Abstract

Management of produced water containing back produced polymer (HPAM) is a real challenge since its limited biodegradability and its relatively high concentration in produced water (up to few hundreds of mg/L) make it difficult to discharge into surface water. The preferred option is to conduct Produced Water Re-Injection (PWRI). When PWRI requires stringent water specifications as low as 10 mg/L of dispersed hydrocarbon (HC), 2 mg/L of total suspended solids (TSS) and 5 µm particle cut size (d100), tertiary treatments become mandatory. It is, for example, the case for PWRI in matrix mode for unconsolidated and shallow sand reservoirs. The objective of this study was to better understand the impact of HPAM polymer on tertiary treatment with a focus on ceramic membrane performances in order to optimize the design of produced water treatment facilities.

Maturity assessment of these water treatment technologies highlighted numerous major risks in presence of polymer. A R&D plan was then conducted on labscale prototypes using synthetic Produced Water (PW) containing polymer.

The tests performed with low pore size membrane (< 1 µm) met the specifications but the polymer was retained by the membrane which caused severe fouling and thus low productivity. Inversely, with pore size larger than 1µm, the polymer went through the membrane which strongly enhanced the productivity. However, with such large pores, the specifications are not anymore guaranteed. Two strategies were then identified and tested: (i) combine coagulation and membrane filtration or (ii) combine oxidation and membrane filtration using low pore size membranes. The use of coagulant (FeCl3) was very effective to precipitate the polymer and improve filtration performances but the management of the waste stream containing tons of precipitated polymer turned into a major showstopper. Inversely, the use of oxidation as a pre-treatment breaks polymer chains that become small enough to go through the membranes which (i) strongly improves membrane performances and (ii) enables the polymer re-injection.

This combination was successfully tested in batch but also in continuous mode using commercial membranes. The performances were then compared with other type of tertiary treatment technologies such as media filter (sand and walnut). In the context of PWRI in matrix mode for unconsolidated sand reservoirs (or any case that would require such stringent water specifications), membrane technology combined with oxidation is today a promising option deserving qualification tests at a larger scale.

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