Areas Of High Heat Flow Research Articles

Predicting Terrestrial Heat Flow in North China Using Multiple Geological and Geophysical Datasets Based on Machine Learning Method

Geothermal heat flow is an essential parameter for the exploration of geothermal energy. The cost is often prohibitive if dense heat flow measurements are arranged in the study area. Regardless, an increase in the limited and sparse heat flow observation points is needed to study the regional geothermal setting. This research is significant in order to provide a new reliable map of terrestrial heat flow for the subsequent development of geothermal resources. The Gradient Boosted Regression Tree (GBRT) prediction model used in this paper is devoted to solving the problem of an insufficient number of heat flow observations in North China. It considers the geological and geophysical information in the region by training the sample data using 12 kinds of geological and geophysical features. Finally, a robust GBRT prediction model was obtained. The performance of the GBRT method was evaluated by comparing it with the kriging interpolation, the minimum curvature interpolation, and the 3D interpolation algorithm through the prediction performance analysis. Based on the GBRT prediction model, a new heat flow map with a resolution of 0.25°×0.25° was proposed, which depicted the terrestrial heat flow distribution in the study area in a more detailed and reasonable way than the interpolation results. The high heat flow values were mostly concentrated in the northeastern boundary of the Tibet Plateau, with a few scattered and small-scale high heat flow areas in the southeastern part of the North China Craton (NCC) adjacent to the Pacific Ocean. The low heat flow values were mainly resolved in the northern part of the Trans-North China Orogenic belt (TNCO) and the southmost part of the NCC. By comparing the predicted heat flow map with the plate tectonics, the olivine-Mg#, and the hot spring distribution in North China, we found that the GBRT could obtain a reliable result under the constraint of geological and geophysical information in regions with scarce and unevenly distributed heat flow observations.

The Curie depths of the United Arab Emirates: Implications for regional thermal structures and tectonic terranes

We have determined the depth of the Curie isotherm in the United Arab Emirates (UAE) using a modified centroid method based on the fractal distribution of sources. The derived spatial coverage of Curie depths and geothermal gradients are consistent with the geothermal gradients derived from the bottom hole temperatures measured in exploration wells and reveal three NNE–SSW to NE–SW-trending regions of shallow Curie depths. These are: (1) the north-western offshore region of the UAE with Curie depths of 11–25 km; (2) in central UAE ranging from the Shah field in south-central regions of the UAE to the northern offshore region of Dubai, with Curie depths of 10–25 km, high geothermal gradients of 22.1–55.3 °C/km, and high heat flows of 55.3–138.3 mW/m2; and (3) in the eastern region of the UAE from Al Ain to Dibba and the Gulf of Oman, with medium Curie depths of 25–30 km. These regions of shallow Curie depths are flanked by two NS to NE–SW-trending regions of deeper Curie depths between 35 and 50 km with low geothermal gradients and heat flows of 11.1–15.8 °C/km and 27.8–39.5 mW/m2 respectively. We interpreted these regional NE–SW trends to be related to tectonic terranes composed of magmatic arcs and microcontinental fragments that have amalgamated to form the crust beneath the UAE. In addition, many large hydrocarbon fields are located immediately above or on the margins of these shallow Curie depth zones, suggesting that the shallow Curie depth could have played a critical role in the maturation, migration, and entrapment of hydrocarbons in the UAE. Furthermore, since these zones delineate areas of high heat flow (>100 mW/m2) and high geothermal gradients (∼40 °C/km) they represent areas in which future geothermal exploration could be focused.

Modeling of Continental Normal Fault Earthquakes

AbstractThe magnitude of earthquakes on continental normal faults rarely exceeds 7.0 Mw. However, because of their vicinity to large population centers they can be highly destructive. Long recurrence time, relatively small deformations, and limited observations hinder our understanding of the deformation patterns and mechanisms controlling the magnitude of events. Here, this problem is addressed with 2D thermomechanical modeling of normal fault seismic cycles. The 2020 Samos, Greece Mw7.0 earthquake is used as an example as it is one of the largest and most studied continental normal fault earthquakes. The modeling approach employs visco‐elasto‐plastic rheology, compressibility, free surface, and a rate‐and‐state friction law for the fault. Modeling of the Samos earthquake suggests the pore fluid pressure ratio on the fault ranges from 0 to 0.7. The model demonstrates that most of the deformation during interseismic and coseismic periods, besides on the fault, occurs in the hanging wall and footwall below the seismogenic part of the fault. The largest vertical surface displacement during the earthquake is the subsidence of the hanging wall in the vicinity of the fault, while the uplift of the footwall and remote part of the hanging wall is significantly smaller. Modeling of the seismic cycles on normal faults with different setups shows the dependency of the magnitude on the thermal profile and dipping angle of the fault; low heat flow and low dipping angle are favorable conditions for the largest events, while steep normal faults in the areas of high heat flow tend to have the smallest magnitudes.

Ground surface temperature monitoring data analysis and applications to geothermal exploration in volcanic areas, Mount Meager, western Canada

The southern Mount Meager area has been studied for its geothermal resource potential for a half century. Although attempts to commercialize the resource were unsuccessful in the past, a large volume of surface and subsurface geoscience data have been collected and made publicly available, making the Mount Meager area a unique natural laboratory for testing new ideas or tools for geothermal exploration. This study investigates the potential of using a ground surface temperature (GST) monitoring network as a tool in geothermal resource exploration. Twenty-two temperature data loggers were deployed in, and surrounding, the core area of the geothermal prospect for nearly one year. The collected temperature time series were analyzed statistically, and machine learning methods such as hierarchical clustering and k-means classification, were applied to data interpretation. The temporal variation of measured temperature can be divided into four segments: 1) snow free, 2) snow affected, 3) snow curtain, and 4) snow melt seasons. The intensity of daily ground temperature variation in the snow free season shows clear environmental and topographic footprints and is complicated by soil properties. The sites with a short period of near zero GST during the snow curtain period is spatially coincident with high heat flow areas. The measured mean GST shows a close affinity with subsurface heat flow and shallow ground water circulation, suggesting that GST time series contain information indicative of subsurface geothermal anomalies and that a GST monitoring network could be an effective tool for geothermal resource exploration in high latitude and/or elevation areas with seasonal snow cover.

Heat flow data and thermal structure in northeastern Japan

New heat flow data corrected for climate change over Northeastern Japan were obtained using the temperature profile of the borehole of the High Sensitivity Seismograph Network (Hi-net). The obtained spatial distribution of heat flow shows low heat flow on the forearc side, high heat flow along the Ou Backbone Range, and low heat flow in the plains on the back-arc side. However, the distribution is not clearly divided into high and low heat flow along the VF front; for example, the low heat flow extends from near the northern Kitakami Mountains on the forearc side to the Ou Backbone Range crossing the VF, while the high heat flow extends to the central Kitakami Mountains and Sendai plain on the forearc side. In addition, a crustal temperature structure model was developed that considers into account the presence of sedimentary layers, the temperature dependence of thermal conductivity, and differences in heat generation due to lithology. There is a good correlation between this temperature structure and the lower limit of the seismogenic layer, which is between 400 and 450 °C. Compared to previous studies, the crustal thermal structure calculation method assumed is a model whose estimated temperature distribution is sensitive to structural differences; however, a more accurate estimation of the temperature structure is possible if detailed structural information is available. On the other hand, it seems necessary to treat fluid behavior in more detail in areas of high heat flow. However, the estimation of crustal temperature structure, especially in regions with thick sedimentary layers, is considered an improvement over the previous study.Graphical

Main Controlling Factors and Formation Mode of Geothermal Anomaly in Eastern Chenghe Mining Area of Weibei Coalfield

Geothermal anomaly has gradually become a prominent issue affecting the efficient mining of coal with the depth of coal mining increasing in eastern Chenghe mining area of Weibei coalfield. Here, we comprehensively investigated the distribution characteristics of the present geothermal field, analyzed the main controlling factors, and constructed forming mode of geothermal anomaly by the temperature measurement in surface borehole and underground water, combined with coal-rock thermal conductivity test. The results show that the geothermal gradient ranged from 25.7°C/km to 54.3°C/km. The areas with geothermal gradient greater than 30°C/km accounted for 88.31%, and there was the highest gradient value in the southeast F1 fault zone. The heat flow was between 66.81 mW/m2 to 128.49 mW/m2, which belonged to the obvious high heat flow area. Under the action of the main controlling factors such as fault, fold, coal-rock thermal conductivity, and groundwater activity in the region, the geothermal gradient and geothermal heat flow values showed an increasing trend from northwest to southeast. According to the distribution characteristics of heat flow and the action mechanism of main controlling factors, the geothermal anomaly in the study area was finally divided into two forming modes, i.e., fault-deep circulating hot water uplifting type and coal seam heat resistance-fold type. The research provides guidance for the geothermal hazard prevention of coal mine and the rational development and utilization of geothermal resources.

Geodynamic Characteristics in the Southwest Margin of South China Sea

The strike-slip fault system in the southwestern margin of South China Sea (SCS) lies on the transition zone between the continental shelf and slope of SCS, which is an important ocean–continent boundary. By using submarine heat flow data, a seismic shear wave tomography model, and gravity potential field data, this paper investigates the distribution of submarine heat flow in the southwestern margin of SCS, the thermal–rheological structure of the crust and mantle, the temperature–viscosity characteristics of the upper mantle Vs low-velocity layer, the tangential stress field of the rheological boundary layer at the lithosphere base, and the convective velocity structure of the mantle asthenosphere. Our new results show that the deep geothermal activity in the southwestern margin of SCS is intense, and the high heat flow area of the mantle with Qm/Qs >70% is distributed along an NNE-trending strip. Moreover, both the east and west sides of the strike–slip fault zone correspond to two low-value areas with a viscosity coefficient of 1021–1022 Pa⋅s at Moho depth, and beneath the Nansha Block are strong and cold blocks with a viscosity coefficient of 1024–1025 Pa⋅s. The northward and eastward shear stress components τN and τE of the rheological boundary layer at the base of the lithosphere mantle decrease with depth. At 65-km depth, both τN and τE are greater than 5.5 × 108 N/m2. At 100-km depth, both τN and τE are less than 1 × 108 N/m2. The calculation results based on the seismic shear wave model of the upper mantle and the gravimetric geoid model indicate that the depth of 120–250 km is the low-velocity layer, and the average temperature of the mantle at 180-km depth can be up to 1,300°C. Moreover, the average effective viscosity coefficient is close to 1018 Pa⋅s, which satisfies the temperature and viscosity conditions for partial melting or convective migration of mantle material. The mantle convection calculation results show that the average flow rate is 8.5 cm/a at 200-km depth and 2.2 cm/a at 400-km depth.

Curie-Point Depths, Geothermal Gradients and Sub-Surface Heat Flow Estimation from Spectral Analysis of High-Resolution Aeromagnetic Data over Gongola Basin and Its Environs, Northeastern Nigeria

Geothermal energy resources have been established globally to be among the sustainable and environmentally harmless means of energy generation. Curie-point depths (CPD), temperature gradients, and heat flow data over the study area were computed using a spectral analysis method in order to have a preliminary view of the geothermal implications (prospect) of the current area. Aeromagnetic data acquired by the Nigerian Geological Survey Agency (NGSA) in the year 2009 was used for the research. The results showed the minimum, maximum, and the average CPD values as 8.18 km, 31.48 km, and 13.0 km, respectively. The minimum, maximum and average thermal gradients obtained were 18.42 °C/km, 70.91 °C/km, and 50.2 °C/km, respectively. The heat flow data obtained ranged from 33.15 mW/m2 to 177.28 mW/m2, with an average value of 110.65 mW/m2. Locations depicting shallow CPDs anomalies (Alkaleri, Darazo, Dukku, Misau, Wuyo, Deba, and Tula), also showed conformity with high heat flow areas. As such, they are regarded as areas of promising geothermal prospects and are recommended for further detailed investigation. Locations depicting a high magnetic susceptibility contrast from a generated analytic signal map, as well as high temperature gradients, high heat flow, and shallow CPDs are attributed to crustal thinning along the sedimentary basin and magmatic intrusions along basement areas, respectively. The magnetic depth to the basement calculated for the study area using the source parameter imaging (SPI) method ranges from 0.610 km to 3.055 km. The present study has provided an insight on preliminary information, regarding new areas of possible geothermal prospects for further detailed investigation.

A numerical experiment for geological sequestration of CO[formula omitted] in the pre-Comondú sandstones of Las Tres Virgenes geothermal area, Baja California Sur, Mexico

The most recent studies on geological sequestration of CO2 in Mexico point towards high sequestration potential associated with geologically stable zones and high-emission centres. These studies overlook however, the potencial that high heat flow areas in the country can offer to geological sequestration of CO2 by mineral precipitation. Here we present an assessment of the CO2 sequestration capacity of the Pre-Comondú sandstones, that overlie the productive granitic basement of the Las Tres Virgenes geothermal field (10 MWe). Both, the physical properties and mineralogical description of the sandstone are defined from drilling core analyses reported by the Federal Commission of Electricity. The initial formation water saturating the sandstone is determined by means of a batch simulation of equilibrium between the primary minerals in the rock and a 1 M solution of NaCl in water. Injection of supercritical CO2 is then numerically simulated. Simulations are based on the TOUGHREACT software and the equation of State Module ECO2N. Our results show Pre-Comondú sandstone favour mineralization of CO2 through the precipitation of carbonates in moderate geologic times (100–300 yr). Mineral changes occur within two main zones in the CO2-impacted reservoir, the zone lying close to the injection point is dominated by precipitation of low-albite, kaolinite, calcite, and minor siderite, whereas the distal zone responds with moderate changes in the system illite-smectite. Changes in porosity are moderate and consistent with the two mineralization zones. Furthermore, the decline in porosity occurs in the long term, which suggests moderate risk for injection operations. Although high reservoir temperature is unfavorable to CO2 solubility, high pressure can counteract this effect, so the system can benefit from higher mass diffusivity and reactivity. This manifests in an accelerated sequestration rate.

ИЗМЕНЕНИЕ МИНЕРАЛЬНОГО И ХИМИЧЕСКОГО СОСТАВА СИЛЛОВ ПРИ ВНЕДРЕНИИ В ОСАДОЧНЫЙ ПОКРОВ, ВПАДИНА ГУАЙМАС, КАЛИФОРНИЙСКИЙ ЗАЛИВ (СКВАЖИНЫ DSDP 477, 477А, 478, 481/481А)

In the Guaymas Basin of the Gulf of California, changes in the mineral and chemical composition of sills of different thicknesses were studied in hydrothermal systems, which formed during the intrusion of hot sills into highly porous young (Pleistocene) cold sediments filled with seawater. Holes DSDP 477 and 477A were drilled in the high heat flow area and Holes 478 and 481/481A in the low heat flow area. Thick sills from Holes 477, 477A, and 478 (47 m, 30 m and 112 m, respectively) are fresh or very weakly altered mainly due to the fact that practically no water released from the host Pleistocene sediments during their heating penetrated into the sills. Olivine, whose content is small in these sills (a few percent) is unaltered. In mesostasis, the amount of which is also a few percent, there are clay minerals. The high heat flow in the area of Holes 477 and 477A (1250 mW/m2) did not change the unfavorable situation for changes in the mineral and chemical composition of the thick sills without water entering them. Thin sills with a thickness of 0.1 to 0.65 m and sills with a relatively small thickness of 1.2 to 4.5 m, which were intersected in Holes 478 and 481/481A are altered. They are fractured and therefore favorable for the penetration of water released from the heated sediments. In addition, in these sills a large volume is occupied by mesostasis (mainly from 18 to 45 %, in some samples from 53 to 70 %) replaced to varying degrees by clay minerals. Olivine is often completely replaced by clay minerals. In thin basalt sills, their alteration strongly decreases K contents. In some cases, the content of Mn, Mg, P, Na, and Ti decreases in them insignificantly. The low heat flow measured in the areas where Holes 478 and 481/481A (150 and 165 mW/m2) were drilled indicates that mineral and chemical changes in the thin sills occurred without heat and mass input from the convective long-lived hydrothermal systems.

Permian rifting processes in the NW Junggar Basin, China: Implications for the post-accretionary successor basins

The Junggar Basin, bounded by the West Junggar along late Carboniferous strike-slip faults in the west, is a post- orogenic successor basin within the Neoproterozoic to Paleozoic Central Asian Orogenic Belt (CAOB). The Junggar Basin is a key region for understanding the Permian rifting processes since it is located in an extensional step-over zone between the Irtysh and North Tianshan strike-slip fault zones that were most active in the Permian. Based on new seismic reflection profiles, detrital petrology and zircon U-Pb ages, together with regional geological data and a refraction seismic profile, this study investigates the tectonic evolution and the geodynamic mechanics of the basin. The early Permian phase of syn-rift mechanical subsidence in the western Junggar Basin formed half grabens. Volcanic detritus is abundant, and detrital zircon U-Pb ages show sediment supply was entirely local. During the middle Permian post-rift phase with thermal subsidence, sediment supply exceeded subsidence, and there are increasingly distant sources of sediment. The Permian regional extensional stress field between major post- accretionary strike-slip fault zones triggered the reactivation of the pre-existing late Carboniferous strike-slip faults in West Junggar and produced thinning of the crust beneath the Junggar Basin, with a β crustal stretching factor of 1.74. Seismic refraction data reveals asthenospheric upwelling resulted in underplated mafic lower crust (6–10 km). The location of initial rift axis in the Junggar Basin was controlled by the juxtaposition of thin and weak crust beneath the basin and relatively strengthened thick crust in the West Junggar attributed to the cooling of A-type granites, resulting from localized strain. Similar location of post-orogenic rifting in southwestern CAOB, in areas of high heat flow following collision, suggests that Junggar Basin is an example of a more general process.

Distributions of gas hydrate and free gas accumulations associated with upward fluid flow in the Sanriku-Oki forearc basin, northeast Japan

Abstract We applied automated velocity analysis to a 3D seismic data volume to obtain a high-resolution seismic velocity model that we used to investigate the influence of fluid behavior on the subsurface distribution of gas in the Sanriku-Oki forearc basin, northeast Japan. We identified free gas accumulations as zones of low P-wave velocity separated from overlying high-velocity gas hydrates by the clear seismic boundary of the bottom-simulating reflection (BSR) between them. We then used conductive modeling to map upward heat flow in our study area from the depth of the BSR derived from the velocity model. The estimated heat flow demonstrates that upward fluid flux has considerable influences on the distributions of both gas hydrate and free gas. The areas of high heat flow (representing high fluid flux) correspond to underlying permeable geological features such as gas chimneys, faults, and the edges of porous slumps, suggesting that these features provide fluid migration pathways from Eocene to Oligocene source rocks to free gas and hydrate accumulations in overlying sedimentary rocks. The techniques we have employed can contribute to the high-resolution mapping of gas hydrate and free gas accumulations in similar deep-water reservoirs off the eastern continental margin of Japan and at tectonically similar plate subduction margins in other regions.

Heat flow in the Western Mediterranean: Thermal anomalies on the margins, the seafloor and the transfer zones

The Western Mediterranean basin has been formed by Miocene back-arc extension and is underlain by a thin and young lithosphere. This young lithosphere is warm, as testified by an overall elevated offshore heat flow. Heat flow within the Western Mediterranean is, however, highly variable and existing data are unevenly distributed and poorly studied in the central part of the Liguro-Provençal and Algero-Balearic basins. This central part is floored by a young oceanic crust, bordered by different continental margins, cut by transform faults, and filled by up to 8 km of sediments. We present a total of 148 new heat flow data collected during the MedSalt and WestMedFlux cruises in 2015 and 2016 and aligned along seven regional profiles that show an important heat flow variability on the basin-scale, but also locally on the margins.A new heat flow map for the Western Mediterranean outlines the following regional features: (1) a higher average heat flow in the Algero-Balearic basin compared to the Liguro-Provençal basin (94 ± 13 mW/m2 and 78 ± 16 mW/m2, respectively), and (2) a regional thermal asymmetry in both basins, but with opposed heat flow trends. Up to 20% of this heat flow difference can be explained by sediment blanketing, but age and heterogeneity of ocean crust due to an asymmetric and polyphased opening of the basins are believed to have given the major thermal imprint. Estimates of the age of the oceanic crust based on the new heat flow suggest a considerably younger West Algerian basin (16–23 Ma) compared to the East Algerian basin and the West Sardinia oceanic floor (31–37 Ma).On the margins and ocean-continent transitions of the Western Mediterranean the new heat flow data point out the existence of two types of local anomalies (length scale 5–30 km): (1) locally increased heat flow up to 153 mW/m2 on the Gulf of Lion margin results from thermal refraction of large salt diapirs, and (2) the co-existing of both low (<50 mW/m2) and high (>110 mW/m2) heat flow areas on the South Balearic margin suggests a heat redistribution system. We suspect the lateral heat advection is resulting from a regional fluid circulation in the sediments associated to the widespread Plio-Pleistocene volcanism on the South Balearic margin.

Gas Hydrate Estimate in an Area of Deformation and High Heat Flow at the Chile Triple Junction

Large amounts of gas hydrate are present in marine sediments offshore Taitao Peninsula, near the Chile Triple Junction. Here, marine sediments on the forearc contain carbon that is converted to methane in a regime of very high heat flow and intense rock deformation above the downgoing oceanic spreading ridge separating the Nazca and Antarctic plates. This regime enables vigorous fluid migration. Here, we present an analysis of the spatial distribution, concentration, estimate of gas-phases (gas hydrate and free gas) and geothermal gradients in the accretionary prism, and forearc sediments offshore Taitao (45.5°–47° S). Velocity analysis of Seismic Profile RC2901-751 indicates gas hydrate concentration values &lt;10% of the total rock volume and extremely high geothermal gradients (&lt;190 °C·km−1). Gas hydrates are located in shallow sediments (90–280 m below the seafloor). The large amount of hydrate and free gas estimated (7.21 × 1011 m3 and 4.1 × 1010 m3; respectively), the high seismicity, the mechanically unstable nature of the sediments, and the anomalous conditions of the geothermal gradient set the stage for potentially massive releases of methane to the ocean, mainly through hydrate dissociation and/or migration directly to the seabed through faults. We conclude that the Chile Triple Junction is an important methane seepage area and should be the focus of novel geological, oceanographic, and ecological research.

Thermal properties of the crust and the lithosphere\u2013asthenosphere boundary in the area of Poland from the heat flow variability and seismic data

High-resolution 3D seismic P-wave velocity model of Poland (Grad et al., Tectonophysics 666:188–210, 2016) and corrected for paleoclimate heat flow map (Majorowicz and Wybraniec, Int J Earth Sci 100(4):881–887, 2011) gridded to a common mesh are used together with four independent thermal models of the crust and upper mantle to calculate heat flow variation with depth and geotherms. Heat flow at Moho depth are calculated and mapped and both confirm large variability with an elevated mantle heat flow (circa 30–40 mW/m2) in the Paleozoic Platform which is some 10–20 mW/m2 higher than Moho heat flow in the north-eastern and south-eastern Poland which belong to a variety of tectonic terranes (the oldest Precambrian Craton, younger Cadomian, Trans-European Suture Zone, Carpathians). Temperatures calculated for the crust show consistent pattern: higher temperatures beneath the Paleozoic Platform and lower temperatures beneath the Precambrian and Cadomian units. At 10 km depth this difference is about 150 °C, about 300 °C at 20 km depth, and about 400 °C at 50–60 km. Assuming the calculated isotherm 580 °C as Curie temperature the magnetic crust thickness was determined as 5–10 km only beneath the Polish Basin, circa 20 km in Carpathians, circa 30 km in Sudetes, and 35–40 km beneath the Precambrian and Cadomian units. Such a thick magnetic crust results from a great depth of Curie temperature, thick crystalline crust, and thin sediments. Mantle heat flow variability is mainly correlating with measured surface heat flow and influences geotherms. Calculated thermal LAB depth follows patterns of heat flow and Moho heat flow variability through Poland with thinnest lithosphere in the high surface heat flow and high mantle heat flow areas. Comparison of this thermal LAB depth estimates with seismic data based LAB depth shows general coincidences when Precambrian Craton vs Paleozoic Platform are considered along the P4 seismic experiment data model (circa 190 km depth vs some 90 km depth, respectively). However, significant differences exist in many areas and especially for the SE Poland when compared with map for the whole of Poland compiled from other seismic reported data.

Near-surface Heating of Young Rift Sediment Causes Mass Production and Discharge of Reactive Dissolved Organic Matter

Ocean margin sediments have been considered as important sources of dissolved organic carbon (DOC) to the deep ocean, yet the contribution from advective settings has just started to be acknowledged. Here we present evidence showing that near-surface heating of sediment in the Guaymas Basin, a young extensional depression, causes mass production and discharge of reactive dissolved organic matter (DOM). In the sediment heated up to ~100 °C, we found unexpectedly low DOC concentrations in the pore waters, reflecting the combined effect of thermal desorption and advective fluid flow. Heating experiments suggested DOC production to be a rapid, abiotic process with the DOC concentration increasing exponentially with temperature. The high proportions of total hydrolyzable amino acids and presence of chemical species affiliated with activated hydrocarbons, carbohydrates and peptides indicate high reactivity of the DOM. Model simulation suggests that at the local scale, near-surface heating of sediment creates short and massive DOC discharge events that elevate the bottom-water DOC concentration. Because of the heterogeneous distribution of high heat flow areas, the expulsion of reactive DOM is spotty at any given time. We conclude that hydrothermal heating of young rift sediments alter deep-ocean budgets of bioavailable DOM, creating organic-rich habitats for benthic life.

Update and review of heat flow measurements in México

The main objective of this study is to report an update of the surface heat flow database of México. To our knowledge, this work is the first data compilation that integrates existing published and unpublished measurements to create a new heat flow map using a variety of data sources from 108 sites (transient borehole temperatures and temperature-depth profiles). Heat flow measurements in México are still relatively sparse. Updates of heat flow and geological data is required for a better understanding of the thermal regime of México, an accurate characterization of heat flow provinces, and to create a consistent geothermal map.The updated thermal database considers México’s continental and offshore zones. The new heat flow values are mainly located along the Baja California Peninsula and central México. From the new data, we defined the highest and the lowest heat flow values as 1263 mW/m2 and 4 mW/m2, respectively. This updated heat flow database helped us to identify regions with thermal anomalies that show values above average continental heat flow. More importantly, these high heat flow areas do not correspond to the known Mexican geothermal fields.

Wellbore and groundwater temperature distribution eastern Snake River Plain, Idaho: Implications for groundwater flow and geothermal potential

A map of groundwater temperatures from the Eastern Snake River Plain (ESRP) regional aquifer can be used to identify and interpret important features of the aquifer, including aquifer flow direction, aquifer thickness, and potential geothermal anomalies. The ESRP is an area of high heat flow, yet most of this thermal energy fails to reach the surface, due to the heat being swept downgradient by the aquifer to the major spring complexes near Thousand Springs, ID, a distance of 300km. Nine deep boreholes that fully penetrate the regional aquifer display three common features: (1) high thermal gradients beneath the aquifer, corresponding to high conductive heat flow in low-permeability hydrothermally-altered rocks; (2) isothermal temperature profiles within the aquifer, characteristic of an actively flowing groundwater; and (3) moderate thermal gradients in the vadose zone with values that indicate that over half of the geothermal heat flow is removed by advective transport in the regional aquifer system. This study utilized temperature data from 250 ESRP aquifer wells to evaluate regional aquifer flow direction, aquifer thickness, and potential geothermal anomalies. Because the thermal gradients are typically low in the aquifer, any measurement of groundwater temperature is a reasonable estimate of temperature throughout the aquifer thickness, allowing the construction of a regional aquifer temperature map for the ESRP. Mapped temperatures are used to identify cold thermal plumes associated with recharge from tributary valleys and adjacent uplands, and warm zones associated with geothermal input to the aquifer. Warm zones in the aquifer can have various causes, including local circulation of groundwater through the deep conductively dominated region, slow groundwater movement in low-permeability regions, or localized heat flow from deeper thermal features.

More efficient and cost-effective ways of evaluating and high grading unconventional plays

With unconventional exploration expanding into basins with little seismic data and few wellbores, some lower cost technologies should be exploited up front to select areas of greater economic potential. Typically, 3D seismic is used for high grading, but it is expensive, ground access can be limited resulting in partial coverage, and, as with many technologies, interpretations can be ambiguous. However, there are less expensive alternatives, such as remote sensing, gravity and magnetics, geochemistry, and petrography, that can be used to initially identify areas with higher potential. After the initial screening evaluation, the high-graded areas can subsequently be appraised using more expensive techniques. Using less expensive screening alternatives up front can improve results and project economics. Two examples, one from the Bakken in the Williston Basin and another from the Eagle Ford at First Shot Field in Texas, are given showing how such less expensive screening data can be used to locate areas that have either better production and/or oil that is more easily produced from tight rocks. Our Bakken and Eagle Ford examples determined that our integrated approach could add value in different tectonic settings that involve rocks of very different geologic ages and depositional settings. Detecting and investigating igneous events in a sedimentary basin were important steps in our integrated approach. Igneous activity was more common in the upper crust and sedimentary basins than was generally assumed. In both of these examples, production “sweet spots” were related to igneous drivers that create areas of localized convective high heat flow that in turn were associated with recurrent movement of basement faults. Convective heat flow via hydrothermal fluids along faults and fracture zones was much more efficient than the transfer of heat by conductive heat flow. The screening data at the mega- and microscale supported the hypothesis that recurrent movement on faults and lineaments provided conduits for hydrothermal fluids and igneous volatiles. The hydrothermal fluids were interpreted to have had an important impact on in situ hydrocarbon generation, and petrography further suggested that precipitation of minerals from these hydrothermal fluids could affect porosity, permeability, rock fracturability, and overpressuring. The work and our examples proved how less expensive screening techniques, such as remote sensing, gravity, magnetics, geochemistry, and petrography, could be used to high grade unconventional shale oil plays, so the sweet spots could be drilled first.

Localization of intraplate deformation through fluid-assisted faulting in the lower-crust: The Flinders Ranges, South Australia

In this paper we present a hypothesis for localized, intraplate deformation in the continental crust of south-central Australia that involves fluid-assisted reactivation of faults in the mid- to lower crust. Using data from a temporary seismometer deployment in the Flinders Ranges, we show that earthquakes, relocated in a 3D velocity model, cluster in elongated low vp/vs anomalies that extend to depths exceeding 20km, and are aligned with the axis of the Flinders Ranges. In the northern Flinders Ranges these low vp/vs anomalies can be interpreted as fractured Neoproterozoic to Cambrian sediments that separate two cratonic blocks, the Gawler Craton to the west and the Curnamona Province in the east. Previous studies of Helium isotopes in springs to the north of the area provide evidence of mantle-derived fluids that may influence faulting at depth. Our focal mechanism and stress inversion results show a regionally compressive stress field that provides no evidence for stress concentration. We also argue that mechanisms for localized faulting such as thermal weakening and isostatic rebound also fail to account for the occurrence of earthquakes at mid- to lower crustal depth in this area of high heat flow and that the focused seismicity can only be explained by high pore fluid pressure in the lower crust.