Note: Descriptions are shown in the official language in which they were submitted.
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FOAM AND PARTICULATE MATERIAL WITH STEAM ~OR
PERMEAE~ILITY ALTERATïON IN SUBSURFACE FORMATIONS
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BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a steam-drive process
for producing viscous petroleum crude from a permeable
earth formation and more particularly to a method for
treating a subsurface permeable formation containing vis-
cous petroleum crude during a steam-drive process to
improve the sweep efficiency of the steam-drive process.
~rior Art
It has been known to steam-flood an earth for-
mation containing viscous petroleum crude to increase the
mobility of the crude and cause it to move to a producing
location. In some steam-flood field procedures the same
well is used for both steam injection and for crude pro-
duction and other field proce~ures use separate injection
and production wells spaced from each other ~hrough the
petroleum containing formation. A variety of injection
procedures using a variety of injection materials have
been proposed most of which have the objective o~ increas-
ing the efficiency of production of the petroleum crude atthe producing well.
In the particular case of steam injection in~o
an injection well with the objective of moving crude to a
producing well, it has been observed that the efficiency
3~ of the sweep of crude from the formation i5 diminished,
sometimes to zero, when injection steam breaks through
into the producing well. This condition is known as grav-
ity override. ~ot water which separates from the injected
steam tends to sweep through the bottom portions of the
heated interval while the steam vapor tends to override
the hot water, because of differences in densities o the
two fluids. As the hot water flows through the reservoir,
heat is transferred to the rock and reservoir fluids.
This results in a temperture transition from the hot water
ban~ to cooler water ahead of the bank. In practice, this
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means an ordinary waterflood precedes the warm and hot
water banks which causes a gradual reduc~ion in residual
OS oil saturation with distance from the injectorO ~ecause
of ~he unfavorable viscosity ratic the efficiency of this
waterflood will be poor~ However, good recovery efficien-
cy with steam in the upper portion of the heated interval
will result in signif icant reductions in residual oil
saturations. These differences in oil saturations will
adversely affect the naturally~poor relative permeability
ratio of steam and water. As a result, injected steam
will tend to prematurely breakthrough into the offset
producing wells wi~hout sweeping the entire heated inter-
val. If this condition is permitted to continue, the
produc~ion of reservoir fluids can drop to zero and only
steam and water will be produced at the producing wells.
In steam 100ding, the rate of steam injection
is initially high so as to minimize heat losses to the cap
and base rock with time. Frequently~ this procedure
results in the development of a highly permeable and
relatively oil-free channel between injector and producer
Many times this channel develops near the top of the oil
bearing rock. In this case, much of khe injected heat is
conducted to the cap rock as a heat loss, rather than
being condllcted to oil bearing sand where the heat is
needed. In addition, the ~team cannot displace oil effi-
ciency since lit~le oil is left in the channel. Conse-
quently, nei~her the gas drive from the steam vapor nor
the convective heat trans~er mechanisms wor~ efficiently.
This is why as a steam flood breaks through into the
producing well it results in much lower oil recovery.
Further~ while some graphic illustrations of
steam profiles between injection wells and producing wells
represent that steam and hot fluids start all along the
injection well, rise toward the top of the producing
interval in the direction of the producing well and drop
down near the producing well, it is the present inventor's
belief that such a profile is inaccurate. ~ore than
4~ likely, once the steam has risen through ~he producing
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interval it will not drop dowrl in~o the producing well
when steam breakthrough occursO ~his condition has been
~5 shown to exist by temperature profiles along a producing
well. Such a condition further reduces the sweep effi-
ciency of such a steam injection method.
It has been suggested to inject a blocking
barrier into the formation above the steam injection to
reduce the loss of steam through the breakthrough path.
One such barrier is a foam as suggested in V. S O Patent
3,412,793 issued to R. B. Needham on November 26, 1968 for
Plugging ~ligh Permeability Earth Strata. ~he higly per-
meable formation is temporarily plugged with a foam by
introduction of steam and a foaming agent into the forma-
tion wher~by a foam having steam as its gaseous phase is
formed and, upon condensation of the steam due ~o 105s of
heat, the foam collapses. A similar procedure is shown in
UOS. Pa~ent 4,0~6,964 issued to R. E. Dilgren et al on
~ May 2, 1979 for Steam-Channel-Expanding Steam Foam Drive.
~hat patent suggests the addition of a noncondensible gas
to the foam and injection into the steam channel to pro-
vide foam and a relatively high pressure gradient within
the channel. Neither of th~se patents are believed to
provide the relatively permanent solution to the gravity
override breakthrough problems as is disclosed in the
presen~ applica~ion.
Summar~ of ~he Invention
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It is herein proposed to alter the gravity over-
3~ ride path within the formation by carrying int~ the orma-
tion particulate materials which will alter the permeabil
ity of the override path and thus encourage the flow of
injection steam or hot fluids into the ~or~ations where
reservoir fluids remain. The intention of the injection
procedures is to recognize gravity override breakthrough
and to then inject materials in~o that break~hrough path
which will alter the permeability therein and then return
to the injection procedure to reestablish communication
between the injection fluids and the reservoir where the
~ ~esired reservoir 1uids remain. The particulate material
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is carried into the permeability override path with a low velocity fluid thus
accomplishing the desired permeability alteration without damage to the well
bore liner and without "bridging" in the formation.
Accordingly, this invention seeks to provide a novel and improved
process Eor producing petroleum crude from a subsurface earth formation using
a combined series of steps of injecting steam or other hot fluids, injecting
a stable foam material, and mixing particulate material ~ith said foam and
pumping said foam and particulate material into the subsurface formation to
control the permeability of the formation into which said foam have been injected.
Further features of this invention will be readily apparent to those
skilled in the art from the following specifications describing a preferred
embodiment of the invention.
Thus in its broadest aspect this invention provides a method of
treating a permeable earth formation containing a viscous petroleum crude from
within a wellbore penetrating said earth formation comprising the steps of:
~ a) injecting steam down said wellbore and into said formation to heat
and mobilize said viscous petroleum crude;
~ b) preparing a stable foam at the earth surface and pumping said stable
foam down said wellbore and into said formation in a position along said well-
bore to prevent gravity override oE said steam into said formatlon;
(c) and mi~ing particulate material with said foam and positioning saiclparticulate material in said permeable formation as said mobilized viscous
crude moves in response to said injected steam.
It has been demonstrated that particulate material can be carried from
the earth's surface to a subsurface location with a vehicle of stable foam
generated at the earth's surface.
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It has also been demonstrated that the foam and the particulate
material may be carried back lnto the formation for the purpose o:E proping
the formation as for instance when foam plus particulate material are used
in a formation fracturing procedure. It has also been demonstrated, as
described in l].S. Patent 4,086,864 and 3,412,793, that foam may be used to
provide a temperature block in the formation to prevent steam from overriding
into more permeable formations and to prevent heat from being lost into the
formation above the zone of interest.
In accordance with one field procedure of the present invention,
a conventional steam flood of a formation is accomplished with a steam injected
into the formation of interest and production accumulated at a producing
well spaced from the injection well. AEter steam has been injected for a
long enough interval to cause the crude to become mobile and to move into the
producing well, it is
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expected that a steam breakthrough will occur into the
producing well and that breakthrough will be evidenced by
a substantial change in the volume of steam vapor produced
in the producing well. When that event has occured, a
foam plus a small particulate material is injected into
the formation through the zone where the crude has been
produ~ed into the producing wel~ and the particulate
material is carried into the permeability paths within the
formation. The foam is then permitted to collapse and the
particulate material is retained in the formation causing
the permeability to be substantially blocked because of
the grain size of the material carried with the foam.
Steaming of the formation is then reinitiated
and continued production is developed into the producing
well. On the event of another steam breakthrough, the
same procedure with particulate material and foam is per-
formed and the permeable path of the producing formation
are again blocked to prevent the steam from flowing
through the formation in paths not in contact or not con-
taining petroleum crude.
The particulate material carried with the foam
is preferably graded from an analysis of the actual forma-
tion involved and the particle sizes of the added materialare speciically designed to a~complish the desired perme-
ability modification in the producing formation. Samples
are taken in conventional sidewall sampling procedures and
analyses are run in conventional techniques to determine
~0 the grain sizes of the formation and the grain si~es of
the particulate material to be added ~o the flood.
Foam quality is important to the invention here
disclosed. ~oam is formed by mixing together a foamable
solution and a gas. The foam must be a relatively stable
foam capable of carrying the material downhole. A suit-
able foam forming appartus is disclosed in U.S~ Patent
3,603,398, Stanley 00 Hutchison and John C. McKinnell,
is~ued September 7, 1971 for Method of Placing Particulat~
Material In ~n Earth Formation With Foam. That paten-t
4~ also disclosed suitable mechanism for combining the
particulate material with the foam solution. The foam is formed
by bringing a foamable solution of a surfactant and a gas
together. The preferred foam is an a~ueous air foam. Water and~
if desired, a suitable stabilizing agent are mixed to produce a
foamable solution. Suitable foam and other specific surfactants
which go into the foamable solutions that make them are described
in detail in United States Patent No. 3,463,231 to S. O.
Hutchison, et al issued August 26, 1969 for Generation And Use
Of Foamed Well Circulation ~luids. A preferred foam for use in
this invention is a Cll to Cl4 alkyl benzene sulfonate (ABS)
preferably the ammonium salt. The ABS should be added to water
to form a foamable solution in an amount of between 0.5 to 1.0
parts per weight per hundred parts water. The foamable
solution is mixed with air in a gas-to~liquid volume ratio of
between 3 to 50 standard cubic feet to one gallon. Superior
results are obtained when the :~oam has a gas-liquid volume
ratio between 10 to 20 standard cubic feet to one gallon.
It is preferably to form the foam with a noncondensable
gas. Nitrogen is such a useful gas. Other useful gases can
be exhaust gases of a steam generator. One such possibility is
the use of a downhole steam generator with the exhaust gases
from that generator being used as the noncondensible gaseous
material for generating the foam. It is important to the
wellbore environment that the gas material used in forming the
foam be noncorrosive and in that respect low in oxygen. If
exhaust gases are used, it is necessary to adjust the pH of
those gases in order to avoid having an acidic pH in the
injection materials. It has been discovered that the injection
of high pH solutions with steam can cause severe damages to the
sand grains and ~uartz grains in a producing formation and
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in that respect serious damage can be done to the permeability
of the formation.
The grain size of the particulate material added
to the foam should be, as previously described, graded in
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accordance with the analysis of the formation materials.
One such materlal is silica flour which is a ine grain
o5 material having grain sizes in the ran~e of 100 to 600
mesh including clay minerals and clay size materials. The
preferred grading is: the particulate æize range of the
added particulate material should be such that the l0
size oE the particulate ~aterial is between 6 and l00
times smaller than the 9o% ~ize of the formation materi-
als. In that the added particulate materials are intended
to control the permeability of the ~wept portion of the
subsurface reservoir, it is de~irable that the grain sizes
of the particulate material be prefPrably on the small
size so as to insure a proper distribution into the perme-
able formation~ The foam will carry ~he particulate
material into the permeable paths within the formation
and, with control of the injection pre~sure on the oam
the particulate material will be deposited as the foam
collapses with the ormation.
It is further important that the pressure used
in injecting the foam plus particulate material is main-
tained below the pressure that would be expected to
fracture the subsurface formation~ Fracturing of the
formation is not intended with the present invention, it
is the control of the permeability of the formation rather
than the opening of permeable pa~hs that is desired.
During the time that the par~iculate material is
being added in~o the formation, ~he steam injection pro-
cess may continue~ For that reason the foam that i~formed must be able to withstand the temperature of the
steam that is used in heating the subsurface formation.
In accordance with the present invention, a
steam override zone in the subsurface which i~ caused by
the opening of highly permeable paths as the hea~ed and
mobile crude is moved out of the formation can be cvn-
trolled by the injection of foam-containing sand and/or
particulate material~ graded to the size of the permeabil-
ity paths within the formation to control and alter the
~0 permeability paths. An alteration in a steam override
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permeability path can be identified in the fluids produced
at a producing well as the ratio of oil and water changes
05 from that which was observed which indicated the steam
override~ In that respect, a steam breakthrough is evi-
denced by an increase in the volume o steam vapor
produced. An alteration of the permeability path accom-
plished in accordance with the present invention is evi-
denced by a decrease in the volume of steam vaporproduced. Once the permeability has been altered, the
injection well may be returned to a steam injection
condition and the cr~des within the subsurface formation
can again be heated as the steam heating 1uid is injected
~5 into the formation. If and when another steam override
occurs, the formation may then again be treated with the
foam plus particulate materials to accomplish another
alteration of a newly developed permeability path.
Continuous monitoring of the produced fluids for oil and
~0 water content and temperature can permit the present
invention to be used to improve the sweep ef~iciency of a
steam 100d operation.
The invention described herein may be equally
applicable ~o a s~eam flood operation using an injection
well and a producing well or a single well used both fvr
injection and or production re~uently re~erred to as
huf-and~puffr Upon ~he occurenGe of a raduction in back
pressure in the subsur~ace ormation~ it can be assumed
that a permeability path has been opened in the subsurface
permitting the steam to be diverted into formations where
the in-place crude has already been moved. When khat is
observed, the formation may be foamed with the foam plus
particulate material to place the particula~e material in
the permeability path and thus reduce thP diversionary
route through the formation.
While certain preferred embodiments of the
invention have been specifically disclosed, it should be
understood that the invention is not limited thereto as
many variation will be readily apparent to those skilled
~ in the art and the invention is to be given its broadest
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possible interpretation than the terms of the following
claims .
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