Advances in Application of Forward Osmosis Technology for Volume Reduction of Produced/Process Water from Gas-Field Operations

Abstract

Abstract Produced and process water (PPW) associated with gas production are often characterized by low total dissolved solids (TDS) and moderate organic content. The oil and gas (O&G) industry in Qatar currently practices disposal of PPW via deep well injection. To ensure long-term sustainability of the reservoir, Qatar operators aim to reduce the PPW disposal quantity by 50%. Recently, Qatargas had initiated a project to recycle process water and thus, reduce disposal volumes, by using commercial advanced water treatment technologies. For future projects/developments, the authors of this paper have proposed and evaluated, through funding by the Qatar National Research Fund (QNRF), an adaptation of forward osmosis (FO) membrane process for PPW concentration, which can be a cost-efficient alternative to achieve 50% volume reduction of PPW. In the first step of conventional FO, a draw solution (DS) of high osmotic pressure is used as driving force to "pull-in" fresh water from the feed through a membrane into the DS. In the second step, and requiring significant energy, water is recovered from the regenerated DS by various methods depending on the DS used. In this project, brine from thermal desalination plant was used as DS and PPW as feed. Due to the salinity difference between the DS and the PPW, natural osmosis resulted in water permeating from the PPW into the DS, reducing the volume of PPW. Instead of recovering permeated water from the DS, the diluted DS can be directly discharged into the Arabian Gulf bringing an additional benefit by discharging lower salinity brine to the aquatic environment. Commercial flat sheet membranes and hollow fiber (HF) membranes provided by Singapore Membrane Technology Centre have been tested through bench-scale experiments and the impact of various operating parameters such as DS concentration and temperature was investigated. Results indicated that FO can successfully treat the PPW to achieve the target volume reduction of 50%. The average flux for the HF membranes with pretreated feed was 17 L/m2-h (LMH) using 1M NaCl as DS. Organics passage from the feed to the DS was below detection limits which mitigates the potential concern of organics leaching into the Arabian Gulf. Appropriate pretreatment of the PPW is required to minimize membrane fouling. Results showed a flux decline of approximately 10% over 5 hours when the PPW was used without pretreatment. The fouling was attributed to the organics present in the PPW. Different pretreatment options were evaluated to reduce membrane fouling including: ceramic membranes, activated carbon; and an organosilica adsorbent. To validate the project concept, long-term experiments were conducted mimicking field conditions. Overall, the results indicated FO is cost-efficient in reducing PPW injection volume and pilot testing is recommended to further demonstrate treatment feasibility of the process.