US 3174546 A
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Description (OCR text may contain errors)
mam-3am March 23, 1965 FLlCKlNGER I 3,174,546
METHOD FOR SELECTIVELY SEALING-OFF FORMATIONS Filed Aug. 29, 1962 2 Sheets-Sheet 1 L FIG. 2
DON H. FLICKINGER I I INVENTOR.
March 23, 1965 D. H. FLICKINGER METHOD FOR SELECTIVELY SEALING-OFF FORMATIONS Filed Aug. 29, 1962 2 Sheets-Sheet 2 FIG. 6
DON H. FLICKINGER INVENTOR.
e Lana United States Patent C) 3,174,546 METHOD FUR SELECTIVELY SEALING-OFF FORMATIDNS Don H. Flickinger, Tulsa, Okla, assignor to Pan American Petroleum Corporation, Tulsa, Okla, a corporation of Delaware Filed Aug. 29, 1962, Ser. No. 220,224 8 Claims. ((31. 166-42) The present invention relates to a method for directing the flow of fluid to one of several zones of interest in a geological formation penetrated by a cased well. More particularly, it is concerned with a novel technique for the injection of a fluid such as water or gas into a specific section of a reservoir involved in a secondary recovery project. Also, this invention is useful in the selective stimulation of individual zones of a multi-zone well.
At present, there are several techniques used to isolate a zone for the purpose of stimulating it. One technique is to isolate such zone by means of dual packers. In addition to the expense involved in using dual packers and frequent failures of the packers to seat effectively, the operator is forced to conduct any pumping operation through tubing which is usually inefficient and restrictive. If solid materials such as, for example, propping agents, are pumped into such an isolated zone during fracturing, there is additional danger that the packers may become wedged in the casing. Presently accepted methods also in-- volve conducting a treating step, then injecting ball sealers followed by another treating step, and then repeating this cycle, hoping that the ball sealers exclude all of the perforations in one zone, but leave open the perforations in the zone to be treated. This procedure is unreliable. In actual practice the results often obtained show that selective treatment was not secured. For example, in a planned job for the selective treatment of five diflerent zones complete plugging of all perforations occurred after only two stages of treatment, i.e., treatment of two zones. In other instances, there have been indications that no sealing of the perforations has occurred at all.
Briefly, the process of my invention is carried out in a well having a casing therein perforated opposite at least two zones of interest. These perforations are first sealed off by pumping suitable sealers or bridging elements together with a suitable carrier fluid down the well tubular goods. These elements may he in the form of resilient balls having slightly larger diameters than said perforations. This operation is conducted until all perforations are sealed as evidenced by an increase of system pressure on continued pumping and negligible injection rate. Next, the sealer elements covering the perforations opposite the zone of interest are removed, for example by means of a suitable mechanical scraper. Said zone is then subjected to treatment, such as injection of fracturing fluid, acidizing fluid or, in the case of a secondary recovery operation,
water and/or gas, for example, a normally gaseou hy drocarbon, may be introduced into the reservoir at a specific level. After this injection step has been completed and it is desired to repeat the process at a level either above or below the first point of injection, more sealer elements are pumped down the well where they are hydraulically directed to the open perforations through which the treating fluid or fluids passed during the above-mentioned injection step. When all perforations are again sealed off in this fashion, the perforations opposite a second zone of interest are opened in the same manner as described and the treating cycle is repeated. It will be realized that by this method any number of zones in a formation can be treated and that the sequence in which they are treated, i.e., top to bottom or vice versa, is immaterial.
FIGURE 1 is a cross-sectional view of a perforated 3,174,546 Patented Mar. 23, 1965 cased well showing surface equipment used in the process.
FIGURE 2 is a detailed view of a design of scraper element useful in removing ball sealers or the equivalent from perforations.
FIGURES 3 to 6 illustrate the sequence of the principal steps involved in the application of my invention to two separate production zones.
Referring to FIGURE 1 for a more detailed description of a schematic representation of suitable apparatus for carrrying out the steps of my invention, well 2 is in a geological formation 4 having an upper oil-bearing zone 6 and a lower producing zone 8. These zones are separated by an unproductive stratum 10. Opposite zones 6 and 8 are perforations 12 and 14, respectively, in casing 15. A wire line mechanical scraper assembly 16 is lowered into the well by means of cable 18 and placed opposite the set of perforations through which it is desired to inject the fracturing or other treating fluid. The scraper is composed of a sinker bar 20, a centralizer 22 affixed to said bar, a neck 2 at the base of said bar and a circular scraper element 26 fitted rather loosely around neck 24 by means of a slip joint 28. Scraper element 26 is held on neck 2 by means of ring 30.
The structure of scraper 26 is shown by plan view in greater detail in FIGURE 2 in which the ring forming slip joint 28 of this wheel-like member is held in position by means of radial supports 36 extending from said ring to outer rim 38, having vertical ribs 40. These ribs aid in preventing differential pressure sticking of the scraper at the perforations. Also, if desired, holes may be drilled in rim 3% to further reduce sticking of this kind.
When it is desired to remove sealer elements from a given set of perforations, scraper element 26 is moved in a downwardly direction by lowering the sinker bar and circular scraper causing any sealing elements lodged in the perforations and coming in contact with the scraper to be removed and fall to the bottom of the well.
The surface apparatus shown in FIGURE 1 includes a stufling gland 32 on the upper end of casing 15. A lubricator, including valves, as is well-known in the art, may be installed between the upper end of the casing and the stufilng gland so that well apparatus such as a casing perforator or a scraper may be run into and removed from the casing while the well is under pressure.
A high pressure, high volume pump 42 and its suction line .4 are connected to treating fluid tanks, not shown. This pump discharges the well treating fluid into the well through flow line 46. A hopper 48 filled with sealing or bridging elements 50 is connected to flow line 46. These elements are held in place in the hopper by means of pin 52. The hopper is closed at the top by means of a cap 54. A pressure gauge 56 is connected to the system downstream from pump 42 to the top of cap 54 to indicate the pump discharge pressure.
Assuming now that it is desired first to treat lower zone 8, suction line 44 on pump 42 is connected to a supply of liquid 4-5, preferably solids-free, such as oil or water, and the latter pumped into the well. At the same time sealing elements 50, which in this case may be balls of nylon, rubber, combination of rubber with a nylon core, or similar material, are supplied to the well via liquid 4-5 by pulling pin 52. These balls desirably have a density substantially equal to that of liquid 45 and are carried thereby down the well to both sets of perforations 12 and 14, where they lodge on the upstream side of said perforations, as indicated, for example, in FIGURE 3, closing the perforations. Since the number of balls injected is typically substantially greater than the number of perforations, in order to assure that all perforations will be plugged, there is a surplus of balls which ultimately pass on to the bottom of the well. The surface pressure indicated by gauge 56 will then show a sudden increase in pressure, indicating that the perforations are sealed.
Scraper assembly 16 is then lowered into place opposite Zone 8, as shown in FIGURE 4, moved up and down over th e thickness of the perforated section and perforations 14 opened, with the ball sealers previously closing these perforations sinking to the bottom of the well. During this operation it is necessary to maintain a head of liquid 45 in the well suflicient to retain in place the ball sealers opposite zone 6. In most cases, this will require that the well be filled with liquid. Lower zone 8 can now be selectively and positively stimulated with any desired volume of fluid, for example, fracturing fluid or acidizing solution pumped into the well via line 46 to form fractures or channels 47 as shown in FIGURE 4.
After treatment at zone 8, scraper assembly 16 is pulled up above perforations 14 and the latter are closed by pumping down additional ball sealers, as described above. The presence of scraper assembly 16 in the well does not interfere with the introduction of sealers into the system since they have no difliculty in passing through the open spaces created by supports 36. This results in all perforations being sealed off, as shown in FIGURE 3, for examample. By moving scraper 16 on up to zone 6 and passing it back and forth over perforations 12, ball sealers closing these perforations are removed and sink through the liquid in the well which is primarily fracturing or acidizing fluid from the previous treatment. In some instances it may be desirable to remove such fluid before all perforations are again sealed off prior to further treatment of additional zones. In such case, the fracturing liquid, which may contain a propping agent, is pumped out and a clear, solids-free fluid used to carry the ball sealers to the perforations and seal them. After the ball sealers opposite zone 6 have been removed, treatment is administered as previously discussed with the treating fluid entering zone 6, as indicated in FIGURE 5, forming fractures or channels 49. This method of sealing off zones, selectively removing the sealing elements and treating through the thus opcned perforations can, of course, be readily repeated any number of times.
When the last zone has been tested or treated, and the treating fluid removed-if desiredthe lubricator and stufling gland are taken off, after which the scraper 16 is withdrawn from the well. Pump 42 and suction line 44 are removed and flow'line 46 covered with cap 58, as indicated in FIGURE 6. In some cases, the well may be produced through the casing and the pump discharge line. Generally, however, I prefer to cap flow line as shown and run a string of tubing so into the well to a point at which the bottom end of the tubing is at an elevation below the liquid level 62. This tubing string is hung in the casing on a tubing head 64. Both the upper and lower zones 6 and S, as well as any other zones of interest, can then be produced through the tubing either by flowing or pumping. After liquid from each of these producing formations commences to flow into the well, i.e., as the pressure differential across the perforations is reversed and the pressure in the formation becomes greater than the pressure in the well, the ball sealers are displaced from the perforations and either carried up the well with the produced fluids or sink to the bottom. In some instances, oil-soluble sealers may be used, in which case they dissolve in the oil and are thus removed from the system.
From the above discussion it will be seen that the process of my invention possesses a number of advantages over procedures now used in multi-zone treatment or stimulation techniques.
With the process of the present invention, the operator has positive surface indication of control and any zone can be treated with any desired treatment volume with no loss in efficiency from fluid being lost to perforations open in other zones. Thus, the advantages of the technique of my invention over methods now used to exclude intervals from receiving injection fluids include:
(1) Simplicity and economics,
(2) No expensive rig required to complete the job,
(3) Flexibility; change in injection elevations may be made quickly and cheaply,
(4) Positive surface evidence and control; the ball sealers will remain in place with negligible differential pressure. Many times adequate differential pressure exists in injection wells.
In place of the Wire line operated scraper apparatus, which may be of the fixed or retractable design, I have described, it will be apparent that other means could be substituted therefor. For example, a suitable scraper element such as that shown in FIGURE 2 could be attached to the lower end of a tubing string. By rotating and/ or lifting the tubing, the sealer elements could be removed. After the treatment phase is completed and the Well is ready to be placed on production, such tubing can remain in the well and the fluids produced through it.
I. In a method for directing a fluid into one of at least two zones of a geological formation penetrated by a cased well having perforations therein opposite said zones;
the improvement which comprises injecting into said well suflicient sealer elements slightly larger in size than said perforations, directing said elements to all of said perforations and holding them there by means of fluid pressure;
removin said elements only from the perforations opposite a given zone;
injecting said fluid into said given zone via the resulting unsealed perforations, thereafter rescaling the lastmentioned perforations by injecting an additional quantity of said sealer elements suflicient in number to cover said last-mentioned perforations;
directing said elements to all of said perforations opposite said given zone and holding them there by means of fluid pressure;
removing said elements only from the perforations opposite a zone other than the one into which said fluid was injected; and
injecting said fluid into said last-mentioned zone via the resulting unsealed perforations.
2. The process of claim I in which the first zone treated is below the second zone subjected to such treatment.
3. The process of claim 1 in which the first zone is above the second zone subjected to such treatment.
4. In a method for producing a multiplicity of fractures in a formation penetrated by a cased well and having perforations therein extending over a plurality of oil-producing zones;
the improvement which comprises injecting into said well sufficient sealer elements slightly larger in size than said perforations;
directing said elements to all of said perforations and holding them there by means of fluid pressure; removing said elements only from the perforations opposite a given oil-producing zone;
injecting a fracturing fluid into said given zone at a suflicient rate to fracture said given zone; thereafter rescaling the last-mentioned perforations by injecting an additional quantity of said sealer elements suflicient in number to cover said last-men tioned perforations; directing said elements to all of said last-mentioned perforations and holding them there by means of fluid pressure; removing said elements only from the perforations opposite an oil-producing zone other than the one into which said fracturing fluid was injected, and
injecting said fracturing fluid into said last-mentioned zone via the resulting unsealed perforations.
5. In a method for the recovery of petroleum from an underground reservoir having a multiplicity of oil-produc- 5 6 ing zones by means of flooding said reservoir with a fluid injecting said fluid drive agent into said last-mentioned drive agent, said reservoir being penetrated by a cased zone via the resulting unsealed perforations. well and having perforations extending over said zones; 6. The process of claim 5 in which the injected fluid is the improvement which comprises injecting into said water.
well sufiicient sealer elements slightly larger in size 5 7. The process of claim 5 in which the injected fluid than said perforations; is a normally gaseous material. directing said elements to all of said perforations and 8. The process of claim 7 in which said material is a holding them there by means of fluid pressure; gaseous hydrocarbon. removing said elements only from the perforations opit a given ne; 10 References (Iited by the Examiner injecting said fluid into said given zone via the resulting UNITED STATES PATENTS unsealed perforations; thereafter rescaling the last-mentioned perforations by 2754910 7/56 Dernck et 166 42 injecting an additional quantity of said sealing ele- 280O184 17/57 i 166 9 merits sufiicient in number to cover said last-men- 15 2808886 0/57 Ball et 166-9 tionsd -f fi 3,010,514 11/61 FOX 166-41 directing said elements to all of said last-mentioned pero forations and holding them there by means of fiurd 3,686,587 4/63 Zandmer et a1 166 42 pressure;
removing said elements only from the perforations op- 20 posite an oil-producing zone other than the one into which said fluid drive agent was injected, and
ENJAMIN HERSH, Primary Examiner.