US2415729A - Method of cleaning oil wells - Google Patents

Description

Feb. 11, 1947. F. E. DANA METHOD OF CLEANING OIL WELLS Filed Ju ne 26, 1944 STORAGE.

TANK,

PRODUCTION VA LVE.

Smaentor Patented Feb. 11, 1947 man METHOD OF CLEANING OIL WELLS Frank E. Dana, Kilgore, Tex.

Application June 26, 1944, Serial No. 542,137

1 Claim.

This invention relates to a method of cleaning oil wells and more particularly for removing paraffin deposited on the inside of the well tubing or of the oil discharge line. As is well known to those skilled in the art, a serious problem is encountered in the operation of oil wells by reason of the accumulation of deposits of paraflin on the inside of the tubing, which deposits have to be cleaned out at intervals in order that the oil may be efl'iciently removed from the well. Numerous proposals have been made from time to time of methods of removing paraffin from tubing. In many instances, the systems proposed were such as to necessitate the installation, either permanently or temporarily, of considerable additional well equipment, which was expensive and slow, occasioning a serious loss in production time.

In my Patent 2,300,348, dated October 27, 1942, I have disclosed a process of deparaflining the tubing of oil wells, especially pumping wells, which necessitates a minimum amount of additional equipment. Briefly, the said method consists in progressively forcing downwards into the tubing 2. suitable cleaning medium or deparafiining fluid, such as a chemical solvent or oil heated to a temperature suflicient to melt the paraflin, and thereafter pumping out the oil with the dissolved parafl'in. The present invention represents a further development of the aforesaid method, being more especially directed to a method and apparatus for the removal of paraflin from the tubing of flowing well and gas lift wells, that is, wells the tubing of which is not encumbered by elements of pumping equipment, -e g., sucker rods. Essentially the novel method consists in lowering a retaining piston down into the tubing ahead of a column of a cleaning medium, such as heated oil. The diameter of the piston relatively to the diameter of the tubing is so chosen that the piston has a relatively close but not tight fit in the tubing, thereby permitting the passage of a-limited amount of the cleaning medium between the inner wall of the tubing and the piston. By reason of the use of the fluid retaining piston, the hot oil or solvent cleaning medium forms a progressively downwardly moving fluid column, in intimate and efficient contact with the paraffin coated tubing walls, whereby the paraflin deposits are progressively and efiectively dissolved. As the paraffin dissolves and the tubing walls are freed of deposits by the cleanin medium, the piston is simultaneously displaced progressively downwards. Were it not for the presence of the piston, the deparafiining fluid introduced at the top of the tubing would drop down therein in an uncontrolled manner due to the rapid acceleration by gravity and, in view of the great depths involved, which may amount to thousands of feet, the velocity attained by the cleaning fluid would be extremely high. As a result, there would be very little, if any, opportunity for intimate contact between the paraffin deposits on the walls of the tubing and the deparaflining fluid as the latter travels downwards. As a consequence, in

the absence of a retaining piston, it would be economically impossible to increase the time of contact between an accumulated standing column of the deparafiining fluid and the paraflin deposits, in order to bring about an effective solution of the paraflin in the cleaning fluid. It will be obvious that any appreciable increasein contact time prolongs the time during which the well is not in production and thus proportionately increases the cost of the deparaflining operation.

The presence of a retaining piston is especially important and effective where heated oil or any solvent is used as the cleaning fluid, for two basic reasons. First, in its absence, there is no opportunity for intimate and prolonged contact between the hot oil and the paraffin deposits when the oil is first introduced into the tubing, that is, when the oil is most eflective in its dissolving power. Second, the retaining piston simultaneously acts as a telltale or indicator of the depth to which the tubing has been cleaned of paraffin. For, it is obvious that by reason of the close fit of the piston in the tubing, the piston can only descend in the measure that the tubing walls are cleaned of paraflin. Hence, when a depth recorder to which the retaining piston is connected, as will be explained below, indicates that the piston is below the known or estimated level of paraffin deposits, the operator is assured that the tubing has been effectively cleared of parafiln for the desired depth.

It will accordingly be seen that the use of a retaining piston in the manner proposed herein, which piston is progressively displaced downwards, brings about the controlled downward flow of the deparaflining medium and enhances the intimacy of contact between the deparalflning medium and the deposits to be dissolved. Further, the device additionally acts in the nature of a heat retaining piston in the case Where a heated fluid is used in the cleaning operation. To improve the heat retaining efiect of the piston, I provide the piston proper with a plurality of flexible metallic brush members, th assembly forming a metallic brush in intimate contact with the hot oil, thereby not only retaining the heat of the oil better, but also assisting in dislodging the melted paraffin deposits by its scrubbing effect.

While a free unattached piston can be used to carry out the instant invention, practical experience in the application of the present invention has shown that it is best to have the piston attached to the end of a wire line or cable, passing over a reel mounted on the surface, and provided with a suitable depth indicator. As will be detailed below, the use of a wire line makes it possible to control more accurately and readily the tubing cleaning operation.

The invention will be described in greater detail by reference to the annexed drawing, in which Figure l is a diagrammatic representation of a well provided with the necessary equipment to carry out the present invention, the casing of the wen being shown on an enlarged scale in order that certain details may be more readily apparent; and

Figure 2 is a cross section through a portion of the tubing showing the preferred form of retaining piston.

In the following description of the method of this invention, it is to be understood that various deparamning media or fluids may be utilized. I shall describe the invention in connection with the use of hot oil, which in the actual practice of the invention, has proved to be an inexpensive and convenient deparafiining material. In lieu of hot oil, fluids having a solvent action or effective to remove parafcn from the tubing wall by chemical action may be employed.

Referring to the drawing, I designates a portion of a well casing inside of which is arranged in the usual manner the tubing or discharge pipe 2 which has a master valve 2!} mounted at its upper end, and from which the oil is discharged to storage through the line 3 controlled by the opening of master valve 2% and production valve 2. The equipment necessary for the parafiin removal operation includes a portable heating unit mounted on a truck and comprises a boiler 5 and a heat exchanger E connected by a hose 7 to a bleeder pipe 8 which joins on to the main oil production or discharge line 3; the bleeder pipe is controlled by 'a bleeder valve Q. A high pressure pump it is provided to take the fluidgenerally oi1to be used in the cleaning operation from a storage tank H and force it through the heat exchanger 6. A hand or power operated wire line reel and depth recorder i2 is suitably mounted near the upper end of the tubing or on the portable power driven heating. unit, the wire line I3 being arranged to be introduced into the tubing in'the manner to be described hereafter. The heat retainer piston generally designated by the numeral is is attached to the end of the wire line and a suitable weight bar 15 is suspended below the piston.

Referring more'particularly to Figure 2 which shows the heat retainer piston to an enlarged 'scalef It comprises a flexible metallic brush piston about eighteen inches long, this length having proved satisfactory in actual practice, al-

though, obviously, the length. may be varied according to circumstances. The diameter of the piston is about of an inch less than the inside diameter of the tubing being cleaned, so that the cleaning agent can flow around it as well as through it to. a limited extent. The piston is mounted on a short rod is which is attached to the end of the wire line IS; the weight bar I5 is attached to the lower end of the rod. Suitably attached to the rod are flexible metallic brush members i? made of spring steel of suitable length and denseness in brush members to slow up or control the passage of hot oil or solvent through said piston. Conical washers or spray disks i8, i8 are attached to the top and bottom of the brush piston, the diameter of the disks being approximately one-quarter of an inch less than the internal diameter of the tubing and said disks being tapered as illustrated in the drawing to cause an outward spray of the oil or solvent passing through the piston against the tubing walls. The brushes perform a double function when hot oil is used as a deparaffining medium: first, to retain part of the heat supplied by the heated oil and thus aid in dissolving the paraffin, and second, to aid in dislodging the melting paraffin from the surface of the tubing by a scrubbing action.

In practicing the invention, when it becomes necessary to remove the accumulated paraffin deposits from the tubing, say of a flowing well, the truck with the portable heating unit is brought up to the well and the heat exchanger 6 is connected to the bleeder pipe 8 by the hose 1. The master valve 20 and the production valve 4 are then successively closed. The usual bull plug is removed above the master valve 29 and a lubricator head or short tubing of sufficient length to house the weight bar and heat retaining piston which are placed therein and which are suitaly attached to the wire line, is installed in the top of the tubing above the master valve using a packing at the top of the lubricator head to properly seal off the top of the lubricator head against pressure. The depth recorder is set to read zero. The master valve is now opened whereby the lubricator head becomes exposed to the pressure of the flowing well. This pressure must be overcome by the high pressure oil pump before the hot oil can be introduced into the tubing from the heat exchanger. In order to ascertain whether the tubing is completely plugged, cold oil at about 70 F. is forced down the tubing, flowing past the opened bleeder valve 9, and if there is no increase in pressure, it shows that the tubing is not plugged. This having been ascertained, the temperature of the oil is suddenly raised to approximately 300 F. The retainer piston, which has been kept in the lubricator head during the run with the cold oil, is now lowered into the tubing on the wire line, and is progressively lowered as the paraffin melts in the tubing.

Inasmuch as the piston diameter differs but slightly from that of the internal diameter of v the tubing (as indicated above, it is ,4 of an inch less), the hot oil flowing past the piston in the narrow gap between the piston and the tubing is forced into intimate contact with the paraffin deposits, thereby facilitating the solution of the paraiiin in the oil. Hence, the small clearance between the piston and tubing insures that all the parafin is .removed from the tubing before the piston moves downwards, the piston moving as fast as the hot oil melts the parafin from the tubing wall.

By suspending the heat retaining piston on a wire line, complete control is maintained over the progress of the piston, i. e., the cleaning operation. The position of the piston is given at all times by the wire line depth recorder. If the piston is lowered down faster than the paraflin can melt, the piston will set on the parafiin and this will be indicated by slack in the wire line. When this occurs, the piston is drawn back up into the tubing for a short distance, permitting the hot oil to flow around the piston and thoroughly melting the paraffin. Thereupon, the downward progress of the piston is resumed.

In the course of the cleaning operation, the heat retaining piston is usually run down in the tubing to a point which is about a thousand feet lower than the lowest known or estimated paraffin deposit in the tubing. When this point, which is readily given by the depth recorder, has been reached, the piston is slowly withdrawn, hot oil being, meanwhile, continued to be run down into the tubing until the piston reaches the surface, in order to insure that all paraffin is thoroughly removed off the tubing wall. The cleaning action is considerably facilitated at this point by the splashing of the hot oil against the tubing as it flows past the piston during its withdrawal. When the piston has reached the top of the tubing, it is removed therefrom by closing the master valve, removing the lubricator head, whereupon the piston may be withdrawn from the tubing. The bull plug may now be replaced and the well is ready to resume production.

A wire brush flexible retainer piston as described above is especially effective in facilitating, by its scrubbing and brushing action, the removal of the hard deposits of paraffin encountered in tubings which are being cleaned for the first time. Also, the use of a flexible piston is important in the servicing of paraflin choked wells where used tubings are installed, as such tubings are frequently crushed and out of shape, which would not permit a close fitting solid piston to pass through.

Gas lift wells are cleaned in the same manner as flowing wells. Actual tests have shown that the condition of tubing cleaned by the method disclosed herein is perfectly as good as that of a new clean tubing. It may be mentioned that it takes from five to fifteen barrels of oil to clean tubing by the hot oil method disclosed herein, the actual amount necessarily varying with the depth and size of the tubing, the thickness of the deposits, etc. i

As will appear from theabove, my invention is not based upon the circulation of a hot medium through the tubing as proposed heretofore, which wasteful, both as to heat and time. My invention requires a minimum amount of equipment, none of which is permanently installed on the well.

I claim:

The method of cleaning the tubing of oil wells to remove deposits of paraflin therefrom which comprises inserting a retaining brush piston into the top of the tubing, introducing above said piston a column of deparafilning liquid, lowering the piston and the column of liquid in the'tubing while supporting the column of liquid by said piston, and forming a progressively downwardly moving liquid film on the tubing wall in advance of the piston while the latter is being lowered, through passage of the fluid past the piston.

FRANK E. DANA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,713,895 Ford May 21, 1929 304,470 Thomas Sept. 2, 1884 1,342,618 Bashara June 8, 1920 1,888,125 Hart NOV. 1.5, 1932 2,283,048 Collett May 12, 1942 2,300,348 Dana Oct. 2'7, 1942 944,008 Bemis 1- Dec. 21, 1908

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