US2704979A

US2704979A - Control of paraffin deposition

Info

Publication number: US2704979A
Application number: US176378A
Authority: US
Inventors: Gerrit Van Willigen
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1950-07-28
Filing date: 1950-07-28
Publication date: 1955-03-29
Anticipated expiration: 1972-03-29

Description

March 29, 1955 e. VAN WILLIGEN CONTROL OF PARAFFIN DEPOSITION Filed July 28, 1950 8 6 Z R I 2 7M 3 M 20 I PRODUCING ZONE.

INVENTOR GERRIT VAN wuueau BY: k

HIS ATTORNEY United States Patent '0 CONTROL OF PARAFFIN DEPOSITION Geri-it Van Willigen, The Hague, Netherlands, assignor to Shell Development Company, San Francisco, Cal1f., a corporation of Delaware Application July 28, 1950, Serial No. 176,378

3 Claims. (Cl. 103-1) This invention relates to the control of paraflin deposition in a well from which a paraflin-containing 0111s being pumped, and pertains more particularly to a method and apparatus for preventing deposition of paraflin on a string of sucker rods being employed to actuate a well pump.

In producing wells the oil is usually lifted to the surface through a tubing string having at its bottom end a pump, generally a plunger-type pump, which is rec1procated from the surface by a string of sucker rods moving up and down inside the tubing.

If the oil to be lifted is viscous, the sucker rods will encounter considerable resistance in their up-and-down, motion, which resistance will in particular limit the speed of the downward stroke of the rods and plunger and, consequently, the pumping rate. With a paraffin-base oil, paraflin may be depositedon the string of rods, and also on the inner side of the tubing string. This results in a diminution of the annular space between rods and tubing, i. e. of the passage through which the oil is lifted, so that, since the pump stroke and consequently the quantity of oil displaced are constant, the rate of flow increases. a result the flow resistance also increases, which lIl turn creates a demand for more energy from the engine which reciprocates the string of sucker rods. As a matter of fact, paraffin deposits call for frequent cleaning of the tubing and sucker rod strings, which operation involves considerable loss of time and expense.

It is therefore a primary object of the present invention to provide a method and means for controlling the deposition of paraffin on the producing equipment within a well and for preventing the accumulation of paraflin on the string of sucker rods being used to operate the well pump.

It is also an object of this invention to provide a method and an apparatus for the removal of accumulated paraffin deposits from well equipment by the circulation of a paralfin solvent through the producing equipment.

Additional objects and advantages will become apparent from a study of the following description when considered in conjunction with the accompanying drawing, wherein the single figure gives a longitudinal view, partly in cross section, of the producing equipment employed in a well being produced by a reciprocating pump.

Referring to the drawing, a well borehole is shown lined with a string of casing 11 which is closed at the top by a conventional casing head 12. Depending from the casing head 12 within the casing 11 are two concentric strings of tubing which will be hereinafter identified as the outer tubing string 13 and the inner tubing string 14. The inner tubing 14 normally extends to the bottom of the well or to a point substantially adjacent the producing zone of the Well.

A conventional plunger pump 15 is anchored in the inner tubing 14 in a manner well known to the art, said pump 15 being preferably anchored at the level of the producing zone. At this point the inside of the casing 11 is in communication with the space outside thereof through a series of perforations 16 in said casing. The pump is actuated by a string of sucker rods 17 extending up through the inner tubing 14 and passing in a fluidtight manner through the casing head 12, where said sucker rod string is reciprocated by suitable prime mover means (not shown) located at the surface.

At the surface the casing head 12 is provided with suitable conduit means for introducing or discharging fluids from the well. Thus, the inner tubing string is provided with an outlet conduit 18, the annular space 19 between the outer and

inner tubings

13 and 14 is equipped with

discharge conduits

20 and 21, and the annular space 22 between the casing 11 and the outer tubing 13 may be provided with a conduit 23. The flow of fluids through

conduits

18, 20, 21 and 23 is controlled by

valves

24, 25, 26 and 27.

The length of the outer tubing string 13 may vary and depends upon such well characteristics as well depth, well temperature, composition of the oil being pumped, paraffin content of the oil, etc. In general, the outer tubing 13 extends from the casing head 12 down to the lowest point in the well at which paraflin is known to accumulate on the inner surface of the inner tubing string 14.

A fluidtight seal is formed between the bottom of the outer tubing 13 and the outer wall of the inner tubing 14 in any suitable manner well known to the art. For example, a conventional packer can be employed or an annular plate may be welded in place. In the latter case it would be necessary to insert or pull both strings of

tubing

13 and 14 from the well together. To obviate the necessity of pulling the outer tubing 13 when a pump is being replaced, the lower end of the outer tubing 13 is preferably provided with a shoe 28 having an internal seating face 30 of an annular ring 31 carried on the outer surface of the inner tubing 14. When the seating faces 29 and 30 are in engagement a fluidtight seal is formed between the lower end of the outer tubing 13 and the outer wall of the inner tubing 14.

The inner tubing string 14 is provided with fluid ports or perforations 32 in communication between the bore of the inner tubing and the annular space 19 between the

tubings

13 and 14 above the ring 31. In operation, the inner tubing 14 may be filled with a gas or a stagnant liquid, said fluid being introduced through conduit 18. Thus, a considerable length of the reciprocating sucker rods 17, which actuate the pump 15, move in the inner tubing 14 filled with gas or stagnant liquid so that they encounter considerably less resistance than if they had to move in the oil being pumped, especially if this oil is viscous.

The oil from the formation flows into the casing 11 through perforations 16 and thence into the pump 15. The reciprocating pump 15 then lifts the fluid up the inner tubing 14 until it reaches the slots 32 at which point the fluid flows into the annular space 19 between the inner and

outer tubings

14 and 13 and is lifted therein to the head of the well where it is discharged through

conduit

20 or 21. Owing to the fact that the annular passage 19 is considerably larger than the bore of the inner tubing 14, paraflin deposits which are formed in this annular passage 19 on the outer surface of the inner tubing 14 or on the inner surface of the outer tubing 13 cause much less trouble than when the well is produced through a single tubing.

Since the outer tubing 13 extends below the point at which paraflin deposits are formed, no paraflin becomes deposited on the inner surface of the inner tubing 14 or on the sucker rods 17. Below the perforations 32 the temperature of the oil is sufficiently high to prevent depositions of paraflin, while above the perforations the gas or stagnant liquid prevents deposition by preventing the rise of oil to any considerable height above said perforations. As a result, less energy is required by the prime mover to reciprocate the pump and, hence, the rate of pumping may be increased. in addition, the arrangement according to this invention has the advantage that, when the tubing string has to be cleaned, a cleansing medium, for instance steam, hot oil, hot water, etc., can be injected into the inner tubing 14, to emerge again through the annular space between inner and outer tubing 19, thus freeing this annular space from parafiin. This treat-. ment can therefore be carried out without having to pull the system of pump and rods to the surface. It is also possible to separate a portion of the lifted oil, to heat this portion in a heat-exchanger, and then to inject it into the inner tubing 14. This hot oil is then lifted again, together with the oil delivered by the pump, through the annular space 19, so that the production process need not be interrupted. The path of the heated oil can also be reversed, whereby the mixture of hot oil and oil delivered by the pump is lifted) through the inner tubing 14.

It is not necessary, as a rule, to install a double tubing over the whole length of the tubing string, since, especially in the case of deep wells, owing to the high temperatures which prevail at greater depths, the fluidity of the oil is greater, so that it does not offer such great resistance as when it is more viscous; nor will paraffin be deposited at elevated temperature as long as this temperature lies above the setting point. Consequently, the double tubing need only be installed to a depth at which the temperature is such as to cause the above-mentioned difliculties. The double tubing arrangement is also extremely suitable for the injection of chemicals, which are very often applied to prevent formation of emulsion and paratfin deposits, in the same way as described above with reference to a cleansing medium. In this case it is often advisable that the double tubing extends down to very near the ump.

p If a liquid, such as hot oil, hot water, or a solution of chemicals or paraflin solvents, is to be circulated with the oil for cleaning the

tubing strings

13 and 14, the liquid may be injected through conduit 18. This liquid is passed down the inner tubing 14, through slots 32 together with the oil being delivered by the pump 15, and up the annular space 19 to be discharged at the well head through conduit 21. It is to be noted that only a relatively small amount of a solvent is needed with the present apparatus as it is confined to the portion of the

tubing strings

13 and 14 in which the paraflin deposits occur and at no time comes in contact with the producing formation. The cleaning liquid can also be circulated in the reverse direction in the present apparatus by injecting the liquid through conduit 20 into the annular space 19 and flowing it through perforations 32 and up the bore of the inner tubing 14 along with oil to be discharged through conduit 18.

I claim as my invention:

1. An apparatus for producing an oil well, comprising a first tubing string extending from the surface of the ground to the oil producing reservoir, a second tubing string of larger diameter surrounding said first tubing string in spaced relationship therewith and extending into the well to a depth below that of the zone in which substantial quantities of paraflin are deposited from the well fluid, said second string being shorter than said first string, closure means within the lower end of said second tubing string for closing the annular space between said first and second tubing strings, fluid discharge port means through the wall of said second tubing string near the upper end thereof, fluid port means through the wall of said first tubing above said closure means, pump means carried at the lower end of said first tubing string, a string of sucker rods secured to the pump means and extending to the surface within said first tubing string for reciprocating said pump means, means at the surface closing the annular space between the first and the second strings, and means for supplying to said first string a fluid at a pressure sufiicient to prevent the oil from rising within said first string to a level appreciably higher than that of said fluid port means when said pump means is operated.

2. An apparatus for producing an oil well, comprising a first tubing string extending from the surface of the ground to the oil producing reservoir, a second tubing string of larger diameter surrounding said first tubing string in spaced relationship therewith and extending into the well to a depth below that of the zone in which substantial quantities of paraffin are deposited from the well fluid, said second string being shorter than said first string, a first annular member secured to the inner wall of said second tubing string, a second annular member carried outwardly on said first tubing string adapted to coact with said first annular member to close the annular space between said first and second tubing strings, fluid discharge port means through the wall of said second tubing string near the upper end thereof, a plurality of fluid ports through the wall of said first tubing above said annular members, pump means carried at the lower end of said first tubing string, a string of sucker rods secured to the pump means and extending to the surface within said first tubing string for reciprocating said pump, means at the surface closing the annular space between the first and the second strings, and means for supplying to said first string a fluid at a pressure suflicient to prevent the oil from rising within said first string to a level appreciably higher than that of said ports when said pump means is operated.

3. An apparatus for producing an oil well, comprising a first tubing string extending from the surface of the ground to the oil producing reservoir, a second tubing string of larger diameter surrounding said first tubing string in spaced relationship therewith and extending into the well to a depth below that of the zone in which substantial quantities of paraflin are deposited from the well fluid, said second string being shorter than said first string, closure means within the lower end of said second tubing string for closing the annular space between said first and second tubing strings, fluid discharge port means through the wall of said second tubing string near the upper end thereof, fluid port means through the wall of said first tubing string above said closure means, top closure means closing the top of said first tubing string to form a fluidtight chamber in said first tubing string above said fluid port means therein, said first tubing string being adapted to be filled with a stagnant fluid, normally-closed port means through the wall of said first tubing string for introducing said fluid, pump means carried at the lower end of said first tubing string, and a string of sucker rods secured to the pump means and extending to the surface within said first tubing string for reciprocating said pump means.

References Cited in the file of this patent UNITED STATES PATENTS 1,012,777 Wigle Dec. 26, 1911 2,020,550 Herrick Nov. 12, 1935 2,083,799 Roberts June 15, 1937 2,368,777 Price Feb. 6, 1945 2,394,189 Kaufman Feb. 5, 1946

Claims

1. AN APPARATUS FOR PRODUCING AN OIL WELL, COMPRISING A FIRST TUBING STRING EXTENDING FROM THE SURFACE OF THE GROUND TO THE OIL PRODUCING RESERVOIR, A SECOND TUBING STRING OF LARGER DIAMETER SURROUNDING SAID FIRST TUBING STRING IN SPACED RELATIONSHIP THEREWITH AND EXTENDING INTO XXLE WELL TO A DEPTH BELOW THAT OF THE ZONE IN WHICH SUBXXANTIAL QUANTITIES OF PARAFFIN ARE DEPOSITED FROM THE WELL CLOSURE MEANS WITHIN THE LOWER END OF SAID SECOND TUBING STRING FOR CLOSING THE ANNULAR SPACE BETWEEN SAID FIRST AND SECOND TUBING STRINGS, FLUID DISCHARGE PORT MEANS THROUGH THE WALL OF SAID SECOND TUBING STRING NEAR THE UPPER END THEREOF, FLUID PORT MEANS THROUGH THE WALL OF SAID FIRST TUBING ABOVE SAID CLOSURE MEANS, PUMP MEANS CARRIED AT THE LOWER END OF SAID FIRST TUBING STRING, A STRING OF SUCKER RODS SECURED TO THE PUMP MEANS AND EXTENDING TO THE SURFACE WITHIN FIRST TUBING STRING FOR RECIPROCATING SAID PUMP MEANS, MEANS AT THE SURFACE CLOSING THE ANNULAR SPACE BETWEEN THE FIRST AND THE SECOND STRINGS, AND MEANS CIENT TO PREVENT THE OIL FROM RISING WITHIN SAID FIRST STRING TO A LEVEL APPRECIABLY HIGHER THAN THAT OF SAID FLUID PORT MEANS WHEN SAID PUMP MEANS IS OPERATED.