Use of Treating Compounds for Oil Field Emulsions in the Mid ...

Use of Treating Compounds for Oil Field Emulsions III the Mid-Continent Field

By CI,AUDlUS H. M. ROBERTS, * RT. LOUIS, Mo.

THE dehydrating of oil is a problem in the manipulation of physical and chemical forces, some of which are almost too minute to be capable of evaluation; forces which, however, must be directed and utilized to the maximum extent if successful results are to be obtained The result is accomplished without using any materials capable of harming the oil or any of the equipment by which it is produced, handled, transported or refined; and without removing from the oil any constituents originally present in it or otherwise altering its composition.

An emulsion is defined by Clayton 1 as a system containing two liquid phases, one of which is dispersed as globules in the other. In order that this dispersion may be stable, it is further necessary that an emulsifying agent be present, the nature of this agent controlling the type of emulsion produced, as well a~, to some extent at least, its character and resistance to treatment. The emulsifying agent responsible for the formation of petroleum emulsions is not definitely known but, in a consiuprable number of cases, at least, it is fairly definitely known to be colloidal asphalt, that term being understood to include all asphalts and allied substances which occur in colloidal dispersion in crude oil.

Emulsified oil, as it occurs in the petroleum industry, is variously known as "cut oil,"" wet oil" or "B. S." In addition to the water contained in the emulsion, there may be more or less sand, shale or other foreign materials, but these are incidental and are not essential to the formation or stabilization of emulsions, although they frequently make their economical treatment more difficult. There is little difference between the fresh cut oil produced from a well and the B. S. found in the bottom of the storage tanks; the only essential differences are age and uegree of stabilization of the emulsion, concentration and admixture with foreign materials; the cost of treatment also compares favorably with those of fresh emulsions.

Crude oil emulsions are those eithpr where water is dispersed in oil, or less frequently, where oil is dispersed in water, and are usually treated with ease. The determination of the type of an emulsion is extremely

* Research engineer, 'Vm. S. BarnickpJ & Co. I W. Clayton: Theory of Emulsions and EmnlRifieation. J. & H. Churehill,

London. 321

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~22 lTSE OF TREATING COMPOUNDS FOR OIL FIELD EMULSIONS

simple-if it is miscible with water, it is an emulsion of oil in water; if miscible with oil, it is water dispcrsed in oil. Probably more than 95 pCI' cent. of all oil field emulsions are of the water in oil type and this discussion will be limited to a consideration of such emulsions.

KINDS OF EMULSIONS

Oil field emulsions vary from extremely unstable types, which should more properly be called suspensions, to extremely stable types. Emulsions may be roughly divided into three classes, according to their behavior in the hand centrifuge:

1. Those which show only water and clear oil. These are usually suspensions and will usually separate without chemical treatment if allowed to stand. Some rather unstable emulsions occur which are capable of resolution in the centrifuge, especially when diluted with gasoline, but which will not settle to oil and water without chemical treatment.

2. Those which show emulsion, with or without water, and clear oil. These are true emulsions and require chemical treatment to recover the oil.

3. Those which mayor may not show emulsion and water but which also show cloudy oil after centrifuging.

The problems involved in the practical application of Tret-O-Lite, or similar organic or other treating compounds, are as varied as the types of oil and the conditions of production; yet it is possible to set forth certain principles of application;

1. Determination of the proper compound. 2. Determination of the physical and chemical characteristics of the

oil and water, in so far as they pertain to treatment. 3. Determination of the best manner and proper place to introduce

. the treating compound, in order to secure adequate mixing and agitation. 4. Determination of the proper conditions of heating, washing and

settling, in order to develop maximum treating efficiency and to remove most quickly and completely the liberated water and foreign material.

5. Adjustment of the conditions to the production and local conditions on the lease, in order to insure the most economical handling and minimum labor and overhead expense.

The proper kind of compound is determined by careful qualitative and quantitative tests. The gravity of the oil at the well, its initial boiling point and, when possible, its gasoline content, temperature-viscosity curve and pour test should be determined. In many cases, also, a measurement of the interfacial tension between the water and oil will be found valuable. The water should be analyzed, at least qualitatively, and its gravity determined. The percentage of water in the oil is also important. Such details are necessary only for pioneer installations in

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CLAUDIUS H. M. ROBlmTS 323

a given field. Afterwards, the only variations in the plants are those necessary to accommodate them to conditions on each particular lease.

METHOD OF INTRODUCING COMPOUNDS

In general, the most efficient use of these compounds will be realized. by arranging to introduce them into the emulsified oil at the earliest possible moment after production of the oil. On naturally flowing wells, for example, a special mixer or lubricator is frequently used on the flow line. This is an efficient device but requires some little attention to obtain satisfactory results under conditions of fluctuating line pressure and varying weather. A pump, driven by gas, steam or electricity, is also used on flowing wells with excellent results. Electrically-driven compound pumps are used in California with great success while turbine-driven pumps will soon be introduced into the Panhandle field. The use of pumps, which will uniformly 'and dependably deliver a predetermined quantity of the compound under all conditions, is obviously of considerable benefit in obtaining uniform results.

On wells being artificially flowed with gas or air, the methods of introduction of the compound are, in general, the same as for naturally flowing wells, except where it is introduced into the air line to the well, in order that the emulsion may be treated in the well.

On pumping wells, the force feed pump is by far the simplest, chf'apest and most successful method of introducing the compound into the lead lines. The pumps in common use are the Manzell and Hills-McCanna, both of which give excellent results. Comparative tests of Manzell pumps mounted on the derrick floor and operating off the beam and a lubricator at the point where the lead lines were manifolded showed a reduction in chemical cost from 3 to 1~~ c. per bbl., with the production of better oil. This result was obtained on the Lecroy lease of the Gulf Refining Co., at Smackover, and is, perhaps, exceptional. It showed the extreme importance of adequate mixing and reaction time, as well as of uniform addition of chemical.

These pumps give an extremely flexible installation, as they can be regulated to pump from ~~ pt. to 12 or 15 gal. per day, according to the volume of oil to be treated. Furthermore, the compound is used full strength, which eliminates the necessity of providing fresh, soft water, gasoline or other solvents for it.

The compound, when used in aqueous solution, must be mixed with fresh, soft water. Oil field waters are frequently brackish as well as hard and are entirely unsuited. This is the case in the Panhandle field, where, in the few cases where aqueous solutions are used, condensed water must be used.

On pumping wells and, under certain conditions, on flowing and blown wells, another method of introducing compounds is being used success-

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324 USE OF' TRK~TING COMPOUNDS FOR OIL FIELD EMULSIONS

fully. In this m('thod, th('y are usually in aqueous solution and are introdbced into th(' casing, where they mix with the fluid and either completely or partially break the emulsion l)('fore the fluid reaches th(' surface. This is, in some r('sp('cts, the best method of application. It is stilI more or less in the experimental stage, although it is giving excellent results under production conditions and at extremely low costs in a number of fields, notably Smackover.

One difficulty frequently ('ncOlwtered in treating in the well is that it is impossible to control the d('gree of agitation. Since the compound is a chemical reagent, it is used in extremely small quantities, compared to the volurll(~ of oil treated, and it must be completely and uniformly mixed throughout the oil which it is desir('d to tTeat and under such conditions as will furnish the proper degree of agitat ion. Insufficient agitation will give complete treatment only at an excessive chemical cost, while excessive agitation will sometimes cause re-emulsification, thereby producing an emulsion which may be more difficult to treat than that originally produced.

Some wells produce so much caRinghead gas that it is impossible to introduce the Tret-O-Lite solution into the casing. Thi,; can be overcome by mechanical devices, Ruch aR an extra string of sllJall tubing through which the solution is forced, but thiR remedy is not usually welcomed by supPl'intendcnts.

A lllinimulll compound consumption is r('aliz('c! by introducing it somewhere betw('('n the bottom of the well and the flow tank or gun barrel. Treating oil by pump circulation or by tank batching does not, in general, give as economical results as treating it directly and continuously from the well, as produced.

HEATING THE OIL

Seasonal and, ROlllf'tirnes, daily, variation of weather conditions must be com;icif'red in dCRigning treating plants. Suitable arrangements must be made to protl'et thl' compounds, usually in aqueous solution, from freezing in cold weather or from becoming too viscous to feed properly.

How llluch the oil should be hcated depends upon several factors. among which the gravity differential between the water and oil, viscoRity, pour test, initial boiling point and gasoline content of the oil are of chief importance. The lower limit of temperature is that at which the oil congeals or the viscosity becomes too high to permit the water to settle out. The upper lilllit of temperature is somewhat below the initial boiling point of Ow oil, excppt in cases where it is possible to carryon treatment in entirely closed syst.crns. In such cases it would be possible to heat the oil to, or \)('yond, thl' eracking tplllpl'mture, providing it was cooled below its initial point bl'fore exposure to the air. It is essential that oil be not heated beyond the point where it begins to show any appreciable

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CLA UDIUS H. M. ROBERTS

gravity loss, as this cawws a double loss to the producer; first, in n:duetion of price paid for the oil and, :·;pcond, in eorr('i-ipOIHiing 10i-i8 of produl'iioll. This latter 10::;8 is not always appreciated, since it is not gaged, but it is frequently the greater of the two. At Smackover, for instancp, whpre cooking vats have bpen used to trpat millions of balTds of oil, it wa::; found that the average evaporation loss amouuts to 7.9 bbl. ppr hundred.

In many cases it is not necpssary to heat the oil at all, pxcppt during cold weather, and then only enough to maintain "sumnwr conditions" in the treating plant. In other case::; it is necpssary to apply heat to facilitate and accelerate the action of the compound. In all ca::;ei-i, however, the n~lation between chemical COi-it and heating cOi-ii, plu::; possihk losses, should be carefully determined.

For If'asei-i of sufficient production to warrant tlw installation, the boilp]' Ilf'atpJ' (Fig. 1) can lw n'comment!pd :lS i 1](' most efficient heating

Gas

F](;. l.-BOILEI( HEATER I'IS'I'.\LL.\T[O'l.

equipnwnt. It.s capacity varips from about 1000 to [i()OO hbl. per day, according to tPHllwraiurp r\PRir(·d. It is silllph' to install and ni-ip, failliliar to the man on the leaRe amI giveR a ltIinilllUlll of troublp. If properly installpd, it is fool-proof, ah,.:olutely safe' and cannot harm thp oil.

()il hoilers, no longpr i-iafe for stf'allling, lllay 1)(' paRily and ck'aply modified for usp. Boi\('r heaters "hould b<' <'quipp('d with automatie temperature I'Pguiators. TIlPi-ip dpvic{'s are rpiativnly irH'Xp('llsive, al'l~ positive in action and practieally Plilllirmte any fin' haJlard.

For IpasPi-i with production too sillall to justify a boil(~]' IlPater, or whpre there i" no boilpr availahlf', various su bstitutf's may IlP used, sueh as "tpam linp heaters, gas-fin'd line lwntprs or similar df'vie{'s. All these have poor tr,mperature cont.rol and an' a fin' risk.

A typP of heater (Fig. 2) i-iucceRsfulIy uSf'd in the Burbank field, as wdl as in other places, consi:-;is of two or more seetions of largp casing superposed horizontally and suitably int('rcoJllwctf'd. The lower ::;ection is IlPated with steam or diI'pet flamf'. 'I'll(' fluid f'ntf']'i-i OIle end of the upp('r pipp and, being cold, partially displac('s hot fiuid from ttlP lowpr pipe. This passes up and (Jut through til(' diselial'ge pnd of the heater,

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326 USF} OF TREATING COl\lPOfTNnS FOR o IT, FIELD EMULSIONS

lllixinl2: with SOlllP of t.he cold fluid which has traveled across the Upp(~r pipe. H Illay he f'quipped with automatic temperature regulators. It gives good service but the initial cost is high, compared with capacity.

Other methods of heating use the gun barrel as the unit to be heated. There are numerous objections to this practice, among which may be cited bringing incompletely treated oil into the tank and adding to its functions of washing and settling the oil, that of treating it also. These functions are not at all compatible in many cases, especially where agitation is essential to treating. In addition, application of maximum temperature in gun barrels, especially where temperatures ncar the initial point are necessary, is a direct invitation for gravity and volume losses. In gmcral, it is best to apply the Iwat after the introduction of tllf' ('olllpound.

TANK BATTERIES

The tank battery in a treat ing plant i" the most important part of the installation. The equipment required, in addition to the stock tanks, is a gun barrel and a settling tank. These tanks are essentially similar in design and should be arranged with reference to the stock tanks so that the production travels through them by gravity. The entire treating plant, whenever possible, should be arranged so that no rehandling of the oil is necessary.

The gun barrel is a tank nquipped with a flume or conductor, extending nearly to the bottom, into which the lead line empties at the top. The tank is knpt partly full of salt water and through this the oil washes up, dropping mm.;t of its waim content and depositing dirt, sand and other foreign material. Exccss water is removed from the tank by means of a siphon, which automatically regulates the water level at any desired height. The operation of this siphon, by the way, is a most valuable indication of the succ('ss of ireatmpnt, as the siphon will cease to flow when the gun barrel becomes badly contaminated with emulsified oil.

In cases where, as at Smackover, the water settles quite slowly, a settling tank i.~ 1'('(llliJ'(~d. This is silllilar in design to the gun barrel but.

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CLAUDIUS H. M. ROllJ<:RTS 327

is usually not equipped with a siphon, the water which collects in it being bled off periodically and frequently.

The choice of tanks to be used for washing and settling oil should be carefully considered. In general, tanks of large cross-sectional area are desirable, in order that vertical travel of the oil may be as slow as possible. Again, it is usually desirable to use treating tanks the capacity of which is at least equal to the daily production, although this depends upon the relation between the various factors which control the sedimentation of water. Stokes' law expresses the relation between these factors, but not in a form readily adapted for use, inasmuch as the size of the water globules is not constant and the entire body of fluid is in motion due to the flow through the tank. The law may, however, be used as a guide in designing tanks for treating plants.

Lead of Flow Line Gas

~ I Gut; Barrel SeWing

Tank

F~(J. 3.-TANK BATTERY IN TREATIN(J PLANT.

Attention is invited to the usc of flumes in both gun barrel and settling tank. Experience has shown that flumes are superior to flanged connections in the bottoms of the tanks. Vapors and gases are allowed to escape without agitating the tank and convection currents in the fluid, due to line surges, are avoided. Flumes assure the most favorable settling conditions and should always be used. They may be made vaportight, the gas being discharged beneath the deck of the tank.

The use of vapor-tight tanks in treating plants is desirable but not absolutely necessary.

Where the volume of oil to be treated or its slowness in settling water makes it impracticable to supply the necessary tanks, a special type of settling tank, known as the "excelsior tank" or "hay tank," is used. This is a settling tank packed full of excelsior and provided with suitable baffles to prevent channeling. The action of the excelsior does not depend upon filtration as the voids are much too large, although filtration may playa minor part. It is probable that differential wetting has a large part in the action, as well as modification of interfacial tension. In such fields as Tullos-Urania and West Columbia anc~ to some extent at Smackover, the excelsior tank is used with great success in treating oil which

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328 USE OF TREATING COMPOUNDS FOR OIL FIELD EMULSIONS

otherwise settles its water with great difficulty or not at all. In using such tanks it is imperative that only emulsion-free oil and water be run into them. Allowing emulsion to enter an excelsior tank is the best possible way to put it completely out of action.

Usually, the treating plant can be 90 per cent. equipped from materials available on the lease. In many cases no changes whatever in installation are required and in some fields a tin can with a hole in it constitues the treating plant. At times, it is possible to begin treating within an hour or two after a well begins to produce emulsified oil.

PERSONNEL

The matter of personnel assigned to the treating of oil is often of considerable importance. While the treating of oil in a reasonably well designed plant is extremely simple ~nd easy to accomplish, plants occasionally go wrong. This may be due to some change in emulsion conditions, but more frequently to inattention to or complete disregard of instructions on the part of personnel. The best way to insure intelligent and economical operation of treating plants is for each company to employ a competent engineer directly in charge of all treating, under whom are assistants in each field. These men should have full authority over all treating, both as to material and personnel and their recommendations should be followed.

The "cooking vat" method of treating oil at Smackover is an outstanding example of wastagc of oil due to lack of scientific control in treating. The writer, working in cooperation with the Gulf Refining Co., found that, on a production of approximately 15,000 bbl. of emulsified oil, the actual production loss due to cooking the oil amounted to 7.89 per cent. and entailed a loss of over $1200. per day in production, in addition to a treating cost considerably in excess of 5 c. per bbl. The average gravity of the oil from the wells tested (156 wells) was 20.88° Be. (corrected) and the gasoline content was 12.25 per cent. After passing through the vats and being reduced to pipe line oil, the average gravity had been reduced to 18.06° (corrected) and the gasoline content to 4.36 per cent. In addition to this, the "cooked" oil had an average viscosity of approximately 2000 sec. (Saybolt) at 55° F., while the same oil treated with Tret-O-Lite had an average viscosity at the same temperature of approximately 900 sec. The importance of these results and their bearing on pipe line operating costs need hardly be remarked.

A most important factor in the successful and economical treatment of oil is the mechanical condition of the wells. The greater part of the emulsion produced by a well is formed by agitation during the pumping operation. It is imperative that the pumping equipment be kept in as nearly perfect condition as possible and that the speed and duration of pumping be adjusted to the conditions in the well. Conditiom:; in the

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CLA UDIUS H. M. ROBERTS 329

well, such as minute leaks in the valves, cups or tubing, too small to visibly affect the production, are often responsible for the formation of large amounts of emulsion. In order to reduce the difficulty and cost of treatment of the oil and to keep the production at its maximum, the results of centrifuge tests can well be used as the basis of requirements for lllPchanical work on the well.

It is important to make systematic tests in treating plants and to keep adequate operating records, including compound consumption, amount and gravity of oil treated, treating temperature, operating difficulties, etc., which will be found to be of great value in maintaining the quality of the product and decreasing the cost of treating.

USES OF LIVE STEAM

\Vhereas under certain conditions and with certain kinds of oil direct use of live steam is a great aid .to treating, very often it is the cause of stub· born emulsions. Even when this difficulty does not arise, the water condensed from the steam dilutes the salt water present and renders its coalescence and settlement more difficult, due to increasing the interfacial tension and lowering the gravity differential. This trouble is even experi{~nced at times due to leaks in "team coils and, for this reason, steam coils in trpating plant.s should be car('[ully tested.

STORAGE AND TANK BOTTOMS

So far only those problem" involved in the treatment of fresh production have been considered. In addition, there are large quantities of "to rage oil and tank bottoms treated with treating compounds. These classes of oil when old occasionally require different methods of treatment.

A new method of treating such tank bottoms, as well as certain classes of storage oils, consists of re-emulsification under controlled conditions. The chief physical-chemical difference between fresh emulsions and tank bottom" is the effect of age upon the stabilization of the interfacial film. From this it follows that if some method could be devised to at least partially destroy the old film, a llew emulHioll, partaking of part if not all of t he characteristics of fresh emulsion, would be produced. In addition 10 reducing the chemical cost from 20 c. or more per bbl. to from 1 to 5 c., a considerable reduction in installation cost has been achieved.

While the process has been in use for only a little more than a year, and a wide variety of tank bottoms and storage oils, throughout Oklahoma, Texas and Arkansas, have been successfully treated, it may not prove effective in all cases. An installation for the Magnolia Pipe Line Co., at their tank farm at Ringling, Okla., for example, gave the following result,:;; on the first batch of oil treated:

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Gross fluid treated ................................ . Net oil recovered and run .......................... . Gravity (approx.) of fresh oil. .' ..................... . Gravity of recovered oil. .......................... . Gross cost of project ....................... . Gross cost per bb1. of recovered oil. ................. . Cost by items:

Installation and equipment ....................... . Operation, labor, fuel, supplies .................... . Tret-O-Lite. . . . . . . . . . . . . . . . . . ........... .

47,070 bb1. 35,151 bb1. 28° Be. 27.8° Be. $5486.45 15.61 c.

2.00 c. per bhl. 7.9.'5 c. per bbl. 5.66 c. per hhl.

Treodlng Tank 1000-5000 Bhl.

Treed/ng Tank IOOO-sO(}08bl.

B.S. from Field_ Salf Wafer Olsposal

L .

Boiler

-- [ndicafes Gafe Valve Heafer R( S.

-+-lndicafes C!leek Valve

FIG. 4.-LAYOUT OF TANK BOTTOM PLANT. L, Electric light; T, thermometer; RT, recording thermometer; V, sampling valve;

B, sample barrel (connected to B. S. pump); S, live steam line; ES, exhaust steam line; FW, fresh water line; TOL, Tret-O-Lite line; Dl, short drop on return line to tank (for washing down with water); D., long drop (to bottom) on return line to tank; C, inlet connection to bottom of boiler heater at stack end; RL, overhead return line to treating tanks.

NOTE-Steam line heater is necessary only when available water is Ulumitahle for mixing Tret-O-Lite; Tret-O-Lite lines to be 1 in., all other lines 2 in.

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CLAlJJJlUS H. 1\1:. ROHl!;RTS 331

USE OF PURE WATER

If soH, fresh water is not available, condensed water should be pro~ vided. Care must be taken not to pollute surface waters used for treat~ ing with salt waters drawn from treating plants.

SEDIMENTS

In some fields the presence of excessive amounts of fine sand, shale or other foreign material occasionally causes difficulty in satisfactory func~ tioning of treating plants. When the emulsion is broken this foreign material remains in suspension in the water at least temporarily. How~

ever, all but the finest particles settle out wherever the agitation is insuffi~ eient to retain them in suspension. The usual places of sedimentation arc the heater, gun barrel or settling tank, or the flow tank. Even in Smith separators, where the settling time is insignificant considerable sedimentation may occur. This makes it imperative to provide means for bypassing the various units of treating plants, in order that they may be properly cleaned from time to time.

In the Panhandle field, also, there is much difficulty with foreign matter, chiefly shale. The shale readily passes into suspension in the water when the emulsion is broken and some of it can be bled off with the water. A great deal, however, settles in the tanks and can only be adequately removed by draining them and scraping the bottom.

In classifying the kinds of emulsions usually encountered, it was stated that there are some which resist the action of the centrifuge. In these emulsions the oil appears cloudy when examined on glass, but it is impossible, in many cases, to centrifuge out any emulsion at all. This is true even in oils where the emulsion content is so high that the oil appears brown, instead of its customary green or black color. In such emulsions the particle size is so small that it is not appreciably affected by centrifugal force. In other words, the area-volume ratio of the particles is too great to permit sedimentation. Such emulsions are frequently termed "gas-cut," from a frequent cause or, at least, accompaniment of their occurrence.

GAS-CUT EMULSIONS

Gas-cut or, more properly, micro-emulsions, in the past, have been of more or less infrequent occurrence and then have been limited to scattered wells. They occur at Smackover in wells blown with gas or air and, occasionally, in flowing wells. A number have also been studied at various places in Oklahoma, where the wells are spraying or flowing with large volumes of gas. Decrease in gas or a change in the method of production has eliminated the gas-cut emulsion and substituted for it a normal one.

In the Panhandle field almost every well which does not produce pipe line oil, produces gas-cut emulsion, regardless of the method of production and is practically independent of the amount of gas.

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We have found that the simplest and cheapest method of treating the Panhandle emulsion is by the use of controlled agitation. Conditions are such that treatment cold is successful except in winter when the high cold test of the oil makes it necessary to warm the oil to prevent congealing and to allow the water to settle out. Since, in most cases, the cold test is not above 70° F., very little increase in temperature is necessary, although excessive temperatures are sometimes reached, due to inattentive operation and the lack of automatic temperature regulation.

Another method developed in the Panhandle field involves the use of live steam and treating compound which is injected into the oil on the discharge line from a circulating pump.

In treating plants in which a pump is used for handling the fluid, it is important to keep the treating pump in perfect mechanical condition as defective valves or leaky liners in the pump are not infrequently the cause of considerable trouble.

USE OF "WASH DOWN"

In the treatment of oils in which the combination of high interfacial tension, high viscosity and small gravity differential makes the settlement of water a difficult problem, an expedient of great utility is frequently used. This is the" wash down" with water-sometimes hot water. In ordinary gun barrel operation, the oil is allowed to percolate up through water and then settle. This usually serves to separate the water except under the conditions noted. The wash-down installation consists of one or more water lines of any convenient size, which are arranged in the top of the tank so as to throw several streams of water down through the oil. The lines are preferably arranged so as to set up a slow rotation of the fluid in the tank, thus bringing all of it under the streams of water. The fine droplets of suspended water coalesce with the added water and are carried down to bottom. The method, while uniformly successful, is not often used as it requires a special pump for circulating the water. For continuous operation the excelsior tank will usually be preferred, as it can be connected into the regular gravity-operated system. In cases of accumulations of storage oil, especially when live steam has been used in the oil, the wash down has proven most successful, besides being installed more quickly and cheaply than the excelsior tank.

EXCESS WATER

Attention is frequently called to the presence of relatively large amounts oifree water-sometimes as high as 70 or 80 per cent.-in the production to be treated and it is often asked whether increased treating

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CLAUDIUS H. M. ROBERTS

compound economy would not be secured by first separating the ;l-ee water and t.hen treating the emulsion.

In some cases the presence of excess water has actually been shown to be of distinct benefit. Besides cleaning and scouring the line, which is especially beneficial in waxy oils, the excess water definitely assists treating by thoroughly washing the oil during its travel through the lead line. This aids in coalescence of small water particles resolved from the emulsion, accomplishing part of the effect of the gun barrel wash.

On the other hand, on the Lecroy lease of the Gulf Refining Co., at Smackover, a possible harmful effect of excess water was demonstrated. It had a production of approximately 550 bbI. of oil and some 1200 to 1500 LLI. of water. The Tret-O-Lite was being used in aqueous solution and was fed into the lead lines too close to the gun barrel, which required t he use of excessive amounts properly to treat the oil. There was definite evidence of its loss in the water, due to insufficient time interval for transfer of the compound from solution in water to solution in oil. Tret-O-Lite, it may be stated, wiII form a temporary suspension in salt water, when used in aqueous solution, but this is very unstable and there is no loss in the water if sufficient time is allowed before bleeding off the water. The condition was further aggravated by the fact that the gun barrel was inadequate to properly handle the production. The condition was eorrected by installing force feed pumps.

BFFECT OF GRAVITY

There is small basis for the belief that treating compound requirements bear any definite relation to the gravity of the oil, although it is generally true that resolution of emulsions in high-gravity oils is often easier and more economical than in low-gravity oils. A certain degree of agitation, which may be sufficient to accomplish- perfect mixing in a highgravity oil, will be inadequate in a low-gravity oil, due chiefly to its higher viscosity. This inadequacy is sometimes overcome by using an excessive amount of treating compound, rather than by installing a plant more perfectly adapted to the characteristics of the particular oil.

Crude' petroleum may, for our purposes, be considered to consist of two components, first, the oil propel', in molecular solution and, second, the emulsifying agent, in colloidal suspension. That portion of the oil in molecular solution may be considered to be merely the carrier of the emulsifying agent. Since it is probably inert, as far as emulsification is concerned, and since it largely determines the gravity of the oil, it would appear that there is probably no necessary relation between gravity and emulsification. There is, however, a very definite relation between emulsification and the amount, character and particle size of the material present. in colloidal suspension.

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COST OF TREATING

A question of immediate importance in the daily application of good treating compounds is the average cost per barrel of recovered oil. The writer was informed by a representative of the Gypsy Oil Co., which maintains a treating department, that their average cost for all oil treated in 1925 was somewhat less than 1 c. per bbl. Information at hand indicates that the average is probably somewhere between 1H and 2 c. per barrel.

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