Cased Hole Formation Research Articles

Development and Baseline Comparison of a New Pulsed-Neutron Spectroscopy Tool for Carbon- Oxygen Analysis and Three-Phase Saturation Monitoring

A new slim multidetector pulsed-neutron wireline-logging tool has been developed for openhole or casedhole formation evaluation saturation analysis and time-lapse monitoring. With a greater neutron source output and high-spectral resolution gamma ray detectors, the tool can be operated with reduced uncertainty or faster logging speeds. New, fully programable digital electronics provide a range of acquisition modes optimized for specific formation evaluation objectives. Neutrons are generated from a high-output pulsed-neutron generator, which propagates radially outward, passing through the borehole, completion material, and into the formation. Energy is lost through scattering, and neutrons are absorbed by the surrounding material. Gamma rays are emitted from scattering and absorption interactions at discrete energies, which can be measured by one of three spectral gamma scintillation detectors. The energy distribution of these incident gamma rays by inelastic and capture interactions is affected by the elemental composition of the material. A salinity-independent oil-water saturation assessment begins with the deconvolution of neutron-induced gamma ray inelastic spectra into constituent elemental components. Carbon-oxygen ratios (C/O) of elemental yields are then compared to a reference model to determine the relative saturation and porosity-filled volume of oil and water. In PNC (pulsed-neutron capture) acquisition mode, a salinity-dependent oil-water saturation assessment is determined from neutron capture cross section (sigma) measurements, which are compared to formation and porosity fluids using a mass balance approach. Gas saturation assessment is determined from gas-sensitive inelastic (RIN13) and capture (RATO13) ratios. Gas ratios are compared to a reference model to assess the relative saturation of fluids, typically distinguishing gas from water or gas from oil. Gas saturation is not limited to hydrocarbon components and can also be used for saturation analysis of H2, He, CO2, N2, and other non-hydrocarbon-bearing components. A new Omni-mode acquisition combining simultaneous PNC and C/O measurements was also developed. This acquisition mode provides advantages in reducing multipass logging typically required from separate PNC and C/O acquisitions. By including PNC neutron capture sigma, gas-sensitive neutron capture and inelastic measurements, and C/O inelastic measurements, the simultaneous Omni-mode (PNC+C/O) acquisition is specifically optimized for three-phase saturation analysis applications, including baseline CO2 sequestration evaluation for carbon capture, utilization, and storage (CCUS) CO2 and steamflood time-lapse monitoring. Results from a field example are presented to demonstrate the new technology with spectral C/O saturation analysis compared to traditional windows C/O analysis and to compare the performance of the next-generation tool to the legacy tool. Multiphase saturations from C/O and RIN13 measurements and compatibility with legacy interpretations for time-lapse saturation monitoring are also presented.

A new gamma density measurement method for cased-hole formation evaluation

Under complex well conditions, cased-hole formation evaluation has become increasingly important since it effectively reduces downhole operational risks compared to open hole. However, thru-casing gamma density measurement proves much more challenging than open-hole measurement due to gamma's weak penetration power, and difficulties in obtaining accurate cement evaluation. To overcome these challenges, a new gamma density measurement method is introduced in this work. The method composes three aspects: 1) Construction of an extensive Monte Carlo modelling database based on an existing 4-detector gamma density tool; 2) Correlation identification between detectors and environmental parameters by designing a fast forward detector response model; 3) Development of an inverse formation model whose solution targets at both formation density and cement density in circumstances when cement is uncertain. In this process, a novel cement invasion model is also proposed and employed to obtain constraints to accelerate the computation. The correctness of the method is firstly verified using modelled data, then is applied to an offshore well with open-hole density log as the reference. Results show accurate density could be obtained where cement condition is uncertain.

Exploration of Hidden Hydrocarbons in Old Wells Magid Field - Sirte Basin, Libya

Abstract: It is increasingly important to improve field productivity in today's competitive market. One way to achieve this, is to add new wells which are expensive and time consuming. The other alternative is to identify bypassed hydrocarbons, track changes in saturations and detect movement of reservoir fluid contacts from existing well bores already in place. It is considerably more cost effective and often more environmentally friendly to explore for those hidden hydrocarbons in old wells rather than drill new wells. As the field matures, there is a need to reevaluate the formation in older reservoirs and to focus the development strategy and approach on bypassed oil pockets and depletion levels in producing intervals. The ability to acquire essential logging data behind casing adds a new dimension to cased hole formation evaluation for locating and evaluating potential hydrocarbon zones in a mature field as in Magid field. A basic petrophysical evaluation was performed incorporating the data recorded behind casing by applying {Cased Hole Formation Resistivity Logging (CHFRL)} in each of these wells. Based on the analysis of cased hole formation evaluation results. The un-depleted intervals were commercially exploited adding reserve to the asset. Keywards: Hydrocarbon zones, Majid Field, Sirte Basin, Libya, CHFRL

Maximizing the Value of Pulsed-Neutron Logs: A Complex Case Study of Gas Pressure Assessment Through Casing

Casedhole logging for formation evaluation and input to determine the redevelopment potential of an oil producer with a challenging production history was conducted. This included an intelligent assessment of formation gas pressure through casing, which was later confirmed by perforating. The target reservoirs are Triassic sandstones drilled as a gas exploration prospect. Based on openhole log data, the prospect appeared to be oil bearing. The well has been producing oil for several years and is now a candidate for a gas cap blowdown. The presence of heterogeneous layers with varied rock quality and producibility indexes coupled to complexity in fluids distribution and zonal isolation issues complicates the development process and ability to optimize recovery from any contributing level. Recently, a new-generation casedhole formation evaluation tool that provides multiple independent formation property measurements was deployed to enhance knowledge of the formation parameters while describing the current gas and oil volumes. Sigma, neutron porosity, fast-neutron cross section (FNXS), and elemental concentrations, including total organic carbon from inelastic and capture spectroscopy, were simultaneously recorded. Because the well is highly deviated in the zones of interest, the tool was efficiently conveyed on wireline using tractor technology. The evaluation techniques used to study this rich set of data reveal several pieces of information that are essential to the petrophysicists and geologists, and to the reservoir and production engineers. A multimineral solver analysis guided by the prior knowledge of the rocks using cores from offset wells was conducted to quantify the porosity and gas-oil contact levels while giving access to detailed knowledge of matrix and rock composition for refining the reservoir models. Additionally, a novel method to determine gas pressure at the current time from the casedhole log measurements was applied to support reservoir management. The highly sensitive sigma, neutron porosity, and FNXS gas properties can be parameterized as a function of pressure and temperature if the formation and fluid properties are known. This is a well-established principle that can finally be applied independently and directly to multiple measurements. The computations are done independently and checked against each other for consistency and to support optimal parameter setting, in an iterative manner. This is particularly important in this scenario where the complexity of the wellbore environment and history of the well could have complicated the ability to achieve enough precision on the estimated pressures when coming from a single method or if modeling is required. The log results, with validation, and implications for the well redevelopment are presented together with a general discussion on the methodology and applicability based on this well experience. The importance of meticulous job preparation, prejob modeling, and data quality control is also highlighted. The information is key to defining the future well development management strategy and clarify the role that casedhole logging can play as part of the complete well evaluation process.

Lessons Learned From Casedhole Formation Evaluation Along Unconventional Horizontal Wells

Lessons Learned From Casedhole Formation Evaluation Along Unconventional Horizontal Wells

Cased hole formation resistivity contribution in water management and production enhancement of mature reservoirs

Water saturation measurements over time are useful for tracking reservoir depletion, and diagnosing production problems such as water production that is one of the main challenges facing oil and gas producers. It is necessary to manage water production to enhance oil production. In cased hole evaluation, cased hole resistivity finds it utility in two circumstances; as a first resistivity measurement in old and new wells to assess the formation in present conditions, or as a time-lapse technique to describe temporal behaviour of reservoir dynamic and reservoir fluids movements to mainly detect bypassed oil zones and water invaded zones. Five case studies of mature reservoirs suffer from water production problems attributed to different geological and reservoir conditions. In all cases, the remedial workover operations based on the cased hole resistivity results have allowed a significant enhancement of the oil production and the implementation of an optimum field management strategy.

Cased hole formation resistivity contribution in water management and production enhancement of mature reservoirs

Cased hole formation resistivity contribution in water management and production enhancement of mature reservoirs

Responses and data inversion of four-detector scattered-gamma-ray logging in cased holes

In cased holes, detector response of scattered-gamma-ray logging tool is subject to casing, cement sheath, and formation density, while the logging result requires four parameters—casing thickness, cement sheath density, cement sheath thickness, and formation density—for cased-hole formation evaluation and cement bond evaluation. Therefore, It is necessary to study the detector response and logging data inversion. We designed a four-detector scattered-gamma-ray logging tool for cased holes and performed Monte Carlo numerical simulations to obtain relationships between the responses of four detectors versus casing, cement sheath, and formation, respectively; on this basis, forward modeling formulas for the detector responses were established, and an optimization inversion method was applied to obtain the casing thickness, cement sheath density and formation density from the forward model. As demonstrated by the result, detector response was a function of formation density, cement sheath thickness, cement sheath density, and casing thickness; the response of detector count rate versus casing thickness was less influenced by ambient conditions, compared to the other parameters. Relatively accurate casing thickness values could be calculated when the condition of the borehole and formation is normal; accurate cement sheath density values could be obtained when the cement sheath was relatively thick; and relatively accurate formation density values could be obtained when the cement sheath has neither of low density nor of great thickness.

Technology Update: Tool Enables Complete Cased-Hole Formation Evaluation, Reservoir Saturation Modeling

Technology Update For more than 40 years, the industry has used pulsed neutron logging to determine hydrocarbon and water saturations behind casing for reservoir management. Multiphase saturation measurements over time are useful for tracking reservoir depletion, planning workover and enhanced recovery strategies, and diagnosing production problems such as water influx and injection fluid breakthrough. Cased-hole logs also serve as a contingency when openhole logs cannot be run or are not considered for reservoir characterization. Although the cased-hole measurement suite has been greatly improved over many tool generations, the intrinsic physical measurements remained unchanged, which meant that operators could not obtain a complete picture of the rock and fluids behind casing. Input from openhole logs was required from a porosity or bulk density measurement for combination with the neutron porosity. Absent this input, primary formation evaluation in cased wellbores can be ambiguous. An additional challenge with cased-hole logging is correctly compensating for the effects of borehole fluids and the presence of completion hardware. Next-Generation Logs To meet the need for accurate surveillance in cased holes, Schlumberger recently introduced the Pulsar multifunction spectroscopy system. The system builds on innovative technologies originated by the company to provide the first complete cased-hole formation evaluation and reservoir saturation monitoring capability with openhole-equivalent measurements. This next generation in pulsed neutron logging integrates multiple detectors and a high-output pulsed neutron generator (PNG) to significantly improve measurement precision, data acquisition accuracy, and logging speed. The measurements are complemented by powerful algorithms that compensate for variation in the borehole fluids and completion in delivering robust, representative answers in complex conditions. The PNG and four detectors are housed in a 1.72-in.-outside-diameter (OD) tool that is designed for through-tubing access and logging through most completion restrictions. The detector adjacent to the PNG is the compact neutron monitor, which is primarily sensitive to fast neutrons to provide accurate and precise output measurement. There are three scintillation gamma-ray detectors for near, far, and deep detection. The near and far detectors use cerium-doped lanthanum bromide (LaBr3:Ce) scintillators, and the deep detector, farthest spaced from the PNG, has an yttrium aluminum perovskite scintillator. The three gamma-ray detectors are coupled to high-temperature-rated photomultiplier tubes, and their pulses are counted with specialized electronics matched to the high rate and resolution of the LaBr3:Ce scintillators.

Cased-hole interpretation workflow for determining residual oil saturation for mature fields

Formation evaluation for mature oil fields remains a challenge for operators. Rock-petrophysical properties present large uncertainties following years of production. Formation evaluation becomes even more challenging when there is a lack of open-hole logging data as is typically the case. Logging programs for cased-hole formation evaluation are limited by the size of the well completion. In addition, a metallic casing often prevents the effective use of electric measurements. However, pulsed-neutron tools (PNTs) are a viable option for mature fields. We developed a brief review of PNT theory. The high-energy neutrons output at a high count rate fit the need of cased-hole applications. Application of pulsed-neutron technology for mature fields and a case history from west Texas, in which pulsed neutron technology was used to determine remaining oil saturation are discussed. We documented the best practice for data acquisition and the processing workflow. Having a good collaboration between operator and service provider helps to better understand the logging objectives and in job planning, which is important for the success of the logging operation.

Numerical simulation of responses for cased-hole density logging

Stabilizing or stimulating oil production in old oil fields requires density logging in cased holes where open-hole logging data are either missing or of bad quality. However, measured values from cased-hole density logging are more severely influenced by factors such as fluid, casing, cement sheath and the outer diameter of the open-hole well compared with those from open-hole logging. To correctly apply the cased-hole formation density logging data, one must eliminate these influences on the measured values and study the characteristics of how the cased-hole density logging instrument responds to these factors. In this paper, a Monte Carlo numerical simulation technique was used to calculate the responses of the far detector of a cased-hole density logging instrument to in-hole fluid, casing wall thickness, cement sheath density and the formation and thus to obtain influence rules and response coefficients. The obtained response of the detector is a function of in-hole liquid, casing wall thickness, the casing's outer diameter, cement sheath density, open-hole well diameter and formation density. The ratio of the counting rate of the detector in the calibration well to that in the measurement well was used to get a fairly simple detector response equation and the coefficients in the equation are easy to acquire. These provide a new way of calculating cased-hole density through forward modelling methods.

Arithmetic Method of Double-Injection-Electrode Model for Resistivity Measurement Through Metal Casing

Through-casing resistivity (TCR) measurement instruments such as Cased Hole Formation Resistivity are extensively used for the dynamic monitoring of oil reservoirs during the production phase in oil wells to evaluate the residual oil distribution. However, two shortcomings still exist in the common TCR model based on single-injection electrodes: The real value of steel-casing resistance is difficult to acquire, and the effect from mechanical tolerances of electrode scale is unpredictable. This paper proposes an innovative model based on double-injection electrodes. In this new model, all the required variables can be measured simultaneously; furthermore, a compensating arithmetic method is employed to obtain the real casing resistance. Self-adaptive goal-oriented <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hp</i> -finite-element simulations have been performed to prove that the influence of mechanical tolerances of electrode scale can be reduced effectively. Therefore, the TCR measurement accuracy is highly improved.

ABSTRACT: Reservoir Monitoring with Cased-Hole Formation Resistivity

ABSTRACT: Reservoir Monitoring with Cased-Hole Formation Resistivity

Cased-Hole Logging for Evaluating Bypassed Reserves

Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering. Summary. Cased-hole formation evaluation logs are playing a major role inefforts to increase recovery from existing reservoirs. While the logs availabletoday are significant improvements over those of just a few years ago, caremust still be exercised for successful applications. Application limitationsremain, although some of these are being addressed by ongoing research. Introduction Current oilfield economics, while discouraging some exploration and drillingexpenditures, has also produced a growing interest in re-evaluating existingwells to locate bypassed intervals. In mature producing areas, the potentialreserve additions from bypassed reservoirs can be very large; moreover, theeconomics for recompletion can be quite favorable because of the high chance ofsuccess in adding production for moderate capital expenditures. Cased-hole logsproduction for moderate capital expenditures. Cased-hole logs are playing amajor role in locating and evaluating such bypassed hydrocarbon zones. In viewof this role, a review of the common technology, applications, limitations, andpossible future developments in cased-hole logging is appropriate. Cased-hole logs for looking behind pipe are used in a broad spectrum ofapplications, several of which are indicated in Table 1. Although these usesrange from cement evaluation to monitoring EOR processes, for the purpose ofthis discussion our focus will be on recompletions, and specifically thelocation and evaluation of bypassed oil or gas zones. Technology The logs commonly used in formation evaluation behind pipe are listed inTable 2, along with the primary reservoir properties they measure and anindication of some of the other properties they measure and an indication ofsome of the other formation properties that influence their response. This listis not exhaustive, but it does provide an indication of the types of formationproperties that can be measured by common cased-hole tools. Further informationon the operating principles of these tools is readily available in theliterature. Gamma ray logs include both conventional tools that measure total naturalgamma ray count rates and newer spectral gamma ray tools, which measure theindividual contributions of potassium, uranium, and thorium to the energyspectrum of natural gamma rays. These tools are predominantly lithologyindicators and, as such, are useful in predominantly lithology indicators and, as such, are useful in depth control, correlation, and lithology evaluation(especially shaliness). They also detect the buildup of radioactive scale, which in certain cases can indicate zones of prolonged water movement, such asperforations, watered-out zones, or channels behind pipe. Cased-hole neutron logs are also of two primary types: the olderconventional neutron log that measures capture gamma ray count rates with asingle detector and the newer dual-detector, compensated neutron log thatpresents a log trace scaled in porosity units. These logs are good porosity, gas, and indicators, With proper calibration, quantitative estimates ofporosity and semiquantitative estimates of gas saturation can be obtained, provided that shaliness effects are -properly accounted for. Because of theirgas response. they are widely used in monitoring gas/liquid contacts. Pulsedneutron capture (PNC) logs are the primary tools Pulsed neutron capture (PNC)logs are the primary tools used in detecting oil behind pipe. Firstcommercially available in the mid 1960's, they measure the macroscopic thermalneutron capture cross section, using a pulsed neutron source. Present-daytools can be run through tubing as small as 2 in. [5.08 cm]. Because thechlorine present in salt water has a large thermal neutron capture crosssection, these logs can distinguish high-salinity formation water fromhydrocarbons, and hence can yield quantitative estimates of water saturation ifproperly calibrated. They also respond to gas saturation and properlycalibrated. They also respond to gas saturation and porosity, but theirapplications can be severely limited by low porosity, but their applicationscan be severely limited by low brine salinity, low porosity, or shaliness. Pulsed neutron spectral (PNS) or induced gamma ray spectral logs are alsocommonly known as carbon/oxygen (C/O) or gamma ray spectroscopy logs. Theselogs, which were first commercially available in the mid-1970's, measure theenergy spectra of gamma rays from both inelastic neutron scattering and thermalneutron capture to obtain estimates of the relative concentrations ofparticular elements present in the formation. Various ratios of these elementalpresent in the formation. Various ratios of these elemental components (such asthe C/O ratio) can be used to evaluate oil saturation, lithology, and evenbrine salinity; also, count rate or component yield ratios can be used toestimate porosity. JPT

Stratton Field, Texas Gulf Coast: A Successful Cased-Hole Re-Evaluation of an Old Field to Determine Remaining Reserves and to Increase Production Level

Summary Recompletion decisions at Stratton field historically have been complicated by the presence of many thin sand lenses of widely varying pay quality. The advent of a cased-hole formation evaluation tool-the dual detector pulsed neutron log (DDPN)-has simplified matters greatly by revealing current, detailed information about reservoir rock properties and fluid saturations. By using 4 years of recompletion data, DDPN log characteristics and log derived parameters have been identified and used successfully to distinguish between gas-, oil-, and water-bearing zones, to predict when fracture stimulations will be required to produce at commercial gas rates, to tify depleted gas zones, and to rank potential recompletion zones according to their respective absolute open-flow potentials (OFP's). potentials (OFP's). Introduction Stratton-Agua Dulce field, discovered in the late 1930's, is a gulf coast field located about 45 miles [72 km] west of Corpus Christi, TX (see Fig. 1). Production is from the Frio and upper Vicksburg formations (Oligocene shaley sands), with the typical wellbore penetrating more than 25 reservoirs scattered throughout a 3,000-ft [914-m] interval (see Fig. 2 for a type log). The reservoirs are relatively thin sand lenses, ranging from 5 to 20 ft [1.5 to 6.1 m] gross interval. The areal extent of these resvoirs is limited by both the many down-to-the-coast faults in the area and reservoir pinchouts attributed to sand depositional environments. Thus recompletion attempts have been complicated not only by the sheer number of reservoirs, but by the complex geology of the area. It is quite common that recompletion attempts reveal a sand that is wet, depleted, or tight but productive in an ediate offset well. Likewise, sands known to be wet or depleted in some wells often are found to be commercial in offset recompletion attempts. With the increase in hydrocarbon value since 1978, recompletion econonmics have improved vastly and created a need for a tool to help identify the best possible zone remaining in the wellbore. The original suite of openhole logs (for all the older wells this consisted of simply an electric log) was not found to be useful since production from a given reservoir in offset wells could raise a water table into the prospective zone or pressure deplete it. Migration of gas between zones behind pipe also has been found to occur. The tool with the highest degree of success in recompletion attempts is the DDPN. Specifically designed to be run in a cased hole, it consists of a high-energy neutron source and two detectors in a logging sonde. The DDPN had been accepted in areas of the Texas gulf coast with highly saline water before 1978; however, the lower Stratton water salinities (15,000 ppm total Cl ) had delayed use of the log in Stratton. After some experimentation it was determined that indeed the DDPN could be used in Stratton since, although not fully understood, the DDPN routinely recorded capture cross-section values (E) in the range of 24 to 30 c.u. for Stratton's wet, shaly Frio sandstones. Equivalent to a much larger indicated water salinity (50, OW to 80, OW ppm total Cl ), this allowed the required resolution to discriminate between hydrocarbonand water-bearing sands. Additionally, the newer generation of DDPN equipment offered both porosity indicators and gas detection. The DDPN, therefore, was selected for cased-hole recompletion analysis and subsequently assisted in both selection of recompletion zones and updating the condition of producing reservoirs. Theoretical calculations based on DDPN tool responses are used to calculate rock porosities and fluid saturations of behind-pipe zones. Schlumberger's experiences with recompletion results since 1978 have determined certain log characteristics and log-derived parameters useful as guidelines to predict the parameters useful as guidelines to predict the commercial potential of a candidate recompletion zone in Stratton field. They used a (effective porosity times water saturation) product of 10% or less as indicative of a commercial hydrocarbon zone. This paper refines the service company pay cutoff by establishing correlations between actual recompletion attempt results at Stratton and the corresponding DDPN curve readings. Over the last 4 years, we ran 27 DDPN logs in Stratton field (see Fig. 3) and attempted a total of 76 recompletions across the logged intervals. JPT p. 105

Time-Derived Sigma for Pulsed Neutron Capture Logging

Summary This paper reviews field applications of the Dresser Atlas Neutron Lifetime Log™ (NLL) service and examines recent technical advances in the instrumentation and data-analysis system. The major improvement discussed is a new method for computing S, the thermal neutron capture cross section of an earth formation. In the new method, the time after the neutron burst is measured for each gamma ray pulse detected by the instrumentation system within a gate of fixed width. This "average pulse time" is uniquely related to the thermal neutron decay rate observed in a borehole environment. The technique discussed is applicable for any condition where the neutron or gamma ray flux is time-dependent. The advantages of this signal-processing method, however, are most apparent for cases of rapid flux change with time, as in an exponential decay. A simple two-gate method of measurement suffers, statistically, from the lower count rate of the second gate. An average-pulse-time measurement over the same range covered by both gates of a two-gate system is less affected by statistical deviations than the ratio normally formed between the two gates. Some important advantages result from this type of signal processing when applied to the NLL service. First, the statistical accuracy of the log is improved; second, the instrumentation required for implementation of the method is not complicated. Also, the average-pulse-time measurement can be made with either digital or analog equipment, and since it involves only simple arithmetic computations, the method is much simpler to implement than either least-squares or correlation methods. Introduction The NLL service1 was introduced in the early 1960's; it was the first measurement through casing that could distinguish and quantitatively evaluate oil and gas in saline formation water environments. More recently, the Dual Detector Neutron Lifetime Log (DNLL) service2 has been used (1) to explore for hydrocarbon resources behind pipe, (2) to monitor the production behavior of wells, (3) to plan workovers properly, (4) to determine residual oil saturation for enhanced-recovery projects, etc. Although the carbon/oxygen3 (C/O) log provides a reliable cased-hole formation evaluation in fresh and brackish formation water environments, the DNLL service is applicable when logging through casing and/or tubing in saline environments. As discussed in detail in the literature, the basic measurement is the thermal neutron absorption (capture) cross section, S, of a subsurface formation. Advanced methods of processing the data recorded by such a pulsed neutron capture logging system are presently under development. These improvements include (1) the average-time technique4 and (2) the sigma-dependent positioning of a single gate exhibiting a fixed gate width of 600 µseconds. The basic theoretical considerations of these improvements are discussed, and supporting field data are presented.