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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.