US3460626A

US3460626A - Method and apparatus for alleviating erosion in multiple-completion wells

Info

Publication number: US3460626A
Application number: US627551A
Authority: US
Inventors: Henry L Ehrlich
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1967-03-31
Filing date: 1967-03-31
Publication date: 1969-08-12
Anticipated expiration: 1986-08-12

Description

Aug. `12, 1969 H. l.. EHRLICH 3,460,626

METHOD AND APPARATUS FOR ALLEVIATING EROSION 1N MULTIPLWCOMPLETION WELLS Filed Maren s1. 19e? 2 sneets-sneet 1 HENRY L. EHRucmJR.

,4 INVENTOR ATTORNEY ug- 12. 1969 H. r-:HRLICH 3.460.626

METHOD ANI) APPARATUS FON ALLIVTIN EROSION 4IN MULTIPLECOMI.E'1ION WELLS Filed March 31. .1967 2 Sheets-Sheet 2 FIG. 2

HENRY L. EHRLICH, JR. INVENTOR ATTORNEY United States Patent O 3,460,626 METHOD AND APPARATUS FOR ALLEVIATING EROSION IN MULTIPLE-COMPLETION VVELLS Henry L. Ehrlich, Dallas, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed Mar. 31, 1967, Ser. No. 627,551 Int. Cl. E21b 43/12, 33/12, 41/00 U.S. Cl. 166-313 9 Claims ABSTRACT OF THE DISCLOSURE This disclosure describes a well installation and method for use in multiple-completed wells subject to blast- Zone erosion. A packer is disposed within a well between upper and lower production intervals thereof. A conduit extends through the packer and terminates below the top of the upper production interval. This conduit provides for fluid communication between the upper and lower intervals. The conduit is provided with a flow-restricting device which reduces the pressure of the fluid flowing upwardly through the conduit.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the production of subterranean fluids through wells, and more particularly to well installations and methods for alleviating erosion of downhoe well equipment by detrital material contained in smh subterranean fluids.

Description of the prior art In the petroleum industry, downhole well equipment often is subjected to erosion due to the abrasive action of detrital material such as unconsolidated sand grains entrained in petroleum fluids as they enter the well. This problem is most often encountered in multiple-completed wells which produce fluids from two or more levels in a well. The -most common multiple-completed wells are those in which oil and/or gas is produced from two or more vertically spaced subterranean formations. Such formations may be separate lithologic units or they may be different zones of a common reservoir which are separated by relatively continuous strata of impermeable rock such as shale.

A conventional manner of dually producing such formations is to set and cement casing through both formations and then set a casing packer between the formations. A tubing string is extended through the packer with its lower open end landed adjacent the lower productive formation. The casing packer thus effectively seals off the lannular space between the tubing and casing and isolates the lower formation, which is in fluid communication with the interior of the tubing string, from the upper formation. The fluid from the lower formation thus flows through the tubing to the surface of the well or wellhead separately from the uid from the upper formation which is produced through perforations in the casing into the annulus between the casing and the tubing string. The uid from the upper formation flows to the wellhead either directly through the annulus or through an additional tubing string.

Another form of multiple-completed well is somewhat similar to that described above except that the fluids from the two or more formations involved are produced through the tubing string. In this arrangement, the tubing string normally extends past the upper formation and through a packer as described above. The tubing string is provided with a comminglng tool, normally positioned in the vicinity of the upper productive formation, which 3,460,626 Patented Aug. 12, 1969 ICC commingles the fluids from the upper and lower formations. The commingled uids then are withdrawn to the surface of the well through the tubing string.

In each of the above-described forms of multiplecompletions, a section of pipe, such as well tubing, eX- tends past a productive formation and thus is exposed to the produced subterranean fluid as it enters the well through perforations in the wall of the casing. The uid usually is under substantial pressure and passes from the productive formation through the restricted perforations in the casing at high velocities and in jetted iow courses. This particularly is true where the liuid being produced is comprised primarily of gas. Such uid often has a content of sand or other particulate detrital material which impinges against the pipe surface adjacent the perforations. Such detrital material entrained in the incoming fluid abrades and erodes the pipe surface, thus leading to pipe failure, and .also intensifying the corrosion of the pipe.

In the past, numerous conventional techniques have been employed in attempts to protect tubing surfaces and to prevent erosion thereof. Typically, these techniques involve the provision of so-called blast-zone protectors about the tubing adjacent the upper formation. Blast-zone protectors may be utilized in well installations providing for commingled production, such yas disclosed in U.S. Patent No. 3,283,570 to I. W. Hodges, or in well installations providing for separate production, such as disclosed in U.S. Patent No. 3,294,122 to L. G. Sharp. Such blast-zone protectors may take numerous forms. One means proposed for providing blast-zone protection involves wrapping of layers of lead around the tubing on the theory that a malleable material will absorb some of the kinetic energy and the detrital material more readily than the tubing itself. Alternatively, hard brittle materials, such as ceramics and glass, and resilient materials, such `as rubber, have been employed as protective materials for the tubing. While such techniques have met with some success, the resilient coatings usually vbeing the most effective, none of these techniques has proven entirely satisfactory.

One diiculty experienced with the heretofore proposed procedures resides in the fact that the materials used in forming the blast-zone protectors, even though they are sometimes more resistant to the abrasive action of the detrital materials than the metal pipe surfaces, still experience some erosion and ultimately fail; thus leaving the pipe surfaces exposed to the abrasive action of detrital materials as they enter the well. If this condition is undetected the exposed surfaces may fail under the erosive laction of such materials, sometimes within a matter of hours. This, of course, necessitates expensive workovers such as withdrawing the tubing, repairing it if necessary, and providing additional protective material. Another serious consequence of such failure is the placing of the respective formations directly in communication with one another through the well. In this case, production may be obtained only from the formation of relatively high pressure and fluid from the relatively high pressure formation may flow into the lower pressure formation. This latter situation may result in severe damage to the lower pressure formation and, in addition, the fluid may be lost through this formation to other wells.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a multiple-completion well installation and method in which downhole well equipment, such as a tubing string, need not be located within a blast-zone area where it is subject to erosion. The method of the invention is practiced in a well penetrating at least two vertically spaced subterranean formations in which the pressure of the lower formation is greater than the pressure of the upper formation. The well is open to the lower formation through a first production interval and to the upper formation through a second production interval which comprises a section of perforated casing. In carrying out the method of the invention, fluids from the lower and upper formations are produced into the well through the rst and second production intervals, respectively. As the fluid from the lower formation enters the well it is passed through a flow path within the well which extends from the first production interval to the second production interval. As the lower formation fluid is passed to the second production interval, the pressure of the lower formation fluid is reduced to a value less than the upper formation pressure. The lower formation fluid is commingled within the second production interval with the fluid from the upper formation by contacting this latter fluid as it flows into the well through the casing perforaions with the lower formation fluid. The commingled fluids then are withdrawn from the well.

In accordance with a preferred embodiment of the invention, there is provided a well installation which may be utilized in practicing the above-described method. This installation includes packing means disposed within the well to separate the upper and lower production intervals of the well. The packing means may be one or more conventional casing packers. A conduit extends upwardly through the packing means and terminates at a level below the top of the second or upper production interval. This conduit provides a passageway for the flow of fluid from the lower formation to the upper production interval. As the lower formation fluid flows into the second production interval, it is commingled with the fluid recovered from the upper formation. The conduit is provided with flow-restricting means which reduces the pressure of the lower formation fluid as it passes upwardly through the conduit.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE l is an illustration, partly in section, showing one embodiment of the present invention; and

FIGURE 2 is an illustration, partly in section, showing a modified embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGURE l, there is shown a wellbore which extends from the surface 11 of the earth and penetrates vertically spaced

subterranean formations

12 and 14. The well is provided with a casing 16 which is cemented as indicated by reference numeral 17. The casing and the surrounding cement sheath are provided opposite the formation 12 with a plurality of perforations 18 which define an upper production interval of the well, as indicated by bracket 19. In most instances, the production interval 19 will be formed by a plurality of circular perforations produced by a jet or gun perforating technique. It will be understood, however, that other suitable arrangements may be used. For example, the production interval 19 may be formed by so-called shop perforated or slotted pipe in which openings are formed prior to insertion of the casing into the well. Numerous other procedures for providing an opening in a well to the flow of subterranean fluids are well known to those skilled in the art and, accordingly, will not be described further.

A packer 21 is disposed in the well above the top of the upper production interval 19. The well also is provided with a tubing string 22 which extends from the wellhead 24 or surface of the well through the packer 21 to a level above the top of the upper production interval 19. Fluids from the upper formation 12 and, as explained hereinafter, from the lower formation 14 are produced through the interior of the tubing string 22 and carried to the surface of the well where they are passed into a suitable gathering line 25.

The casing 16 and surrounding cement 17 are provided opposite the lower formation 14 with a group of perforations 27 which define a lower production interval as indicated by bracket 28. The lower production interval may be formed by other means as will be apparent to those skilled in the art.

The production equipment thus far described is exemplary only and it is to be understood that other suitable arrangements consistent with the practice of the present invention may be used. For example, the packer 21 and tubing string 22 may be dispensed with and fluids may be produced to the surface of the well directly through the casing 16. Alternatively, tubing string 22 may not extend to the wellhead but instead may terminate within or above packer 21, in which case fluid will likewise be recovered or produced from the well through the casing 16. It usually will be preferred to exten-d tubing 22 to the surface as shown for reasons of well control and manipulation and also to avoid corrosion in the upper portions of the casing string.

It further is to be understood that, while only a single casing string 16 is shown, the well may be provided with a plurality of casing strings. For example, the well may be provided with a conductor pipe or surface string and one or more intermediate strings, as will be readily apparent to those skilled in the art. In addition, while the casing string 16 is shown as extending completely to the surface of the well it will be understood that other suitable arrangements may be used. For example, the perforated casing adjacent the formation 12 and/ or the formation 14 may take the form of a so-called scab liner. Such a liner or liners may occupy only selected portions of the well, such as

opposite formations

12 and 14, in which case remaining portions of the well may be uncased. Further, in certain circumstances such as where the formation 14 is not subject to sand problems, the lower completion interval may be an open hole. In this case, the casing string 16 may be set into the top of the formation 14 and cemented in the well, and the well then drilled deeper to provide an open hole completion. These and other completion procedures are well known to those skilled in the art and, accordingly, will not be discussed further.

As is known by those skilled in the art, the pressures of subterranean formations normally increase with their depths. For example, an oil and/or gas reservoir found at a depth of 5,000 feet typically may exhibit a pressure on the order of 2,000 p.s.i., whereas, a deeper underlying reservoir found at 10,000 feet may be expected to be at a pressure on the order of 4,000 p.s.i. In the method of the present invention, this normal order of pressure relationships is utilized to advantage in a method of recovering fluids through a multiple-completion well. Therefore, for the purpose of describing this method it will be assumed that the pressure of formation 14 shown in FIG- URE 1 is greater than the pressure of formation 12.

It will be recognized by those skilled in the art, that by reference to the pressure of a designated formation or by the term formation pressure, is meant the pressure of the formation adjacent the well under static conditions. This pressure may be determined for a given formation by conventional techniques. For example, the pressure of a formation in the vicinity of a well may be determined by a so-called pressure build-up test in which the well is shut in for such time as is necessary to establish a pressure equilibrium or near pressure equilibrium between the well and the formation. The static downhole pressure of the well when it is shut in with respect to the formation, i.e., when there is no fluid flow from the formation into the well, is, of course, substantially equivalent to the formation pressure.

It further will be recognized that the flow of fluids into the well depends upon an established differential between the pressure within the formation penetrated by the well and the downhole pressure within the well opposite the formation. The downhole pressure of the well at any given rate of production is designated as the operating pressure of the well for this production rate and formation. The operating pressure of the well for a designated formation may, of course, vary widely depending upon the conditions under which the well is operated.

Returning now to FIGURE 1, the well is provided with packing means which separates the upper and

lower production intervals

19 and 28, respectively. As shown in FIGURE 1, this packing means may take the form of a pair of

conventional casing packers

30 and 31. Extending through the

packers

30 and 31 is a conduit 32 which provides a passageway for the tlow of fluid recovered from the lower formation 14 upwardly to the upper production interval 19 of the well. The conduit 32 include, in addition to certain instrumentalities described hereinafter, a perforated section 33 which provides for the entry of the lower formation fluid into the conduit.

It will be recognized that considerable distance may separate

formations

12 and 14 and it usually will be desirable to utilize a plurality of packers as shown. This will aid in centering the conduit 32 within the well and also will prevent the casing between these packers from being contacted by well fluids, thus lessening corrosion problems within this area. However, the packing means may take another suitable form such as a single casing packer. Also, while the conduit 32 usually will comprise a tubing string, those skilled in the art will recognize that the conduit may comprise any suitable structure. For example, in appropriate circumstances the conduit may consist simply of the bore of a conventional packer.

As noted previously, the pressure of formation 14 is greater than the pressure of formation 12. By way of example, formation 12 may be a gas reservoir at a depth of 5,000 feet exhibiting a formation pressure of about 2,000 p.s.. and formation 14 may be a gas reservoir at a depth of about 10,000 feet and having a formation pressure of about 4,000 p.s.. In view of these pressure relationships the conduit 32 is provided with flow-restricting means in order to reduce the pressure of the lower formation fluid as `it passes from the lower production interval 28 of the well upwardly through the conduit 32 to the upper production interval 19. Desirably, the pressure of the lower formation fluid is reduced to a value such that it is approximately equal to the desired operating downhole pressure within the upper production interval 19. Thus, if it is desired to produce the formation 12 under a flowing pressure gradient from the formation to the well of 1,000 p.s.., such that the operating downhole pressure within the interval 19 is 1,000 p.s.., the flow of the lower formation lluid through the conduit 32 is restricted such that it exits from the conduit against a back pressure of about 1,000 p.s.. It is recognized that under practical operating conditions it may be diiiicult to achieve such a pressure reduction within closely defined limits of accuracy. However, the pressure of the lower formation fluid should at least be reduced to a value such that it enters the upper production interval against a back pressure less than the pressure of the formation 12, .e., 2,000 p.s.., in the cxample given above. If the pressure is not reduced to at least this level there exists the possibility of the uid from the lower formation flowing into the upper formation 12 with the attendant deleterious results noted above.

While the flowing pressure gradient from the formation 12 into the well may vary widely depending upon local conditions, it usually will be desirable to produce the formation 12 under a pressure gradient of at least 2000 p.s.. or of the formation pressure, whichever is greater. Therefore, it is preferred in carrying out the invention to reduce the pressure of the lower formation fluid to a value which is less than the pressure of formation 12 by at least the greater of 200 p.s.. and 10% of the pressure of formation 12.

IPressure reduction within the conduit 32 may be accomplished by means of any suitable flow-restricting de- 6 vice. Thus, as shown in FIGURE 1, the conduit 32 is provided with a conventional downhole choke 34. The size of the choke 34 may be selected in accordance with practices Well known to those skilled in the art in order to achieve the desired pressure gradient thereacross. The pressure reduction to be achieved across the choke 34 will, of course, depend upon the frictional losses occurring in ow from theY lower production interval upwardly through the conduit 32 to the choke 34. Thus, if a total pressure reduction of 2,500 p.s.. is desired between the upper and lower production intervals and the frictional losses in fluid flow upwardly through the conduit 32 result in a pressure gradient of p.s.., the choke should be chosen so as to achieve a pressure gradient thereacross of 2,400 p.s.. The conduit 32 is also provided with a check valve 35 in order to provide for unidirectional flow from the rst production interval to the second production interval. Thus, should the natural order of pressure relationships be reversed, the valve 35 will ensure that fluid will not ow from the upper production interval 19 to the lower production interval 28. In some instances the valve 35 will be unnecessary. The choke and check valve are mounted in a removable tool 36 which is threaded to the conduit 32 as indicated by reference numeral 37. It usually will be desirable to connect the tool 36 near or at the upper end of conduit 32 as shown in order to provide for simplicity of installation and withdrawal of this tool.

The elimination of tubing, a commingling tool or other like downhole well equipment from the blast-zone area opposite the perforations 18 greatly reduces the possibility of erosion of such equipment and makes unnecessary the provision of a vblast-zone protector for such equipment. In addition, by the present invention, such erosion as takes place within the upper production interval will usually prove to be beneficial. ln this: regard, detrital material entrained in the fluid entering the well through perforations 18 may tend to cause additional perforations in the casing. For example, fluid flowing through the lowermost perforation 18 may be of a velocity such that entrained detrital material will tend to erode the opposite wall of the casing at the area generally designated Iby reference numeral 18a, ultimately causing a perforation at this location. The presence of such additional perforations will increase the cross-sectional area open to the flow of fluid from the formation with the attendant result that the entrained detrital material from the formation 12 will enter the Well at a reduced velocity. This diminishes the ibrasive action of the entrained detrital material and may allow the subsequent location of downhole equipment within the blast-zone area, if this should become desirable. For example, after the formation of one or more additional perforations as described above, the abrasive action may be reduced such that a tubing string may be extended through interval 19 in the event it becomes desirable to produce

formations

12 and 14 separately.

If the formation 12 is a gas reservoir, and if the perforations 18 are equally open to fluid flow, gas normally will enter through each of these at substantially the same velocity. However, in some cases, the fluid ilowing through the lower perforations of the production interval 19 may -be at a relatively low velocity as compared with fluid issuing through the perforations in the upper portion of the production interval 19. This condition may exist, for example, where formation I12 is an oil and gas reservoir with gas production primarily through the upper perforations and oil production primarily through the lower perforations. As will be understood by those skilled in the art, the oil normally will enter through at a relatively low velocity with a resultant low erosion potential. Also, even though formation 12 is primarily a gas reservoir, the flow velocity through the lower perforations may be relatively low because of localized permeability dissimilarities in the formation adjacent the well. For example, the permeability of the formation 12 7 adjacent the lower perforations may be low due to a tight rock structure or to localized damage to the formation as may occur during completion of the well.

In View of the above discussion, it will be recognized that the location of the upper end of conduit 32 may vary depending upon the local conditions. Usually it will be preferred to terminate the conduit 32 at a point below the bottom of the production interval 19 as shown. However, in some instances it will be possible to extend the conduit 32 partially into the upper production interval 19 without serious erosion problems. In any case, the conduit32 should terminate below the top of the upper production interval 19.

It usually will be desired to monitor either continuously or intermittently the production rate from the formation 14 and also the bottornhole pressure at the lower production interval 28. While, as described hereinafter, such measurements can be taken through the use of suitable wireline tools, it sometimes may be desirable to make these measurements at frequent intervals and/or over extended periods of time. In such situations, it is preferred to maintain the necessary measuring tools in the well during normal operations. A preferred installation for accomplishing this objective is shown in FIG- URE l.

With further reference to FIGURE 1, the tubing 32 is provided with a flow measuring device 38 and a pressure measuring device 42. The measuring

devices

38 and 42 may be of conventional design and may be provided with suitable communication channels for telemetering the desired information to the surface. Alternatively, the

devices

38 and 42 may include recording means which may be withdrawn from the well as desired. The pressure measuring device should be located below the flow-restricting means 34 as shown in order that it may be responsive to the downhole pressure at the lower production interval. It usually will .be desirable to similarly locate the flow meter 38 although this latter device may under appropriate circumstances be located at any position within the flow path from the lower production interval to the upper production interval.

The total flow from the well may be measured at the wellhead by conventional practice. Thus, it can be seen that knowing the production rate of the lower formation 14, the production rate from the upper formation 12 can be determined.

As noted previously, the bottornhole pressure at the upper production interval 19 should, during normal operation of the well, be maintained at some desired value less than the pressure of the formation 12. An increase in the `bottornhole pressure will result in a lower production rate from the formation 12, and, of course, a bottomhole pressure in excess of the formation pressure will result in iluid ilow from the well into the formation with possible deleterious effects. Such a pressure increase at interval 19 may be due to factors such as shutting in or throttling of the well at the wellhead or a rise in the production rate from the lower formation 14.

With reference to FIGURE 2, there is shown a modied form of the invention in which the flow-restricting device is adjustable and responsive to pressure changes in the upper production interval 19. Also, in the embodiment of FIGURE 2, the packing means separating the upper and lower production intervals and the conduit providing a ow path are fonmed as a single unit. The installation shown in FIGURE 2 is otherwise somewhat similar to that illustrated in FIGURE l and like elements in FIGURE 2 are designated by the same reference numerals as used in FIGURE 1.

In the embodiment of FIGURE 2, the well is cased adjacent the lower formation 14 by means of a liner 40. The liner 40 is cemented in place and the liner and the surrounding cement sheath 42 are provided with a plurality of perforations 44. The perforations 44 dene a lower production interval 46 in the well, similar to 8 the production interval 28 described above with reference to FIGURE 1. The packing means separating the upper and lower formations takes the form of an annular plate 48 which is formed integrally with the liner 42. Extending through the packing element 48 is a conduit 50 similar in function to the conduit 32 in FIGURE l. This liner, packing element, and conduit installation may be utilized in those instances where it is not desired to case the entire interval of the well between the upper and lower formations. This embodiment oers certain advantages in that the complete downhole installation including the liner, packing element and conduit may be run into place within the well as a single unit and in a single operation.

The conduit 50 is provided with a dow-restricting means which is responsive to pressure changes in the upper production interval 19. More specifically, there is provided an adjustable flow-restricting device 54 and means responsive to an increase in pressure within the upper production interval 19 for decreasing the rate of flow of the lower formation iluid through the conduit 50. The flow-restricting device 54 is connected in the tubing 50 by means of a threaded coupling 55. Thus, the device 54 may be withdrawn or run into place by suitable wireline techniques. The device S4 comprises a valve member 56 which has an upper face 57 and which is slidably mounted within an outer case 58. The valve member is biased away from a valve seat 59 by means of a compression spring 60 which is interposed between appropriate shoulders on the valve member and the case as shown. Upward movement of the valve member is limited by means of a stop element 61 on the outer case.

When the valve 56 is open as shown, fluid from the lower formation travels upwardly through the conduit 50, through passages 62, and thence through the throat 64 of the valve member. The compression in the spring 60 and the surface area of face 57 are balanced such that the valve remains in an open position under the desired back pressure within the upper production interval 19. From an examination of FIGURE 2, it can be seen that an increase in pressure within interval 19 above the desired level will cause the valve member 56 to move downwardly, thus throttling further the fluid ow through the restricting means until it reaches a value consistent with the pressure desired in interval 19. Of course, should this pressure then decrease, the valve member will open somewhat thus increasing the flow rate of the lower formation fluid as necessary.

It will be noted that the modification of FIGURE 2 does not include downhole devices for measuring flow rate or pressure. Such production measurements may be accomplished in this embodiment through the application of suitable wireline techniques. For example, a downhole tlow meter such as that described in Godbey, I. K., New Flowmeter Gives Water-Injection Profiles, The Oil and Gas Journal, Mar. l2, 1962, pp. 92-95, may be lowered to a position below interval 19 and the ilow rate from formation 14 measured. The flow rate of upper formation 12 then may be determined from total production rate measurements taken at the surface of the well. Alternatively, the production rates from

formations

12 and 14 may be determined by measuring the flow from the well with both formations producing and also with formation 14 shut in. It will be recognized that downhole pressure measurements also may be taken through the use of suitable wireline tools.

As is known to those skilled in the art, the erosion of a surface by abrasive particles depends upon factors such as the velocity and quantity of the particles, and also their size, shape and hardness. Of these, the Velocity of the particles as they strike the surface usually is the single most important factor. While erosion and ultimate failure of well tubing may occur at low velocities depending upon local conditions, experience has shown that in most wells, blast-zone erosion becomes significant at particle velocities of about 20 feet per second. While blast-zone protectors such as those noted above afford a measure of protection, these oftentimes are readily susceptible to erosion at the higher particle velocities, particularly those on the order of 200 feet per second and above. Accordingly, while the invention may be utilized under any conditions in which the iluid from an upper formation has entrained therein sand or other detrital material, it is particularly useful where particle velocities are at least 20 feet per second, and especially so where particle velocities are at least 200 feet per second.

Having described certain specific embodiments of the instant invention, it will be understood that further modifications thereof may be suggested to those skilled in the art, and it is intended to cover all such modifications as fall within the scope of the appended claims.

What is claimed is:

1. In the recovery of fluids through a well penetrating at least two vertically `spaced upper and lower subterranean formations, the pressure of said lower formation being greater than the pressure of said upper formation, said well being open to said lower formation through a lower production interval and to said upper formation through an upper production interval comprising a section of perforated casing, the method comprising:

producing fluid from said lower formation into said well through said lower production interval, producing iluid from said upper formation into said well through said upper production interval whereby said fluid flows into the interior of said section of casing through perforations therein, said fluid having entrained therein abrasive detrital material, flowing said lower formation fluid through a flow path within said well from said lower production interval to said upper production interval,

within said ilow path, reducing the pressure of said lower formation iluid to a value less than the pressure of said upper formation,

commingling said lower formation lluid with said upper formation iluicl by contacting said upper formation fluid as it flows into the interior of said section of casing through the perforations therein with said lower formation fluid, and

withdrawing said commingled iluids from said well.

2. The method of claim 1 wherein the pressure of said lower formation fluid is reduced within said flow path to a value which is lower than the pressure of said upper formation by at least the greater of 200 p.s.i. and of the pressure of said upper formation.

3. The method of claim 1 wherein detrital material entrained in the lluid from said upper formation enters into the interior of said casing at a velocity of at least feet per second.

4. The method of claim 1 wherein detrital material entrained in the iluid from said upper formation enters into the interior of said casing at a velocity of at least .200 feet per second.

5. The method of claim 1 wherein detrital material entrained in the iluid from said upper formation erodes at least one additional perforation in said section of casing and further comprising the step of, subsequent to the eroding of said additional perforation, locating downhole equipment within said upper production interval.

6. In a well penetrating at least two vertically spaced upper and lower formations, said well being open to said lower formation through a lower production interval and to said upper formation through an upper production interval comprising a section of perforated casing, the combination comprising:

packing means within said Well separating said upper and lower production intervals,

a conduit extending through said packing means and terminating at a level below the top of said upper production interval and opening into the interior of said casing, said conduit providing a passageway for the flow of fluid recovered from said lower formation to said upper production interval within which said lower formation fluid is commingled with fluid recovered from said upper formation,

adjustable ilow restricting means within said conduit for reducing the pressure of the lower formation fluid as it passes through said conduit, and

means responsive to an increase :in pressure within said well above said packing means for adjusting said restricting means for decreased iluid flow through said conduit.

7. In a well penetrating at least two vertically spaced upper and lower formations, said well being open to said lower formation through a lower production interval and to said upper formation through an upper production interval comprising a section of perforated casing, the combination comprising:

a conduit extending through said packing means and terminating at a level below the top of said upper production interval and opening into the interior of said casing, said conduit providing a passageway for the ilow of fluid recovered from said lower formation to said upper production interval within which said lower formation lluid is commingled with lluid recovered from said upper formation,

flow restricting means within said conduit for reducing the pressure of the lower formation fluid as it passes through said conduit, and

a check valve in said conduit allowing unidirectional ilow from said lower production interval to said upper production interval.

8. In a well penetrating at least. two vertically spaced upper and lower formations, said well being open to said lower formation through a lower production interval and to said upper formation through an upper production interval comprising a section of perforated casing, the combination comprising:

packing means within said well separating said upper and lower production intervals a conduit extending through said packing means and terminating at a level below the top of said upper production interval and opening into the interior of said casing, said conduit providing a passageway for the ilow of fluid recovered from said lower formation to said upper production interval within which said lower formation fluid is commingled with fluid recovered from said upper formation,

flow restricting means within said conduit for reducing the pressure of the lower formation iluid as it passes through said conduit, and

pressure measuring means within said passageway and located below said ilow restricting means.

9. The combination of claim 8 further comprising flow measuring means within said passageway.

References Cited UNITED STATES PATENTS Re. 26,319 12/1967 Tamplen 166-115 2,371,840 3/1945 Otis 166-45 X 2,531,258 1l/1950 Cranll 166-116 2,649,914 8/1953. Otis 166-114 2,839,144 6/1958 Ault 166-224 X 2,869,645 l/l959 Chamberlain et al. 166-115 X 3,171,483 3/1965 Fredd 166-114 X 3,283,570 11/1966 Hodges 166--45 X 3,357,492 12/1967 Hubby 166-45 X 3,371,717 3/1968 Chenoweth 166--148 X CHARLES E. OCONNELL, Primary Examiner IAN A. CALVERT, Assistant Examiner U.S. Cl. X.R. 166-115, 133, 224

ggo UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3:"6O626 Dated u August l2, 1969 Inventor(s) Henry I.. Ehrlich It :ls certified that error appears in the aboveidentifed patent and that said Letters Patent are hereby corrected as shown below:

|- Column l, line lbf, "multple-i-completed" should read"` multplycompleted; line 39, "multiple-Completed" Should read --multiply-completed--g line Lil, "multiple-completed" Should read multiplycompletedg line 65, "multiple-completed" should read multply-completed Column i?, line 3M, "and should read Of Column F3, line l5, "include" should read --ncludes--g line g, "QOOO" should read -200 COlUmU 6, 1H@ "brasive" should read -abrasive.

Column lO, line 72, "JAN" Should read -IAN SIGNED N'D SEALED A APR 7 4970 (SF-m Amm:

i WmIAll E. 'SCHUH-IER, JR.. EA'cl MOHM It cmissionefr `of Iabents