Predicting waterflood residual oil saturation in Australian fields
Engineering Honours Degree 2005
University of Adelaide
Residual Oil Saturation (Sor) is an important reservoir property, and has a large impact on reserves calculations. Determination of Sor is a difficult process which can be both expensive and time consuming. There are many factors that affect Sor, causing a large variation in Sor between fields, and this makes Sor very difficult to predict, even for seemingly similar reservoirs. The three main categories of factors that affect Sor are 1) rock properties, 2) fluid properties and 3) the type of displacement process. This project focuses on waterflood Sor, and investigates the effect that rock properties have on Sor. The project carries on ideas presented by Behrenbruch in his paper on the Buffalo Field in the Timor Sea .
The report presents new methods for predicting waterflood Sor using readily available data. To do this, the relationships between residual oil saturation (Sor), irreducible water saturation (Swir), permeability (k), porosity (φ) and wettability (ω) were studied. The best relationship that was seen was between the Land Constant (C)squared and the Rock Quality Index (RQI)cubed :
C = Soi - Sor RQI = Square root of permeability over porosity
The research was conducted using data from the Corallina, Laminaria, Skua and Buffalo fields, located in the Timor Sea, in Australia. 108 Special Core Analysis (SCAL) samples were used in the project, and were tested using Centrifuge, Centrifuge Relative Permeability (cent kro) and Relative Permeability Steady-State (rel perm SS) laboratory methods. Although there are only a limited number of samples, the fit of the available data for each individual field is very good, especially for a plot of C vs RQI with the poor data removed. While there is a separation of the trends between fields, and they do not all sit on the same line, the slope of the trends is similar, suggesting a general relationship. Reasons for the differences between fields are included in the report.