Spatio-temporal variations of shallow seismic velocity changes in Salton Sea Geothermal Field,California in response to large regional earthquakes and long-term geothermal activities

We measure spatio-temporal variations of seismic velocity changes in Salton Sea Geothermal Field,California based on cross correlations of daily seismic traces recorded by a borehole seismic network from December 2007 to January 2014.We find clear co-seismic velocity reductions during the 2010 M 7.2 El Mayor–Cucapah,Mexico earthquake at~100 km further south,followed by long-term recoveries.The co-seismic reductions are larger with longer post-seismic recoveries in higher frequency bands,indicating that material damage and healing process mostly occurred in the shallow depth.In addition,the co-seismic velocity reductions are larger for ray paths outside the active fluid injection/extraction regions.The ray paths inside injection/extraction regions are associated with smaller co-seismic reductions,but subtle long-term velocity increases.We also build 3D transient water flow models based on monthly injection/extraction rates,and find correlations between several water flow parameters and co-seismic velocity reductions.We interpret the relative lack of co-seismic velocity changes within the geothermal region as unclogging of fracture network due to persistent fluid flows of geothermal production.The long-term velocity increase is likely associated with the ground water depletion and subsidence due to net production.

Integrated application of gravity,aeromagnetic,and electromagnetic methods in exploring the Ganzi geothermal field,Sichuan Province,China

The Ganzi geothermal field is located in the Songpan-Ganzi orogenic belt in Sichuan Province.Many hot springs are exposed along the Yalahe valley in Ganzi geothermal field,which is a favorable area for hightemperature geothermal resource exploration.However,the geological model of heat exchange,the regional structure controlling hydrothermal convection and the development model of geothermal reservoirs are still unclear.Therefore,further studies are necessary to meet the geothermal exploration requirements in the middle and deep strata of this geothermal field.In this study,a geological model of the geothermal system of Ganzi geothermal field is proposed.We are convinced that there exists a hydrothermal convection system in the Ganzi geothermal field,the heat transfer of which is accomplished through deep-rooted major faults.Therefore,the identification of deep-rooted major faults and the description of geothermal reservoirs are the research objects of the integrated geophysical methods.The main factors controlling the geothermal reservoirs in the deep-rooted Xianshuihe major fault and Yalahe fault zones are analyzed by using gravity,aeromagnetic,and electromagnetic methods and techniques.The analysis results of regional gravity and aeromagnetic anomalies show that the Xianshuihe major fault has produced obvious gravity and aeromagnetic anomalies on the surface,and thus the position and strike of this fault can be accurately predicted by inversion of the aeromagnetic anomalies.Geothermal reservoirs show low-resistivity anomalies in the electromagnetic profile.The inversion results of the controlled source audio-frequency magnetotelluric(CSAMT)data show that geothermal reservoirs are mainly developed along the Yalahe valley,and the west side of the valley is more favorable for geothermal exploration.This study is of guiding significance to the efficient exploitation and utilization of the Ganzi geothermal field.

Factors controlling the distribution of granite reservoirs of hydrothermal system type in South China:A case study of Huangshadong geothermal field in Yuezhong Depression,China

The granitoids widely distributed in South China are characterized by multi-stage evolution via episodic intrusions,in a complex geodynamic setting.Since granites have high radioactive heat generation and excellent thermal conductivity,a deep moderate-to high-temperature geothermal system can be formed in the presence of high-quality,fissured granite geothermal reservoirs and thermal insulation with appropriate cap rocks.The key to exploring deep geothermal resources is to identify high-quality fissured granite geothermal reservoirs of a certain scale in a thermal anomaly zone with high background heatflow values.To determine the controlling effects of the distribution and development characteristics of granite geothermal reservoirs on the generation and enrichment of deep geothermal resources,this study analyzed the characteristics of the geothermal reservoirs in the Huangshadong geothermal field in the Yuezhong Depression,Guangdong Province,and their controlling effects on the formation of geothermal resources.The results are as follows.The hydrothermal system in the Huangshadong geothermal field mainly distributed in the contact zones between magmatic plutons and surrounding rocks,is significantly controlled by faults,followed by neoid volcanic apparatus and magmatic activities.That is,the geothermal system therein is under joint control of structures and magmas.Moreover,fractured zones of neoid transtensional faults conduct the geothermal water in the hydrothermal system and control its shallow discharge.Therefore,the hydrothermal system in the study area is characterized by the control of transpressional tectonic zone and volcanic apparatus,and geothermal water conduction through fractured zones of transtensional faults.

Simulation of thermal breakthrough factors affecting carbonate geothermalto-well systems

Fractures play a pivotal role in carbonate thermal storage systems,serving as primary hydraulic conductivity channels that significantly influence thermal breakthrough times and heat extraction efficiency in geothermal-to-well systems.Their impact is critical for well placement and system life prediction.This paper focuses on a geothermal-to-well system within the carbonate reservoir of the Wumishan formation in the Rongcheng geothermal field,Xiong'an new area.It employs a combination of field tests and numerical simulations to determine the permeability of the reservoir and the evolution of fractures between wells.It also examines the influence of fracture width and roughness coefficient on the seepage and temperature fields under various injection scenarios and predicts thermal breakthrough times for production wells.The results show:Higher permeability is observed near well D16 compared to well D22 within the studied geothermal-to-well systems.Wider fractures between wells result in faster temperature decline in production wells.Lower injection flow rates lead to slower temperature reduction in injection wells.The use of roughness coefficients minimizes temperature variations in production wells.This study not only offers guidance for the development and utilization of the geothermal well system,but also contributes to a deeper understanding of the groundwater seepage and heat transfer process influenced by fractures.

Present Geothermal Fields of the Dongpu Sag in the Bohai Bay Basin

The Dongpu sag is located in the south of the Bohai Bay basin,China,and has abundant oil and gas reserves.To date,there has been no systematic documentation of its geothermal fields.This study measured the rock thermal conductivity of 324 cores from 47 wells,and calculated rock thermal conductivity for different formations.The geothermal gradient and terrestrial heat flow were calculated for 192 wells on basis of 892 formation-testing data from 523 wells.The results show that the Dongpu sag is characterized by a medium-temperature geothermal field between stable and active tectonic areas,with an average geothermal gradient of 32.0℃/km and terrestrial heat flow of 65.6 mW/m2.The geothermal fields in the Dongpu sag is significantly controlled by the Changyuan,Yellow River,and Lanliao basement faults.They developed in the Paleogene and the Dongying movement occurred at the Dongying Formation depositional period.The geothermal fields distribution has a similar characteristic to the tectonic framework of the Dongpu sag,namely two subsags,one uplift,one steep slope and one gentle slope.The oil and gas distribution is closely associated with the present geothermal fields.The work may provide constraints for reconstructing the thermal history and modeling source rock maturation evolution in the Dongpu sag.

The Statistical Prediction of the Vitrinite Reflectance and Study of the Ancient Geothermal Field in Songliao Basin,China

The resource of the gas from coal and coal measures deep in Songliao Basin has been drawing more and more attention to . It is necessary to find out the evolution regularity of the geothermal field of the basin in addition to a series of geological studies in order to predict its resources because the ancient geothermal field of the basin is one of the main factors controlling the generation , evolution and disappearance of oil and gas . In the recent twenty years , it is generally believed that vitrinite reflectance is the best quantitative marker for the ancient geothermal field . In the present paper , a systematic study of the vitrinite reflectance value of Songliao Basin and its influence factors is made by multiple statistical analysis so as to reconstruct the evolutional process of the Moho and the corresponding geothermal field . Then , an overall prediction is made of the vitrinite reflectance and the distribution of J3-K1 fault basin group at the bottom of Songliao Basin , which provides the evidence for the further prediction of the gas potentiality from coal and coal measures deep in the basin .

Causes of geothermal fields and characteristics of ground temperature fields in China

There are many arguments on energy sources and main controlling factors of geothermal fields, so a systematic study on the distribution of ground temperature fields shall be necessary. In this paper the thermal conduction forward method of geothermal field is used to simulate cooling rate of abnormal heat sources and heat transfer of the paleo-uplift model. Combined with a large number of geothermal field exploration cases and oil exploration well temperature curves of domestic and foreign, the following conclusions are drawn:(1) According to the magmatic activity time, the magmatism activities are divided into two categories: Magma active areas(activity time < 500 000 years) and weak/magma inactive areas(activity time > 500 000 years). The latter has a fast cooling rate(the cooling time of the magma pocket buried around 10 km is less than 200 000 years) after it has intruded into the shallow layer and it has no direct contribution to modern geothermal fields;(2) China belongs to a weak/magma inactive area such as Tengchong region and Qinghai-Tibet region because the chronological data of these regions show that its magma activity time is more than 500 000 years;(3) The temperature of most geothermal fields can be obviously divided into three segments in the vertical direction: A high geothermal gradient segment(Segment H) at the surface, then a low geothermal gradient segment(Segment L) at a secondary depth, and finally a lower temperature segment(Segment D) at a deeper depth. The temperature isoline presents a mirror reflection relation on the temperature profile, indicating that geothermal field is dominated by heat conduction, rather than having an abnormally high temperature "heat source" to provide heat;(4) Near-surface(0-5 km) materials' lateral heterogeneity caused by tectonic movement shall probably be the main controlling factor of ground temperature fields.

Geothermal Field and Tectono-Thermal Evolution since the Late Paleozoic of the Qaidam Basin,Western China

The Qaidam basin is the largest intermountain basin inside Tibet, and is one of the three major petroliferous basins in western China. This study discussed the geothermal field and tectono-thermal evolution of the basin, in an effort to provide evidence for intracontinental or intraplate continental dynamics and basin dynamics, petroleum resources assessment, and to serve petroleum production.

Geology and development of geothermal field in Neogene Guantao Formation in northern Bohai Bay Basin: A case of the Caofeidian geothermal heating project in Tangshan, China

Taking the Gaoshangpu-Liuzan geothermal field in the Nanpu sag of the Bohai Bay Basin as the research object, this paper discusses the geological conditions and potential of the geothermal resources of the Guantao Formation in the study area, and introduces the development practice of geothermal energy heating in Caofeidian. The average buried depth of the Guantao Formation is 1500–2500 m, the lithology is dominated by sandy conglomerate, and the average thickness of thermal reservoir is 120–300 m. The average porosity of thermal reservoir is 28%–35%, the permeability is(600–2000)×10^(-3) μm^(2), and the temperature of thermal reservoir is 70–110 ℃. The formation has total geothermal resources of 13.79×10^(18) J, equivalent to 4.70×10^(8) t of standard coal. Based on a large amount of seismic and drilling data from oil and gas exploration, this study carried out high quality target area selection, simulation of sandstone thermal reservoir, and production and injection in the same layer. The geothermal heating project with distributed production and injection well pattern covering an area of 230×10^(4) m^(2) was completed in the new district of Caofeidian in 2018. The project has been running steadily for two heating seasons, with an average annual saving of 6.06×10^(4) t of standard coal and a reduction of 15.87×10^(4) t of carbon dioxide, achieving good economic and social benefits. This project has proved that the Neogene sandstone geothermal reservoir in eastern China can achieve sustainable large-scale development by using the technology of "balanced production and injection in the same layer". It provides effective reference for the exploration and development of geothermal resource in oil and gas-bearing basins in eastern China.

Surface geochemical anomaly pattern of medium-to-high temperature geothermal systems in South China and its application

The existence of thermal storage will correspondingly increase the temperature of surrounding strata and promote the continuous expansion,volatilization,upward migration,and loss of gas in the strata.As a result,a low-concentration gas field will be formed in the strata above geothermal reservoirs.Geothermal reservoirs could in turn heat formation water and increase the solubility of soluble inorganic salts in the surrounding rocks and the total dissolved solids(TDS)content in the formation water.Since water can strongly wet and permeate strata,the dissolved inorganic salts migrate into upper strata along with water,giving rise to the formation of a high-concentration inorganic salt field in the strata above geothermal reservoirs.A higher geothermal reservoir temperature corresponds to more significant characteristics mentioned above.Therefore,a medium-to-high temperature geothermal system has a surface geochemical anomaly pattern of high inorganic salt concentrations and low gas concentrations(also referred to as the high-salt and low-gas pattern).This pattern is applied to the surface geochemical exploration of the two geothermal fields in Guangdong Province,i.e.,the Huangshadong geothermal field in Huizhou City and the Xinzhou geothermal field in Yangjiang City,revealing low-concentration gas fields above both.The application results also show that the exposed thermal spring water in both geological fields has higher concentration of dissolved inorganic salt than the surface water and nearby seawater,forming high-amplitude anomalies on the surface above geothermal reservoirs.These characteristics,as well as the measured temperature at known geothermal wells,verify the validity of the high-salt and low-gas pattern of medium-to-high temperature geothermal systems proposed in this study.Moreover,the high-salt and low-gas pattern proposed predicts three favorable medium-to-high temperature geothermal zones in the surface geochemical exploration of the Shiba Basin near the Huangshadong geothermal field.

Controlling effects of cap rocks on the formation of deep geothermal resources

Cap rocks with high thermal insulation are important for deep geothermal systems at a depth of 3000‒6000 m.Based on the deep geothermal geological conditions in the Fujian-Guangdong-Hainan area of South China,this study established an ideal geological model of reservoir-cap rock assemblages and simulated the geothermal field distribution of cap rocks of different thicknesses and thermal conductivity.The simulation results show that the vertical geothermal temperature distribution in an uplifted area of a depression was present as inverted mirror reflections relative to the elevated area of the basement.Specifically,the isotherms above the elevated area are convex in shape,while those below the elevated area are concave.There is a temperature equilibrium line between the convex and concave isotherms.The heat flow moves from the depressed area to the uplifted area below the temperature equilibrium line and migrates in an opposite direction above the line.On this base,this study conducted the inversion of geothermal temperature fields in typical areas with thin,moderately thick,and thick cap rocks.The results indicate that,at the depth of 3000e6000 m,areas with thin cap rocks(igneous rock zone in the coastal area of Fujian)mainly host moderate-to low-temperature hydrothermal resources;areas with moderately thick cap rocks(Yuezhong Depression)have the geothermal temperature ranging between 100℃and 200℃and may develop moderate-to high-temperature hydrothermal resources and hot dry rocks(HDRs),with the former superimposing on the latter;and areas with thick cap rocks(onshore Beibuwan Basin)have a geothermal temperature of 120‒220℃,and contains mainly moderate-to high-temperature hydrothermal resources and HDRs.Therefore,it is recommended that the evaluation,exploitation,and utilization of deep geothermal resources be carried out according to the burial depth of the temperature equilibrium line and the specific demand for geothermal resources.

Characteristics of the Reservoir of the Rehai Geothermal Field in Tengchong, Yunnan Province, China

The Rehai geothermal field in Tengchong County, Yunnan Province is a significant high-temperaturehydrothermal convective system. The geothermal reservoir is composed of granite. Various geothermometersare used to evaluate the reservoir temperature. The most likely temperature of the reservoir as representedby T_(Na-K-Ca) is about 230℃. The chemical and isotopic compositions of fluids before boiling within the reser-voir are estimated. The mixing and dilution of cold and warm waters are discussed. The Rehai geothermal fieldis a high-temperature (hot) water system with the subsurface boiling zone close to the surface. The reservoirpressure at different depths is calculated. And finally the water-rock equilibration is inferred.

Characterization of deep ground geothermal field in Jiahe Coal Mine

Research into the characteristics of geothermal fields is important for the control of heat damage in mines. Based on measured geothermal data of boreholes from 200 m to 1200 m in a Jiahe Coal Mine, we demonstrate non-linear but increasing relations of both geo-temperatures and geothermal gradients with increases depth. Numerically, we fitted the relationship between geo-temperatures and depth, a first-order exponential decay curve, formulated as: T(h) = 4.975 + 23.08 exp(h/1736.1).

Unsteady temperature field of surrounding rock mass in high geothermal roadway during mechanical ventilation

To explore the spatial-temporal evolution law of rock mass temperature in high geothermal roadway during mechanical ventilation, a series of experiments were conducted based on the physical simulation test system of thermal and humid environment in high geothermal roadway, which is a method independently developed by China University of Mining and Technology. The results indicate that during ventilation, the disturbed region of the temperature extends gradually from shallow area to deep area in the surrounding rock mass of the roadway. Meanwhile, the temperature increases as the exponential function from shallow area to deep, with steady decrease of the temperature gradient and heat flux. As the ventilation proceeds, the relationship between dimensionless temperature and dimensionless time approximately meets Hill function.

Gas Geothermometry in the Hveragerdi High-Temperature Geothermal Field, SW Iceland

Five gas geothermometers based on the concentrations of CO\-2, H\-2S, H\-2, CH\-4, N\-2 and Ar in fumaroles and wet\|steam wells are applied to estimating subsurface temperatures in the Hveragerdi high\|temperature geothermal field, SW Iceland. The results for fumaroles indicate that the calculated subsurface temperatures decrease from the northern part to the southern part of the field. The CO\-2\|geothermometer gives the highest temperature values, with an average of 256℃ for the northern part, and 247℃ for the southern part. The H\-2S\|geothermometer reveals an aquifer temperature of 211℃ for the northern part, and 203℃ for the southern part. The H\-2\|geothermometer gives an average subsurface temperature of 229℃ for the northern part, and 184℃ for the southern part, which agrees excellently with the measured temperatures in wet\|steam wells. The measured borehole temperatures in the field range from 215℃ to 230℃ for the northern part, and from 167℃ to 198℃ for the southern part. The CO\-2/H\-2\|geothermometer gives the lowest subsurface temperature values, with an average of 203℃ for the northern part, and 143℃ for the southern part. The CO\-2/N\-2\|geothermometer gives 249℃ for the northern part and 235℃ for the southern part. For the data from wells, the CO\-2\|, H\-2S\|, and H\-2\|geothermometers, give average subsurface temperatures of 247℃ for the northern part and 246℃ for the southern part, 213℃ for the northern part and 220℃ for the southern part, and 217℃ for the northern part and 216℃ for the southern part, respectively. The CO\-2/H\-2\|geothermometer indicates an average subsurface temperature of about 200℃ for both the northern part and the southern part. The CO\-2/N\-2\|geothermometer gives an average subsurface temperature of 180℃ for the northern part and 259℃ for the southern part. The discrepancy between the estimated subsurface temperatures obtained by the various gas geothermometers has been explained in this paper. By integrating the solute geothermometric results, mixing model studies and gas geothermometric results, the maximum subsurface temperatures of the Hveragerdi high\|temperature geothermal system may be considered to be about 240-260℃.

Geochemical characteristics of geothermal water in Weiyuan geothermal field, Huzhu County, Qinghai Province

According to the chemical composition of thermal water from Geothermal Well DR2010 located in the Weiyuan Geothermal Field of Huzhu County in Qinghai Province, the groundwater recharge, age and geothermal resource potential of the thermal water are discussed by using the methods of Langelier-Ludwig Diagram, isotopic hydrology and geochemical thermometric scale. The analysis results indicate that the Weiyuan Geothermal Field is located in the northern fringe of Xining Basin, where the geothermal water, compared with that located in the central area of Xining Basin, is characterized by greater water yield, shallower buried depth of thermal reservoir and easier exploitation. Due to its active exchange with the modern cold water, the thermal water here shows relatively younger age. These findings provide a hydro-geochemical evidence for the exploitation of Weiyuan Geothermal Field.

Low-Temperature Properties of CePt_3P Tuned by Magnetic Field

We present low-temperature magnetization, magnetoresistance and specific heat measurements on the Kondo lattice compound CePt_3P under applied magnetic fields up to 9.0 T. At zero field, CePt_3P exhibits a moderately enhanced Sommerfeld coefficient of electronic specific heat γCe=86 mJ/mol·K^2 as well as two successive magnetic transitions of Ce 4f moments: an antiferromagnetic ordering at T_(N_1) = 3.0 K and a spin reorientation at T_(N_2)=1.9 K. The value of T_(N_1) shifts to lower temperature as magnetic field increases, and it is ultimately suppressed around B_c ～3.0 T at 1.5 K. No evidence of non-Fermi liquid behavior is observed around B_c down to the lowest temperature measured. Moreover, γ decreases monotonously with increasing the magnetic field. On the other hand, the electrical resistivity shows an anomalous temperature dependence ρ∝T^n with the exponent n decreasing monotonously from ～2.6 around B_c down to ～1.7 for B = 9.0 T. The T-B phase diagram constructed from the present experimental results of CePt_3P does not match the quantum criticality scenario of heavy fermion systems.

Characteristics of shallow geothermal fields in major cities of Tibet Autonomous Region

Based on the project titled "Investigation and evaluation of shallow geothermal energy in major cities of Tibet Autonomous Region", the distribution characteristics and occurrence conditions of shallow geothermal fields in these cities were introduced in this paper. To this end, relevant data in Lhasa, Shigatse and Nyingchi Cities through vertical thermometry was a focus, so as to analyze groundwater temperature and the distribution law of strata with constant temperature. Then through comprehensive comparisons and analysis of the relationship between groundwater temperature and climate, differences in this aspect of Nagqu City were taken as a typical case to clarify formation of geothermal field and corresponding influence on groundwater temperature, furthermore providing basic data for rational development and utilization of shallow geothermal energy in Tibet Autonomous Region.

Numerical Simulation for Hot Dry Rock Geothermal Well Temperature Field

Study on temperature distribution simulation during cementing of hot dry rock (HDR) geothermal well is rare. It has important guiding significance to simulate the construction process of temperature distribution of hot dry rock on site construction. Based on numerical simulation of HDR considering heat-fluid-solid coupling, the influence of temperature distribution on well cementing is analyzed when the drilling fluid cycles and reaches stable state, respectively, and when the cement slurry is injected during the cementing process. It is found that the seepage at the well bottom accelerates the flow velocity of wellbore;the stable temperature change is less than the cyclic temperature change;and the upper and lower temperature variation of the stratum is greater when the cement slurry is injected. Therefore, as to cement retarder involved, the influence of temperature variation on concretion should be considered during cementing of the hot dry rock geothermal well.

Oxygen Isotope Study of Silica Sinter from the Osorezan Geothermal Field, Northeast Japan

Silica sinter developed on the northern shore of Lake Usoriyama in the Osorezan geothermal field was examined for the occurrence, texture, crystallinity of silica minerals, and the concentrations of trace elements and oxygen isotopes. The silica sinter consists of a thick eastern mound (layer A) and a thin western part (layer B). Most of the silica sinter is composed of alternating bands of thin layers of silica minerals with colors varying from white to yellow and reddish gray. There is a unique stromatolitic texture, an aggregate of stratified concentric layers that extends upward and is red to reddish gray in color in the middle of layer A. Silica minerals, mainly opal-A and opal-CT, dominate the mineralogical constituents of the sinter. The δ18O of the silica mineral in layer A varies between 13‰ and 26‰, while layer B has higher values, between 19‰ and 33‰. The hydrothermal fluid from which the silica sinter precipitated is dominated by meteoric water is similar to present-day hot spring water.