Publications

Investigation of oil injection into brine for the Strategic Petroleum Reserve : hydrodynamics and mixing experiments with SPR liquids

O'Hern, Timothy J.; Torczynski, J.R.; Cote, Raymond O.; Castaneda, Jaime N.

An experimental program was conducted to study a proposed approach for oil reintroduction in the Strategic Petroleum Reserve (SPR). The goal was to assess whether useful oil is rendered unusable through formation of a stable oil-brine emulsion during reintroduction of degassed oil into the brine layer in storage caverns. An earlier report (O'Hern et al., 2003) documented the first stage of the program, in which simulant liquids were used to characterize the buoyant plume that is produced when a jet of crude oil is injected downward into brine. This report documents the final two test series. In the first, the plume hydrodynamics experiments were completed using SPR oil, brine, and sludge. In the second, oil reinjection into brine was run for approximately 6 hours, and sampling of oil, sludge, and brine was performed over the next 3 months so that the long-term effects of oil-sludge mixing could be assessed. For both series, the experiment consisted of a large transparent vessel that is a scale model of the proposed oil-injection process at the SPR. For the plume hydrodynamics experiments, an oil layer was floated on top of a brine layer in the first test series and on top of a sludge layer residing above the brine in the second test series. The oil was injected downward through a tube into the brine at a prescribed depth below the oil-brine or sludge-brine interface. Flow rates were determined by scaling to match the ratio of buoyancy to momentum between the experiment and the SPR. Initially, the momentum of the flow produces a downward jet of oil below the tube end. Subsequently, the oil breaks up into droplets due to shear forces, buoyancy dominates the flow, and a plume of oil droplets rises to the interface. The interface was deflected upward by the impinging oil-brine plume. Videos of this flow were recorded for scaled flow rates that bracket the equivalent pumping rates in an SPR cavern during injection of degassed oil. Image-processing analyses were performed to quantify the penetration depth and width of the oil jet. The measured penetration depths were shallow, as predicted by penetration-depth models, in agreement with the assumption that the flow is buoyancy-dominated, rather than momentum-dominated. The turbulent penetration depth model overpredicted the measured values. Both the oil-brine and oil-sludge-brine systems produced plumes with hydrodynamic characteristics similar to the simulant liquids previously examined, except that the penetration depth was 5-10% longer for the crude oil. An unexpected observation was that centimeter-size oil 'bubbles' (thin oil shells completely filled with brine) were produced in large quantities during oil injection. The mixing experiments also used layers of oil, sludge, and brine from the SPR. Oil was injected at a scaled flow rate corresponding to the nominal SPR oil injection rates. Injection was performed for about 6 hours and was stopped when it was evident that brine was being ingested by the oil withdrawal pump. Sampling probes located throughout the oil, sludge, and brine layers were used to withdraw samples before, during, and after the run. The data show that strong mixing caused the water content in the oil layer to increase sharply during oil injection but that the water content in the oil dropped back to less than 0.5% within 16 hours after injection was terminated. On the other hand, the sediment content in the oil indicated that the sludge and oil appeared to be well mixed. The sediment settled slowly but the oil had not returned to the baseline, as-received, sediment values after approximately 2200 hours (3 months). Ash content analysis indicated that the sediment measured during oil analysis was primarily organic.