US1740103A - Alternate pressure-balancing method for initiating gas lift in oil wells - Google Patents

Description

.Det4 17, 1929. F, W, LAKE 1,740,103

ALTERNATE PRESSURE BALANCING METHOD FOR INITIATING GAS LIFT IN OIL WELLS Filed July 18, 1927 7 ////Y/"//// f v r NVE/V 0R' Francas Zlczce A TTORNE Y p Patented i i FRANGIS LAKE, OF WHITTIER, CALIFORNIA, ASSIGNOR T 'UION OIL COMPANY ee. la.' 'i929 ITED STATES PATENT oFFicE Oli CALIFORNIA, OF LOS ANGELES, CALIFORNIA, A CORPORATION OF CALIFORNIA ALTERNATE PRESSUBE-BALANCING METHOD FOR INITIATING GAS LIFT IN OIL WELLS Application filed July 18,

This invention `relates to the so-called gas li'fwmethod of flowing deep wells,particular starting gas lift and which ordinarily cannot.

be removed by direct application of a reasonable gas pressure in attempting to initiate gas lift. l

u tube.

Gas lift, as now commonly practiced, consists in passing gas under pressure into a well containing a lowtube, so that the gas passes around the lower end of the flow tube in a stream and in its passage atomizes the oil as fast as it is forced up to said tube end by the natural rock pressure in the well, A

the Vatomiz'ed oil being carried to the surface in the gas stream. The gas may be introduced either through the flow tube` or through the casing, the atomized oil being discharged from the other of the two; however, it is preferred usually to introduce the gas into the casing and discharge the oil from the flow But, as above indicated,the initiation of'gas lift usually offers diiculties, due to the fact that during a preceding period of idleness a relatively great hydrostatic head of oil has' accumulated'in the well hole, which head usually cannot be overcome by steady application of a moderate-pressure to one side of the flow tube. This condition arises for 4the reason that, as pressure sapplied to one side of the tube to depress the oil level therein, the hydrostatic head increases in the other side. While some of the oil is forced back into the formation (dependingv upon the viscosity of the oil,fthe friction of the' formation, and the like) the effective rock pressure in the vicinity of the well increases until* it is suicient to balance the increased hydrostatic head. Thus, upon any attem tto start' gas lift by straight application o pressure to one side in order to force over the entire excess load of accummulated oil and uncover the lower end of the tube for passage of gas thereunder, the hydrostatic head will increase until it roaches the maximum, that is, until 1927. Serial No. 206,679.

thousand feet'. Moreover,the pressure which would be high enough to start gas lift by such steady` application, that is,a normal starting pressure, under these conditions, would be excessive for all other, purposes, since when'the oil level is lowered and gas lift started, normal continuation lof gas lift may be and should be carried on with a much lower pressure, lthis being made possible by the much lower density ofthe gas-and-oil column in tlfe'low'tube during normal gas lift as compared with the oil before gas lift. Thus, it is clear that it is not convenient or desirable to maintain said excessive pressure merely for the purpose of overcoming said hydrostatic head.

The term hydrostatic head except where otherwise defined, is used throughout this case to mean the pressure of that portion of the oil body accumulated in the well hole, which stands asa column inthe tube and casing above the lower end of the flow tube. When a well has stood idle for a short time (a few hours or a few Vdays according to the. well), the head will havereached substantially its maximum height and will be in sub'- Y stantial equilibrium with the rock pressure in the vicinity of the hole. The term rock pressure is used to signify the natural expulsive pressure which forces the oil into the well from the formation, and under the conditions just 'described approximately equals said hydrostatic head in the well hole. Oibviously,

head is less than the static head represented by the length of theflow tube between itsv points of intake and discharge.`

If gas under pressure be applied to the casing, for example, of a well containing an accumulated head of oil, oil will be forced up into the tub'e, thereby increasing the static head therein, as aboveindicated. Of course, if the level stands sutliciently high in the well`, the available gas pressure may elevate the oil in the tubing sufficiently to dischargesome oil from the tubing without uncovering the lower end thereof, but discharge will cease as soon as the oil level becomes depressed to such a point that the head in the tubing above lto tubin the oil level balances the gas pressure being ap lied.

n order to initiate gas lift by straight application of pressure, a starting pressure must be employed sufficient to depress the oil level low Venough to allow the passage of gas under the tubing, this pressure belng here termed the normal starting pressure. Such a pressure. must be at least equal tothe ,in-

" creased static head thereby'developed in the flow tube. This increased head of oil in the is here termed the normalstarting head and its ma itude is dependent upon the relative size o the tubing and'casing,the amount and density and viscosity of the oil in the well, the rock pressure, the friction of the formation, etc. The normal startin head as the term is herein employed is de ned as the hydrostatic head of oil in the flow tube above the point of admission to said iow tube at the time gas would break into the How tube. In like manner, the normal starting pressure is defined as the gas pressure necessary to, depress the oil levely in the gas admission tube to the point of gas admission to the flow tube and -sutiicient to start gas lift in the flow tube when said pressure is applied to the surface of the oil in vsaid gas admission tube.'

It is observed that the definition applies whether discharge How is from thetube and gas application is through the casing, or vice versa. If a gas tube is employed and is connected by'a jet to the flow tube in the manner common to air or gas lift, the starting head or pressure may be equal to the hydrostatic head of the oil in the-How tube above the jet when gas is Iirst forced into the gas tube, and it may be equal to or slightly greater thanthe hydrostatic head ofoil above the jet when first applied.

vThe general object of the present invention,`is to overcome the hydrostatic head and depress the oil level a proximately to the lower end of the flow tu e by the application of gas under a pressure less than that required to initiate gas lift by steady application to either the tube or the casing in the usual manner.

The object is attained vby promoting the absorption of a large amount of gasl (natural gas preferred) b the oil body, coupled with a depression of t e oil level to as low a point as possible with the available pressure, whereby the absorbed gas materially reduces the specific gravity of at least the upper portion of the oil body and whereby the available pressure then becomes sufficient to elevate and discharge the column of the so-lightened oil in conjunction with the expansive and lifting properties of the absorbed gas.

Briefly stated, this inven'tion resides in applying gas under pressure (preferably nat- `iral gas)` to awell, the gas being alternately applied lirst 'onone side of the low tube and then on the other side, the accumulated pressure being meanwhile retained and the alternation repeated several times untilthe oil level is depressed as :Ear as possible and the pressure balanced on the two sides, one side then being released while pressure is maintained on the other. In one form of the invention the gas .pressure used may be less than rock pressure and less than` necessary to depress the oil level tothe lower end of the flow tube. The gas, for example, is applied lirst to the casing while the` tube is closed and the pressure built up tol a desired value' in the casing. The casing is then closed to retain the pressure therein as far as possible and period of time sufliciently long.I to reach the maximum condition, this maximum condition being a balancing or equalizing of thepressures in tube and casing, the depression of the oil level within both kthe tube and the casing to the lowest possible point by the available pressure, and the absorption of a .maximum uantity of gas by the oil. Upon suddenly re easing the ressure'either in the tube or in the casing w ile maintainingA thepressure in the other, the head of lightened oil ordinarily Will be. forced out by the applied pressure and gas lift thereby initiated,

due to the fact. that under the improved'conditlons the available pressure will be sulicient to overcome the eiective hydrostatic head on the discharging side above the point of gas admission.

Modifications of the eneric method herein disclosed are describe and claimed in my companion applications, Serial Numbers, 206,677 and 206,681.

In the accompanying drawings, wherein various steps of the present method are diagrammatically represented, l

Fig. 1 indicates the original oil level in the tube and in the casing at the time when gas lift is to be initiated;

Fig. 2 represents the effect pr'oduced on the oil levels when the -low tube is closed and the pressure is built in thecasing;

Fig. 3 indicatesthel possible change in the oil levels when the casing is closed to hold the pressure and the pressure is applied to the How tube; i v

Figui indicates v the possible level relation when the flow tube is again closed and pressure is again applied to the casing;

Fig. 5 represents the approach to a maximum4 condition 'showing the casing closed and indicating the application of pressure to the flow tube, the absorption of considerable quantities of gas by the oil being also indicated; and

which normal gas lift commences wherein gas travels under the lower end of the tube and atomizes the oil as it flows into the well.

An ordinary well casing 1() is shown as receiving flow tube' 12 which depends into the .oil body inthe well for a considerable distance below the level of the accumulated oil. A gas connection 16 is'provided at the Fuppenend of the casing and leads to a compressor or pump 18 which may be connected also with the tube 12 by means of a line 2Q. Operation is ordinarily commenced by closing the valve 22 in the flow tube and 23 in line as indicated in Fig. 2 and introducing gas into the casing until the maximum avaiblable pressure has been built, up whereby the oil level will be depressed from its original position 15 to the point 24, at which time the oil in the tube 12 rises to the level 25 where the pressure produced therein combined with the static head equals the gas pressure in the casing. This condition having been reached, the valve 26 in the gas connection 16 will be closed, the valve 23 will be opened, pressure will be applied to the surface of the oil in the tube 12 whereby the same will be depressed againstthe pressure in the casing and the oil level in the casing will rise somewhat as indicated by the level 28. Under these conditions absorption of an appreciable amount of gas will take place andalso some of the oil will be gradually forced back into the sands as indicated by the arrows in Figs. 3, 4 and 5. Gas absorption on the closed side together with whatever leakage may occur will, of course, allow the oil level upon said closed side to rise to some extent, but this rise will be overcome in the next step. Thus, followinnr the condition indicated in Fig. 3, when the tube 12 is again closed and the pressure is applied to the casing as indicated in Fig. 4, the.oil level will be depressed perhaps to a point 30 while the level in the tube w1ll rise possibly to the level 32, and further forcing of the oils back into the sands and further absorption of gas will result. Repetition of these steps will eventually produce the condition indicated in Fig. 5 Where the levels have been forced down to as low a point as is possible with the available gas pressure and a large amount of gas has been absorbed by the upper portion of the oil body. Gas'absorption has been facilitated by the rlsing and falling or surging movements of the columns which probably occurred as above lndicated whereby at least some agitation has been produced and absorption has been assisted there= by. By observation as to the quantities of gas` which are passed into the well and the pressure attained both on the tube andon the casing, it is possible to compute the probable extent of absorption, and approximate the level in the well witha view to obtaining an idea as to the probability of starting flow of the well. lVhen these conditions are thought to have been reached the pressure on the tube 12 will be suddenly released by opening valve 22 with the result that if the conditions are right, the pressure maintained on the casing will be suiiicient to carry over the column of lightened gas-laden oil, as indicated in Fig. 6.

Ordinarily, the entire excess head will come over at this time whereupon normal gas lift will commence, the gas flowinginto the lower end of the tube and atomizing the oil as it rises in the well. In any event, at least an appreciable quantity of the oil can be so forced over,.although flow may cease if the 'hydrostatic head in the tube becomes too great. In this case, the entire ,operation would be repeated to further increase thev absorption of gas in order to lighten the oil body, the tubebeing released again when this condition has been attained.v As a variation of this process, it is sometimes possible, especially where the hydrostatic head is small, to succeed in starting gas lift in the well by applying pressure merely to the one side andclosing the other until pressure is built up to the maximum, the

closed side being then suddenly released.

This modiiication, however, can be employed only where a slight amount of agitation and absorption is required to assist Athe available pressure. Another variation resides in leaving one side open during the .first application of pressure until pressure has been built up to the maximum on the other side. In thisv instance, the hydrostatic head so developed will assist to further increase the pressure in the well whengasis applied to the formerly opened side.

While' a compressor y1s indicated as being the means for providing gas under pressure,

it is to be understood that gas from a well flowing under suiiiciently high pressure might be conducted direct to the well being started in the present method.

As an example of one method of operation, the casing was closed and pressure built up in the tube to 700#, the oil head of course, rising in the casing. The tube was then closed and casing pressure built up to 620#. Then the tube pressure by increase in tube to 76011:,

the casing to 7 00#, then in the then in the casing to 820# and then in the tube to 82041:. Upon release of the tube pressure, the well began to flow and gas lift was then continued at 100:11; It is also possible to build pressure to higher values in the first stages and thus reach a pressure balancein only one or two applica was raised to 725#, followed y tions on each side, but from an operating standpoint this is not so convenient.

The above disclosures, however, areto be considered asillustrative of the generic invention, and'not as limiting, since many variations may be made withinthe scope of the following claims.

I claim:

1. In a method for establishing gas lift in an oil well containing a body of oil into which a flow tube depends,comprising introducing gas to the surface of oil on one side of the tube under a pressure less than the normal starting pressure to cause absorption of gas by oil'inA the well.

2. In a method for establishing gas liftv in an oil well containing a body of oil into which a flow tube depends, comprising introducing gas to the surface of oil on one side ofthe tube under pressure less than the normal starting pressure to produce a maximum attainable pressure to cause gas absorption by oil in the well,7and suddenly releasing said pressure.

3. A method for establishing gas lift in an oil well containing a body of oil into which a low tube depends, comprising introducing gas to the surface of oil on one side of the tube under pressure less than the normal starting pressure to obtain a maximum `attainable pressure and to cause absorption of gas in the oil, suddenly releasing the pressure on the one side and applying gas under said pressure upon the other side.

4. A method for establishing gas lift in an oil well having a casing containing a body of oil 4into which a flow tube depends, comprising introducing gas into the tube upon the surface of oil therein under pressure less than the normal starting pressure, introducing gas lunder said pressure into the casing, and releasing the pressure on one'side while continuing it on the other side.

5. In a method for establishing gas lift in an oil well having a casing containing a body of oil into which a flow tube depends, the steps comprising introducing gas into the tube upon the surface ofthe oil therein under pressure less than the normal starting pres-y sure, thus producing a maximum attainable pressure, holding said pressure, introducing gas under said pressure into casing, holding said pressure and repeating this operation to produce a maximum absorption of gas by the oil in the well.

6. A method according to claim 5 wherein after the last holding stage the pressure is suddenly released on one side while being applied on the other side to discharge a quantity of oil.

7. A method accordingto claim 5 wherein after the last holding stage the pressure is released on'one side while being applied on the other side to discharge a quantity of oil,

and the steps are repeated until successive melones portions of oil havel been discharged to lower the oil level to a point suiicient for establishing of normal gas lift by the available pressure.

8. A method for establishing gas lift in an oil well containing a casing into which a flow tube depends comprising introducing gas to the surface ofoil in the well under pressure less than the normal starting pressure by alternately applying said gas to the tube and then to the casing tobuild up a maximum available pressure therein, and suddenly releasing the pressure on one side of the tube.

`9. ln a method for initiating gas lift in an oil well comprising collecting a body of oil in a well and continuously applying to the surface thereof a' soluble gas under a pressure less than the normal starting pressure to charge the oil with gas.

10. A method for establishing gas lift in an oil well wherein a ilow tube is positioned within the well casing, comprising bringing gas under pressure to one side of the tube and into contact with an accumulated body of oil for the absorption of gas by the oil, and suddenly releasing the pressure on one side of the tube while applying it to the other side of the tube to cause the oil body to surge.

11. A method for initiating gas lift in an oil well containing a casing and a quantity of accumulated oil into which a ilow tube depends, comprising maintaining a pressure on one side of the tube, depressing the oil level on the other side by applying gas to the oil surface on said other side under a pressure sufficient at least to depress said last named oil level to a point where the pressure will be. capable of discharging any hydrostatic head remaining upon release of -pressure on the one side, and releasing said one side, said pressure being less than the hydrostatic head represented by the distance between the lower end of the flow tube and the point of discharge at the surface. A

12. A method of initiating gas lift in an oil well containing a' body of oil into which a flow tube depends, which comprises applying pressure to the oil on both sides of the flow tube and releasing pressure on one side while maintaining it on the other.

13. A method according to claim 12 wherein the pressures applied on the two sides are substantially equal.

14. A method according to claim 12 wherein the steps are repeated to depress the oil level.

15. A method for initiating gas lift inan said oil level at least to a point Where the pressure will be sufficient to discharge any hydrostatic head remaining upon said release.

16. A. method for establishing gas lift in an oil Well wherein a flow tube is positioned Within the Well casing, comprising bringing gas under pressure to one side ofthe tube and into Contact With an accumulated body of oil for the absorption of gas by the oil, suddenly releasing the pressure on one side of the tube 4and applying it to the other side of the tube to cause the oil body to surge.

17. In a method for establishing gas liftV in an oil Well containing a body of oil into which a flow tube depends, the steps of applying gas to the surface of the oil on the one side of the tube under pressure less than the normal starting pressure to obtain a maximum pressure attainable with the available gas pressure and to cause absorption of gas by the oil, applying gas under pressure to the other side, and subsequently releasing the pressure on the one side and applying it on the other side.

Signed at Los Angeles,in the county of Los Angeles and State of California, this 12th day of July, A. D. 1927 FRANCIS W. LAKE.

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