Special Issue on geophysics applied to detection and discrimination of unexploded ordnance

Unexploded ordnance (UXO) presents serious problems in Europe, Asia, as well as in the United States. Explosives and mines from World War I and World War II still turn up at European and Asian construction sites, backyard gardens, beaches, wildlife preserves and former military training grounds. The high rate of failure among munitions from 60-90 years ago is cited as one of the main reasons for such a high level of contamination. Apart from war activities, military training has resulted in many uncovered ordnance. It is especially true in the United States, where most UXO has resulted from decades of military training, exercises, and testing of weapons systems. Such UXO contamination prevents civilian land use, threatens public safety, and causes significant environmental concern. In light of this problem, there has been considerable interest shown by federal, state, and local authorities in UXO remediation at former U.S. Department of Defense sites. The ultimate goal of UXO remediation is to permit safe public use of contaminated lands. A Defense Science Board Task Force Report from 1998 lists some 1,500 sites, comprising approximately 15 million acres, that potentially contain UXO. The UXO-related activity for these sites consists of identifying the subareas that actually contain UXO, and then locating and removing the UXO, or fencing the hazardous areas off from the public. The criteria for clearance depend on the intended land end-use and residual hazard risk that is deemed acceptable. Success in detecting UXO depends on the ordnance's size, metal content, and depth of burial, as well as on the ability of geophysical systems to detect ordnance in the presence of metallic fragments from exploded UXO and other metal clutter

West Coast Regional Carbon Sequestration Partnership - Report on Geophysical Techniques for Monitoring CO2 Movement During Sequestration

The relative merits of the seismic, gravity, and electromagnetic (EM) geophysical techniques are examined as monitoring tools for geologic sequestration of CO{sub 2}. This work does not represent an exhaustive study, but rather demonstrates the capabilities of a number of geophysical techniques on two synthetic modeling scenarios. The first scenario represents combined CO{sub 2} enhance oil recovery (EOR) and sequestration in a producing oil field, the Schrader Bluff field on the north slope of Alaska, USA. EOR/sequestration projects in general and Schrader Bluff in particular represent relatively thin injection intervals with multiple fluid components (oil, hydrocarbon gas, brine, and CO{sub 2}). This model represents the most difficult end member of a complex spectrum of possible sequestration scenarios. The time-lapse performance of seismic, gravity, and EM techniques are considered for the Schrader Bluff model. The second scenario is a gas field that in general resembles conditions of Rio Vista reservoir in the Sacramento Basin of California. Surface gravity, and seismic measurements are considered for this model

A Feasibility Study of Non-Seismic Geophysical Methods for Monitoring Geologic CO2 Sequestration

Because of their wide application within the petroleumindustry it is natural to consider geophysical techniques for monitoringof CO2 movement within hydrocarbon reservoirs, whether the CO2 isintroduced for enhanced oil/gas recovery or for geologic sequestration.Among the available approaches to monitoring, seismic methods are by farthe most highly developed and applied. Due to cost considerations, lessexpensive techniques have recently been considered. In this article, therelative merits of gravity and electromagnetic (EM) methods as monitoringtools for geological CO2 sequestration are examined for two syntheticmodeling scenarios. The first scenario represents combined CO2 enhancedoil recovery (EOR) and sequestration in a producing oil field, theSchrader Bluff field on the north slope of Alaska, USA. The secondscenario is a simplified model of a brine formation at a depth of 1,900m

Geophysical Techniques for Monitoring CO2 Movement During Sequestration

The relative merits of the seismic, gravity, and electromagnetic (EM) geophysical techniques are examined as monitoring tools for geologic sequestration of carbon dioxide (CO{sub 2}). This work does not represent an exhaustive study, but rather demonstrates the capabilities of a number of geophysical techniques for two synthetic modeling scenarios. The first scenario represents combined CO{sub 2} enhanced oil recovery (EOR) and sequestration in a producing oil field, the Schrader Bluff field on the north slope of Alaska, USA. EOR/sequestration projects in general and Schrader Bluff in particular represent relatively thin injection intervals with multiple fluid components (oil, hydrocarbon gas, brine, and CO{sub 2}). This model represents the most difficult end member of a complex spectrum of possible sequestration scenarios. The time-lapse performance of seismic, gravity, and EM techniques are considered for the Schrader Bluff model. The second scenario is a gas field that in general resembles conditions of Rio Vista reservoir in the Sacramento Basin of California. Surface gravity, and seismic measurements are considered for this model

Berkeley UXO Discriminator (BUD)

The Berkeley UXO Discriminator (BUD) is an optimally designed active electromagnetic system that not only detects but also characterizes UXO. The system incorporates three orthogonal transmitters and eight pairs of differenced receivers. it has two modes of operation: (1) search mode, in which BUD moves along a profile and exclusively detects targets in its vicinity, providing target depth and horizontal location, and (2) discrimination mode, in which BUD, stationary above a target, from a single position, determines three discriminating polarizability responses together with the object location and orientation. The performance of the system is governed by a target size-depth curve. Maximum detection depth is 1.5 m. While UXO objects have a single major polarizability coincident with the long axis of the object and two equal transverse polarizabilities, scrap metal has three different principal polarizabilities. The results clearly show that there are very clear distinctions between symmetric intact UXO and irregular scrap metal, and that BUD can resolve the intrinsic polarizabilities of the target. The field survey at the Yuma Proving Ground in Arizona showed excellent results within the predicted size-depth range

Advanced 3D Geophysical Imaging Technologies for Geothermal Resource Characterization

We describe the ongoing development of joint geophysical imaging methodologies for geothermal site characterization and demonstrate their potential in two regions: Krafla volcano and associated geothermal fields in Northeastern Iceland, and Coso Hot Springs in California, USA. The Coso field is a high temperature reservoir similar to Krafla in Iceland. Each area is a locus of significant geothermal energy production. The complex geology of these sites also makes them excellent targets for developing and testing of strategies for joint imaging of magnetotelluric (MT) and micro-earthquake (MEQ) data. Our ultimate aim is to construct coupled 3D resistivity and velocity models of these geothermal systems and use them to better understand and exploit them.Lawrence Berkeley National Laboratory (Subcontract 6927716

Geothermal Play Fairway Analysis, Part 2: GIS Methodology

Play Fairway Analysis (PFA) in geothermal exploration originates from a systematic methodology developed within the petroleum industry and is based on a geologic, geophysical, and hydrologic framework of identified geothermal systems. We tailored this methodology to study the geothermal resource potential of the Snake River Plain and surrounding region, but it can be adapted to other geothermal resource settings. We adapted the PFA approach to geothermal resource exploration by cataloging the critical elements controlling exploitable hydrothermal systems, establishing risk matrices that evaluate these elements in terms of both probability of success and level of knowledge, and building a code-based ‘processing model’ to process results. A geographic information system was used to compile a range of different data types, which we refer to as elements (e.g., faults, vents, heat flow, etc.), with distinct characteristics and measures of confidence. Discontinuous discrete data (points, lines, or polygons) for each element were transformed into continuous interpretive 2D grid surfaces called evidence layers. Because different data types have varying uncertainties, most evidence layers have an accompanying confidence layer which reflects spatial variations in these uncertainties. Risk layers, as defined here, are the product of evidence and confidence layers, and are the building blocks used to construct Common Risk Segment (CRS) maps for heat, permeability, and seal, using a weighted sum for permeability and heat, but a different approach with seal. CRS maps quantify the variable risk associated with each of these critical components. In a final step, the three CRS maps were combined into a Composite Common Risk Segment (CCRS) map, using a modified weighted sum, for results that reveal favorable areas for geothermal exploration. Additional maps are also presented that do not mix contributions from evidence and confidence (to allow an isolated view of evidence and confidence), as well as maps that calculate favorability using the product of components instead of a weighted sum (to highlight where all components are present). Our approach helped to identify areas of high geothermal favorability in the western and central Snake River Plain during the first phase of study and helped identify more precise local drilling targets during the second phase of work. By identifying favorable areas, this methodology can help to reduce uncertainty in geothermal energy exploration and development

Geothermal Play Fairway Analysis, Part 1: Example from the Snake River Plain, Idaho

The Snake River Plain (SRP) volcanic province overlies the track of the Yellowstone hotspot, a thermal anomaly that extends deep into the mantle. Most of the area is underlain by a basaltic volcanic province that overlies a mid-crustal intrusive complex, which in turn provides the long-term heat flux needed to sustain geothermal systems. Previous studies have identified several known geothermal resource areas within the SRP. For the geothermal study presented herein, our goals were to: (1) adapt the methodology of Play Fairway Analysis (PFA) for geothermal exploration to create a formal basis for its application to geothermal systems, (2) assemble relevant data for the SRP from publicly available and private sources, and (3) build a geothermal PFA model for the SRP and identify the most promising plays, using GIS-based software tools that are standard in the petroleum industry. The study focused on identifying three critical resource parameters for exploitable hydrothermal systems in the SRP: heat source, reservoir and recharge permeability, and cap or seal. Data included in the compilation for heat source were heat flow, distribution and ages of volcanic vents, groundwater temperatures, thermal springs and wells, helium isotope anomalies, and reservoir temperatures estimated using geothermometry. Reservoir and recharge permeability was inferred from the analysis of stress orientations and magnitudes, post-Miocene faults, and subsurface structural lineaments based on magnetics and gravity data. Data for cap or seal included the distribution of impermeable lake sediments and clay-seal associated with hydrothermal alteration below the regional aquifer. These data were used to compile Common Risk Segment maps for heat, permeability, and seal, which were combined to create a Composite Common Risk Segment map for all southern Idaho that reflects the risk associated with geothermal resource exploration and identifies favorable resource tracks. Our regional assessment indicated that undiscovered geothermal resources may be located in several areas of the SRP. Two of these areas, the western SRP and Camas Prairie, were selected for more detailed assessment, during which heat, permeability, and seal were evaluated using newly collected field data and smaller grid parameters to refine the location of potential resources. These higher resolution assessments illustrate the flexibility of our approach over a range of scales

A new-generation EM system for the detection and classification of buried metallic objects

A prime requirement in discrimination between UXO and non-UXO metallic fragments (clutter) is to determine accurately the response parameters that characterize a metallic object in the ground. Lawrence Berkeley National Laboratory has been involved in assessing and comparing existing systems, and designing an optimum system for UXO detection. A prototype of a new electromagnetic system will be built based on the results of this study. The detection and characterization of metallic objects can be considered a two-step process: location and identification. A multi-component transmitter-receiver system is essential for the identifying of the principal dipole moments of a target. The ground response imposes an early time limit on the time window available for target discrimination. Once the target response falls below the ground response, it will be poorly resolved, especially since the ground response itself will be variable due to the inhomogeneous nature of the near surface. For a given range of targets and given ambient noise characteristics, one can optimize system bandwidth so as to maximize the observable signal-to-noise ratio. A sensor with four or more decades of flat frequency response is needed to record the secondary magnetic fields associated with the target