US 3159215 A
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Description (OCR text may contain errors)
R. F. MELDAU ETAL 3,159,215
MBUsTIoN Dec. 1, 1964 ASSISTED PETROLEUM RECOVERY BY SELECTIVE CO IN MULTI-BEDDED RESERVOIRS 4 Sheets-Sheet l Filed Sept. 25, 1958 .5.. SMM,
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||UUM IBH Q zfwx Dec. 1, 1964 R F MELDAU ETAL 3,159,215
ASSISTED PETROLEM ECOVERY BY SELECTIVE GOMBUSTION IN MULTI-BEDDED RESERVOIRS Filed Sept. 23, 1958 4 SheeCS-Sheel'l 2 INVENTRS ROBERT E MELD/w ./oH/v McK//v/vE/.L
DCC l, 1964 R. F. MELDAU ETAL 3,159,215
ASSISTED PETROLEUM RECOVERY BY SELECTIVE COMBUSTION IN MULTI-BEDDED RESERVOIRS Filed sept. 2s, 1958 4 sheets-sheet s TO SEPARATOR FUEL GAS 4 WATER INVENTORS ROBERT F. MELD/1U JOHN C. McK/NNELL R. F. MELDAU ETAL RECOVER Dec. l, 1964 3,159 TIoN ASSISTED PETROLEUM Y BY SELECTIVE COMBUS IN MULTI-BEDDED RESERVOIRS 4 Sheets-Sheet 4 Filed Sept. 25, 1958 REDUCTION OF OIL/WATER VISCOSITY RATIO WITH TEMPERATURE INCREASE OOO 20o 25o TEMPERATURE- F.
um SMN Ram E mum I N R Erc .m VR NMM M .|00 R J Y B 4 G F United States Patent Office y aisazls Patented Dec. l, 1964 3,159,215 ASSSTED PETRLEUM REQUVERY BY SELEC- 'HVE CQWUS'HON EN MULTl-EEDDED RESER- VHS Robert F. Meldau, Whittier, and .lohn C. McKinneil, Taft, Calif., assignors to California Research Corporation, San Franeisco, Calif., a corporation of Delaware Filed Sept. 23, i953, Ser. No. 762,818 Claims. (Cl. 16o-10) The present invention relates to assisted oil recovery methods. More particularly, it relates to an improved method of assisting recovery of oil from an underground reservoir by consecutively and simultaneously injecting thermal energy to selected portions of the reservoir.
It is `an object of the present invention to increase the recovery of petroleum from an underground reservoir that comprises a series of oil-permeable zones coutaining mobile oil separated by relatively thin, impermeable zones, such as sandstone formations that have shale or other uid barriers between said members. The method of the invention is specifically useful where more than one Huid-impermeable zone separates several oil-bearing zones. However, the method is also useful in any reservoir where the fluid-permeable, e.g., sand, zones are sutliciently isolated from each other to permit wells penetrating them to be sealed or packed-off from each other.
In assisted oil recovery, frequently referred to as secondary recovery of oil from an underground reservoir, it has been proposed to ignite an oil-producing formation and then supply a critical amount of oxygen in the form of compressed air to that formation to form a coinbustion 4front that both heats the oil and generates gas to force oil to flow from the air injection well toward a fluid-producing well. In practice, it has been found that it is diflicult to ignite and `maintain combustion in reservoirs such as those encountered in California and the Gulf Coast area where oil-producing zones frequently comprise a plurality of oil-producing zones that are formed of sand and are interlaminated by shale beds that lie parallel to the sand beds. One of the reasons for this diiiiculty is the differences in fluid permeability of the various oilproducing zones. Where these differences exist, theair and combustion will preferentially occur in the zone of greatest permeability (the path of least resistance to ilow). Additionally, the cost of an assisted oil recovery project using all air as the injection iluid has been found to be more expensive than conventional water flooding operations, since the investment in air compressor horsepower, as compared to equivalent water pump capacity, is relatively great. While this added cost is justified by the greater recovery of oil using a combustion drive, as compared to a water drive, the oil-bearing zone must be thick and relatively uniform in permeability to obtain maximum benefit. However, when the oil zone is relatively thin or non-uniform in permeability, We have found that much of the heat generated by the combustion process is lost to the overlying and underlying shale and sand zones.
In accordance with a preferred method of carrying out the present invention, one of the more permeable, oil-bearing zones in a series of multiple zones is packed off in an injection well so that oxygen, in the form of air, can be pumped into that zone to ignite and continue combustion therein. When the invention is practiced in a pair of permeable oil-bearing zones, it is preferred to initiate combustion in the more iluid permeable zone if one of the zones has a greater permeability to fluid ilow than the other. The fluid-impermeable zones either overlying or underlying this rst oil-bearing zone prevent vertical flow of iluids to adjacent oil zones. Suicient air is then supplied to this middle zone to maintain combustion of a part of the hydrocarbon iluid so that the burning front is progressively advanced away from said injection well an adequate distance through the oilbearing zone tow-ard one or more production wells. In advancing the combustion front, the overlying and underlying shale and sand bodies are progressively heated by conduction losses from the combustion front and form a heat reservoir that extends from near the injection well to the combustion front. After the combustion front has been advanced in this way, a drive liquid, such as water, conveniently supplied at surface temperatures is pumped into the adjacent heated oil-bearing zones. Where oil-producing zones both overlie and underlie the combustion zone, water may be pumped into both the overand underlying beds. The water thus supplied moves into a heated oil bearing strata and both the displacing water and the displaced oil -are progressively heated as they move together from the injection well toward the producing well.
The progressively heated oil in the overlying and underlying beds is displaced by the heated Water in a more efiicient manner than if the oil and water were at normal formation temperature. -When the oil in the overlying and underlying beds is progressively displaced by heated water, the oil is recovered in a more efficient manner than if the oil and water were at normal` formation temperature before contacting the heated zone as in a countercurrent liow of liquid and air in the parallel zones. Additionally, the areal sweep eiliciency of the injected water is improved because of the inproved mobility ratio of the displacing water to the displaced crude oil. This ratio is progressively reduced as both the Water and oil are gradually heated by absorbing heat losses from the middle strata wherein corn.- bustion is occurring, and from the overlying and underlying impermeable strata. Since the flow of both injected air and injected water produce flow in the same direction through all three strata, hydrocarbon fluids can be intermingled as they are produced from all of the oil-bearing zones into the production wells.
Further objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.
In the drawings:
FIG. 1 is a schematic representation in vertical section of a series of oil-bearing zones separated by shale zone fluid barriers through which an injection well and one production well penetrate to illustrate a preferred method of carrying out the invention.
FIG. 2 is a schematic representation of the thermal profiles through a plurality of producing zones such as those shown in the systems of FIGS. 1 and 3.
FIG. 3 is a View similar to FG. 1 illustrating an alternative system for injecting water and air to assist recovery of petroleum in accordance with the invention.
' FIG. 4 is a graph illustrating the reduction of oil/ water viscosity ratio with temperature increase.
As an aid to the understanding of the method of the present invention, reference is now made to the drawings, and in particular to FIG. 1. As there shown, our method is directed to assisting recovery of petroleum from an underground reservoir system comprising a plurality of hydrocarbon containing zones including a rst or middle zone 1t) that has both an overlying oil-bearing zone l2 andan underlying zone 14. Both oil zones 12 and 14 are isolated from middle zone 1@ by shale members 16 and 18 respectively. Further, otherr shale zones, such as 20, overlying upper oil zones 12, and 22 underlying lower zone 14, may separate other hydrocarbon Lproducing zones from those illustrated 'in the present' embodiment. The term earth formation is also used hereinafter to deiine such a Vmulti-bedded series of zones that deiine such a petroleum reservoir.
In the embodiment of the invention of FIG. 1,'all of the cil-bearing zones 10, 12 and 14 are penetrated bysa iirst well 24 indicated as an assisted-recovery injection well, and a second well 2d, operated as a producing well. Since, in accordance with the invention, it is desired to ignite and burn mid-zone to create' an eX- pandingv heat reservoir that vwill drive petroleum toward well 26, a pair of packers 28 and V30are positioned lin injection well 24 respectively to isolate middle zoneV 16 from upper and lower zones 12 and 14. An air injection line V32 that may include a burner 34 is positioned within the nowvisolated zone, indicated as 31, and is connected to'an air compressor 36 at the earths surface. With zone 10 isolated in this manner, ignition and combustion of the -oil zone 1d may be initiated by supplyine fuel gas from line 38 through valve 4i). After ignition of oil- I bearing zone 10, fuel gas may be cutoff by closing valve 4i) and combustion continued merely by supplying air Yunder pressure. The combustion front, indicated generally as 42, is then progressively advanced toward production Well 26 a distance sulicient to establish the proper size heat bank for the particular system being treated. This 4distance will, of course, depend upon the thickness of sand zone 10, shale members 16 and 18, the thermal dilusivity in said sand and shale members and the velocity of the burn front. Then, with the-combustion fron-t 42 mov-ing toward producing well 26, in accord-l ance withthis invention, we inject water into overlying .'As indicatedby dash lines 44 and 46 in the respective zones 12 and 14, progress of water in said zones will be v greater where the-temperature is higher due to the de- As indicated, such creased viscosity of the heated oil. water iioodingrof zones 12 and 14 Vvis accomplished by supplying water through line 48 discharged by water f pump 150. A cross-over pipe. 52 permits water pressure 'to beappli'ed to lower zone 14- through packers 28 and 30 that isolate zone 10 from the remainder of the Well v bore.
v Oil produced fromall of the three zones, 10, 12 and 14 is permitted to intermingle iin producing'well 26. As indicated, the outflow from that well is transmitted to a separator (not shown), wherein thesecondary drive fluid may be separated 'from V'the produced oil.V
FIG. 2 in general illustrated the thermal fronts in the three adjacent zones when the .different drive fluids are flowing, as in the arrangement of FIG. 1. As indicated, the combustion front such as thatfin, middle zone 10- of FIGS. 1 and 3 will'be relatively uniform in area and substantially vertical to the overlying and underlying uid impermeable beds. The temperature of this Zone indicated as 1000 F., will be in the range of from 750-1500" 'temperature suiciently great to cause heating in the area directly above and below the combustion sand.
In the art of water o'oding, the displacement eiciency of crude oil is improved if the mobility ratio of the `dis- Vand lunderlying sand beds 14 and 12. In the schematic placing water to the displaced oilris reduced. The mobility ratio is defined as the ratio:
Relative oil permeability Y is a function of the oil and water saturations and `the characteristicsnof the producing sand. Y The oil/water viscosity ratio depends markedly upon temperature.
The object of the present invention is to reduce thisy mobility ratio of the displacing water to the displaced oil and consequently impr-ove the recovery of oil by malring use of heat normally lostin. an underground combus-` tion process. FIG. 4 shows the reduction in oil/water viscosity ratio as the temperature is increased from F. to y300" F. for representative crude. oils. As ,an example, an increase in temperature from 100 F. to 3009 F. in a system containing 15 yAPI oil will result in a thirty-fold reduction of oil/water viscosity ratio.
It is preferred to progressively advancethe burning front from the injection well toward the production weil for a time suiiicient to heat the adjacent upper and lower oil-impermeable zones by conduction of heat from said burning front and reduce the oil/water viscosity ratio 1n Vboth the upper and lower oil-permeable zones, to a value less than about 200. Flood water is then injected through the injection well into the upper and lower producing zones to successively absorbheat romsaid oil impermeable zones. Air 4and flood water are simultaneously pumped into the respective zones to advance both the water and oilV in said zones toward said production well while maintaining said oil/water viscosity ratio in Vsaid upper and lower oil-permeable zones at said value. Qll is produced at theV production well fromV all producmg zones. Y Y
The mechanism for improved oil recovery in the adjacent water ooded sands is as follows:
First: The injected Water is heated by contact with progressively warmer environment as it moves toward the .position of the combustion front in the combustion sand. Y v
Second: Oil displacement by the injection water is irnproved as the injection water approaches progressively warmer oil in theoil-bearing sands in which wateris injected. The displacement of oil by water 1s a maximum where theo'il reaches a'maximum temperature and mlmmum viscosity. This point will always be behind the position of thercombustion front but will vary, depending upon .the system in which the process is applied.
It is, of course, understood that displacement of. oil by water in a water-ooding operation is not strictly a piston-like displacement wherein equal amounts of formation oil are displaced by a corresponding volume of the driving Water. Rather, the displacement is effected by ein.` trainrnent of oilparticles released from the-interstitial spaces in the oil reservoir by water flowing pasty these spaces. Hence, reduced viscosity of reservoir oil as compared to the entraining water greatly Vincreases the eiciency'of oilY displacement by the injection of water.
However, the freedom of the oil particles to enter the -llood Water is also dependent upon the relative sizes andV .9 from the injection wells to the production wells to reduce the possibility of such channeling.
In FIG. 2, the general temperature profiles of a progressing multi-bedded fire and water flood in a system such as that shown in FIG. l are illustrated by the isotherm lines, designated as 100 F., 200 F., etc. In the example illustrated by FIG. 2, the thickness of the burned middle sand is about 10 feet, the thermal diffusivity is about 0.05 square feet per hour, the burn front velocity is about 0.5 feet per day, and the maximum burn front temperature is 1000 F. The temperatures indicated represent increases over original reservoir temperatures. It will be noted that the maximum temperature extends over quite a limited area, but an increase in temperature of from 100 F. to 300 F. is quite broad through both of the adjacent sands.
FIG. 3 illustrates an alternative arrangement for carrying out the method of the present invention, wherein separate wells are used for the injection of air and Water into the selected oil-bearing sands. As indicated, well 64 is drilled into middle sand It) and has an air supply line 32 that supports a burner 34 opposite that zone to start combustion of the residual petroleum therein. As shown, well 6d may be cemented oi at bottom 66 above lower producing zone 14. Zone 10 and well 64 are also isolated from upper zone l2 by cement 72 located adjacent upper shale section 16. Perforations 68 through casing 65 and cement 72 permit communication between zone 10 and well 64. It will be noted that air injection well 64 is positioned ahead of water injection well 70 so that combustion may be started and extended both vertically and horizontally in middle zone l prior to the time the combustion front passes through well 70. Communication between well 70 and middle zone l0 is prevented by cement 72 that bridges between casing 7l and upper and lower shale members 16 and 18. Perforations 74 opposite both zones 12 and 14 permit access through casing 71 for well 70.
As further shown in the embodiment of FIG. 3, combustion in the middle zone lil is desirably stopped some distance from production well 26 to prevent well damage. The approach of the combustion front can be detected by a thermocouple 80 positioned in producing well 26 adjacent to, or opposite, oil-producing zone l0. Thermocouple 80 disconnects power to drive motor 92 and air compressor 36. For this purpose, lines 82 and S4 from thermocouple 80 energize sensitive relay 86 when the temperature in the well reaches a preselected value. This controls, in turn, circuit breaker 90 through switch 88 to cut off power for air compressor 36. Thus, when the temperature of the produced fluid in zone reaches the preselected value, the combustion process dependent upon air is automatically stopped. After such a temperature value is produced in fluid flowing out of middle zone l0, it may be desirable to inject water into the middle zone, as well as into the upper and lower producing zones 12 and 14. Thus, further maximum thermal economy can be obtained in assisting recovery from the reservoir. An estimate of flow rates can also be used lto determine the proper time to stop air injection in zone l0. For this purpose a ilow meter and integrating system can be substituted for thermocouple 80.
In each of the systems shown in FIGS. l and 3, it is, of course, desirable to maintain sutlicient pressure in middle zone 10 to prevent backflow of oil or water from the producing horizons l2 and 14 due to higher pressures that may exist in said producing sands. This backow after combustion ends can be eliminated by injecting low volumetric rates of water, air or gas into middle zone l0 at the injection well such as 24 in FIG. l, and e4 in FIG. 3.
The present method, of course, maybe used either in a line drive system or a five spot, or circular, pattern of the injection and producing wells. A line drive system is one in which a plurality of injection wells are drilled into the formation along a line, such as the edge, of a producing iield, or a geological fault, so that the produced oil is driven toward a similar line or pattern of producing wells at a distance selected to permit maximum recovery of oil from multiple producing horizons. On the other hand, a live spot, or circular, pattern of wells for assisted oil recovery is one where the injection well is in the center of a plurality of producing wells that are radially spaced outwardly from the injection well. In either of such systems, the combustion front is moved progressively outward from the injection well toward the producing well, and progressively with said lateral movement at least one adjacent and parallel producing horizon is ooded by any secondary drive iluid, including water containing other miscible or immiscible materials, that will progressively absorb heat from the thermal bank or reservoir. Then, the heat is carried vertically and outwardly from said heat bank to the liquids in said adjacent formation by conduction and by lthe drive fluids flowing therethrough.
It will be apparent to those skilled in the art that the present system permits an appreciable increase in eciency of assisted recovery from a multi-bedded oil-producing reservoir stratified by impermeable horizons. Greater use of the thermal energy supplied by the compressed air and the burned oil in one zone is utilized to improve progressively the water ood eiiiciency of the adjacent oil-producing beds. Various changes in the method of injecting and recovering fluids in multi-bedded reservoirs and arrangements for positioning injection and production wells will occur to those skilled in the art. All such modications or changes falling within the scope of the appended claims are intended to be included therein.
l. The method of assisting recovery of oil from an underground reservoir that includes at least a pair of substantially parallel, permeable hydrocarbon fluid producing z-ones separated by a relatively thin fluid-impermeable zone and said reservoir having at least an injection Well and a production well penetrating all of said zones which comprises the steps of initiating combustion of said hydrocarbon fluid in one of said uid producing zones adjacent said injection well, said one zone having greater permeability to lluid ilow therethrough than the other of said pair of producing zones, injecting air through said injection well into said one zone to establish combustion of said hydrocarbon fluid and to extend the burning area vertically -across the thickness of said one zone to form a burning front, continuing said airV injection to maintain said combustion burning front and to advance it progressively a distance toward said production well greater than the thickness of said one oil producing zone whereby the adjacent thinner oil-impermeable zone is progressively heated by conduction from said burning front to form a heat reservoir for said other adjacent uid producing zone, then injecting water through said injection well into said other producing zone to permit heat from said oil-impermeable zone to be absorbed progressively therein as said water ows concurrently with said combustion burning front, and continuing to inject said air and Water, respectively, to simultaneously and progressively move through said producing zones and assist recovery of oil from both of said producing zones into said production Well.
2. The method in accordance with claim l wherein other production zones are parallel to said pair of oil producing zones and separated therefrom by other relatively thin Huid-impermeable zones, and wherein combustion is initiated and maintained in at least the middle fluidproducing zone by injecting air therein through an injection well and water is injected under pressure through said injection well intoboth the overlying and underlying producing zones, said Water moving concurrently with said combustion to assist recovery of oil from said production zones.
f, 3. The method of assisting recovery of oil from an underground reservoir that includes at least three substantially parallel permeable hydrocarbon fluid-producing zones, each of said fluid-producing zones being separated by a relatively thin u-id-imperrneable zone, and said reservoirhaving at least one injection well and at least one production well penetrating said zones which com-V thereinto for a timesuiiicient progressively to 'force hydrocarbons to il'owfromsaid zone into said at ieast one Y production weil and-to-signiiicantly increase the temperature of the adjacent oil-impermeable zones by thermal conduction fromsaid combustionffront, then introducing tlooding waterthroughv said injection well into the upperV and ylower yfluidproducing zones to conduct heat Ystored in said fluid-impermeable zones to the tluids in said'upper'land lower fluid producing zones, said water advancing substantially in `the' Vsaule direction as saidfad- VVancing combustion front and continuingsupply of both air and water, respectively, to all of said producing zones to simultaneously andprogressively move through said producingzonesland assist recovery ofoilsimultaneously from all ofsaid zones in said production wel-i. Y Y 4. The lmethod Yof assisting recovery of oil from an underground reservoir that includes at least a pair of t substantially parallel, permeable oii producing zones separatedy by a relatively thin iiuid impermeable zone and said rcservoirhaving at least a production -well penetrating all of Vsaid zones and at-leastonc injection well perzones by conduction of heat from said burning front and l mitting separate communication between earthssu-rface and said pair of oil producing zones which comprises the steps vof initiating combustion'of a portion of the oil in one Vof said producing'zones adjacent'said injection Well, saidonerzone having Agreater permeability to filuid ow therethrough than the other of said pairiof oil producing zones, injecting air `.through said-injection well into said one zone-toextend combustion of 'said-oil vertically across theV thickness of said `orte-zone to form aburningvfront, continuing air Vinjections through said injection well lto progressively advance said burning front yfrom said injectionwell toward said-productionwell forat'ime sufcient toreduce theoilwaterviscosityuratio to a value .less than` about 200, then introducing water through said injection well into said other producing zone to absorb heat from v said oil-impermeable'zone, said water advancing in the same direction las said burning front and continuing to pump said Vair Vand water, respectively, to assist` recovery of oil simultaneously and progressively from both of said recovery of oil from at least two of the oil-producing zones, said multibedded reservoir including at least three substantially parallel, permeable oil-producing zones separated by-relatively thin Huid-impermeable zones and said reservoir having a production Well penetrating said zones and at least one injection well permitting simultaneous but separated communication between the earths surface and Vtherniddle zone and Vbetween the earths surface and the other oil-producing zones which comprises the steps of initiating Vcombustion of a portion-of the oil in the middle zone adjacent to said injection well, injecting air through said injection well into said middle zone to extend combustion of said oil vertically across the thickness ofrsaid middle zone -to form a burning front, progressively advancing said burning front from said injection well toward said production well for a time sutiicient'to heat the adjacent upper and lower oil-impermeable permeable V,zones at said value, and simultaneously pro- 1 ducing oil into said production Well from all ofsaid producing zones.
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Y Campion et al. Aug. 25, 1959