US3148730A

US3148730A - Secondary recovery process

Info

Publication number: US3148730A
Application number: US39043A
Authority: US
Inventors: Don R Holbert
Original assignee: Sinclair Research Inc
Current assignee: Sinclair Research Inc
Priority date: 1960-06-27
Filing date: 1960-06-27
Publication date: 1964-09-15
Anticipated expiration: 1981-09-15

Description

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P 1964 D. R. HOLBERT 3,148,730

SECONDARY RECOVERY PROCESS Filed June 27, 1960 on. STRATUM Y1 9! l- Q l6 WATER .STRATUM g gig- I PRODUCING INPUT WELL I WELL) I3 I 1 u on. BANK '3 OIL sTRATuM j I] "a a VISCOUS SLUG WATER STRATUM E IO 1 PRODUCING INPUT WELL WELL 3 VISCOUS SLUG WATER STRATUM g INVENTOR DON R. HOLBERT MM V 4 ATTORNEYS United States Patent C) 3,148,730 SECONDARY RECOVERY PROCESS Don R. Holbert, Tulsa, Okla., assiguor, 'by mesne assignments, to Sinclair Research, Inc., New York, N.Y., a corporation of Delaware Filed June 27, 1960, Ser. No. 39,043 9 Claims. (Cl. 1669) This invention concerns a water drive process for recovering petroleum hydrocarbons from an underground formation. More particularly, my invention relates to a water drive method for improving the recovery of oil from an oil-bearing subterranean stratum having vertical permeability and underlain by a water-bearing formation.

One well known secondary recovery procedure for obtaining petroleum oil from underground formations is the so-called water drive method in which water is injected into the formation from an input well and conveyed toward an adjacent or cooperating output well to push oil to the latter well for recovery at the earths surface. A factor of utmost economic significance is the amount of water that must be injected for a given increment of oil recovery. When the expense involved in transferring water through the formation from an input to an output well taken with the cost of recovering the water at the output well exceeds the value of the oil recovered the process is obviously uneconomical. Accordingly, it is apparent that there can be merit in any method which leads to a decrease in the amount of water necessary for recovering a given amount of oil by this technique.

In many instances a subterranean formation in which a water drive is conducted is underlain by a formation containing large amounts of Water, frequently even to the exclusion of oil, and such formations often exhibit vertical permeability to water. In this situation water injected into an input well leading to the oil-bearing formation will, in going to the output well bypass a significant portion of the oil-bearing formation even though communication in both the input and output wells is only with the oil-bearing formation, that is the wells do not extend into the lower water-bearing stratum. This bypassing is by way of the water-bearing formation and is undesirable since it greatly increases the amount of water which must be injected to transport oil to the output well for recovery. Such by-passing is due to the presence of paths of vertical permeability in the oil and water layers and to the absence of flow barriers, e.g. shale, intermediate the oil and water-bearing strata. My present method is particularly designed to obviate or reduce water bypassing in these situations.

In the water-flooding process of this invention, I provide in the underlying water-bearing stratum, an aqueous medium which is more viscous than the aqueous medium employed in flooding the oil-bearing formation. The water-flooding medium is then charged to the oil-bearing formation from an input well and moved toward an output well. By correlating the introduction and movement of the separate media, I avoid excessive by-passing of the oil-bearing formation by the water-flooding medium and the latter is in effect barred or deterred from travelling from the input to the output well by way of the lower water layer.

The amount of the more viscous liquid in the waterbearing formation can be varied depending upon the method of operation. Although a slug of the viscous liquid of any substantial width will afford some advantage, the slug at initial injection usually will be at least about 20 feet wide, preferably at least about 30 or 40 feet wide. This injected liquid could occupy completely the waterbearing formation between the input and output wells; however, this may be uneconomic. In any event, the viscous liquid slug will be thick enough to prevent water breaking through the slug in the lower stratum too early in the process and the longer this breakthrough is delayed the greater should be the benefit with respect to the waterto-oil ratio produced at the output well.

The manner of providing the viscous liquid in the Water layer can be varied. For instance, due to the vertical permeability of the formation the viscous liquid can be injected from an input well into the oil-bearing stratum from which the liquid will flow naturally to the lower water layer. I prefer, however, that direct communica tion with the underlying water-bearing stratum be established through a well adjacent thereto which may w tice constitlgeihe-loweLparLofitheawgt er input well 2r even be a separate well communicating only with the watermformation. The viscous liquid may then be injected into the waterbearing layer, preferably across its entire vertical face communicating with the well. Alternatively, a watgr input well comrn i nicating only with the oil-bearing laye an be fractured t o provide less restricted paths of communication down to the water layer and then the viscous liqfl injected. The viscous liquid could be provided imsituahy injecting a thickenin'gagent into the water-bearing stratum from an adjacent well.

It seems rh'o st advantageous to position the leading edge of the viscous liquid in the lower water-bearing formation somewhat ahead, say at least about 5 or 10 feet, of the water-flooding medium introduced into the oilbearing stratum and then continue to iw v er qu nusinsdiumand the rmj nediaemuausimg neously or intermittently until the viscous slug extends at least about 5 or 10 feet ahead and behind the main bank of oil being pushed from the input towards the output well. The initial overall width of the viscous slug will usually not exceed about 150 feet and is preferably not greater than about feet. The size of the slug may vary depending upon factors such as its viscosity, thickness of the water-bearing formation and flood pattern well spacing. It may be advantageous to continue injection of the viscous slug at least until the rate of its advance has been slowed down to the rate of advance of the regular Water displacing the oil bank.

After the slug is formed, injection of the viscous liquid can be stopped and the ordinary water-flooding medium introduced into the oilor both the oiland water-bearing formations to push the oil bank and its underlying viscous aqueous liquid slug towards the output Well. This injection will most advantageously continue until the oil bank and lower slug reach the vicinity of the output well.

In another procedure the lower viscous slug may be completely formed before water is injected into the oilbearing formation. Subsequently water can be injected into both formations or only-into the oil stratum t6move the main oil bank towards the middle of the viscous slug. After the oil bank travels away from the input well the water-flooding medium could be introduced into the oilor both the 0iland water-bearing strata for continuing the recovery procedure by pushing the oil bank and underlying viscous slug towards the output well. In any event, some portion, preferably substantially all, of the main oil bank should be above the viscous slug for a major part of the distance travelled by the oil bank from the input to the output well.

The viscous liquid used in my process is composed predominantly of water and preferably will be essentially the same base medium as that used in water-flooding the oil-bearing formation and may therefore contain sodium chloride. The viscosity of the thicker liquid will be greater than that of the water-flooding fluid. Generally, the viscosity of the thicker liquid will be in the range of about 1 to 50 centipoises, preferably about 2 to 10 centipoises, more than the viscosity of the water-flooding 3 medium and frequently the viscosity of the latter will approximate 1 centipoise. If the viscosity of the liquid provided in the water-bearing formation is too great, the water-flooding medium may finger into the viscous slug and cause an early breakthrough due to the low mobility of the viscous liquid and the differences in perme ability existing across the formation. Generally, the viscosity of the thicker aqueous liquid will not exceed about 50 centipoises.

The aqueous viscous liquid can be formed by adding to an aqueous medium a water-dispersible, preferably organic, material. Among the organic additives suitable for incorporation in the aqueous medium are hydroxylcontaining compounds such as sugar, glycerol, glycols, e.g. ethylene glycol; polyethylene oxides corresponding to the formula RO(C H O) H, e.g. Polyox, a high molecular solid weight polyethylene oxide resin produced by Union Carbide Chemicals Co.; polyamides of the formula e.g. PAM, a white, powdery solid material; and gear gum. The polyethylene oxides, however, are preferable due to their lower cost. These additives are included in the aqueous medium to form the viscous liquid used in this invention and generally the additives will not be greater than about 2% of the medium, preferably not exceeding about 1%, and the amount present will be sufiicient to provide the medium with the desired viscosity.

The method of my invention may be better understood by reference to FIGS. 1 to 3 of the drawings which illustrate diagrammatically one embodiment of the present invention at separate stages of operation.

FIGURE 1 shows an initial stage of my process. There is provided input well 10 extending through oil-bearing stratum 11 and water-containing formation 12. The output or producing well is shown at 13 and need only extend through the oil-bearing stratum 11. Well 10 houses tubing 15 to be used for introducing the viscous liquid into the water-bearing formation.

Strata

11 and 12 exhibit vertical permeability towards water.

Into tubing 15 I inject salt water containing about 4 lbs. per gallon of sugar or 0.7 lbs. per gallon of PAM- 200, giving in each case a liquid medium having a specific gravity of about 1.05 and a viscosity of about centipoises, at 80 F. temperature until a bank or slug 16 of this medium extends through the water-bearing stratum 12, across essentially its entire vertical face and about 25 feet towards the producing well 13. Fresh water is then injected across the entire face of the oil-bearing stratum by way of the annulus between tubing 15 and the wall of well 10. aroundtubing 15 .at the .junctureof stratalLandJLtg ensure properwdi sstion" -of..theduiectedsflllis1r The introduction of the water-flooding medium into formation 11 and of the viscous liquid into stratum 12 is continued to maintain the leading edge of the slug 16 about 25 feet ahead of the principal oil bank 17 formed in stratum 11, see FIGURE 2. These injections can continue as long as desired; however, I prefer the operation illustrated in FIGURE 3.

Most advantageously the introduction of the viscous liquid is discontinued after the width of the slug is about 60 feet and extends considerably to the rear of oil bank 17. Then fresh water or brine is introduced into both the oil and water-bearing strata to maintain the oil bank 17 above the viscous slug 16 as they are pushed towards the output well. I prefer to continue this relationship until the oil bank reaches well 13. As the oil bank and its underlying viscous slug proceed toward the output well water acceptance in stratum 12 is significantly lessened as compared with that occurring when the viscous slug is not present and accordingly the water-to-oil ratio produced at well 151 decreased.

If desired, a packer can be set I claim:

1. In a method employing a water-flooding medium and cooperating input and output wells for recovering oil from an underground oil-bearing formation underlainby a water-bearing f9 rn ia t i9 i s a id formations exhibiting paths of vertical permeability to water between the oil and water formation, the steps comprising introducing into the water-bearing formation a viscous aqueous medium and introducing in said water-bearing formation said water-flooding medium to move said viscous aqueous medium towards an output well, introducing through an input well in communication with the oil bearing formation said water-flooding medium into said pillaging fpr rrra;

tion to move an oil bank towards said output well to maintain an oil bank ahead of said water-flooding medium and above said viscous aqueous medium, introducing said water-flooding medium into both of said oiland waterbearing formations to maintain said oil bank ahead of said water-flooding medium and at least a portion of said oil bank directly above said viscous aqueous medium over a major portion of the travel of said oil bank to said output well and recovering oil from said output well, said viscous aqueous medium having a viscosity of about 1 to 50 centipoises greater than said water-flooding medi- 2. The method of claim 1 in which the viscous aqueous medium has a viscosity of about 2 to 10 centipoises greater than said water-flooding medium.

3. The method of claim 1 in which said oil bank travels above and behind the leading edge of said viscous aqueous medium.

4. In a method employing a water-flooding medium and cooperating input and output wells for recovering oil from an underground oil-bearing formation underlain by a water-bearing formation, said formations exhibiting paths of vertical permeability to water between the oil and water formations, the steps comprising introducing into the water-bearing formation a viscous aqueous medium, introducing through an inputwell in cornmunication with the oil bearing formation saidwater floodingmedium into said oil-bearing formation to move an oil bank towards said output well, continuing introduction of said viscous aqueous mgliurnand said waterfio'odingniediurrifto maintain an oil bank ahead of said water-flooding medium and above said viscous aqueous medium, discontinuing introduction of said viscous aqueous medium, introducing said water-flooding medium into both of said oiland waterbearing formations to maintain said oil bank ahead of said water-flooding medium and at least a portion of said oil bank directly above said viscous aqueous medium over a major portion of the travel of said oil bank to said output well and recovering oil from said output well, said viscous aqueous medium having a viscosity of about 1 to 50 centipoises greater than said water-flooding medium.

5. The method of claim 4 in which the viscous aqueous medium has a viscosity of about 2 to 10 centipoises greater than said water-flooding medium.

6. In a method employing a water-flooding medium and cooperating input and output wells for recovering oil from an underground oil-bearing formation underlain by a water-bearing formation, said formations exhibiting paths of vertical permeability to water between the oil and water formations, the steps comprising introducing in the wafer-bearing formation a slug of viscous aqueous medium and introducing in said water-bearing formation said water-flooding medium to move said viscous aqueous medium towards an output well, introducing through an input well in communication with the oil-bearing formation said water-flooding medium into said oil-bearing formation to move an oil bank towards said output well and to maintain said oil bank ahead of said water flooding medium and at least a portion of said oil bank directly above and behind the leading edge of said slug of viscous aqueous medium over a major portion of the travel of said oil bank towards said output well and recovering oil from said output Well, said slug of viscous aqueous medium having a viscosity of about 1-50 centipoises greater than said water-flooding medium.

7. In a method employing a water-flooding medium and cooperating input and output wells for recovering oil from an underground oil-bearing formation underlain by a water-bearing formation, said formations exhibiting paths of vertical permeability to water between the oil and water formations, the steps comprising providing from an input well and in the water-bearing formation a viscous aqueous medium, introducing through an input Well in communication with the oil-bearing formation said water-flooding medium into said oil-bearing formation to move an oil bank toward said output well and to maintain said oil bank ahead of said water-flooding medium and at least a portion of said oil bank directly above said viscous aqueous medium over a major portion of the travel of said oil bank towards said output well, and recovering oil from said output well, said viscous aqueous medium having a viscosity of about 1 to 50 centipoises 20 greater than said Water-flooding medium.

8. The method of claim 7 in which the viscous aqueous medium has a viscosity of about 2 to 10 centipoises greater than said water-flooding medium.

9. In a method employing a water-flooding medium and cooperating input and output wells for recovering oil from an underground oil-bearing formation underlain by a water-bearing formation, said formations exhibiting paths of vertical permeability to Water between the oil and water formations, the steps comprising introducing into the water-bearing formation a slug of viscous aqueous medium and introducing said water-flooding medium into both of said oil-and-water bearing formations to maintain said oil bank ahead of said water-flooding medium and at least a portion of said oil bank directly above said viscous aqueous medium over a major portion of the travel of said oil bank to said output well and recovering oil from said output Well, said viscous aqueous medium having a viscosity of about 1-50 centipoises greater than said Water-flooding medium.

References Cited in the file of this patent UNITED STATES PATENTS 2,072,982 Dale Mar. 9, 1937 2,272,672 Kennedy Feb. 10, 1942 2,341,500 Detling Feb. 8, 1944 2,402,588 Andresen June 25, 1946 2,731,414 Binder Jan. 17, 1956

Claims

1. IN A METHOD EMPLOYING A WATER-FLOODING MEDIUM AND COOPERATING INPUT AND OUTPUT WELLS FOR RECOVERING OIL FROM AN UNDERGROUND OIL-BEARING FORMATION UNDERLAIN BY A WATER-BEARING FORMATION, SAID FORMATIONS EXHIBITING PATHS OF VERTICAL PERMEABILITY TO WATER BETWEEN THE OIL AND WATER FORMATION, THE STEPS COMPRISING INTRODUCING INTO THE WATER-BEARING FORMATION A VISCOUS AQUEOUS MEDIUM AND INTRODUCING IN SAID WATER-BEARING FORMATION SAID WATER-FLOODING MEDIUM TO MOVE SAID VISCOUS AQUEOUS MEDIUM TOWARDS AN OUTPUT WELL, INTRODUCING THROUGH AN INPUT WELL IN COMMUNICATION WITH THE OIL BEARING FORMATION SAID WATER-FLOODING MEDIUM INTO SAID OIL-BEARING FORMATION TO MOVE AN OIL BANK TOWARDS SAID OUTPUT WELL TO MAINTAIN AN OIL BANK HEAD OF SAID WATER-FLOODING MEDIUM AND ABOVE SAID VISCOUS AQUEOUS MEDIUM, INTRODUCING SAID WATER-FLOODING MEDIUM INTO BOTH OF SAID OIL- AND WATERBEARING FORMATIONS TO MAINTAIN SAID OIL BANK AHEAD OF SAID WATER-FLOODING MEDIUM AND AT LEAST A PORTION OF SAID OIL BANK DIRECTLY ABOVE SAID VISCOUS AQUEOUS MEDIUM OVER A MAJOR PORTION OF THE TRAVEL OF SAID OIL BANK TO SAID OUTPUT WELL AND RECOVERING OIL FROM SAID OUTPUT WELL, SAID VISCOUS AQUEOUS MEDIUM HAVING A VISCOSITY OF ABOUT 1 TO 50 CENTIPOISES GREATER THAN SAID WATER-FLOODING MEDIUM.