US1740105A - Rock-over method for establishing gas-lift operations in oil wells - Google Patents

Description

.177,1929. Ew. LAKE 1,740,105

ROOK OVER METHOD FOR ESTABLISHING GAS LIFT OPERATIONS `IN OIL WELLS Filed July 18, 1927 N www @E BY A T'TORNE y Patented Dec. l?, 1929 PATENT OFFICE FRANCIS W. LAKE, `OIE' WHITI'IER, CALIFORNIA, ASSIGNOR TO UNION OIL COMPANY OF CALIFORNIA, OF LOS ANGELES, CALIFORNIA, A CORPORATION OF CALIFORNIA ROCK-OVER METHOD FOR ESTABLISHING GAS-LIFT OPERATIONS IN OIL WELLSA Application led July 18, 1927. Serial No. `2(),6,681.

This invention relates to the so-called gas lift method of flowing deep wells, particularly oil wells, and has been designed to overcome the excess hydrostatic head of oil which 5 ordinarly accumulates in such wells prior t0 starting gas lift and which ordinarily cannot be removed by direct application of a reasonable gas pressure in attempting to 1ni'tiate gas lift.

D Gas lift, as now/.commonly practiced, consists in passing gas underpresure into a well containing a flow tube, soithat the gas passes around the lower end of the flow'tube in a stream and in its passageatmniZes-the oil as fast as it is forced up to said tube end by the natural rock pressure in the well, the atomized oil being carried to the surface in the gas stream. The gas may be introduced either through the iow 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 fro`m the iiow tube. 52" But, as above indicated, the initiation of gas liftusually oifers'diiiculties, 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 3U head usually cannot be overcome by steady application of a moderate pressure to one side 'of the flow tube. This -condition arises for the reason that, as pressure is applied to one side of the tube to depress the oil level therein, the hydrostatic 'head increases in the other side. lVhile some of the oil is forced back into the formation (de ending upon the viscosity of the oil, the riction of the Cab formation, and the like) the eifectiverock pressure in the vicinity of the well increases until it is suicient to balance the increased hydrostatic head. Thus, upon any attempt to start gas lift by straight lapplication of pressure to one side in order to force over the entire excess load of accumulated oil and uncover the lower end of the tube for passage i of gas thereunder, the hydrostatic head will increase until it reaches the maximum, that is, until it is equal to the entire'height of the flow tube, which height may be as much as several thousand feet. Moreover, the pressure which would be high enough to start gas lift by such steady application, thatis,

a much lower pressure, this being made possible by the much lower density of the gasand-oil column in the flow tube duringnormal lgas lift as compared with the oil before gaslift.- Thus, it is clear that it is not convement 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 thewell hole, which 'stands as a column inthe tube and Ycasing-above the lower end of the flow tube.

When a well has stood idle for a short time (a few hoursor a few days according to the well), the head will have reached substantially its maximum height and will be in substantial equilibrium with the rock pressure in the vicinity -of the hole.v 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. Obviously, then, in a non-flowing Well under these conditions the said rock pressure or hydrostatic head -is less than the static head represented by the length of the flow tube between its points of intake and discharge.

If gas under pressure be appliedl to the casing for example, of a .well containing an accumulatedhead of oil, oil willv be forced up into the tube, thereby increasing the static head therein, as above indicated. Of course, if the oil level stands sufficiently high in the well,1 the available gas pressure may elevate the oil in the tubing sulliciently to discharge some oil from the tubingwithout 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 pressure being applied.

In order to initiate gaslift by straight application of pressure, a starting pressure under the tubing, this pressure being here termed the normal starting pressure. Such a pressure must be at least equal,towthe.in-'- creased static head thereby developdin lthe' iow tube. This increased head of oil in the tubing is here termed the normal "starting head, the relative size of the tubing and casing, the amount and density and viscosity of the oil linl the well, the rock pressure, the friction of the formation, etc. The normalstarting head as the term is herein employed' is defined as the hydrostatic head of oil in the flow tubeabove the point of admission to said flow tube at the time gas would 'break into the flow tube. In like manner, the normal starting pressure is defined as the gas pressure necessary to depress the oil level in the gas -admission tube tol the pointv of gas admission tothe flow tube and `suflicient to start gas lift in the liow tube when said pressure is applied to the surface of the oil in said gas admission tube. It is observed that the definition applies whether discharge iiow isfrom the tubeand gas application is through the casing, or vice-versa. If a lgas tube is employed and is connected by, a jet to the flow tube in a manner common to air or gas lift, the starting head or pressure may be equal to the hydrostatic head -of the oil in the flow tube above the`jet when gas is irst forced into the gas tube, and it may be equal to or slightly greater than the hydrostatic head of oil above the jet whenfirst applied.

The general object of the present invention,

is to overcome the hydrostatic head and de `press the oil level approximately to the lowf erend of the flow tube by the application of gas under a pressure less than that required to initiate gas lift by steady application to either the tube or' thecasing in the usual manner, and less than the hydrostatic head naturally existing in the well vprior to gas lift initiation,

This object is attained 'hy promoting the absorption of a large amount of gas (natural gas preferred) by the oil body, coupled with a depression of the 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 i.

i of the' oil bodv and whereby the availble pressure then becomes suicientto elevate and disch-arge the column of the so-lightened oil in conjunction with the expansive and lifting properties ofthe. absorbed gas.

For convenience the present method is termed the rock-over method, since it comprises producing a series of impulses in one direction altei-natedwith impulses inthe op-` posite direction-for the purposev of alternatey raising' and lowerin each of the oil coll v l 'umns in the tubing an casing, the impulses must be employed sufficient tokdepress the oilfg .level low enou h to allow the passage of gas.V

being timed and' applied tora'se the rising celumn higher'and higher'in each instance forced out at the top,:this eiiect being assisted Lbygas which has been absorbed under the pressure produced. and by the agitation. re-

sulting from'the alternating or rocking ac- `tion'. and its magnitude is dependent upon such as 'airl but preferably a solublegas such as naturalgas, under a` ressure which, if steadily applied, is insu cientto overcome the normal starting head of the well`,this gas under pressure being applied first to one side of the tubing and then to the other, while the opposite side is released in each instance, so as to rock the two oil columns to and fro as above indicated and to agitate and mix the oil body in the casing and in the flow tube whereb appreciable quantities of gas are absorbed y the oil and serve to lighten the oil columns, this absorbed gas being capable .of expandingbin the upper portion of the column to be discharged so that such expansion evei 1 tually will assist the operation sufiiciently to until the rising oilcolumnf is eventually i carry over at least a small proportion of the oil body, and repeating the alternate pressure applications as often as necessary to estab lish flow.

Subject 'matter disclosed of the generic invention, is covered in my copending and'206,6

In the accompanying drawings wherein oil mnlvements are represented diagrammati- Ca y,

Fig. .1 indicates the oil level as it stands initially inthe casing and flow tube;

Fig. 2 indicates the iirst operation of a method which is usually practiced wherein gas under pressure is applied to the casing outside the flow tube;`

Abut not herein' claimed, together With various modifications applications, Serial Numbers 206,67 7

Fig. 3 indicates the second operation wherein the pressure application is yreversed time;

Fig. 4*-indicates a subsequent operation wherein the pressure is again applied to the casing and the quantity of oil is v thereby pushed out 'from the top ofthe liow tube.

Fig. 5 indicates the condition nally attained, that is, normal gas lift. f' l In these drawings there is shown a well casing 10 into which a flow tube 12 depends through the casing head, said casing head be.

ing also provided with a connection 14 throughwhich gas under pressure may be introduced from compressor C. The level of.

the oil whichhas accumulatedin the tube and and yapplied to vthe iiow tube at the proper izo maaien the casing prior to institution of gas lift proceedings is indicated by line 15, it being the l function of the present invention to reduce this static head by forcing said oil level down to the lower end of the flow tube kl2 whereby gas `will flow undersaid tube to atomize the oil and thereby initiate normal gas lift.,

Ordinarily, the operation is started by iirst p applying the gas under pressure to the surface of the oil in the casing, said gas being introduced through the connection 14 and the flow tube 12 being left open at its upper. end. The pressure is built up in'the casing to the avail# able maximum to cause the oil level to rise in the tube as high as possible and until the static head of oil in the tube equalizes said pressure, the depressed oil level in the casing being indicated at 16, and the level attained in the tube being indicated at 18 in Fig. 2.

0 Under these conditions some oil-may be forced.

` back into the formation, thus further lower- 'ing the oil level. The pressure in the casing is then released and the gas under pressure is transferred to the flow tube by way of con- `nection 19 to follow up the gravity descent of the oil column so as to take advantage of the momentum of such descending column;

Under thispressure application the oil level in the casing is elevated to as high a point as possible, by depression of the level in the tube to as loW a point as possible. In Fig. 3

the dotted line 2O represents the probable limit of descentl of the oil column in tube 12 which would occur by gravity and momentum alone and the dotted line 22 represents the corresponding elevation in the casing, While the line 24 represents the depression of the oil in the column 12 underthe application of pressure, andthe line 25 indicates the corresponding elevation in the casing. These points having been reached the tube pressure is released and gas under pressure is again applied to the casing, the momentum of the moving oil again being relied upon to assist depressing theoil column as far as possible. This alternate'application of gas under pres sure on one side with released pressure on the other side, is repeated as often as necessary and the oil columns are thereby caused to surge back and forth in conjunction with the influences of gravity and momentum whereby an appreciable amount of agitation is produced and contact of the oil with the gas is increased with a resultant increase in gas absorption, which absorption, of course, is materially assisted by the pressure under which the gas is introduced. The gravity descent of the oil column in the casing, which eventually-perhaps would reach point 26 with Y o0 a corresponding elevation in the tube to the point 27, taken in conjunction with the application of pressure to thecasing` through the connection 14 will cause an eventual depression of the oil level in the casing to the point 28 as indicated in Fig. 4 with a consequent if the headwere suciently low.

All of the alternate pressure applications y are properly timed at intervals to correspond with the beginning of descent of'the respective oil columns,I this timing beingdetermined by Watching the pressure gauges; the result is that said columns are caused not only to surge back and forth but also to rise higher and higher on the respective sides until a quantity of the oil is sent over. It is important that this rocking or surging motion so timed as to obtam the lmaximum surge with the greatestl possible rapidity, since such timing vresults in taking the greatest advantage of the .momentum of the moving oil columns. In this fashion the combined influence of such momentum 'of the oil bodies, together with the pressure under which the gas is introduced` and the expansive influences of the absorbed gas, eventually result in establishing continuous flow from the Well, by depression of the oil level-to approximately the lower end of the iow tube 12 as indicated in Fig. 5, so that the gas will iiow around the lower end of said tube, thereby atomizing the adjacent oil and carryingzit upward through the tube in amounts corresponding to the natural oil flow into the well. rdinarily, How may then be continued with a lower pressure than Was required for starting.

Usually it is not possible to cause flow of any great amount of oil over the top in the beginning, since the'head of the relatively heavy oil in the flow'tube above the level in the casing will become too great to be overcome by the gas pressure. But at each sue-r cessive impulse an additional small amount of oil ordinarily will be expelled and at each operation additional amounts of gas will be absorbed until the oil body is isuiicientlyrely'norm'al How, if desired, mayv be 'established from the casing rather than from the tubing and it is to be understood that the invention is the same regardless of the direction of the flow finally established, especially since the initiating steps will be the same.

The method above outlined may be varied by keeping the flow tube closed for a time when the casing is placed under pressure, in order to increase gas absorption. Sometimes when the hydrostatic head is low and only a slight amount. of absorption and agitation is required to start gas lift, the Well will commence to How upon sudden release of vthis cient to continue gas lift.

It is to beunderstpod that the above/disv; closures are merely illustrative, and that many variations of the inventionl maybe made Within the scope of the following clalms as will be apparent to-those slzilled in the art.

I claim:

l. In a method for initiating gas lift infan oil well containing a casing and a body of oil into which a flow tube depends, the steps'comprising introducing gas under pressure into. the casing on one side ofthe tube to elevate a column of oil on the other side of the tube, re-

leasing the pressure and allowing the elevated oil column to return to be mixed with said l body of oil. f

2.' In a method for initiating gas lift in an oil well containing-a casing into which a-flow tube depends, the steps'comprising introducing gasunder pressure into the casing' to an- Y proximate the maximum pressure attainable with the available pressure whereby the oil f body becomes charged with a gas, releasing p ing introducing gas under pressure into the the pressure in the casing, and-repeating these operations until the oil becomes charged with gas suicient to insure discharge of a portion of the oil` v3. In a method for initiating gas lift operation in an oil well containing a casing into which a flow tube depends, the steps compriscasing whereby an oil column is elevated in the tube and the oil body becomes charged with gas, releasing the pressure in the. casing and allowin -t-he oil column to'return, re-

,peatin this operation until the oil becomes charge withgas 'suilicient to insure discharge ofl a portion of the oil, then placing the, casing again under pressure and venting the flow tube to discharge a portion of Vthe charged oil.

4. In a method for initiating gas lift operation in an. oil well having a casing containing abody of oil into which `a ilow tube depends. the steps comprising introducing gas into the casing under pressure less than, the,

normal starting pressure wherebysaid pressure-elevates the oil column in the tube, re-

' leasing the pressure in the casing land allowing the oil column to return, repeating this operation until the oil becomescharged with i gas sufficient to insure discharge of a portion j of the oil, then placing the casing a ain under pressure and ventingthe flow tu e to dis- -charge a portion of the charged oil, and re- Y iframes peating this operation to force out` successive portions of theoil until the level 1n the well is lowered suiiiciently to establish normal gas lift operation.

5. In a method for initiating gas lift operations in an oil well containing a casing in ,which theflow tube depends, the steps comprising introducing gas under pressure into the casing to approximately the maximum pressure attainable with'the available pressure and for elevation vof an oil column in. the tube, releasing the pressure in the casin to allow said oil column to descend 'an' simultaneously applying the available gas pressure to the descending'columnuntil said descending column has been depressed as faras possible, releasing the pressure in' the tube to allow the oil column in the casing to descend, and repeating these operations until y normal gas lift is established.

' 6. In a method for initiating gas lift operations in an oil well containing a casing into which a ow tube depends, the steps of introducing gas into the lcasing under pressure less than that normally required to force gas under the lower end ot the flow tube, to depress the oil body in the casing as far as possible and to .elevate an oil-column in the tube as far-as possible with said pressure, releasing thel pressure in the casing to allow the oil column in the Vtube to descend and Simultaneously applyingpressure to the tube to depress the column therein as far as possible, releasing the'pressure in the tube and repeitfing the above steps to establish normal gas 1 t.

" 7. In a method for initiating gas-lift operations in an oil well, the steps comprising bringing gas under pressure into contact with the surface of an oil body in a well, and agitatino the oil to charge the same with gas.

8. In a method for initiating gas lift oper- -ations in an oil well, the steps comprising bringing a` soluble gas under pressure-into contact with the surface of an oil body in a well, and afgitating the oil by liuctuating the level thereof to charge the oil with the gas. f9. In a method for initiating gas lift in oil wells, the steps comprising bringing -'gas under pressure into contact' with fil in a wellV into which a tube depends and by variation in gas pressures upon 'the opposite sides of the tube causing the oilbody to rock to and fro whereby' the oil is mixed with and becomes charged with gas.`

10. In a method for initiating gas lift in an oil well containing a casing and a body of accumulated oil into which a flow tube depends, thesteps comprising alternately applying series of impulses on opposite sides of the flow tube to alternately raise and lower the oil columns in the tube and casing. .11. In a methodsfor initiating gas lift in an oil well containing a casing and a body of accumulated oil into which a flow tube de-

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