Yaser Salimidelshad - School of Mining Engineering, College of Engineering, University of Tehran, Tehran, Iran
Ali Moradzadeh - School of Mining Engineering, College of Engineering, University of Tehran, Tehran, Iran
Ezatallah Kazemzadeh - Faculty of Upstream Petroleum Industry, Research Institute of Petroleum Industry (RIPI), Tehran, Iran
Mohammad Reza Esfahani - Research Institute of Petroleum Industry, Department of Research and Technology of the Rock and Fluid Reservoirs, Tehran, Iran

The reservoir management and enhancing production efficiency significantly relies on the precise determination of reservoir rock properties which reduce costs and risks of production planning. Therefore, studying the hysteresis phenomenon of the reservoir rock is an essential part of research as a less studied parameter. In this study, for the first time, the effects of hydrostatic pressures on the changes in the radius of the pores and the structure of sandstone and carbonate rock sample grains using microscopic images were studied. The results of microscopic images show that the changes occurred are strongly dependent on the rate and time of loading/unloading as well as the rock type. The variations for the carbonate sample are higher than that for the sandstone sample, and at loading rates above 4000 psi, the reduction of the size of the pores has intensified with a steeper gradient. According to the scanning electron microscopy (SEM) images, due to the pressure applied to the calcite sample, in addition to cracking in the rock matrix, the sharpness of the particles’ edges is reduced and at higher pressures, they are almost rounded. While in the sandstone sample, we only observed compaction of particles.

Hysteresis, Loading/unloading, Reservoir rock, Microscope, SEM