US3380531A

US3380531A - Method of pumping viscous crude

Info

Publication number: US3380531A
Application number: US642284A
Authority: US
Inventors: Clayton D Mcauliffe; Simon Ralph; Jr Carl E Johnson
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1967-05-18
Filing date: 1967-05-18
Publication date: 1968-04-30
Anticipated expiration: 1985-04-30
Also published as: ES351383A1

Description

April 30, 1968 c. D. M AULIFFE E 3,380,531

METHOD OF PUMPING VISCOUS CRUDE Filed May 18, 1967 4 Sheets-Sheet 1 H W a2 5 "Nu. .dl'

10 m r"] 4 50\ GOAT if SODIUM ra HYDROXIDE WATER 5 ken I /////////////Z' 25 22 5] Y 9: I2 I I '3;

.l 5 2 I r E :-z.- I i I VISCOSITY g 31; I DETECTOR 52 3 .I 3 I I M l I 54 :,ll l l l l l CONTROLLER OIL OR 67 1--. EMULSION EMULS'ON 7 a4 STORAGE BREAKER 69 lax/ 7o 66 68 WATER c A 'T $'L3L/FFE L r /v c DISPOSAL RALPH SIMON 73 I, CARL s. JOHNSOMJR.

BY (f/4,, p

ATTORNEYS April 30, 1968 c D, c F r- ET AL 3,380,531

METHOD OF PUMPING VISCOUS CRUDE Filed May 18, 1967 4 Sheets-Sheet 5 CAUSTIC SOLUTION STORAGE EMULSION STORAGE INVENTORS CLAYTON D. MCAUL/FFE RALPH SIMON CARL E. JOHNSON, J.

ATTORNEYS United States Patent 3,380,531 METHOD OF PUMPING VESCOUS CRUDE Clayton D. McAulitie, Fullerton, Ralph Simon, Whittier,

and Carl E. Johnson, Jr., Laguna Beach, Calitl, assignors to Chevron Research Company, San Francisco, Calif., a corporation of Delaware Continuation-in-part of application Ser. No. 503,210,

Oct. 23, 1965. This application May 18, 1967, Ser.

No. 642,284 i 16 Claims. (Cl. 166-45) ABSTRACT OF THE DISCLOSURE The invention is directed to improving the pumpability of crude oil from a well by forming a low viscosity oil-in-water emulsion near the pump in the well.

This application is a continuation-in-part of Ser. No. 503,210 filed Oct. 23, 1965, and now abandoned.

The present invention relates to a method of pumping viscous crude oil. More particularly, it relates to a method of pumping viscous crude by causing an oil-inwater emulsion of said crude to be formed at a point adjacent the actuating element of a downhole pump and then pumping said emulsion having a substantially lower viscosity than the native oil from the well bore.

Viscosity frequently limits the rate crude oil can be produced from a well. For example, in wells that are pumped by a sucker rod string, viscous drag by the crude oil on the string slows its free fall by gravity on the downstroke. On the upstroke, this drag also slows the string, decreases oil flow through the production tubing, and increases the power required to raise oil and rod string. In some instances where the oil is highly viscous, such as the Boscan field in Venezuela, the strength of the sucker rods limits the depth at which the pump can be operated. Alternatively, hydraulic pumps can be placed at the bottom of the well, but they must still overcome the high viscous drag that requires high power oil pressures and high pump horsepower.

The downhole pump usually provides the pressure required to pump the produced oil from the wellhead to surface gathering tanks. Where viscosity is high, this may require the use of extra strength wellhead equipment (packings, gaskets, heavy walled pipes and the like) to withstand the pressures required to move such viscous oil from wellhead to storage tank.

It has been proposed heretofore to reduce the viscosity of heavy crude oils prior to pumping by introducing low viscosity crude oils, white oil, kerosene or the like into the well bore to dilute or thin the produced crude. In rod pumped wells, it is common to surround the sucker rod string with an extra tubing. Low viscosity oil is pumped down this tubing so that the string is surrounded by lower viscosity oil. This added light oil then mixes with the viscous crude near the traveling valve of the pump to lighten and thin the column of crude oil being pumped from the well through the annulus formed by the inner and the production tubings of the well. Alternatively, low viscosity oil can be pumped down hollow sucker rods and the diluted crude oil produced through the annulus between the hollow rod string and the tubing.

As noted above, wells are also frequently pumped by downhole hydraulic units. In these wells at low viscosity oil is used as a power fluid. Frequently it is also mixed with the crude under production. In such a system it is common to reclaim the lower viscosity or high gravity ice components from the mixed, produced fluid for reuse as the power oil. However, in some wells the native crude contains so little low viscosity components that it is necessary to import oil from other sources for use as the power fluid. Economically, this may make it necessary to use a closed hydraulic system. To operate as a closed system, the downhole hydraulic pump is connected to the surface by two pipes to supply and return the power oil and thereby prevent it from commingling with the crude. Obviously, the viscosity of the produced crude is not reduced by the power oil and great hydraulic power is required to lift the crude.

None of the above described systems greatly reduces the viscosity of the native crude oil, unless excessive volumes of the high gravity fluids are used. Furthermore, it is expensive to reclaim the less viscous oil added to the produced crude.

In accordance withthe present invention, it is a pri mary object to reduce the power required to pump high viscosity crude down to values that are substantially the same as that required to pump water, and at the same time, reduce the cost of extracting the viscous crude oil from the produced fluid on stream.

Broadly, the invention has to do with a process of increasing the pumpability of a viscous crude pumped from a well bore by means of a downhole pump in said well here, which comprises forming adjacent said downhole pump an oil-in-water emulsion of the viscous crude, said emulsion having a substantially lower viscosity than the unemulsified crude, and pumping the oil-in-water emulsion to the surface of the ground.

in one aspect, the invention provides a method of increasing the rate of pumping a viscous crude from a well bore provided with a downhole pump, which method involves contacting the crude adjacent the pump with water and a base, in the presence of an emulsifying agent for said viscous crude, emulsifying the crude to form an oilin-water emulsion, and pumping the oil-in-water emulsion from the well bore to the surface. The amount of water introduced by the basic solution and any connate water present with the oil are suflicient to produce an oil-in-water emulsion having a substantially lower viscosity than the unemulsified crude oil. In general, the oil-in-water emulsion contains, by volume, about 50 to oil and 30 to 50% water, based on the emulsion. The amount of base used is such that the emulsion has a pH in about the range 8 to 13.8, preferably around 9 to 10. pH of emulsion being produced can be determined continuously or intermittently by known means, such as continuously recording pH meters, and Universal pH indicator paper. The viscosity of the emulsion can be varied by adjusting its water content, the viscosity being lowered with increase in water content, and increased by raising the oil content.

The invention is particularly useful when applied to asphaltic crudes, for example, the heavy California crude oils, Which upon contact and agitation wit-h an aqueous basic solution are converted into an oil-in-water emulsion. Accordingly, we have found that the viscosity of the produced stream can be reduced by a factor of to 1000 that of the original viscous asphaltic crude by introducing into the well adjacent the pump, or the actuating element thereof, an aqueous solution of a base, for example, sodium hydroxide, to react with the saponifiable constituents of the crude to produce an emulsifying agent in situ. The basic solution is injected through a flow line whose outlet in the well bore is below the intake of the downhole pump so that agitation of the oil and alkaline solution by the pump creates the required oil-in-water emulsion. As hereinabove mentioned the amount and concentration of the base solution to be injected is such as to neutralize the acidic components of the oil to a pH in the range 8 to 13.8, preferably 9 to 10, to produce an emulsion containing about 50 to 70% oil and 50 to 30% water, by volume, based on the emulsion. Obviously, the solution of the base to be added will vary in amount and concentration depending on the crude to be emulsified and the amount of connate water. Thus from very dilute solutions, less than 0.1%, to very strong solutions, up to 50%, will be used depending on acidic constituents of the oil and the connate water.

The base in forming the aqueous alkaline solution can be an alkali metal hydroxide, such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, or ammonium hydroxide. Other inorganic basic materials, such as sodium phosphate, sodium metasilicate, sodium carbonate, can be used. In addition to the inorganic bases, it is also possible to use strong organic bases such as the amines, for example, ethylamine, propylamine, triethanolamine, thus forming emulsifying amine soaps with the acid contained in the asphaltic crude. Generally, it is preferred to use an alkali metal hydroxide or ammonium hydroxide, and more preferably, a caustic solution formed of sodium hydroxide. However, the particular base will be selected on the basis of price and availability at the oil field where the viscous crude is to be produced.

As hereinabove mentioned, the invention is particularly useful when applied to asphaltic crudes that contain saponifiable constituents capable of forming with the base solution the effective emulsifying agent required in forming the oil-in-water emulsion. Examples of such crude oils are the naphthenic-base crude oils such as the heavy California crude oils, for example, those of Kern County, Coalinga, the Valley crudes, and the coastal crudes (Santa Maria); the heavy Venezuelan crudes, for example, Boscan, Tar Zone crude oils; the heavy Mexican crude oils, for example, the Ebano and Panuco types; the heavy crude oils of the Texas Gulf Coast area; the asphalt-containing crudes in Mississippi; the naphthenic oils from the Mid-Continent fields; the intermediate 'base oils, such as those of Kuwait, Iran, Bahrein, Iraq; and the Arabian crude oils.

Various crude oils have different susceptibilities to form the desired oil-in-water emulsions required to obtain the benefit of the present invention. Specifically, it is desirable to evaluate the crude oil for its ability to form the desired emulsion prior to injecting sodium hydroxide or other alkali metal hydroxide solution into a crude producing well to form the prescribed oil-in-water emulsion. In general, the amount of alkali metal hydroxide, such as sodium hydroxide, to be injected will be such that its concentration, expressed in normality, will have a value falling between 0.002 N and 0.75 N, based on total Water present before emulsification, that is, the water not only contributed by the alkaline solution but also any connate water present with the oil to be emulsified. Generally, the emulsions are most readily formed by crude oils having high acid numbers. The emulsion is also more easily formed with fresh waters whose salt content is low. If the native or connate water from the formations producing oil has a salt content such as to interfere with the formation of the emulsion, the problem can be overcome by supplying greater quantities of fresh water from the surface or additional preformed emulsifying agent.

The following table illustrates efiective ranges of sodium hydroxide in weight percent concentration in the aqueous phase that have been used to emulsify samples of crude oil to form oil-in-water emulsions. The discontinuous oil phase was maintained at about 70%, by volume, to produce oil-in-Water emulsions from the crude oils over the given preferred ranges.

NaOH Conc.,

Crude oil: weight percentage in Water Midway-Sunset A 0.41.4 Midway-Sunset B 0.050.5 Midway-Sunset C (ll-1.0 West Coalinga A 0.05l.0 West Coalinga B 0.1-0.5 Boscan 0.050.3 Casmalia 0.10.6 Cat Canyon 0.1-l.0

There are certain oil-bearing formations in which the formation water has a sufficiently high alkali metal carbonate content to permit formation of alkali metal hydroxide in situ by injecting an alkaline earth metal hydroxide, such as calcium hydroxide, a relatively less expensive alkaline material, which reacts with the formation water to form insoluble alkaline earth metal carbonate and aqueous alkali metal hydroxide.

For example, in the Boscan field in Venezuela, formation water has a high sodium bicarbonate content, calcium hydroxide is locally available and inexpensive, while sodium hydroxide must be imported. The invention can be practiced in the Boscan field by injecting either a saturated solution of calcium hydroxide or a dilute dispersion of solid calcium hydroxide in water into the borehole adjacent the downhole pump, there to react with the formation water forming calcium carbonate precipitate and dilute aqueous sodium hydroxide which causes the formation of an oil-in-Water emulsion pursuant to the invention.

Alternatively, with connate waters that do not contain the alkali metal bicarbonate, such as sodium bicarbonate, we have found that the oil-in-water emulsion can be formed by adding sodium carbonate Na (CO along with calcium hydroxide to precipitate the calcium ion as solid calcium carbonate and form the dilute aqueous sodium hydroxide solution. The basic solution then forms the oil-in-water emulsion required to obtain the advantage of the present invention. It is also advantageous with waters that contain calcium or magnesium salts to add sodium carbonate along with the alkali metal hydroxide to form calcium carbonate or magnesium hydroxide. Even when these compounds do not form a precipitate, they are sufficiently inactivated so that they do not interfere with the reaction of the basic solution with the crude to form an oil-in-water emulsion.

With non-asphaltic crudes, for example, Minas and Red Wash crudes, that are nevertheless viscous because of a high paraffin content but contain little, if any, saponifia-ble material, it is possible to form the required oil-in-water emulsion downhole by injecting preformed emulsifying agent together with sufiicient alkaline solution to maintain the specified concentration of base. A suitable emulsifying agent can be obtained in known fashion by caustic extraction of certain low-gravity aspaltic crudes, such as those produced from numerous formations in California oil fields, for example, Casmalia, San Ardo, Midway-Sunset, West Coalinga, and Poso Creek.

A good source of saponifiable materials suitable for making the emulsifying agent are naphthenic acids, having for example, an average molecular weight in about the range 300700. These are obtainable commercially, and can be introduced downhole along with the aqueous alkaline solution, the latter being of sufiicient concentration and amount to provide the specified alkaline content and to form the emulsion having the desired composition, If need be Where the saponifiable materials are insoluble in the alkaline solution, they can be present in the form of a dispersion in oil, for example, oil of like character to be recoverd.

Desirably the resulting low-viscosity oil-in-water emulsion is then either pumped to a storage tank or into a pipeline. The emulsion may thereafter be broken by the addition of acids, such as hydrochloric, sulfuric or carbonic, in a concentration equivalentto the amount of hydroxyl ion added. The water can be separated from the oil by passing it through a heater treater, or electric dehydrator. If required, emulsion breakers, for example such salts as ammonium chloride, sodium chloride or calcium chloride may be added to produce complete breaking of the oil-in-water emulsion.

In another aspect, the invention provides a method of improving the pumpability of crude from a well by forming an oil-in-water emulsion in the well by mixing with the oil an aqueous solution containing a nonionic surfactant. In many instances it is possible to utilize the connate water already present in the well and form the oilin-water emulsion by injecting a nonionic surfactant down the well. This form of the invention is especially useful when the connate water has a relatively high salt content.

The oil-in-water emulsion which is formed by mixing the nonionic surfactant solution and the oil in a well adjacent a downhole pump is relatively stable while the mixture is being moved. The mixture tends to separate into a separate oil phase and a separate water phase when left standing and therefore the mixture can be easily broken down into separate oil and water phases.

The oil-in-water emulsion may be formed with as little as surfactant solution. It is preferred, however, to have substantially more surfactant solution present in the well when forming the emulsion. A /50 ratio of surfactant solution and oil has given good results.

An aqueous surfactant solution is added to the oil to form the desired mixture. As indicated, the amount of water may be as little as about 15 percent. The surfactant is added to the water before the water is mixed with the oil. Nonionic surfactants useful in the present invention can be divided into five basic types by linkage. (See Emulsion Theory and Practice, by P. Becher, ACS Monograph, No. 162, 1965, Reinhold Publishers, New York.) These five types are ether linkage, ester linkage, amide linkage, miscellaneous linkage and multiple linkage.

Further objects and advantages of the present invention will become apparent from the following detailed description, including exemplification of the invention applied to viscous crude oils, taken in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a schematic, vertical sectional view of one form of apparatus suitable for practice of the method of this invention and represents schematically .a system for controlling operation of a well having a sucker rod actuated downhole pump.

FIGURE 2 is an enlarged cross-sectional view of a part of the downhole apparatus shown in FIGURE 1, particularly illustrating operation of the pump on the downstroke.

FIGURE 3 is a view similar to FIGURE 2 showing the pump on the upstroke.

FIGURE 4 is a vertical sectional view of a downhole hydraulic pumping system using the method of this invention, and illustrating schematically the surface operating equipment associated therewith.

FIGURES 5 and 6, respectively, indicate the down stroke and upstroke of the operating unit of FIGURE 4, showing in greater detail use of an aqueous caustic solution as the power fluid and its mixture with the crude oil at the intake of the pump unit.

The method of the present invention is illustrated in FIGURE 1 by a rod actuated downhole pump unit 24 equipped to dilute the production crude with a high gravity (low viscosity) oil. Eadie Patent 2,672,815 is representative of the prior art. As particularly distinguished from the prior art, the present invention permits reducing the viscosity of the pumped fluid to just about that of water. This reduced viscosity is achieved by injecting an aqueous solution of a base, hereinafter typified by sodium hydroxide, into the well adjacent the actuating element, traveling valve 30 of pump 24 so that reciprocation of valve 30 will intimately mix the solution with the viscous crude oil, including any water, entering the well from at producing formation. The emulsion-creating sodium hydroxide solution flows from tank 10 through line 14 under the control of valve 12 and metering pump 16 injects it into well tubing 18. The solution then intermixes with the well fluids above the discharge side of pump 24 in annulus 20, formed by tubing 18 and pipe string 22. At this point crude oil, being lifted by the plunger, or traveling valve, 30 of pump 24, also flows out of slots 26 into annulus 20. The reciprocation of plunger 39 then agitates the aqueous hydroxide solution and oil enough to create the desired oil-in-Water emulsion.

Metering pump 16 supplies the hydroxide solution to tubing 18 at a rate sufficient to form with any native, or formation water entering the well, an oil-in-water emulsion with a concentration of about 30% to 50% water and about 70% to 50% oil, by volume, based on the emulsion. Lower oil concentrations can, of course, be

used with some additional reduction in viscosity of the produced fluid, if the water cut is even higher. As indicated schematically in FIGURE 1, the viscous crude oil from formation 32 enters the well bore through slots 34 in liner 36. The intake of pump 24 is through tailpiece 35, formed as slotted tubing, connected to the bottom of conduit 22.

FIGURES 2 and 3 illustrate in greater detail the construction of pump 24 and respectively illustrate the pump during an upstroke and a downstroke of traveling valve 30. As is well understood in pump art, ball 38 of traveling valve 30, and ball 48 of standing valve 4%), respectively, control the fluid intake and output from pump 24 when rod 17 is reciprocated. As indicated (FIGURE 2), ball 38 lifts off valve seat 39 when valve 30 drops in barrel 37 of pump 24 so that fluid trapped in barrel 37 by ball 48, seated on valve seat 49 rises through central opening 41 in valve 30. On the upstroke of sucker rod 17 (FIGURE 3), ball 33 seals on valve seat 39 to force oil trapped above ball 38 out through slots 26 in tubing 13 to mix in annulus 20 with aqueous hydroxide flowing down tubing 18. At the same time, ball 48 of standing valve 40 lifts from valve seat 49 to admit additional crude oil. The crude oil enters the well from formation 32 through openings 34 in liner 36 and slotted liner 35. The lower end of pump 24 is landed on seat 31 formed above liner 35 and anchored there by tail stock 33.

Desirably the viscous oil is pumped into annulus 2% by pump 24 through slots 26 in tubing 18, at a rate suficient to intimately mix it with the aqueous hydroxide solution flowing down tubing 18 and thereby form the required oil-in-water emulsion.

Alternatively, where the rate of pumping is not high and it is diflicult to mix the basic solution and crude adequately, the basic solution may be advantageously introduced through valve 82 and line 8% to a point below the pump intake. Line runs down the annular space between casing 19 and tubing 22, so that the solution flows into liner 35 to mix with the production fluids, viscous crude and any water, as they pass through pump 24. With such an arrangement, obviously internal tubing 18 can be removed or used for additional flow capacity since the oilin-water emulsion flowing directly around sticker rod string 17 does not appreciably retard its motion either on the upor down-stroke. Because the viscosity of the oil-inwater emulsion is low, the rod string 17 drops freely by gravity. Very light hydrocarbon solutions, kerosene or the like, could be used to reach a similar reduced viscosity 7 but they seldom are because of the cost. However, even if cost were not considered, the resulting dilution does not approach the low viscosity of our oil-in-water emulsion, which can be adjusted to about that of water. At this low viscosity the oil-in-water emulsion will contain about 50% oil as the discontinuous phase. The remaining 50% is water, as the continuous phase.

FIGURE 1 also illustrates one way of automatically controlling the properties of the oil-in-water emulsion to an optimum degree. As stated, the oil-in-water emulsion contains 50 to 70% oil and 30 to 50% water. In general, the higher the water content the more fluid or less viscous is the emulsion. Accordingly, the viscosity of the oilin water emulsion can be controlled to the desired extent, depending on properties of crude and water produced by the formation, again sutficient alkaline solution being used to provide a pH of about 8 to 13.8 in the aqueous phase of the emulsion. The produced oil-in-water emulsion flows up production tubing 22 under the hydraulic pressure applied by pump 24 to gauge, or storage, tank 64 from wellhead 51 through flow line 50. To maintain the quality of the emulsion, two measurements are made on the oil-inwater emulsion flowing through line 50. One of these determines viscosity. Bypass lines 53 and 52 supply a sample through detector 54. The flow rate is similarly measured by orifice 56 and flow rate detector 58. The viscosity and flow rates, as measured by

detectors

54 and 58, respectively, are then used to regulate addition of sodium hydroxide solution, from tank 10, and any required additional water, from tank 13, to line 14 through

valves

12 and 15, respectively, by the operation of controller 60. By proper regulation of

valves

12 and 15 an optimum amount of sodium hydroxide of proper concentration can be supplied downhole through feedline 14 and injection pump 16 into tubing 18.

If desired, emulsion produced from the well is piped directly to storage tank 64 from wellhead 51 by

lines

50 and 62. As mentioned above, one of the advantages of so doing is that flow resistance through

lines

50 and 62 is substantially reduced so that power input to downhole pump 24 to force the production fluid up tubing 22, and through wellhead 51 to storage tank 64 is also reduced. If it is desirable to break the emulsion before the oil is stored, the emulsion can be fed to emulsion breaker or treating tank 66 by closing valve 65 in line 62 and opening valve 67 in line 68. The emulsion can be broken by treatment with salts and/ or acids or heat. After breaking, oil from the top of tank 66 may be sent to storage by line 69 under the control of valve 70. The water phase is disposed of through valve 72 and line 73.

The embodiment of FIGURES 4, S and 6 illustrates application of the invention to another conventional well pumping system. In this embodiment, pump 124 is operated hydraulically, rather than mechanically. As seen in FIGURE 4, pump 124 is supported in the well on pipe 126. Pipe 126 also carries the pressurized actuating fluid which conventionally is hydraulic oil. However, in accordance with the present invention, an aqueous solution of sodium hydroxide, capable of forming the oil-inwater emulsion is used as the power fluid. Surface hydraulic pump unit 130 driven by engine 132 supplies this aqueous hydroxide solution from tank 134 and line 136. The discharge of surface pump 130 then flows to downhole pump 124 through surface pipe 138 and injection tubing 126.

FIGURES and 6 illustrate fluid flow through well pump 124. It will be seen that pump 124 engages tailpipe 102 through passage 103 in packer 100, so that the pump intake is submerged in the liquid produced by the well. Tailpipe opening 104 of pump 124 then admits oil to lower, or intake, chamber 105. In this embodiment of our invention, intake chamber 105 of pump 124 also serves as a mixing chamber to create the required oilin-water emulsion by agitating the crude oil with the aqueone hydroxide solution flowing down hydraulic tubing 126. This solution reaches chamber through passageway 107 that conducts the discharge from the upper, or power section, 110 of pump 124. Power fluid actuates piston element 112 of power section 110 to drive plunger 114 up and down in pump section 116.

As will be understood by those familiar with hydraulically-operated, oil-well pumps, slide valve 117 alternately reverses connections between the opposite ends of chamber 118 to drive piston 112 down and up as shown by the arrows in FIGURES 5 and 6, respectively. Slide valve 117 connects the exhaust from chamber 118 to line 107 so that the aqueous hydroxide solution is continuously supplied under pressure to pump intake chamber 105. Lower section 116 of pump 124 then pumps the emulsion from

discharge ports

120 and 121 to well casing 125 and pipeline 144 for storage in tank 145. The intake ports for pump section 116 are indicated to be under the control of

check valves

122 and 123.

Similar check valves

111 and 113 control the flow out of

discharge ports

120 and 121, respectively, on alternate strokes of piston, or plunger, 114.

The two above specific embodiments illustrate use of the method of the present invention in both mechanically actuated and hydraulically actuated pumping units. It will be apparent to those skilled in the oil well pumping art that many other mechanical forms of apparatus can be used to create an oil-in-water emulsion that will reduce the pumping power required to lift viscous crude oils. In addition to the alternatives mentioned above it is also known to use hollow sucker rods for mechanical pumping systems to drive the downhole pump. In these units, a diluent flows down the hollow rod string and discharges into the tubing just above the pump plunger. The diluent and crude oil mix at this point. Obviously, in such equipment our aqueous hydroxide solution can be substituted, in the same way as in the embodiment of FIGURE 1, to reduce the viscosity of the entire system to about that of water by creating an oil-in-water emulsion.

As discussed before, some downhole hydraulic pumps operate as a closed system. That is, the hydraulic fluid is returned by a separate line to the power unit, such as pump in FIGURE 4, without loss, by mixing it with the produced crude oil. By using an aqueous alkali solution, as in the present invention, the return line can end adjacent the pump to create the desired oil-in-water emulsion. If the hydraulic pressure at the pump discharge is low, it may be desirable to use a nozzle to jet mix the crude oil and aqueous hydroxide solution. The degree of mixing need not be great, but should at least be suflicient to permit intimate contact of the viscous crude by the alkaline solution. If desired, and for somewhat better volume control, a separate line can be used to supplement or replace the supply of aqueous alkaline solution to the pump intake. For example, in FIGURES 4 to 6 a supply line can be tapped into tailstock 104. Flow is then controlled by valve 142.

In creating the desired oil-in-water emulsion downhole, it is important that the base be present in such concentration as to ensure the formation of a stable oil-in-water emulsion. At too low concentrations the emulsion is difficulty formed, and unless an oil-in-water emulsion is formed, the advantages of the present invention cannot be obtained. High concentrations tend to invert the emulsion, forming water-in-oil emulsions that frequently have greater viscosity than the oil alone.

The method of the present invention was used to increase the pumping of an oil well in a California field delivering a producing stream containing about 300 barrels of oil and 45 barrels of water per day. At standard temperature and pressure the produced stream of water and oil had a viscosity 0 fover 200,000 centipoises. The subject well prior to conversion to the present method was being pumped through a system somewhat similar to that of FIGURES 1 to 3. The sucker-rods were hollow 9 and a hydrocarbon diluent, Railroad Diesel of 31 API gravity, was added at a rate of 24 barrels per day. The diluent discharged into the surrounding tubing just above the pump plunger.

The production tubing in the well had an IJD. of 4 inches and the pump was set at a depth of 1530 feet. The stroke of the sucker-rod string was 10 feet and the power available gave a maximum pump rate of 4 strokes per minute. The fluid level in the well stood at about 350 feet from the earths surface so that the pump was submerged about 1200 feet. The flow line from the wellhead to the gauge tank was 1640 feet long and was also 4 inch I.D. pipe.

To perform the method of this invention, an auxiliary pump was used to pump a 0.10 N aqueous solution of sodium hydroxide down the hollow sucker rod string. The solution Was made up using soft, fresh water available at the well site. Using the produced crude, prior to converting from hydrocarbon diluent to sodium hydroxide solution, several oil-in-water emulsions were prepared at the wellhead using said solution to establish that stable oil-in-water emulsions could be made with the fluid then being produced.

A two-hour production run was then made of the well with the pump adjusted to 3 strokes per minute. The well produced at a net daily rate of 160 barrels of oil and 40 barrels of emulsified water, but with no free water production observed. (Hydrocarbon diluent volume of 24 barrels was subtracted.) The flow line pressure at the wellhead was 160 p.s.i.g., with production being discharged at atmospheric pressure to a gauge tank.

The auxiliary pump used to supply sodium hydroxide solution was then connected and the solution substituted for the hydrocarbon diluent. It was supplied to the hollow sucker-rod string at a rate of 100 barrels per day. The hydraulic pumping unit was maintained at a rate of 3 strokes per minute. In 35 minutes an oil-in-water emulsion appeared at the wellhead, the emulsion having a pH about 9. Ten minutes later the oil-in-water emulsion reached the gauge tank. The wellhead pressure in the flow line decreased to 10 p.s.i. (a drop of 150 p.s.i.).

With the pump unit still maintaining 3 strokes per minute, however, the wellhead sample changed from an oil-in-Water emulsion to a creamy, smooth water-in-oil emulsion after another 20 minutes. The flow line pres sure also increased to 140 p.s.i., indicating that additional salt Water was entering the well and inverting the emulsion. Forty minutes later the oil production sampled from a valve at the well-head was noted to have a rope-like consistency, and contained some free water. The water was brownish in color, indicatingv slight emulsification, or extraction of colored material from the oil. Ten minutes later the flow line pressure again reduced to p.s.i. A gauge of fluid production on the above conditions for two hours indicated fluid production was at the rate of 470 barrels per day. Subtracting the 100 barrels per day aqueous hydroxide injection, the net yield of the well was 370 barrels per day; an increase of 170 barrels per day, or an 85% increase over previous fluid production from the well. Net oil produced was at a rate of 220 barrels per day.

A review of the results of the above run indicates that the back pressure on the pump is reduced by reducing viscosity of the fluid in the tubing and flow lines. This back pressure reduction increased pump efliciency. The sucker-rod string dropped freely so that the full stroke of the surface unit was transmitted to the pump; this also contributed to the increased pump efliciency. Thus, essentially the only load on the pump was the weight of the sucker-rod string and the hydrostatic head required to lift the fluid from its level in the well to the earths surface, a total of 350 feet.

If the weight of the sucker-rod string, less buoyancy, and the hydrostatic head of 350 feet are subtracted, the

lifting force on the sucker-rod at the start of the pump stroke was 3250 pounds and 4350 at the end of the stroke while crude plus hydrocarbon diluent was being pumped. When the oil-in-water emulsion was pumped, lifting force varied from to 950 pounds during the pump stroke. If crude had been pumped without diluent, the lifting force would have been considerably higher than with the hydrocarbon diluent. Thus, the effect of pumping oil-in-water emulsion is even greater than the comparison between emulsion and hydrocarbon diluted crude.

Emulsions of the oil-in-water type created by downhole pumping, as disclosed by this invention, can be broken to their constituent oil and water phases by treating with salts and/ or acids. Examples of salts are sodium chloride, ammonium chloride and calcium chloride. Thus, brine or sea water can be used. In the event acids are used, the acid, for example, hydrochloric, sulfuric or carbonic, can be added to the emulsion in proportions up to the chemically equivalent amount of base added in forming the emulsion.

In accordance with another form of the invention, a nonionic surfactant solution is used to form the oil-inwater emulsion. Apparatus such as illustrated in FIG- URES 15 is also useful in this embodiment. All that is required, for example, in the setup illustrated in FIGURE 1 is to replace the source 10 of sodium hydroxide with a source of a suitable nonionic surfactant. In a similar manner, the source of caustic solution storage in FIGURE 4 is replaced by a suitable source of surfactant solution.

The oil-in-water emulsion may be formed with as little as 15% surfactant solution. It is preferred, however, to have substantially more surfactant solution present in the well when forming the emulsion. A 50/50 ratio of surfactant solution and oil has given good results.

As indicated above, the upper oil/ water ratio is limited by the amount of water needed to produce a suitable oil-in-water emulsion for pumping. The upper limit for oil in most surfactant and crude oil mixtures is about 85 percent. Thus the minimum amount of water that can be used in accordance with the present invention usually is about 15 percent. It is preferred, however, to have excess water available to insure that inversion of the emulsion will not occur. Inversion of the emulsion to a water-in-oil emulsion is extremely undesirable since water-in-oil emulsions are very viscous.

An aqueous surfactant solution is added to the oil to form the desired mixture. As indicated, the amount of water may be as little as about 15 percent. The surfactant is added to the water before the water is mixed with the oil. Nonionic surfactants useful in the present invention can be divided into five basic types by linkage. (See Emulsion Theory and Practice, by P. Becher, ACS Monograph, No. 162, 1965, Reinhold Publishers, New York.) These five types are ether linkage, ester linkage, amide linkage, miscellaneous linkage and multiple linkage. The ether linkage, nonionic surfactants are preferred for use in the present invention. The surfactants preferred for use in the present invention are selected from the group having the general formulas:

where R, R and R =any hydrocarbon group and 11 and n =4 to 100.

As indicated above, other surfactants, such as the ester A list of highly preferred surfactants is set out below: linkage and the amide linkage, may be used in accord- TABLE I ance with the invention. The general formula for the e N ester linkage is: lopuet-ary ame R 11 NI? CmHzs 14 (Ii infiifoo 430 6 1 4 R-C-O-(CHzCHgOLJI IQEPAL CO 6 where R=any hydrocarbon group and 77:4 to 100. fa s The general formula for the amide linkage surfactant IGEPAL CO 730 1 IGEPAL 00 350.

(11x5, 000. 100 if (CHQGH'OMH 710. 10 11 Gal )1 070. 50 R C O N DME Prtgniet-arl lnuixturo,

n c eiuica ysimilar (CHZCHZO) to IGEPAL co 887. where R=any hydrocarbon group and 77 and 77 :4 to "Su1table ester l1nl age surfactants, for example, mclude surfactants h v'n th own r o The hlghly preferred nonlonic surfactants for use in aca 1 g 6 011 1 g gene a] f rmulas cordance with the invention are the nonylphenoxypoly H (e thyleneoxy) ethanols. Superror results have been 011- 20 CHH% C O (CEHUOG) (CZH4O)4H tamed W1th surfactants contammg l0l5 moles ethylene oxide per mole of nonylphenol. These surfactants have decreasing water solubility with increasing temperature. Cum?C O (CflHnOGPWZHHOMOH Emuls1ons formed w1th these types of surfactants have good stability up to 160 F. and fair stability in the 160- h 175 F. range. At temperatures in the 200 F. range, sep- 0,,H 0 c 1, 11 Manon g 011 Watter 2 53 'i ii i Table II sets out the results of a number of demonf use a OW Wa er i g actan 8 Opera 6 a strations showing various combinations of oil/water rag s i s a 1 t d fr tios, surfactants, and surfactant percentages useful in h Y li are l f 1 are 56 69 e Om a forming transportable emulsions in accordance with this group avmgt e genera 0mm invention. The results show that suitable mixtures may R O OH CH O) H be formed with water containing .05 percent surfactant 2 2 based on added water. It is usually preferred, however, and to form the mixture with at least about .1 percent surfactant based on added water. The advantage that is obtained by forming the transportable mixture is readily seen in the case of Boscan crude. The viscosity of pure Boscan crude is 80,000 centipoises at 70 F. However, the viscosity of an emulsion containing 75 percent Boscan R2 and 25 percent Water is only centipoises at P. where R, R and R =any alkyl radical and where 77:4 Table II shows properties of various mixtures of Boscan to 100. crude, water and surfactants.

TABLE 11 Chemical Mixture Viscosity Water Sample. No. Oil/Water Remaining in Ratio Namo Vol. percent in F. Cps. Oil Separated Water at 200 l.,

percent 25 C0 710 0.10 117 03 11.7 75 25 00 710 0.10 112 7 2. 0 75/25 CA 530 0.10 115 55 10.8 75/25 CA 030 0.10 103 07 2. 0 75/25 DM 970 0. 10 121 00 12.5 75/25 DM 970 0. 10 10s 00 2. 4 75 25 DME 0. 10 109 91 10. 5 75/25 DME 0. 10 104 3. 0 75/25 NIW 0. 10 120 50 75/25 NIW 0. 10 122 55 10. 0 75/25 NIW 0. 10 110 45 2. 1 30 20 NIW 0. 10 127 40 30/20 NIW 0.10 43 10 0 75/25 NIW 0. 05 11s 11 75/25 NIW 0. 05 120 43 10. 3 30 20 NIW 0. 05 123 25 11. 0 35 15 NIW 0. 05 30 20 00 710 0.10 123 07 10.2 75/25 00 730 0.10 115 92 s. 0 80/20 00 730 0.10 110 147 3. 0 75/25 CO 350 0.10 110 142 11. 0 80/20 C0 850 0.10 111 137 12. 0 75/25 CO 887 0.10 112 102 12.0 80/20 CO 837 0.10 117 133 11.0 75/25 CO 435 0.10 103 104 3. 7 80/20 00 430 0.10 117 11. 0 30/20 CA 530 0. 10 110 48 s. 0 75/25 DM 710 0. 10 120 04 9. 0 30 20 DM 710 0. 10 120 55 10. 5 80/20 DM 070 0. 10 115 93 0. 7 80/20 DME 0.10 114 11. 0 75/25 NIW 0. 15 110 03 11.0 75/25 NIW 0. 20 117 72 15. 0 75/25 Visco-llll 0. 20 114 45 75/25 vim-1111 0. 30 105 81 isco-llll 0. 05 751 5 $11, 111 3,85 s 45 iscol 5 75/2" {10 730 10 1m 95 t 1 '13504111 0.05 75125 CO 8 M5 114 30 The advantages of the method of the present invention have been demonstrated with a number of other crude oils. TAB LE W Table III sets out the properties of mixtures prepared I Water Wet -Q Dispersedin with California crude oils utilizing fresh water and vari- Olw Glass Wall dummy Water Toluene ous surfactants. The California crude oils are namely in- Y N dicated as A, B and C. The A crude has an API gravity es '1 31 of 12.17 and a viscosity of 14,000 centipoises at 70 F. fi The B crude has an API gravity of 12.17 and a viscosity I YZg, of 19,000 centipoises at 70 F. The C crude has an API gravity of 10.15 and a viscosity of 70,000 centipoises at The data given in Tables V and VI indicate that the 70 F. upper limit for oil in most aqueous solution, crude oil TABLE III Chemical Emulsion Viscosity Producing Oil/Water Chemical Concentration Zone Ratio in Water, Temperature, Viscosity,

Volume percent F. cps.

99. 9. 9. 99 HD-IHHHHHHH QOOQQOOOQ In Table IV, the properties of mixtures prepared with mixtures is about 85 percent in order to form a suitable the California crudes nominated A, B and C with aqueous mixture for pumping. solutions containing IGEPAL CO 850 are shown. As indi- It has been found that the water with which the mixcated in the table, the mixture is prepared with both fresh tures of the present invention are formed is not limited and produced waters. Suitable mixtures were formed with to distilled or potable water. The nonionic surfactants are 0.04% surfactant. not aliected by salts in solution in the water; and, there- 'IABLE IV Chemical Emulsion Viscosity Producing Oil/Water Water Concentration Zone Ratio in Water, Temperature, Viscosity,

Volume percent F. cps.

75/25 Prodiuced As is evident from the data presented in Tables II, HI fore, formation water, and even seawater, can be used in and IV, a tremendous improvement in viscosity can be forming the mixtures in accordance with the present invenobtained by forming transportable emulsions of the vistion. This is a particularly desirable feature in field 0pcous crudes in accordance with the present invention. erations since it may not be economical to obtain large T bl V b l shows th ff t f gradually decreasing quantities of relatively fresh water for use in the process the water content in the aqueous surfactant mixture. The the eelmate Writer in the Well y have high Salt d 11 d i T bl V was a California rude t A tent. Table VII sets out the properties of a Boscan crude, oil maintained at 140 F. A 0.1 percent IGEPAL CO 850 aqueous surfactant mixture when the water utilized was in tap water at 72 F. formed the aqueous solution. It is 100 percent Seawaten TWO emulsions were p p with apparent h t i1-in.watr emulsions were f d t h 0 different surfactants and with seawater obtained directly 75/25 to the 15 mixtures because the mixtures were ffem the Oeean at Huntington Beach, Califwater wet and had electrical conductivity.

TABLE VII TABLE V A B Water Wet Elect. Con- Dispersed in 65 O/W Glass Wall ductivity Ratio 75/ 5 75/25 Water Toluene Oil Temperature, F 140 Seawater Temperature, 50 41 Surfactant C0 730 Visco 1111 Surfactant Concentration in Seawater,

Volume Percent 0.1 0.1 Dispersed in Water Yes Yes 70 Conducted Electricity Yes Yes EmulsionViscosity (cps. at 98 F.) 183 Under 200 Table VI below shows the effect of varying the oil/ water 8 After standing at for no Hour, Volume Percent Water ratio 1n mixtures of California crude 011 D. The D crude Remaining in Crude as was at a temperature of F. and was mixed with an aqueous surfactant solution formed of 0.1 percent DM In a demonstration conducted to show the advantages 970 at 72 F. 75 of this aspect of the present invention, a nonionic sur- 15 factant was added to a producing well in the Huntington Beach Field in California. The nonionic surfactant was IGEPAL CO 850 and has the general formula:

Where R=C H and 11:20.

The well originally was producing 13 barrels of oil and 15 barrels of water per day. The well was completed in three producing Zones with the operating fluid level covering only the bottom zone. The nonionic surfactant was added to the annulus between a producing string and the casing. The surfactant was mixed with water at the surface for injection in the annulus. One-tenth of a pound of surfactant per barrel of oil produced was added to the well. Thus, when the well was producing 13 barrels of oil per day, 1.3 pounds of surfactant was used. This daily amount of surfactant was mixed with from 2 /2 to 5 barrels of water for daily injection. The surfactant solution was metered into the well over a 24 hour period. As indicated above, the oil production without surfactant was 13 barrels of oil per day and 15 barrels of water. With the surfactant added to the well, 14 barrels of oil per day and barrels of water per day were produced. The major improvement, however, occurred in improving the efiicien-cy with which the oil was produced. For example, the pressure drop in the 900 feet of 2 /2 inch tubing in the well was 800 psi. before the surfactant was added. The pressure drop in the line after the addition of surfactant, was reduced to only 5 p.s.i. The polished rod horsepower prior to the addition of surfactant was 3 horsepower and after the addition of surfactant was only 2 horsepower. The peak torque prior to the addition of surfactant was 55,000 in-ch/ pounds and with surfactant, was reduced to 30,000 inch/pounds. Downhole pump efficiency without surfactant was 47% and with surfactant was 60%. In addition, the use of surfactant caused the fluid level over the pump to be reduced from 600 feet to 300 feet. The surfactant also had a marked effect on the process of rod drop. The frictional drag on the pump rod during downstroke was reduced to the original drag by the use of surfactant. The above figures indicate that wells utilizing the method of the present invention can be handled with smaller pumping units and lighter rod strings. It is also expected that oil recovery will be improved due to the lowering of the fluid level in the well.

While certain preferred embodiments of the invention have been specifically disclosed, it should be understood that the invention is not limited thereto as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

We claim:

1. In the method of pumping viscous crude from a well bore by a downhole pump in said well bore, the improvement of increasing the pumpa'bility of said viscous crude, which comprises forming adjacent said pump an oil-inwater emulsion of said crude, said oil-in-water emulsion having a substantially lower viscosity than the unemulsified viscous crude, and pumping said oil-in-water emulsion from said well bore.

2. The method of claim 1 further characterized in that the emulsion is formed by adding a nonionic surfactant to the well.

3. The method of claim 2 where the surfactant is selected from the group consisting of 16 and R1 O-o-wmcmonga where R, R and R =any hydrocarbon group and n and n. =4 to 100.

4. The method of claim 1, wherein the aqueous phase of the emulsion has a pH in "about the range 8 to 13.8.

5. The method of claim 4, wherein the emulsion contains, by volume, about 50 to oil, and 30 to 50% water, based on the emulsion.

6. The method of claim 5, wherein the base is an alkali metal hydroxide or ammonium hydroxide.

7. The method of claim 5, wherein the base is sodium hydroxide.

8. The method of increasing the rate at which a viscous asphaltic crude can be produced from a formation traversed by a well bore provided with a downhole pump, which comprises introducing an aqueous basic solution into said well bore at a point adjacent to the actuating element of said pump to neutralize the saponifiable constituents of said crude to a pH in about the range 8 to 13.8 and to convert said viscous crude into an oil-inwater emulsion, the water introduced by the basic solution and any connate water being sufiicient to produce an oil-in-water emulsion having a substantially lower viscosity than the unemulsified crude oil, and then pumping said emulsion from said well bore at a higher rate than is possible using the same power input to said pump to produce untreated quantities of viscous crude.

9. The method of claim 8 in which the aqueous phase of the emulsion has a pH in about the range 9 to 10.

10. The method of claim 9, wherein the emulsion contains, by volume, 50 to 70% oil, and 30 to 50% water.

11. The method of claim 10, wherein the base is an alkali metal hydroxide or ammonium hydroxide.

112. The method of increasing the rate of pumping a viscous parafiinic crude from a well bore provided with a downhole pump, which comprises contacting the crude adjacent the pump with an emulsifying agent, water, and a base, emulsifying said crude into an oil-in-water emulsion, said oil-in-Water emulsion containing by volume, 50 to 70% oil and 30 to 50% water, based on the emulsion, maintaining a pH in the aqueous phase of said emulsion in about the range 8 to 13.8, and then pumping said emulsion from the well bore to the surface.

13. The method of claim 12 wherein the base is an alkali metal hydroxide or ammonium hydroTide.

14. The method of claim 13 wherein the emulsifying agent is derived from naphthenic acids having an average molecular weight in about the range 300-700.

15. The method of claim 14 wherein the base is sodium hydroxide.

16. The method of claim 13, wherein the emulsifying agent is the alkali metal extract of an asphaltic crude.

References Cited UNITED STATES PATENTS 2,530,673 11/1950 Zinszer 166-45 3,073,387 1/ 1963 Dunning et a1. 16645 3,120,266 2/1964 Martin et al. 16645 X 3,196,947 7/ 1965 Van Poolen 16645 ERNEST R. PURSER, Primary Examiner.