Health, safety and environmental factors (HSE), along with strong efficacy, have driven biocide selection
to assure the integrity of more than 2,000 km of pipelines and flowlines shipping treated seawater. The
seawater treatment facility (SWIS) is the world’s largest for oil reservoir injection with a capacity of 14
million BPD. SWIS treats seawater from the Arabian gulf and transports it across the giant Ghawar and
Khurais fields to water injection facilities, consuming over one million gallons of biocides annually to
ensure pipeline integrity and reservoir health. A long term biocide HSE study was launched in 2014.
In 2014, when a facility upgrade opened the previously closed biocide injection system, a transition was
made to formaldehyde-free biocides to protect people. A pair of mostly formaldehyde and quaternary
ammonium (QUAT) was replaced by a pair of predominantly glutaraldehyde and THPS with QUAT in the
blend. The new pair achieved successful microbial control. A subsequent transition used blends that were
compatible with membranes. Laboratory tests screened for compatibility and microbial control on both
planktonic and sessile bacteria.
A field trial was carried out for two sets of biocide pairs, each being tested during a period of six months
with the monitoring of sessile and planktonic bacteria and biocide residuals across the SWIS. Final results
showed strong efficacy for the new pairs without negative effects in the flux membrane recovery.
In addition to protecting the people, the biocide study aims to protect the environment. New downstream
treatment facilities, recently commissioned, will rely on both reverse osmosis (RO) and nanofiltration (NF)
membranes. These facilities will enable the transition from groundwater to seawater by making seawater
compatible with reservoirs. During laboratory and field tests, membranes experienced a varying degree
of irreversible flux loss by chemistries such as QUAT and THPS. This added a new criteria of membrane
compatibility to already formaldehyde-free biocides. Laboratory testing was set to determine fouling of
the membranes when exposed to biocides, the flux recovery by cleaning and the estimated life of
membranes based on exposure, frequency and concentration. The criteria for success was set as a
permanent flux loss <20% for 60,000 ppm hours of exposure. The two best performing pairs progressed
to field testing during 2021 with successful results in the control of planktonic and sessile bacteria across
all the extension of the SWIS.

The challenges and tradeoffs in the study to protect people, environment and pipeline integrity are unique,
but biocide relation to RO and NF membranes might become more widespread in arid regions. Membrane
compatible biocides are typically short-lived, while this pipeline network is lengthy. This is the first attempt
to test novel biocide mixtures that are formaldehyde-free, membrane compatible, and protective of
extensive pipeline networks.
Having transitioned from highly flammable biocides, the renewed study banned carcinogen chemistries
and explored less-toxic biocides and bioderived biocide enhancers. Biocide active reagents and
surfactant blends were mandated to be compatible with membranes, whether for RO or NF, to enable
the transition away from groundwater withdrawals at certain downstream facilities.