Spin–Spin Relaxation Time Investigation of Oil/Brine/Sand Systems. Kinetics, Effects of Salinity, and Implications for Wettability and Bitumen Recovery

Abstract

Improving the efficiency of secondary and tertiary oil recovery is one of the major challenges of the crude oil industry. Arguably the most significant advance made in recent years has been the realization of the importance of water chemistry during oil recovery. This has led to the concept of low-salinity waterflooding for conventional oil reservoirs, for which reducing the total salinity of the injection water has been found to improve oil recovery rates. Although the precise mechanisms responsible for the improvements are not completely understood, it is acknowledged that specific interactions in the crude oil/ brine/rock (COBR) systems will modify wettability and interfacial energy. The present paper extends investigations of COBR interactions to higher viscosity oils and considers implications for heavy oil recovery. We have used NMR relaxation time measurements to study interactions in oil/brine/sand (OBS) systems containing either natural bitumen or a polybutene hydrocarbon (Glissopal). Exposing the oil-coated sands to water or aqueous group 1 and group 2 metal chloride solutions enabled the T 2 relaxation time spectrum to be determined as a function of time. The observed decreases in the geometric mean T 2 values with time obey first-order kinetics; for bitumen-coated sands, the rate constants are consistent with diffusion of water through the bitumen. Opto-digital microscopy verified the formation of ∼1−3 μm diameter water droplets in the initially dry bitumen coating, suggesting that water nucleation and growth also occur. This was not observed for the Glissopal-coated sand samples. No evidence was found for displacement of either viscous oil from the sand grains, although optical microscopy did reveal rearrangement of the bitumen coating, which possibly exposes fresh sand surfaces to the aqueous phase. This behavior is consistent with the finding that the original T 2 parameters determined for fresh sand are not fully restored simply by contacting the bitumen-sand surface to water or aqueous salt solutions under the ambient experimental conditions. Glissopal-coated sands exhibited smaller time-dependent T 2 changes compared with bitumen-coated sands. While not displacing viscous oils from the sand surface under the experimental conditions used, it is conjectured that water ingress into the surface oil layer could weaken oil/sand interactions which by analogy with recent studies on conventional oil recovery could provide an additional heavy oil recovery mechanism under more dynamic or higher temperature conditions.

Asphaltene adsorption on quartz sand in the presence of pre-adsorbed water

“…Excess bulk water is responsible for the longer relaxation time components. In contrast to this, the sand sample that had been subjected to asphaltene adsorption under 0% RH conditions shows a much smaller short relaxation time component, with the majority of the response comprising a longer relaxation time, typical of a predominantly hydrophobic sand sample [36]. For the sand produced at 100% RH, however, the spectrum is seen to indicate mixed wettability characteristics.…”

“…that for all the samples tested, T 2gm decreases with time indicating that the surfaces become more hydrophilic as water penetrates (and/or displaces [58]) the adsorbed asphaltene film [36]. For the 100% RH sample, which has the lowest asphaltene adsorption, T 2gm is seen to decrease within minutes, almost reaching the baseline value for ambient sand.…”

“…We were interested to assess the extent to which asphaltene adsorption had changed the wettability of each sand sample, and to this end we used a low-field NMR approach to quantify the distribution of water between the bulk phase and sand surface, as described elsewhere [36].…”

“…Conversely, water-wet hydrophilic surfaces would be expected to produce shorter relaxation times. Thus, by measuring relaxation spectra over time, fluid-solid interactions can be monitored, thereby enabling wettability or wettability changes to be inferred [36].…”

Interfacial Chemistry in Steam-Based Thermal Recovery of Oil Sands Bitumen with Emphasis on Steam-Assisted Gravity Drainage and the Role of Chemical Additives

“…Also interesting was the observation of tighter w/o emulsions using additized steam. The formation of w/o emulsions of this type has been suggested as being an additional recovery mechanism, perhaps applicable to SAGD, since the resultant expansion of the oil phase could increase the effective contact angle between bitumen and the solid surface [135].…”