Summary
We present a systematic study of laboratory tests of alternative chemical
formulations for a chemical flood design and application. Aqueous and
microemulsion phase behavior tests have previously been shown to be a rapid,
inexpensive, and highly effective means to select the best chemicals and
minimize the need for relatively expensive coreflood tests. Microemulsion phase
behavior testing was therefore conducted using various combinations of
surfactants, cosolvents, and alkalis with a particular crude oil and in
reservoir conditions of interest. Branched alcohol propoxy sulfates and
internal olefin sulfonates showed high performance in these tests, even when
mixed with both conventional and novel alkali agents. Systematic screening
methods helped tailor and fine tune chemical mixtures to perform well under the
given design constraints. The best chemical formulations were validated in
coreflood experiments, and compared in terms of both oil recovery and
surfactant retention in cores. Each of the four best formulations tested in
corefloods gave nearly 100% oil recovery and very low surfactant adsorption.
The two formulations with conventional and novel alkali agents gave almost zero
surfactant retention. In standard practice, soft water must be used with
alkali, but we show how alkali-surfactant-polymer (ASP) flooding can be used in
this case even with very hard saline brine.
Introduction
Many mature reservoirs under waterflood have low economic production rates
despite having as much as 50 to 75% of the original oil still in place. These
reservoirs are viable candidates for chemical enhanced oil recovery (EOR) that
uses both surfactant to reduce oil/water interfacial tension (IFT) and polymer
to improve sweep efficiency. However, designing these aqueous chemical mixtures
is complex and must be tailored to the reservoir rock and fluid (i.e., crude
oil and formation brine) properties of the application. The early success of a
systematic laboratory approach to low-cost, high performance chemical flooding
depends on the efficiency of designing a formula for coreflood injection in
accordance with sound evaluation criteria. A general, a three-stage procedure
has been developed previously to screen hundreds of potential chemicals (i.e.,
surfactant, cosurfactant, cosolvent, alkali, polymer, and electrolytes), and
arrive at a mixture having good recovery of residual oil in cores (Jackson
2006; Levitt 2006; Levitt et al. 2006). Additionally, furthering laboratory and
field-testing in this area contributes to an expanding research database to
help broaden reservoir types that can become candidates for routine chemical
EOR application.
This paper describes a systematic laboratory approach to low cost, high
performance chemical flooding, and explores novel approaches to ASP flooding in
reservoirs containing very hard saline brines. The design strategy first uses
microemulsion phase behavior experiments to quickly select and optimize
concentrations of injected chemicals. Assessment of formula optimization
strategies are carried out through varying surfactant-to-cosurfactant ratio,
reducing cosolvent concentration, reducing total surfactant concentration,
selecting a suitable alkali, and using formation brine in the injection
mixture. Formulations performing well in phase behavior are validated in
coreflood experiments that adhere to necessary design criteria such as pressure
and salinity gradients, surfactant adsorption, and capillary effects.
We illustrate the application of our design approach in prepared Berea
sandstone cores previously waterflooded with very hard saline brine, and show
how ASP flooding can use some of the same brine in the chemical formulation.
Conventional ASP flooding requires soft water that may not always be available,
and softening hard brines can be very costly or infeasible in many cases
depending on the location and other factors. These new results demonstrate high
tolerance to both salinity and hardness of the high performance surfactants,
and how novel alkalis--in particular sodium metaborate--can provide similar
benefits in such harsh environments as sodium carbonate has shown in
environments without divalent cations. This experimental success begins to
vastly increase the range of conditions for economical EOR using chemicals.
© 2009. Society of Petroleum Engineers
View full textPDF
(
798 KB
)
History
- Original manuscript received:
19 February 2008
- Meeting paper published:
20 April 2008
- Revised manuscript received:
22 January 2009
- Manuscript approved:
25 January 2009
- Published online:
28 October 2009
- Version of record:
28 October 2009
View Cart
