Phase behavior, interfacial tension (1FT) measurements, fractionation studies, and core tests have been used in the formulation of a crude-oil-sulfonate (CROS)/ethoxylated-alcohol micellar fluid for application in a changing ionic environment that attains a relatively high hardness concentration as a result of ion exchange. By varying the hydrophile/lipophile balance (HLB) of the nonionic cosurfactant, phase behavior can be shifted from lower to upper phase and the optimum can be found. It is shown that the solubilization of oil and brine and the value of the optimum can be controlled further by blending different nonionic surfactants with CROS samples whose properties were altered by controlling variables in the manufacture. Effects of such system variables as surfactant and hardness concentration and the ratio of CROS/nonionics have a significant effect on phase behavior. The 1FT vs. solubilization parameter correlation was in reasonable agreement with that of Huh 1 and is shown.to hold over a wide range of surfactant and hardness concentrations, but the intercept is different for each CROS/nonionic pair. 1FT's and phase behavior from core-test effluents are shown to agree with the phase-behavior studies. Fractionation phase-behavior studies indicate that chromatographic separation will affect the process significantly only if oil is inefficiently displaced; this is supported by core tests. Excellent oil recovery was attained in Berea over a wide range of concentrations and HLB's, and with small slugs. Oil recovery in field core tests was poor because of stringent capillary desaturation requirements.
A successful post-test evaluation well was drilled in the Sloss Field, Kimball County, Nebraska, following a micellar-polymer flood. Drilling and sampling procedures are discussed which help insure valid data. Sulfonate loss, adsorption plus partitioning, was determined to be 0.4 of a pound per barrel (1.1 Kg/m3) of pore space. From core analysis and logging survey, oil was displaced over the entire pay interval from the average post waterflood residual of 30%, although some of the lower permeability zones had a final oil saturation of up to 16% compared to the average of 8%. The polyacrylamide polymer used in the mobility control bank was severely degraded causing the loss of mobility control. The degradation was not caused by a simple thermally induced hydrolysis. Limited tests indicate well workover fluids may have contributed to the degradation.
Crude oils from mature fields are routinely associated with high water cuts and high operating costs. High water cuts increase the process heat requirements, chemical requirements, overall vessel volumes, equipment footprints and weights. If a significant quantity of water can be removed at lower temperatures, the subsequent production equipment size, weight and cost can be reduced or eliminated. A method to accomplish this ambitious separation goal is being developed by NATCO. This separation process includes a compact treatment vessel that combines electrostatic coalescence and separation in either a series or parallel process. The vessel design permits both capacity expansions as well as performance improvement by the addition of more coalescing / separating stages. The overall oil-water separation process includes a series of processing steps for:Free gas removalPreliminary free-water separationElectrostatic water coalescenceOil dehydration, andSeparated water treatment. This paper will concentrate on steps 3 and 4 of this 5-part scheme. In laboratory equipment using a pipe vessel, NATCO has processed up to 3000 bfpd/ft2 of fluids and achieved an 85 - 95% water removal from oil streams containing as much as 40% water. This compact separation technology has the potential to be applied to either surface or subsea facilities. Using this compact electrostatic separation technology in a subsea environment can provide huge process and economic advantages in deep water applications. Introduction Weight and space are at a premium in the offshore environment. The compact electrostatic separator combines several advantages to work well offshore. The separator vessel is " pipe size??; therefore it has a small footprint and weight. In addition the operation is simple with minimal and conventional controls. Description of Electrostatic Technologies Evaluated Alternating Current (AC) Alternating Current (AC) is an older Electrostatic Dehydration technology. The AC process used here applies an alternating electric field at 60 Hz. The voltage can be varied to optimize the emulsion oscillation, which causes the water droplets to deform and accelerates their coalescence. See Figure 1. Bimodal AC Bimodal AC is a newer technology that utilizes a higher AC carrier frequency. The potential is modulated between lower and higher voltages at a slower frequency. This additional modulation facilitates additional drop coalescence.
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