US2225434A - Method for treating oil wells - Google Patents

Description

Patented Dec. 17, 1940 UNIED STATES No Drawing. Application October 1938,

Serial No. 235,995

3 Claims.

This invention relates to a certain new and useful'improvement in re-agents and methods for the treatment of oil wells.

As is well recognized in the majority of oil fields throughout the world, the problems involved in maintaining well efficiency are of considerable economic importance.

Considering the unusually great cost of oil well pumping equipment and the large overhead expense attendant upon pumping operations, it is usually extremely necessary that the maximum volume of oil be extracted from the well in minimum time and at minimum cost.

One of the factors which materially impairs well efl'iciency results from the gathering and deposition upon the walls of the well-casing, tubing, and the pump-rods of various substances precipitated from the oil as it passes upwardly toward the well-head.

As is well understood by those familiar with the art, paraflin-base oils are so called by reason of the inclusion of a solid wax-like high-melting substance termed parafiin,which is recovered as the end product in the distillative refining of the crude oil; In the crude oil, the parailln is more or less held in solution, but the effectiveness with which the crude oil dissolves such parafiin end products varies widely, so that there are a large variety of commonly occurring crude oils, customarily referred to as non-cutting oils, which seem to have a relatively low solvent power and, therefore, readily deposit thick coatings of paraffin on the walls of the casing, tubing, and groundline pipes through which they are transported.

Paraffin deposition in oil pumping equipment presents a particularly difficult problem, for it is dependent upon temperature variations in the well, the physical and chemical nature of the oil from which the paraflin is deposited, the physical and chemical nature of the parafiin itself, and even to some extent the casing size and rate of oil fiow.from the well. For example, in the Texas- Oklahoma oil fields, many wells are drilled to a depth of approximately 6,600 feet, which is roughly 5,000 feet on an average below sea level. The average temperature in this locality at a depth of feet below ground level is approximately 60 F. throughout the year. The average bottom hole temperature in this area is 126 F.

Now. most types of paraifin, so far as I am aware, congeal and begin to precipitate out at 90 F. Under pressure and average well conditions, it is found that paraffin begins to accumulate on the well-casing and on the pump-rods at approximately 103 R, which corresponds to a depth of approximately 3,300 feet. Consequently the upper 3,300 feet of easing are usually congested and the congestion increases in thickness as the top of the well is approached, where the tempera- 5 ture drops to about F.

Further, the temperature variation throughout the length of the casing in an oil well is usually, but not necessarily, uniform. Considering the various factors which affect this problem, the character of paraflin deposition may also vary widely. In some cases, it will take the form of a relatively thin film, increasing uniformly in thickness toward the top of the well. In other cases, it may be thin along short lengths of the casing and thick at short lengths of the casing, due to peculiar temperature and pressure conditions at particular strata through which the tubing passes. In addition, the paraflin deposit may be very loosely consolidated and of relatively 2 coarse grained structure. On the other hand, it may be very densely consolidated and of relatively fine grained structure.

Several eiforts have been made to overcome the problem of paraffin deposition. Within the last g5 few years, considerable effort has been made to introduce various solvent agents at the bottom of the oil well for lntermingling with the out-pouring oil in a continuous manner, it being claimed that, if an initially clean well is continuously treated with such agents, the deposition of paraflin will be prevented.

Unfortunately for the oil well industry, such methods of treatment, so far as I am informed, have had rather limited success and are not broadly applicable in the field. In the first place, such existing methods, to be effective at all, are costly and require considerable modification of existing oil well equipment. Moreover, since the treating agents are relatively expensive andcannot be recovered, the continuous introduction of such treating agents will materially increase the cost of oil production beyond an economically justifiable point.

Apart from these economic considerations, the continuous treatment methods seem to basically unsound in scientific principle. The theory back of such continuous introduction methods resides in the addition of high solvent power agents, which will materially increase the o solvent power of the eflluent of the well. It has never been contended that these additional agents modify the chemical nature of the oil. The only thing accomplished is to change the solubility factor of the oil by incorporating it in a composite solution, the component parts of which have 'different solvent powers. Thus, by taking a quantity of low solvent power oil and adding thereto a. predetermined quantity of high solvent power addition agent, the average solvent power of the resulting solution is increased. The difiiculty with this theory can be demonstrated most readily by a hypothetical example.

t it be assumed that a given crude oil at given conditions of temperature and pressure is capable of holding in solution .5 cc. of paraifin per cc. of oil. Let it further be assumed that such oil contains 3.5 cc. of parafiin per 100 cc. of oil. Obviously 3.0 cc. of paraffin will necessarily be deposited at the given conditions of temperature and pressure. In order to hold this amount of parafiin in solution, it will be necessary to add a predetermined quantity of some selected solvent agent in accordance with its solvent power. If it be assumed that a selected solvent agent has a solvent power of 20%, which is incidentally an abnormally high solvent power, it will be evident that at least 15.0 cc. of such solvent will be added to dissolve the 3.0 cc. of paraifin, which would otherwise be precipitated under these circumstances.

Thus, the volume of liquid which must be pumped is increased by 15%, thereby adding to the operation cost of the well. Further, this 15% of excessive solvent will materially add to the cost of well operation. Still further, the additlon of such large quantities of highly solvent re-agent will reduce the viscosity of the oil to such an extent as to impair somewhat the efficient operation of the valves and other parts of the pumping equipment. Taking all these factors into consideration, it will be readily understood that continuous treatment processes do not provide an adequate solution for this problem.

My invention hence has for its primary objects the provision of a new and unique method treatment which is periodic in character and, for want of a better term, may be referred to as batch treatment, which process and re-agent results in substantial economies in the actual treatment itself, as well as in the operation and efliciency of the well, which is exceptionally simple and convenient in use and operation, which is unusually flexible and adaptable to a wide variety of varying oil well conditions, which operates on fouled and clogged wells, as well as initially clean wells, and which is very speedy and, therefore, requires a minimum amount of shutdown time of the well equipment.

Numerous other objects and advantages of the invention will be apparent from the following description, which discloses fieferred modes of practicing the invention.

As will be familiar to those skilled in the art, an oil well consists of a long tubular casing, which extends several thousand feet into the ground. Inside of the casing is tubing which extends to the oil level. Extending coaxially downwardly through the tubing is a pump or well-rod, which is provided at its lower end with a pumpplunger of any conventional structure and design.

Oil well plungers are ordinarily so constructed with a series of valves which open on the downstroke and close on the up-stroke and are, furthermore, so adjusted as to allow for a stroke of approximately ten feet. If the pump-rod is pulled upwardly from its lowest position for a distance substantially greater than the ten-foot stroke, such as, for instance, a distance of twelve feet, the valves will automatically open and allow the supported column of oil to drain back into the bottom hole, thereby evacuating the tubing.

A well operator ordinarily knows the depth of his well, the weight and pressure conditions of 5 the supported column of oil in the tubing from the well-head down to the bottom hole, and can very readily, by a simple arithmetical calculation determine the number of minutes required to drain out or empty the tubing down to a predetermined depth. The skilled well operator also knows the temperature gradient in his well from the well-head to the bottom hole, as well as the physical characteristics of the parafiin contained in the particular crude which he is pumping. He, therefore, can very readily ascertain, with fairly close accuracy, the depth at which the congealed parafiin formation commences. Familiarity with the well will permit estimation of the conditions of paraflin deposition peculiar to his particular well. In the event that any-of these factors are not already known by the well operator, they may be readily ascertained by more or less conventional observation and inspection.

Further, the nature and character of the paraf fin contained in the crude in any particular well under consideration may be finally ascertained by centrifuging tests made in a laboratory.

When the well efliciency has dropped to an economically unfavorable point, the well may be restored to maximum efficiency in accordance with my present invention by lifting the pumprod a distance of approximately 12 feet from its lowest point of stroke and allowing the tubing to drain down or evacuate to a point slightly below the lowest level of paraflin formation. While the pump-rod is in elevated position, the upper ten or twelve feet thereof will be accessible from outside the well-head. This section of the pumprod will be found to be coated with a film or layer of deposited paraflin substantially identical with that on the adjacent portion of the tubing. Therefore, a core or sample portion of this deposited paraflin may be removed from the wellrod and taken to a laboratory or other convenient location, where it may be subjected to a control test to determine the quantity and dilution of treating agent to be used.

As a treating agent for the carrying out of the present invention, I may use a liquid or dispersion consisting of any selected organic solvent of the class including trichlorethylene and perchlorethylene. Depending upon the character and density of consolidation of the parafiin deposit, I have discovered that I may use solutions ranging in concentration from complete saturation to a dilution of 1% by volume.

In order to ascertain the particular type of solution most economically suited to the purpose, 1.0 cc. of the cored sample is placed upon a watch glass. A trichlorethylene containing liquid or dispersion of any calculated or known standard strength is allowed to drop slowly upon the paraffin sample from a burette, pipette, or other calibrated instrument. As the drops fall upon the sample, they will be quickly absorbed into the mass, which will ultimately assume a more or less colloidal or jelly-like form. Eventually the paraffin mass will have absorbed a maximum of the trichlorethylene solution, at which point the mass will begin to lose its solid form and shape and the mass in the watch glass will more or less dissolve to a slushy consistency. At this point, the volume of standard liquid is ascertained and the quan- 75 tity of trichlorethylene required may be calculated.

Since the well operator will know within fairly accurate limits the volume of deposited paramn within this casing, the amount of trichlorethylene required may be readily calculated The well operator also knows the cubical content or capacity of his casing from the wellhead down to the lowest limit of parafiin deposito prevent further evacuation of the tubing and thevevacuated space is filled with the liquid or dispersion having the desired concentration of trichlorethylene. The tubing thus filled is allowed to stand for a suflicient length of time to permit the trichlorethylene tothoroughly pe'netrate and disintegrate the paraflln film. The

length of time required will obviously vary, de-

pending upon the consolidation and density of the paraflin film. In any event, however, the

skilled operator, guided by the watch glass test above described, may gauge this length of shutdown time quite accurately. and, after some ratherbrief experience with the present method,

will be'able to determine this shut-down period within very accurate limits.

After the liquid or dispersion has been in the well for the desired length of time, the pumping-operation is re-commenced, and the now disintegrated paramn layer will be expelled in front of the rising oil flow. If desired, a by-pass tap may be installed at the well-head, so that the liquid or dispersion, which now contains substantially all of. the deposited paraffin and is in somewhat sludge-like form, may be discharged into a suitable waste receptacle for subsequent reclamation. If desired, on the other hand, the parafiin carrying liquid or dispersion may be permitted to discharge through the ground lines directly into the crude oil reservoir tanks, in which case it will actually have the effect of cleansing and clearing the ground lines and will not in any material respect affeet the quality or character of the crude oil in such reservoir tank.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. A batch-treatment method of removing the deposited paraffin incrustation from the casing and ground lines of oil pumping and gathering equipment which consists of periodically ceasing pumping operations and evacuating the tubing and ground lines to be treated, filling the same with trichlorethylene, permitting the solution to remain in the tubingdor a predetermined time until the trichlorethylene has penetrated the incrustation and deglutinated it to a jelly-like consistency, and then resuming pumping operations and expelling the deglutinated incrustation and solution ahead of fresh crude oil.

2. The method of treating paraflin'clogged oil wells for the removal of the paraflin incrustation therein which comprises the steps of lifting the well rod a substantial distance to evacuate the upper portion of the well casing, removing from the well rod a sample of the paraflln incrustation, determining the absorptive qualities thereof by continuously adding small quantities of trichlorethylene to the sample until the latter is reduced to a jelly-like consistency and thereupon filling the evacuated portion of the well casin with trichlorethylene in a concentration suflicient to reduce the quantity of parafiin incrustation in the evacuated portion of the well casing proportionately to the quantity required to reduce said sample to jelly-like consistency, and allowing the solution to remain in the casing for a predetermined time.

3. A batch-treatment method of removing the deposited paraffin incrustation from the casin and ground lines of oil pumping and gathering equipment which consists of periodically ceasing pumping operations and evacuating the tubing and ground lines to be treated, filling the same with hydrocarbon liquids of the class consisting of trichlorethylene and perchlorethylene, permitting the solution to remain in" the tubin for a predetermined time until the trichlorethylene has penetrated the incrustation and deglutinated it to a jelly-like consistency, and then resuming pumping operations and expelling the deglutinated incrustation and solution ahead of fresh crude oil.

JOHN J. HARRIGAN.