Porosity measurements and form analysis of mineral grains in thin sections from oil- gas reservoir rocks using quantimet 720 and besi

Abstract

Submicroscopic and image analyzer techniques have been applied for the measurement of the porosities of oil—gas—water reservoir rocks from thin sections. Backscattered electron scanning images (BESI) were made predominantly at low magnifications of × 30 and × 60. Porosity data from linear traverses were obtained and differences in porosities between two sandstone reservoirs and a carbonate reservoir were determined. A large number of the measured pores contained clayey material. The surface occupied by this material was subtracted from the apparent porosity measurements with the image editor of the Quantimet 720 to give the real porosity. A sample from one of two sandstone reservoirs contained oil and could not be hardened using the common procedure for impregnation of the sample by a polyester resin. Gamma radiation was applied and hardening occurred in one weekend after 5 Mrad (50 kGy) had been absorbed. Hardening of this sample gave no problems, if the oil had been removed by monostyrene before a start was made with the impregnation process; such a sample was used for the present porosity study. Form analysis was done of individual mineral grains using BESI and Quantimet. The grains were represented in a number of shape classes of a diagram used for shape classification. Form-separation of individual minerals was also possible.