SEM IMAGING OF DRY AND SATURATED POROUS ROCKS FOR MODELING FLUID DISTRIBUTION ON PORE SCALE

摘要

Scanning electron microscopy(SEM) is the only direct observational method that has a high enough resolution to allow for the investigation of details of the pore space morphology or very small objects like liquid films in the pores.We tested different preparation methods to obtain sedimentary rock samples that are suitable for highresolution SEM imaging as a basis for a realistic description of the pore space.The produced photomicrographs were used directly in an applied modeling tool to simulate fluid distributions,e.g.,at primary drainage. To compare the model predictions with actual observations,sandstone and chalk plugs were saturated with synthetic formation water,and initial water saturation was established by injection of synthetic oil or crude oil at high temperature.The saturated samples were frozen in liquid nitrogen and investigated using SEM at low temperatures (Cryo-SEM) to obtain detailed information on the pore level fluid distribution. Good results were achieved for saturated sandstone.The geometry of the wetting phase films attached to the pore walls and at the contact of the grains,as well as water-filled smaller pores,was clearly observed.The distribution of fluids could be fittingly simulated with our modeling tool.Due to the predominance of micro- and nanopores in chalk,the Cryo-SEM resolution impedes the distinction of fluids at high magnification in this rock type.The distribution of the fluid phases could only be clearly imaged in chalk macropores.