WO2016127382A1

WO2016127382A1 - Reciprocating pump

Info

Publication number: WO2016127382A1
Application number: PCT/CN2015/072966
Authority: WO
Inventors: Mengjin Yu; Yuanjian CHEN; Lei Cheng; Hongfei PAN
Original assignee: National Oilwell Varco Petroleum Equipment (Shanghai) Co., Ltd.
Priority date: 2015-02-13
Filing date: 2015-02-13
Publication date: 2016-08-18

Abstract

A reciprocating pump comprising a hydraulic cylinder (151) having a hydraulic piston (152) slideably arranged therein, and a rear cylinder head (175), the hydraulic piston comprising a piston rod (153) extending thereform, the reciprocating pump further comprising a stem (193) projecting from said rear cylinder head (175) into said hydraulic cylinder (151) and a bore (190) extending through at least a portion of said hydraulic piston (152) for receiving at least a part of said stem (193). Also disclosed is a method for allowing the hydraulic piston (152) to stroke only a portion of the length of a hydraulic cylinder (151) wherein the method comprises the steps of filling a portion of the hydraulic cylinder with hydraulic fluid to form a hydraulic lock such that the hydraulic piston cannot stroke to the rear end of the cylinder.

Description

RECIPROCATING PUMP

BACKGROUND

The present invention relates to a reciprocating pump, a method for allowing a hydraulic piston to stroke a portion of the length of a hydraulic cylinder in a reciprocating pump, a mud pump and a method for removing a pump piston from a cylinder sleeve of a mud pump. The present invention particularly, but not exclusively relates to a mud pump, cement pump and a method for facilitating access to parts of a mud pump or cement pump.

In the drilling of a borehole in the construction of an oil or gas well, a drill bit is arranged on the end of a drill string, which is rotated to bore the borehole through a formation. A drilling fluid known as “drilling mud” is pumped through the drill string to the drill bit to lubricate the drill bit. The drilling mud is also used to carry the cuttings produced by the drill bit and other solids to the surface through an annulus formed between the drill string and the borehole. The density of the drilling mud is closely controlled to inhibit the borehole from collapse and to ensure that drilling is carried out optimally. The density of the drilling mud affects the rate of penetration of the drill bit. By adjusting the density of the drilling mud, the rate of penetration changes at the possible detriment of collapsing the borehole. The drilling mud may also carry lost circulation materials for sealing porous sections of the borehole. The acidity of the drilling mud may also be adjusted according to the type of formation strata being drilled through. The drilling mud contains inter alia expensive synthetic water or oil-based lubricants and it is normal therefore to recover and re-use the used drilling mud, but this requires inter alia the solids to be removed from the drilling mud. This is achieved by processing the returned drilling mud. The returned drilling mud flows from a wellhead located at a top of the well through a flow line. The first part of the process is to separate the solids from the solids laden drilling mud. This is at least partly achieved by flowing the returned drilling mud on to a screen of a vibratory separator to screen the returned drilling mud of large solids. The screened drilling mud flows into a series of partitioned sections in an active mud tank. Further processing equipment such as centrifuges and hydrocyclones may be used to further clean the mud of solids. Each piece of further processing equipment is located on top of the respective portioned section of the active mud tank, drawing pre-processed mud from the previous portioned section and outputting processed drilling mud into the partitioned section therebelow. The solids are: disposed of； cleaned and used as aggregate or the like； or certain solids, such as Lost Circulation Material is returned to clean drilling mud. It is not uncommon to have 30 to 100 m³ of drilling fluid in circulation in a borehole.

The clean drilling mud is pumped into an additions unit of the active mud tank. Additives, such as weighting agents, viscosity control agents and lost circulation material are added to the clean drilling mud in the additions unit. The prepared drilling mud is now pumped into further testing unit of the active mud system and tested before being pumped into the suction tank of the active mud tank.

A mud pump is then used to pump the prepared and tested drilling mud from the suction tank into a top of the drill string and circulate drilling mud through the drill string to the drill bit and back to the surface through the annulus. The mud pump comprises a pumping section and a power section. The power section may comprise an electric motor, hydraulic motor or the like driving a reciprocating piston in the pumping section. The prepared and tested drilling mud flows from the suction tank through a supply hose or pipe, through an inlet valve in the pumping section of the mud pump into a cavity and is pushed out of the cavity through a discharge valve by action of the reciprocating piston into a further pipe or hose which leads to a goose neck on top of a top drive or swivel and into the top of a string of drill pipe extending into the borehole.

The power section may comprise a reciprocating hydraulic ram which comprises a cylinder having a cylinder head on either end and a piston slideably arranged therein defining two chambers. A piston rod is connected at one end to one side of the piston and passes through one of the chambers and through one of the cylinder heads. Hydraulic fluid is alternately pumped or fed under pressure into the chambers to reciprocate the piston rod. The piston rod is connected at the other end to a pump piston in a pumping section of the mud pump. Reciprocating the pumping piston alternately sucks drilling mud under low pressure into a cavity in the pumping section through an inlet valve and pushes the drilling mud out of the cavity through an outlet valve under a high pressure.

The borehole in the formation can be several kilometres long and several kilometres deep, so the mud pump is typically able to discharge drilling mud at between 200 bar and 1000 bar at between 300 and 3600 litres per minute.

The mud pump may comprise dual acting reciprocating pistons or single action. The mud pump may comprise a duplex reciprocating piston, triplex piston, or any other number of pistons. It is advantageous to maintain a constant flow of drilling mud through the drill string at a constant pressure. Surges in the flow of drilling mud and surges in pressure may cause problems downhole. Such problems may include: the constant return of drilled solids； build-up of solids in the annulus； maintaining pressure in the well to inhibit collapse of the borehole； and maintaining a constant weight of mud in the well.

The flow of drilling mud through the drill string traditionally stops and starts when a section of drill pipe is added or removed from the string of drill pipe during tripping and drilling. However, continuous circulation systems while tripping and continuous circulation systems while drilling are becoming more popular. With these systems, flow of drilling mud downhole is more continuous and pressure can be maintained at a constant level more easily.

Mud pumps are used on land rigs and offshore rigs. Mud pumps are generally located on or beside a land rig or on an offshore drilling platform. However, the mud pump may be located on the sea bed or between the seabed and a surface of the sea.

In deep wells or wells in formations which may easily collapse, it is common to line the borehole with casing. The casing is hung from a wellhead. Similarly, liner is used to case a borehole, except that the liner is hung from the bottom of an existing casing. The casing or liner is cemented in place by pumping cement down through the casing and up through an annulus between the casing and the borehole. Top and bottom plugs are used to facilitate the cementing operation. A cement pump may be used to flow cement into the well and then flow of drilling mud or water behind a bottom plug may be used to push the bottom plug down and force the cement up through the annulus. The mud pump may be used to pump the drilling mud or water behind the bottom plug. A cement pump may also be used in the general construction industry in pumping cement for: below ground structures, such as foundations； above ground structures such as car parks, housing, commercial buildings and sky scrappers； and in the marine industry in construction above and below water structures, such as quays and oil platforms.

SUMMARY AND STATEMENTS OF INVENTION

The inventors have observed that the hydraulic cylinders used in the power sections of mud pumps and cement pumps are large and cumbersome and that it is advantageous to reduce their size and weight to increase portability and reduce the footprint of the mud pump.

The inventors have observed that a hydraulic cylinder requiring two stages of piston rod extension may be used in any suitable reciprocating pump. Such a reciprocating pump may be used for pumping cement in the general construction industry.

In accordance with the present invention, there is provided a reciprocating pump comprising a power section having a hydraulic cylinder and a hydraulic piston slideably arranged therein and a rear cylinder head, the hydraulic piston comprising a piston rod extending forwardly thereform, the power section further comprising a stem projecting from the rear cylinder head into the hydraulic cylinder and a bore extending through at least a portion of the hydraulic piston for receiving at least a part of the stem.

Preferably, the bore also extends through a portion of the length of the piston rod. Advantageously, the bore is lined with a liner and may have a flange at an opening thereof. Preferably, the stem is between 100 and 1000mm long. Preferably, the stem is of a circular cross-section, although may be triangular, square, cross-shaped, pentagonal, hexagonal, oval or of any other suitable cross-sectional shape. Preferably, the cross-sectional area is in the order of 1 to 10％of the cross-sectional area of the hydraulic cylinder, advantageously 2 to 5％and most preferably 3.5％. Preferably, the piston is double acting, but may be single acting for example, the single action hydraulics may be used for extending the hydraulic piston and another means is used to retract the hydraulic piston, such as a linear actuator, pneumatics or a spring.

Advantageously, the reciprocating pump further comprises hydraulic fluid in the bore to create a hydraulic lock when the stem attempts to enter the bore preferably, to selectively prevent the hydraulic piston from retracting fully. The quantity of hydraulic fluid in the bore can be accurately supplied or metered by a pump through a fluid path. Preferably, the bore extends into the piston rod. Advantageously, the stem has a seal thereabout sized to provide a seal between the stem and the bore to inhibit hydraulic fluid passing thereacross.

Advantageously, the reciprocating pump further comprises hydraulic fluid in a zone defined by the rear cylinder head, a portion of the hydraulic cylinder and at least a portion of the length of the stem which forms a hydraulic lock to selectively prevent the hydraulic piston from retracting fully. Preferably, no more than the length of the stem. Preferably, the hydraulic piston head is prevented from retracting more than full retraction by an end stop near or at the rear cylinder head. Preferably, the stem is rigid and made of a steel, other metal or plastics material.

Advantageously, the stem has a central passage. Preferably, the central passage selectively allows the flow of fluid therethrough. Preferably, the central passage selectively allows the flow of hydraulic fluid between the bore and outside the hydraulic cylinder. Advantageously, the fluid path fluidly connects the bore central passage with a hydraulic fluid supply and advantageously has a non-return valve in said fluid path to inhibit release of the hydraulic lock. Advantageously, the fluid path also has a shuttle valve to selectively allow hydraulic fluid to drain from the central passage and bore. Preferably, the fluid path also has a pump for injecting hydraulic fluid into said hollow stem and preferably, the bore.

Advantageously, the hydraulic cylinder further comprises a transducer to locate the position of the hydraulic piston in the hydraulic cylinder. Preferably, the transducer comprises a transducer wire or rod and a magnet ring. Advantageously, the reciprocating pump further comprises a transducer rod or wire fixed to the rear cylinder head and extending through the bore. The transducer may be of the type sold under the trade name Temposonics R-series Rod Model RF.

Preferably, the hydraulic cylinder has a rear inlet port for allowing hydraulic fluid to flow into the hydraulic cylinder behind the hydraulic piston to extend the piston rod, the reciprocating pump further comprising a pump for flowing hydraulic fluid under pressure into the hydraulic cylinder behind the hydraulic piston to extend the piston rod. Preferably, the rear inlet port is arranged in the rear cylinder head.

Preferably, the hydraulic cylinder further comprising a forward cylinder head, the piston rod extending through an opening in the forward cylinder head. Advantageously, the hydraulic cylinder has a forward inlet port for allowing hydraulic fluid to flow into the hydraulic cylinder in front of the hydraulic piston to retract the piston rod. Preferably, the reciprocating pump further comprises an accumulator for flowing hydraulic fluid under pressure into the hydraulic cylinder in front of the hydraulic piston to retract the piston rod. Advantageously, the hydraulic cylinder has a rear outlet port for allowing hydraulic fluid to flow out from the hydraulic cylinder behind the hydraulic piston when the piston rod is retracted, the reciprocating pump further comprising an accumulator for flowing hydraulic fluid under pressure into the hydraulic cylinder in front of the hydraulic piston to retract the piston rod.

Advantageously, the piston rod has a distal end outside the hydraulic cylinder having a pump piston attached thereto.

Advantageously, the reciprocating pump further comprises a pump section. Preferably, the pump piston is arranged in a cylinder sleeve and the reciprocating pump further comprises a valve block having cavity for receiving fluid to be pumped, an inlet valve for selectively allowing low pressure fluid into the cavity and an outlet valve through which fluid under high pressure flows from the cavity. Preferably, the valve block comprises a portion surrounding the cylinder sleeve or is integral or otherwise fitted thereto so that fluid in the cavity can be pressurised by action of the pump piston.

The present invention also provides a mud pump comprising at least two reciprocating pumps of the invention, wherein the mud pump further comprises an inlet manifold and an outlet manifold.

The present invention also provides a method for allowing a hydraulic piston to stroke a portion of the length of a hydraulic cylinder in a reciprocating pump as claimed in any preceding claim, wherein the method comprises the steps of filling a portion of the hydraulic cylinder with hydraulic fluid to form a hydraulic lock such that the hydraulic piston cannot stroke to the rear end of the cylinder. Advantageously, the stroke is limited by the length of the stem. As the stem approaches the bore, the hydraulic piston slows and stops as a tip of the stem enters the bore, a hydraulic lock forming within the bore and the zone defined by the rear cylinder head, portion of the hydraulic cylinder and the substantially the length of the stem. Preferably, the portion of the cylinder is substantially equal to or less than the length of the stem projecting into the hydraulic cylinder.

Advantageously, the method further comprises a method for removing a pump piston from a cylinder sleeve

A method for removing a pump piston from a cylinder sleeve of the reciprocating pump comprising a hydraulic cylinder having a hydraulic piston slideably arranged therein, and a rear cylinder head, the hydraulic piston comprising a piston rod extending thereform, the reciprocating pump further comprising a stem projecting from the rear cylinder head into the hydraulic cylinder and a bore extending through at least a portion of the hydraulic piston for receiving at least a part of the stem, wherein the piston rod has a distal end outside the hydraulic cylinder having the pump piston attached thereto arranged in the piston sleeve, further comprising hydraulic fluid in a zone defined by the rear cylinder head, a portion of the hydraulic cylinder and at least a portion of the length of the stem which forms a hydraulic lock and hydraulic fluid in the bore to facilitate a hydraulic lock when the stem attempts to enter the bore to selectively inhibit the hydraulic piston from retracting fully, the method comprising the steps of retracting the hydraulic piston to further retract the pump piston from the cylinder sleeve by removing at least a portion of the hydraulic fluid from the bore and zone.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention reference will now be made, by way of example only, to the accompanying drawings, in which:

Figure 1 is a schematic view of a drilling rig comprising a mud pump in accordance with the invention；

Figure 2 is a schematic view of a section of a prior art mud pump in operation, the section comprising a hydraulic cylinder of a pump section and a power section；

Figure 3 is a schematic view of the hydraulic cylinder of the power section and part of the pumping section shown in Figure 2, during inspection and repair whilst not in use；

Figure 4 is a schematic view of a hydraulic cylinder of a power section in accordance with the present invention and part of the pumping section of a mud pump in operation；

Figure 5 is a schematic view of the hydraulic cylinder of the power and part of the pumping section shown in Figure 4, during inspection and repair；

Figure 6 is a side view of the hydraulic cylinder shown schematically in Figure 4；

Figure 7 is a view in section of the hydraulic cylinder shown in Figure 6 taken along the line VII-VII；

Figure 8 is a view in section of the hydraulic cylinder shown in Figure 7 taken along the line VIII-VIII；

Figure 9 is a hydraulic diagram of a mud pump comprising a hydraulic cylinder as shown in Figure 6 in normal use；

Figure 10 is a hydraulic diagram of a mud pump comprising a hydraulic power ram as shown in Figure 6 during inspection and repair；

DETAILED DESCRIPTION

Referring to Figure 1 there is shown a drilling rig generally identified by reference numeral 1. The drilling rig 1 has a derrick 2 arranged on a drill floor 3 supported on legs 4. The legs 4 are seated on a substructure 5 on ground 6.

A swivel 7 is raised and lowered on a travelling block 8 on wireline 9, which passes over a crown block 10 located at a top of the derrick 2 and down to a drawworks 11 on the rig floor 3. A section of drill pipe 12 depends from the swivel 7, passes through a rotary table 13 and is connected at a lower end to a drill string 14. The drill string 14 passes through a wellhead 15 into a bore hole 16 in formation 17. A bottom hole assembly 18 is arranged on a lower end of the drill string 14, which has a drill bit 19 on the lower end thereof. An annulus 21 is defined between the borehole 16 and the drill string 14.

A flow line 20 is fluidly connected at one end to the annulus 21 at the wellhead 15 and the other end to an active mud system 22. Returned drilling mud M flows from the annulus 21, through wellhead 15, into flow line 20 and to the active mud system 22. The active mud system 22 comprises an active mud tank 23 and a series of pieces of mud processing equipment, such as: a shale shaker 24, a degasser 25, a mud conditioner 26, and a centrifuge 27. Further mud processing equipment may be used, such as gumbo separators and hydro cyclones. The flow line 20 flows returned drilling mud M directly on to screens of the shale shaker 24. Screened drilling mud S flows from the shale shaker 24 into partitioned section 27. Each piece of further mud processing equipment is located above a partitioned

section

27, 28 and 29 of the active mud tank 23, being fed from the previous partitioned section using a small pump and flowing processed drilling mud into the partitioned

section

27, 28, 29 therebelow.

The processed drilling mud then passes into additions section 30, into which additives are added, such as bentonite, barite and lost circulation material. The processed drilling mud is tested and when acceptable, is pumped or allowed to flow into suction tank 31. A mud pump 32 is located downstream of the suction tank 31. The processed and tested drilling mud P flows from the suction tank 31 through a supply hose 33 to the mud pump 32. The processed and tested drilling mud P flows into the mud pump 32 directly from the suction tank 31 under pressure provided by the head of drilling mud in the suction tank or may be pumped with a small pump to maintain a relatively constant supply pressure which pressure is typically is between 1 to 5 bar and preferably 3 bar. The processed and tested drilling mud P is then pumped by the mud pump 32 through a hose 34 to the swivel 7 where the hose is fluidly connected to a top of the drill pipe 12 and flows through the drill string 14 therefrom.

The mud pump 32 comprises: a pumping end 35 comprising an inlet manifold 38 and an outlet manifold 39 connected to a number of pumping sections and a power end 36 comprising at least one motor 37 driving piston rods.

In a top drive rig (not shown) the rotary table is replaced or supplemented by a top drive. In a top drive rig, the hose 34 is connected to a goose neck and rotary connection which is fluidly connected with a quill in the top drive which is in turn selectively connected to the drill pipe 12 and drill string 14.

Referring to Figures 2 and 3, there is shown schematically a section 40 of a known mud pump. The section 40 of the mud pump comprises a pumping section 41 and a power section 42.

The mud pump comprises a two sections 40 having the two pumping sections 41 coupled with inlet manifold 38’ and outlet manifold 39’ .

The pumping section 41 comprises a valve block 43 defining a cavity 44, an inlet valve 45 and a discharge valve 46. A cylinder 47 is in fluid communication with the cavity 44. A pump piston 48 is slideably arranged in the cylinder sleeve 47.

The power section 42 comprises a hydraulic cylinder 51 having a hydraulic piston 52 therein. A piston rod 53 has a first end 54 fixed to a front face 55 of the hydraulic piston 52. The piston rod 53 passes through an opening 57 in a cylinder head 58. A second end 56 of the piston rod 53 is fixed to a rear face 59 of the pump piston 48.

In use, drilling mud is drawn into the cavity 44 from a suction tank, like suction tank 31. The drilling mud flows from the suction tank through supply hose 33’ and an optional pump (not shown) to an inlet manifold 38’ . The drilling mud is supplied to the inlet manifold 38’ at approximately three bar pressure. The drilling mud flows through inlet valve 45 by retracting the pump piston 48 from a front end 49 of the cylinder sleeve 47 towards a rear end 50 of the cylinder sleeve 47, which creates a low pressure zone in cavity 44.A force is induced on inlet valve 45 by the pressure differential which is sufficient to open the inlet valve 45 and close the outlet valve 46. The pump piston 48 is retracted by operation of the hydraulic cylinder 52. Hydraulic fluid under pressure enters port 60 in a forward end 61 of the hydraulic cylinder 51, filling forward chamber 62. The hydraulic piston 52 strokes rearward in hydraulic cylinder 51 retracting pump piston 48 in concert. Hydraulic fluid in rear chamber 63 is expelled through port 64. When the hydraulic piston 52 reaches the end of the stroke ST, the hydraulic fluid stops flowing into chamber 62. The pump piston 48 reaches the rear end 50 of the cylinder 47 as shown in Figure 2, in concert with hydraulic piston 52. Hydraulic fluid is now pumped into rear chamber 63, moving the hydraulic piston 52 forward pushing the pump piston 48 forward to pressurise the drilling mud in the cavity 44 to a predetermined pressure, such as 500 bar, whereupon discharge valve 46 opens. The rest of the forward stroke pushes the drilling mud through discharge valve 46 into outlet manifold 39’ . The hydraulic fluid in forward chamber 62 is expelled through port 60. The cycle is then repeated.

The stroke of the hydraulic piston 52 is monitored and may be controlled using a transducer rod 65 which has a rear end 67 fixed in locking piston 66. A forward end 68 of the transducer rod 65 is slideably arranged in a counter bore 69 in the hydraulic piston 52 and piston rod 53. The transducer rod 65 thus stays fixed in relation to the power cylinder 51 and the hydraulic piston 52 and piston rod 53 moves relative thereto.

A seal assembly (not shown) is provided about pump piston 48 to prevent drilling mud escaping between the pump piston 48 and the cylinder sleeve 47. The seal assembly is subject to wear and is thus checked and cleaned regularly and is repaired or changed regularly. The piston itself and the cylinder sleeve are also checked and cleaned regularly and are repaired or changed regularly. The power section may also need to be removed and replaced and cleaned and repaired regularly. There is thus a mechanism for retracting the pump piston 48 from the cylinder sleeve 47.

The hydraulic cylinder 51 has an extended rear locking portion 70. The locking portion 70 has a locking cylinder 71, the locking piston 66 slideably arranged therein. The locking piston 66 has a rearwardly extending rod 73 and a forwardly extending piston foot 72. A cylinder head 75 is arranged on the end of the locking cylinder 71. The cylinder head has an opening 78 therein sized for allowing the rearwardly extending rod 73 to pass therethrough. The opening 78 is provided with a hydraulic seal assembly to inhibit hydraulic fluid from leaking from the chamber 76. A shoulder 74 is located between chamber 63 and the locking cylinder 71. A locking chamber 76 is defined by the cylinder head 75, the locking cylinder 71 and the shoulder 74. A locking port 77 allows the flow of hydraulic fluid into and from the chamber 76.

When the hydraulic cylinder 51 is in normal use, hydraulic fluid is contained and trapped in chamber 76 hydraulically holding the locking piston 66 against shoulder 74. The locking piston 66 need not have a hydraulic fluid tight seal against the shoulder 74, such that hydraulic fluid may pass between

chambers

76 and 63. The locking foot 72 projects through an opening defined by the shoulder 74 into the chamber 63, preventing the hydraulic piston 52 from retracting too far, so that the pump piston 48 will remain in cylinder sleeve 47 during reciprocation of the hydraulic piston 52.

Before servicing or inspection commences, the mud pump is switched off by stopping the flow of hydraulic fluid to and from hydraulic cylinder 51. Pressure in the drilling mud is released and may be drained from the cavity 44 in the pump section 41. Hydraulic fluid in chamber 76 is removed by letting it flow through lock port 77. The locking piston 66 is sucked rearward towards cylinder head 75. The hydraulic piston 52 is pulled rearward to abut shoulder 74 by pulling on the rearwardly extending rod 73. The pump piston 48 retracts with the hydraulic piston 52 until the pump piston 48 exits the cylinder sleeve 47 and can be inspected, serviced, repaired and replaced. The pump piston 48 is then inserted back into the cylinder sleeve 47 by allowing hydraulic fluid to flow through lock port 77 into chamber 76 to push the locking piston 55 forward, whereupon the piston foot 72 abuts and pushes the hydraulic piston forward expelling hydraulic fluid from chamber 62 through port 60.

The mud pump comprises a two sections 40 having the two pumping sections 41 coupled with inlet manifold 38’ and outlet manifold 39’ . However， a mud pump of comprises a plurality of sections 40 with the pumping sections 41， coupled with inlet manifold 38’ and outlet manifold 39’ ： two are used in a duplex mud pump, three in a triplex mud pump and six in a hex mud pump. However, any suitable number of piston and cylinders may be used in the power section of a mud pump.

Referring to Figures 4 to 8, there is shown schematically a section 140 of a mud pump of the invention. The section 140 of the mud pump comprises a pumping section 141 and a power section 142.

As shown in Figures 9 and 10, the mud pump comprises two sections 140 having the two pumping sections 141 coupled with inlet manifold 38 and outlet manifold 39 shown in Figure 1.

The pumping section 141 is not shown in Figures 4 and 5, save for the cylinder sleeve 147 and pump piston 148, but may be identical to the pumping section shown in Figure 2. Referring to Figures 9 and 10, each pumping section 141 comprises a valve block 143 defining a cavity 144, an inlet valve 145 and a discharge valve 146. A cylinder sleeve 147 is in fluid communication with the cavity 44. A pump piston 148 is slideably arranged in the cylinder sleeve 147.

The power section 142 comprises a hydraulic cylinder 151 having a hydraulic piston 152 therein. A hydraulic seal assembly 152a is provided on the hydraulic piston 152 to inhibit hydraulic fluid from passing between the hydraulic piston 152 and the hydraulic cylinder 151. A piston rod 153 has a first end 154 of reduced diameter which passes through the hydraulic piston 152 and has a locking ring 154a fixing the piston rod 153 to the hydraulic piston 152. The piston rod 153 extends from a front face 155 of the hydraulic piston 152 passing through an opening 157 in a cylinder head 158. The opening 157 is provided with a hydraulic seal assembly 158a to inhibit hydraulic fluid from leaking from chamber 162. A second end 156 of the piston rod 153 is fixed to a rear face 159 of the pump piston 148. The piston rod 153 may comprise a linkage 153a.

In normal operation, drilling mud is drawn into the cavity 144 from a suction tank, like suction tank 31. The drilling mud flows from the suction tank through supply hose 33 and an optional pump 133a to an inlet manifold 38.The drilling mud is supplied to the inlet manifold 38 at approximately three bar pressure. The drilling mud flows through inlet valve 145 by retracting the pump piston 148 from a front end 149 of the cylinder sleeve 147 towards a rear end 150 of the cylinder sleeve 47, which creates a low pressure zone in cavity 144. A force is induced on inlet valve 145 by the pressure differential which is sufficient to open the inlet valve 145 and close the outlet valve 146.

Figure 9 shows both the pump pistons 148 in a retracted position with the connected hydraulic piston 152 similarly in a retracted position at the end of its normal stroke. In normal operation, one pump piston 148 may be extended, whilst the other pump piston is retracted, i.e. 180 degree phase shift, so that the pumped fluid in the outlet manifold 34 is smoother. The pump piston 148 is extended in a power stroke using the power section 142. The power stroke occurs by operation of a hydraulic system 180. A drain shuttle valve 198 is in a no-flow position, disallowing fluid from draining from power chamber 163 to a hydraulic fluid source 183. A power shuttle valve 200 is moved to a flow-through position allowing a large quantity of hydraulic fluid to be pumped with pump 201 from the hydraulic fluid source 183 through inlet port 164 into power chamber 163, pushing the hydraulic piston 152 forward along cylinder 151. The hydraulic piston 152 strokes forward in hydraulic cylinder 151 pushing the pump piston 148 in concert. Hydraulic fluid in return chamber 162 is expelled through port 160, loading an accumulator 187. When the hydraulic piston 152 reaches the end of the stroke, the hydraulic fluid is stopped from flowing into power chamber 163 by moving power shuttle valve 200 to a no-flow position. A shoulder 155a is provided on the cylinder head 158 to provide an end stop which the front face 155 of the hydraulic piston 152 may abut to limit the stroke ST of the hydraulic piston 152. The forward cylinder head 158 has an annulus 160a for distributing hydraulic fluid flowing to and from the port 160 evenly around the piston rod 153 and inhibiting hydraulic locks at the forward end of the stroke ST.

The pump piston 148 reaches the front end 149 of the cylinder 147, in concert with hydraulic piston 152. During the forward stroke ST, the drilling mud in cavity 144 is pressurised to a predetermined pressure, such as 500 bar, whereupon discharge valve 146 opens. The rest of the forward stroke ST pushes the drilling mud through discharge valve 146 into outlet manifold 39.

At the end of the forward stroke ST, the drain shuttle valve 198 is moved to a flow-through position to allow hydraulic fluid to flow from the power chamber 163 back to the source of hydraulic fluid 183 to retract hydraulic piston 152. Pressure built up in accumulator 187 pushes hydraulic fluid through port 160 into return chamber 162, forcing the hydraulic piston 152 rearward towards rear cylinder head 175. However, the piston head 152 is slowed and prevented from passing a predetermined point.

The stroke of the hydraulic piston 152 is monitored and may be controlled using a transducer rod 165 which has a rear end 167 fixed in cylinder head 175. The rear end 167 is electrically connected to a connector block 165a for connection to a control system 165b. A forward end 68 of the transducer rod 65 is slideably arranged in a counter bore 169 in the hydraulic piston 152 and piston rod 153. A ring magnet 165c is fixed in a stem cavity 190 which takes the form of an enlarged counter bore 190. The transducer rod 165 thus stays fixed in relation to the hydraulic cylinder 151 and the ring magnet 165c in the piston rod 153 moves with respect to the transducer rod 165 with motion of the piston rod 153, allowing the exact position of the piston rod to be known, monitored and recorded by the control system 165b. The positional data can be used to activate the shuttle valves to limit stroke length.

The stem cavity 190 is lined with a liner 191, which has a flange 192 covering the end of the piston rod 153. Preferably, the inner diameter of the liner 191 is approximately 25 to 100mm and most preferably, 71mm. A hollow stem 193 is fixed to the rear cylinder head 175 about the rear portion 167 of transducer 165. The hollow stem 193 extends preferably between 100 to 1000mm and most preferably, 490mm from the rear cylinder head 175 into the chamber 163. The hollow stem 193 is preferably between 0.5 and 3mm smaller in external diameter than the inner diameter of the liner 191, and most preferably, approximately 70mm in diameter. A small diameter flow bore 196 is provided in the rear cylinder head 175 to fluidly connect the hollow stem 193 to a release shuttle valve 181 to selectively relieve a hydraulic lock in stem cavity 190. The hollow stem 193 has an annulus 197 between the transducer 165 and the inner wall of the hollow stem to allow hydraulic fluid to flow therethrough. In normal use, the relieve shuttle valve 181 is in an flow-through, although a non-return valve 185 prevents hydraulic fluid from flowing out of through the hollow stem 193. The stem 193 is preferably made from a mild carbon steel, although may be made of any other suitable material such as stainless steel or plastics material. A free distal end of the stem 193 is in axial alignment with the stem cavity 190, preferably within a tolerance of 0.5mm. A free distal end 194 of the stem 193 is provided with a seal 194’ to provide a hydraulic seal between the stem 193 and the liner 191. The hollow stem

Towards the end of the retraction stroke ST, an entrance 195 defined by the flange 192 in the rear end of the piston rod 153 comes into close proximity of the free distal end 194 of the hollow stem 193. Hydraulic fluid trapped in the stem cavity 190 slows the piston rod 153 towards the end of its retraction stroke and eventually stops the hydraulic piston 152 from retracting any further than the position shown in Figure 7, with the seal 194’ on the tip of the distal end 194 of the hollow stem 193 just inside or on the flange 192 of the liner 191. The kinetic energy in the retracting hydraulic piston 152 and piston rod 153 is transferred to the hydraulic fluid contained in the stem cavity 190, causing the hydraulic piston 152 and piston rod 153 to slow and to stop. A hydraulic lock 190’ is thus created within the stem cavity 190, bound by the stem cavity 190, the tip of the stem 193 and the hydraulic fluid locked in the hollow stem 193 by non-return valve 185. A hydraulic lock 176 in chamber 163 also may inhibit further retraction of the hydraulic piston 152. The cycle continues with a forward stroke ST.

A seal assembly is provided about pump piston 148 to prevent drilling mud escaping between the pump piston 148 and the cylinder sleeve 147. The seal assembly is subject to wear and is thus checked and cleaned regularly and is repaired or changed regularly. The piston itself and the cylinder sleeve are also checked and cleaned regularly and are repaired or changed regularly. The power section may also need to be removed and replaced and cleaned and repaired regularly. There is thus a mechanism for retracting the pump piston 148 from the cylinder sleeve 147.

When it is required to retract the pump piston 148 from liner 147, the mud pump is stopped and pressure in cavity 144 relieved, as previously described with reference to Figure 2. The hydraulic fluid in hydraulic lock 176 is removed from the hydraulic cylinder 151 through outlet port 177. A drain shuttle valve 198 is activated to move to the position shown in Figure 10, whereupon hydraulic fluid from hydraulic lock 176 is allowed to flow through the drain shuttle valve 198 to the supply of hydraulic fluid 183. Preferably simultaneously, the hydraulic lock 190’ in the stem cavity 190 is removed by moving release shuttle valve 181 to a drain diversion position, as shown in Figure 10. The hydraulic fluid in stem cavity 190 flows through the hollow stem 193, through small diameter flow bore 196, through release shuttle valve 181, to drain into the supply of hydraulic fluid 183. The hydraulic piston 152 moves rearwardly by the pressure created by the accumulator 187 on the front face 155 inducing a sufficient force to overcome the hydraulic fluid behind the hydraulic piston 152, and in the stem cavity, which are now both open to drain, which is now substantially at atmospheric pressure. The hydraulic piston 152 finally abuts an end stop 199 on the rear cylinder head 175.

The pump piston 148 and cylinder sleeve 147 can now be accessed easily for inspection, maintenance, repair and replacement. Once the pump piston 148 and cylinder sleeve 147 are inspected, maintained, repaired or replaced, the pump piston 148 is inserted back into cylinder sleeve 147 by movement of the hydraulic piston 152. The shuttle valves 198 are activated to move to the no-flow position shown in Figure 9, which inhibits flow of hydraulic fluid from the hydraulic cylinder 151. The power shuttle valve 200 is activated to the flow-through position allowing flow of hydraulic fluid to flow from source 183 through the pump 201 through inlet port 164 to allow a predetermined amount of hydraulic fluid into the chamber 163 to create a hydraulic lock 176 behind the hydraulic piston 152. Preferably simultaneously, the release shuttle valve 181 is moved to the flow-through position and a pump 182 is activated to allow a small quantity of hydraulic fluid to flow from the supply 184, through a check valve 184 and the non-return valve 185, through the release shuttle valve 181, through small diameter flow bore 196 and the annulus 197 into the stem cavity 190, filling the stem cavity 190 until the tip 194 of the stem 193 sits on or just inside of the stem cavity 190. The hydraulic locks 176 and 190’ are each predetermined quantities of hydraulic fluid in the volume. Once the predetermined volume of either or both has been reached, the

pumps

201 and 182 are stopped.

The volume of the hydraulic lock 176 is bound by the hydraulic cylinder 151, the rear cylinder head 175 and the length of the hollow stem 193. The volume of the hydraulic loch 190’ is the volume bound by the stem cavity 190 and the tip of the stem 193, which is easily controllable.

The relieve shuttle valve 181 is then returned to its original position disallowing flow of hydraulic fluid from source 183 by the non-return valve 185.

Claims

A reciprocating pump comprising a power section (142) having a hydraulic cylinder (151) and a hydraulic piston (152) slideably arranged therein, and a rear cylinder head (175) , the hydraulic piston (152) comprising a piston rod (153) extending forwardly thereform, the power section (142) further comprising a stem (193) projecting from said rear cylinder head (175) into said hydraulic cylinder (151) and a bore (190) extending through at least a portion of said hydraulic piston (152) for receiving at least a part of said stem (193) .
A reciprocating pump as claimed in Claim 1, further comprising hydraulic fluid in said bore (190) to create a hydraulic lock when the stem (193) attempts to enter said bore (190) .
A reciprocating pump as claimed in Claim 1 or 2, further comprising hydraulic fluid in a zone defined by the rear cylinder head (175) , a portion of said hydraulic cylinder (151) and at least a portion of the length of the stem (193) which forms a hydraulic lock to selectively prevent the hydraulic piston (152) from retracting fully.
A reciprocating pump as claimed in Claim 1, 2 or 3, wherein said stem (193) has a central passage (197) .
A reciprocating pump as claimed in Claim 4, further comprising a transducer rod or wire (167) fixed to said rear cylinder head (175) and extending through said central passage (187) .
A reciprocating pump as claimed in Claim 4 or 5, further comprising a fluid path (196) fluidly connecting said bore central passage (197) with a hydraulic fluid supply (183) .
A reciprocating pump as claimed in Claim 6, further comprising a non-return valve in said fluid path (196) .
A reciprocating pump as claimed in any preceding claim, further comprising a pump (181) for flowing hydraulic fluid under pressure into said hydraulic cylinder (151) into said bore (190) to move the hydraulic piston (152) .
A reciprocating pump as claimed in any preceding claim, wherein said hydraulic cylinder (151) has a rear inlet port (164) for allowing hydraulic fluid to flow into said hydraulic cylinder behind said hydraulic piston (152) to extend the piston rod (153) , said reciprocating pump further comprising a pump (201) for flowing hydraulic fluid under pressure into said hydraulic cylinder (151) behind said hydraulic piston (152) to extend the piston rod (153) .
A reciprocating pump as claimed in any preceding claim, said hydraulic cylinder (151) further comprising a forward cylinder head (158) , the piston rod (153) extending through an opening (157) in said forward cylinder head (158) .
A reciprocating pump as claimed in Claim 10, wherein said hydraulic cylinder (151) has a forward inlet port (160) for allowing hydraulic fluid to flow into said hydraulic cylinder in front of said hydraulic piston (152) to retract the piston rod (153) .
A reciprocating pump as claimed in Claim 11, further comprising an accumulator (187) for flowing hydraulic fluid under pressure into said hydraulic cylinder (151) in front of said hydraulic piston (152) to retract the piston rod (153) .
A reciprocating pump as claimed in any preceding claim, wherein said piston rod (153) has a distal end outside said hydraulic cylinder having a pump piston (148) attached thereto.
A reciprocating pump as claimed in Claim 13, wherein the pump piston (148) is arranged in a cylinder sleeve (147) and the reciprocating pump further comprising a valve block having cavity (144) for receiving fluid to be pumped, an inlet valve (145) for selectively allowing low pressure fluid into the cavity (144) and an outlet valve (146) through which fluid under high pressure flows from the cavity (144) .
A mud pump comprising at least two reciprocating pumps as claimed in Claim 14, wherein said mud pump further comprises an inlet manifold (38) and an outlet manifold (39) .
A method for allowing a hydraulic piston to stroke a portion of the length of a hydraulic cylinder in a reciprocating pump as claimed in any preceding claim, wherein the method comprises the steps of filling a portion of the hydraulic cylinder with hydraulic fluid to form a hydraulic lock such that the hydraulic piston cannot stroke to the rear end of the cylinder.
A method in accordance with Claim 16, wherein the portion of the hydraulic cylinder filled with hydraulic fluid to form a hydraulic lock is the bore.
A method for removing a pump piston (148) from a cylinder sleeve (147) of the reciprocating pump comprising a hydraulic cylinder (151) having a hydraulic piston (152) slideably arranged therein, and a rear cylinder head (175) , the hydraulic piston comprising a piston rod (153) extending thereform, the reciprocating pump further comprising a stem (193) projecting from said rear cylinder head (175) into said hydraulic cylinder (151) and a bore (190) extending through at least a portion of said hydraulic piston (152) for receiving at least a part of said stem (193) , wherein said piston rod (153) has a distal end outside said hydraulic cylinder having said pump piston (148) attached thereto arranged in said piston sleeve (147) , further comprising hydraulic fluid in a bore (190) which forms a hydraulic lock when the stem (193) attempts to enter said bore (190) to selectively inhibit the hydraulic piston (152) from retracting fully, the method comprising the steps of retracting the hydraulic piston (152) to further retract the pump piston (148) from the cylinder sleeve (147) by removing at least a portion of the hydraulic fluid from the bore (190) .