APPLICATION OF LINEAR X-RAY ANALYSIS USING ABSORPTION COEFFICIENTS FOR DIRECT DETERMINATION OF IN SITU CORE SATURATION FOR PC MEASUREMENT

摘要

Measurement of the in situ distribution of fluid saturation in a rock sample is a prerequisite for determination of capillary pressure(Pc)curves by the Direct Measurement of Saturation(DMS).A common method for measurement of fluid saturation in rock is linear x-ray scanning.The use of linear x-ray for Pc measurement by DMS has not previously been reported.Lambert’s equation provides a means to accurately quantify fluid saturation using an x-ray scanning technique.The equation relates the intensity of an x-ray beam that emerges from a saturated rock to the incident beam intensity,and the absorption coefficients and thickness of rock matrix and fluids that occupy the pore space.To demonstrate the application,imbibition Pc curves were obtained by linear x-ray measurements for four Kansas outcrop chalk plugs.The wettability of three of these plugs had been altered to illustrate the different Pc curves that could be obtained.The procedures used cells containing the saturating fluids,air,octadecane,and brine to obtain accurate determination of the absorption coefficients before saturating the rock samples.Subsequently,the plugs were saturated and spun by centrifuge with a free water level to obtain the positive and negative portions of the imbibition Pc curves.Accurate measurement of the free water level can be obtained from images obtained by magnetic resonance(MRI)or by x-ray scanning techniques.A reference rock sample provided control over experimental variations.