CA1180266A - Foam and particulate material with steam for permeability alteration in subsurface formations - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

FOAM AND PARTICULATE MATERIAL WITH STEAM FOR
PERMEABILITY ALTERATION IN SUBSURFACE FORMATIONS

A method is disclosed for altering the permeability of a gravity override path through a subsurface earth formation resulting from hot fluid (steam) injection into the subsurface formation. The method includes adding selected sized particulate material to a foam and injecting the foam into the gravity override path to deposit the particulate material thus altering the permeability in the path. The method may including the use of a noncondensible gas in the foam as well as a variety of combinations of the hot fluid injection and foam plus particulate material injection to maximize the sweep efficiency of the hot fluid injection into the subsurface formation.

Description

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FOAM AND PARTICULATE MATERIAL WITH STEAM ~OR
PERMEAE~ILITY ALTERATïON IN SUBSURFACE FORMATIONS
~5 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 ~ ~0~66 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 2~

~1 --3--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 ~ .
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 -~. ~g~2B~

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 - 4a -1 1~02B6 01 _5_ 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 , . ~

~ 18~2~6 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 - 6a -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 01 ~-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 possible interpretation than the terms of the following claims .

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Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of treating a permeable earth formation containing a viscous petroleum crude from within a well-bore 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 wellbore to prevent gravity override of said steam into said formation;
(c) and mixing particulate material with said foam and positioning said particulate material in said perme-able formation as said mobilized viscous crude moves in response to said injected steam.

2. The method of Claim 1 wherein said steam injected down said wellbore is injected until a steam gravity over-ride occurs around said wellbore within said formation and then said foam and particulate material are injected into said steam gravity override zone as a permeability adjuster for said formation.

3. The method of Claim 1 wherein said foam is pre-pared using a foaming agent and an inert gas.

4. The method of Claim 3 wherein said inert gas is exhaust gas from a surface steam generator.

5. The method of Claim 3 wherein said inert gas is noncondensible at subsurface temperatures and pressures during the said steam injection process.

6. The method of Claim 1 wherein said stable foam has a gas-to-liquid volume ratio of between 3 and 50 to 1 standard cubic feet per gallon and is formed from a foamable solution containing between 0.5 and 1.0 parts per weight surfactant per 100 parts liquid.

7. The method of Claim 1 wherein said particulate material is a graded mixture with size distribution deter-mined from analysis of the subsurface formation being treated.

8. The method of Claim 7 wherein the 10% size for the particulate material ranges from between 6 times smaller and 100 times smaller than the 90% size of the subsurface formation grain sizes.

9. The method of Claim 8 wherein said particulate material is sand.

10. The method of Claim 8 wherein said particulate material is silica flour.

11. The method of Claim 2 wherein said steps of injecting steam until a gravity override occurs and said injection of said foam and particulate material are alter-nated to provide for a continuing permeability adjustment of said formation as said mobilized viscous crude moves in response to said injected steam.