Summary
In offshore operations, seawater is often injected to maintain reservoir
pressure for enhanced oil recovery. A sulfate-reducing membrane (SRM) is
typically used to reduce the sulfate content in the seawater from 2900 mg/L to
less than 50 mg/L to prevent souring of the reservoir by sulfate reducing
bacteria and formation of barium and strontium sulfate scale when seawater is
mixed with formation water. A two-cartridge in-series filtration pilot unit
installed on a deepwater platform in the Gulf of Mexico (GOM) has demonstrated
that cartridge filtration can be used upstream of the SRM to pretreat seawater
to meet the SRM feed seawater specification of a silt density index (SDI)
<5 and a nephelometric turbility unit (NTU) <1. Scanning electron
microscopy/energy dispersive spectroscopy (SEM/EDS) was used to determine the
composition of the material deposited on the surface of a used cartridge
filter. From the SEM/EDS results, it was concluded that the filters were
blocked predominantly by coccoliths (calcium compounds), diatoms (silicon
compounds), iron oxide corrosion products, and broken, crushed marine debris,
that formed a fine-grained membrane cake on the filters. It was found that a
two-filter in-series configuration is a better seawater filtration system than
using a single filter if seawater with an SDI <3.5 is required. With the
installation of a 50-micron nominal filter upstream of a 10-micron absolute
filter, the service life of a 10-micron filter was increased by 20 times.
Introduction and Background
Selecting a filtration system for a GOM deepwater waterflood system is a
significant challenge (Walsh et al. 2006). While deepbed multimedia filtration
likely delivers acceptable water quality to maintain injectivity, such
filtration is heavy, particularly when liquid full, and occupies a great deal
of space compared to alternatives such as cartridge filtration. If deep-bed
filtration is installed and not needed, it is a waste of space and weight. If
it is not installed, and it turns out to be needed, then retrofitting a system
is almost impossible, and the success of the waterflood can be seriously
jeopardized. Therefore, the system selection regarding waterflood filtration
must be made with great care. In this paper, we describe a pilot study done on
site at a deepwater GOM tension-leg platform (TLP) to assess the suitability of
alternative systems to multimedia filtration.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
19 June 2006
- Manuscript approved:
18 July 2006
- Version of record:
20 December 2006
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