A study was undertaken to investigate the treatment of oilfield produced water by ultrafiltration in order to remove the oil to make steam generator quality water. To simulate commercial operation, tubular membranes were used in ultrafiltration experiments along with samples that were shipped quickly and directly from oil producers' sites in Western Canada. Permeation rates, oil content, degree of recovery, and other results were monitored at various operating conditions for several produced water samples. It was observed that the more stable produced waters are more amenable to treatment by ultrafiltration than destabilized produced waters. This reduces the amount of water treatment chemicals and in combination with the complete removal of oil, provides a stable and clean feed to subsequent softening and other water treatment operations. other factors inclUding membrane fouling by the oil and membrane operations at unusually high temperatures were investigated.
Steam stimulation of oil wells in the arid regions of Western Canada requires large volumes of water for steam generation and subsequent injection into the formation. When the oil is recovered from the formation, the steam that has condensed into water is pumped from the wellhead in combination with the oil. Recycling of this produced water to steam generator quality is difficult since it is contaminated with heavy oil, large amounts of dissolved inorganic salts, and silica. The economics and environmental advantages of recycling the produced water are expected to improve as overall water demand increases, thus providing increased incentives to treat produced water.
The wellhead fluid from a typical steam flood recovery operation may contain 2 to 10 barrels of water per barrel of oil product, part as a water-in-oil emulsion and part as the reverse emulsion. The first treatment is usually a free water knockout (FWKO) followed by high temperature settling (HTS) of the oil rich FWKO effluent. The water rich effluent from these two operations is described as produced water and is further treated in a skim tank to remove residual oil. The water from the skim tank is often disposed of by deep well injection or can be treated further for recycle to the steam generator. Several Canadian producers currently recycle produced water using a combination of conventional treatment and oil removal processes. Not only do the steam generator specifications require complete removal of the oil, most water softening and silica reduction treatment units require the removal of oil for optimal operation. This usually results in the use of oil removal with induced gas flotation (IGF) and sand filtration units and the addition of large amounts of emulsion destabilizing chemicals.
Cross flow ultrafiltration (UF) processes have been demonstrated for the efficient and economical treatment of industrial waste streams containing oils such as cutting oil from metal machining operations. Since UF is a cross flow filtration and free of filtration cakes and backwash procedures, it can handle higher oil levels than sand filtration. For this reason UF can be considered for replacing IGF units and its high level of water recovery will reduce the water load on the skim tank.
