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Hydraulic injections produce fluid-filled fractures that reduce the seismic velocity of the rock compared to intact rock. The travel times of microearthquakes induced by the injections may be used to discern changes in the rock velocities, as well as locating the microearthquakes. Determining the volumes of rock where the velocities have changed provides indirect evidence for the location of the injected fluid, and the character of the changes produced in the fractured rock. Available data are generally insufficient to resolve both the spatial and temporal changes within the rock. To extract information about temporal changes, and to obtain an improved image of the velocity structure, we chose a parameterization scheme in which the velocities of each block are allowed to change from the background velocity only after a threshold number of microearthquakes have occurred in the block. Regularizing by constraining the velocity of all the altered blocks to be similar helps stabilize the inversion. The regularization can be relaxed somewhat to allow the velocity of an altered block to be different from other altered blocks if the travel-time data are compelling. The parameterization scheme is justified since observations show that the volume of the seismically stimulated rock increases linearly with the volume of the injected fluid. We applied the method to data collected in a region of Precambrian crystalline rock that was injected with 21,600 m 3 of water. We use travel times from a total of 3886 microearthquakes that were induced by the injection. The mean RMS travel-time residual decreases about 7%. The velocity structure contains a low-velocity zone located near the injection region. Other distinct low-velocity zones are identified. The pattern of microearthquake locations found using our method appears to contain more structure than the pattern found in locations determined using a homogeneous velocity structure. Two clear low-velocity regions found near the point where water was injected into the rock are separated by a region whose velocity did not change. The region of unaltered velocity had a large number of microearthquakes.

The extraction of heat or thermal energy from the Earth—heat mining—has the potential to play a major role as an energy supply technology for the 21st century. However, even if reservoir productivity goals are achieved, the role of heat mining with today's energy prices and development costs is limited to only a small fraction of the Earth's surface. A generalized multi‐parameter economic model was developed for optimizing the design and performance of hot dry rock (HDR) geothermal systems. Key technical and institutional obstacles to universal heat mining are discussed in a more general context. Advanced concepts in drilling technology are reviewed in light of their potential impact on overcoming some of these obstacles to universal heat mining

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 10/sup 4/ 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 and Q/sup -1/ of coda waves. Both are increased by nearly the same amount (35approx.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.

Summary Field testing of a hydraulically stimulated, hot, dry rock (HDR) geothermal system at the Fenton Hill site in northern New Mexico indicated that significant reservoir growth occurred as energy was extracted. Tracer, microseismic, and geochemical measurements provided the primary quantitative evidence for the increases in accessible reservoir volume and fractured rock surface area that were observed during energy extraction operations that caused substantial thermal drawdown in portions of the reservoir. These temporal increases suggest that augmentation of reservoir heat-production capacity in an HDR system may be possible.

The Phase I Hot Dry Rock Geothermal Energy reservoirs at the Fenton Hill field site grew continuously during Run Segments 2 through 5 (January 1978 to December 1980). Reservoir growth was caused not only by pressurization and hydraulic fracturing, but also by heat-extraction and thermal-contraction effects. Reservoir heat-transfer area grew from 8000 to 50,000 m2 and reservoir fracture volume grew from 11 to 266 m3. Despite this reservoir growth, the water loss rate increased only 30%, under similar pressure environments. For comparable temperature and pressure conditions, the flow impedance ( a measure of the resistance to circulation of water through the reservoir) remained essentially unchanged, and if reproduced in the Phase II reservoir under development, could result in “self pumping”. Geochemical and seismic hazards have been nonexistent in the Phase I reservoirs. The produced water is relatively low in total dissolved solids and shows little tendency for corrosion or scaling. The largest microearthquake associated with heat extraction measures less than minus one on the extrapolated Richter scale.

Field experiments with fluorescent dye and radioactive tracers (Br82 and I131) have been employed to characterize a hot, low-matrix-permeability, hydraulically fractured granitic reservoir at depths of 2440 to 2960 m (8,000 to 9,700 ft). Tracer profiles and residence time distributions (RTD's) have been used to estimate sweep efficiencies and fracture volumes and to diagnose normal and pathological flow behavior both in injection and in production wells. The effectiveness of one- and two-dimensional (1- and 2D) theoretical dispersion models using single and multiple porous, fractured zones with velocity- and formation-dependent effects is discussed with respect to actual field data.

Abstract Two 3-km-deep boreholes were drilled into hot granite in northern New Mexico to extract geothermal energy from hot, dry rock. Both boreholes were hydraulically fractured to establish a flow connection. Fracture-to-borehole intersection locations and in-situ thermal conductivity were determined from flowing temperature logs. In-situ measurements of rock permeability and compressibility show a strong dependence on pore pressure. An estimate of the minimum horizontal earth stress was derived from fracture extension pressures and found to be one-half the overburden stress. It was found that fracture growth was remarkably simple to achieve in the low-permeability granite and that these factures appear to be "self-propped." The present connection has a large flow impedance that probably cannot be reduced to a useful level. Establishment of a prototype heat exchange system will require redrilling prototype heat exchange system will require redrilling to intersect directly one of the fractures. Introduction A program designed to demonstrate the feasibility of extracting energy from hot, dry rock has been initiated at the Los Alamos Scientific Laboratory. Basically, it is proposed that man-made geothermal energy reservoirs can be created by drilling into relatively impermeable rock to a depth where the temperature is high enough to be useful, creating a reservoir by hydraulic fracturing, and then completing the circulation loop by drilling a second hole to intersect the hydraulically fractured region, or by drilling into the immediate vicinity of the first fracture and then creating a second fracture that intersects the first one. Thermal power would be extracted from this system by injecting cold water down the first hole, forcing the water to sweep by the freshly exposed hot rock surface in the reservoir-fracture system, and then returning the hot water to the surface where the thermal energy would be converted to electrical energy or used for other purposes. System pressures would be maintained such that only one phase, liquid water, would be present in the reservoir and the drilled holes. The concept is described in more detail by Smith et al., and estimates of heat extraction rates have been reported by Harlow and Pracht and McFarland and Murphy. Briefly, it was Pracht and McFarland and Murphy. Briefly, it was found that a large fracture about 1 km in radius, in hot, 200 to 250C rock, is sufficient to provide an average of 60 MW of thermal power for 20 years. In addition, the thermal contraction associated with the cooling of the rock will result in thermal stress cracking, crating additional porosity and heat-transfer surfaces, so that hundreds of megawatts of thermal power may be provided ultimately. DRILLING AND COMPLETIONS The hot, dry rock concept is being investigated in a series of field experiments at Fenton Hill, located on the west flank of a dormant volcano, the Valles Caldera, in the Jemez mountains of northern New Mexico. In Dec. 1974, the first deep borehole, GT-2, was drilled to a depth of 2.929 km (9,609 ft) in granite, where the temperature was 197C (386F), cased to 2.917 km (9,571 ft), and then fractured in the open hole below the casing. The variation of equilibrium temperature and geology with depth is shown in Fig. 1. The Precambrian crystalline rocks were encountered at 730 m (2,400 ft). From this depth to the bottom the geothermal gradient is reasonably constant, although it is somewhat lower in the gneiss as compared with the deeper formations (44C/km vs 57C/km). The steeper gradient in the sediments above 730 m is caused by their lower thermal conductivity. Based on the conductivity measurements at 2.77 km (9,100 ft), the geothermal heat flow at this site is 0.16 W/sq m, 2 times the worldwide average. SPEJ p. 317

Earlier tracer tests run in the Phase 1 system proved useful in determining the geometry of the annular spaces behind casing. Based on this experience the following experiment will be run in the EE-2 wellbore in order to estimate the state of the 9-5/8-in. casing below 10,750 ft.

This procedure covers only Experiment 2039, the temperature and tracer logging in EE-1. The purposes of this experiment are to; seek evidence of any flows behind the EE-3 casing; seek evidence of any flows behind the cemented-in liner; determine any changes in flow "acceptance" (pressure and injection rate characteristics) of the formations since Experiments 2031 and 2033; determine how much flow enters the "thief" zone; and determine how much flow enters the formations just above, and below, the cemented-in liner.

This is a detailed examination of microseismic event locations obtained from experiments 2018, 2020, 2023 and 2025. It suggests that the major difference in pressure behavior between systems that open at lower pressure and those that open at higher pressure can be ascribed to a lithologic boundary. The boundary appears to be defined by a discontinuity in joint orientation rather than an abrupt change in stress field. Examination of rock types determined from cuttings in EE-2 and EE-3 have defined two major intrusive events that contact roughly coincides with the inferred fracture orientation boundary.

Analysis of the accelerometer system response to 11 microseismic events created in Experiment 2007 indicates that they are located in an ellipsoidal volume whose major axis direction is N 48° E and dips 47° to the SW. The intermediate axis is essentially horizontal and whose direction N 42° W is the strike of the plane containing the two major axes. The dimensions of the three axes are 315,100 and 65 m respectively. The relationship of this seismic feature to the downhole wellbore map is shown in Figures 1 and 2. It will be noted that the ellipsoid is tangent to the injection point in EE-3 and descends at a 45 angle. The plan view shown in Figure 1 indicates that the zone of seismic activity nearly cut the EE-2 wellbore at a depth of 11500 ft (TVD). Examination of the EE-2 wellbore geology and drilling history shows a well defined zone from 11450-11550 ft TVD with a very fast drilling rate (30 ft/hr) and extensive alteration. Laney labels it as a fault zone. This then coudl be an unpressurized part of the planar feature described above.

This report seeks to understand the nature of the "thief" zone inside the EE-3 by pumping 150-200K gallons of heated water into that zone. The questions they seek to answer are; does the thief zone represent a potential danger to future operations in the form of earthquakes, aquifers, damage to equipment or tubulars, or require that it be sealed; is a connection into the the thief zone from EE-2 a disaster point; could the connection into the thief zone provide a low back-pressure condition.

Field testing of a hydraulically stimulated, hot dry rock (HDR) geothermal system at the Fenton Hill site in northern New Mexico indicated that significant reservoir growth occurred as energy was extracted. Tracer, microseismic, and geochemical measurements provided the primary quantitative evidence for the increases in accessible reservoir volume and fractured rock surface area that were observed during energy extraction operations that caused substantial thermal drawdown in portions of the reservoir. These temporal increases suggest that augmentation of reservoir hear-production capacity in an HDR system may be possible. [DJE 2005]

The purpose of this experiment was to run temperature, spinner and tracer surveys in EE-2, while injecting water, so as to determine the extent, if any, of damage to the casing cement, and also to determine locations and flow fractions of the fracture between the bottom of the casing and top of the sand.

Following fracturing it will be necessary to evaluate the success of each treatment. The primary method will be to measure impedance.

A plan is presented here to enlarge the effective heat transfer area of the EE-1/GT-2B system by isolating the high fluid conductivity short path length connections with a recementing of the free casing in EE-1.

The roentgenologist bears the responsibility for diagnosis of lesions of the colon above the level of direct visualization by the sigmoidoscope. With improved x-ray technic and dissemination of knowledge of methods of examination, there has been steady progress in diagnostic accuracy. There still remains, however, a reducible error, particularly in relation to small lesions of the colon. As has been repeatedly emphasized, early and accurate diagnosis of small lesions, particularly those of a polypoid type, offers the best hope for successful treatment of cancer of the colon. The relationship of the two conditions has been well established. However, the probable multiplicity of polyps of the colon or rectum de serves re-emphasis. Statistical observations indicate that lesions of the colon or rectum will be multiple in 30 to 40 per cent of all cases (1, 4). We, as roentgenologists, should not be content, therefore, to think that our job is done when the presence of a single polyp has been established by x-r...

Two hot dry rock geothermal energy reservoirs were created by hydraulic fracturing of Precambrian granitic rock on the west flank of the Valles Caldera, a dormant volcanic complex, in the Jemez Mountains of northern New Mexico. Heat was extracted in a closed-loop mode of operation, injecting water into one well and extracting the heated water from a separate production well. The first reservoir was produced by fracturing the injection well at a depth of 2.75 km, where the indigenous rock temperature was 185°C. The relatively rapid decline in temperature of the water produced from the first reservoir, 100°C in 74 days, indicated an effective fracture radius of about 60 m with an average thermal power extracted of 4 MW. A second, larger reservoir was created by refracturing the injection well 180 m deeper. Downhole measurements of water temperature at the reservoir outlet as well as temperatures inferred from chemical geothermometry showed that the thermal decline of this reservoir was negligible; the effective heat transfer area of the new reservoir must be at least 45,000 m2, nearly 6 times larger than the first reservoir. In addition, reservoir residence time studies employing visible dye tracers indicated that the mean volume of the second reservoir is 9 times larger. Other measurements showed that flow impedances were low and that downhole water losses from these reservoirs should be manageable. The geochemistry of the produced water was essentially benign, with no scaling problems apparent. Moreover, the level of induced seismic activity was insignificantly small.

ESTIMATIONS made from vital statistics of the United States 1 indicate that carcinoma of the large intestine accounted for approximately 33,000 deaths in 1948. Yet no other site of internal cancer is so amenable to modern treatment, with a low morbidity and a low mortality and an encouraging survival rate. This is especially true if the disease is recognized in the early phase. In spite of medical and lay cancer education, the average duration of symptoms is still over six months in all patients coming to surgery for carcinoma of the rectum and colon. Therefore, reiteration and discussion of features and recognized concepts which if utilized will lead to the early detection and treatment of malignant and premalignant lesions continue to be vital. The intimate relationship of polypoid lesions to carcinoma is so well established that the early detection and removal or destruction of these neoplasms is mandatory in the

This month's article has been prepared in collaboration with Dr. Robert D. Moseley, Jr., Chairman of the Department of Radiology at the University of Chicago. Dr. Moseley came to the University of Chicago in January 1949 as an assistant resident in radiology, having received his M.D. degree from the Louisiana State University School of Medicine. He was assigned by the University as its representative at the Los Alamos Scientific Laboratory for the year 1950, and subsequently served two years in the United States Navy. He returned to the University of Chicago as an instructor in radiology in July 1954, and in July 1958 he became a professor and chairman of the department.—Paul C. Hodges, M.D.