NAMS 2002 Workshop - ICOM 2008

Desalination I – 2
Monday July 14, 3:00 PM-3:30 PM, O’ahu
Characterizing RO Membrane Performance when Desalinating High pH
Produced Water from the Oil Extraction Process
R. Franks (Speaker), Hydranautics, Oceanside, CA, USA, rfranks@hydranautics.com
C. Bartels, Hydranautics, Oceanside, CA, USA
Produced water is water brought to the surface as part of a high temperature oil
and gas extraction process. Produced water can range in salinity and
composition depending on its original source, but due to the nature of the
produced water, the subsequent treatment steps, particularly the desalination of
the produced water by reverse osmosis, faces unique challenges not
encountered in the treatment of typical surface or well waters. For this reason, an
improved understanding of the effect produced water has on RO membrane
performance is required. The purpose of this study is to characterize the water
transport, salt transport, and longevity of an RO membrane for the treatment of
produced water.
The typical method for dealing with produced water is deep well injection. But oil
production is limited by the well’s capacity to receive the produced water. For this
reason, a combination of technologies is used to treat produced water for
environmental, industrial, and agricultural reuse. Among these technologies is
desalination by reverse osmosis. Specifically, reverse osmosis membranes are
used in the final treatment step after oil, grease, solids and hardness removal
and pH elevation. The RO step is designed to remove the remaining dissolved
salts and organics, including sodium, silica and boron.
Due to the nature of the oil extraction process, produced water contains a unique
mixture of dissolved salts and organics. The passage of salt through the RO
membrane treating produced water at an elevated pH is distinctive from the
common RO performance of many municipal and industrial applications
operating at a neutral pH. A better understanding of salt passage is achieved by
comparing the performance of membranes treating produced water with their
performance on more typical feed waters and synthetic waters.
To do this, a review of the theories governing salt passage is first considered,
including the variation in salt passage with increasing pH. The salt transport
theories, along with years of accumulated data from RO systems treating more
common feeds, are used to predict ion passage in a produced water system.
To compare theoretical and actual performance, samples from an RO membrane
treating produced water in the field were analyzed. The analysis considered