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The energy dependence of the ionization produced in germanium by energetic germanium atoms was measured. Germanium solid-state detectors served simultaneously as crystalline Ge sample, neutron target, and ionization detector. The spectrum of ionization produced by prompt Ge recoil atoms energized by monoenergetic neutron bombardment was observed in a pulse-height analyzer, and the edge of the spectrum was identified with the ionization produced by Ge recoil atoms having the calculated maximum recoil energy. The electron-hole pair production of Ge recoils was measured in this manner from 21.4 to 997 keV, using monoenergetic neutrons from 400 keV to 18.6 MeV. In this energy range, the ratio of the ionization produced by a Ge recoil relative to that of an electron of the same energy increased from ~0.15 to ^0.7. At very low Ge recoil energies, most of the energy goes into atomic processes. At high recoil energies, where electronic processes become important, the ionization produced by a Ge recoil appears to approach that for an electron of the same energy. The corresponding partition of energy between electronic processes and atomic processes for an energetic Ge atom in a Ge lattice agrees favorably with predictions of the theory of Lindhard et al. These data together with the earlier results of ionization produced by energetic Si atoms within a Si lattice agree with the A and Z dependence of the partition of energy predicted by Lindhard.

Formation damage studies using artificially fractured, low-permeability sandstone cores indicate that viscosified fracturing fluids can severely restrict gas flow through these types of narrow fractures. These studies were performed in support of the Department of Energy's Multiwell Experiment (MWX). The MWX program was a coordinated research effort to study methods to evaluate and enhance gas production from low-permeability lenticular reservoirs of the Western United States. Extensive geological and production evaluations at the MWX site indicate that the presence of a natural fracture system is largely responsible for unstimulated gas production. The laboratory formation damage studies were designed to examine changes in cracked core permeability to gas caused by fracturing fluid residues introduced into such narrow fractures during fluid leakoff. Polysaccharide polymers caused significant reduction (up to 95%) to gas flow through cracked cores. Polymer fracturing fluid gels used in this study included hydroxypropyl guar, hydroxyethyl cellulose, and xanthan gum. In contrast, polyacrylamide gels caused little or no reduction in gas flow through cracked cores after liquid cleanup. Other components of fracturing fluids (surfactants, breakers, etc.) caused less damage to gas flows. The results of fluid leakoff tests indicated that polysaccharide polymers caused a filter cake buildup at or near the crack entrance while polyacrylamide polymers did not cause a filtercake buildup within the time period of the tests. For xanthan gum gels filtercake buildup was reduced for gels containing polymer breakers. For gels containing polymer breakers, 100 mesh sand was an effective fluid-loss control agent for narrow fractures. Other factors affecting gas flow through cracked cores were investigated, including the effects of net confining stress and non-Darcy flow parameters. Results are related to some of the problems observed during the stimulation program conducted for the MWX. Introduction The MWX has been an extensive program to characterize and stimulate gas production from low-permeability lenticular gas reservoirs of the Western United States. Three closely spaced wells were drilled into the Cretaceous Mesaverde group in Garfield County near Rifle, Colorado. After extensive geological and geophysical characterization, a series of stimulation treatments were performed in sandstones of the paludal, coastal, and fluvial intervals of the Williams Fork formation at the MWX site. A number of reports have been published which describe the work that has been performed at the MWX site. Core studies indicated that dry core matrix permeabilities to gas at reservoir stress conditions were less than 10 40d and frequently less than 3 40d. At typical levels of water saturation for the reservoir, these values may be reduced by an order of magnitude. Porosities ranged from 3 to 12%. Clays generally averaged less than 10% and were predominantly illite and mixed-layer clays. P. 551^

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The Multi-Well Experiment (HWX) is a researchoriented field laboratory whose objective is develop the understanding and technology to allow economic production of the several years supply of natural gas estimated to be within the low permeability, lenticular gas sands of the Western United States. Features of MWX include:(1) close-spaced wells (~125 ft,~38 m) for reservoir characterization, interference testing, wellto-well geophysical profiling, and placement of diagnostic instrumentation adjacent to the fracture treatment; (2) complete core taken through the formations of interest: (3) a comprehensive core analysis program; (4) an extensive logging program with conventional and experimental logs; (5) determination of in situ stresses in sands and bounding shales: (6) use of various seismic surveys and sedimentological analyses to determine lens morphology and extent; (7) use of seismic, electrical potential and tilt diagnostic techniques for hydraulic fracture characterization: and (8) a series of stimulation experiments addressing key questions. This paper presents the current MWX accomplishments in the above areas since drilling started at the site in September 1981 through December 1982.

This report summarizes recent reviews, observations, and analyses believed to be imperative to our understanding of the recent two million cubic feet salt fall event in Big Hill Cavern 103, one of the caverns of the Strategic Petroleum Reserve (SPR). The fall was the result of one or more stress driven mechanical instabilities, the origins of which are discussed in the report.The work has lead to important conclusions concerning the engineering and operations of the caverns at Big Hill. Specifically, Big Hill, being the youngest SPR site, was subjected to state-of-the-art solutioning methods to develop nominally well-formed, right-circular cylindrical caverns. Examination of the pressure history records indicate that operationally all Big Hill SPR caverns have been treated similarly.Significantly, new three-dimensional (3-D) imaging methods, applied to old (original) and more recent sonar survey data, have provided much more detailed views of cavern walls, roofs, and floors. This has made possible documentation of the presence of localized deviations from "smooth" cylindrical cavern walls. These deviations are now recognized as isolated, linear and/or planar features in the original sonar data (circa early 1990s), which persist to the present time. These elements represent either sites of preferential leaching, localized spalling, or a combination of the two.Understanding the precise origin of these phenomena remains a challenge, especially considering, in a historical sense, the domal salt at Big Hill was believed to be well-4 characterized. However, significant inhomogeneities in the domal salt that may imply abnormalities in leaching were not noted. Indeed, any inhomogeneities were judged inconsequential to the solution-engineering methods at the time, and, by the same token, to the approaches to modeling the rock mass geomechanical response. The rock mass was treated as isotropic and homogeneous, which in retrospect, appears to have been an over simplification. This analysis shows there are possible new opportunities regarding completing an appropriate site characterization for existing operating cavern fields in the SPR, as well as expansion of current sites or development of new sites. Such characterization should first be consistent with needs identified by this report. Secondly, the characterization needs to satisfy the input requirements of the 3-D solutioning calculational methods being developed, together with 3-D geomechanical analyses techniques which address deformation of a salt rock mass that contains inhomogeneities. It seems apparent that focusing on these important areas could preclude occurrence of unexpected events that would adversely impact the operations of SPR. 5 ACKNOWLEDGEMENTS

The Multi-Well Experiment (MWX) is a researchoriented field laboratory and it is the major production teChnology activity of the Western Gas Sands Project. A major activity is the core analysis program. Over 3600 ft (1097 m) of core were taken from two wells separated by only about 110 ft (34 m) at depth. All maj0r categories of core analysis are reviewed and results through December 1982 are included. Those include routine core analysis, restored state reservoir parameter measurements, electrical measurements, mechanical rock property data, mineralogy, organic maturation and geochemistry. This paper also describes the laboratory work on core and formation invasion and the development of instruments that were used in the field processing of the core.

A pressure coring operation was performed in two tight sandstone lenses of the Mesaverde group during the drilling of one well of DOE's Multi-Well Experiment. The goals were:to obtain accurate water saturation data;to measure the amount and composition of gas on a foot-by-foot basis; andto recover fluids for water chemistry analysis. This application of pressure coring bad not been tried before; it was felt to be the best approach for accurate water saturation measurements in tight sandstone core. Several changes to usual pressure coring procedures were adopted. These included the procedures were adopted. These included the development of an organic noninvasive coring fluid, compatible with the oil-based drilling fluid used, that would help preserve water saturation. Three 15-ft pressure cove barrels were taken in two sandstone lenses 20 and 30 ft thick; all three barrels were filled with sandstone. Goals 1 and 2 were met. Water saturation values are reported and discussed. The type and duration of the water extraction processes ave shown to be very important in determining water saturations in tight sands. Gas species and amount are available on a foot-by-foot basis. Introduction The Multi-Well Experiment (MWX) is a research-oriented field laboratory and it is the major production technology activity of the Department of Energy sponsored Western Gas Sands Project. The overall MWX objectives are to Project. The overall MWX objectives are to thoroughly characterize lenticular gas sand reservoirs and evaluate technology for their production. A major activity of the Multi-Well production. A major activity of the Multi-Well Experiment is the core program. This paper deals with one major aspect of the M" core program, the design and execution of a pressure core operation in tight sands with accompanying pressure core analysis. The effect of water saturation is extremely important in tight sands; permeability is very strongly dependent upon water saturation. For example, water saturations of 15%, 30%, 40% and 50% reduced the permeabilities of a Multi-Well Experiment core sample by factors of 0.61, 0.33, 0.25 and 0.05 respectively. Thus, an unambiguous technique to accurately measure water saturation becomes extremely important. There is general concern with the accuracy of water saturations measured in core because fluids may be excluded when core is brought to the surface. Additionally, drilling fluids may penetrate into the cove, especially if water-based penetrate into the cove, especially if water-based fluids are used. It was believed that pressure coring would circumvent the first problem and the core could be brought to the surface intact with all its fluids. The use of organically based drilling fluids, with suitable tagging, would alleviate the second problem. Therefore, a pressure coring operation was undertaken in the tight sandstone of the Mesaverde group in the second well, MWX-2, of the Multi-Well Experiment. At the time it was undertaken it was felt to be the best approach for water saturation measurements in tight sandstone core. This application of pressure coring had not been tried before. Specifically, the goals of the project were to:obtain accurate water saturation data.obtain both the amount and species of gas foreach foot of pressure core taken.Obtain fluids from the thawing of the pressurecore for water chemistry analysis. P. 229