The Influence of Reservoir Rock Properties On Ultimate Oil Recovery In Radial-core Waterfloods
Authors: Boukadi F.B.H. , Watson R.W. , Owolabi O.O. 
Published: March 2010

The most commonly used secondary oil recovery technique is waterflooding. The effects of rock properties such as porosity and permeability and fluid properties such as viscosity have been shown by previous investigators to influence the results of waterflooding and consequently ultimate oil recovery. The objectives of this present study are to consider the influence of rock properties such as tortuosity, wettability, pore-throat diameter, pore length and surface area on ultimate oil recovery realized in radial-core waterfloods and to incorporate the results of these analyses into generalized stochastic models for waterflooding performance predictions.

To accomplish these objectives, waterflood experiments were conducted in Berea sandstone and Indiana limestone radial cores. Core plugs were obtained from each of these cores and further analyzed using the Amott-Harvey method to determine wettability and mercury injection to determine surface area, median pore-throat diameter and pore length. The analyses of the data indicated that pore-size distribution in water-wet systems is the principal factor in a direct proportionality relationship between the average initial oil saturation and the average residual oil saturation. Mercury porosimetry was used to characterize Berea sandstone and Indiana limestone cores. The analyses of the results of mercury porosimetry experiments suggested that steep-convex uni-modal capillary pressure curves are characteristic of Berea sandstone. By contrast, poly-modal capillary pressure curves are characteristic of Indiana limestone cores.

The results of these analyses were incorporated into stochastic models. The stochastic models indicated that oil recovery is strongly correlated to surface area, wettability, median pore-throat diameter, initial water saturation, residual oil saturation and tortuosity.

Introduction

The most commonly used secondary oil recovery technique is waterflooding. A prerequisite of the understanding of waterflood performance is a knowledge of the basic properties of the reservoir rock. Craig(1) indicated that these properties consist of two main types:rock skeletal, such as porosity, permeability and pore-size distribution, andcombined rock-fluid properties such as capillary pressure (static characteristics) and relative permeability (flow characteristics).

Besides porosity and permeability, pore-size distribution expressed in terms of pore-throat diameter, surface area and pore length and surface rock wettability, is used to determine the mechanisms by which oil is recovered by waterflooding. The objectives of this study are:To investigate the influence of rock properties such as porosity, permeability, surface area, pore-throat diameter, pore length, wettability and tortuosity on ultimate oil recovery.To determine the functional relationships between ultimate oil recovery and these rock properties using statistical analyses.To incorporate these functional relationships into a generalized stochastic model for predicting oil recovery by waterflooding.

Mercury Porosimetry

Mercury porosimetry analysis is used to investigate the mechanisms of non-wetting phase trapping and the influence of rock microscopic properties on ultimate oil recovery. Lowell and Shields(2) pointed out that the experimental method of mercury porosimetry for the determination of porous properties of solids is dependent on several variables such as wetting or contact angle between mercury and the surface of the solid. To monitor changes in these variables, Ritter and Drake(3) u