Note: Descriptions are shown in the official language in which they were submitted.
K 8980 CAN
WATERFLOOD OIJ~ RECOVERY PROCESS
USING INTERNAL OLEFIN SULFON~TE SURFACTANT
Background of the Invention
rhis inventioll relates to a surfactant-aided waterflood or
chem1c.l1 Çlood process ln whlcll oil is displaced toward a production
location by in~ecting a surfactant-containlng aqueous fluid into a
subterranean reservoir. More particularly, the invention relates to
improving such a process by in;ecting a relatively large and relatively
dilute slug of aqueous fluid and using a surfactant which is predominantly
an internal olefin sulfonate surfactant.
~ Internal olefin sulfonates (IOS's) are sulfonates derived
from linear, branched chain, or alicyclic olefins in which there is a
double bond between a pair of carbon atoms not inclusive of a terminal
carbon atom. U. S. Patent No. 4,393,937 by R. C. Dilgren and K. B.
Owens indicate that IOS's can be used in steam-foam-forming mixtures
which contain olefin sulfonate surfactants, although such surfactants are
preferably at least in maJor part alpha-olefin sulfonate surfactants.
In general, previously propose~ chemical flooding procedures
have utilized inJections of relatively complex and costly surfactant-
containing aqueous liquids in the form of small but highly concentrated
slugs of surfactant systems which commonly contain substantial quantities
of cosurfactants~ alcohols and sometimes oil. Some of the systems were
oil-based surfactant-containing fluids. In most instances~ the processes
required aqueous prefloods. Not only were such systems of questionable
economics but in view of the multiplicity of their ingredients there was
an uncertainty as to whether such 81ugs could be propagated intact through
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the reservoir. ~owever, such prior processes did achieve a virtually
total displacement of oil from cores in laboratory tests.
A particularly distinguishing feature of the present process is
its simplicity. In a preferred embodiment the invention entails only an
injection of a relatively large and relatively dilute slug of a single
surfactant. No other ingredient need be included, with the exception of
a mobility control agent, where such a control is desired. In addition,
the present process tends to require less chemicals in the surEactant-
containing fluid than was employed in most but not all of the earlier
processes.
Summary of the Invention
The present invention relates to a fluid drive oil process in
which oil is displaced within a subterranean reservoir by injecting a
surfactant~containing aqueous fluid into the reservoir. The surfactant-
containing fluid is in~ected in the form of a relatively dilute and rela-
tively large volume solution. The solution preferably contains about 0.5
to 2 percent surfactant and equals about 0.25 to 0.5 pore volume of the
reservolr within the fluid drive pattern. The surfactant contained in the
solution consists essen~ially of one or a mixture of surfactants that are
~0 predominantly internal olefin sulfonate surfactants, preferably those con-
taining about 15-30 carbon atoms and having molecular structures causing
them to concentrate at oil/water :Lnterfaces and reduce the interfacial
tension between the solution and the oil.
_rief Description of the Drawings
Figure 1 shows a graph of comparative oil recoveries versus
salinities of aqueous liquids containing, respectively, an internal olefin
sulfonate surfactant and a petroleum sulfonate surfactant.
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Figure 2 shows a graph of, respectively, oil saturation and oiL
cut with amount of produced liquid in a core Elood using an internal ole-
fin sulfonate surfactant.
Figure 3 shows a graph of oil recovery with amount of fluid in-
jected using internal olefin sulfonate surfactants in cores oriented,respectively, vertically and horizontally.
Descrlption of the InventLon
The present invention is, at least in part~ premised on a dis-
covery that when surfactants are contained in aqueous liquids which are
relatively dilute and used in relatively large volume, internal olefin
sulfonate surfactants of the specified molecular structures are capable
of displacing significantly greater amounts of oil within permeable earth
formations than can be displaced by other types of sulfonate surfactants.
Figure 1 shows the results of comparative tests of injecting,
15- respectlvely, an internal olefin sulfonate surfactant, C20 24 IOS, and a
petroleum sulfonate "Witco TRS-10" as surfactants in aqueous liquid solu-
tions of surfactants ~Jhich were injected in~o Berea sandstone cores which
had been previously saturated with Whitecastle crude oil and then water-
flooded to a residual oil saturation with Sl)SW (Synthetic D Sand Water
contalning 10.~ percent NaCl, 1.()8~ MgCl2~6 1120, 0.59% CaCl2~2 ~l2)
Tlle preparatioll of the C20 24 IOS sulfonate surfactant was
conducted as folk~ws: ~ sulfonation of ~ C20 24 predominantlY linear
- internal olefin was carried out in a three-stage falling film reactor at
sulfur trioxide to olefin molaL- ratios between 1.05 and 1.15. Each of
the reactor stages was heated to 50C. The gaseous S03 was delivered
to the reactor as a 1.3% by weight concentation in nitrogen. The acid
reaction mixture (ARM) was collected over one-an-hour time period. The
~R~I was aged for 3 hours at 35C, then the ~RM was neutralized with NaO~I
at a 1:1 ratio of NaOII to S03 consumed. Each of the mixtures was diluted
* Trade Mark
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with water to give about ~ 25% by weight concentration of IOS. Finally,
hyclrolysis was completed in a one-gallon autoclave at 140nC for 3 ilours
Witil 100~ rpm stirr-ing.
1`he oil recovery experiments were conductecl in 10-inch long,
2-inch diameter Berea cores at a temperature oE 159F. In each test the
floocling sequence (following establishment of residual oil saturation)
was 0.5 pore volume of a solution containing 1% of the inclicated surfac-
tanc, the inclicatecl amount or so~lium chlori(le and enough P-lsher-700
water-thickellillg polyacrylamide polymer ava:ilable from Dow Chemlcal Com-
pany) to provide a viscosity of about 8 cp. Each solution was followedhy 1.0 pore volume of drive water containing 1.6% sodium chloride and the
same type of polymer in an amount providing a viscosity of about 12 cps.
As indicatecl in Figure 1, the oil recovery peaked at sodium
chloride concentrations of respectively, 0.5 and 0.8 in the chemical
slugs and drive waters. The internal olefin sulfonate was significantly
more effective than the petroleum sulfonate. It not only recovered more
oil but operated over a broader concentration range of sodium chloride.
~ lthougll the optimum NaCl concentration for displacing oil with
a solution containing 1% oE the above internal olefin sulfonate
surfactant is about 2.6%, in the experiments performed to evaluate the
e~fect of the presence of multivalent lons in cores which had heen
flooded to residual oil saturation with SDS water prior to the injection
of the surfactallt, it became apparent that the ~ixing of the SDS water
with an IOS surfactant slug whicil containecl 2.6% NaCl pushed the system
into an over optimum region. When successive experiments were performed
with decreasing amounts of salt in the surEactant slugs, it became
apparent that, with respect to earth formations containing a relativel~
saline l)rine and a significant proportion of multivalent ions, such as
tlle SDS water, the extent of oil clisplacement by C20_24 IOS surfactant
contai~ lg chemical slug peaks at a salt concentration oE about 0.8%.
* Trade Mark
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Figure 2 shows a typical oil desaturation curve and oil
cut curve for a core flood using a 0.5 pore volume aqueous sur-
factant system containing 1~ IOS surfactant and 0.8% sodium
chloride in a core containing SDS water and residual oil. The
liquids recovered in the steep linear portion of the oil satura-
tion curv~ (between 0.3 to 0.9 pore volume) were produced in the
form of clean oil and water. At about 0.9 pore volume produced
liquid, the first trace of surfactant appeared in the effluent.
That was marked by flattening meniscus and the first appearance
of turbidity in the aqueous phase. Thereafter, a mixture of oil
and finely dispersed oil-in-water emulsion was producecl and
after about 1.`2 pore volume, most of the production occurred as
an emulsion requiring an emulsion breaking treatment. The arrows
and labels on the oil saturation curve mark the end of the chemi-
cal slug, the duration of the production of clean oil and water,
and the region of increasing emulsification.
Figure 3 shows the results of oil recovery experiments
with Berea cores containing White Castle S* sand oil preflooded
to a residual saturation with 2.6~ aqueous NaCl. The surfactant
slugs used contained a C20 24 IOS surfactant with mobility con-
trol and were conducted at a temperature of 159F with the cores
mounted, respectively, in vertical and horizontal positions. The
viscosit~ of the reservoir oil was 4.2 cp. The composition of
the chemical slugs were 1% surfactant, 2.60~ NaCl, 2100 ppm
Pusher-700 and 500 ppm foramldehyde. The viscosities were 8.7
centipoise for the vertically displaced flood and 9.9 centipose
for its horizontally displaced flood.
The vertical drive recovered 84~ of residual oil at 1
Vp and 95~ at 1.5 VpO Most of the oil was recovered at a 50%
3~ oil cut. Results of the horizontal experiment were less striking
but still quite favorable, producing 80% of the residual oil at
1 pore volume and 87~ at 1.5 pore volume.
* Trademark
Internal olefin sulfonates often contain about 30% active matter
and an excess of sodium hydroxide. For example, a 1% solution by weight
(based on active material) of the C20 24 IOS surfactant exhibits a p~l of
10.5. Many crude oils have appreciable acid numbers. In order to deter-
mine the primary surfactant characteristics of such an IOS surfactant inthe absence of any cosurfnctants comprising alkali metal soaps o the
petrole~m acLds in tlle oll, compar~tive tests were made with IOS samples
as recelved and as nautralt7.e~ with ~ICl. ~omparatlve oil dlsplacement
experiments were conducted ln 10-lnch long, 2-inch diameter ~erea cores
using in one case, a solution of IOS at pH of 10.8 and, in a second case,
a solution of the same surfactant neutralized to a pH of 8.7. The cores
wPre preflooded with 2.9% sodium chloride and the same concentration was
used in the aqueous liquid containing the surfactants. The ~ores were
oriented vertically and the surfactant pumped upward at 1 foot per day
with no mobility control. About 45% waterflood residual oil was recovered
with 1 Vp of each of the surfactant solutions and 93% with 2 Vp~ No
substantial difference in oil recovery between the neutralized and un-
modified surfactants were noted. The oil used has an acid number of
about one.
In general, IOS surfactants suitable for use in this invention
are those having a higll content of :Lnternal olefins in the 12-30 carbon
atom range. Such olefins are commercially manufactured by processes such
as the chlorination dehydrochlorination of paraffins or paraffin dehydro-
genatioll. They can also be prepared by isomerization of alpha-olefins or
by the isomerization~disproportionation as employed in the Shell Higher
Olefin Process. Internal-olefin-rich products'are manufactured and sold,
for example, by Shell Chemical Company and by Chimica Augusta Company.
Preferably, the carbon content of the internal olefin sulfonate surfac-
tants is about 15 to 30 carbon atoms per molecule in a molecular struc-
ture causing the surfactants to concentrate at oil/water interfaces.
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Known types of microscopic tests, emulsification tests, inter-
facial tension measurements, or the like can be utili~ed for determining
interfacial activity of internal olefin surfactants. ~uch microscopic
tests are performed ~y microscopic observations of emulsification and
oil~stringer formation in small droplets of oil which are deposited in
flowing streams of aqueous liquids containing the surfactants being tested.
By conducting core flood tests with different concentrations of sodium
chloride in aqueous liquLds containing a particular surfactant, determl-
nations can be made of the salinity range at which the surfactant is
most active.
The C20 24 internal olefin sulfonate surfactants prepared by
sulfonating isomerizatlon-dlsproportlonatlon streams or -lnternal olefin
sulfonate surfactants of similar compositions available from other so~rces
are particularly suitable. Where desirable, at least a portion of the
surfactant in the surfactant-containing aqueous liquid used in the present
invention can comprise one or more other types of synthetic, olefin or
petroleum sulfonate surfactants, as long as the total concentration of
surfactant in the aqueous liquid is predominantly an internal olefin
sulfonate surfactant containing about 12 to 30 carbon atoms having the
specified tendency to concentrate at oil/water interfaces.
Where mobility control is desired, substantially any of the
conventional water-thickening polymers can be used. Pusher~700, available
from Dow Chemical Company, is particularly suitable, with or without an
aldehyde such as for~aldehyde.
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