Summary
Alkaline/surfactant/polymer (ASP) flood processes have been applied
increasingly in oil fields because of their contribution to high ultimate oil
recovery. However, a major technical challenge is determining how to
significantly reduce the amount and the cost of chemicals used so that ASP
floods can become cost-effective as well. On the other hand, some field
applications show that alkali, surfactant, and polymer concentrations remain
relatively high in the produced liquids of ASP floods. Thus, successful
detection and reuse of these chemicals can substantially minimize the capital
cost and the environmental impact. In this paper, several methods are applied
to detect each chemical and quantify its concentration in the produced liquids.
In addition, reinjection tests of the produced chemicals are conducted for
further enhancing oil recovery. More specifically, first, the total
interactions of each chemical with the oil/brine/rock system are studied. With
the developed detection methods for each individual chemical used in ASP
floods, the total loss of each chemical is measured. The chemical loss is
caused by its chemical reactions with the crude oil and the reservoir brine, as
well as its adsorption onto the rock surface. Second, coreflood tests are
performed for alkaline floods (AFs), surfactant floods (SFs),
alkaline/surfactant floods (ASFs), and ASP floods (ASPFs) to determine their
respective tertiary oil recoveries. Hence, a better understanding of how each
chemical contributes to enhanced oil recovery (EOR) is achieved. Third, typical
chemical concentrations in the produced liquids are measured and compared with
those in the injected slugs to determine the potential of reusing these
chemicals in practice. Finally, the coreflood tests of reusing these produced
chemicals are carried out by reinjecting the produced liquids into new
sandpacks or Berea-sandstone cores. The reinjection coreflood-test results show
that the produced chemicals can be reused effectively to enhance oil recovery.
It is anticipated that the detection methods and reuse schemes studied in this
experimental work should facilitate the design, optimization, and
implementation of ASP field flood projects.
Introduction
Chemical EOR operations are increasingly applied in oil fields as
tertiary-oil-recovery methods. In the literature, there are excellent
comprehensive studies on chemical flooding. A variety of chemical floods are
conducted, such as AF, SF, polymer flood (PF), ASF, alkaline/polymer flood
(APF), and ASPF. In particular, as one of the most effective EOR techniques,
ASP flooding has been applied to recover the residual oil in sandstone and
carbonate reservoirs since 1980. It has been reported that successful
applications of ASP floods in oil fields can enhance oil recovery up to
20%.
Generally speaking, an ASP flood is a modified waterflood. Field
applications of AFs alone usually result in poor oil recovery because of the
alkaline loss caused by the chemical reactions with the reservoir rocks, the
low acid number of the crude oil, and the adverse mobility ratio. The major EOR
mechanisms of an ASP flood are described briefly as follows. In conjunction
with the added surfactant, the surfactants generated in situ by the chemical
reactions between the injected alkali and the natural organic acids in the
crude oil can result in ultralow interfacial tension (IFT). The ultralow IFT at
the oil/brine interface helps to emulsify and mobilize the residual oil in an
oil reservoir. In addition, the reservoir-rock surface becomes more negatively
charged at higher hydroxyl ion concentrations. These negatively charged ions
not only prevent the adsorption of anionic chemicals, such as anionic
surfactants and polymers, but they also change the wettability of the rock
surface. Also, the added surfactant can increase the salinity tolerance of the
alkali. To achieve the same displacement efficiency as that of a micellar PF,
the surfactant concentration required in the ASP flood can be reduced by one
order of magnitude. On the other hand, the injected polymer can significantly
reduce the mobility ratio. The adsorption of polymer onto the reservoir rock
can reduce the effective water permeability. Hence, polymer flooding improves
both the areal and the vertical sweep efficiencies.
© 2005. Society of Petroleum Engineers
View full textPDF
(
1,614 KB
)
History
- Original manuscript received:
11 February 2004
- Revised manuscript received:
21 December 2004
- Manuscript approved:
25 May 2005
- Version of record:
15 October 2005
View Cart
