Hot Site Research Articles

A hybrid model of the CO2 geochemical cycle and its application to large impact events.

A hybrid model of the carbonate-silicate geochemical cycle is presented which is capable of calculating the partitioning of carbon dioxide between the atmosphere, ocean, and sedimentary rocks. The ocean is subdivided into a shallow, mixed layer, which remains in equilibrium with the atmosphere, and a massive, deep layer which does not. Gradients in dissolved carbon content are established between the mixed layer and the deep ocean as a consequence of downward fluxes of fecal matter and of dead planktonic organisms. The dissolved carbon content and alkalinity of the ocean as a whole are controlled by weathering and metamorphism of sedimentary rocks. Equilibrium solutions are derived for the preindustrial atmosphere/ocean system and for a system that may be similar to that existing during the Late Cretaceous Period. The model is then used to determine how the modern and ancient marine biospheres might be affected by an oceanic impact of a large asteroid or comet. Such an event could perturb the carbon cycle in several different ways. Global darkening caused by stratospheric dust veil could destroy most of the existing phytoplankton in a period of several weeks to several months. At the same time, dissolution of atmospheric NOx compounds synthesized during the impact would lower the pH of ocean surface waters and release CO2 into the atmosphere. Both effects might be enhanced by an influx of CO2 released from upwelling of deep ocean water near the hot impact site, from oxidation of dead organic matter, and from the comet itself. The net result could be to raise surface temperatures by several degrees and to make the surface ocean uninhabitable by calcareous organisms for as much as 20 yrs (the time scale for mixing with deep ocean). It appears unlikely, however, that an impact could create a "Strangelove ocean," in which surface waters remained corrosive to calcium carbonate for thousands or tens of thousands of years. Thus, disruption of the carbon cycle by an impact event cannot by itself explain the scarcity of calcium carbonate in sediments found within the first few centimeters above the K/T boundary.

Cross-hole seismic surveys: applications for studying sub-surface fracture systems at a hot dry rock geothermal site : Fehler, M; Pearson, C GeophysicsV49, N1, Jan 1984, P37–45

Cross-hole seismic surveys: applications for studying sub-surface fracture systems at a hot dry rock geothermal site : Fehler, M; Pearson, C GeophysicsV49, N1, Jan 1984, P37–45

History and Archaeology of the Hot Wells Hotel Site, 41BX237

During the month of April 1984, archaeologists from the Center for Archaeological Research, The University of Texas at San Antonio, conducted a surface survey and test excavations at the Hot Wells Hotel site in south San Antonio. The purpose of the project was to locate and map the foundations of a large brick resort hotel, built in 1901 and burned in 1925, and to locate and test remains of any other structures on the Hot Wells site. One additional brick foundation that appears contemporary with the hotel was located and mapped. Artifacts recovered pertained primarily to the hotel, or to later residents in the area.

Adsorption of mixtures of acetone and benzene vapors on graphitized carbon black

Further description and interpretation of a previously determined set of adsorption isotherms of mixtures of acetone and benzene on Carbopack C at 20°C are presented. The individual and combined isotherms are represented as three-dimensional plots covering a full range of surface coverage up to, and slightly beyond, monolayer coverage. A limited set of isotherm data is also presented for hydrogen-treated Carbopack C. The experimental procedure was a chromatographic method, mass spectrometric tracer pulse chromatography, which allowed the determination of the isotherm of one component at a fixed partial pressure of the second component. This protocol permitted the development of full isotherms, rather than the more restricted isotherms obtained with classical experiments at fixed gas phase composition or fixed total pressure. The adsorbent was selective for benzene at 20°C, and the isotherms of benzene were not significantly affected by adsorbed acetone. However, the isotherms of acetone were critically dependent on the partial pressure of benzene. Very low surface coverages of benzene prevented the adsorption of disproportionately large amounts of acetone (up to a ratio of 1:100). This amplification effect was similar to that observed for poisoning and promotion effects on Fischer—Tropsch catalysts. The experimental results are discussed in terms of two possible adsorption mechanisms. Both models emphasize the significance of a small number of high energy sites (mostly chemisorbed oxygen or sulfur) on the surface of the Carbopack C. These “key” sites may anchor segregated adsorption of acetone clusters stabilized by direct lateral interactions, or they may influence the work function or ionization potential of the surface adjacent to the site by influencing the electron density in the delocalized pi orbital of the graphite surface. Removal of the hot sites by treatment with hydrogen at high temperature reduced the adsorption of acetone and the poisoning effect of benzene.

Human chromosome hot points. 1. Hot point at 3p14 in three populations.

A chromosome hot point, 3p14, in healthy peasants, mentally retarded patients (MR), and epileptic patients (EP) was studied. The frequency of the hot point, 3p14 break, was significantly higher in EP. It may be caused by folic acid reduction in patients' serum induced by the antiepileptic drugs. The difference between hot point and fragile site is discussed.

Effects of respirators under heat/work conditions.

Physiological responses and perceived strain of five unacclimatized male subjects were studied. The subjects were exposed to heat during an exercise task and were evaluated while wearing half and full facepiece, cartridge-type, air-purifying respirators, and without a respirator. The exercise consisted of walking on a treadmill for a period of 1 hour in a controlled environmental chamber at each of two different energy expenditure levels (200 and 400 Kcal/hr) (approximately equal to 58 and 116 Watts) and two different heat exposures (air temperatures of 25 degrees C and 43.3 degrees C). The results indicated that wearing a full facepiece respirator imposed significant physiological strain added to that caused by the heat and workloads used in the study. Five of the six physiological measures show this increased physiological strain: heart rate; minute ventilation; oxygen consumption; energy expenditure; and oral temperature. There was no detectable effect on sweat rate. Although subjective ratings indicated more discomfort with increasing physiological strain, the observed correlations between such measures were low (Tb less than .60). The net consequence of the significant effects indicates that workers' tolerance to moderate or higher levels of work under hot conditions while wearing a respirator is reduced. The reduction is more pronounced when wearing a full mask than when wearing a half mask. Changes in respirator design which minimize respiratory dead space are suggested to alleviate this problem. Otherwise, prevention of excessive physiological strain from respirator use when working at moderate or higher levels at hot job sites could necessitate more rest breaks or limiting work time under such conditions.

Wheat in tropical environments. II. Crop growth and grain yield

In order to understand the effect of temperature on yield and the genetic adaptation of wheat to hot low latitude environments, replicated plot experiments with 14 or more diverse spring wheat genotypes were conducted over two winter seasons (1973–74 and 1974–75) and several sowing dates in central Mexico (latitude 19–20°N). There were two hot low-altitude sites (60 and 940 m) and two cool highland sites (2249 and 2640 m); mean January temperatures were 21, 20, 11 and 7°C, respectively. Cloudiness reduced solar radiation and diurnal temperature range at the lowest site. Crops were grown under optimal agronomy and irrigation, with disease control, although it was not possible to prevent serious foliar disease (Helminthosporium saticum subsp. tritici) during grain filling at the lowest site.

Cross‐hole seismic surveys: Applications for studying subsurface fracture systems at a hot dry rock geothermal site

The use of cross hole seismic surveys for delineating the location and size of subsurface fracture systems is investigated. The radiation pattern for P and S waves emitted by a seismic source in a borehole is derived. Experimental work in relatively homogeneous granite suggests that the derived relationship adequately describes the radiation pattern for both explosive sources and acoustic transducers placed in fluid‐filled boreholes. Using the above functional expressions for the S‐ and P‐wave amplitudes, we have developed a technique to estimate Q and locate discrete fractures in crystalline rock that compose the Hot Dry Rock Geothermal Reservoir at Fenton Hill, New Mexico. To calculate Q, we measure the P‐ and S‐wave amplitudes as a function of distance from the source, compensate for the radiation pattern and geometrical spreading effects, and match the relative attenuation to a function of the form [Formula: see text] using a least‐squares regression technique. For undisturbed parts of the reservoir, we obtain values of Q on the order of 160 for P waves and from 170 to 150 for S waves. Using our method we are able to detect a decrease in the average Q due to extensive fracturing following heat extraction from the Fenton Hill reservoir. We have also been able to locate discrete large‐scale fractures in the reservoir by noting regions characterized by a sudden change in signal amplitude, wave form or frequency content that cannot be explained by radiation pattern effects or increases in source‐receiver separation. These localized attenuating regions in the Fenton Hill Hot Dry Rock reservoir are probably open fractures.

Fault plane solutions for microearthquakes induced at the Fenton Hill hot dry rock Geothermal site: Implications for the state of stress near a quaternary volcanic center

Fault plane solutions of earthquakes induced during attempts to stimulate two hot dry rock reservoirs at Fenton Hill have significantly different patterns of first motions. The fault plane solution for the lower reservoir indicates strike slip, either left lateral strike slip on a N‐S vertical plane or right lateral slip on an E‐W vertical plane. In contrast, the solution for the upper zone includes largely vertical slip on a N‐S nearly vertical plane, or oblique slip on a nearly horizontal plane. Because the N‐S nodal plane is common in both solutions we infer that this represents the true fracture plane. Faulting thus seems to occur on a series of parallel faults or joints that intersect both reservoirs but a change in the slip vector indicates a major change in the state of stress between the upper and lower reservoirs. This latter conclusion is surprising because the two reservoirs are separated by less than 1 km. We suggest that this rapid change in the stress field may be related to the structure and subsidence of the nearby Valles Caldera.

Interpretation of seismic data from hydraulic fracturing experiments at the Fenton Hill, New Mexico, hot dry rock geothermal site : Aki, K; Fehler, M; Aamodt, R L J Geophys Res, V87, NB2, 10 Feb 1982, P936–944

Interpretation of seismic data from hydraulic fracturing experiments at the Fenton Hill, New Mexico, hot dry rock geothermal site : Aki, K; Fehler, M; Aamodt, R L J Geophys Res, V87, NB2, 10 Feb 1982, P936–944

Acoustic emissions as a tool for hydraulic fracture location: Experience at the fenton hill hot dry rock site : Albright, J N; Pearson, C F Soc Petr Engr J, V22, N4, Aug 1982, P523–530

Acoustic emissions as a tool for hydraulic fracture location: Experience at the fenton hill hot dry rock site : Albright, J N; Pearson, C F Soc Petr Engr J, V22, N4, Aug 1982, P523–530

In-situ stress measurement in the Carnmenellis granite—II. Hydrofracture tests at Rosemanowes quarry to depths of 2000 m

Hydrofracture stress measurments were conducted in the Carnmenellis granite at the Camborne School of Mines Hot Dry Rock Geothermal Energy Research site at Rosemanowes Quarry near Penryn, Cornwall, U.K. Tests were conducted at depths of up to 2000 m in borehole RH 12, which was drilled with nominal diameters of 311 mm and 216 mm and at an inclination of up to 32° from vertical. The tests were successful in establishing reliable values for the minimum horizontal stress, and estimates of the maximum horizontal stress. Stress anisotropy was very significant throughout the tested depth, with maximum and minimum horizontal stresses of about 70 and 30 MPa respectively at a vertical depth of 2000 m. The overburden stress at this depth was estimated as 52 MPa. The bearing of the maximum horizontal stress was established in a separate programme of overcoring stress measurement at approximately 130° relative to true north. The stress magnitudes determined by the overcoring tests were close to those measured by the hydrofracture tests at the same depth. The effects of hole inclination, test procedure and premature cracking of the borehole wall due to high compressive stresses are discussed in relation to the in-situ stress interpretation.

Twig Elongation Patterns of Chamaecyparis lawsoniana

Twig elongation was measured during two growing seasons for 12 native populations of saplings of Chamaecyparis lawsoniana and for co-occurring saplings of Pseudotsuga menziesii, Tsuga heterophylla, or Abies concolor at some sites. Growth of lateral branches of C lawsoniana was always early, and sometimes completed more quickly, on the hot and open sites but was always late and brief on the colder ones; moderate coastal sites had more prolonged elongation centered in midsummer The rate of growth increased with the rise in daytime air temperature in the spring, with populations at cold sites responding most to rising temperature Rates of growth after the peak were not related to temperature. Early growth cessation of populations in open, hot sites occurred despite their high predawn water potentials. Twig elongation of Pinaceae associated with C lawsoniana was of shorter duration than for Chamaecyparis Pseudotsuga in the mixed-evergreen zone was more responsive to temperature than was C. lawsoniana Phenology of rooted cuttings of four populations of C lawsoniana grown in a garden varied much less than did saplings studied in the field; no phenological differences were significant Genetic variability of phenology of C lawsoniana is smaller than that of competing Pinaceae Its phenological pattern appears to be important in restricting C lawsoniana to sites with dependable summer moisture and perhaps in determining its northern range limit.

Properties of seismic wave scattering around water injection well at Fenton Hill hot dry rock geothermal site

To determine the scattering properties of microcracks created by water injection in hot dry rock a method for analyzing trajectory ellipsoids of seismic particle motions has been applied. Lengths and directions of three principal axes of trajectory ellipsoids were calculated, and a distribution of the shape of these ellipsoids suggests existence of a strong scattering region around the injection point. This strong scattering has an anisotropic property presumably due to microcrack orientation in the original rock.

Geology of the Fenton Hill, New Mexico, hot dry rock site

The Phase I prototype hot dry rock (HDR) geothermal system was developed in Precambrian basement rocks at Fenton Hill, New Mexico. Core and cuttings samples from the four deep wells indicate that the reservoir of this Phase I HDR system lies within a homogeneous biotite granodiorite body of very low permeability. Natural fractures, although present, are typically sealed with secondary minerals. The biotite granodiorite is intrusive into a heterogeneous metamorphic complex comprised of gneisses of variable composition and minor mafic schist, amphibolite, and metavolcanic rocks. The deeper part of this metamorphic section is the site of a deeper Phase II system currently under development. Differences in geology between the phase I and underlying Phase II systems will provide an opportunity for further testing of HDR development techniques.

Acoustic Emissions as a Tool for Hydraulic Fracture Location: Experience at the Fenton Hill Hot Dry Rock Site

Abstract Microearthquakes with magnitudes between −6 and −2 have been observed in three successive massive injections of water at the hot dry rock geothermal energy development project's demonstration site at Fenton Hill, NM. The injections were part of a program to increase the heat transfer area of hydraulic fractures and to decrease the flow-through impedance between wells in the energy extraction system under construction. The microearthquakes were used in mapping the location of the extended hydraulic fractures. The large shear- to compressional-wave-amplitude ratio observed in the signals suggests that the microearthquakes result from shear failure, probably on preexisting planes of weakness that intersect or make up the main hydraulic system. Failure resulting from increased pore pressure is a likely cause for the microearthquakes. Knowledge of the failure criterion for the reservoir rocks permits calculation of the pore pressure increases necessary for failure. At Fenton Hill, it appears that pressures 2 Pa (0.00029 psi) above hydrostatic are necessary. For this hypothesis of microearthquake occurrence to hold, the effective reservoir permeability must be four orders of magnitude above that for the bulk rock, as would be the case if there were permeable joints or fractures in the reservoir before hydraulic stimulation.

Interpretation of seismic data from hydraulic fracturing experiments at the Fenton Hill, New Mexico, hot dry rock geothermal site

An attempt was made to synthesize the results of active seismic experiments carried out by the Los Alamos National Laboratory's Hot Dry Rock Project staff for determining the geometrical and physical properties of the fracture system produced by hydraulic fracturing in a hot, low‐permeability rock. Interpretation of data from several reflection, transmission, and attenuation experiments using seismic probes in the frequency range from a few hundred to more than 104 Hz led us to postulate the existence of a highly complex fracture system consisting of major discrete vertical cracks intersected by several inclined joints which are surrounded by a large volume of rock containing small‐scale cracks. We found an interesting coincidence between the mean square fluctuation of P arrival time arid Q−1 of coda waves. Both are increased by nearly the same amount (35∼40%) when fluid pressure in the reservoir is increased. Another coincidence is the scale length of the inhomogeneity of roughly 3 m obtained from the frequency dependence of attenuation and also from the spatial variation of P arrival time. These results suggest that the seismic attenuation in the fractured region is caused primarily by scattering.

Handling of High Pour Point West African Crude Oils

Abstract Micro earthquakes with magnitudes between -6 and -2 have been observed in three successive massive injections of water at the hot dry rock geothermal energy development project's demonstration site at Fenton Hill, NM. The injections were part of a program to increase the heat transfer area of hydraulic fractures and to decrease the flow-through impedance between wells in the energy extraction system under construction. The micro earthquakes were used in mapping the location of the extended hydraulic fractures. The large shear- to compressional-wave-amplitude ratio observed in the signals suggests that the microearthquakes result from shear failure, probably on preexisting planes of weakness that inter-sect or make up the main hydraulic system. Failure resulting from increased pore pressure is a likely cause for the micro earthquakes. Knowledge of the failure criterion for the reservoir rocks permits calculation of the pore pressure increases necessary for failure. At Fenton Hill. it appears that pressures 2 Pa (0.00029 psi) above hydrostatic are necessary. For this hypothesis of microearthquake occurrence to hold, the effective reservoir permeability must be four orders of magnitude above that for the bulk rock, as would be the case if there were permeable joints or fractures in the reservoir before hydraulic stimulation. Introduction A hot dry rock geothermal energy extraction system consists of two wells connected by a flow-through fracture system constructed in relatively impermeable rock. Fracture surfaces serve as heat exchangers. Water is injected into the fracture system through one well, returned heated to the surface through a second well, cooled during power generation, and reinjected. Knowledge of fracture system location and dimension is an important element in reservoir construction and development. During construction, fractures are targeted for intersect drilling and are driven between wells. In later evaluations of reservoir capacity and lifetime, the dimensions are an important constraint in modeling efforts. This paper describes a technique for using the location of very small (local magnitude -6 to -2) micro earthquake-., that accompany hydraulic stimulation experiments in low-permeability basement rocks to locathydraulic fractures. Because these events, which are induced by high pore fluid pressures, occur in a narrow band around the hydraulic fracture, their locations can be used to infer fracture location and orientation. As an unexpected by-product from this study, we developed a technique to estimate effective reservoir permeability through use of these locations and a very simple model of the type of rock failure that causes micro earthquakes. In our experience at Fenton Hill. microseismicity (Table 1) usually is associated with massive hydraulic fracturing (MHF) experiments if the maximum injected water volume exceeds a critical volume equal to twothirds to three-fourths of the maximum amount injected into this fracture during all previous MHF experiments. After this critical volume is exceeded, the rate of seismicity rapidly increases from a very low level. Fig. 1 shows a sample histogram of event frequency vs. time for several sample experiments. Microseismic data associated with two MHF experiments and one flow test carried out in low permeability crystalline rock at the Los Alamos Natl. Laboratory, Fenton Hill, hot dry rock demonstration site were available for analysis. During the two MHF experiments, event locations were distributed in a narrow zone around an almost vertical, north-by-northwest- trending plane surrounding the hydraulic fracture. In contrast, during the flow test, event locations were scattered in a much larger, almost spherical volume. This change in the distribution of event locations is caused by transition from one- to three-dimensional (1- to 3D) fluid flow in the medium surrounding the hydraulic fracture. SPEJ P. 523^

Interaction of seismic waves with a viscous liquid layer

abstractThe interaction of seismic waves with a layer filled with a viscous fluid is studied. This study is intended to provide the basis for designing active seismic experiments to detect the existence of hydraulically induced fractures in a Hot Dry Rock Geothermal energy system. We compute transmission and reflection coefficients for P, SV, and SH waves incident at arbitrary angles onto a fluid layer embedded between two homogeneous half-spaces. We find that coefficients for SH waves at normal incidence can be written in terms of two dimensionless parameters. One of these parameters, I, is the ratio of acoustic impedance of the fluid to the acoustic impedance of the solid. The other dimensionless parameter, γd, is a measure of the amount of energy the SH wave loses during one pass through the fluid layer. We find that the amplitude of the SH wave transmitted through the fluid layer is equal to the amplitude of the incident SH wave if I is nearly 1 and γd is small. As γd increases, energy is lost due to viscous dissipation in the fluid and transmitted wave amplitude diminishes. If I is not nearly 1, some energy is reflected by the fluid layer. Three dimensionless parameters are required for solution for the case of P waves normally incident on the fluid layer. One parameter, R, is the ratio of the bulk modulus to effective shear modulus of the fluid. The second parameter is the ratio of elastic impedance of the solid to the shear impedance of the fluid and the third is γd. We find that the value of R is a good measure of the importance of fluid viscosity on the propagation of P waves through the fluid. Detailed studies of the effects of fluid and solid physical properties on the amplitudes of transmitted and reflected waves when waves are normally incident provide valuable insight into the importance of physical properties in the calculations for non-normal incidence. Finally, reflection and transmission coefficients are computed for P and SV waves incident at arbitrary angle on a viscous fluid layer. Physical properties of fluid and rock are chosen to be those thought appropriate for the Los Alamos National Laboratory Hot Dry Rock Geothermal test site located at Fenton Hill, New Mexico.

Geothermal regimes of the Costa Rica Rift, east Pacific, investigated by drilling, DSDP-IPOD Legs 68, 69, and 70

Drilling durin Deep Sea Drilling Project Legs 68, 69, and 70 on the southern limb of the Costa Rica Rift was used to study geothermal processes in the ocean crust. Two areas were drilled. One was a geothermally hot site on 6.2-m.y.-old crust, where topography is smooth, heat flow is close to that predicted by conductive cooling of the lithosphere (200 mWm −2 ), and hydrothermal circulation may be sealed within the crust. The other was on 3.9-m.y.-old crust, where rough topography is associated with low heat flow (15 to 50 mWm −2 ) and possible open convection of sea water. At both sites, about 250 m of siliceous-calcareous sediments overlies igneous basement. In the hot area, it blankets the topography, whereas in the cold area, basement outcrops still occur. Operations included numerous down-hole experiments in both areas and hydraulic piston coring of a 230-m sediment section in the hot area. Diagenesis of the sediments appears closely related to temperature. At the hot site, chert was found near basement, and the chemistry of pore fluids, sampled from both sediments and basement, is strongly influenced by reactions within the basement. Strong lateral gradients in the composition of pore fluids occur in the sediments. At the cold site, no chert was found, and bacterial processes within the sediment dominated the chemistry of the pore fluids. Basaltic basement in both areas consists mainly of pillow lavas and thin flows, with occasional more massive units. The basalt is relatively magnesian. The degree of alteration is very small in the cold area, but much more extensive in the hot area. Ease of drilling also shows a strong contrast. Basement penetration reached 562 m in the hot area and was halted because of lack of time; at the cold site, 43 m of basement was cored only with difficulty. The most intensive in-hole experiments were conducted in the hot area. Successful runs with the borehole televiewer allowed basement lithology to be determined and showed the presence of more and less fractured zones. Pulse tests using a single borehole packer gave values of basement permeability of about 2 to 40 millidarcies. Numerous temperature logs established a broadly conductive in situ temperature gradient, with temperatures reaching 120 °C at 562 m into the basement. However, anomalously low temperatures in the upper part of the hole, which persisted after drilling disturbance had decayed away, showed that cold ocean water was flowing down the hole and into the basement at about 90 m below the base of the sediments, at rates of about 80 to 100 m/hr. The packer records indicate a pressure at this depth of ∼ 10 bars below hydrostatic. Costa Rica Rift United Scientific Team, made up of shipboard participants on Legs 68/501, 69 and 70, who were, in reverse alphabetical order: