US2258616A - Treatment and producing of oil wells - Google Patents

Description

Patented Oct. 14, 1941 UNITED STATES PATENT OFFICE 2,258,616 TREATMENT AND PRODUCING OF 011.

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John F. Kendrick, Chicago, Ill., assignor to Sullivan Machinery Company, a corporation of Massachusetts No Drawing.- Application July 8, 1939, Serial N0. 283,487

21 Claims. (Cl. 166-21) In many oil fields the producing formation is permeated in itslower portions by water under pressure. Under such conditions water usually ultimately appears in the well discharge, and the control of the water is a very serious problem. If the well has been drilled to the bottom of the sand, the encroachment of the water progresses through various stages until finally the well may be producing large quantities of liquid of which but a small portion may be oil. First the water may finger ahead of the water table; then as the flooding advances the water rises higher and higher in the sand and more and more reduces the flow area-for the oil. When this process has gone on to such an extent that the production from the well is largely water, it will be found that the fluid in the well gnerally consists of a column of mostly water, surmounted by a cap of crude oil, and in the static state the water component is probably high enough completely tocover the face of the oil sand. The formation of such a cone" increases the flow area for the water at the expense of the flow area for the oil, the rate at which thistakes place depending largely on the character of the formation. This may result in the almost complete saturation with water of the sands adjacent the well, most of the oil gaining access to the well as globules that have to pass through the water. When this condition is attained, methods of attempting to cope with the water generally used in the petroleum industry have met with an unsatisfactory degree of success.

Although it is impossible to state positively and beyond question the reasons for this lack of success of methods of coping with the water problem heretofore attempted, certain observations seem to be sound, and these are advanced for what they may be-worth, thoughitis .to be understood that these are tentative only, and that my invention is not dependent upon their soundness. It is be-' lieved to' be generally regarded as true that a given sand will oifer a greater resistance to the- It is beflow of oil than to the flow of water. lieved that once a given body of sand is wet with water, it will not again be permeable freely to oil until the water has been displaced. It is believed that a well which, when shut in, has a column of tion, within any reasonable period, reassume any condition such that a mere resumption of production will result in a permanently increased oilwater ratio. It is believed that when a well has so.

far gone to water that upon stratification of the liquid column which will stand therein when production is interrupted, there will be a water column in the well to a height above the top' of the producing formation, improved oil production will rarely, if ever, result from shutting in the well-at least not within any commercially practicable time. On the other hand, if the water be driven duced, different procedures must be adopted to' secure desirable quantities of oil, depending upon the height to which the water table has risen, whether the water has fingered ahead of the water table, the thickness of the oil sands, etc. Un-

der some conditions, the subjection of the formation to a suitable back pressure, and production at a rate correlated to the back pressure needed, will enablea great improvement in the percentage of oil'in the total quantity of liquid produced; and where the conditions are such that with a comparatively small difference in pressure maintained between the reservoir and the well there can be.

secured a satisfactory production, while the small pressure difierential holds in check the water, very good results can be obtained by a procedure involvingonly the treatment of the well to restore to availability for oil delivery portions of the formation adjacent the well which have become water-sealed, and the maintenance'upon resumed production of correlated back pressure and pumping rate adapted to preclude or at least delay renewed water ingress in objectionable quantities. This procedure is described and claimed in my copending application Serial No.

193,160, of which this present application is a continuation-in-part.

When the water table rises higher and higher in the sands, a greater diiferencein pressure between the reservoir and the well will generally be necessary to produce the desired amount of oil, and where the-reduced pressure diiference and controlled rate of production will not 'produce enough oil, because, for example, of reduced flow area for the oil, resulting from the rising of the water table, a greater diflerence in pressure, with improved rate of oil production, may be'safely employed in many cases by taking advantage of the difference in the horizontal and vertical permeabilities, by steps generally equivalent in their eii'ect to converting the well to a partially penetrating one-a type of well in which the water problem is at least substantially delayed. This operation can be variously performed, and it will be evident that in thick sands it may be possible and desirable to repeat it several times in pace with the advance of the water, with, ordinarily, preconditioning of the sands, as hereinabove mentioned and as hereinafter more fully described, preceding, and sometimes, as will be later explained, also following the procedure adopted for damming the water channels.

According to the present invention, from a major aspect, a well is so treated as to restore to availability for oil delivery portions of the formation adjacent the well which have become water-sealed, and the lower and larger water channels are then dammed-as, but without limitation thereto, by plug off the bottom of'the well by cementing or a squeeze operation-and, if' desired, as a modification, procedure for the promotion of restratification may be reapplied following the technique adopted for the damming 'of water channels which are closed.

According to the present invention, from another aspect, a well is so treated as to restore to availability for oil delivery portions of the formation adjacent the well which have become watersealed, the lower water channels are then dammed, and the well is then produced, desirably with a controlled back pressure, with a diflerential in pressure between the formation and the well adequate, despite reduction in the available flow area for the oil, to effect oil production at a satisfactory rate.

It is an object of my invention to provide an improved method of treating oil water wells. It

is another object of my invention to provide an improved method of treating and producing oil water wells. It is another object of my invention to provide an improved method of treating oilproducing formations. It is still another object of my invention to provide an improved method of treating oil-water wells, utilizing a fluid lighter than the water for forcing down the well the water in the latter, and thereafter selectively sealing the. formation to reduce the flow area for water influx to the well. It is yet another object of my invention to provide an improved method of treating an oil-water well utilizing a liquid of lighter specific gravity than the water ofthe well for forcing down the well the water in the latter, then promoting restratification of the fluids in the producing formation, and then damming in substantial measure the water channels. It is still a further object of my invention to provide an improved method of treating oil water wells including effecting restratification of the oil and water in the formation adjacent the well and then sealing the major water channels. Further, from this aspect of my invention, it is an object thereof to provide an improved method of treating oilwater wellsincluding effecting restratiflcation of the oil and water in the formation and then plugging off the bottom of the well. Still another object of the invention is to effect restratiflcation of the fluids in the formation adjacent an oilwater well and then to plug oil? the bottom of the well by cementing the latter. Another object is to provide an improved method of treating oilwater wells including effecting restratification as hereinabove mentioned, and following this. by

squeezing cement into the formation to seal 01! from communication with the well at least the lower water channels. It is still another object of the invention to provide an improved method of treating and producing oil-water wells involving effecting restratiflcation of the liquids in the formation surrounding the well, damming the water channels, and producing the well under a controlled back pressure to retard subsequent water encroachment. It is still a further object of the invention to provide an improved method of treating and producing oil-water wells which includes effecting restratification of the liquids in the formation adjacent the well, plugging oi! the bottom of the well, and repeating the process with plugging to greater heights as the sands bethat the invention possesses a treating aspect, and

a treating and producing aspect; and from its treating aspect comprises steps of effecting restratification of the liquids in the formation adjacent the well and of damming the water channels, and in some practices of modifications thereof may involve also a step of formation treatment further to promote restratiflcation, subsequent to the damming step; and that each of the steps is capable of being carried out in numerous ways. From the standpoint of the treating and producing aspect, it will be evident that there may be accomplished the further step of correla-' tion of production rate and back pressure maintenance when these are desired or needed also by widely varying techniques and means. Accordingly, to maintain this application within reasonable lengths I shall describe in detail individual steps, and then give, as simply as possible, a very brief statement with respect to the complete process.

The first step in the present invention, from any of its aspects, as in the case of the methods described and claimed in my copending application Serial No. 193,160, is the actual forcing of the water which may be standing in the well, downwardly until its uppermost portion is at least below the top of the producing formation. This may be accomplished in various ways. Liquids, gaseous fluids, or a liquid and a gaseous fluid jointly, may be used. A preferred method is to introduce a quantity of ordinary crude oil into the casing, selecting the quantity in accordance with the circumstances, but when crude oil alone is used as the means for effecting the desired forcing, using a quantity sufficient to insure bringing the lowermost end of the oil column in a well at least somewhat below the uppermost point of communication of the formation with the well bore. It will be rational, where conditions are relatively unknown, to start, assuming the treatment is to be initiated with the tubing withdrawn, with a quantity of oil which when confined in a vertical column of a cross section equal to that of the bore of the casing, will exert a force equalto or somewhat in excess of the bottom hole pressure, though such an amount may be unnecessary if there is a substantial oil cap already at the top of the liquid in the casing, or

again inadequate if, for example, the water pro-- ing, oil may be causedto flowinto the well by gravity and be forced down by the gaseous pressure in the necessary manner.

Gaseous pressures from within the formation penetrated by v the well, or gaseous pressures from other higher pressure'oil or gas wells, or gaseous pressures produced by compression of easing head gases, or other suitable gaseous media, may all be used for forcing down the liquid in the casing.

Where the weight of a vertical column of crude oil equal in cross section to the bore of the easing and of a height equal to the depth of the well would be inadequate, or where the formation pressure makes it necessary, mechanical pumping may be used to force the liquid into the well. Other liquids than crude oil may-be used, natural or artificial, andunder some conditions, as when it is desired to clean the formation or to change the characteristics of thewater to assist in restoring the channels to oil delivery, suitable special fluids may be utilized, singly or in combination.

Sometimes. gaseous pressure alone may be introduced. This may be possible when the column in the well includes, as above suggested; a

cap of oil of substantial volume, but generally,

though not necessarily exclusively, it is believed that when it is thought that there isno (or an inadequate) cap of oil already inthe well, it will be best to introduce, prior to the application of gaseous pressure, oil or other suitable liquid sufficient in quantity at least to start the desired restratiflcation. It is believed, however, that under some conditions, by introducing a sumcient quantity of gaseous fluidcompletely to displace all the liquid above the top of the formation, and then very gradually lowering the gaseous pressure at a rate to keep step with the inflow of oil from the formation and maintain a cumulative back pressure only slightly below the formation pressure, it will be possible thereby to accumulate the necessary quantity of oil for effective processing'directly from the formation.

Introduction of the fluid through the casing, or through the tubing, or through both, is of course possible, and also introduction with the tubing withdrawn.

With reference to the water, the decision will be affected very materially by the well conditions. When the formation pressure is very high and the well is deep, the use of a liquid column will be a natural, though not an imperative, choice. Again,this will be so if the formation pressure is high enough to indicate. having in mind the depth of I the well, a possibility of resumption of natural flow when the production is largely free of water. When -the formation pressure is low a gaseous pressure, or a. gaseous pressure with an exenough, or if there be introduced a cap of the i needed vertical length. Particular choice may under some conditions be almost a matter of preference; and it will be found that almost all conditions encountered will be met satisfactorily by at least one of the choices available.

While it is within the contemplation orlmy invention 'to proceed, when circumstances permit,directly' to the sealing o'r damming procedure immediately after the completion of the displacement of the liquid by the gaseous pressure, ordinarily, after the ,water in the well has been forced down, it will be desirable to apply a procedure which will promote a restratification of mation may be comparatively simple.

the selection of the agent or agents to be used in the step of forcing down iii the liquids in the producing formation, with the result that the water that may have flooded the larger channels at least, will be replaced by oil.

If the present invention is applied to a well soon after it commences to make an objectionable amount of water, the cone which may have developed may be relatively small and the problem of effecting a restratifioation within the for- Indeed, as above indicated, in some cases it may be urinecessary to provide, between the completion of the forcing-down of the water and the application ofthe subsequent water channel. plugging procedure, any further distinct step for the purpose of promoting restratification. On the other hand, if the well has been pumped hard for a 1 within the formation will start to take place, but

ordinarily it will be found that'the rapidity and adequacy of restratification may be promoted and assured by shutting the well in long enough to permit the oil and water in the vicinity of the well to stratify, with the result that the water that-may have flooded the larger channels at least will be replaced by oil. Restratification ,should take place rather rapidly in a well with a high productivity index, and more slowly as the productivity index becomes smaller. 'And th time required for this step to take place may be shortened in many cases, where it may be necessary, by the use of more oil to expel the water from the well, Experience will be the best aid in gauging what if any period of shutting in may be necessary, but the minimum duration of this step will, in a field where" the process is first beingapplied, be determined by the cut and try method. After the conditions of the field have been experimentally determined, this step can of course be put upon a more definite basis.

It will not be necessary to keep the well shut in until restr atification is complete, and ordinarily, it is believed, it will be sufficient if the well is kept shut in until some of the oil channels, particularly but not solely some of the upper ones, have been freed of water, thus increasing the flow area for oil. However, as compared with the method of. procedure described in my oopending application above mentioned, in which subsequent production follows the .restratification without any intermediate damming, sealing or plugging step, it may be desirable to effect more thoroughly the restratiflcation step before the next, in this case the plugging, step is applied.

Under some circumstances, itrnay be advantageous to follow the shut-in period with a period of pumping at a greatly reduced rate, in order 5 that the oil passages may be freed the more readily of the water that blocks them to oil flow;

This slow pumping may cause the discharge into the well bore of the water in some of the oil pasfrom the well, but will instead return to thesands. Ordinarily leaving the fluids undisturbed by shutting in the well, and, if indicated, stimulating circulation by very slow pumping, will effectively promote the desired restratification. In some cases the use of a liquid or gas that will mix with the water and reduce the capillary attraction of the latter so that a small difference in pressure will cause flow through the sands may prove desirable. There will be conditions where a surface tension lowerer will shorten the time required for restratification, and in other -instances restratiflcation will be possible only with its use. As the surface tension of most crude oils is about half that of the average oil field brine, at least a fifty percent solution with the brine in the well will be desirable. One of the commercial alcohols will generally be found best suited to average conditions, and in general the principal objection to the use of a surface tension lowerer will be the expens involved. The step of very slow, circulation-promoting pumping may be of especial advantage if a surface tension lowerer is used.

As will be evident, the quantity of fluid used in forcing down the liquid in the well, the nature of that fluid, and the extent to which it is forced into the formation, may exercise a marked effect on the later stages of the process. If a comparatively large quantity of fluid of lower speciflc.

gravity than the water be utilized, and this fluid be forced into the formation to such an extent that the perhaps only slightly water-permeated sands (in a'case, for example, where the well is treated early) have their oil-flow channels largely cleared of water by the forcing-down step described, the need for any extensive shutting in of the well and of any period of very slow pumping may be obviated. Such a possibility also exists in the case of a well making large quantities of liquid from a loose formation. Usually, it is believed, since the flow under'pressures above theformation pressure will take the paths of least resistance, during the flrst step above described, the water in the well bore will be rather largely forced out, and threads of oil (or of the other fluid of lower specific gravity) will penetrate the water-filled portion of the sands as water is displaced from water-filled channels therein; but it should be mentioned that this hypothesis of the results of the process is not to be regarded as so related to the process that the later substantiation of a different theory, accounting for the end results obtained by the steps disclosed would in any way derogate from the process itself. a In conclusion, with respect to the present general discussion of the step or steps adopted to promote restratiflcation after the water has been forced down. it should again be noted that there is, as it were, a correlation between the subsequent procedure for promoting restratiflcation and the first step described, and that the extent to which the latter is carried markedly affects, or in some cases even obviates, special restratiflcation-promoting procedure.

We come now to a procedure which is not a step in the methods which form the subject matter of this application, but which may be highly useful in effecting successful application of such methods. a

At the end of the shut-in period, or the period of very slow pumping to promote restratification, the well and the upper portion of the sand adjacent the well should be substantially filled with oil, with the water occupying the bottom of the well and of the sands adjacent thereto. An electrical log taken at this stage may yield much information of value in determining the best sub sequent procedure. For instance, it will disclose the location of the boundary between the oil and the water, which will aid in estimating the distance to plug back, or if the squeeze is used, the distance to drill out after the squeeze. Also, it may indicate the relative permeabilities of the oil sections of the sand, and may disclose, it one be present, a water-bearing streak, which might indicate, frequently, that there is no alternative but to continue to pump both water and oil.'

When a considerable program of well treatment is initiated in a field where the structure is reasonably uniform from well to well, electrical logging may be restricted to a few representative wells, but generally it'may be expected to put subsequent operations on a sufiiciently sound basis to justify its cost.

In my copending application above mentioned, I have described and claimed processes which are particularly applicable where the allowable is determined by potential, or where, because the allowable is produced at a relatively high rate for just a short part of the day, the water may have fingered ahead of the water table and resulted in the premature flooding of the well. The application of some or all of the above described steps under such conditions may result in entirely freeing the well of water, and this condition, it may be noted in passing, might be indicated on the electrical log. In such wells as those just mentioned, it will frequently be possible to produce nearly water-free oil simply by slow production under back pressure, particularly where the productivity index is relatively large arid/0r the allowable is relatively small. This should also be the case in a relatively high capacity well in a relatively thick sand, even if the water table has flooded the lower part of the well.

Under such conditions it will only be necessary to reduce the delivery of the pump to approximately that of the oil component of the fluid delivered when both oil and water were produced.

In the case of the sucker rod pump, this would be accomplished by reducing the size of the plunger, length of stroke and/or the strokes per minute. The pump would be located with its inlet well above the water level-preferably, in many cases, above the top of the sand-and production would be resumed at a fraction of the original oil component and stepped up at intervals until the allowable was reached or water returned in objectionable quantities.

It should be noted that the ability to pump even a small quantity of water-free oil would be a definite indication that the oil and water had the formation to some step which will provide.

means to impede the flow of water. The simplest step for this purpose is to plug the lower portion of the well with cement or a suitable substitute. This will make possible a differential pressure gradient between the oil flowing radially and the water flowing spherically, even under those rare conditions when the average vertical permeability of the sand is nearly equal'to the mean horizontal permeability. More commonly the horizontal permeability substantially exceeds the vertical permeability, and under such conditions the variation in pressure gradients becomes larger, but on the one hand this will not ordinarily enable, without the use of some means to impede the fiow of water, oil production at the desired rate without the flow of water in' objectionable quantities, while on the other hand, if the well is plugged back and there is present the condition of a substantially lower vertical than horizontal permeability, there may be effected, by the maintenance of suitable production procedure and conditions, oil delivery in substantial quantity without serious presence of- Water in the well sealing material is flowed down through the tubing, and a suitable proportionate rate of flow of oil and sealing material be maintained, the oil and sealing material would be flowed onto the sand concurrently, with the oil on top. Thereby the sealing material would be largely confined to the water channels, and undesirable sealing of the oil flow channels avoided. After injection of the sealing fluid, the tubing would be raised, so as to prevent its being stuck in the sealing material, and when the latter sets as long as required, pumping can be resumed. Obviously, when this method is practicable in a fairly thick sand, it

discharge for a considerable period. Therefore,

the best results are to be expected by forcing the "It-.- 5"" well and effecting stratification, plugging the water at the bottom of the well, and then utilizing a controlled rate of production under a back pressure where control of the water requires back pressure maintenance and limited (not unrestricted) production. It will be under-' stood that the back pressure may be lowered and the production rate. increased, under this procedure, to effect a larger oil production than would be possible with production under controlled back pressure immediately following the completion to the desired degree of stratification, i. e. without damming the water channels.

Some of the several modes of damming off the water may now be considered. It will be understood that at the conclusion of the step or steps adopted for effecting stratification the oil and water would be generally stratified in the sands and the well would contain a column of oil as a result of applying the oil-water process. If the sucker rods and pump had not already been pulled procedure, this would be .done, and the tubing incident to the stratification-effecting thus left free for the injection of a sealing material. lower end above the top of the water zone; and

if so, it would be lowered to bring its bottom a suitable distance into the water zone. As the oil in the tubing might contaminate the sealing material, it might well be removed by slow swab- The tubing might be disposed .with its tubing containing suitable sealing material, for

example cement, and an anular column of oil in the space between the tubing and the casing, if oil be flowed into the annular space between the casing and the tubing atthe same time the could be repeated to keep pace with the advance of the water table. As the seal would, for reasons above explained, increase the resistance to the flow of water, a faster rate of production could be obtained, with a greatly reduced percentage of water produced. Very rapid or unrestricted production would even now generally cause the water to reappear in objectionable quantities.

However, restratification with slow production under back pressure as described in copending application No. 193,160, will generally reduce the water component desirably.

Plugging back of wells with cement or a suitable substitute therefor by the batch process is currently practiced; and in certain instances will prove a quitesatisfactory procedure for increasing the potential rate of oil production if applied following the effecting of stratification. As the well will, contain a column of oil following the application of the restratification eifecting procedures, as above noted, it may be advisable to take steps to prevent the oil from mixing with the cement. The cementing or plugging operation can be done best through the tubing. With thetubing set low, the oil in the tubing can be removed by slow swabbing, or pumping, or be forced out by compressed gases, or a septum, as described before.v 'Where contamination is not objectionable this procedure would not be necessary. Or the cement could be placed with a dump bailer, either through the casing or tubing. Several designs of such bailers reduce the dangers of contamination.

- At this point, it may be noted that from one aspect my invention includes procedures combining bottom plugging with restratification irrespective of the order of application of these steps, although it is believed that best results will be obtained if the procedure for effecting stratification precedes the plugging step. However, if restratification has not been used as the initial procedure, the plugging-35 by placing cement in the usual waymay be followed by the restratification process without departing from the sumed; but this in its. various aspects will be treated at a later point herein.

Perhaps the best results in many instances may be looked for from a serial application or a restratification step or steps and of a squeezing process, followed, where necessary, with slow production under back pressure, or a second restratiflcation with slow production under back pressure. ,The squeeze'technique, as now generally practiced, consists of setting a retainer, run into the well on a string of tubing, above the formation, which retainer acts as a dam against which pressure can be exerted. A relatively small batch of slurry is then pumped through the tubing, and allowed to remain undisturbed until it has taken an initial set. This is repeateda number of times, until the formation is completely covered, as is evidenced by the pressure building up. The well is then allowed to stand long enough to permit the cement to fully set, when the retainer is drilled out. The crust of cement that may. be

left on the face of the sand is generally broken away by the formation pressure, when the well is bailed dry. However, a squib shot or a casing perforating gun is sometimes used to crack of! a thick deposit. It is obvious that a substitute for cement could be used in the same way.

The principle on which the squeeze works is not clearly understood, as it has been shown by investigators that cement slurry will set up in oil, and that cement slurry cannot be forced into a truly porous media, yet, the squeeze is frequently successful. Failure appears to be the result of the almost complete sealing of both oil and water channels, or the drilling out of the plug, to too great a depth. The restratification sumed at a slow rate, and be stepped up progressively until the desired rate is reached. In any event, the possible production rate without recurrence of water in serious quantity may be expected to be markedly increased over what would be possible, in many cases, were the sealing or plugging step not employed. When it is desired to determine the maximum possible rate 01' production, it can be stepped up until water is again produced in undesirable quantities, the whole procedure, or merely the restratiflcation procedure, repeated, and production continued at the rate found by these tests to be most satof oil and water in the formation, prior to the application of the squeeze, will generally result in more uniformly successful results. It will be noted that this batch technique does notsubject the formation to high pressures, until the face is largely covered with cement that has taken an initial set, and has therefore lost its fluidity.

Resaturating the upper structure with oil'will' change its characteristics sufliciently to exclude the cement, while the water bearing portion. is

not affected. Also, a surface smeared with oil a will not bond as effectively with cement as a washed surface, therefore, the crust of cement can be broken away easier, subsequent to restratiflcation. And if the boundary between the oil and water is determined after restratiflcation, as can be done with one of the electrical logging instruments, the operator will know just how far to drill out the cement plug, as it is unwise to drill farther than necessary, especially where shooting must be resorted to to remove the crust of cement.

After the retainer and cement have been drilled out, it is generally the custom to keep the well bailed out, so. as to utilize the pressure from the formation to break up the crust of cement remaining on the face of the sand. If this is insufdcient, shooting is resorted to. It will be noted that this results in an initial flow,

.when thecrust gives way at a high difference in pressure, which is suflicient frequently to cause Under such conditions, it will be possible to restratify the oil and water, as described above and in my copending application, and resume production at a suitably slow rate under back pressure, and so obtain a satisfactory production of oil.

In this way the technique of the squeeze is supplemented, not altered, by combination with my invention described in my copending application Serial No. 193,160, and a new and valuable process provided.

If desired, following squeeze cementing. the well may again be subjected to the step or steps disclosed for effecting stratification, for the purpose of assuring maximum productivity.

The producing of the well after the plugging or sealing operation, however these are perth'fe water to again cone up and flood the well.

nels operative will be substantially isfactory. Whether production should be under a maintained back pressure will depend on the conditions at the well. Generally, unless the well is considered depleted, the maintenance of a back pressure correlated to the production rate so as to hold the water in check and delay its return in objectionable quantity, will be found desirable, it is believed. Of course, over a period of time it is to be expected that the production rate would have to be'reduced, as the sands are depleted, and eventually a point will be reached where both water and oil would have to be amped to exhaust the sands to the economic No extended discussion of modes of maintaining back pressure is needed, as when the well has standing in it a column of liquid suflicient to counter-balance the formation pressure this may be caused to maintain the formation under the desired back pressure simply by so regulating the pumping rate that the liquid column is not pumped down too fan: or course, also, it will be understood that 'cumulative gaseous and liquid back pressures-may be applied by maintaining the casing head under a desired gaseous pressure. And of course further, if desired, a largely gaseous back lized along methods more fully explained in my copending application above identified.

As a general thing, throughout continued produetion, the rate of production and the maintained back pressure will be controlled to insure .a definitely higher percentage of oil in the total fluid produced than prior to the processing of the well. Ordinarily the liquid produced will be largely if not exclusively oil, and the quantity of oil may be expected ordinarily to exceed that which was obtained just prior to the treatment described, because the number of oil-flow chanincreased.

As the various steps of my improved method of treating oil-water wells, and myimproved method of treating and producing oil-water wells, have been quite fully explained, and as the actual steps employed, and even the total number used, will vary with conditions, it is impossible, without inordinately extending this speciflcation, to describe all of the combinations which may be utilized under varying conditions. It is believed that it will be found that the step of forcing down the water will, perhaps in a majority of the situations encountered, best be performed by the introduction of a suitable quantity of crude o with or without the use of a surface tension lowerer; that this forcingdown step will probably in many cases desirably be followed by the shuttingdn of the well for a period-short though it be-to promote restratipressure may also be uti- I flcation; and that slow pumping to further restratification will not in most instances be required. When it is applicable, the squeeze process, because of its greater likelihood of sealing the water channels, will probably be selected to follow restratification and effect sealing of the water channels. In a majority of cases, restratification following plugging the water channels will perhapsnot be required. Resum'ed oil production at a rate considerably lower than the still other forms than those disclosed for purposes of illustration, without departing from its spirit or the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

l. The method of treating oil-water wells which includes restoring to availability for oil delivery portions of the formation adjacent the well which have become water sealed by forcing, through the medium of a liquid of lighter specific gravity than the water, the water standing in the well into such position in the formation that there will be a reduced interference with the I entry of oil into the well, then plugging off the bottom of the well by cementing, and thereafter repeating before a resumption of production the procedure utilized to restore to availability for oil delivery the portions of the formation adjacent the well which had been water sealed.

2. The method of treating and producing oilwater wells which includes the steps of utilizing a liquid lighter than the water to force down the well the water in the latter, thereafter selectively sealing the formation to reduce the flow area for water influx to the well, and thereafter producing the well under a back pressure so related to the formation pressure as to retard undesired water recurrence but to permit oil production at a satisfactory rate. l

3. The method of treating an oil-water well which includes introducing a liquid of lighter specific gravity than the water in the well into the latter to force down the well the water therein, then shutting in the well for a period for pro- Inoting rest-ratification of the fluidsin the producing formation, and then damming in substantial measure the water channels.

4. The method of treating an oil-water well which includes introducing a liquid of lighter specific gravity than the water in the well into the'latter to force down the well the water therein, then subjecting the formation to a back pressure and producing, while such back pressure is maintained, oil ata low rate controlled to confin the production substantially to oil,

thereby to promote restratification of the fluids in the producing formation, and then damming in substantial measure the water channels.

5. The method of treating and producing an oil-water well which contains a liquid column consisting at least in part of water, which method includes the steps of subjecting the liquid column in the well to a pressure through the medium of a fluid column at least the lower portion of which is a column of liquid lighterthan the water until by the pressure so exerted'nt'least the water portion of the'liquid column in the well is" forced to a position wherein improved oil entry to the well wlll'be possible, shutting in the well for a period, sealing by a cementing process at least some of the lower water channels, and

then producing the well while maintaining by the fluid contents thereof a back pressure upon the formation, the rate of production and the back pressure being correlated to hold in check the water in the formation.

6. The method of treating and producing an oil-water well which contains a liquid column consisting at least in part of water, which method includes the steps of subjecting the liquid column in the well to a pressure through the medium of a fluid column at least the lower portion of which is a column of liquid lighter than the water until by the pressure so exerted at least the water portion of the liquid column inthe well is ,forced to a position wherein improved oil entry to the well will be possible, effecting an initial delivery of liquid from the well at a rate and under a backpressure correlated to effect a delivery of oil at a rate materially below the previous rate of delivery of oil alone, then plugging off at least some of the lower water channels, and then producing the well while maintaining by the fluid contents thereof a back pressure upon the formation, the rate of production and the back pressure being correlated so as at least largely to hold the water in the formation.

7. The method of treating an oil-water well which contains a liquid column comprising water at least in its lower portion and including an overlying oil cap, which method includes the steps of introducing into the well a column of oil of such a height as when superimposed upon the liquid in the well to establish a column of oil above the water of a height suflicient to overbalance the formation pressure, effecting a disposition of the water in the formation such that there will be a reduced interference with the entry of oil to the well. and. then plugging the lower portions of the formation to reduce the freedom of water ingress from the formation to the well.

8. The method of treating and producing an oil-water well which includes introducing into the well a quantity of a liquid of lower specific gravity than the. water therein sufficient when introduced into the casing to exert a hydrostatic pressure at least equal to the formation pressure, forcing down the well the liquid previously in the latter, then da'mming at least some of the lower meansof water ingress to the well, and

then producing the well under a back pressure provided by the fluid contents of the well and at a rate correlated to such back pressure to preclude a proportion of water in the well discharge in excess of a predetermined percent.-

9. The method of claim 8 in which the well is shut in for a period intermediate the forcing.

down of the liquid and the damming operation.

10. The method of claim 8 in which a restratifi'cation within the producing formation. is promoted between the forcing down of the liquid and the damming operation by the subjection of the formation to a back pressure and the production, while such back pressure is maintained, of oil at a low rate controlled to confine the production substantially to oil.

11. The method of treating an oil-water well well and the contiguous producing formation by a procedure which includes forcing into the well a quantity of crude oil suflicient to fill the well completely full from the casing head to a point below the top of the producing formation, forcing thereby the liquid previously in the well below the top of the formation, and subsequently cementing the lower part of the well to dam thereby at least some of the lower water passages.

12. The method of treating an oil-water well which includes effecting the establishment within th well of a substantial gaseous pressure and then introducing into said well a cap of a liquid of a lower specific gravity than the water in the well of such height that the hydrostatic pressure of the cap and the gaseous pressure within the well are effective to force down the liquid reviously standing in the well and displace the water in the well into the producing formation, and thereafter sealing prior to the resumption of production at least some of the lower waterdischarging passages in the formation.

13. The method of treating an oil-water well which includes effecting the establishment with in the well of a substantial gaseous pressure and then introducing into said well a cap of a liquid of a lower specific gravity than the water in said well of such height that the hydrostatic pressure of the cap and the gaseous pressure within the well are efiective to force down the liquid previously standing in the well and displace the water in the well into the producing formation, shuttingin said well for a period to provide opportunity for a repositioning of the liquids within the formation, and thereafter damming prior to the resumption of production at least some of the formerly water-delivering passages in the formation.

14. The method of treating an oil-water well which includes the steps of introducing into the well a cap of a liquid of lower specific gravity than the water in the well and then building up a gaseous pressure within the well to act upon the introduced cap and with the latter to produce a pressure suflicient to force the water in the well to a position below the uppermost limits of the producing formation, and thereafter selectively sealing the formation, prior to a resumption of production, to increase the ratio of oil to water in the well discharge.

15. The method of treating and producing an oil-water well, which includes introducing into the well a liquid of lighter specific gravity than the water therein to 'act upon the liquid therein,- thereby forcing the water in said well down the well and producing a condition conducive to effective selective sealing .of the formation, plugging at least a partof the water passages, and.

thereafter producing the well under a back pressure provided by a liquidcolumn of lower specific gravity than the water and maintained of a height sufiicient to exert a hydrostatic pressure on the formation adequate to holdwater in the formation in check.

16. The method of treating and producing an oil-water well, which includes introducing into the well a liquid lighter than the liquid therein, thereby forcing the water in said well down the well and producing a condition conducive to effective selective sealing of the formation, plugging at least a part of the water passages, and thereafter producing the well under a back pres- 2,258,616 7 which includes effecting a reconditioning of the sure furnished by a cumulatively acting liquid and a gaseous pressure together exerting on the formation a pressure sumcient to preclude water in the well discharg in excess of a predetermined percentage.

17. The method of treating and producing an oil-water well, which includes the steps of introducing into the'well a cap of a liquid of lower specific gravity than the water in said well, to act upon the top of the liquid column in the latter, then closing in the well until the gaseous pressure building up therein from the formation, cumulated with the hydrostatic pressure of said cap, forces the liquid originally in the well'down and there occurs within the formation such a rearrangement of the fluids therein that a greater percentage of water passages will be sealed upon cementing than would be the case otherwise, then cementing at least the lowest part of the well bore and thereafter producing the well under a back presure while restricting the rate of production to preclude water in the well discharge beyond a predetermined proportion.

18. The method of treatingand producing an' oil-water well, which includes introducing into the well aquantity of a gaseous fiuid sufiicient in volume and pressure to force down the liquid in the well and displace the water in the latter to a position below the uppermost limits of the producing formation, thereafter slowly bleeding down the gaseous pressur at a rate less than the rate .at which the oil can enter the well from the formation, to build up an oil column in the well, then forcing down the well the oil column so produced, to promote restratification in the formation, then sealing at least a part of the water-discharge passages, and then producing said well at a rate not materially exceeding the potential rate of oil ingress to the well.

19. The method of treating oil-water wells which includes introducing into the latter a surface tension lowerer and a fluid for forcing the liquid column standing in the well down the latter, and subsequent to at least a partial restratification of the oil and water in the producingformation cementing the well to seal a larger proportion of the water delivery channels than of the oil delivery channels.

20. The method of treating and producing oilwater wells which includes forcing crude oil into the well to initiate restratification, selectively sealing the well to reduce the water discharge from th formation, and repeating the forcing of crude oil into the formation, and then producing the well under correlated conditions of production rate and back pressure to maintain a production largely of oil.

21. Th method of treating an oil-water well which includes effecting a restratification of the fluids in the well by the forcing down of the water therein through a fiuid column consisting at least in part of a liquid of lighter specific gravity than the water in the well, locating the water level, sealing the formation by the squeeze process, redrilling to a point determined by the survey to be above the water level, again effecting JOHN I". KENDRICK.