William E. Kenyon

Magnetic resonance, digital image analysis, and permeability of porous media

The results of an experimental and theoretical study of consolidated, acid‐cleaned fused glass beads are presented. Measurements of the spin‐lattice lifetime, permeability, and capillary pressure curves in conjunction with digital analysis of scanning electron microscope images and theoretical modeling lead to a description of this porous material consistent with the fast diffusion picture of nuclear magnetic relaxation.

Formation factor of carbonate rocks with microporosity: model calculations

Abstract Influences of variation of porosity at a microscopic level on cementation exponent m are computed using the effective-medium theories. It was found that solution pores or vugs lead to an increase in the cementation exponent m , whereas large grains, such as filled solution pores lead to a decrease in m . Application to data on a set of carbonate rocks from a given field gave reasonable agreement.

T1‐permeability correlations

We begin by presenting evidence which indicates a strong correlation exists between single fluid Darcy permeability and the T1 parameter characterizing the relaxation of nuclear magnetism within sandstones and carbonates. After defining terms, we discuss why NMR decay of water in rocks might reveal information about rock microgeometry. Finally, we discuss efforts being made to understand how to relate the length scale measured in NMR with that involved in permeability.

NMR Relaxation of Clay-Brine Mixtures

Effective interpretation of nuclear magnetic resonance (NMR) logs in shaly sands requires an understanding of the NMR contribution of clays. Of particular importance is the role of clays in the rapidly relaxing part of the NMR signal. In this study we measured the transverse relaxation time spectrum (T 2 ) of brine mixed with four clays (illite, smectite, kaolinite and glauconite) as a function of compaction. The Larmor frequency was 2 MHz and the echo spacing 0.16 msec. Mild compaction was achieved by centrifuging the clay slurry at three successive pressures ranging from I to 125 psi. Highly compacted samples were produced in a uniaxial press at six sequential pressures ranging from 500 to 16,000 psi. Each clay-brine slurry and its associated compacted sample showed a single peak in the T 2 distribution spectrum. A second peak, which could be interpreted as the clay-bound water, was never observed. The T 2 peak position shifted to faster relaxation times as compaction increased, in proportion to the pore volume-to-surface ratio, V p /S. The single peak and V p /S proportionality are consistent with fast diffusion between the pore water and the monolayer of water on the clay surface. Surface relaxivity varied among the four clay minerals; glauconite, the clay with the highest magnetic susceptibility and iron content had the largest surface relaxivity. These results have important implications for the interpretation of NMR logs in shaly sands. Because of the effects of compaction and to a lesser extent the iron content on a clays T 2 peak position, it is not possible to independently determine clay type from some characteristic relaxation time. These data also imply that it is not feasible to estimate the cation exchange capacity from a single time cutoff of the T 2 distribution without additional information such as laboratory measurements or other log data.