J. A. Quirein and J. L. Baldwin
Schlumberger Well Services, Houston, Texas
R. L. Terry
Schlumberger Well Services, Denver, Colorado
M. Hendricks
Energy Reserves Group, Denver, Colorado
ABSTRACT
Fundamental in the quantitative evaluation of shaly formations is the estimation of the bulk volumes of clay, total porosity, and clay bound water. Using clay bound water, total porosity, and salinity, Qv (cation-exchange capacity per unit pore volume) or Swb (bound-water fraction) may be readily obtained, thus enabling determination of water saturation with either the Waxman-Smits or Dual Water saturation equations.
The proposed approach for determining the clay volumes and associated clay bound water volumes in the presence of multiple clay types relies upon the use of laboratory and core data. Such data is combined with log data using regression techniques to provide first-order estimates of how each logging tool responds to expected clay or mineral types. These estimates are then improved using a GLOBAL approach.
The output is a level-by-level display of the clay–mineral types and volumes, porosities, and water saturations, all having been determined numerically in accordance with the GLOBAL method. Field examples are presented and compared with core and SARABAND results as available. Emphasis is placed upon measuring the contribution of each of the available tools in the determination of the clay types and volumes. In particular, the utility of natural gamma radioactivity measurements as an aid in the identification of clay minerals is demonstrated.