Hot Brine Research Articles

Novel approach for modelling low enthalpy geothermal in deep sedimentary aquifers: a case study of 40 years of production data in the Dogger formation

Geothermal energy in the Paris urban area has been exploited since the early 1970s. Deep drilling in the Paris sedimentary basin has targeted hot brine in the Dogger formations from a mid-Jurassic carbonate rocks series. More than a hundred wells have been drilled to depths ranging from 1400 to 2000 m and decades of production and reinjection have resulted in variations in the aquifer pressure and temperature in some areas. The regional numerical model discussed herein is aimed at assessing the potential interactions between doublets and for assessing the impact of the addition of more wells in the future. While the integration of a 3D refined geological model into a large-scale reservoir model needs heavy computational resources, local models simplifying the main productive areas into one or two layers surrounded by impermeable units can be used to approximately assess the reservoir characteristics. The modelling of a semi-regional area of the Dogger reservoir in the Southern part of Paris (Cachan/Orly) has been performed, using a conventional double-layer approach to simulate the natural state and production history of the area using the simulator Waiwera, a fast parallel open-source geothermal simulator from the University of Auckland in New-Zealand. Calibration of a natural state model, which describes the conditions before any geothermal operations, has been performed, including an analysis of the impact of boundary condition values on the ability of the model to match the data available in the public domain. The temperature and pressure distributions, instead of being based on geostatistical mapping methods have been obtained from a calibrated natural state model. The implementation of a regional lateral cross flow observed from past studies proved to be essential for matching the measured temperatures and pressures along with variations in the deep heat flux. A calibrated model has been obtained from matching the available production data with mismatches of no more than 1.5 °C. The modelling results confirm the dominance of the shallower productive zone in the aquifers and give insights into the extent of the cooler areas created by the long-term operations. Thus we have used the Dogger reservoir, with multiple data sets available, as a case study for calibrating a semi regional numerical model of a deep sedimentary aquifer used for geothermal direct-use. Our modelling study accounts for the conceptual understanding of the sedimentary aquifer with its heterogeneities and calibrates the numerical model against the measured historical data. Based on the calibrated reservoir model, the pressure and temperature responses in deep productive areas can be determined enabling operators or decision makers to test future strategies for sustainably operating the geothermal resource.

Energy, Exergy and Exergo-economic analyses of supercritical CO2 cycles for the exploitation of a geothermal resource in the Italian water dominant Amiata site

Alternative powerplant layouts to commonly applied flash technology is investigated for the water dominant geothermal location of Amiata Mountain, Italy. The proposed solution avoids flashing the brine stream by a borehole pump capable of maintaining pressurized conditions, thus reducing the amount of non-condensable gases released when reaching the ground level. Therefore, the need of a gas treatment section is completely avoided. The heat recovered from the hot brine at ground level is transferred to different supercritical CO2 cycle configurations, equipped with high efficiency Printed Circuit Heat Exchangers (PCHE). The optimal 45.5% calculated exergy efficiency was achieved for the recuperative cycle with intercooling and reheat, which however didn’t show the optimal electricity costs (8.092 c€/kWh) because of the more complex heat exchangers network. The lowest cost of electricity (7.4 c€/kWh) was found for the recuperative cycle configuration. These costs are in line with the current levels of geothermal binary cycles, but almost doubled compared to the current single flash +ORC solution, due to a 40-50% reduction of power output with sCO2 cycles. On the other hand, sCO2 binary cycles could guarantee an almost zero environmental impact, which is the main reason for social concerns related to the current flash powerplants.

Structural inheritance and hydrothermal alteration impact on fluid circulation in a clay-rich shear zone

Deep geothermal power plants in the Upper Rhine Graben (URG) harness natural hot brines circulating within the fracture network of basement rocks. The nature and geometry of the fault network must be documented in detail to reduce the risk of targeting low-permeability structures during drilling. Fault zones and associated fracture networks exhibit variable hydraulic properties depending on the nature of their deformation, hydrothermal alteration, and mineral infills. The Schauinsland mine, located on the eastern shoulder of the URG, is considered an analogue for exploited geothermal basement reservoirs. It provides a 3D exposure of a clay-rich shear zone and a perpendicular ore vein, analogous to present-day brine circulation pathway encountering a heterogeneously permeable structure. Petrophysical, petrographical, mineralogical and geochemical investigations of this shear zone offer the opportunity to reconstruct its formation and the associated fluid pathways. A statistical analysis of the dataset was carried out to highlight correlations between deformation and hydrothermal alteration processes. Through repeated seismic cycles, the core zone shifted from a conduit to a barrier for fluid circulation, due to the precipitation of secondary minerals within the remaining open spaces, resulting in a multi-core structure. Observations show that the damage zones within the transition zone of the shear zone likely constitute the optimal zone for present-day fluid circulation.

Linking dolomitization to sequence stratigraphy: Insights from the Upper Jurassic Arab Formation, offshore oilfield, UAE

This petrographic, petrophysical, and geochemical study revealed that dolomitization in the Upper Jurassic Arab Formation reservoir, United Arab Emirates, can be constrained within 2nd, 3rd, and 4th order sequences. The formation represents a 2nd order regressive sequence/cycle (highstand systems tracts, HST) that was deposited across a carbonate ramp with shoal under hot arid climatic conditions during the Kimmeridgian-Tithonian. Deposition occurred subsequent to maximum marine transgression (maximum flooding surface, MFS) and was accompanied by a progressive increase in the degree of restriction of the connectivity between the inner platform (supratidal, upper intertidal and lagoon) and the open sea. Sporadic dolomitization took place in transgressive systems tracts (TST) of the 3rd and 4th order cycles of earliest stages of the 2nd order regression, below the parasequence boundaries and within bioturbation sites. Subsequent rapid and extended 2nd order marine regression cycles were embossed by trends of progressive increase in salinity, which resulted in concomitant systematic decrease in limestone deposition and increase in intensity of seepage reflux/sabkha dolomitization by seepage reflux of hypersaline brines. Dolomitization is most prevalent in the 4th order HST sequences and was accompanied by occlusion of the moldic and intercrystalline pores in the dolostones by gypsum/anhydrite cement. Dolomitization that was accompanied by limited formation of gypsum/anhydrite in the late 2nd order HST is attributed to reflux of penesaline (salinity saturated with Ca-sulfate) /mesohaline (below Ca-sulfate saturation) brines. The reflux of the latter brines is attributed to smaller extent of relative sea-level falls, i.e., partial restriction of the inner platform. The precipitation of dolomite cement in moldic pores and as thin overgrowths around replacive dolomite is attributed to the flow hot basinal brines (i.e., hydrothermal fluids). This interpretation is supported by the presence of saddle dolomite, along with depleted δ18O values, relative enrichment in 87Sr isotope, and high fluid-inclusions homogenization temperatures. The greater amounts of these post-dolomitization cements in the dolopackstones and dolograinstones caused stronger obliteration of their near-surface isotopic signatures compared to the dolomudstones and dolowackestones.This study demonstrates that linking dolomitization of limestones across carbonate ramps under hot-arid climatic conditions to different orders of changes in the relative sea level and lithology of the succession indicates the involvement of various types of dolomitizing fluids and geochemical conditions, including: (i) domination of seepage reflux of hypersaline and mesohaline/penesaline brines, (ii) dolomitization below the seafloor during marine transgression, and (iii) dolomitization within bioturbation sites.

Techno-economic investigation of an entirely solar-powered hybrid HDH/RO desalination plant for moderate water demand under various operating conditions

The study presented a scalable, entirely solar-powered hybrid desalination system suitable for moderate demand and valid for various water salinities. The system merged two desalination techniques: HDH (humidification-dehumidification) and RO (reverse osmosis). The required power for all components was obtained from a photovoltaic (PV) system. The experiments were conducted to evaluate the separate units' and hybrid system's performances under different conditions, including various sprayed hot water (to the HDH) temperatures, RO feed water temperatures, air velocities, and water salinities. Based on the recorded data, the techno-economic analyses were conducted to assess the gain output ratio (GOR), recovery ratio (RR), specific energy consumption (SEC), the total amount of dissolved solids (TDS), and production cost. As a result, the RO unit's productivity increased almost linearly with feed temperature, showing a maximum hourly yield of 60 L/m2. In contrast, HDH productivity showed exponential growth with feed temperature, achieving a maximum hourly yield of 18 L/m2. The SEC of the RO unit decreased from 1.1 kWh/m³ to 0.63 kWh/m³ when using the rejected HDH's hot brine. The hybrid system's accumulated productivity reached 535 L/m2, significantly higher than the standalone HDH (58.5 L/m2) and standalone RO (368 L/m2). Additionally, the hybrid system demonstrated substantial improvements in GOR and RR, with daily values of 11.15 and 55.73 %, respectively. Economically, the yielded water cost was significantly lower, at 0.63 $/m³ for the HDH/RO system compared to 3.51 $/m³ for the standalone HDH.

Coupled evolution of basin structure and fluids recorded by microfractures: A case study of deep-buried ordovician in the tarim basin

The fluid activity in the deep strata of sedimentary basins is commonly related to tectonic activity, and the cements filled in fractures are a good carrier for the tectonic-fluid coupling evolution. Compared to macrofractures, microfractures have characteristics of high frequency and easy identifiable periods. Abundant microfractures infilled by carbonate cements (MCCFs) developed in carbonates of the Ordovician Yingshan and Yijianfang formations in the platform basin area of the Tarim Basin. Based on the study of petrology, U-Pb dating, and geochemical characteristics, this study determined the stages of MCCFs and clarified the tectonic-fluid coupling evolution process recorded by MCCFs in the study area. The formation order of these MCCFs is D1, C1, C2, D2, C3, and C4. The precipitation times of MCCFs have a good correspondence with orogeny around the Tarim Basin and active times of strike-slip faults in the platform basin area. The six stages of MCCFs in the Ordovician Yingshan and Yijianfang formations in the SLU recorded the tectonic-fluid coupling evolution process of concentrated seawater in the late Middle Ordovician, meteoric water at late Ordovician, organic acids during the Silurian, Mg-rich hot brine at the end Devonian-early Carboniferous, and magmatic hydrothermal fluids during the Permian. This not only indicates a close connection between fluid activity and tectonic activity in sedimentary basins, but also confirms that the formation of MCCFs in carbonate formations is closely related to regional tectonic-fluid coupling activities. This study provides a good example for studying macro scale tectonic-fluid coupling activities in basins using microfractures.

Disconformity-controlled hydrothermal dolomitization and cementation during basin evolution: Upper Triassic carbonates, UAE

Petrography, fluid-inclusion microthermometry, stable isotope analyses, and radiometric (206Pb/238U) dating of Upper Triassic dolostones, saddle dolomite, and quartz and calcite cements were used to constrain the timing and conditions of dolomitization and cementation in the context of the tectonic evolution of a basin in the northern United Arab Emirates. Dolomitization (ca. 152.4 Ma) and precipitation of saddle dolomite (ca. 146.8 Ma), calcite (ca. 144.6 Ma), and quartz cements are attributed to focused synrifting flow of hot basinal brines into grain-supported limestones in which permeability was enhanced by incursion of meteoric waters beneath a disconformity surface. Another calcite cement generation (ca. 99.7 Ma) was formed by flow of hot brines during tectonic compression related to the obduction of Oman ophiolites in the Late Cretaceous. Thus, this paper provides new insights into (1) stratigraphic controls on and timing of hydrothermal (hot basinal brines) dolomitization, (2) the origin of closely associated intraformational limestones and dolostones, and (3) linkages between diagenesis and thermochemical modifications of basinal brines during tectonic evolution of sedimentary basins.

Pb-Zn-Ba deposits in the Nigerian Benue Trough: A synthesis on deposits classification and genetic model

The Benue Trough stretching about 800–1000 km with a width ranging between 100 and 150 km, is a megarift structure whose origin was related to the opening of the south Atlantic during the early Cretaceous. This mega rift structure contains economically significant Pb-Zn-Ba-F deposits that form well-defined metallogenic belt about 600 km long in Nigeria. In the Southern Benue Trough (SBT), the Pb-Zn-Ba-F deposits are localized in four districts namely Abakaliki, Ishiagu, Wanikande and Gabu-Oshina and are hosted by carbonaceous shale; in the Central Benue Trough (CBT) the deposit is hosted in the silicified limestone and arkosic sandstone localized in Arufu, Akwana and Azara districts; while in the Northern Benue Trough (NBT) ores deposits occur in the arenaceous sediments of Yolo, Gombe and Gulani districts. Previously published sulfur (S) isotopic data of sulfides suggest that the ore-forming S was sourced from marine sulfates and the reduction of sulfate mainly by thermochemical sulfate reduction process in the CBT and NBT. Whereas in the SBT, bacterial sulfate reduction process is dominant. The compiled C-O isotopic compositions suggest that limestone and slightly metamorphosed sedimentary rocks supplied ore-forming materials to the hydrothermal systems through water/rock interaction. The available bulk Pb isotopic compositions for the ore minerals, the host sedimentary and crystalline rocks comprising the basement rocks as well as the basaltic rocks from the Trough suggest that the arkosic sandstone which is composed of detrital feldspars that was eroded from the Precambrian basement rocks could be the likely source of ore-forming metals. Our model proposed that the ore-forming fluids were sourced from the hot connate-brine that was expelled through compaction during the development of the deep sedimentary basins. Mesozoic magmatic events distributed throughout the basin likely provided the initial thermal flow and elevated the geothermal gradient. The hot brines could have leached the metals from the syn-rift continental formations. The tensional fractures serve as the conduit through which the metals migrated, leached abundant sulphate and precipitated their contents in the transcurrent fault system as sulfides, barite and associated polymetallic ores. The geological, mineralogical, and geochemical characteristics of the Nigerian Benue Trough Pb-Zn deposits are consistent with Mississippi Valley-type (MVT) Pb-Zn deposits in North Africa and the typical MVT ore deposits worldwide.

An Experimental Investigation on the Relation between Corrosion and Thermohydraulic Behavior in Heat Exchangers for Geothermal Applications

The potential use of carbon steel in CO2-saturated brine is studied for its potential use in heat exchangers in geothermal applications. A dedicated setup, including a double-pipe heat exchanger, is developed to study the relation between corrosion and the thermohydraulic behavior inside heat exchangers. Hot brine flows inside the inner carbon steel tube, thus corroding the inner surface of this tube. The thermohydraulic behavior of the heat exchanger, i.e., the pressure drop over the pipe and the heat transfer rate through the pipe, are continuously monitored. On the other hand, weight-loss experiments and microscopic analyses are performed on samples that are periodically removed from the setup. The corrosion rate is studied as a function of temperature, i.e., the entrance vs. the exit of the heat-exchanging section, and flow. Therefore, an experiment with static brine and a uniform temperature is used as a reference. The corrosion rate is generally higher in dynamic compared to static conditions. Furthermore, the corrosion rate increases with increasing temperature in dynamic conditions, whereas it decreases with increasing temperature in static conditions. These observations might be explained by the different corrosion products that formed. The corrosion products have no significant effect on the pressure drop over the pipe, but clear fluctuations in the heat transfer coefficient are observed. The origin of these fluctuations should be further studied before the observed heat transfer coefficient can be used as a measure for corrosion.

Hybrid vacuum membrane distillation-multi effect distillation (VMD-MED) system for reducing specific energy consumption in desalination

This study focuses on the integration of vacuum membrane distillation into the multi-effect distillation (VMD-MED) system, incorporating heat recovery mechanisms to augment fresh water productivity and minimize the specific thermal energy consumption of the desalination process when compared to stand-alone vacuum membrane desalination systems. The hybrid system was devised by integrating the experimental output of VMD (permeate flux and hot brine) as heat source to MED. Two hybrid systems were investigated in this study: VMD/MED, wherein the heated brine from VMD served as a heat source for MED, facilitating the recovery of sensible heat from VMD; and VMD-HR/MED, where the latent heat of VMD vapor during condensation was utilized to pre-heat the feed water for MED. Based on the performance parameters, it was concluded that the VMD-HR/MED hybrid system outperformed both the stand-alone VMD and VMD/MED hybrid system in terms of efficiency. The latent heat recovery from the condenser of VMD in VMD-HR/MED hybrid system reduces the specific thermal energy consumption (STEC) to 38.42 kWh/m3, however, it enhanced the gain-output-ratio (GOR) and productivity of the system. Additionally, a rise in GOR and a simultaneous decrease in STEC were observed with increasing feed flow rates and vacuum pressure.

Widespread diffuse venting and large microbial iron-mounds in the Red Sea

For decades, hydrothermal activity along the Red Sea Rift was only inferred from metalliferous sediments and hot brines. Active hydrothermal fluid discharge was never directly observed from this young ocean basin, but could be key to understanding the evolution of hydrothermal vent fields and associated life. Here we report the discovery of widespread diffuse venting at Hatiba Mons, the largest axial volcano in the Red Sea. The active vent fields are composed of iron-oxyhydroxide mounds, host thriving microbial communities and are larger and more abundant than those known from any other (ultra) slow-spreading mid-ocean ridge. Diffuse venting, controlled by intense faulting, and the lack of vent-specific macrofauna, are likely causes for the abundant microbial mats that dominate and built up the hydrothermal mounds. These microbe-rich hydrothermal vent fields, occurring in a warm ocean, may be analogous to Precambrian environments hosting early life and supporting the formation of large iron deposits.

Linking carbonate-hosted Zn[sbnd]Pb deposit to deep mantle activity: Evidence from in situ U[sbnd]Pb geochronology of calcite from the world-class Huayuan Zn[sbnd]Pb ore field in South China

Carbonate-hosted ZnPb deposits are a major source of zinc, lead, and some critical raw metal resources worldwide (e.g., germanium and gallium). However, the timing and geodynamics setting of their mineralization remain enigmatic, leading to ongoing debates about their origins. To shed light on these issues, we utilized LA-ICP-MS in situ UPb dating of ore-related calcites to determine the timing and geodynamic setting of mineralization events in the world-class Huayuan carbonate-hosted ZnPb ore field in South China. The petrographic and cathodoluminescence features, fluid inclusion characteristics, and the Pb isotope data indicate that the tested calcites were formed from the same ore-forming fluids as the intergrown sphalerite and were not overprinted by possible later hydrothermal fluids. Our results show that the calcite UPb ages of 510–495 Ma refute the previously proposed Mississippi Valley-type (MVT) model, which suggested that the younger Caledonian orogeny (460–420 Ma) played a significant role in the genesis of the Huayuan ZnPb ore field. Instead, our findings link the formation of this ore field to crustal extension and high heat flux resulting from mantle upwelling events in northeast Gondwana during the Cambrian. The findings indicate that deep mantle processes can trigger shallow crustal fluid circulation to create a giant carbonate-hosted ZnPb ore field in a long-dormant rift.We present a genetic model proposing that the extensive carbonate platform of the Qingxudong Formation was likely a “brine factory” that supplied the brines to the Proterozoic basement through reactivated syn-rift faults. The high heat flux from upwelling mantle not only heated these brines to high temperatures but also caused early maturation of organic matter in the lower Cambrian Niutitang black shales to generate hydrocarbons. The hydrocarbons migrated into the limestone of the Qingxudong Formation. Meanwhile, the hot brines leached Zn and Pb from the Proterozoic basement rock. These ZnPb bearing brines ascended to the Qingxudong Formation where they mixed with the hydrocarbons. These hydrocarbons acted as reducing agents for ZnPb sulfide precipitation, forming the Huayuan giant ZnPb ore field. Furthermore, UPb dating results of syn-mineralization calcite, together with the relationships between the ores and host rocks, indicate that ZnPb mineralization occurred over timespans during or shortly after host-rock deposition and continuing during lithification for several million years in this ore field. The similar prolonged duration of mineralization may be relatively prevalent in other carbonate-hosted ZnPb deposits/ore fields. We therefore recommend that reliable age dating for all mineralization stages is necessary to establish genetic models for carbonate-hosted ZnPb deposits.

Prediction of the state of the ice-bearing massif during the penetration of a vertical mine shaft with freezing

Te subject and purpose of the work. Te article is devoted to the problem of sinking shafs traversed by the method of artifcial freezing of shafs at the stage of elimination of ice and rock fencing. Te relevance of the study is explained by the increased requirements for the reliability of the process during the tamponage of the fxed space of the trunks and during the operation of the trunks for an indefnite time. Te novelty of the article consists in the development of the parameters of the technology that eliminates the uneven load on the tubing support during the expansion of the inner ring layer during artifcial thawing by pumping hot brine into freezing columns. Te methodology of the work includes a complex of studies: analysis of literary sources, theoretical and feld studies, modeling of processes and experimental verifcation of the data obtained. Te results of the work. It was revealed that the stresses in the support lead to the separation of concrete from the tubing column and the formation of water-flled cavities. It is established that forced thawing of the array by pumping hot brine into freezing columns causes uneven loads on the tubing support and threatens with an accident. It is determined that the most acceptable option is thawing by feeding warm air into the barrel and circulating a coolant with an optimal temperature. Use of results. Te technology can be in demand in the construction of capital mining facilities in particularly unfavorable conditions. Conclusions. Te most favorable mode of artifcial thawing is created when heated air is fed into the barrel and the coolant into the columns with an increase in the coolant temperature smoothly while maintaining the required level.

Formation of barite in the Ab Torsh deposit, Kerman province, Iran: Insights from rare earth elements, O and S isotopes, and fluid inclusions

Barite can form in a variety of geological environments, as it occurs in a wide range of mineral deposits. To determine the origin and physicochemical conditions under which the Ab Torsh barite deposit formed, an extensive study was conducted using petrographic, Rare Earth Element (REE) geochemical, O and S isotopic, and fluid inclusion methods. Barite mineralization occurs at Ab Torsh as a stratabound vein in the Senonian carbonate rock units. Barite-quartz is accompanied by subordinate malachite, chrysocolla, Fe-Mn oxide-hydroxides, galena, azurite, fluorite, pyrite, and bornite. The ∑REE values are very low in barite (5.32–14.56 ppm), with chondrite-normalized patterns showing enrichment of Light Rare Earth Elements (LREE) relative to Heavy Rare Earth Elements (HREE). The low ∑REE content and REE element ratios (Ce/La, (La/La*)N, and (Gd/Gd*)N) indicate that seawater with a highly altered geochemical signature (connate water) acted as a Ba ore-forming fluid. The δ18O and δ34S values in barite (+10.4–+11.1 ‰ and +27.3–+27.8 ‰, respectively) and the δ34S values in galena (+6.3 and + 7.9 ‰) indicate that the sulfate (and thus sulfur) originated from sulfate-bearing connate waters and/or evaporites. Thermochemical Sulfate Reduction (TSR) was the most likely mechanism for the formation of the reduced sulfur in galena. The salinity and homogenization temperatures in the aqueous fluid inclusions of barite and quartz (2.7–19.3 wt% NaCl equivalent and 110–275 °C, respectively) indicate that basinal fluids containing a meteoric water component were the source of the mineralizing solutions. The fluid inclusion data demonstrate that two fluid mixing have occurred: one between the hot basinal brines and cold meteoric waters, and another between heated and cold meteoric waters. It is estimated that the hot fluids derived from a maximum depth of about 9 km. The Ab Torsh deposit is classified here as a structure (unconformity)-related barite deposit. It is concluded that intense faulting and brecciation of the host rocks caused by post-Cretaceous compressional tectonics probably provided the channels necessary for the upward migration of deep mineralizing fluids from a basinal brine source. Barite formed where these ascending hot, Ba-bearing hydrothermal fluids encountered cooler, sulfate-bearing connate waters trapped in the overlying Senonian strata and/or the descending cold meteoric waters that dissolved evaporite-bearing rock units.

Use of Hot Brine Solution as a Sitz Bath in the Treatment of Haemorrhoids- ACase Study

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Research and Development on Coatings and Paints for Geothermal Environments: A Review

AbstractGeothermal power plants are complex systems, where the interplay between different metallic components transforms the enthalpy of hot brine in the form of electricity or usable heated water. The naturally occurring variety in brine chemistry, linked to the presence of specific key species, and its thermo‐physical properties, leads to the development of different power plant configurations. Key species and power plant configuration in turn determine the extent of damage experienced by each component in the power plant: erosion, corrosion, and/or scaling, often acting combined. Paints and coatings, compared to changing the component alloy, have represented a preferred solution to mitigate these issues due to advantages in terms of costs and repairability. This is reflected in the large number of publications on research and development in this area within the past ≈50 years, with even an increasing trend in the past 10–20 years, indicating the strong interest to develop this clean and sustainable energy source. Therefore, in this work, the first of its kind after 1980, an in‐depth review of all published work on research performed on paints and coatings for geothermal applications, subdivided by the material system, is provided.

Comments: Who Holds the Rights to US Geothermal Heat Sources?

A recently enacted law in Texas, which went into effect in mid-June, declares the landowner or the owner of surface rights as the holder of subsurface geothermal energy and associated resources. If the surface and mineral rights of the land have been separated, the owner of the surface estate prevails. Senate Bill 785 amended a section of the Natural Resources Code to define heat as a byproduct of geothermal energy and associated resources, but excludes mineral, oil, gas, or any product of oil or gas. It also excludes “the ownership and use of groundwater,” including “minerals dissolved or otherwise contained in groundwater, including hot brines.” The law entitles the owner “to drill for and produce the geothermal energy and associated resources.” As with pore space rights for underground carbon storage, legislating surface and subsurface rights for geothermal energy and underground hydrogen storage is an evolving frontier. Privately held rights vs. state or federal lands contribute to the complexity of these relatively nascent efforts to advance decarbonization. Ownership of geothermal rights varies widely from state to state, often dictated by a state’s definition of what constitutes “geothermal resources.” California’s definition, for example, says “the natural heat of the earth, the energy, in whatever form, below the surface of the earth present in, resulting from, or created by, or which may be extracted from, such natural heat, and all minerals in solution or other products obtained from naturally heated fluids, brines, associated gases, and steam, in whatever form, found below the surface of the earth, but excluding oil, hydrocarbon gas, or other hydrocarbon substances.” Other states, such as Utah, define a geothermal resource by a temperature threshold (“water or steam at temperatures greater than 120°C naturally present in a geothermal system”). At that mark, a separate lease is required because the resource is no longer part of the water rights. Once geothermal resources are defined, who holds the rights may be murky. In California, Hawaii, and New Mexico, the mineral estate is the owner. Wyoming considers geothermal heat as part of the water rights—“underground water, including hot water and geothermal.” Other states consider rights as held by the surface estate unless they have been specifically transferred. Yet, many states have no clearly defined guidance about privately held ownership, and the parties involved in disputes head to the courts to hash out the ambiguity. The rules governing development of geothermal energy on federal lands are more defined. Geothermal was the first type of renewable energy that the US Department of the Interior Bureau of Land Management approved for production on public lands. The first project was given the go-ahead in 1978. A federal lease allows future exploration and development. However, it does not include the right to move ahead with any ground-disturbing activities to explore for or develop the resources. Each stage of development under the lease requires separate authorizations and compliance with the National Environmental Policy Act. Two examples of state-controlled lands are well-known geothermal fields in California, The Geysers and the Salton Sea projects. The state’s leases in The Geysers are on school lands. Revenue and royalties are deposited into the California State Teachers’ Retirement fund. Royalty rates range from 10 to 12.5% of the gross value of geothermal steam, calculated by multiplying the gross value of electric power with the agreed percentage of steam that began initially as 36% in 1999, increasing to a maximum of 42% of the value of electricity. While innovation steadily advances technologies to produce geothermal energy, the determination of clear law and regulations is playing catch-up ... state by state and case by case in courts. And until it does, scaling up of this promising energy source in the US is at risk of being hamstrung.

Neoproterozoic Zn-Pb mineralization in the world-class Sichuan-Yunnan-Guizhou Zn-Pb triangle, southwest China: Insights from apatite geochemistry and in situ sericite Rb-Sr geochronology of the Daxiao deposit

The Sichuan-Yunnan-Guizhou (SYG) zinc-lead triangle, located in southwestern China, is an important producer of zinc, lead, silver, and critical raw metals such as germanium. In this region, most Zn-Pb deposits hosted in the later Ediacaran to Permian carbonate rocks are believed to be Mississippi Valley-type (MVT) deposits, while the origin of the Zn-Pb deposits found in the Mesoproterozoic basement remains controversial. To address this gap, our study conducted in situ LA-ICP-MS/MS muscovite Rb-Sr dating and apatite major, trace and Sr isotope analysis on the Daxiao deposit hosted in the Mesoproterozoic basement. The in situ Rb-Sr dating of sericite yielded a Neoproterozoic age of 766 ± 31.3 Ma, challenging the previously proposed Indosinian orogen-related MVT model. Instead, it links the formation of this deposit to an extensional setting that coincided with the breakup of the Rodinia. We identified a specific type of apatite, recognized as ore-stage apatite based on texture and analyzed composition, within the deposit. The ore-stage apatite exhibits high 87Sr/86Sr ratios (ranging from 0.78384 to 0.81082), similar to those of the Archean basement rocks.Based on our study and previous data, we proposed a new genetic model for the Daxiao Zn-Pb deposit, and possibly other basement-hosted Zn-Pb deposits in the SYG triangle. During the Neoproterozoic (∼766 Ma), the study area experienced an extensional setting characterized by crustal thinning and magmatic activity resulting from the breakup of the Rodinia. Basinal brines infiltrated the deep Archean basement along faults and were heated to high temperatures by magma and/or high geothermal gradients. These hot brines continuously extracted Pb, Zn from the Archean basement and migrated upward into the Mesoproterozoic host rock, where they precipitated lead–zinc ores in favorable structural positions. The Daxiao Zn-Pb deposit, along with the coexisting sediment-hosted stratabound copper (SSC) deposits, basement-hosted gold and uranium deposits, and late sulfide mineralization in the iron oxide-copper–gold (IOCG) deposits, suggests a Neoproterozoic regional mineralization event associated with the breakup of Rodinia. Our study also highlights the potential of using in situ sericite Rb-Sr dating to precisely determine the age of other hydrothermal ore deposits, such as Carlin-type Au deposits, which have long been a subject of uncertainty.

Variations in extent, distribution and impact of dolomitization on reservoir quality of Upper Cretaceous foreland-basin carbonates, Abu Dhabi, United Arab Emirates

Petrography, petrophysics, and geochemistry of an Upper Cretaceous, foreland-basin carbonate reservoir, Abu Dhabi, United Arab Emirates, are used to constrain the spatio-temporal variations in the extent of dolomitization and its impact on reservoir quality. Dolomitization in highstand systems tracts (HST) is attributed to repeated tidal and evaporative pumping as well as seepage reflux of penesaline brines during restriction of the platform due to 4th and 5th order cycles of relative sea-level fall and particularly below parasequence boundaries. This interpretation is supported by the presence of rare poikilotopic gypsum cement and scattered laths and micro-nodules of calcitized gypsum in the dolomitized peritidal dolostones. Dolomitization along bioturbation sites, which is most common in the transgressive systems tracts (TST), is attributed to the development of suitable localized geochemical conditions (e.g., microbial sulfate reduction and related increase in carbonate alkalinity). Porosity and permeability of the dolostones are strongly controlled by depositional textures of precursor limestones and by subsequent diagenetic evolution. Dolomitization of mudstones, wackestones and matrix-rich packstones has resulted in the formation of micropore-dominated microcrystalline dolostones whereas dolomitization of the shoal grainstones resulted in the formation of coarse-crystalline dolostones with abundant well-connected intercrystalline and moldic macropores. Mesogenetic alterations of the dolostones, which are attributed to the flow of hot basinal brines along steep faults, include dolomite cementation and, subsequently, dissolution and calcitization of dolomite (dedolomitization) and calcite cementation. The lack of systematic differences in porosity and permeability of dolostones between the oil and water-saturated dolostones suggest that most diagenesis occurred prior to completion of oil emplacement and/or reflect the shallow maximum burial depths of the formation (around 1.3 km). This study demonstrates that variations in the distribution and extent of dolomitization within a sequence stratigraphic context across an oilfield should be considered as primary control on the spatio-temporal reservoir lithology and heterogeneity in carbonate successions.

Influence of Low-Temperature Hydrothermal Events and Basement Fault System on Low-Resistivity Shale Reservoirs: A Case Study from the Upper Ordovician to Lower Silurian in the Sichuan Basin, SW China

High graphitization is responsible for low-resistivity shale development with poor reservoir quality. This paper provides an explanation of organic matter graphitization and determines the impact of high graphite content on low-resistivity shale reservoir quality at the Wufeng-Longmaxi Formation in the Southern Sichuan Basin. Fine veins are frequently developed at shale samples with Ro > 3.5%, graphitized organic matter > 25%, and resistivity < 5 Ω•m, which are dominated by three mineral assemblages: brunsvigite, barite-hyalophane-barium feldspar-potassium feldspar-anhydrite, and calcite-ankerite. These filling minerals are characterized by an Eu positive anomaly and high Ba, Fe, and Mn contents, suggesting that low-resistivity shale was modified by magmatic-related low-temperature hydrothermal fluid. Temperature measurements of brine inclusions and a semi-empirical geothermometer of chlorite show that low-temperature hydrothermal fluid experienced the chlorite stage (150–180 °C), the low-sulfidation stage (120–150 °C), and the low-temperature calcitization stage. Paleozoic fault systems and late Permian hydrothermal activities associated with the Emeishan mantle plume control the graphitization of low-resistivity shale. The water formation and seawater infiltrated into the deep crust along the Paleozoic basement faults under gravity, developing alkaline hot brine through mantle plume heating and then causing a water-rock reaction with basement rocks. They migrated upward along deep and large Paleozoic faults through convective thermal circulation in the Tiangongtang area, the Shuanglong-Luochang area, and the Xuyong area. Cation exchange and redox reactions occurred during the interaction between high-temperature hydrothermal fluid and cool wall rocks. The migration of alkaline hot brine via the Wufeng-Longmaxi shale introduced a subsequent water-rock reaction, resulting in the development of hydrothermal mineral assemblages that intricately filled fractures. It increased formation temperature and enhanced thermal maturity and graphitization of organic matter at the Wufeng-Longmaxi low-resistivity shale, resulting in a wide distribution of low-resistivity shale at the Changning Block.