This paper (SPE 52607) was revised for publication from paper SPE 36737, first presented at the 1996 SPE Annual Technical Conference & Exhibition, Denver, 6-9 October. Original manuscript received for review 25 October 1996. Revised manuscript received 17 August 1998. Paper peer approved 1 September 1998. Summary In naturally fractured formations such as coal, permeability is sensitive to changes in stress or pore pressure (i.e., changes in effective stress). This paper presents a new theoretical model for calculating pore volume (PV) compressibility and permeability in coals as a function of effective stress and matrix shrinkage, by means of a single equation. The equation is appropriate for uniaxial strain conditions, as expected in a reservoir. The model predicts how permeability changes as pressure is decreased (i.e., drawdown). PV compressibility is derived in this theory from fundamental reservoir parameters. It is not constant, as often assumed. PV compressibility is high in coals because porosity is so small. A rebound in permeability can occur at lower drawdown pressures for the highest modulus and matrix shrinkage values. We have also history matched rates from a boomer well in the fairway of the San Juan basin by use of various stress-dependent permeability functions. The best fit stress/permeability function is then compared with the new theory. P. 539

The propagation of energetic particles along and across the interplanetary magnetic field is governed by the large-scale field geometry and by scattering in small-scale turbulent fields. Values of the scattering mean free path parallel to the field, h•(R), are reviewed in prompt solar bursts and nonimpulsive (corotating) events. Analysis of intensity and anisotropy profiles in combination is a powerful tool for elucidating X•(R). A consensus is found: at 1 AU, X• = 0.08-0.3 AU over a wide range of rigidity, R = 5 x 10 -4 to 5 GV. Efforts to explain the discrepancy between empirical values of X• and scattering theory are discussed. Quantitative measures of x• in rare scatter-free events, where h• >• 1 AU, are discussed because they can provide important details of the scattering process and the magnetic power spectra. Cross-field diffusion due to random walk of field lines is revisited. Recent values deduced from magnetic power spectra in interplanetary space, magnetic diffusion at the sun, Jovian electron propagation, and cosmic ray events are evaluated. Again, a consensus is sought, and a reasonable mean is K•_r/13 = 102• cm 2 s -•. Previous arguments against a significant Kñ r are reassessed, including the problem of the persistence of intensity fluctuations in cosmic ray events. Combining the consensus for K•_r/13 with that for h• gives K•_r/K• < 0.1 at 1 AU, and thus neglect of K_• r in the modeling of solar cosmic ray events appears justified (although account needs to be taken of coronal propagation). The outlook for the future includes better empirical values of h• down to Ep ---10 keV and Ee '" 1 keV, comparison with scattering theories at these energies, and comparison between empirical and theoretical X• in other regions such as the magnetosheath and upstream solar wind. A. terms of K•_r. 1977. Zwickl and Webber [1977] studied several different characteristics in many flare events and reached an important consensus for the value of K• at low proton energies, 3-30 MeV.

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