Sandstone porosity related to vitrinite reflectance

Abstract

Vitrinite reflectance (VR) and the volume fraction of quartz cement in sandstones are both measures of thermal exposure. This paper shows how porosity reduction by quartz cementation can be related to VR for heating at a constant rate, using simple models for quartz cementation and VR. This relationship reveals that the heating rate is an explicit parameter, which means that there is no pure relationship between porosity (volume fraction quartz cement) and VR. However, the rate of quartz cementation and the rate of change of TTI (time–temperature integral) have a close exponential dependence on temperature. Porosity reduction by quartz cementation as a function of VR therefore nearly follows the same curve for very different temperature histories. This property of porosity reduction by quartz cementation is used to calibrate average specific surface parameters as a function of porosity. The calibration procedure is demonstrated on two datasets, where the average specific surface depends on porosity to the power of an exponent that is somewhat greater than 3.