Mineralogical Studies of California Oil-Bearing Formations I - Identification of Clays

A progress report of an experimental investigation into the role of clay inreservoir performance is presented. The paper gives some of the reasons forconsidering clay as a significant component and outlines the objectives of abroad field of study which it is intended to pursue. Descriptions of theanalytical methods used are given; these include X-ray diffraction, electronmiscroscopy, thin section petrography, infrared spectroscopy, and cationexchange analysis. A suite of the more important clay minerals has beenassembled and characterized by these methods for use as standards in coreanalysis. From the data obtained it appears that although no one method ofanalysis is diagnostic for all of the clay minerals the infrared techniqueshows considerable promise in this direction. For the present, one or moresupplementary methods should be used to confirm the clay mineralidentifications. The methods of analysis are applied to field cores taken from representativeand widely differing strata especially as regards their susceptibility todamage by fresh water. Wells completed in the Stevens and Gatchell Zones in SanJoaquin Valley are particularly clear-cut examples of this behavior withStevens Zone wells being more adversely affected by fresh water. Cores fromthese zones have been studied and are discussed. It appears that differences inthis behavior can be ascribed to differences in the nature of the containedclays. The value of the infrared spectra of the clay fractions in establishingthe identity of the predominant clay minerals is given particular emphasis. Introduction It is a challenge to the technical resources of the petroleum industry thatwhen the economic limit of production is reached, from 40 to 70 per cent of theoil in California reservoirs remains unproduced even by use of the bestpresently known methods of recovery. The magnitude of this abandoned volume ofoil can be appreciated when it is considered that to 1950 in excess of 8billion bb1 has been produced from California reservoirs with estimatedeconomically recoverable reserves in known fields and pools totaling nearly 4billion bbl. If for every barrel of oil produced there is at least anotherbarrel still in place, it is evident that the revenue obtained from therecovery of only a few per cent of this volume would repay the cost of therequired research manyfold. T.P. 3059