Supersaturation in a Wide Range of Recombined Oils

Abstract

We have studied the limits of supersaturation in binary alkane mixtures and recombined crude oils at elevated pressures. Our study has interrogated these fluids using an optical cell with an internal volume of approximately 1 μL that includes a thermally pulsed wire which nucleates bubbles to "break" supersaturation, thereby acting as a reference. In parallel, we have made measurements in a larger and more conventional optical cell with an internal volume closer to 1 mL absent the aid of a nucleation device. For both, we demonstrate a maximum supersaturation of approximately 800 psi for conventional black oils. In contrast, supersaturation is demonstrated to be minimal for volatile oils. We show that the higher surface tension of conventional black oils favors surface-mediated nucleation, while the lower surface tension of volatile oils gives rise to nucleation that primarily takes place in the bulk. Among the surfaces studied, optically smooth high-pressure windows that permit observation of the nucleation process show the lowest tendency to nucleate bubbles.

Development of a Downhole Measurement System for Phase Behavior of Reservoir Crude Oils and Retrograde Condensates

“…Field examples in Section show that thermal nucleation is necessary to quickly and accurately measure the bubble point pressure of a crude oil. These field observations are consistent with 10 years of laboratory benchmarking with recombined crude oil samples summarized in Figure (further details provided in ref ). Figure A shows that P b increases with GOR content indicating that P b is a very good proxy for GOR or gas content as long as it is measured carefully, which is important for deepwater examples #3 and #4 in Section where the GOR measurement is noisy or negative.…”

“…In the downhole environment, it is imperative that a measurement of P b take only a few minutes so that multiple measurements can be made during each station; to date, we have performed up to 50 measurements during one station alone. To facilitate bubble nucleation downhole, rather than waiting for bubbles to emerge from solution, we developed a novel method in which an approximate 10 μs current pulse is applied across a Pt–Ir wire (25 μm diameter) immersed in the sample fluid; details concerning the anomalous nucleation resulting from this technique have been extensively published in the literature (Figure A). − Thermocapillary forces for lower temperature phase transitions generally lead to bubbles being ejected from the wire surface (Figure A, left). At higher temperatures, thermocapillary forces draw bubbles to the wire surface, reducing the optical signature (Figure A, right).…”

“…(D) Supersaturation normalized by P b vs surface tension. Reproduced with permission from ref . Copyright 2020, American Chemical Society.…”

“…In contrast, the maximum in supersaturation of Figure 11C likely indicates a transition from nucleation dominated by the bulk fluid properties (homogeneous nucleation) to that dominated by heterogeneous nucleation. 1,12,14 The exact transition of this crossover likely depends on the particular configuration of the measurement device. Even for our small measurement volume (with a corresponding large surface area to volume ratio), we measure supersaturation as large as 800 psi (Figure 11C).…”