US2300348A - Method for cleaning oil wells - Google Patents

Description

F. E. DANA METHOD FOR CLEANING OIL WELLS Filed April 21, 1941 Oct. 27, 1942.

lll IIIIIIIIIIII Patented Oct'. 27, -194.2

lUNITED STATES PATENT OFFICE METHOD FOR CLEANING OIL WELLS f l Frank E. Dana, Kilgore, Tex. Appllcatn April 21, 1941, Serial N0. 389,639

(Cl. 16S- 23) 4 Claims.

This invention relates to a method for cleaning oil wells, and more particularly, for removing parafiin depositedfon the inside of the tubing or oil discharge pipe and outside of sucker rods. As is Well known to those skilled in the art, considerable diniculty is encountered in the operation of oil wells by reason or the accumulation on the inside of the tubing and on the outside of the sucker rods of deposits of paraffin. In the coursel of the normal pumping operation, a point is reached, sooner or later, when the obstruction caused by these deposits is such, that the well has to be shut down and the paraiiin deposits cleared away. Obviously, this occasions loss of production time, which is particularly serious in the case of some of the paraffin removing systems previously employed. 'Ihat is, the procedure in the case of some of the cleaning operations required the removal of the sucker' rods from the tubing, which is necessarily a slow operation. Also, other cleaning systems hitherto proposed involved the use of additional equipment, some oi which had to be installed or introduced into the well proper, thus again involving considerable expense and loss of time. A further disadvantage of parafiin removing system using a solvent medium, resided in the fact that, the solution of paraiin in the solvent medium, resulting from the cleaning operation, was permitted to escape into the well proper. thus eventually leading to the obstruction of the producing sands and to a reduced output.

The paramn removing system forming the object of the present invention has been devised with a view of eliminating the drawbacks of the prior methods. By means of the present invention, wells can be cleared of their paraiiin deposits in a rapid and inexpensive manner, with a minimum loss of production time, utilizing the tubing already installed in the well and the associated pumping equipment. As will appear below, the structure of the well tubing and related equipment is rendered instantly available for the deparafiining operation by including in the original well tubing a simple and inexpensive release valve, which thereafter forms a permanent part of the'installation.

In order that my invention may be clearly understood, it should be pointed out that parain usually deposits in well tubing al1 the way from the top of the well to a depth of 1000 to 2000 feet, depending upon the characteristics of the oil eld. In the practice of my invention, a spring controlled release valve is installed in the tubing of the well at a point which is approximately 1000 feet beneath the lowermost paraflin deposit. The vprocedure in cleaning a well is briefly as follows: The well pump is shut off and hot oil or equivalent paraln melting or solvent medium is forced down through the top of the tubing in quantity suiiicient to displace all of the cold oil in the tubing which is present therein above the release valve. The oil is forced down at such a pressure, that the release valve is opened and the cold oil is discharged into the annular space between the tubing and casing and down into the bottom of the well. Inasmuch as substantially cold oil only is discharged into the casing, there is no danger of any appreciable quantity of paraln reaching the lower end thereof and, hence, the oil strata. When all of the cold oil above the release valve has been discharged into the casing, as stated above, the introduction of hot oil, or other deparafiining fluid, into the tubing is discontinued, the release valve closes automatically and the hot oil is permitted to stand in the tubing for a length of time suilicient to melt the accumulated paraflln oli` the tubing and the sucker rods. At the end of this period, the usual well pump is set in operation,

and the solution or mixture of molten parailinl in oil is pumped out of the tubing through the top thereof and is discharged into any suitable receiver.

It will be seen, therefore, that my method does not involve pulling of the tubing, the use of additional equipment or the continuous circulation of cleaning media, 'all of which are attended by loss of time and expense. My procedure simply involves a method wherein a deparafning iluid is introduced through the top of the tubing in quantity suflicient to form in the tubing a column of deparaiilning iluid considerably more extensive than the region in the tubing in which the paraflin accumulations occur; the oil displaced by the deparanining uid column is discharged from the tubing at a point considerably below the lowermost region of parallin deposits. When all such oil has been discharged from the tubing the introduction of the deparaflining fluid is discontinued, and the'fluid remains in the tubing until the accumulated paramn has 4become displaced from the tubing wall and dispersed in the column of deparaffining iiuid, whereupon the uid with its parain content is discharged through the top of the tubing.

The invention will be described in greater detail by reference to the annexed drawing in which,

Figure 1 is a diagrammatic representation oi a control valve 24.

i this invention, it is to Ibe understood, that various deparaining media or uids may be utilized and, therefore, I shall describe the invention in connection with the use of hot oil, which is an inexpensive and convenient deparaining material. In lieu of hot oil, fluids having a solvent action or eiecting removal of paraffin from the tubing wall by chemical action may be employed.

Referring to the drawing, I designates portions of a well casing inside of which is arranged in the usual manner the tubing or discharge pipe 2. Inside the tubing, the sucker rods 3 are reciprocated in the usual manner by the pumping jack 4, thus operating the pump 5, and lifting to the surface the oil which is discharged to storage through the line 6 controlled by the valve 1.

The coupling member 8, carrying the release valve, generally designated as 9, is installed in the tubing at a point which is approximately about 1000 feet lower than the lowest known or estimated deposit of parailln in the tubing. Referring more particularly to Figure 2: The coupling member is connected to the tubing in any suitable manner, as .by threaded joints. On one side thereof it is provided with the housing I3 for the ball valve I and the spring I4, which normally retains the valve against its seat I6. The valve housing is connected to the coupling members by means of passage I8, which is suitably dimensioned to permit the desired volume of flow past the ball valve I5. At its lower end, this housing is suitably closed o bythe threaded plug I9 which likewise serves to'adiust the compression of the spring I4. The overall width of the coupling member is such, as to permit its ready insertion inside of the casing and, in order to prevent the housing from hanging on obstructions while going in or coming out of the casing, the top and bottom ends thereof are suitably rounded off as at I2. 'I'he coupling member and its associated parts are made of materials which are suitable to withstand the particular conditions existing in the well where the device is installed. Further, while Figure 2 shows the valve housing as a separate unit and attached to the coupling member, as .by welding, it is obvious that the housing assembly can be made integral with the coupling member.

The equipment necessary for the paraflin removing operation is completed by the provision of a portable heating unit, comprising a boiler 2I and a heat exchanger 21, connected by a hose 22, to a bleeder pipe 23 which joins onto the main oil discharge line 1 to the storage tank through A high pressure pump 25 is provided to take the fluid to Ibe used in the cleaning operation-generally oilfrom a storage tank A23 and force it through the heater 21.

In practicing the invention, when it becomes necessary to clean well tubing of parailin, the well pump is stopped and the valve 1 connecting the tubing to the storage tank is closed off. The portable heating unit and high pressure pump are now brought up to the well and the4 heater is connected to the bleeder pipe 23; the valve 24 in 75 this pipeisiopened and the high pressure pump is started to force iluid-oil-from the storage tank thrcugh the heater 21 and then down into the tubing through the top thereof. As the hot oil is forced in through the top, the pressure applied by the pump to the oil together with weight of the column of oil in the tubing above the release valve will overcome the force of the spring I4, normally retaining the valve I5 against its seat, the compression of the spring having been originally adjusted with due regard 'to the height of the column and the pump pressure. When the release valve opens, cold oil will 4be discharged through the outlet 30 to the annular space between the tubing and casing, eventually reaching the bottom of the well. As mentioned before, Athe release valve is installed a considerable distance beneath the lowermost parailln deposit area, and only sufllcient hot oil is injected into the tubing to'substantially replace the`cold oil above the release valve, but no more. This is an important point and, inasmuch as the volume of the cold oil in the tubing above the release valve can readily be calculated, it is therefore feasible to avoid the injection of a quantity of hot oil greater than that necessary to replace such volume. The displacement of the cold oil above the release valve leads to two important results: First, the oil discharged into the casing through the release valve, consists of cold oil only, is free of any increase in paralln content, so that the return of such oil underground will not occa.- sion' any further dilculty .by reason of clogging of the production sands. Second, the large volume of hot oil introduced into the tubing, ex? tending as it does over a region appreciably greater than the paraiiln deposit area and enhanced by the increased capacity of the clean tubing in the last thousand feet thereof, will facilitate the rapid melting and removal of the parailin deposits, by reason of the large quantity of heat contained in the injected hot oil.

Since the amount of paraiiin that is deposited in the tubing varies in different oil elds, it is not possible to stat`e precisely the amount of hot oil that is to be used in all cases. The amount of oil which is to be displaced by the in jected hot oil and which is to be estimated, will depend on length of tubing, tubing size, sucker rod size and volume in cubic inches or gallons of paraffin to be melted. The paraflin volume is estimated from past cleaning operations. A factor which is also to be taken into consideration in the selection of the particular equipment to be used in carrying out my invention, is the resistance offered to the injection of hot oil by reason of the obstruction to ow created by the paraflin deposits. The particular equipment which is used in my operations is capable of injecting 2 to 20 barrels of oil per hour, at any temperature deemed necessary from F. to 500 F.

As the piston of hot oil is forced down by the high pressure pump, forcing the cold oil ahead of it and out through the release valve, the paraffin deposits start to melt and become intimately mixed with the oil through the entire length of the heated oil column. When the desired quantity of hot oil has been introduced into the tubing, valve 1 is opened and a sufficient volume of hot oil is injected in flow line or pipe 6, to clean this line to storage. Tile injection of the hot oil by the high pressure pump is then discontinued and valve 24 is closed. Usually, the accumulated paraffin has during the injection period become dislodged, molten, and distributed in the injected hot-oil; the well pump is therefore immediately put back in operation to discharge the hot oil in solution through the top of the tubing and line 6 to any suitable point. The cleaning operation described herein, not only removes the paraflin from the inside of the tubing and oi the sucker rods, but also cleans the tank line 6 of parain deposits.

In this connection, it should be pointed out that the parain to be removed is a constituent of paraiiin base crude oils; the percentage of paraffin content varies in differentdistricts, but is known to vary in content from 2% to 20%.

with its molten paramn The parafiin accumulates on the walls of the tubing and sucker rods during producing periods-varying from weeks to years-and deposits in those areas, where the oil reaches lower temperatures due to the presence oi cold water around the casing at points above the oil formations. Tests have proven that even when the total volume of paraiiin melted by the hot oil is as high as of the total volume, the paraffln dispersed in the oil will remain therein and will not reset on the sucker rods or tubing and can be brought to the surface of the well, even though the temperature of some of the injected hot oil, when it reaches the surface, has fallen to 68 F.-"IO F., which is approximately the producing temperature; note that ordinarily, paraffin melts in hot oil at about 145 F. The important result that ows from this fact is, that the pumping out of the injected hot oil and its parafn content need not be speeded up unduly, which avoids overloading of the pumping equipment.

The simplicity and ease of operation of my novel system of paraffin removal will be apparent from a readingi of the foregoing description. The only additional piece of equipment necessary in the well proper is the release valve with its associated coupling member, and this is readily installed with the tubing. The well pump itself is used for discharging the molten or dissolved paraffin, through the top of the tubing and the method of operation is such, that return of the molten or dissolved paraffin to the bottom of the well is completely precluded. My method of operation avoids the necessity of withdrawing the sucker rods, the well pump, or even of the tubing sections, with the attendant loss of production time, as was frequently the case heretofore in the cleaning of wells. Further, the release valve serves an addition and useful purpose: It occasionally happens that by reason of circumstances, the cleaning of the well is neglected for some time; the tubing then becomes so choked up with paraiiin deposits, that a high resistance or back pressure is created to the lift of the column of the oil raised by pump in the tubing. The back pressure thus created is frequently sufficient. to damage the well pump and to cause the tubing to crack. Where the tubing of a well is provided with a release valve, as described herein, damage to the tubing will be avoided, since the valve will open and release the pressure as soon as the latter reaches a dangerous, predetermined value.

As will appear from the above, my invention is not based upon a circulation of a hot medium through the tubing as practiced heretofore. In my procedure, a column of cold oil is displaced by a corresponding column of hot oil. In comparison with the circulation method of cleanrequiring less time and less heat. In the circulation method considerable heat is wasted by reason of the heating up of the entire length of tubing and of the oil therein, while in practicing the method of my invention, the heating is restricted to a certain region of the tubing, as set out above.

While the preferred method of well cleaning,

according lto this invention, contemplates the use of a release valve as described above, the method is advantageously employed under certain conditions, without the use of such a valve. Thus, in cleaning a seized well, the tubing of which is not provided with a release valve 9 and the well pump of which is provided with conventional means for unseating the valves of the pump, as is well known in the art, the procedure is as follows: The well pumping operation is discontinued, and by suitably manipulating the sucker rods at the surface of the well, in a manner well known to those skilled in the ar-t, the standing and travelling valves 3| and 32, respectively, of the well pump 5 are lifted olf their seats, so as to enable the desired amount of cold oil to run out of the tubing direct to the oil formation, while hot oil is being introduced at the top to take its place as a fluid column. The pump valves are then reseated with their customarily provided reseating mechanism, and the well pump is set in operation to withdraw to the surface the column of the mixture of hot oil and molten paraffin in solution. It will therefore be apparent that in this method and construction, the valve means for forming the deparaflining fluid column is located within the tubing and that the cleaning operation may also be carried out successfully, in this instance, without the provision of a special release valve, so that the installation of the latter in the tubing may therefore be postponed until such time as the tubing has to be withdrawn for some other purposes.

'I'he invention may likewise be applied to the servicing of flowing wells, without resorting to the use of a release valve. In this case, the high pressure pum-p at the surface must be sufllciently powerful to force the hot oil down into the tubing against the existing bottom hole pressures. The injection of hot oil is stopped when an adequate amount has been introduced into the tubing and the oil is permitted to stand therein for a length of time sufcient to melt the paraffin. Flowing of the well is then resumed, so as to bring to the surface the hot oil and molten paraffin. Similarly, I also contemplate the application of this invention to the cleaning of wells operating by gas lift; here, following the release of the casing pressure and closing of the gas lift valves, the same procedure is followed as in the case of the cleaning of flowing wells. After a suitable amount of hot oil has been injected into the casing, the gas lift is again put into operation bringing to the surface the oil with its molten paraiiln. l

I claim:

1. In an oil well, the method of treating the tubing thereof to remove deposits of paraffin therefrom which comprises, introducing a deparaining fluid through the top of the tubing to form a progressively increasing, downwardly moving fluid piston upon the oil in the tubing, until there is formed in the tubing a column of deparailining iiuid in contact with the tubing surface and of a length at least substantially equal to the depth of normal paraln deposits ing oil tubing, my method has the advantage of in said tubingv simultaneously discharging on 3. In al method according to claim 1, in which the deparailining uid is constituted by a paramn solvent.l

4. In a method according to claim 1, in which the oil displaced by the column of deparalning uid is discharged from the tubing at a substantially constant rate, whereby a liquid column is continually maintained throughout the tubing during the deparaflining' operation.

FRANK E. DANA.

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