A Novel Technique for the Determination of Microscopic Pore Size Distribution of Heterogemeous Reservoir Rocks
Authors: Elgaghah Shedid 
Published: December 2007

Fluid flow through porous media is affected by petrophysical properties and their distribution. Standard techniques of core analysis provide an average of varying petrophysical properties and pore size distribution of porous rocks. However, these techniques have severe assumptions, which may influence the results obtained negatively.

The major objectives of this study are to develop a new technique capable to provide the microscopic pore size distribution of heterogeneous reservoir rocks and to apply this technique to interpret the formation damage problem due to sulfur deposition. The current methods of calculating the pore size distribution were reviewed and evaluated. To achieve the objectives of this study, ten reservoir rock samples extracted from an actual oil reservoir were photographed using scanning electron microscope (SEM) and analyzed using computer software to provide the pore size distribution. In order to investigate the application of the proposed technique, actual sulfuric crude oil was flooded through actual core sample and the in-situ deposited sulfur along the damaged core sample was calculated. In addition, this newly-developed technique was used to quantify plugged and opening pores of the core under study.

The results showed that a new technique capable of explaining and providing the required information about pore size distribution and its applications on a microscopic scale was developed. In addition, the influences of fluid flow characteristics of elemental sulfur through reservoir rock were presented. The newly-proposed technique provided valuable data such as pore size distribution, minimum and maximum pore diameters, plugged and non-plugged areas, and deposited amount of damaging element. The judicious applications of the attained results represent an impact in studying and/or evaluation of formation damage, designing the microbial enhanced oil recovery process, and development and validation of many oil reservoir simulation models.

1. Introduction and Review

Reservoir rocks are characterized to have complex pore structure arose from infinitely many random events caused by several interacting factors in the geologic environment and history of the deposition, for instances: compaction, cementation, leaching, oxidation, fracturing and dolomization. Fluid flow through porous medium attracted a real attention of petroleum engineering and geology. Particularly, formation characterization of pore throat size and its distribution plus pore throating blocking. The complex pore size distribution is considered as one of the most important factors controlling the displacement efficiency of oil reservoirs. Pore size distribution is widely used in the oil industry to analyze fluid flow and permeability damage resulted from liquid and solid invasion of drilling fluids (Donaldson et al., 1977; Chilingar et al., 1983; Aminian et al., 1998), asphaltene and/or wax deposition in the reservoir rock (Donaldson et al., 1985) specially around the wellbore hole, and growth of bacteria during microbial enhanced oil recovery (MEOR) processes (Zajic et al., 1985), and water saturation exponent (Dixon, 1990).