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Hvalfjordur Sub-Sea Tunnel Project, Iceland
Published in C.V.J. Varma, A.R.G. Rao, Tunnelling Asia ’97, 2020
Colin G. Rawlings, Milan Simic
The stratigraphic lava pile is generally dipping 5-10° towards the SE (140 - 160°). The lava successions on the northern side of Hvalfjordur are stratigraphically below the successions on the southern side. Two relatively dense subvertical fault and dyke systems exist. The dykes generally range in thickness from 2-8m (up to 15m thick). The major fault and dyke system has a northeast to southwest trend and the minor fault and dyke system has a northwest to southeast trend. Geothermal alteration has affected the core of the volcanoes and the immediate surroundings have suffered high thermal alteration, usually resulting in reduced strength and secondary clay minerals filling the joints. Groundwater flows are expected to be most pronounced along the faults and dykes. The geothermal gradient is expected to be about 150° C per km depth.
Geothermal Energy Resources
Published in Brian D. Fath, Sven E. Jørgensen, Megan Cole, Managing Air Quality and Energy Systems, 2020
The geothermal gradient expresses the increase in temperature with depth in the Earth’s crust. Down to the depths accessible by drilling with modern technology, i.e., over 10,000 m, the average geothermal gradient is about 2.5–3°C/100 m. For example, if the temperature within the first few meters below ground level, which on average corresponds to the mean annual temperature of the external air, is 15°C, then we can reasonably assume that the temperature becomes about 65–75°C at 2000 m depth, 90–105°C at 3000 m, and so on for a further few thousand meters. There are, however, vast areas in which the geothermal gradient is far from the average value. In areas in which the deep rock basement has undergone rapid sinking, and the basin is filled with geologically “very young” sediments, the geothermal gradient may be lower than 1°C/100 m. On the other hand, in some “geothermal areas,” the gradient is more than 10 times the average value (further details are given in Dickson and Fanelli[2]).
Geophysical investigation techniques: heat
Published in Ian Acworth, Investigating Groundwater, 2019
Groundwater assumes the temperature of the surrounding rock. A profile of groundwater temperature carried out down a borehole is therefore equivalent to measuring the geothermal gradient. Groundwater temperatures have been extensively measured across the Great Artesian Basin (Cull and Conley, 1983). The temperature is normally established a year or so after the borehole is completed to avoid the impact of disturbances caused by drilling. The temperature of water in wells tapping aquifers in Lower Cretaceous and Jurassic sediments generally ranges from about 30 °C to 50 °C, but, in many areas of the basin, temperatures at the well head are as much as 100 °C. Water is discharged from mound springs along the western margin at temperatures ranging from about 20 °C to 40 °C. The average geothermal gradient in the GAB is 48 °C/km, which exceeds the global average of 33 °C/km. Polac and Horsfall (1979) noted a range from 15.4° to 102.6 °C/km with the wide variation taken as indicating significant movement of water vertically along fracture zones (Polac and Horsfall, 1979).
A comprehensive review on current methods of geothermal analysis of oil reservoir – case study
Published in Petroleum Science and Technology, 2022
Mohammad Zeyghami, Mohammad Taghizadeh Sarvestani
Geothermal analysis is an important step performed in any reservoir study. The main goal of geothermal analysis is to find temperature gradient of the reservoir. Sub-surface temperature increases with depth and the rate at which this happens with respect to increasing depth is called geothermal gradient (Cosentino 2001). In most hydrocarbon-producing areas, the gradient is usually in the range of 0.6 to 1.6 °F per 100 ft of depth increase (1.1 to 2.9 °C per 100 m) (Holstein and Lake 2007). Determination of reservoir temperature and its gradient is an important task in basic reservoir engineering studies, because the results affect the accuracy of resistivity logs analysis, physical properties of reservoir fluids and hydrocarbon phase state (Ren et al. 2020), and some downhole operations design (Hirakawa 1982). Moreover, calculation of hydrocarbon volumes (estimation of oil and gas formation volume factors, gas solubility), predictions of the gas hydrate prone zones, determination of heat flow density and evaluation of geothermal energy resources (Lima, Tokita, and Hatanaka 2013) require knowledge of the undisturbed formation temperature (Kutasov and Eppelbaum 2005).
Diagenesis impact on a deeply buried sandstone reservoir (Es1 Member) of the Shahejie Formation, Nanpu Sag, Bohai Bay Basin, East China
Published in Australian Journal of Earth Sciences, 2019
M. Kashif, Y. Cao, G. Yuan, W. Jian, X. Cheng, P. Sun, S. Hassan
The burial and thermal history of the Nanpu Sag suggests continuous and rapid subsidence and deposition developed during the Neogene (Figure 2b; Guo et al., 2012; Wang, Zheng, Xu, & Dong, 2008). The overall burial depth of the Shahejie Formation in the structural belt 2 and 3 areas occurs more than 4000 m below present-day sea level. The current geothermal gradient is 32 °C/km, the average surface temperature is 14 °C and the maximum temperature is 135 °C at depths greater than 4000 m. In the studied part of Nanpu Sag (surrounding the Caofeidian sub sag), there are three main source rocks at greater depths (Ed3 > 4500 m, Es1 > 5400 m and Es34 > 6000 m). The subsurface temperature of Ed3 and Es1 is almost 140 °C and 170 °C, respectively and about 200 °C for Es34. The Ed3 source rocks (0.8% Ro) are mature in the oil generation window and the Es34 (>2% Ro) are highly mature (Guo et al., 2012). The Es1 source rock reached hydrocarbon generation initiation at ca 23 Ma, reaching a high maturity to generate wet gas (Figure 2c).
The impact of rock fracturing and pump intake location on the thermal recovery of a standing column well: model development, experimental validation, and numerical analysis
Published in Science and Technology for the Built Environment, 2019
Gabrielle Beaudry, Philippe Pasquier, Denis Marcotte
As the local geothermal heat flux and far-field thermal conditions affect groundwater temperature and thereby SCWs performance, temperature profiles were measured in the IW prior to any heating or cooling activity (see Figure 3). Submersible temperature sensors with 0.25 °C accuracy and 20 s response time were taken down the well with a thermal stabilization period of 60 s between each displacement. The latter were used since the fiber-optic system was not put into place before November 2017. Shallow temperatures in the borehole (0–30 m) showed significant variations attributable to seasonal temperature fluctuations. A geothermal gradient of 2.3 ± 0.1 °C/100 m associated with the local geothermal heat flux was observed from 60 m depth (8.9 °C) down to 150 m (10.8 °C).