Wettability quantification - Prediction of wettability for Australian formations

Abstract

As a rock-fluid interaction property, wettability is well recognized to influence the flow in multi-phase systems such as hydrocarbon reservoirs. In the laboratory, wettabilty measurements are made according to certain standard procedures and the results are expressed as indices for comparative purposes. The two most commonly used wettability indices are the USBM index, related to areas under capillary pressure curves, and the Amott-Harvey wettability index related to imbibition characteristics. If such measurements are not available, relative permeability curve characteristics may be used to quantify wettability. As is the case with most special core measurements, wettability tests are expensive and time consuming, with the consequence that the number of plugs subjected to wettability testing is usually limited, often resulting in a poor definition of reservoir wettability characteristics. One objective of the study presented is to introduce a mathematical expression, which may be used to gauge relative wettability, as an alternative to the above-mentioned indices. The model has been validated using data from Australian hydrocarbon basins. A genetic algorithm approach was utilised to tuning parameters in the wettability model presented. The model compares favourably with laboratory measurements and may be used to predict USBM indices if experimental values are not available. As such, the formulation presented may also be used in wettability classification. One of the relative permeability characteristics used to gauge wettability is the ratio of relative permeability end points. A second objective in the presented research is to predict this ratio, useful for the prediction of relative permeability characteristics. In considering possible analytical forms, the final derived formulae are extensions of the Carman-Kozeny equation. Copyright 2011, International Petroleum Technology Conference.