Waterflooding of carbonate reservoirs : EOR by wettability alteration
Doctoral thesis
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http://hdl.handle.net/11250/183693Utgivelsesdato
2008-05-30Metadata
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- PhD theses (TN-IPT) [21]
Originalversjon
Waterflooding of carbonate reservoirs : EOR by wettability alteration by Tina Puntervold, Stavanger : University of Stavanger, 2008 (PhD thesis UiS, no. 50)Sammendrag
Oil production is generally divided into three stages, primary recovery,
secondary recovery and tertiary recovery. In primary recovery, which is
usually (but not necessarily) the first production stage, the natural energy of
the reservoir is used to displace the oil from the reservoir. The drive
mechanisms are pressure depletion of the reservoir pressure, in the form of
solution-gas drive, gas cap drive, natural water drive, or fluid and rock
expansion, or gravity drainage. In this stage, only 10-30 % of the OOIP (oil
originally in place) is produced (Castor et al., 1981).
Secondary recovery is usually initiated when primary production is
declining, adding additional energy to the reservoir in order to maintain
pressure or provide a more efficient oil displacement. Gas injection and
waterflooding are two secondary methods, the latter being the most common.
The recovery factor after the secondary stage is usually 30-50 % of OOIP
(Castor et al., 1981).
The tertiary recovery stage, comprising miscible gas injection, chemical
injection and thermal energy methods, typically takes over when secondary
recovery becomes uneconomical. However, oil production does not always
follow this chronological order. Therefore, the term ‘Enhanced Oil Recovery’
(EOR) is nowadays more widely used than ‘tertiary recovery’. Another term,
IOR (Improved oil recovery) is also often seen, and in addition to EOR this
term includes reservoir characterization, reservoir management and infill
drilling (Green and Willhite, 1998). The EOR methods most commonly target
the oil left in the waterflooded reservoir, which especially in carbonate
reservoirs can be a substantial amount. There are five categories of EOR
processes (Green and Willhite, 1998): mobility-control (polymers, foams),
chemical (surfactants, alkaline agents), miscible (hydrocarbon solvents, CO2),
thermal (steam, in-situ combustion) and other processes, such as microbial
EOR, immiscible CO2 etc. Seawater injection should perhaps be categorized
under other processes, as it is a superb EOR fluid to chalk. This will be
discussed later in chapter 3...