US2550435A - Air chamber for slush pumps - Google Patents

Description

April 24, 1951 Filed Oct. 31, 1947 .MUD TANK H. L. WILLKE AIR CHAMBER FOR SLUSH PUMPS 7 Sheets-Sheet l IN V EN TOR.

ATTORNEY April 24, 1951 w|LLKE 2,550,435

AIR CHAMBER FOR SLUSH PUMPS Filed Oct. 31, 1947 7 Sheets-Sheet 2 PUMP N22 DISCHARGE FROM PUMP NZI 5 4 FIG. 2

' INVENTOR.

flreerflwm/re ATTORNEY April 24, 1951 i w K 2,550,435

AIR CHAMBER FOR SLUSH PUMPS Filed Oct. 31, 1947 '7 Sheets-Sheet 4 v) D w in a u J U 8 U 0 U u! I z a E I! a g S z i E 9 P r- M U U a '3 3 m w w l. G)

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flQFAQrf L CUM/ks BY ATTORNEY April 24, 1951 H. L. WILLKE 2,550,435

AIR CHAMBER FOR swsu PUMPS Filed 001;. 51, 1947 7 Sheets-Sheet s HTTORNEY April 24, 1951 H. WILLKE AIR CHAMBER FOR SLUSH PUMPS Filed Oct 51, 1947 '7 Sheets-Sheet 6 wdI 0:23.". i I Nmz N OI ' INVENTOR. firerf L Ll/IY/A ATTORNEY April 24, 1951 Filed Got. 51, 1947 N \PUMP RESUL AN'T D\SC.

FIGrIO H. WILLKE 2,550,435

AIR CHAMBER FOR SLUSH PUMPS '7 Sheets-Sheet 7 CRANK ANGLE-DEGREES TIME. PER CYCLE I INVENTOR. fiZ/Ae FILL W/Y/Ae Big HTTORNEY Patented Apr. 24, 1951 AIR CHAMBER FOR SLUSH PUMPS Herbert L. Willke, Toledo, Ohio, assignor to The National Supply Company, Pittsburgh, Pa., a corporation of Pennsylvania Application October 31, 1947, Serial No. 783,358

1 Claim.

This invention relates to improvements in slush pump operation with particular reference to an air chamber applicable for use with multi-cylinder reciprocating power driven pumps used in circulating mud systems for rotary drilling to obtain eflicient operation when connected in series to increase the discharge pressure to maintain the required volume of circulating mud as the bore hole depth increases.

In the drilling of deep Wells, say of the order of 10,000 feet or more, it becomesdifiicult to maintain a suflicient volume of circulating mud at a desirable pressure to insure the drill cuttings to be floated to the surface at a sufficient rate to avoid clogging the circulating system. The preferred rate of flow should be in the order of from three to four feet per second in the annulus between the drill pipe and the outer casing to freely bring the cuttings out of the bore hole. The mud is circulated by means of a slush pump, pumping the especially prepared drilling mud from a slush pit through a rotary swivel and down through the drill pipe where it mixes with the churned up formation or cuttings at the bottom of the hole and returns to the surface through the annulus between the inner wall of the bore hole and the outer wall of the drill pipe, carrying with it the drill cuttings. The returned mud and entrained drill cuttings'are conveyed to one end of the slush pit where the solids are screened out and the mud in suspension is then ready for further use in the circulatory system. I

During the initial drilling and the shallower depths one slush pump is usually sufficient to efliciently handle the circulation of the mud but in order to be prepared against pump failure, greater depths, sudden cave-ins or drilling into high pressure formations, it is good practice to provide duplicate pumping equipment operative- 1y connected up for immediate service should the occasion demand its use. Another reason for providing stand-by equipment is to preclude the temporary interruption of mud circulation should the operating pump fail unexpectedly. stoppage of the mud circulation system leads to stuck bits, shear-offs and other serious trouble. If single pumps, large enough to handle the very deep drilling requirements, were used and set up in duplicate, the equipment would not only be very cumbersome and massive, difiicu-lt to move and handle, but also the cost would be prohibitive. To eliminate the above objections and to provide adequate equipment economically, a pair of power driven slush pumps of moderate or standard size can be hooked up so they may be used in parallel or independently for the shallower depths and also compounded for series operation for the greater depths or emergency requirements. When power pumps are operated in series an air cham-' ber should be installed between the two pumps. It is, therefore, the principal object of my in-. vention to provide an air chamber of sufiicient capacity for use with the series operation of a pair of power driven pumps, such that it is possible to efliciently maintain the required volume of circulating mud at a desired pressure as the bore hole depth increases. Another object of my invention is to provide for greater flexibility in the operation of a pair of power driven pumps operated in series and provided with an air chamber of substantial vol ume interposed in the connecting duct between the discharge chamber of the first pump and the suction chamber of the second pump to provide extra volume at a satisfactory operating pressure in cases of emergency such as killing high pres: sure formations suddenly encountered, freeing stuck bits, washing over a fish and other unusual conditions requiring a sudden increase in volume while still maintaining operating pressure. Another object of my invention is to provide for the full utilization of all standard equipment when operating a pair of series connected power driven pumps with an air chamber operatively positioned in the connecting duct between the delivery chamber of the first pump and thesuction chamber of the second pump to furnish a substantially constant volume of circulatingmud at a satisfactory operating pressure regardless of depth or size of the bore hole.

One of the most valuable features of my invention provides for a wide latitude in the use of the equipment at hand in being able to main-' tain a substantially constant volumeof the circulating mud at the required pressure at great depths by operating a pair of standard size pumps in series with an air chamber of substantial size operatively positioned between the discharge chamber of the first pump and the suc-' tion chamber of the second pump. 'Furthen;

where good circulation is maintained in sufficient volume and pressure, a much lighter weight circulating mud may be used. Also by using a plu-' rality of smaller standard size pumps greater portability is possible, and in some instances this is an important factor due to the inaccessible places rigs are sometimes located. 1

Further objects and advantages of my invention will become apparent and in part specifically referred to in the description and specification to follow, which, taken in conjunction with the accompanying drawings, discloses the preferred form of apparatus in accordance with my invention. It should be understood, however, that the disclosure is illustrative of the principles of my invention in its broader aspects.

Fig. 1 is a top plan view of a pair of power driven pumpsoperating in series and including an air chamber interconnected between the pumps and incorporating the features of my invention.

Fig. 2 is a fragmental elevation of the piping diagram between the low pressure pump and the high pressure pump and the' relative location" of the air chamber interposed" in the'line.

Fig. 3 is a flow curve showing graphically the rate of discharge of two doubleacting pistons the first or low pressure duplex pump shown in Fig. 1, for one crankshaft revolution, the cranks being 90 apart. Fig. 3 also shows the resultant discharge obtained by the" summationof the four separate discharges and showing for comparison purposes the average rate of discharge of the pump per revolution;

Fig. 4 is a flow curve showing graphically the rate of suction of the second or high pressure double'acting' duplex pump shown irrFig. l which is connected'in series to the first or low pressure pump and operates with similar characteristics. Fig. 4' also shows the resultant suction and the average rate of suction per revolution of the pump.

. Fig: 5 is adiagram showing. the suction curve or Fig; 4;.represented by thedashed lines, superimposed upon the discharge curve of Fig; 3. represented" by the solid lines. Fig: 5 further shows that" while the average rate of discharge from Fig: Sis-substantiaHythe same as theaverage suctionrat'e of Fig. 4 the two curves do not coincide since the rate of discharge and the rate of suction are different at all times. during the cycle excepting as shown at points A and B. Fig. "5' also shows graphically the difference in the discharge andsuction rates at any instant.

Fig. 6 diagrammatically represents the crank positions of the two cranks for both the low pressure pump (No. l) and the high pressure pump LNo. 2) when the two ,pumpsare operating in uni'sonor phase .1' of their cycle and as graphically shown in. the curves of Figures 3, 4 and. 51

Fig. 7: diagrammatically represents the crank positions ofthe two cranks for both the low pressure pump (No. 1) and. the high pressure pump (No.. 2) when the two pumps are operating in phase 2 of their cycle and as graphically illustrated'by the curves of Fig. 10.

Fig. 8 diagrammatically represents the crank positions of the two cranks for botl'rpumps when the two pumps are operating in phase 3 of their cycle.

Fig. 9 diagrammatically represents the crank positions of the two cranks for'both pumps'when the two pumps'are. operating in phase 4 of their cycle.

7 Fig: 101s a composite diagram illustrating the approximate maximum volumetric difference existing with duplex pumps" compounded or operating in series when. their cranks are" in the position shownv in'Fig. '7 or phasez; The solid lines of the curves indicate the characteristics of the discharge from the low pressure pump (no. 1'') While the dashed lines indicate the suction from the high'pressure pump ('No'. 2).

Inpumpoperation it is common practice to consider one complete revolution of the crank shaft as a cycle comprising a plurality of angular increments, known as phases. In duplex pump operation the corresponding cranks of each pump may coincide or they may differ from each other by a slight angular increment or to a much greater angular difierence until they are back in unison. For the purpose of illustration I' have divided the cycle into quarters and refer to each quarter as a phase. I have designated that portion of the cycle where both pumps are operating in unison as phase 1. During this phase the relative positions of both cranks of bothpumpsare cl'early shown in Fig. 6 and produce the flow curves as indicated in Figures 3 and 4. When the curve of Fig. 4 is superimposed upon: the: curve of. Fig. 3 the resultant graph clearly shows the diflerence in the discharge rate from the low pressure pump (N0. 1) and the suction rate of the high pressure pump (No. 2) at any instant.

As the pumps continue'to operate; the-low'pressure pump (No. 1') does not always pick up a full charge from the mud tank and the pumps cease tooperatein unison. When this occurs the low pressurepump speeds up relatively with respect to" the high pressure pump to equalize the volume of fluid pumped. Insodoing the low pressure pump makes more revolutions for a given time than thehighpressure pump-so that eventually their respective cranks are operating at 90 apart. Ihave designated this crank relationship as phase z and is theositioncfthe cranks shown in Fig. '7 from" which thecomposite diagram (Fig. 10) is constructed. Fig. lfl graphically s'howsthe ap roximate maximum volumetric difl'erence existing in duplex pumps when compounded or operated in series.

It is understood that as the pumps continue tooperate'the relative positions of'the' cranks of thelow pressure'pump continues-to vary with respect to the cranks of thehigh pressure ump and eventually pass through all four quarters or phases until they returnto the position designated as phase 1 when they are again operating in unison. Curvesmay be plotted for'each' phase or fractional phase but I consider the graphs shown in Figures 3, 4', 5' and 10 to be typical of all phases'and; therefore, further exemplification is unnecessary.

In the drawings the numeral l represents the first or low pressure'duplex 'pump while 2 represents the second or high pressure duplex pump of a-pair'of pumps operating'inseries. By series operation it is understood that the low pressure pump I draws circulating mud from the storage tank 3; through line 3a and during its operation discharges it through lines 4' and valve 5, past a T'connection 6 (Fig: 2) and into outlet line 1 and into the suction line 8 of the high pressur pump 2-", through said pump and onout through the discharge line 9 from the high pressure pump 2 and-on to the rotary'swivel (not shown) for circulation purposes.

A check valve 3'cis inserted in the line at to keep-the circulating-mudin line 1 from entering the suction line 31). Line 31), leading from the storage-tank 3'to pump 2, is only tobe used'when pump 2 is operating independently of pump 5. Valve 3d should remain closed when pumps l and 2 are operating in series.

A specially designed air chamber N in which air at-atmospheric' pressure is-trapped and whose capacity-is-verycarefully calculated, is interposed intheuineconnecting the discharge from the low pressure pump I to the suction of the high pressure pump 2 at the T connection 6. This air chamber l performs a most beneficial function in substantially equalizing the cyclic pulsations of the fluid discharge from the low pressure pump I and the cyclic fluctuation of the suction of the high pressure pump 2 since the same amount of fluid must be displaced for thesame time interval of each pump. It is impossible to entirely equalize the volumes between the-two pumps, hence the important function of the air chamber interposed between the discharge of the first and the suction of the second pump. The excess volume discharged from the first or low pressure pump that cannot be immediately utilized by the second or high pressure pump is stored in the air chamber until needed by the high pressure pump to supplement a ,momentary deficiency of the volume discharged from the low pressure pump.

The above condition creates a volumetric difference in identical duplex pumps operating in series that can best be explained by reference to the diagrams in Figs. 3 to inclusive and Fig. and is corrected to a workable degree by the use of the special air chamber which is an important part of my invention. Referring to the diagram in Fig. 3 it will be noted that the area under the resultant discharge curve is representative of the volume of the fluid displaced during one revolution of the crankshaft. The amount of fluid displaced is a summation of the piston areas multiplied by the pump stroke length for the two double acting pistons. This known amount of fluid divided by the area will give a Scale Factor which may be used to determine the amount of fluid displaced during any' ortion of the crankshaft revolution.

Referring to Fig. 4 the Scale Factor for the resultant suction curve will be the same as for the resultant discharge curve inasmuch as the same amount of fluid will be required for one cycle. By superimposing the curve of Fig. 4 on Fig. 3 as shown in Fig. 5 it will be apparent that the average discharge and the average suction are substantially the same, however, the two curves do not coincide as the rate of discharge and the rate of suction are different at all times during the cycle of operation excepting as shown at points A and B. The difference is graphically illustrated in Fig. 5 and shows this difference at any instant during the cycle. The area above or below the Neutral line multiplied by the Scale Factor is equal to the Volumetric Differential between the two pumps. An examination of the curves shown in Fig. 5 indicate that substantial differences momentarily exist between the resultant discharge rate and the resultant suction rate even though the cranks in the pumps are synchronized, that is, the related cranks are in the same-angular position during any instant and remain so for one or any number of crankshaft revolutions. For an interval corresponding to a portion of the time required for one cycle, a volume will be discharged by the low pressure pump I in excess of the volume required by the suction of the high pressure pump 2. This volume difference is dependent upon the relative speeds of the pumps and the relationship of the cranks in the two pumps. The approximate maximum volumetric difference will occur when the cranks are in the position indicated as phase 2 and shown in Fig. 7.

Research and exhaustive tests have proven that the maximum volumetric .difference in units per cycle multiplied by a factor will give the minimum amount of free air units necessary for satisfactory series operation of any type of reciprocating pump. The maximum size of the air chamber is arbitrary. Any size air chamber providing more free air units than the minimum requirements will give satisfactory performance. Air chamber volume based on the ratio of the air volume at operating pressure to the fluid differential per cycle provides an accurate method of determining the proper air chamber size to be used, since it takes into account not only the volume but also the operating pressure. The ratio adopted for duplex pumps connected for series operation most clearly defining the chamber requirements is 1.5 to 1 for the minimum ratio for economical application at the rated pressure of the pump.

It will be noted that with series operation for duplex pumps the greatest volumetric difference occurs while the pumps are operating in phase. In the case of triplex pumps the greatest volumetric difference results from operation between phases. The same method is used for arriving at a suitable minimum size air chamber for series operation of triplex pumps as is used for duplex pumps. The air chamber volume is based on the ratio of the air volume at operating pressure to the fluid differential per cycle. As with duplex pumps, the ratio adopted for triplex pumps connected for series operation as most clearly defining the chamber requirements is 1.5 to 1 for the minimum ratio at the rated pressure of the pump.

As a concrete example, considering the compression as isothermal, a formula of the following order has been developed:

V0 Vd X R X Po Pa wherein Vc=Chamber volume (free air capacity in cu. in.) Vd=Volumetric difference per cycle (cu. in.) R=Ratio of volume occupied by air to volumetric difference per cycle (Vd) Po=0perating pressure (rated pump pressure) Pa=Atmospheric pressure.

Assuming a pump operating at 8'70 pounds per square inch, having a volumetric difference per cycle of 2'70 cu. in. using a ratio of volume 00- cupied by the air to the volumetric difference per cycle of 1.5, the air chamber should be designed to accommodate a volume of 14.7 or 24,000 cu. in.

While my invention has been disclosed as carried out by the apparatus of the above described specific construction, it should be understood that many changes may be made therein without departing from the spirit of the invention in its broader aspects and I do not wish to be limited or restricted to the specific details set forth but wish to reserve to myself any further embodiments, modifications and variations that may appear to those skilled in the art or fall within the scope of the appended claim.

Having fully disclosed my invention, what I claim as'new and desire to secure by United States Letters Patent is:

In a means to combine the output of two reciprocating liquid pumps wherein a first pump having a rate of discharge varying within one cycle discharges to a second pump having a suction rate varying within one'cycle, said pumps 7: being independently and positivelyadriverb so-that the average discharge volume ofsa-idfirstpump iniany one cycle equals appi oximately the-average suction volume' of the second pump duringthe same-cycle, the improvement: comprising: an air 5 8; REFERENCES CITED.

The" fiallowin'g.v references are of record; in i the file of this patent:

UNITED STATES PATENTS Number Name Date 1,049,894 Merrill Jan. '7, 1913 1,200,408 Bushnell "Oct. 3, 1.916 1,707,307 Ho1dsw0rth Apr. 2, 1929 1,877,091 V-ickers Sept. 13, 1932 2,256,743 Kleckner' Sept. 23, 1941 FOREIGN PATENTS Number Country Date 15,098 Great Britain 1897

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