East Mesa Geothermal Field Research Articles

An Incomplete Inventory of Suspected Human-Induced Surface Deformation in North America Detected by Satellite Interferometric Synthetic-Aperture Radar

We used satellite interferometric synthetic-aperture radar (InSAR) data to document ground deformation across North America suspected to be caused by human activities. We showed that anthropogenic deformation can be measured from space across the continent and thus satellite observations should be collected routinely to characterize this deformation. We included results from the literature as well as new analysis of more than 5000 interferograms from the European Remote Sensing (ERS) satellite, Envisat, the Advanced Land Observing Satellite (ALOS), and other satellites, collectively spanning the period 1992–2015. This compilation, while not complete in terms of spatial or temporal coverage nor uniform in quality over the region, contains 263 different areas of likely anthropogenic ground deformation, including 65 that were previously unreported. The sources can be attributed to groundwater extraction (50%), geothermal sites (6%), hydrocarbon production (20%), mining (21%), and other sources (3%) such as lake level changes driven by human activities and tunneling. In a few areas, the source of deformation is ambiguous. We found at least 80 global positioning system (GPS) stations within 20 km of of these areas that could be contaminated by the anthropogenic deformation. At sites where we performed a full time series analysis, we found a mix of steady and time-variable deformation rates. For example, at the East Mesa Geothermal Field in California, we found an area that changed from subsidence to uplift around 2006, even though publicly available records of pumping and injection showed no change during that time. We illustrate selected non-detections from wastewater injection in Oklahoma and eastern Texas, where we found that the detection threshold with available data is >0.5 cm/yr. This places into doubt previous results claiming detection below this threshold in eastern Texas. However, we found likely injection-induced uplift in a different area of eastern Texas at rates in excess of −2 cm/yr. We encourage others to expand the database in space and time in the supplemental material.

The spatial and temporal subsidence variability of the East Mesa Geothermal Field, California, USA, and its potential impact on the All American Canal System

The spatiotemporal variability of subsidence around the East Mesa Geothermal Field (EMGF) near the All American Canal (AAC) has been measured using 30 temporally averaged interferograms from 1992 to 2000. Deformation rate maps from two shorter time periods indicated the maximum subsidence rate of the EMGF was reduced from −43 mm year−1 (1992–1997) to −34 mm year−1 (1996–2000) corresponding to decreasing net geothermal water production. The maximum subsidence on the East Highline Canal was −9.5 ± 0.5 and −2.4 ± 0.8 cm for each shorter time period. Interferometric synthetic aperture radar (InSAR) stacking demonstrated its utility in monitoring subsidence of the canal caused by the nearby geothermal plant at regional coverage superior to ground levelling networks. Such data on the subsidence of surface and subsurface hydrodynamics along the US–Mexico border are scarce, and are particularly significant in a zone of present and likely future acute water resource management sensitivity.

Integrating reservoir engineering and satellite remote sensing for (true) continuous time-lapse reservoir monitoring

The poem “The Blind Men and the Elephant” is based on an ancient Indian fable in which each man described rather differently what he sensed about an elephant. A similar situation can, and sometimes does, occur in reservoir description. Evidence shows that a reasonably thorough understanding of a reservoir is not very likely without viewing it from many angles and perspectives. This paper will show how two different perspectives of a reservoir—reservoir engineering and satellite remote sensing—can improve reservoir description and even allow (true) continuous time-lapse reservoir monitoring. The idea is simple. If subsidence occurs over an oil field, satellite remote sensing can detect the subsidence, and reservoir engineering can model the subsidence. By integrating reservoir engineering and satellite remote sensing, we can continuously monitor the hydrocarbon production. We use two examples, one from East Mesa Geothermal Field and one from Lost Hills Oil Field, to illustrate the idea. The principle of satellite synthetic aperture radar (SAR) is fairly straightforward. A microwave sensor, which can be on a spacecraft, passes a spot on the ground and takes a “shot” of it. After a certain period, the same sensor passes over the same spot and takes a second “shot” (Figure 1). By comparing the two shots with a reference elevation map, a detailed surface deformation map can be obtained for the period between the passes. Figure 1. Principles of SAR for measuring deformation (from http://www-star.stanford.edu/sar_group/). The image shows two passes of the same microwave sensor over the same location on earth. The difference between the two passes is determined by both earth topography and surface deformation. When data from a reference elevation map or a third pass is used for comparison, the topography effect can be eliminated. What remains is solely surface deformation. SAR can measure surface deformation at very high resolution (a …

Land subsidence caused by the East Mesa Geothermal Field, California, observed using SAR interferometry

Interferometric combination of pairs of synthetic aperture radar (SAR) images acquired by the ERS‐1 satellite maps the deformation field associated with the activity of the East Mesa geothermal plant, located in southern California. SAR interferometry is applied to this flat area without the need of a digital terrain model. Several combinations are used to ascertain the nature of the phenomenon. Short term interferograms reveal surface phase changes on agricultural fields similar to what had been observed previously with SEASAT radar data. Long term (2 years) interferograms allow the study of land subsidence and improve prior knowledge of the displacement field, and agree with existing, sparse levelling data. This example illustrates the power of the interferometric technique for deriving accurate industrial intelligence as well as its potential for legal action, in cases involving environmental damages.

Nonisothermal Effects During Injection and Falloff Tests

Summary Numerically simulated pressure transients during injection and falloff tests are analyzed to develop methods for obtaining the correct permeability/thickness of the reservoir and the skin factor for the well. The results show that to analyze correctly the pressure transients governed by a moving thermal front, the fluid-property values must correspond to the temperature of the injected fluid. For pressure falloff tests and for injection tests conducted in a well cooled by previous injection or drilling, however, the physical properties of the in-situ reservoir fluids must be used. The application of conventional isothermal methods for calculating skin values from injection and falloff data will give erroneous results. A new method is presented for calculating skin values from injection and falloff data that accurately corrects for nonisothermal effects. Examples are given to illustrate this analysis method. The technique is applied to the analysis of injection test data from a well located in the East Mesa geothermal field in southern California.

Thermoelectrical self‐potential anomalies and their relationship to the solid angle subtended by the source region

The calculation of self‐potential (SP) anomalies produced by thermoelectric sources is shown to be equivalent to calculating the weighted solid angle subtended at the observation point by the source region and its images where the weighting function is the source intensity. This interpretation provides an easy way of visualizing the effect of different source geometries, and describes the nonuniqueness associated with SP sources. For example, changes in a model which keep the product of source intensity and area constant do not appreciably change the produced anomaly. Similarly, deepening a source requires an increase of source intensity or size to produce the same anomaly. When conductivity contrasts become small or nonexistent, the number of image sources becomes finite or zero, respectively, further simplifying the calculation. As an example, the SP anomaly of a dipping rectangular source of constant intensity is computed using the method. This model is applied to SP data from the East Mesa geothermal field.

Improved Energy Recovery From Geothermal Reservoirs

Summary Numerical stimulation methods are used to study how the exploitation of different horizons affects the behavior of a liquid-dominated geothermal reservoir. Our reservoir model is a schematic representation of the Olkaria field in Kenya. The model consists of a two-phase vapor-dominated zone overlying the main liquid-dominated reservoir. Four different cases were studied, with fluid produced from:the vapor zone only.the liquid zone only,both zones, andboth zones but with lower values for vertical permeability and porosity assumed. The results indicate that production from the shallow two-phase zone, although resulting in higher enthalpy fluids, may not be advantageous in the long run. Shallow production gives rise to a rather localized depletion of the reservoir, whereas production from deeper horizons may yield a more uniform depletion process if vertical permeability is sufficiently large. The exploitation from deeper zones causes boiling and subsequent upflow of steam that condenses at shallow depths. This tends to make temperatures and pressures more uniform throughout the reservoir, resulting in maximum energy recovery.Brief consideration is given to the possibility of achieving similar improvements in energy recovery from vapor-dominated reservoirs through production from deeper horizons. This appears unlikely but cannot be completely ruled out because of uncertainties about the characteristics of vapor-dominated systems at depth. Introduction In the development of a geothermal resource, an appropriate production strategy must be selected. This ineludes deciding on the optimal well spacing and depths of completion. In many cases, these decisions are based solely on achievable levels of power production and well completion costs. without due consideration being given to ultimate energy recovery. Thus. the production wells often are located very close to each other, and drilling is terminated as soon as sufficiently hot and productive horizons are penetrated. Completing production wells near the top of the reservoir may lead to a more rapid decline and a low recovery ratio for the geothermal resource, Selection of an exploitation strategy should be based on appropriate reservoir engineering calculations that will result in an optimal balance between energy recovery and investment costs. Calculations aiming at an optimization of field development were carried out by Morris and Campbell for the East Mesa geothermal field in the Imperial Valley, CA.The economic value of a geothermal well depends not only on its deliverability, as in he case of an oil well, but also on the enthalpy of the produced fluids. If there are two-phase or vapor zones in the field (e.g., Baca, U.S.; Olkaria, Kenya; Broadlands, New Zealand), there is an incentive to produce from them rather than from deeper liquid reservoirs, because fluids of higher enthalpy can be obtained. The short-term benefits are obvious, but in the long run a lower-energy recovery ratio from the field may result.In this work, the behavior of a liquid-dominated geothermal reservoir in response to production from different horizons is studied by use of numerical simulation methods. We use the Olkaria geothermal field in Kenya as an example of a two-phase vapor-dominated zone overlying the main liquid-dominated reservoir. One of the important questions in the Olkaria field development is which zone it is most beneficial to produce. This paper is the first attempt to answer that question. We also briefly consider the possibility of improving energy recovery from vapor-dominated reservoirs by tapping deeper horizons. JPT P. 1920^

A plausible two‐dimensional vertical model of the East Mesa Geothermal Field, California

A two‐dimensional conceptual model of the East Mesa Geothermal system is developed on the basis of existing geological, geophysical, geochemical, heat flux, and borehole logging data. Hot water rising in a set of faults is assumed to charge the reservoir, which is overlaid by a clay‐rich cap. The temperature‐depth distribution observed at the site implies that the liquid is converting at a high Rayleigh number. In this approximation, liquid rises up the fault and spreads isothermally into the nearby sections of the reservoir. The cooling effect of the surface on the flow in the reservoir is confined to a thin layer adjacent to the cap‐reservoir interface near the fault. This layer grows with the distance from the fault. Eventually, the entire depth of the reservoir is cooled by the surface. The mathematical model is based on the flow of liquid water in a saturated porous medium. Results are obtained for the velocities, pressures, and temperatures in the entire system consisting of fault zone, aquifer, and clay cap. Finally we compare the predicted surface heat flux to that measured at the site in shallow wells. It is concluded that the model represents a plausible description of fault zone controlled systems like that at East Mesa.

Geothermal Reservoir Energy Recovery : A Three-Dimensional Simulation Study of the East Mesa Field

Summary This paper describes the reservoir simulation model developed for East Mesa field properties and summarizes the reservoir engineering evaluation of the reserves and field performance. Geothermal reservoirs should be evaluated in terms of efficient "energy mining" rather than fluid recovery. The results indicate the behavior of the field under various scenarios of development designed to operate a 64-MW electric power plant. Introduction The East Mesa geothermal field is in an area of anomalously high heat flow on the east flank of the Salton Trough at the southeast corner of the Imperial Valley in California. Twenty-four wells have been drilled thus far, including 10 by Republic Geothermal Inc. in the northern portion, five by the U.S. Bureau of Reclamation in the central area, and eight by Magma Power Co. to the south (Fig. 1). Because of the already extensive investigations, a great deal is known about the East Mesa reservoir and its properties. Republic now is proceeding with commercial development at the northern end of the field, starting with a 64-MW power plant project.Geothermal resource development differs most significantly from petroleum resource exploitation in that an additional factor is involvedie., the recovery of thermal energy. The problems of fluid flow in a porous media are, of course, similar to the petroleum industry problems, but the ultimate recovery is measured in terms of energy mining efficiency. The produced fluid acts only as a transport mechanism and may be cycled through the reservoir to extract heat from the rock as many times as is economically feasible.This paper presents the reservoir model developed for Republic's East Mesa properties and summarizes the reservoir simulation study performed to optimize the exploitation of this resource. Reservoir Properties Petrophysical Properties Logs, ditch cuttings, and cores show that the upper 10,000 ft (3048 m) of stratigraphic section at East Mesa is a sequence of deltaic clastic sediments that includes abundant amounts of fine- to medium-grained sandstones, fine- to coarse-grained siltstones, and lesser amounts of mudstones. Mineralogically, the sands are compositionally equivalent to Colorado River delta sands, being mostly quartz (70%), lithic fragments (20%), and feldspars (10%). Post-depositional alterations are principally the addition of authigenic carbonate and quartz as overgrowths and veinlets and the conversion of the detrital phyllosilicates to illite and chlorite.The basic petrophysical properties of sand/shale discrimination, porosity (phi), and permeability (k) employed in the model were obtained from log analyses for eight existing wells in the Republic area (i.e., Producers 16–29, 16–30, 38–30, 58–30, and 78–30/78-30RD and Injectors 18–28 and 52–29). Table 1 summarizes net sand thickness (h), average sand porosity (phi) weighted for the presence of shales, and geometric mean sand permeability (k) for four depth-interval groupings. The data show good sand development in the wells between 2,500 and 7,000 ft (762 and 2134 m). Although the properties vary considerably between wells, they generally improve away from the center of the temperature anomaly, show a gradual decline with increasing depth, and exhibit rapid deterioration below 7,000 ft (2134 m). JPT P. 735^

Interpretation of self‐potential survey results from the East Mesa Geothermal Field, California

A dipolar self‐potential anomaly of about 90 mV peak‐to‐trough amplitude and 5km peak‐to‐trough length has been measured over the East Mesa geothermal field in the Imperial Valley of Southern California. The anomaly does not appear to be related to surface features. A surface field similar in form to the measured self‐potential anomaly is generated by a source configuration consisting of dipolar current distributions along a series of three steeply dipping planes that are roughly coincident in location and depth extent with known faults. The source currents could be generated by the interaction of heat or fluid flow with changes in thermoelectric or electrokinetic coupling coefficients across faults. However, source potentials associated with these currents are considerably greater than those generated by estimated in situ coupling coefficients and heat and fluid flows. This implies that in situ coupling coefficients are much larger than those derived from room temperature measurements; that heat or fluid flows are much greater than those assumed for the East Mesa field; or that some other mechanism is responsible for the generation of the anomaly.

Results of Interference Tests From Two Geothermal Reservoirs

Results are presented from interference tests on two liquid-dominated geothermal reservoirs in the U.S. The collected pressure data show that interference effects can be masked by earth tides and other effects. Well known techniques of petroleum engineering and hydrogeology are used to estimate hydraulic characteristics and to infer the presence of barrier and leaky boundaries. Introduction An important facet in the problem of geothermal energy development is assessing the productivity and size of a geothermal reservoir. Modern techniques of well-test analysis (pressure drawdown, buildup, and interference tests) developed in petroleum engineering and hydrogeology have been applied successfully to two liquiddominated geothermal reservoirs in the U.S.: one in the Raft River Valley of Idaho and the other at East Mesa in the Imperial Valley of California. These tests gave reasonable estimates of the permeability and storage parameters for the two reservoirs. In addition, the tests also parameters for the two reservoirs. In addition, the tests also illustrate the type of instrumentation that can be used in testing geothermal wells as well as the nature of the data that can be collected. A large body of literature is available on well testing in both petroleum engineering and hydrogeology. Ramey recently has summarized the practical aspects of modern well-test analysis. This paper reviews the results of interference tests performed with a very sensitive pressure-measuring performed with a very sensitive pressure-measuring device on two geothermal reservoirs. As used in this paper, the term "interference test" denotes the fluid production from one well and measurement of pressure transients in a nearby observation well. The geologic setting for each reservoir is given and the instrumentation is presented. Some unusual features of the data are discussed, followed by the methods of interpretation that were used. Description of the Geothermal Reservoirs Raft River Valley Field, Idaho The Raft River Valley geothermal field (Fig. 1) is located on a graben filled with Tertiary and Pleistocene sediments and volcanics, with an aggregate thickness of about 5,000 ft. The sediments rest on a basement of quartzites, schists, and quartz monzonites of Precambian age. Precambian age. Wells RRGE 1 and RRGE 2 were drilled in 1975 and successfully produced hot water at approximately 295 deg. F from a geothermal reservoir occurring at the base of the sediments at 3,500 to 5,000 ft below the land surface. Well RRGE 2 is northeast and 4,000 ft from Well RRGE 1. Both wells are artesian with wellhead pressures of about 150 psi when shut in. During construction, both wells indicated free flows of about 400 gal/min. The completion details for the two wells are summarized in Table 1. Subsurface correlations of borehole data suggest that the sediments dip toward Well RRGE 2 with apparent northeasterly dips increasing from about 3 deg. in the upper portion to about 7 deg. toward the bottom. Also, it is known portion to about 7 deg. toward the bottom. Also, it is known that Well RRGE 1 pierced a fault zone between 3,800 and 4,500 ft. Apparently, Well RRGE 2 did not intercept any faults. East Mesa Field, California The East Mesa geothermal field (Fig. 2) is located on the eastern part of the Salton Trough in the Imperial Valley of California. JPT P. 10

Geology and Reservoir Analysis of East Mesa Geothermal Field, Imperial County, California: ABSTRACT

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