Wettability and Its Effect on Oil Recovery

Abstract

wide acceptance of the conclusion that most reservoirs are at wettability conditions other than VSWW. This conclusion has led to a resurgence of interest in satisfactory proce­ dures for measuring reservoir wettability and determining its effect on oil recovery, especially with respect to waterflooding. De­ termination of reservoir wettability and its effect on oil recovery by methods that in­ volve core samples will be referred to as ad­ vanced core analysis for wettability (ACAW). Reservoir wettability is not a simply de­ fined property. Classification of reservoirs as water-wet or oil-wet is a gross oversim­ plification. Various procedures for meas­ uring wettability have been proposed. Two methods of quantifying wettability based on rocklbrine/oil displacement behavior, the modified Amott test 2 and the USBM test, 3 are in common use. Each method depends on water saturation measurements and re­ lated capillary pressures or flow conditions to define a wettability scale. The tests show that reservoir wettability can cover a broad spectrum of wetting conditions that range from VSWW to very strongly oil-wet. With­ in this range, complex mixed-wettability conditions given by combinations of preferentially water-wet and oil-wet surfaces have been identified. In this paper, the 'adopted scales of reservoir wettability and their relationships to interface boundary con­ ditions are considered together with the dra­ matic effects that wettability can have on oil recovery.