WO2003001062A1

WO2003001062A1 - High-pressure pump

Info

Publication number: WO2003001062A1
Application number: PCT/NO2002/000222
Authority: WO
Inventors: Per Vatne
Original assignee: Viking Technology As
Priority date: 2001-06-22
Filing date: 2002-06-21
Publication date: 2003-01-03
Also published as: NO20013173D0; NO20013173L; EP1407144A1

Abstract

A high-pressure pump (HP), especially developed for pumping of abrasive media like drilling mud and cement slurry, is disclosed. The pump comprises reciprocally acting diaphragm pumps (MP) that are driven by hydraulic power generated by a hydraulic power pack (not shown), and each diaphragm pump (MP) includes a respective pump chamber (A, B) and at least two valves (V1, V2 and V1', V2') on the pumping side. The hydraulic power pack (not shown) drives a hydraulic motor (HM) with a substantially constant displacement volume corresponding to twice the stroke volume of each pump chamber. The motor (HM) is in direct hydraulic communication (P) with each pump chamber (A, B) via respective pressure controlled flow regulating valves that are controlled by a synchronizer (CS) connected to the hydraulic motor (HM).

Description

High-pressure pump

The present invention relates to a high-pressure pump, in particular for pumping abrasive media such as drilling mud and cement, comprising alternately acting diaphragm pumps driven by hydraulic power generated by a hydraulic power pack, where each diaphragm pump comprises respectively a pump chamber and at least two valves on the pumping side.

Although the invention has been developed for pumping of drilling mud, it is also suited for pumping of other media such as cement. When drilling for oil and gas, both onshore and offshore, drilling mud is pumped down through the drill pipe and returns up through the well annulus. The drilling mud has many functions, with pressure regulation and control being the most important. The drilling mud has a specific gravity of more than 1, occasionally as high as 2. Various chemicals and particles are added to the drilling mud. Both oil based and water based muds are used. The drilling mud is pumped down through the drill pipe at high pressures, some times as high as 35 MPa. Pumping of drilling mud is the largest single consumer of power associated with drilling of deep wells, at times consuming more than 3000 kW.

Existing mud pumps, often with a 40-50 year old construction, exhibits many drawbacks. They are often highly voluminous and heavy, weighing upwards of 30 tons. They require expensive and strong secondary components related to the piping system, e.g. surge dampening means, safety valves etc. Furthermore, these pumps provide a pulsating fluid that requires special piping installation. They require extensive maintenance and are costly to operate. Cylinder liners and pistons need regular replacements, depending on the required pressure and mud volume. In addition, the motor or motors driving the mud pumps must be equipped with speed regulation.

The presently proposed high-pressure pump is hydraulically driven, and requires a hydraulic power pack in addition to the mud pump itself, which power pack is driven by either an electric motor or a diesel aggregate. The hydraulic pump or pumps in the hydraulic power pack are driven at a constant speed, which is more cost effective and simpler to install than DC motors with variable revolutions. The high-pressure pump does not require any adjustments, neither electrical nor hydraulic. The volume and pressure of the delivered drilling mud corresponds to the volume and pressure of the supplied hydraulic oil. However, an internal and integrated hydraulic/mechanical control of the entire high-pressure pump is effected by means of a hydraulic motor, a synchronizer and a number of valves.

The following advantages may be achieved by use of the present invention:

Non-pulsing pump flow and no requirement for pulsation dampers.

Pressure control across the entire range with adjustment on the power generation side, on the hydraulic pumps, i.e. no requirement for safety valves on the high- pressure mud side. This also means that it is possible to maintain any pumping pressure across any flow range, 0 - max.

The valves last longer due to fewer strokes.

Fewer parts that can break down - no pistons/cylinder liners. - More flexible installation; the motors and drive trains may be located in a different room from the pumping room.

Lower operating costs.

With pressure boosters, the pump may be used as a cement pump at any pressure.

In accordance with the present invention, there is provided a high pressure pump of the type mentioned by way of introduction, characterised in that the hydraulic power pack is driving a hydraulic motor with an approximately constant displacement volume corresponding to twice the stroke volume of each pump chamber, which motor is in direct hydraulic communication with each of the pump chambers via respective pressure controlled flow regulating valves controlled by a synchronizer connected to the hydraulic motor.

In one embodiment, the pressure controlled flow regulating valves comprise a respective first pressure controlled flow regulating valve which on the inlet side is influenced by the pressure in the hydraulic connection, and on the other side (the pilot side) is influenced by the respective control pressure; a respective second pressure controlled flow regulating valve which on the inlet side is influenced by the outlet pressure from the first pressure controlled flow regulating valve and on the other side (the pilot side) is influenced by the respective control pressure.

Appropriately, the respective control pressures are determined by respective valve pairs that receive the pressure in the hydraulic connection, where one valve in the valve pair is opened by the synchronizer connected to the hydraulic motor.

In an expedient embodiment, the synchronizer is a shaft with a number of cams in direct connection with the hydraulic motor.

In one embodiment, each cam acts on a valve via a push rod.

In an advantageous embodiment, the pressure controlled flow regulating valves are pressure controlled seat valves.

Other and further objects, distinctive features and advantages will become apparent from the following description of a currently preferred embodiment of the invention, which description is given for descriptive purposes without thereby imposing any limitations, and which is given in connection with the appended drawings, in which:

Fig.l is a perspective view of a possible arrangement of the various main components of a high-pressure pump according to the present invention;

Fig.2 shows the same as Figure 1, but from the opposite side;

Fig.3 shows a flow diagram for a high-pressure pump according to the present invention;

Figs.4A and 4B are more detailed views of a valve pair that controls the pressure to the flow regulating valves;

Fig.5 shows a pump diagram for the two chambers in the high pressure pump; and

Figs.βA and 6B are more detailed views of the cams that actuate the pressure control valves. A general description of the high-pressure pump according to the invention will now be given with reference to figures 1 and 2. Following this a more detailed description with reference to figure 3 will be given.

The high-pressure pump HP is developed with regard to pumping of drilling mud, which is highly abrasive in nature. Although the high-pressure pump HP may conceivably be used for any suitable medium, the following description will refer to an example in which the medium is drilling mud.

In its simplest form, the present high-pressure pump HP comprises a hydraulic power pack (not shown) driven by an electric motor or a diesel aggregate and the following additional components: A hydraulic motor HM supplied with hydraulic oil from the hydraulic power pack; a synchronizer CS with an associated control block CB having a number of valves; a first valve manifold VM1 that volume regulates and directs the hydraulic oil to various locations/components; two diaphragm pumps MP having respective pump chambers that are alternately supplied with/relieved of hydraulic oil on one side of the pump diaphragm and effect pumping of drilling mud on the other side of the diaphragm; a second valve manifold VM2 that alternately controls the suction and the pumping of drilling mud.

The volume delivered by the hydraulic motor HM is equal to the volume to be pumped by use of the diaphragm pumps MP. Thus the volume delivered by the hydraulic motor HM is equal to twice the stroke volume of each pump chamber. Consequently, the rotational speed of the hydraulic motor HM corresponds to and directly controls the volume flow at the shift between the two pump chambers. The displacement volumes between these chambers correspond to each other, thus giving a constant volume flow of abrasive medium from the high-pressure pump HP. The pump chamber volumes are relatively large - the stroke volume of each pump chamber is typically of the order of 30 litres. For a delivery of 1200 litres/min, this gives a relatively low frequency of about 40 strokes per minute. This frequency constitutes only a third of that of conventional pumps. It will be appreciated that it is perfectly possible to have more than two pump chambers. A full-scale mud pump may as an example include four high-pressure pumps delivering a total of 4800 litres/min. This will be approximately the same as two conventional 1600 horsepower triplex pumps. This provides an installation in which only 25% of the capacity is down whenever one of the pumps requires replacement of a valve or a diaphragm. I.e. that only one pair of pump chambers is shut down and isolated, while the three other pairs operate as normal.

The pump chambers have a spherical form and, as mentioned previously, have a diaphragm that isolates the hydraulic oil in the top of the chamber from the mud in the lower part of the chamber. The diaphragms have a large surface area that renders the diaphragm movement short and slow, resulting in a long service life for the diaphragm. The concept has similarities with that which is found for pulsation dampers used with conventional mud pumps. These pulsation dampers have a diaphragm separating the gas (nitrogen) and mud and are subjected to a frequency three times that of the proposed pump; nevertheless they have a relatively long service life.

The pump chambers are mounted directly over the second valve manifold VM2 for mud. The valve manifold VM2 is equipped with a check valve in the same way as the valves of a conventional pump. However, these valves will have a service life three times of that for a conventional pump, as the frequency is only a third. The construction includes no replaceable components for daily maintenance and operation. Maintenance may be planned, and will be limited to one major workover once a year. Workovers will also entail lower spare part costs compared with regular overhauls on existing pumps. This allows considerable annual savings per pump. New rigs will often have two or three such pumps installed.

As indicated, the pump may optionally be provided with pressure boosters and an extra set of pump chambers for pumping cement. This operation requires extremely high pressures, up to 51 MPa. This will result in a considerable reduction in the equipment quantity, since the installation of the traditional cement unit can be omitted. Reference is now made to Fig.3, which schematically outlines the individual components of the high-pressure pump HP and the flow chart for the hydraulic oil and the drilling mud.

The right hand side of the figure shows a schematic view of two pump chambers A and B. As shown, chambers A and B are separated by respective diaphragms M and M'. On the top side of the diaphragm M, M' there is hydraulic oil, and on the underside, there is drilling mud. Pump chambers A and B are alternately acting. When chamber A performs a pumping stroke, chamber B goes through a suction stroke.

In order to achieve a pumping action with suction of drilling mud and subsequent pumping, the outlets from the respective pumping chambers A and B communicate with the second valve manifold VM2. The valve manifold VM2 comprises two valves VI, V2 and VI ', V2' for each chamber A, B. The valves VI, V2 and VI ', V2' are opening/closing valves, and are in their simplest embodiment in the form of check valves. One of the valves VI for chamber A is in communication with a feed pump (not shown) that applies drilling mud to the valve VI, as marked with PI. The second valve V2 communicates with the outlet from the chamber A on one side and with a line for discharging drilling mud, as marked with Dl on the other side. When chamber A performs a pumping stroke, the valve VI is kept closed because the sum of the pressure from the chamber A and the force of the spring in the valve VI is greater than the pressure applied by the feed pump. The valve V2 is forced to the open position by the pressure from the chamber A, and will consequently deliver pressurised drilling mud to Dl.

During supply of fresh drilling mud, reference is made to chamber B. The feed pump applies pressure to the valve VI'. Since the diaphragm M' is to return and no hydraulic oil has been applied, the feed pump only need to overcome the back pressure from the spring in the check valve VI ' and simultaneously force the hydraulic oil partly out of the chamber B. The valve V2' is kept closed by the sum of the pressure in the discharged pressurised drilling mud Dl and the spring force in the valve V2'. The valves VI -V2' operate in slave mode following the movements of the diaphragms M, M' in the respective chambers A, B. The left hand side of Figure 3 schematically shows a hydraulic motor HM that may advantageously be a vane motor having substantial capacity and with a constant displacement volume equal to twice the stroke volume of each pump chamber. The motor HM is supplied with hydraulic oil via a line P from the hydraulic power pack (not shown) and the prevailing pressure is indicated by p. The hydraulic motor HM delivers the oil onwards through the pressure line P, which communicates with the inlet to the respective pressure controlled flow regulating valves Fa and Fb, such as pressure controlled seat valves. The outlet from valve Fa communicates with the pump chamber A and the inlet to a pressure controlled flow regulating valve Sa, such as a pressure controlled seat valve, via line PA. Similarly, the outlet from valve Fb communicates with the pump chamber B and the inlet to a pressure controlled flow regulating valve Sb, such as a pressure controlled seat valve, via line PB.

Valves Fa and Fb have the same construction but act alternately in concert with the alternating action between chambers A and B. The valves Sa and Sb also have the same construction and act alternately in concert with the alternating action between chambers A and B. Further, it is to be noted that the valves Fa, Sa and Fb, Sb are of such a construction that the valve area of the spring side of the valves is larger than the valve area of the inlet side.

The hydraulic motor HM communicates directly with the synchronizer CS, which in turn is connected to the control block CB. The control block CB comprises a number of valves V5-V8 and V5'-V8'. In the embodiment shown, the synchronizer includes four mechanical cams C1-C4 that rotate at the same speed as the hydraulic motor HM. Each cam C1-C4 actuates a respective shut-off valve V5, VI, V5' and V7' by a push rod, and ensures that the valves are kept open/closed each half revolution. The entire control of the opening/closing sequence for the valves Fa, Fb, Sa, Sb is effected by use of the synchronizer CS and the valves V5-V8 and V5'-V8'.

Reference is now made to Figures 4A and 4B, which schematically show the opening and closing sequences for valves Fa, Fb, Sa and Sb. Each valve V5, V7, V5' and V7' communicates, on the inlet side, with the pressure line P via line PC, and is directly subjected to the pressure p from the hydraulic motor HM. Looking at valve V5 in isolation, this one is kept closed due to the area differential. The effective area of the upper chamber of the valve, i.e. the pilot chamber, is thus larger than the area on the inlet side. Valves V6 and Fa work in the same way as V5 and are pressure controlled flow regulating valves, such as pressure controlled seat valves, which are opened or closed due to the difference in area. When V5 is kept closed the pressure p on the pilot side of valve Fa and valve V6 will cease, allowing these valves to be opened. When Fa opens, the oil on the pilot side of the valve must be evacuated. The evacuation takes place through valve V6. A check valve Tl prevents the return oil from valve Fa from coming into contact with the pilot side of valve V6. The oil on the pilot side of valve V6 is evacuated through the throttle valve El and onwards out through the return passage D. When valve Fa opens, pressurised oil flows to the chamber A.

Correspondingly, figure 4B shows valve Fa in the closed position. Valve V5 is now forced open by cam CI, enabling pressurisation of the pilot chambers in the valves Fa and V6 with pressure p via line PC. The difference in area between the pilot side and the inlet side in the valves Fa and V6 keeps them closed. It will be appreciated that the pressure p in line P and line PC is the same, but the capacity of line PC is small compared with line P. When the valve Fa is closed, there will be no connection between the pump chamber A and the pressure p from the hydraulic power pack. The pump chamber A is then made ready to be refilled with new drilling mud by opening valve Sa.

The opening and closing sequences for valves Fb, Sa and Sb with associated throttle valves El and check valves Tl will be the same.

The oil in the control block CB never passes further than to the spring side (pilot side) of valves Fa, Sa and Fb, Sb, and does not return to line P until it has been drained back via D. As mentioned previously, this is to be considered as a strict controlling system for the operation of the valves Fa, Sa and Fb, Sb.

An operational sequence will now be described in greater detail in connection with Fig. 3. Chamber A performs a power stroke by means of the hydraulic oil that applies the diaphragm M. The valves Fa and Sa operate the chamber A, and the valves V5-V8, in turn, control the valves Fa and Sa. In the instantaneous picture shown in Figure 3, valve Fa is open, admitting the oil in line P into the chamber A. Valve V5 is closed, not admitting oil from line PC. The valve V6 is open in order to allow drainage of the oil located on the spring side of the valve Fa, thus enabling this to open. Valve Sa would potentially be able to allow oil to pass through and back to the tank. However, valve V7 is open, allowing oil and thereby the pressure p in line PC to pass through and on to the pilot side of valve Sa. The difference in area between the pilot side and the inlet side of valve Sa ensures that the valve is kept closed and the pressure p in the line P is transferred all the way to the chamber A. Valve V8 is kept closed due to the difference in area between the pilot side and the inlet side in the valve. Thus it will be appreciated that the valves V5 and V6 control the timing for opening/closing the valve Fa, and the duration for which it should remain open/closed. Correspondingly, valves V7 and V8 control the time for opening/closing the valve Sa and the duration for which it should remain open/closed.

Simultaneously with the above operational sequence for chamber A, chamber B performs a filling stroke by means of the feed pump (not shown) and the valves VI' and V2'. The oil above the diaphragm M' is forced back by operation of the valves Fb and Sb, which in turn are controlled by the valves V5'-V8'. At the instant shown in Fig.l, valves Sb is open, allowing oil from the chamber B to pass through and return to the tank via return line RB. Valve Fb is closed, and does not allow oil from line P to pass through. Valve V5' is open in order to transfer the pressure p from line PC to the pilot side of the valve Fb. The difference in area between the pilot and inlet sides ensures that the valve remains closed. On the pilot side, the valve V6' is influenced by the pressure p. The difference in area between the pilot and inlet sides maintains the valve V6' in the closed position. The valve V7' is in the closed position, not allowing the pressure from line PC to pass through. Valve V8' is open, allowing the oil from the pilot side of the valve Sb to pass through, thus allowing this to open.

Regarding the shift between the chambers A and B, the design of the cams C1-C4 ensure a relatively abrupt opening /closing of the valves V5, V7, V5', V7'. Fig.6 shows the cams CI and C3 that operate the valves Fa and Fb, as well as the cams C2 and C4 that operate Sa and Sb. The cams C1-C4 thus control the timing of the opening and closing of the valves Fa, Sa and Fb, Sb. When the push rod is lifted up by the cams, the valves V5, V7, V5', V7' will be forced open. The pressure p is then in direct communication with the pilot side of the valves Fa, Sa and Fb, Sb, as well as valves V6, V8 ,V6', V8'. The valves close gradually as the oil fills the pilot chambers of the valves. That part of the cams where the valves V5, V7, V5', V7' are forced open is called "the closed sector", as shown in Figure 6.

In the opposite incident, the valves Fa, Sa and Fb, Sb, as well as valves V6, V8, V6', V8', will be opened when the push rod is held in the lowered position by the cams ClC4. The pressure p from line PC then ceases on the pilot side of the valves, and the valves are opened by the pressure on the inlet side of the valves. That part of the cam where the push rod is in the lowered position is called "the open sector".

Fig.5 shows the pump diagram for chambers A and B. Oil based drilling mud is compressible. The compressibility has no effect on the present pump, but it will have an effect on the volumetric efficiency on the pumping side. The maximum flow on the suction side is approximately 25% higher than the constant flow on the pumping side.

An operational sequence will now be described in connection with Figure 5. In a given shift between pump chambers A and B, valve Fa must be opened while valve Fb must be closed. Pump chamber A is then prepared for a pumping stroke while pump chamber B is refilled with fresh drilling mud.

In order not to let pressurised oil to chamber A pass through valve Sa, it is necessary to ensure that Sa is fully closed before valve Fa can open. From Figure 5, it appears that the cam C2 of valve Sa is in the closed sector two degrees before the cam CI of valve Fa can commence the opening sequence. Thus the valve Sa has had time to close fully prior to the compressed oil being sent to pump chamber A.

Correspondingly, it is necessary to ensure that Fb is fully closed before valve Sb can be opened in order to lead the return oil away from pump chamber B. Fig.5 shows cam C3 in the middle of a closing sequence. From the figure, it appears that the cam must be rotated 10 degrees further before the closing sequence is completed. From the figure, it also appears the cam C4 must rotate through two degrees after the cam C3 has reached the closed sector before the opening sequence of the cam C4 commences. Thus the valve Fb has time to fully close before the valve Sb opens to evacuate oil from pump chamber B.

In order for the volume of drilling mud pumped out from the high pressure pump and through Dl to be constant, it is crucial for the change-over in valves Fa and Fb to overlap. Thus the difference in area between the displacement curves of chambers A and B must be constant. This is shown in the diagram on Figure 5. Depending on the size of the valves, there will be a certain lag in the response time for the closing and opening sequences. Consequently the chambers must be synchronised to adjust the closing sequence of chamber A to match the opening sequence of chamber B.

When one of the valves Fa or Fb is to be closed, it will take some time to fill the pilot side of the piston with oil, due to the inertia of masses. Thus, some time will pass from when the push rod in valve V5, V7, V5', V7' is lifted, admitting pressurised oil into the pilot side of the valves, until the valve closes. It is a matter of milliseconds, but still a time delay that must be taken into consideration in order to synchronise the opening and closing times of the valves Fa and Fb.

Conversely, when the valve Fa or Fb is to be opened, the response time will be minimal. The oil on the pilot side is now unpressurised, and is only to be evacuated. When the push rods are lowered as a result of the rotation of the cams, the pressure on the pilot side will disappear and the valve will open immediately. This is the reason why the cams CI and C3 of the valves Fa and Fb have different opening and closing sectors.

The closing sequence of the cam C3 requires a rotation of a total of 16 degrees in order to lift the push rod. From the diagram in Figure 5, it can be seen that the oil flow through the valve Fb requires 10 degrees from the open to the closed position, and that the cam C3 must rotate through six degrees before the valve Fb responds.

The stated values should be regarded as purely preliminary. More detailed testing needs to be carried out. The required overlap will to a certain degree depend on the volume of oil that is to flow through the system. Large volumes of oil will give a time delay due to the inertia of the system. Low rotational speeds will give a direct mechanical control of the cam movements - Fb would probably start closing even during the six degrees prior to the start of the opening sequence of Fa.

Correspondingly, the cam CI will take five degrees to lower the push rod in valve V5 so that the pilot pressure in valve Fa ceases and the valve opens. We see from the diagram in Figure 5 that in order to evacuate the oil on the pilot side of valve Fa, the cam must be rotated through 10 degrees from the closed to the open position. The diagram in Figure 5 shows that the evacuation of oil in valve Fa commences immediately upon cam CI initiating the opening sequence.

As described above, the response time for closing the valve Fa or Fb will be longer than for the opening of valves Fa and Fb. As is apparent from Figure 5, this is compensated for in that the cam C3 initiates the closing sequence for valve Fb six degrees before CI initiates its opening sequence for valve Fa. The diagram in the figure shows that the valve Fb then begins to close at the same time as the valve Fa opens. When the total volumetric flow across valve Fa and valve Fb then is constant, the displacement volume of drilling mud will remain constant. The overlap of the cams therefore ensures a steady, non-pulsating flow of drilling mud.

Claims

P a t e n t C l a i m s

1.

A high-pressure pump (HP), in particular for pumping abrasive media such as drilling mud and cement, comprising alternately acting diaphragm pumps (MP) driven with hydraulic power generated by a hydraulic power pack (not shown), each diaphragm pump (MP) comprises respectively a pump chamber (A, B) and at least two valves (VI, V2 and V1',V2') on the pumping side, c h a r a c t e r i s e d i n that the hydraulic power pack (not shown) drives a hydraulic motor (HM) with an approximately constant displacement volume equivalent to twice the stroke volume of each pump chamber, which motor is in direct hydraulic communication (P) with each pump chamber (A, B) via respective pressure controlled flow regulating valves that are controlled by a synchronizer (CS) connected to the hydraulic motor (HM).

2.

A high-pressure pump according to claim 1, c h a r a c t e r i s e d i n that the pressure controlled flow regulating valves comprise a respective first pressure controlled flow regulating valve (Fa, Fb) which on the inlet side is influenced by the pressure in the hydraulic connection (P) and on the other side (the pilot side) is influenced by the respective control pressures, a respective second pressure controlled flow regulating valve (Sa, Sb) which on the inlet side is influenced by the outlet pressure from the first pressure controlled flow regulating valve (Fa, Fb) and on the other side (the pilot side) is influenced by the respective control pressures.

3.

A high-pressure pump according to claim 2, c h a r a c t e r i s e d i n that the respective control pressures are determined by respective valve pairs (V5, V6; V7, V8; V5', V6'; V7\ V8') that receive the pressure in the hydraulic connection (P), where one valve (V5, V7, V5', V7') of the valve pair is opened by the synchronizer (CS) connected to the hydraulic motor (HM).

4.

A high-pressure pump according to one of Claims 1-3, c h a r a c t e r i s e d i n that the synchronizer (CS) is a shaft having a number of cams (C1-C4) directly connected to the hydraulic motor (HM).

5.

A high-pressure pump according to Claim 4, c h a r a c t e r i s e d i n that each cam (C1-C4) acts on a valve via a push rod (PR).

6.

A high-pressure pump according to one of Claims 1-5, c h a r a c t e r i s e d i n that the pressure controlled flow regulating valves (Fa, Fb and Sa, Sb) are pressure controlled seat valves.

7.

A high-pressure pump according to one of Claims 1-6, c h a r a c t e r i s e d i n thatthe valves (VI, V2 and VI', V2') on the pumping sides are check valves.