Treatment of Produced Water with Back Produced ASP

Abstract

Crude oil production from ageing oil fields is normally sustained by various enhanced oil recovery (EOR) ways such as water injection, polymer injection and alkaline surfactant polymer injection (ASP). One of the main ageing fields (90% water cut) in Oman is considered for this study. This field is being operated with waterflood for more than 15 years. In order to enhance the oil recovery in this field, chemical enhanced oil recovery (cEOR) using polymer flood was implemented in 2010 by Petroleum Development Oman (PDO) Company. ASP is a recovery method planned as a final resort of cEOR to recover more oil from the studied field. ASP breakthrough is expected to impact the performance of deoiling facilities in this field. Results showed that using ceramic membrane (100 nm pore size) managed to remove oil from produced water completely for high and low OiW concentrations, however only 2% recovery factor was achieved. Using aluminum sulfate chemical as a coagulant to treat the oily produced water was only effective at concentration higher 500 mg/L. In comparison, aluminum sulfate was very effective in treating the produced water contaminated by polymer (500 ppm of polymer concentration) and at 150 mg/L of aluminum sulfate, the outlet OiW reached 39 ppm (v). When Aluminum sulfate was used at concentration of 500 mg/l, the OiW concentration reached 2 ppm (v), which is lower than the polishing unit in the water treatment system. When ASP was introduced to the produced water, the oil droplet stability has increased and at 500 mg/L of aluminum sulfate, the outlet OiW in the treated stream was around 65 ppm (v) however at 700 mg/L of aluminum sulfate, zero ppm of OiW was achieved. Introducing gas bubbles (N2) as flotation with the help of the coagulant agent had improved OiW removal efficiency by almost 15% for the PW with ASP.