Disconnected Gas Transport in Steady‐State Three‐Phase Flow

Abstract

We use high‐resolution three‐dimensional X‐ray microtomography to investigate fluid displacement during steady‐state three‐phase flow in a cm‐sized water‐wet sandstone rock sample. The pressure differential across the sample is measured which enables the determination of relative permeability; capillary pressure is also estimated from the interfacial curvature. Though the measured relative permeabilities are consistent, to within experimental uncertainty, with values obtained without imaging on larger samples, we discover a unique flow dynamics. The most non‐wetting phase (gas) is disconnected across the system: gas flows by periodically opening critical flow pathways in intermediate‐sized pores. While this phenomenon has been observed in two‐phase flow, here it is significant at low flow rates, where capillary forces dominate at the pore‐scale. Gas movement proceeds in a series of double and multiple displacement events. Implications for the design of three‐phase flow processes and current empirical models are discussed: the traditional conceptualization of three‐phase dynamics based on analogies to two‐phase flow vastly over‐estimates the connectivity and flow potential of the gas phase.

In‐Situ Capillary Pressure and Its Interrelationships With Flow Characteristics During Steady‐State Three‐Phase Flow in Water‐Wet Berea Sandstone

“…2. The results of this study, consistent with previous ones (Alhosani, Selem, et al, 2021;Zankoor, Khishvand, McCaskill, et al, 2021), show that gas may flow in the form of disconnected gas clusters during steady-state flow. This behavior was evident by some disconnected gas clusters which had local capillary pressure values that varied across the cluster and were higher than those of the larger more connected ones.…”

“…The local changes in gas pressure could result in movements of gas-oil interfaces toward the pore corners or invasion of gas in some small pore elements. This hypothesis is consistent with the observations in this and a previous study (Alhosani, Selem, et al, 2021), that gas can be transported in the form of disconnected clusters during steady-state three-phase flow.…”

“…More recently, similar observations were reported by Alhosani, Selem, et al. (2021), who showed that gas flows as disconnected globules when injected simultaneously with oil and water through intermittent opening and closing of flow paths.…”

“…Moreover, some intermediate greyscale values between the gas and oil phases and blurry interfaces were observed at some locations in the image (see Figure S1 in Supporting Information S1) which were shown after segmentation as gas patches within the oil phase. It is worth mentioning, however, that the injection flow rates in our study were significantly lower than that used by Alhosani, Selem, et al (2021) (The highest Q t in our study was 0.092 cc/min compared to Q t = 0.8 cc/min in theirs), which reduces the intermittency behavior as discussed by Alhosani, Selem, et al (2021).…”

“…Our analysis also revealed that none of the gas clusters extended from the inlet to the outlet of the FOV during gas injection and the extension of these clusters in the pore space was even more reduced during the waterflooding test. This finding is particularly interesting for steady-state flow conditions and implies that either the gas had established a connected flow path outside the FOV or that the gas flows in the form of disconnected globules, as described by Alhosani, Selem, et al (2021). In that study, the authors attributed such transport to the flow intermittency phenomenon, where fluids alternate in filling the same flow paths during simultaneous fluid injection.…”