Reproducible Wettability Alteration of Low-Permeable Outcrop Chalk

Abstract

A total of 41 chalk core plugs, cut with the same orientation from large blocks of outcrop chalk, have been aged in crude oil at 90°C for different time periods, in duplicate sets. Different filtration techniques, filtration temperatures and injection temperatures were used for the crude oil. Oil recovery by spontaneous, room temperature imbibition, followed by a waterflood, was used to produce the Amott water index for cores containing aged crude oil and for cores where the aged crude oil was exchanged by fresh crude oil or decane.The main objective was to establish a reproducible method for altering the wettability of outcrop chalk. A secondary objective was to determine mechanisms involved and the stability of the wettability change.The aging technique was found to be reproducible and could alter wettability in Ro "rdal chalk selectively, from strongly waterwet to nearly neutral-wet. A consistent change in wettability towards a less water-wet state with increased aging time was observed.

Wettability and Oil Recovery by Imbibition and Viscous Displacement from Fractured and Heterogeneous Carbonates

“…3.13b, it can be seen that they fall into a narrow range and are close to the correlated results for Berea 500 sandstone (Zhang, et al, 1996) and a wide range of other rock types (Viksund et al, 1998). Whitestone UZ showed slightly faster imbibition at early time; this could be related to the inherent heterogeneity.…”

“…3.1c), it can be seen that the curves for Gambier, Whitestone UZ, Edwards (GC) fall very close to each other and to the normalized spontaneous imbibition behavior for the Berea 500; they lie towards the lower values of dimensionless time of the Viksund et al (1998) spread.. On the other hand, the normalized imbibition behavior of Lueders and Fort Riley limestones were essentially identical. They exhibited longer dimensionless times than the Viksund spread, and fell close to the average curve for Berea 90 (a batch of Berea sandstone with permeability around 90 mD with distinctly different character than the Berea 500).…”

“…Furthermore, whether the rate of imbibition increases or decreases with increase in initial water saturation appears to depend on a delicate balance between reduction in capillary driving force versus increase in transmissibility of the invading wetting phase. (Viksund et al, 1998;Baldwin and Spinler, 2002) Use of an initial saturation of 0% provides a convenient common starting point for comparison of recovery of mineral oil from VSWW rocks.…”

“…If all the curves are normalized according final recovery (except for Whitestone LZ), and compared with the range of normalized imbibition obtained for a wide variety of rocks by Viksund et al (1998) (see Fig. 3.1c), it can be seen that the curves for Gambier, Whitestone UZ, Edwards (GC) fall very close to each other and to the normalized spontaneous imbibition behavior for the Berea 500; they lie towards the lower values of dimensionless time of the Viksund et al (1998) spread.. On the other hand, the normalized imbibition behavior of Lueders and Fort Riley limestones were essentially identical.…”

“…In contrast to MXW cores, the presence of initial water saturation has only moderate effect on VSWW imbibition behavior (Viksund et al, 1998;Xie and Morrow, 2001). Scaled spontaneous imbibition results of the three chosen carbonate samples are compared in Fig.…”