Method for pumpin paraffine base crude oil

Abstract

The method of inducing and maintaining the flow of paraffine base oil in a well structure which comprises heating and maintaining the well structure at a temperature below the fracturing and melting temperature of the paraffine, within that range of temperature where the paraffine is dissolved and/or reabsorbed and carried, in fluid state by the oil and above that chill temperature where the paraffine in the oil solidifies and separates from the oil.

Description

This invention has to do with oil production and is more particularly concerned with a novel method of inducing the flow and the pumping of paraffine ladened oil through well structures.

Throughout the world, there are a great number of oil deposits in which the oil contains and is ladened with so much paraffine that the oil cannot be effectively and economically pumped. As a result of the above, many large oil reserves have been substantially abandoned on the premise that the oil cannot be economically and effectively pumped from the earth formation in which it is found, through and by means of conventional well structures and production equipment or means.

Paraffine, which is commonly found in crude oil, when chilled or cooled, separates from the oil and jells or sets up. As a result of the above, when crude oil containing paraffine is pumped from the earth formation in which it is found, upwardly through a well structure and cools as it rises in the well structure, the paraffine therein separates and jells or sets up in the well, creating a blockage which seriously impedes and often stops the flow of fluid in the well structure.

As the amount or percentage of paraffine in crude oil increases, the tendency for the paraffine to impede flow or plug a well increase at a rapid rate.

In the past, efforts to unplug paraffine plugged wells and to induce the flow and production of paraffine ladened crude oil, the well structures and the oil-bearing formations about the well structures have been heated to melt the paraffine and to thereby cause it to flow and, at the same time, permit the oil to flow.

The melting point of paraffine is, subject to limited variations, about 126.degree.F. Accordingly, the above noted efforts by the prior art to unplug paraffine plugged wells and to induce the free-flow of fluids in their formations and through the wells, the plugged well structures and their related formations have to be heated to over 126.degree.F, to melt the paraffine, and to provide sufficient excess residual heat so that the oil and paraffine in the formation and well remain fluid for a sufficiently protracted period of time to effect adequate and rewarding production of oil.

Heating of wells, as practiced by the prior art, for the purpose set forth above has involved the injection of live steam into the wells and into their related oil-bearing formations for a sufficient period of time to melt the paraffine and to heat the wells and the formations to a sufficient extent to induce the flow of production fluids. Then the introduction of steam is ceased and production flow commenced. Production is continued until the wells have cooled sufficiently to permit the paraffine to set or jell and until the wells are again plugged, whereupon steam is again injected and the wells and their related formations are again heated.

It will be apparent that in those cases where the temperature in the oil-bearing formation is about 65.degree.F, a great amount of steam must be injected into a well and the formation for an exceedingly long period of time and at great expense, to raise the temperature of the well structure and the formation adjacent thereto to 126.degree.F and above. In practice, in most cases where paraffine is present in sufficient amounts to create the problems recited above, the cost of heating the well exceeds the revenues to be gained from that production which can be induced.

Still further, paraffine, in the presence of water has a greater tendency to separate from its carrier or mother crude oil and to jell or set up. In the case of heating wells by steam injection, the steam condenses in the well, as the heat is absorbing by the well structure and the formation, leaving a considerable amount of water in the well, which water augments the tendency for the paraffine to separate from the oil and to set up.

It has been determined that the paraffine in most oil deposits which are ladened with paraffine is dissolved and in solution in the oil. This is true even when the temperature of the oil, in its formation is, for example, at about 75.degree.F and well above the melting point of paraffine.

In one known case, in an oil deposit below the Great Salt Lake in the State of Utah, oil, heavily ladened with paraffine is at a temperature 78.degree.F in the formation in which it is found and the paraffine is in dissolved solution in the oil. In that case, when the oil is cooled from between 10.degree.F. and 15.degree.F, as it is pumped up through the well, the paraffine separates from the oil and, being below its melting point of 126.degree.F, solidifies or jells, plugging the well.

It has been further determined in the above noted case that upon raising the temperature of the oil, 10.degree.F. or 15.degree.F., that is, back to its natural or original temperature, and slightly above, the separated and solidified paraffine is dissolved and re-absorbed by the oil and is carried thereby.

The oil with the paraffine dissolved therein and carried thereby is considerably stiffer and flows more slowly than does paraffine and oil heated above the melting point of the paraffine, but it flows uniformly and continuously.

It has also been determined that upon heating paraffine ladened oil to near and above the melting point of paraffine, that is to near 126.degree.F or above, fracturing takes place and the paraffine separates from the oil and is presented in a separate state where it readily solidifies upon a slight decrease in temperature.

From the foregoing, it is apparent and it is now understood that there is a range of temperature, well below the melting point of paraffine where the paraffine is readily absorbed and carried by the mother crude oil, in a liquid state. It is further apparent and it is now understood that there is a temperature range below the formation temperature of the oil where the paraffine in the oil will separate therefrom and, when thus separated, solidifies.

It is an object and feature of my invention to induce and maintain the flow of paraffine ladened crude oil in a well structure by heating and maintaining the temperature of the well structure at or slightly above the temperature of the paraffine ladened oil in the formation in which it is found and at a temperature well below the melting point of paraffine and below that temperature where fracturing of the oil and paraffine commences.

It is another object and feature of this invention to heat a well structure as above noted by dry heat, free of water.

It is still another object and feature of my invention to heat a well structure, as set forth above, by conducting steam through a steam conducting line extending from the top of the well to the bottom thereof and thence back to the top of the well, whereby the entire well structure is suitably maintained at a temperature below the fracturing temperature of the oil and paraffine and above that low, chilled temperature where the paraffine separates from the oil.

It is an object and a feature of my invention to provide a method and apparatus of the character referred to above which is such that a small amount of heat continuously and economically supplied to a related well structure results in steady, continuous and profitable production of well fluids.

Still another object and feature of my invention is to provide an apparatus for heating a well structure wherein the steam and/or water supply therefor is in a closed heat insulated circuit whereby little or no water is consumed and a minimum of heat generated is wasted.

The foregoing and other objects and features of my invention will be fully understood from the following detailed description of a typical preferred form and carrying out of the invention throughout which description reference is made to the accompanying drawing in which my apparatus is diagrammatically illustrated and is shown related to a typical well structure and oil bearing formation.

The apparatus that I provide includes an elongate string of small diameter pipe or tubing such as is commonly referred to in the petroleum production art as macaroni tubing and which will hereinafter be referred to as heating tubing T. The heating tubing T enters the upper or top end of a related well structure W at a suitable fitting 10 at the top of the well casing C. The tubing extends downwardly through the casing to and through a perforated liner L at the lower end of the casing and extending into or through the oil producing zone Z with which the well structure communicates and extends back, up through the liner and casing and exits the well at said fitting 10.

The heating tubing T extends through the annulus defined by the casing and liner and a string of production tubing P extending longitudinally through said casing and liner and in which a suitable well pump (not shown) is arranged. The well pump can be of any suitable form and in the accompanying drawing, I have indicated the provision of sucker rod R for the pump within the production tubing P and have shown a polish rod R' for the rod R, projecting upwardly from the top of the well structure.

The production tubing can, as indicated, connect with a fitting 11 atop the fitting 10. The fitting 11 carries a packing structure for the rod R' and has a lateral outlet 11' with which a production pipe 12 is connected, to conduct the production fluid from the well structure and deposit it in a suitable receiver tank or the like (not shown).

The apparatus next includes a receiver tank O adjacent the top of the well in which a supply of thermal oil is contained. The thermal oil can be any oil suitable as a heat transfer medium and is adapted to be heated and circulated through the heating tubing T.

The tank O has an outlet fitting 15 connected with the inlet end of the tubing T, at the fitting 10 by a line 16.

The line 16 is provided with a motor driven circulating pump 17.

The tank O next has an inlet fitting 18' connected with the outlet end of the tubing T, at the fitting 10 by a line 18.

Finally, the tank O has a heating coil 20 within it, which coil has inlet and outlet ends 21 and 22.

In practice, the tank O can be provided with a thermo insulating jacket or cover about its exterior.

The apparatus shown next includes a steam generator, boiler or heater H adjacent the tank O. The heater H can be of any suitable form of heating or steam-generating means. In practice, I have employed a steam-generating means utilizing electric resistance heating elements, with great success.

The heater H has an outlet 30 connected with the inlet 21 of the coil 20 in the tank 0 by a line 31 and has an inlet 32 connected with a return line 33, which line connects with the outlet end 34 of a heating jacket 35 about the production pipe 12. The inlet end 36 of the jacket 35 is connected with the outlet end 22 of the coil 20 in the tank O by a line 37.

The jacket 35 about the pipe 12 serves as a condenser for the steam and, at the same time heats the production in the pipe and assures its free flow therefrom and into the production receiving means that is to be provided.

In practice, a feed pump 38 is provided in the line 33 to conduct water from the condenser jacket 35 into the heater H.

With the apparatus set forth above, the thermal oil in the tank O is heated by steam generated by the heater H and is conducted through the coil 20 in the tank O. Heated thermal oil is circulated by the pump 17 through the heating tubing T whereby the well structure from the top thereof down to the pump, liner and production formation is heated to a temperature below 126.degree.F or the melting point of paraffine and above that minimum temperature where paraffine is readily dissolved by the mother crude oil.

The thermal oil flowing from the tubing T is conducted back to the tank O for re-heating and recirculation through the well structure.

The steam flowing from the coil 20 in the tank O is conducted into the heat transfer and condensing jacket 35 where its residual heat is used to maintain the temperature of the production at a temperature where it remains fluid and free flowing.

The condensed steam or hot water in the jacket 34 is drawn from the jacket and is fed back into the heater 11 by the feed pump 36.

By controlling the B.T.U. input into the heater H and/or by controlling delivery rate of either or both of the pumps 17 and 38, it will be apparent that easy and flexible control of the temperature in the well structure can be achieved.

In practice, in addition to other conventional and suitable control and monitoring means, temperature gauges 50 and 51 can be advantageously placed at the inlet and outlet ends of the tubing T. By use of such gauges, and noting the temperature of the thermal oil introduced into the tubing T and the temperature of said oil flowing therefrom, an adequate determination of the well structure throughout its entire extent can be attained.

While it is not necessary that the production zone Z be heated, it will be noted that due to the fact that the apparatus heats the well structure to a notably higher temperature than the mean temperature of the formation, and that said higher temperature is maintained substantially constant, the formation will in fact become heated to an extent that the well fluids will flow more readily. This conductive heating of the formation will extend slowly outwardly from the well, with the passage of time, thereby assuring continuous production by the well.

It is to be noted that when practicing my invention, that is, when heating the production to a temperature below the melting point of paraffine, where the paraffine is dissolved in and carried by the oil, the production fluid is stiffer and flows more slowly than the crude oil would flow if the paraffine was removed. The production flows more slowly than it would if it were heated above 126.degree.F, or the melting point of the paraffine in the oil. Accordingly, in one respect, in practicing my invention, the production is made noticeably stiffer and such that it flows more slowly than it would flow if heated to above the melting point of the paraffine.

It is the above fact which leads the inventor of this new method to believe that no one in the prior art has conceived or practice the method hereinabove described. The concept or mere idea of creating a condition which stiffens and slows the flow of production in a well is contrary to all normal and accepted practices. It is generally believed that in order to induce the flow of production in a well where blockage and plugging up of the well by solidified paraffine is encountered, the temperature of the well must be elevated to and/or above the melting point of the paraffine, whereupon the well's production will flow freely and rapidly.

In the practice of the present invention, while fast or rapid flow of production is not achieved, slow, steady, uniform and economically profitable production is achieved by a steady induction of a relatively small amount of heat.

The above end gained by the practice of my invention makes the operation and production of many wells which cannot be profitably operated by raising the temperatures thereof above the melting point of paraffine, extremely profitable to operate.

To the best of the inventor's present knowledge, a well temperature of about 100.degree.F. is satisfactory and will suffice to establish and maintain economical and profitable production in most wells where paraffine plugging or stoppage has proved to be a problem. Such a temperature is sufficiently below the melting point of paraffine (126.degree.F) to prevent its separating from the crude oil, is sufficiently high so that the paraffine is readily dissolved and/or reabsorbed into and carried by the crude oil and is sufficiently warm or hot so that the combined paraffine and crude oil production is not so stiff that it cannot be pumped and caused to flow at a reasonable rate through the well structure.

An additional feature and advantage to be gained in carrying out of the present invention resides in the fact that materially less heat than is commonly employed in other methods or processes where heat is employed to induce production flow, with the result that considerably less volatile hydrocarbons are caused to separate from the crude oil and said oil contains more values as it reaches the technical process of refining.

While, for the purpose of this disclosure, I have described our invention related to a well structure which includes a pumping means for the oil production, it will be readily seen and appreciated that this invention can be readily and satisfactorily related in and with free-flowing wells.

In many instances where pumps are required to induce the flow of production fluids, by employment and use of my invention, the flow of production can be made sufficiently free so that the pumps can be operated with less applied energy and/or can be put out of service.

Having described only one typical preferred form and application of my invention, I do not wish to be limited or restricted to the specific details herein set forth, but wish to reserve to myself any modifications and/or variations that may appear to those skilled in the art to which this invention pertains.

Claims

I claim:

1. The method for maintaining continuous, uniform, free flow of paraffine ladened crude oil in a well structure including an elongate vertical well bore extending downwardly from ground level to a production zone, a casing in the bore, a production tubing extending freely through the casing, a pump related to the lower end of the tubing and heating means at upper end of and extending through the well structure, said method comprising heating and maintaining the well structure and paraffine ladened crude oil therein at a temperature above that chill temperature at which the paraffine in the crude oil separates from the crude oil and solidifies, within that temperature range in which the paraffine is and remains dissolved in the crude oil, below the melting temperature of the paraffine and below the fracturing temperature at which the paraffine separates from the crude oil.

2. The method set forth in claim 1 which includes heating the well structure without the introduction and admixing of water and foreign fluids into and with the structure and crude oil.

3. The method set forth in claim 1 wherein the well structure and the paraffine ladened crude oil is heated and maintained at a temperature below 126.degree.F and above that minimum temperature at which the paraffine dissolves in the oil.

4. The method as set forth in claim 1 wherein the well structure and the paraffine ladened crude oil is heated and maintained at a temperature below 125.degree.F and at least 10.degree.F above that temperature at which the paraffine dissolves in the oil, said well structure is heated without the introduction and admixing of water and foreign fluids into the structure and crude oil.

5. A method as set forth in claim 1 wherein said heating means of the well structure includes an elongate heat transfer conductor tube extending downwardly into and thence upwardly through the well structure, a fluid heating medium, heater means adjacent the top of the well to heat said medium and means to circulate the medium through the heater means and the tube, said method including heating the oil by heat transfer between the oil and heated fluid medium and through a heat transfer conductor therebetween, whereby the oil is heated without the introduction of water.

6. The method set forth in claim 5 wherein the well structure and the paraffine ladened crude oil is heated and maintained at a temperature below 125.degree.F and at least 10.degree.F above that temperature at which the paraffine is dissolved in the oil.

7. The method set forth in claim 5 wherein the well structure and the paraffine ladened crude oil is heated and maintained at a temperature below 125.degree.F and at least 10.degree.F above that temperature at which the paraffine is dissolved in the oil, said well structure and oil is heated by conduction of heat from a heated fluid medium circulated through the well structure and without the introduction of water into the crude oil.