US3237692A - Use of low-grade steam containing dissolved salts in an oil production method - Google Patents

Description

March 1, 1966 E. w. WALLACE ETAL 3,237,592

USE OF LOW-GRADE STEAM CONTAINING DISSOLVED SLTS' IN AN OIL PRODUCTION METHOD Orlginal Filed Feb. 28, 1965 7M gw A m .o I' v l2, vll-I' r i A 'L' ,l :f l: g

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EIR AGENT United States Patent O USE F LOW-GRADE STEAM CONTAINING DIS- SOLVED SALTS IN AN OIL PRDUCTION METHOD Eugene W. Wallace, Oak View, and John A. Pryor, Ventura, Calif., Bryant W. Bradley, Houston, Tex., and George H. Holliday, West Covina, Calif., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware Original application Feb. 28, 1963, Ser. No. 261,684. Divided and this application May 12, 1965, Ser.

3 Claims. (Cl. 166-40) The present application is a divisional application of copending application Serial No. 261,684, filed February 28, 1963, and now U.S. Patent No. 3,193,009.

This invention relates to an improved method for recovering hydrocarbon material from an underground formation which may be in the form of oil sands, oil shale or tar sands. The invention pertains more particularly to a method for the secondary recovery of oil, particularly highly viscous oil, or other hydrocarbon materials that are substantially nonflowable under reservoir conditions.

This invention constitutes an improved method for supplying heat and/ or other energy in the form of a driving medium to an underground formation containing tar sands, oil sands or oil shales for the purpose of increasing the oil recovery therefrom. The method is applicable to formations containing oil of high viscosity which may be nonproducible, i.e., nonflowable under original conditions and to those containing low to medium viscosity oils of which varying amounts may have been recovered by conventional primary means.

The primary production of petroleum hydrocarbons from oil-bearing formations is usually effected by drilling through or into the oil-bearing sand and providing access to the formation around the borehole so as to permit oil to flow into the bore-hole from which it may be recovered by conventional methods. If the formation contains an oil of low or medium viscosity at reservoir conditions, the well may be produced either by flowing or pumping in a manner well known to the art. If on the other hand the formation contains a highly viscous oil at reservoir conditions, it may be necessary to heat the formation in the vicinity of the borehole to reduce the viscosity of the oil so that the oil may flow into the borehole. In time, even the wells containing free flowing oil become depleted although a substantial amount of oil still remains in the producing formation underground. The residual oil left in the formation underground is very difficult to produce and considerable research has been carried out on secondary methods of recovering this residual oil. Various methods have been devised such as heating, underground combustion, flooding with water or a miscible fluid, etc.

The flooding of underground formations for the pri mary or secondary recovery of a hydrocarbon material such as oil presents many problems. In the water flooding of oil-bearing underground formations, it is necessary to employ flood water free of clays, colloidal material, undissolved salts, etc., which would tend to plug the face of the oil formation and perhaps within the oil formation itself when the water is injected thereinto. In addition, many producing formations being flooded contain a certain amount of swelling clays in the form of a bentonite or montmorillinite clay, which upon swelling, reduces the permeability of the formation. Saline water tends to prevent the swelling of clays of this type and its use is often preferred in water flood projects. Whatever water is used, it should be compatible with the formation into which it is injected so as not to reduce the permeability of the formation.

3,237,692 Patented Mar. 1, 1966 ICC Unfortunately, the water available in or around many oil fields is usually hard and contains alkaline earth metal salts such as those of calcium and magnesium. In the event that hot water or hot water and steam are to be injected into the producing formation, the use of ordinary oil field water normally available containing calcium and magnesium salts would cause the formation of considerable scale in steam generation equipment. The water could be treated in a conventional manner with phosphate to precipitate the calcium and magnesium salts as a nonscaling phosphate sludge within the steam generation equipment. This phosphate sludge however is of a form that readily plugs a formation when the Water is being injected into it.

It is therefore a primary object of the present invention to provide a method of recovering hydrocarbon material from underground formations by heating them with a material which is compatible with the formation and may be readily injected thereinto.

A further object of the present invention is to provide a method of flooding an underground oil-producing formation with a hot fluid that has no tendency to scale equipment nor any tendency to plug an underground formation into which it is being injected.

Still another object of the present invention is to provide a method of flooding with a hot fluid an underground formation to recover hydrocarbon material therefrom wherein the water phase of the flood fluid contains dissolved salts that are compatible with the formation being flooded and have a tendency to prevent the swelling of certain clays which may be in the formation.

A further object of the present invention is to provide a method of flooding an underground formation with a hot fluid for the recovery of hydrocarbon material therefrom wherein the treatment of the flood fluid is relatively inexpensive.

These and other objects of this invention will be understood from the following description taken with reference to the drawing, wherein:

FIGURE l is a schematic view illustrating three wells taken in cross section and extending into the earth with associated equipment diagrammatically illustrated on the surface of the earth; and, y

FIGURE 2 is a schematic view of another form of steam generation equipment for use with the equipment of the present invention.

Referring to FIGURE l of the drawing a water Well 11 is shown as being drilled in the earth 12 and into a waterproducing formation 13 to serve as a supply for water in a flood project for the recovery of hydrocarbon from a hydrocarbonproducing formation 14 which is traversed by a well 15a. The well 15a is provided with casing 15b which may have a tubing string 16 therein. It is to be understood that instead of using well 11 as a source of water that the water could be supplied from any other source. The Well 11 is provided with a discharge line 17 having a control valve 18 therein. The water line 17 leads through valve 19 into the top of a chemical treatment tank 20 which is preferably mounted in side-by-side arrangement with a second chemical treatment tank 21 in the event that it is necessary to re-generate the chemical in one tank while the other tank is being used.

In accordance with the method of the present invention, a method of treating waters containing calcium and/ or magnesium salts is vto pass them through a tank containing sodium ion exchange resin (e.g., sodium zeolite) which carries out an ion exchange so that calcium and magnesium salts are converted to sodium salts which are discharged in the fluid stream through valve 22 in line 25 to a suitable steam generation unit 26 having coils 27 therein for example.

When the flow of hard Water is through valve 19 into chemical treatment tank 20 and it is necessary to regenerate the chemical in treatment ytank 21, valve 28 in the other line 29` going to tank 21 would be closed while valve 3ft in line 31 would be open with valve 32 closed so that sodium chloride brine could be flushed through the other tank 21 to regenerate the sodium zeolite in tank 21 with the salt water being discharged through valve 33 and line 34. Tank 20 would be provided with a similar valve 35 and discharge line 36.

The system may be provided with a water hardness analyzer 37 adapted to actuate the valve or other mechanism 38 from a chemical injection tank 39 which is connected to line 25 by line 40. Thus, in the event that a small amount of calcium or magnesium salts were still present in the water, the hardness analyzer 37 could control the injection, through valve 38 from tank 39, of a small amount of a chelating agent to for-m water soluble calcium and magnesium salts. One suitable chelating yagent is an aqueous solution of the tetrasodium salt of ethylene diamine tetra-acetic acid.

The steam generation unit for heating the water may be in the form of a spiral set of coils27 through which the water ows with a suitable burner 41, such as a gas or oil-,tired heater, positioned in the bottom to heat the coils.

The low grade steam from the steam generating unit 26 .is discharged through line 42 and valve 43 and thence down through well tubing 16 to be discharged preferably adjacent to t-he producing formation 14. The bottom 'of the `well a may be closed in any suitable manner, as by cement 44. The annular space 45 between the well casing 15b and the tubing string 16 may be closed by a packer 46 of any suitable type at a level close to the top of the producing formation 14.

A water pump 47 is provided in the line 25 to the steam generating unit 26 which may be in the form of a boiler, steam generator or field heater. By adjusting the pump rate and the setting of the burner 41, the water content of the steam in the discharge line 42 can be controlled. Since the water coming into the boiler, steam generator 26 or eld heater carries with it soluble salts, it is essential that these salts remain in solution while the steam in being formed and while the steam and water are being discharged from the boiler, steam generator or field heater through line 42 and into well 15a. Preferably, the liquid phase of the low grade steam being produced by the field heater, boiler or steam generator 26 has from 5 to 25 percent water in it depending on the amount of salts that it is necessary to carry from the boiler, field heater or steam generator and down into the Well. If a boiler 50 of the type shown in FIGURE 2 is employed, where pure `steam is discharged out the dome 51 through line 5-2, a valve 53 in the water discharge line 54 from the bottom of the boiler 50 can be adjusted, either manually or automatically, to periodically or continually bleed a small amount of water laden with soluble salts out line 54 and down line 55 with the steam. The dissolved salts concentration inthe water carried by either line 42 or line 55 is several fold greater than the dissolved salts concentration in the water supply.

Although the apparatus of the present invention has been operated between from about 150 to 600 p.s.i.g. steam generating unit pressure, the same equipment could be operated at 2500 p.s.i.g. or more. The operating pressure generally depends on various well characteristics such as well depth and well pressure since it is necessary to force the steam and hot water to the bottom of the well or to the point adjacent a producing formation. Both the steam and Water are injected into the formation at high temperatures to reduce the viscosity of the hydrocarbons therein and/ or vaporize the lighter components. If the producing formation is of varying permeability, the water in the steam has a tendency to block the larger interstices between the sands to prevent fingering of the steam into the formation thus giving a more uniformrrate of movement of heat through the formation. The presence of concentrated soluble salts in the injection water-'reduce the tendency of clays to swell.

After heating the formation 14 through well 15a for a predetermined time, the well 15a may be produced in any conventional manner through its tubing string 16 by closing the steam injection valve 43 and opening valve 60 on production line -61 leading from the well. If a steam d-rive is to be carried out through the producing formation 14, which must necessarily be of a permeability sufficient to allow the passage of steam therethrough, a second well 62 would be drilled in the formation 14 at some distance from the well 15a. The well 62 would be produced in any conventional manner through its production flowline 63 when valve 64 was open.

It is realized that most of the calcium and magnesium salts in the hard Water coming from the supply source 11 may be converted to sodium salts in the chemical treating tanks 20 or 21. Instead of removing small amounts (say a few parts per million) of residual hardness from the treated water 'by adding a chemical from tank 39 to form water soluble calcium and magnesium salts, the chemical addition from tank 39 can be omitted with the result that a small amount of scale formation in the field yheater, boiler or steam generator tubes 27 will take place. This can be overcome by shutting the system down from time to time and removing the scale from the eld heater, boiler or steam generator tubes in a conventional manner. In addition, it is to be realized that the water from the supply source 11 can be treated in one or more various ways, as needed, las by adding lime or lime-soda ash to reduce calcium and magnesium hardness, adding magnesium oxide to reduce silica content, adding sodium sulte to remove oxygen from the water and hence prevent corrosion, adding suitable materials to re-saturate the `water with bicarbonates to prevent scale deposition, etc., and that sodium ion exchange treatment may be deleted or used in conj-unction with these treatments and when used may be conducted with parallel or series flow of the water through two or more tanks containing sodium ion exchange resin. All of these treatments are conventional and need to be only employed where the composition of water demands it. To date, low grade steam having at least l0 percent wate-r in it has been employed successfully. Further, it is to be realized that low grade steam may be discharged down through the annular space 45 between t-he well casing 15b and the tubing string 16 or down through both said annular space and tubing string 16.

We claim as our invention:

1. In a method of recovering a hydrocarbon material from an underground formation in which it occurs, said method comprising the steps of drilling a well from the ground surface into said hydrocarbon-containing underground formation,

obtaining a supply of water containing ions of a scaleforming alkaline earth metal salt,

treating the water to convert the alkaline earth metal salt to a soluble alkali metal salt,

generating substantially pure steam from said treated water, Y subsequently adding to said steam a quantity of water having sodium salt dissolved therein in a concentration greater than the dissolved salt concentration of l the water supply, and

injecting the substantially pure steam and salt water mixture through said well and contacting the hydrocarbon-containing underground formation in communication therewith for a time sufficient to improve the flow characteristics of said hydrocarbon material.

2. The method of claim 1 including the subsequent step of stopping the injection of low-grade steam into the well, allowing the hydrocarbon of beneiiciated flow characteristics to flow into the well, and subsequently producing said hydrocarbon up the well.

3. In a method of recovering a hydrocarbon material from an underground formation in which it occurs, said method comprising the steps of drilling a Well from the ground surface into said hydrocarbon-containing underground formation, obtaining a supply of Water containing ions of a scaleforming alkaline earth metal salt,

treating the Water to convert the alkaline earth metal salt to a soluble alkali metal salt,

generating substantially pure steam from a supply of said treated water in a steam generator and discharging pure steam therefrom and injecting it into said well,

discharging from said steam generator separately from said pure steam discharge and into said well a supply of salt-laden water having salt dissolved therein in a Cil concentration greater than the dissolved salt concentration of the Water supply, and

contacting' the hydrocarbon-containing underground formation in communication With said well with a mixture of said pure steam and said salt-ladened Water for a time sucient to improve the ow characteristics of said hydrocarbon material.

References Cited by the Examiner UNITED STATES PATENTS 2,738,325 3/1956 Rydell l66-9 X 2,852,077 9/1958 Cocks 166-9 3,193,009' 7/1965 Wallace et al. 166-11 CHARLES E. OCONNELL, Primary Examiner.

S. I. NOVOSAD, Assistant Examiner.

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