Well Stimulation Apparatus And Method

Abstract

An intensifier unit includes a pair of sequentially operated reciprocating ram assemblies, novel valving systems for controlling the relative movement of the ram assemblies to effect an output of working fluid having a minimum of pressure fluctuations, and a novel pneumatic control system for controlling the valving systems in response to the positions of the ram assemblies. In the preferred embodiment, the unit is mounted on a truck for use in high pressure operations, such as well fracturing, erosion drilling, or the like, and the rams have relatively large diameters and relatively long strokes for providing a minimum of wear and fatigue cycles. In the method, the ram assemblies are returned quicker than they are extended, and are sequentially pressurized prior to initiation of their forward strokes and prior to the decompression of the stroke of the preceding working cylinder to provide an essentially uninterrupted pressure delivery of working fluid to the well.

Description

BACKGROUND OF THE INVENTION

Hydraulic well stimulation operations such as those involved in fracturing geological formations adjacent deep well bores, erosion drilling, and the like present difficult problems due to the depth of the formation to be fractured, the high pressures required to be generated, the corrosive and abrasive nature of the fluids to be pumped, the long pumping times, and various other factors known to persons skilled to the art.

In conventional practice, these operations are often performed by a series of mechanically geared or revolving crank pumps having relatively short strokes and relatively high cycles per minute, for example 8 inch strokes and 120 cycles per minute. Such pumps tend to fatigue and to break-down rather readily when used for well stimulation, because of the extreme pressures and the high cycles per minute rate of operation, and because the working fluid is either abrasive (contains a high solids or sand concentration) or corrosive (contains a high hydrochloric acid concentration) or both, which causes the valves and packings to deteriorate quickly.

Such pumps also exhibit pressure pulsations or transient fluctuations which aggravate the adverse effects created by the high rate of fatigue and wear cycles. As a result, effective and profitable well stimulation may not have been realized.

The ideal hydraulic well stimulating apparatus should have a pumping system with the following features: First, it should have a long stroke in order to reduce the number of fatigue and wear pressure cycles for longer service life; Second, it should minimize the pressure fluctuations in the output to minimize the strain on the pumping system; Third, it should be capable of operating at pressures from 10-20,000psi or more to be able to stimulate deep wells; Fourth, it should be portable, capable of being easily transported from site to site; Fifth, it should be capable of operating for long periods of time to stimulate hitherto unstimulatable wells; and Sixth, it should be inexpensive to operate and maintain.

SUMMARY OF THE INVENTION

The present invention is directed to a new apparatus and method for pumping high pressure contaminated and corrosive fluids at relatively high horsepower for well stimulation purposes and the like. In general, the invention provides a two-cylinder intensifier which maximizes volume per stroke and reduces the rate of operation using large diameter pumping rams having relatively long strokes. The system circuit includes novel valve systems for controlling the supply of high pressure driving fluid to the rams and a novel control circuit for controlling the valve systems to effect movement of the rams for converting high horsepower to a smooth, high pressure fluid flow with a minimum of fatigue cycles.

In the preferred embodiment, the fluid intensifier comprises at least one pair of sequentially operated intensifier ram assemblies each including a pumping ram and a power ram for driving the pumping ram on its forward pumping stroke. A bridge member or yoke is connected to each assembly, preferably between the pumping ram and power ram, and return rams are adapted to drive each ram assembly on its return stroke by pressing against the yoke.

A high horsepower source, such as 1,100 horsepower turbine engine, drives a series of pumps, preferably of variable output, and these pumps deliver driving fluid at a high pressure to the power rams. The pressure of the driving fluid is in turn multiplied by the ram assemblies, wherein the diameters of the power rams are greater than the diameters of the pumping rams, and the working fluid is delivered to a well or the like at an increased or multiplied pressure, for example 10-20,000 psi or more, by alternating forward strokes of the ram assemblies. The strokes of the pumping rams are relatively long, for example 70 inches, to minimize the frequency of operation, and the consequent number of fatigue cycles and total wear.

The ram assemblies are driven on their return strokes by a precharged accumulator which is adapted to return the ram assemblies quicker than they are extended in order that the returning ram may be pressurized while the extending ram decelerates. The ram assemblies, as controlled by the novel valve systems and the novel pneumatic control circuit, cooperate to produce a smooth, relatively pulseless output having a relatively constant pressure.

Each valve system comprises a control valve for admitting driving fluid to the ram to effect the forward stroke of the power ram, a pressure relief valve for decompressing the power ram, at the completion of its forward stroke, and an exhaust valve for exhausting the power ram after its decompression to enable the return rams to effect the return stroke. Each system also includes a differential check valve for pressurizing the power ram, prior to the admittance of driving fluid to the ram, to a pressure less than the driving pressure to achieve a smooth transition of output pressure as the rams reciprocate back and forth. In addition, each valve system includes a directional control valve for admitting driving fluid to the differential check control valve before the ram starts to extend and for admitting driving fluid to the exhaust valve to keep this valve open while the ram returns.

The pneumatic control circuit, on the other hand, includes a relay control valve and a holding valve for responding to the movement of each ram assembly, and a reversing valve actuated by the movement of both ram assemblies. The circuit is operatively connected to two pairs of tappet valves, one for each ram assembly, which signal the completion of the forward and return strokes of the ram assemblies. The circuit responds to actuation of the tappet valves and alternately pressurizes and actuates one ram while the other ram decelerates to reverse, by sequentially operating the valve systems, and provides a reliable means of controlling the intensifier output and of achieving the objects of the invention.

One object of the present invention is to provide a reliable, efficient and dependable pressure multiplier with an optimized service life, and an improved method of fracturing wells and the like.

Another object is to provide a pressure multiplier with reduced frequency of operation and with an increased stroke length and pumping ram diameter, so as to minimize wear and optimize valve life.

An important object is to provide a means for returning the rams faster than they are extended to provide a time interval, and to pressurize the return ram in that time interval to provide a smooth, relatively pulseless high pressure output.

These and other objects will become apparent from the drawings, the following description and the appended claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the two-cylinder fluid pressure intensifier of the present invention mounted on the bed of a truck;

FIG. 2 is an arrangement drawing of the partial system drawings shown in FIGS. 3A-C;

FIGS. 3A is a diagrammatic system drawing showing the intensifier ram assemblies, the air supply unit, the accumulator, the supply tank, and the main valve station of the present invention;

FIG. 3B is a diagrammatic system drawing showing the pneumatic control panel of the present invention;

FIG. 3C is a diagrammatic system drawing showing a main pumping unit for use in the practice of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment consists of a two-cylinder fluid pressure multiplier or intensifier which converts high pressure driving fluid flow into a smooth multiplied high pressure working fluid output especially adapted for fracturing geological formations adjacent well bores or the like. The apparatus accomplishes this result with a pair of intensifying ram assemblies having relatively long forward and return strokes and large diameters for reducing the frequency of operation, and includes means for effecting relative movement of the ram assemblies in a manner which minimizes pressure fluctuations in the working fluid output to provide for improved efficiency and service life.

Referring generally to FIG. 1, the intensifier of the present invention may be conveniently mounted on the bed of a truck, and includes a pair of ram assemblies comprising pumping rams PA and PB which receive working fluid through inlets 20 and discharge working fluid through outlets 21 at the end of the truck, and power rams RA and RB connected to the pumping rams PA and PB respectively. The truck carries a driving fluid (preferably hydraulic oil) supply tank T1, and a high horsepower source such as a turbine engine TM1 drives a pair of main pumps P1 and P2 which deliver driving fluid from tank T1 to a valve station M1 which sequentially admits fluid to the power rams RA and RB to effect the forward pumping strokes of the ram assemblies.

The intensifier also includes a precharged accumulator AC1 for driving a pair of twin return rams QA and QB (rams QB are not shown in FIG. 1) to effect the return strokes of the ram assemblies. A diesel engine D1 drives a pair of small pumps (not shown) which supply the accumulator AC1 and main pumps P1 and P2 respectively, and also a compressor (not shown) and the compressor supplies air to a pneumatic control panel AP1 mounted on one side of the truck and adapted to control the valve station M1 in response to movement of the ram assemblies.

The Intensifying Ram Assemblies

Referring more specifically to FIG. 3A, a preferred embodiment of the invention is shown wherein the power rams RA and RB have 9 inch diameters and are adapted to reciprocate on 70 inch strokes within hydraulic cylinders 22 and 23 having inlet ports 24 and outlet ports 25. The pumping rams PA and PB have 5 inch diameters and are disposed for reciprocation in hydraulic cylinders 27 and 28, and bridge members 30A and 30B carrying tappet cams 31 and 32 are connected between the pumping rams PA and PB and the power rams RA and RB respectively. The twin return rams QA and QB are disposed within cylinders 34 and are connected at the opposite ends of each bridge, and preferably on opposite sides of each pumping ram to move the ram assemblies on their return strokes.

Accumulator

The accumulator ACI is pre-charged with driving fluid to about 1,000 psi and has a pair of branch lines 35 and 36 including check valves V12A and V12B connected to the return ram cylinders 34. A small auxiliary pump P3 (approximately 6 GPM) driven by the diesel engine D1 is adapted to charge the accumulator by delivering fluid from the supply tank T1 through filter F2 to an intersection 38 to the accumulator charge line 40 connected to the accumulator AC1 and to lines 35 and 36. This branch circuit includes a pressure relief valve V6 adapted to spill fluid over to tank T1 when the pressure in lines 35 and 36 exceeds 1,000 psi. The accumulator AC1 supplies 1,000 psi fluid to the return rams QA and QB to effect the return strokes of the intensifying ram assemblies, and receives fluid from the return cylinders 34 on the forward strokes of the pumping rams PA and PB. Pump P3 discharges at 1,000 psi and its discharge pressure is controlled by relief valve V13.

Main Hydraulic Pump Unit BP1

Referring to FIGS. 3A and 3C, the main hydraulic pump unit BP1 may include any of a number of pumping means, preferably of variable output, for supplying fluid to the intensifier ram assemblies. For purposes of the present disclosure, the unit BP1 is shown as including a pair of "Kelsey-Hayes" 500-600 HP hydraulic fluid pumps P1 and P2 driven in tandem by a variable speed 1800 rpm "Solar" turbine engine TM1 and having a 1,100 hp or more output. The pumps P1 and P2 are charged through a line 42 and filters F1A and F1B by a supercharging pump P4 (approximately 600 GPM) which is driven by the diesel engine D1 and whose output is controlled at 150 psi by the pressure relief valve V9.

Each pump P1 and P2 includes three six-piston sections which discharge through corresponding outlets 43-45 and 46-48, and outlets 44 and 47 are preferably connected to outlets 45 and 48, respectively, so that one section discharges through line 50 and 51 and two sections discharge through lines 52 and 53. The outputs of the pump P1 and P2 may be varied by control units PM1 and PM2, respectively, each of which includes an unloading valve 54 consisting of a main by-pass and pressure relief valve 55 and a normally open pilot control valve 56.

Under normal operation, the pumps P1 and P2 deliver fluid through lines 50-53 to a main fluid output line 60 connected to the main hydraulic valve station M1. The pump unit BP1 is preferably provided with means for changing the outlet pressure when the turbine speed is changed, for example by a change in altitude, and includes a remote selector (not shown) adapted to selectively energize solenoid valves AV18A-D, to load selected pump sections according to the power available at the turbine. The selector is also used to protect the pumps P1 and P2 from being overloaded.

A pressure sensing valve PV9 senses the pressure in line 50, and when the pressure reaches 5,100 psi, actuates valves AV18A and AV18C which in turn cause their corresponding control valves 54 to unload one section of each pump to tank T1, causing valve 55 to act as a relief valve, and the pumps run at two thirds capacity. In the present illustration, a maximum load condition with only two sections of each pump operating is set at 6,500 psi at the pump outlet, and is selected by actuating solenoid valve AV18E, so that fluid is returned through relief valve PV5 to tank T1. Normally, however, the maximum load condition is 5,200 psi, and this pressure level is maintained by relief valve PV6 also connected to return line 62.

The flow through lines 50-53 is controlled by the air actuated check valve PV8 which receives hydraulic fluid through line 65 from the auxiliary pump P3 (FIG. 3A). When valve PV8 is open, fluid is delivered through check valve PV7 and thence through lines 50 and 52 to close check valves 66 and 67, and through line 60 to lines 51 and 53 to close check valves 68 and 69. In this blocking mode, the fluid delivered by pumps P1 and P2 is diverted through the control units PM1 and PM2 to the supply tank T1 via check valves 71-74 and return line 62, or through pressure relief valves 55 and return line 75.

Main Hydraulic Valve Station M1

The main valve station M1 (FIG. 3A) includes two identical valve systems VA and VB for controlling the fluid supply from line 60 to the power rams RA and RB respectively. The valve systems include pneumatically actuated shut-off valves V1A and V1B having ports 1-3. When valves V1A and V1B are open (connecting ports 1-2), they admit fluid from line 60 to the inlet ports 24 of the power ram cylinders 22 and 23 and effect the forward strokes of rams RA and RB.

The station M1 also includes pneumatically actuated directional control valves V2A and V2B having ports 1-7 and loops LA and LB between control valves V2A and V2B and the inlets 24 of cylinders 22 and 23. The loops LA and LB include decompression check valves V3A and V3B connected in parallel with differential check valves V4A and V4B, respectively, the latter valves V4A and V4B being set at 150 psi less than the driving pressure in line 60.

The directional control valves V2A and V2B are movable between pressurizing and exhausting positions and are biased normally to the pressurizing position (connecting ports 2-5), so that fluid from line 60 is normally delivered to the loops LA and LB enabling power rams RA and RB to be pressurized to 150 psi less than the working pressure of line 60. When in their exhaust position (connecting ports 2-4), fluid from line 60 flows into and opens exhaust valves V5A or V5B connected to the outlets 25 of cylinders 22 and 23, and permits the rams RA and RB to be exhausted.

The valve systems VA and VB are adapted to effect the forward stroke of one ram while, at the same time, effecting the return stroke of the other ram at a faster rate, in order that the returning ram may be pressurized prior to its forward stroke. This feature enables the returning ram to reverse and precharge to 5,050 psi (150 psi less than the working pressure 5,200 psi) as the first extending ram decelerates to reverse. This keeps high pressure fluctuations in the output to a minimum and insures that the intensifiers will deliver stable pressure output.

Pneumatic Control Panel

Referring to FIGS. 3A-3B, the pneumatic control panel AP1 is supplied with pressurized air from the air supply unit AS1, which includes an air tank 80 supplied with air by a compressor 81 driven by the diesel engine D1. The panel AP1 receives air from the tank 80 through line 82 and includes a solenoid operated remote start/stop switch AV16 and a manually operated start/stop switch AV12.

A directional control switch AV14 having ports 1-4 is spring biased to the normal operating position (connecting ports 1-2) and has a reset position (connecting port 1-3). A reset circuit for returning the power rams RA and RB to their starting positions is connected to port 3 of switch AV14, and a manual directional control valve AV11 is connected to port 2 of switch AV14. The valve AV11 has two positions, position 1 for automatic movement of the rams, and position 2 for inching movement of the rams.

When pulled out to position 1, valve AV11 delivers air to intersection 85 and through shuttle-valve AV9 to intersection 86 where the air is diverted in three directions. Line 87 diverts air to the main pump unit BP1, line 88 diverts air to a reversing control valve AV7 having ports 1-6 and thence to shut off valve V1A or V1B in the main valve station M1, and line 89 diverts air to the relay valve AV3A. Branch line 90 diverts air from line 87 to the relay valve AV3B. Air is also delivered via intersection 85 and line 91 to tappet valves AV1A-B and AV2A-B (FIG. 3A) positioned for actuation by the cams 31 at the forward and return extensions of the ram assemblies. A branch line 92 connects this air to ports 6 of directional control valves V2A and V2B, biasing them in their pressurizing position.

It will be noted that the reversing control valve AV7 has two positions: position 1 (opening ports 1-2) for admitting air to valve V1A through check valve AV8A and line 94, and position 2 (opening ports 1-3) for admitting air to valve V1B through check valve AV8B and line 95. Panel AP1 also includes holding valves AV4A and AV4B having ports 1-4 and movable between normally open positions (connecting ports 1-2), and blocking positions (connecting ports 2-3). These valves are moved to their blocking positions when air passes through valve AV7, to valve AV4A by air in line 97, and to valve AV4B by air in line 98.

When pushed in to position 2, valve AV11 delivers air to a crank-operated three-position inch control valve AV10 spring biased to position 3 which completely stops the flow of air and movement of the rams. In position 1, valve AV10 connects with valve station M1 and causes fluid to be pumped into cylinder 22 and fluid to be exhausted from cylinder 23, causing ram RA to move forward and ram RB to return. The opposite result is attained when valve AV10 is in position 2, as the connection causes ram RA to return and ram RB to move forward. During inch conditions, the tappet valves AV1A-B and AV2A-B are inoperative, and valve AV10 is used to set the tappet valves AV1A-B and AV2A-B and to check clearances, etc.

Sequence of Operations

Reset

Before the operating cycle is commenced, the system is reset. To do this the diesel engine D1 is started and auxiliary pump P3 fully charges the accumulator AC1 to 1,000 psi. Engine D1 also starts the compressor 81 so that air passes through line 82 to the control panel AP1. The solenoid start/ stop valve AV16 is then energized, and the manual start/stop valve AV12 is placed in the stop position. The system reset valve AV14 is then depressed, held, and valve AV12 is pulled to the start position to connect air from line 82 to intersection 100. The air branches via line 101 to hydraulic valve PV8, opening this valve and admitting fluid into the pump unit BP1, where it is blocked by check valves 66-69 and flows through line 60 to valve unit M1 at the accumulator pressure 1,000 psi.

Air also branches from intersection 100 through line 102 to intersection 103 and through shuttle valves AV17A and B and lines 104 and 105 to ports 7 of directional control valves V2A and V2B, causing these valves to counteract the pressure on ports 6 thereof and to connect ports 2 to ports 4 and ports 3 to ports 5. Air also passes from line 102 via branch lines 107 and 108 through shuttle valves AV13A and AV13B to ports 4 of air valves AV3A and AV3B, setting them in position 1.

The opening of valve PV8 feeds fluid from auxiliary pump P3 through supply line 60 and through ports 2-4 of valves V2A and V2B to open exhaust valves V5A and V5B and connect the main intensifier rams RA and RB to exhaust. With these main rams to exhaust, the accumulator AC1 supplies oil to the small return rams QA and QB effecting the return strokes of both intensifier units. On completion of the return strokes, tappet valves AV2A and AV2B are depressed, completing the system reset cycle. The system reset valve AV14 is then released.

Neutral

The system is then placed in the neutral or stop position. With the system in the cycle reset position, as described above, the prime mover TM1 is actuated to start the main pumps P1 and P2. Since the diesel engine D1 is still running, fluid from the boost pump P4 is fed at 150 psi through filters F1A and F1B into the main pumps P1 and P2. The main pumps P1 and P2 discharge through lines 50-53 and, since unloading valves 54 are open, through by-pass valves 55 and line 75 back to the supply tank T1 at zero pressure.

Ram RA Forward -- Ram RB Prepressurized

With the pumps recycling to tank, the system is ready to start an automatic cycle. With both main power rams RA and RB fully returned and resting on tappet valves AV2A and AV2B, with all pumps running, and with air valve AV7 in position 1, shown, the inch/auto valve AV11 is pulled to position 1 to connect air to intersection 85 from which it is diverted to the tappet valves AV1A-B and AV2A-B via line 91 and to intersection 86 via shuttle valve AV9.

Since the tappet valves AV2A-B are initially engaged, air passes through these valves and through lines 110 and 111 via shuttle valves AV5A and AV5B and shuttle valves AV13A and AV13B to port 4 of relay valves AV3A and AV3B, moving these valves to position 1. Constant air pressure in line 92 is applied to ports 6 of valves V2A and V2B to bias these valves toward the positions shown in the drawings.

The air supply to intersection 86 is diverted in three directions:

1. Via line 87 to solenoid valves AV18A-D for loading the main pumps P1 and P2 and through branch 90 to port 1 of relay valve AV3B where it is blocked. 2. Via line 88 through reversing valve AV7 to port 3 of control valve V1A, opening this valve and commencing the forward stroke of ram RA, and through branch 97 to port 4 of ram RA, and through branch 97 to port 4 of valve AV4A to hold this valve in blocking position. 3. Via line 89 to port 1 of relay valve AV3A where it is blocked.

The main pumps P1 and P2, when loaded, deliver fluid thru valve V1A into the main intensifier cylinder 22, starting the forward stroke of power ram RA and displacing oil from the small return rams QA into the accumulator AC1, or, the accumulator is fully charged, displacing fluid through relief valve V6 to tank T1. At the same time, driving fluid passes through ports 2-5 of valve V2B to valve V4B in loop LB. Valve V4B closes when the pressure on the outlet port, which is connected to intensifier ram RB, reaches 150 psi less than the pressure in line 60, causing the intensifier ram RB to be pressurized to within 150 psi of the moving intensifier ram RA.

Ram RB Forward -- Ram RA Stops

On the completion of the forward stroke of intensifier ram RA, the tappet valve AV1A is depressed, causing air to be admitted via line 115 and shuttle valve AV6A to port 1 of holding valve AV4A. However, since valve AV4A is still being held in a blocking position by air on port 4 thereof, it remains blocked. Air is also admitted via branch line 116 to port 5 of reversing valve AV7, operating this valve (connecting ports 1-3 and ports 2-4) and effecting a transfer of the air being delivered through line 88 from line 94 to line 95. Accordingly, air passes through check valve AV8B and is admitted via line 95 to port 3 of valve V1B, opening this valve and permitting driving fluid to be admitted to ram RB to commence the start of its forward stroke. Air is also admitted via line 98 to port 4 of holding valve AV4B, moving this valve to its blocking position.

At the same time, but at a slower rate set by valve AV8A, port 3 of valve V1A exhausts via line 94 through valves AV8A and AV7, resetting valve V1A to the closed position. This stops the forward movement of intensifier ram RA. In this condition, ram RB is receiving the full main pump output through valve V1B.

Reversal-Ram RA Returns and Pressurizes -- Ram RB Stops

As the pressure exhausts from port 3 of V1A, port 4 of valve AV4A also exhausts, at the same rate and at the same time, resetting valve AV4A and opening port 1 to port 2. This allows air from the tappet valve AV1A to be admitted through valve AV4A to port 5 of relay valve AV3A, shifting this valve to position 2 and connecting port 1 to port 2. The air in line 89 is therefore directed through this valve and through shuttle valve AV17A to port 7 of the directional control valve V2A via line 104, counteracting the air pressure against port 6 from line 92 and opening ports 2-4 and ports 3-5. This action admits driving fluid to exhaust valve V5A. Cylinder 22 decompresses at a rate set by valve V3A, and on completion of decompression, exhaust valve V5A opens and exhausts ram RA through valve V5A.

With intensifier ram RA fully opened to exhaust, the charged accumulator AC1 actuates the small return rams QA and ram RA starts its return stroke, first releasing tappet valve AV1A and, on completion of the return stroke, operating tappet valve AV2A. The releasing of tappet valve AV1A exhausts port 5 of relay valve AV3A, and the operating of tappet AV2A admits air to port 4 of AV3A, causing this valve to move to position 1 and block the air flow through line 89. The releasing of tappet valve AV1A also exhausts port 5 of reversing valve AV7 through line 116. However, since this valve is not spring biased, it momentarily remains in the reversed position until actuated again.

Meanwhile, the intensifier ram RB is still making its forward stroke, displacing fluid from the return rams QB into the accumulator AC1. The intensifier ram RA is pressurized through valve V2A and sits at the start of its forward stroke. On completion of the forward stroke of ram RB, the tappet valve AV1B is actuated and air is admitted via line 118, shuttle valve AV6B, and line 120 to port 6 of reversing valve AV7, moving this valve to position 1 and connecting port 1 to port 2. Air is also admitted to port 1 of the blocked valve AV4B.

Ram RA Forward -- Ram RB Prepressurized Again

As it reverses, valve AV7 supplies air through line 94 to open valve V1A, and this admits fluid from the main pump supply to cylinder 22, thereby starting ram RA on its forward stroke again. Simultaneously, valve AV7 cuts off air pressure to lines 95 and 98, and consequently these lines exhaust through valve AV8B and valve AV7. The exhausting of line 95, as was the case for the exhausting of line 94, described previously, causes valve V1B to close and cut off the supply of driving fluid to ram RB. As a result ram RB stops. The exhausting of line 98 releases valve AV4B, opening port 1 to port 2 thereof and enabling air in line 118 to actuate relay valve AV3B to position 2, connecting port 1 to port 2.

This action enables air from branch line 90 to be admitted through relay valve AV3B and shuttle valve AV17B to port 7 of directional control valve V2B, opening ports 2-4 and enabling driving fluid to be admitted to exhaust valve V5B. Cylinder 23 is accordingly decompressed at a rate set by valve V3B in loop LB, and on completion of a decompression, exhaust valve V5A opens and, under the pressure exerted by the accumulator AC1 on return rams QB, and ram RB exhausts through valve V2B and starts its return stroke.

The system thus starts another cycle. The forward stroke takes a longer period of time to complete than the return stroke, in order that the returning ram may be pressurized while awaiting its next forward stroke. In addition, the system, by pressurizing the returned ram to within 150 psi of the forward moving ram, provides a smooth, relatively pulseless output flow which minimizes the mechanical wear on the valving and extends the service life of the system.

Adjustment of Ram RA or Ram RB

A manual system is provided to set the tappet valves, check clearances, etc. Ram RA is adjusted by moving the air valve AV11 to the inch position, position 2, thereby connecting the air supply to valve AV10, and by moving AV10 to position 1. Air then passes to intersection 125 and intersection 126. From intersection 126 air branches through shuttle valves AV5A and AV13A to port 1 of relay valve AV3A, setting this valve in the blocking position 1. Air also branches through line 127 through shuttle valve AV6B and valve AV5B to port 5 of relay valve AV4B, where it actuates this valve to position 2. Air also passes through line 120 to port 6 of reversing valve AV7, setting this valve in position 1.

From intersection 125, air passes through shuttle valves AV15 and AV9 to intersection 86 where it is diverted in three directions. Line 87 supplies air to the solenoid valves AV18A-E which control the supply pumps P1 and P2. Line 89 connects air to port 1 of relay valve AV3A, where it is blocked, and line 88 connects air through valves AV7 and AV8A to port 3 of V1A, thereby opening this valve and admitting driving fluid from line 60 to ram RA, starting its forward stroke.

At the same time, branch line 90 delivers air through relay valve AV3B and shuttle valve AV17B to port 5 of the directional control valve V2B, causing driving fluid to be admitted to valve V5B and effecting ram RB's return stroke.

Since all motion stops when valve AV10 is moved to position 3, ram RA may be adjusted forwardly by intermittently moving valve AV10 into position 1 and into position 3 to effect inching movement.

Ram RB is similarly adjusted by pushing air valve AV10 to position 2. This connects air to intersections 130 and 131. From intersection 131, air passes through shuttle valve AV6A and holding valve AV4A to port 5 of relay AV3A, actuating this valve to position 2, and also through line 116 to port 5 of reversing valve AV7, also actuating this valve to position 2. Air is also connected through line 132 and via shuttle valves AV5B and AV13B to port 4 of relay valve AV3B, actuating this valve to position 1.

From intersection 130 air is diverted through shuttle valves AV15 and AV9 to intersection 86, where it is again diverted in three directions. Air in line 87 is again supplied to solenoid valves AV18A-E. This time, however, air in branch line 90 is blocked at port 1 of relay AV3B; valve AV7 connects air in line 88 to port 3 of valve V1B, actuating this valve and admitting driving fluid to ram RB; to start its forward stroke; and air in line 89 passes through relay valve AV3A and shuttle valve AV17A to port 7 of directional control valve V2A, actuating this valve and admitting driving fluid to exhaust valve V5A effecting the return of ram RA.

Thus, by a similar pneumatic network, ram RB may be adjusted by intermittently moving valve AV10 into position 2 and into position No. 3 (stop position). Only when this valve is moved to position 1 or 2 are the main pumps loaded. During inch conditions, the tappet valves AV1A-B and AV2A-B are inoperative.

Emergency Stops

During movement of either intensifier unit, an emergency stop can be effected by depressing valve AV12 or de-energizing valve AV16. These valves interrupt the air supply and exhaust the system. This action immediately unloads the main pumps and stops any movement of the intersifier rams RA and RB.

It is therefore apparent that a pressure intensifier constructed in accordance with the present invention provides certain desirable features and advantages. For example, an intensifier using the turbine and main pumps described above has the following theoretical outputs:

Full Pump

13,900 psi .times. 130 gpm = 1,060 hp = 1,800 rpm at 4,300 psi

16,800 psi .times. 108 gpm = 1,060 hp = 1,500 rpm at 5,200 psi

2/3 Pumps

21,000 psi .times. 72 gpm = 980 hp = 1,500 rpm at 6,500 psi The intensifier is thus capable of driving high pressure output which is useful for well fracturing purposes and the like.

Moreover, the intensifier is able to deliver high pressure output with a minimum of pressure fluctuation and at a variety of pressures so that the output consists of a smooth, relatively pulseless flow which minimizes the power shocks on the intensifier. The intensifier is well suited to a long stroke, large diameter intensifier ram assembly, which reduces the frequency of operation so that there are fewer fatigue and wear cycles on the valves producing improved service life and reducing the overall maintenance expense.

In addition, the valve systems together with the pneumatic control circuit of the present invention operate to return the rams faster than they are extended to provide a time interval in which the return ram is pressurized while the extending ram is decelerating to reverse. As soon as the extending ram reverses, the valve system and pneumatic control circuit operate the pressurized ram to provide the relatively pulseless output flow described above. The valve systems and pneumatic control circuit are unique and enable the intensifier to operate nearly continuously and relatively free of maintenance expense.

The foregoing features enable hitherto low yielding wells to be fractured more economically than in the past, and also enable wells which have come untapped to be stimulated. The apparatus of the present invention, therefore, from the practical standpoint, provides a significant advance in the art.

While the methods and forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made therein without departing from the scope of the invention.

Claims

What is claimed is:

1. Hydraulic well fracturing equipment including a first intensifier having a hydraulic ram and a second intensifier having a hydraulic ram, each said intensifier having a common outlet for delivering fracturing fluid at high pressure to a well or the like, a source of hydraulic operating fluid under high pressure for operating said rams, main control valves operable to apply fluid from said source to each of said rams, adjustable decompression valves operable to bleed off the hydraulic pressure from each of said rams, relatively larger valves for each of said rams providing for rapid exhaust of the hydraulic fluid therefrom, and pneumatic control means responsive to the approach of one of said intensifier rams toward the end of its stroke for performing the following steps in sequence

1. open the main control valve to the other of said intensifiers to start its ram on a working stroke,

2. close the main control valve to said one intensifier ram,

3. operate the decompression valve of said one ram to bleed off hydraulic pressure therefrom, and

4. operate said larger exhaust valve of said one ram to provide for the rapid exhaust of the fluid therefrom.

2. The fracturing equipment of claim 1 further comprising means for returning said one intensifier to its starting position at a rate which substantially exceeds the movement of said other intensifier under the influence of said hydraulic pressure, and valve means for prepressurizing said one intensifier to a pressure somewhat less than the working pressure of said other intensifier.

3. The system of claim 2 in which said prepressurizing means includes a differential check valve.

4. In an intensifier having first and second reciprocating ram cylinders, a source of driving fluid at a driving pressure, means for effecting the return strokes of said ram cylinders, pneumatic control indicators positioned for actuation by said ram cylinders on their forward and return strokes, a pair of identical first and second valve systems for controlling the forward and return strokes of said ram cylinders, said first valve system comprising:

a directional control valve connected to said driving fluid source and movable to a prepressurizing position in response to actuation of the indicator on the return stroke of a first ram cylinder and to an exhausting position in response to actuation of the indicator on the forward stroke of said first ram cylinder,

a differential check valve connected between said first ram cylinder and said directional control valve for prepressurizing said first ram cylinder in response to movement of said directional control valve to its prepressurizing position,

a pressure release valve operatively connected between said first ram cylinder and said directional control valve for decompressing said first ram cylinder in response to actuation of the indicator on the forward stroke of said first ram cylinder,

an exhaust valve operatively connected between said first ram cylinder and said directional control valve for exhausting said first ram cylinder in response to movement of said directional control valve to its exhausting position, and

a control valve connected to the driving fluid source and responsive to actuation of the indicator on the forward stroke of a second ram cylinder to admit driving fluid to said first ram cylinder to effect its forward stroke.

5. In well fracturing equipment, the improvement comprising:

at least two sequentially operating reciprocating working cylinders for supplying a working fluid under high pressure to the well,

a separate ram cylinder connected for operating each of said working cylinders,

a source of driving fluid under pressure,

means for delivering the driving fluid to said ram cylinders at a driving pressure,

a separate valve system for each ram cylinder, including means for prepressurizing each ram cylinder to a pressure less than said driving pressure, means for admitting driving fluid to each ram cylinder at said driving pressure to effect its forward stroke, and means for decompressing and exhausting each ram cylinder at the completion of its forward stroke,

a bridge member operatively connected between each ram cylinder and each working cylinder, a pair of return cylinders operatively connected to each bridge member for effecting the return strokes of said ram cylinders at the completion of their forward strokes,

and control means for controlling said valve systems and said return cylinders to effect return strokes of said ram cylinders at a rate substantially faster than said forward strokes thereof to provide time for prepressurization of said ram cylinders for enabling said ram cylinders to produce a smooth, relatively continuous and pulseless output flow of said working fluid to said well.

6. The equipment of claim 5 wherein said actuating means comprises a pre-charged accumulator connected to said return cylinders.

7. In well fracturing equipment, the improvement comprising:

at least two sequentially operating reciprocating working cylinders for supplying a working fluid under high pressure to the well,

a separate ram cylinder connected for operating each of said working cylinders,

a source of driving fluid under pressure,

means for delivering the driving fluid to said ram cylinders at a driving pressure,

a separate valve system for each ram cylinder, including means for prepressurizing each ram cylinder to a pressure less than said driving pressure, means for admitting driving fluid to each ram cylinder at said driving pressure to effect its forward stroke, and means for decompressing and exhausting each ram cylinder at the completion of its forward stroke,

return cylinders operatively connected to effect the return strokes of said ram cylinders at the completion of their forward strokes,

and control means for controlling said valve systems and said return cylinders to effect return strokes of said ram cylinders at a rate substantially faster than said forward strokes thereof to provide time for prepressurization of said ram cylinders for enabling said ram cylinders to produce a smooth, relatively continuous and pulseless output flow of said working fluid to said well.