--> Abstract: NMR Characterization of the Water Adsorbed by Montmorillonite Impact on the Analysis of Porosity Logs, by D. Chitale; #90911 (2000)
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Abstract: NMR Characterization of the Water Adsorbed by Montmorillonite Impact on the Analysis of Previous HitPorosityNext Hit Logs

CHITALE, DATTATRAYA, Halliburton Energy Services

Reservoir rocks contain interstitial pore water as well as the water adsorbed by the clay minerals. Chitale, et al. (SPWLA 41st Annual Logging Symposium, June, 2000) have demonstrated for montmorillonite that NMR measurements show the adsorbed clay water is 500 mg per g of dry clay, a value in close agreement with values reported in the literature. This paper highlights the impact of the water adsorbed by montmorillonite on the interpretation of conventional Previous HitdensityNext Hit and Previous HitneutronNext Hit logs which require knowledge of the exact bulk Previous HitdensityNext Hit and the Previous HitneutronNext Hit Previous HitporosityNext Hit for wet clay end-members for interpretation.

The wet clay density values for montmorillonite presented in the standard charts (Schlumberger, 1994 and Halliburton, 1994) range between 2.0 to 2.7 g/cc. The adsorbed water associated with montmorillonite is the minimum water volume that can be contained in an aggregate of montmorillonite particles. Consequently, this volume is also the minimum contained in wet montmorillonite. For a dry density of 2.6 to 2.7 g/cc, the wet clay density must then be less than 1.7g/cc. The value of 500 mg per g of dry clay results in a minimum Previous HitporosityNext Hit of wet montmorillonite of 0.57. Since the neutron Previous HitlogNext Hit measures both water and the hydroxyls, the neutron Previous HitporosityNext Hit for water-saturated montmorillonite must be greater than 0.57. As the volume of montmorillonite in a reservoir decreases, the fractional NMR Previous HitporosityNext Hit and neutron Previous HitporosityNext Hit representing montmorillonite must also decrease, whereas the bulk density will increase proportionately.

Rationalization of the wet clay-end-member values for the Previous HitdensityNext Hit and the Previous HitneutronNext Hit logs based on the adsorbed water in montmorillonite enhances the quality and accuracy of the overall Previous HitlogNext Hit interpretation. This enhancement will be illustrated with a shaly sand Previous HitlogTop analysis as an example.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California