various regions are compared with European and World average drilling data. Drilling time in Italy is similar to Europe and world averages. The proposed model directly estimates both the drilling cost and time to be used in fundamental research and feasibility studies for geothermal power plants applicable worldwide. [ABSTRACT FROM AUTHOR]

The Taupo Volcanic Zone (TVZ) in the central North Island of New Zealand lies across the boundary formed in the late Mesozoic between two major basement regions: the Waipapa and Torlesse composite terranes. However, the precise location of this terrane contact within the TVZ is not well constrained because it is buried beneath Pleistocene volcanic and volcaniclastic sequences locally >3 km thick. Here we report new U-Pb zircon detrital age spectra from basement sandstones and younger Waikora Formation greywacke gravel from five geothermal well core samples and one surface sample. We combine these new data with existing TVZ zircon xenocryst and xenolith age spectra from volcanic host rocks, to correlate these materials with each basement terrane and constrain the likely spatial location and uncertainty of the terrane boundary under the TVZ. Its position with respect to surficial geothermal systems suggests that, at depth, the terrane boundary may have been reactivated by Quaternary extension in the evolving Taupo Rift. Put another way, the past and current position of the Taupo Rift fundamentally may have been controlled by the terrane boundary, which may ultimately be partly responsible for providing enhanced fracture permeability for deep-seated geothermal fluids. [ABSTRACT FROM AUTHOR]

Development of an accurate reservoir model and prediction of reservoir behaviour associated with geothermal exploitation using that model are fundamentally important for sustainable geothermal utilisation. Gravity observation for a few tens of days after a field-wide shut-in of geothermal wells potentially provides valuable constraints to improve reservoir models. We investigated the applicability of superconducting gravimeters (SGs) to short-term observations after shut-ins, as a first step towards the development of a method for reservoir model improvement using short-term gravity data. Results from a reservoir simulation of a shut-in at a geothermal field in Japan showed that gravity change at 20 days after the shut-in was 10 nm/s2. To detect such changes with SGs, locations of SG stations should be chosen to minimise noise sufficient to resolve the signal. Considering that field operations and traffic in geothermal fields can make SG data noisy, laboratory gravity measurements were carried out with a SG to investigate the influence of noise level on signal detection. Test masses, which produced a gravity change (7.7–9.0 nm/s2) comparable to the simulation result, were repeatedly placed and removed above the SG during both day and night times with different ambient noise levels. Test results showed that noise level greatly affected signal detection. The signal was only detected twice, under low-noise conditions with the standard deviations of 1.1 and 5.3 nm/s2. In addition, tests in which the SG was operated without a cryogenic refrigerator revealed that the absence of the refrigerator did not increase the noise level. Enhancing the portability of a SG by reducing its weight can make multi-location noise surveys feasible. Our method, of combining reservoir simulations and preliminary noise surveys, would enable successful SG observations to be made in relatively short periods after shut-ins, which would possibly contribute to the development of a method to obtain additional constraints to be used for reservoir model calibration. [ABSTRACT FROM AUTHOR]

Geothermal exploration is a complex process that spans a number of disciplines. Before a decision is made to drill a geothermal well, there is need for an extensive exploration process to determine the most suitable location. The process of evaluating and analyzing data from individual scientific disciplines can be complex and tedious. Attempts have been made at solving this problem using GIS-based tools but the uptake of these tools is often hindered by the limited knowledge of GIS by decision makers. This paper presents an approach for solving the geothermal exploration question through a web-based spatial decision support system (SDSS) that incorporates the various geosciences through a multi-criteria spatial decision analysis model. The results reveal a decision-making gap that is to be filled using a novel, automated exploration SDSS. This approach hypothesizes an easier and faster decision-making process. The research focuses on Olkaria, an active geothermal area in Kenya, East Africa and highlights a pragmatic approach to identifying priority areas for drilling. It evaluates contributions made by many disciplines in identifying potential sites ideal for harnessing geothermal energy and the gaps that emerge in an effort to synergize the results from the different disciplines. [ABSTRACT FROM AUTHOR]