Influence of suspended microcrystalline polymer system on characteristics of produced water from High Ca and Mg oilfields and corresponding oil removal methods

Suspended microcrystalline polymer flooding is a new promising EOR technology developed to improve oil recovery from high Ca and Mg reservoirs. However, as the technology is currently in the research and field experimental stage, the characteristics of its produced water and the corresponding water treatment methods are still not clear. In this study, the effects of polymer concentration on physical characteristics of the three simulated produced waters, namely, polymer flooding produced water (PFPW), high Ca and Mg PFPW (HPFPW) and suspended microcrystalline PFPW (SMPFPW), were investigated to understand the particularity of SMPFPW. Pattern of oil droplet diameters in SMPFPW exhibited a bimodal distribution with peak diameters at 4 and 150 μm. The viscosities of three waters are SMPFPW ≥ PFPW > HFPW in descending order. The absolute ζ potential of SMPFPW was 1.01 ∼ 2.42 times higher than that of HPFPW, but was substantially lower than that of PFPW due to high ionic strength. At same polymer concentrations (0 ∼ 300 mg/L), the oil content in SMPFPW is 1.78 ∼ 2.47 times that in HPFPW and 1.49 ∼ 1.87 times that in PFPW because of its unique spatial structure of polymers. From degreasing experiments, oil removal rate of SMPFPW by gravity sedimentation is higher than that of PFPW but slightly lower than that of HPFPW, polymer concentration play vital roles in oil-water separation. An inexpensive and practical routine, gravity sedimentation coupled with two-stage composite material filtration, for oil removal is proposed for SMPFPW on the basis of lab experiments.