Routine laboratory permeability measurements require both overburden correction and in the case of lower permeability gas measurements also Klinkenberg-type correction, accounting for slippage of gas when flowing through a porous medium. These corrections are necessary for obtaining representative permeability values for dynamic simulation. The objective of this paper is to determine the most suitable technique for determining representative, equivalent reservoir permeability. Laboratory permeability is routinely measured using different types of gases, most often helium and air, less often liquid. Single phase permeability measurements should be independent of the measuring fluid. However, laboratory permeability measurements using gas tend to overestimate sample permeability due to gas slippage. This effect was first reported by Klinkenberg (1941). Influencing factors are type of gas, mean experimental pressure and rock properties. The so called ‘Square-root model’ (Florence et al. 2007) accounts for all of these factors and is an extension of Klinkenberg’s original equation. The applicability of the Square-root model and earlier Klinkenberg-type models of Jones and Owens (1979) and Sampath and Keighin (1981) for correcting single-point laboratory gas permeability measurements are investigated on a comparative basis. Furthermore, Klinkenberg-type corrections are best made after overburden correction. The study presented involves a parametric approach of the gas slippage influencing factors, in addition to a comparison of alternative formulations. In comparing various Klinkenberg-type corrections, it is shown that the Square-root model compares most favourably and is most suitable for correcting laboratory data in the absence of specific measurements, as validated by comparison with laboratory deduced measurements. Datasets from the Asia-Pacific region and elsewhere are used to exemplify the methodology.

Irreducible water saturation plays a significant role in estimating hydrocarbon initially-in-place and petroleum recovery. Yet, laboratory measurements for determining irreducible water saturation take considerable time and money. For this reason available data may not cover all requirements, giving rise to the practise of using correlations to fill in gaps. Described in this paper are the reasons for irreducible water saturation being an elusive parameter that not only depends on pore structure characteristics but also the type of experiment and laboratory procedures, as well as changing plug conditions during experimentation. This paper reviews traditional methods, as well as recent and novel approaches to quality assure laboratory data and for correlating irreducible water saturation for prediction. To gain insight into the dependence of irreducible water saturation on detailed pore structure characteristics, most notably grain size and sorting, the usefulness of global characteristics envelopes is explored (Behrenbruch and Biniwale, 2005). In this multidimensional plot, irreducible water saturation is plotted against porosity, permeability, hydraulic radius, porosity group, flow zone indicator (grain size) and sorting, giving an insightful overview of the interdependence of parameters. The second part of this paper compares novel correlations with commonly used correlations. Traditional and more recent correlations are covered, from simple correlations versus the logarithm of permeability to more sophisticated approaches using more variables, including porosity and others. Most notably, it is shown that an approach of correlating irreducible water saturation with grain size (or flow zone indicator [FZI]) and sorting shows great promise. Data from two Australian fields are used to demonstrate the methodology, showing a significant increase in fitting accuracy. This approach may eventually lead to a universal correlation.