WO2016207631A1 - Strata fracturing apparatus and method - Google Patents

Strata fracturing apparatus and method Download PDF

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Publication number
WO2016207631A1
WO2016207631A1 PCT/GB2016/051872 GB2016051872W WO2016207631A1 WO 2016207631 A1 WO2016207631 A1 WO 2016207631A1 GB 2016051872 W GB2016051872 W GB 2016051872W WO 2016207631 A1 WO2016207631 A1 WO 2016207631A1
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WO
WIPO (PCT)
Prior art keywords
proppant
pressure
fluid
hydraulic
additive
Prior art date
Application number
PCT/GB2016/051872
Other languages
French (fr)
Inventor
Roger Bacon
Original Assignee
Rab Hydraulics Limited
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Filing date
Publication date
Application filed by Rab Hydraulics Limited filed Critical Rab Hydraulics Limited
Publication of WO2016207631A1 publication Critical patent/WO2016207631A1/en

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B21/00—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
    • E21B21/06—Arrangements for treating drilling fluids outside the borehole
    • E21B21/062—Arrangements for treating drilling fluids outside the borehole by mixing components
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/25—Methods for stimulating production
    • E21B43/26—Methods for stimulating production by forming crevices or fractures
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
    • C09K8/60—Compositions for stimulating production by acting on the underground formation
    • C09K8/62—Compositions for forming crevices or fractures
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
    • C09K8/60—Compositions for stimulating production by acting on the underground formation
    • C09K8/80—Compositions for reinforcing fractures, e.g. compositions of proppants used to keep the fractures open
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/12—Methods or apparatus for controlling the flow of the obtained fluid to or in wells
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/25—Methods for stimulating production
    • E21B43/26—Methods for stimulating production by forming crevices or fractures
    • E21B43/267—Methods for stimulating production by forming crevices or fractures reinforcing fractures by propping
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B15/00—Pumps adapted to handle specific fluids, e.g. by selection of specific materials for pumps or pump parts
    • F04B15/02—Pumps adapted to handle specific fluids, e.g. by selection of specific materials for pumps or pump parts the fluids being viscous or non-homogeneous
    • F04B15/023—Pumps adapted to handle specific fluids, e.g. by selection of specific materials for pumps or pump parts the fluids being viscous or non-homogeneous supply of fluid to the pump by gravity through a hopper, e.g. without intake valve
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B7/00—Piston machines or pumps characterised by having positively-driven valving
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B9/00—Piston machines or pumps characterised by the driving or driven means to or from their working members
    • F04B9/08—Piston machines or pumps characterised by the driving or driven means to or from their working members the means being fluid
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K2208/00—Aspects relating to compositions of drilling or well treatment fluids
    • C09K2208/34—Lubricant additives

Definitions

  • the present invention relates to a strata-fracturing apparatus and a method of fracturing strata, and is concerned particularly with pumping apparatus for a hydraulic fracturing system.
  • Hydraulic fracturing is a technique for extracting gas and oil from rock formations, typically shale formations, deep underground.
  • the method involves drilling a well initially vertically downwards, until the shale formation is reached, and then substantially horizontally into the formation itself. Fluid and some particulates are then injected into the formation at high pressure to shatter the shale and thereby to release the gas from small pockets therein. The gas is then forced up through the well bore along with the fluid, where it is captured.
  • Figure 1 shows schematically a fracking operation beneath ground. A ground level is indicated generally at 10 and a subterranean shale formation is shown at 12.
  • a well head 14 is connected to a pumping apparatus 16 and a supply of fracking, or stimulant, fluid is shown at 18.
  • a well casing 20 extends vertically down into the shale 12 and then horizontally along the formation.
  • a region in which the shale is fractured, to liberate gases and oil, is indicated at 12a.
  • the fluid pressures required to "stimulate" the formation in this way are considerable: typically 12500 psi and the surface pumps are therefore very powerful.
  • reciprocating pumps are used, which are noisy. Often the location of the pumping apparatus is close to a residential area, where the noise levels are unacceptable, as are the emissions from the diesel engines that drive the pumps.
  • Embodiments of the present invention aim to provide pumping apparatus that addresses at least some of the aforementioned disadvantages with the existing apparatus and methods .
  • apparatus for pumping a stimulant fluid in a hydraulic fracturing system comprising an engine and a pressure converter arranged in use to be driven by the engine at a first pressure, and to pump stimulant fluid at a second, higher pressure.
  • the pressure converter preferably comprises a hydraulic power unit.
  • the hydraulic power unit may comprise at least one loading actuator and at least one displacement actuator, connected to the loading actuator by a beam so that in use force is transmitted from the or each loading actuator to the or each displacement actuator through the beam.
  • the hydraulic power unit comprises a reciprocating intensifier.
  • the apparatus also comprises a hydraulic control module for supplying hydraulic fluid to the pressure converter .
  • the engine comprises a gas turbine engine.
  • the apparatus may include additive supply means arranged in use to introduce an additive into the stimulating fluid downstream of an output of the pressure converter.
  • the invention also provides a method of hydraulically fracturing a subterranean formation, the method comprising pumping pressurised stimulant fluid to the formation with a pressure converter driven by an engine.
  • the method includes using a reciprocating intensifier as the pressure converter.
  • the method includes driving the pressure converter using a gas turbine engine.
  • the method comprises introducing an additive into the stimulant fluid downstream of an output of the pressure intensifier.
  • the additive may comprise a proppant .
  • a method of introducing a proppant into a well, for a hydraulic fracturing system comprising introducing the proppant into a pump for pumping stimulant fluid into the well, wherein the proppant is supplied to the pump from a reservoir via at least one inlet valve and is expelled from the pump together with stimulant fluid via at least one outlet valve.
  • the method comprises drawing the proppant into a cylinder from the reservoir during an induction stroke of a piston in the cylinder and pushing the proppant together with stimulant fluid into a well bore during a pressure stroke of the piston.
  • the proppant may comprise pellets or capsules or bags or proppant.
  • the pellets or capsules or bags may be soluble.
  • the pellets or capsules or bags may comprise an additive in addition to the proppant.
  • the additive may comprise a lubricant .
  • the method may comprise introducing proppant into a well bore in pellet or capsule or bag form, and causing the pellet or capsule or bag to dissolve at a down well structure .
  • a proppant for a hydraulic fracturing method comprising an aggregate material in a pellet, capsule or bag form, wherein the pellet, capsule or bag is soluble and is arranged to dissolve to release the proppant .
  • Figure 1 shows schematically a hydraulic fracturing system
  • Figure 2 shows schematically in plan view a pumping apparatus for a hydraulic fracturing system, according to an embodiment of the present invention
  • Figure 3 shows schematically the apparatus of Figure 2 in side view
  • Figure 4 shows schematically the apparatus of Figures 2 and 3 in end view
  • Figure 5 illustrates schematically a control apparatus of an intensifier part of the apparatus of Figures 2-4;
  • Figure 6 shows schematically a control apparatus of a second embodiment;
  • Figure 7 shows schematically a first embodiment of proppant injector in accordance with the present invention
  • Figure 8 shows a second embodiment of proppant injector in accordance with the present invention.
  • FIGs 9 to 12 show, schematically, a sequence of steps for charging and discharging proppant into a line from a pump, according to an embodiment of the present invention.
  • FIG 2 shows in plan view a pair of identical pumping modules, generally at 100.
  • Each one comprises a gas turbine engine 112, having an input attenuator 112a and a discharge attenuator 112b, driving a hydraulic power unit in the form of a reciprocating pressure intensifier 114 via hydraulic lines 116, as will be described later.
  • the intensifier 114 multiplies the pressure applied by displacement actuators 118.
  • Figures 3 and 4 show the pumping modules respectively in side view and end view.
  • a reservoir of hydraulic fluid is indicated at 120.
  • the intensifier 114 is configured at a 45 degree angle to the horizontal. This is for economy of space aboard a truck (not shown) that is used to deliver the apparatus to the site .
  • Figure 5 shows schematically at 200 a control system for the intensifier of Figures 2-4.
  • a pair of primary hydraulic loading actuators 210 translate load via a loading beam 212 into two pairs of displacement actuators 21 .
  • the primary hydraulic loading actuators 210 are arranged in diametric opposition and are arranged to move in the direction of arrows A in a reciprocating manner.
  • the displacement actuators are used to displace stimulation fluid in a wellbore (not shown) for the fracturing of subterranean strata.
  • Two sets of displacement actuators are used, again in diametric opposition in an alternating cycle, and moving in a reciprocating manner in the directions of arrows A.
  • the loading beam 212 transfers load from the primary loading actuator 210 to opposed displacement actuators 214 and also resets the previous displacement actuators for the next stroke.
  • a hydraulic control module 216 supplies pressurised hydraulic fluid alternately to the opposed primary actuators 210, and a hydraulic power module 218 provides hydraulic energy to the control module 216.
  • Discharge check valves 220 prevent the backflo of pressurised fracturing fluids into the displacement actuators 214, and intake check valves 222 prevent the backflow of pressurised fracturing fluids into the intake line .
  • the valves are all controlled electronically and the reciprocating action of the bifurcated intensifier provides a self-resetting effect in which one set of displacement actuators re-charge with stimulation fluid during discharge by the other set.
  • FIG. 6 shows schematically the control arrangements for an alternative embodiment, in which sand, as a proppant, is added to the stimulant fluid.
  • a proppant is usually used in a hydraulic fracturing process to keep open the tiny fractures induced in the formation, thus allowing more of the trapped gas to escape.
  • Various proppants are used, but one common substance is silica sand.
  • FIG 6 the features that are identical with those in Figure 5 have been given the same reference numerals.
  • four proppant injectors, or sand dosing units 300 are connected downstream of the discharge check valves 220 of the displacement actuators 214.
  • the sand dosing unit 300 charges with sand 312 after stimulant fluid has been drawn into the displacement actuator. Then, during the pressurised pump discharge stroke of the displacement actuator, the sand is discharged into the line to mix with the stimulant fluid.
  • the ball valve is sufficiently robust to withstand the pressure in the discharge, and the sand is never drawn into the charging stroke of the displacement actuator.
  • the embodiments of the invention described above provide a reliable pumping apparatus that moves more slowly than previously considered pumps, and so is more stable, less noisy and less prone to damage. It also weighs less and so is easier to transport, and when coupled with the gas turbine engine produces less pollution than other pumps.
  • FIG.7 shows in more detail a first embodiment of proppant dosing device 400, for injecting proppant into a pressurised stimulant-intake portion of a pumping system.
  • the dosing device comprises a hopper 402 for containing a reservoir of proppant 404 and a valve 406 which controls communication between the hopper and an inlet line 408 leading to the pump (not shown) .
  • the inlet line 408 carries stimulant fluid to the pump in use and the proppant becomes mixed with the stimulant at the dosing device.
  • a control module M controls the position of valve 406, so that the valve can move between a first position, shown in the drawing, in which the proppant is isolated from the line 408, and a second position ⁇ not shown) in which the proppant is connected to the inlet line, and in which position the stimulant becomes dosed with proppant.
  • Arrows B indicate the directions in which the valve moves between the two positions.
  • FIG 8 shows an alternative embodiment of proppant dosing device 500.
  • a proppant supply line 502 supplies proppant 504 under pressure in the direction of Arrow C.
  • a gate 506, operated by a hydraulic actuator 506a in the directions of Arrows D controls access of the proppant 504 into a pressurised stimulant line 508 downstream of the pump (not shown) .
  • the pumping apparatus described herein can be said to be a "high volume - low velocity" pump, in that large pistons are travelling very slowly, which reduces noise and also wear.
  • valves operate more slowly, and open more fully, as compared with previously considered pumping systems. This makes them less susceptible to wear from proppant contamination. This allows that the proppant can be introduced directly into the pump, which would be very damaging to previously considered pumps.
  • Figures 9-12 show four stages in the action of the pump, in which proppant is introduced directly into the pump along with the stimulant fluid.
  • FIG. 9 shows a start position of the pump.
  • a displacement unit is shown generally at 600, and comprises a cylinder 602 and a piston 604 which reciprocates within it in the direction of Arrow E.
  • a discharge valve 606 is controlled by a discharge valve actuator 608 to discharge stimulant and proppant to a line 610 leading to the well (not shown) .
  • the stimulant fluid is drawn in via a valve that is omitted from this drawing for reasons of clarity.
  • Proppant 612 is held in a reservoir 614 and is allowed into the cylinder by inlet valve 616 under the control of actuator 618.
  • Figure 10 shows the cylinder moving backwards in the direction of Arrow F.
  • the inlet valve is open and proppant 612 is drawn into the cylinder 602.
  • the outlet valve remains closed.
  • the piston 604 is fully withdrawn and is about to return in the direction of Arrow G.
  • the cylinder 602 is fully charged with proppant.
  • the inlet valve 616 is closed and the outlet valve 606 is open to the line 610.
  • the size and/or content of the capsules and the properties of the proppant carried could be selected according to the nature of the strata or rock formation being developed.
  • the density of the stimulant fluid could be tailored to suit the formation.
  • the rate of dissolution of the pellets/capsules could be selected so as to control the point at which the proppant is released.
  • the pellets could be dissolved by a targeted solvent or the dissolution could be initiated by a catalyst, for example when a predetermined pressure has been reached or after a sufficient quantity of proppant has been transferred to the end of the wellbore.
  • pellets or capsules may also incorporate additives, such as wellbore lubricants.

Abstract

Apparatus for pumping a stimulant fluid in a hydraulic fracturing system comprises an engine and a pressure converter arranged in use to be driven by the engine at a first pressure, and to pump stimulant fluid at a second, higher pressure. A pair of primary hydraulic loading actuators (210) translate load via a loading beam (212) into two pairs of displacement actuators (214). The primary hydraulic loading actuators (210) are arranged in diametric opposition and are arranged to move in the direction of arrows A in a reciprocating manner. The displacement actuators are used to displace stimulation fluid in a wellbore (not shown) for the fracturing of subterranean strata. Two sets of displacement actuators are used, again in diametric opposition in an alternating cycle, and moving in a reciprocating manner in the directions of arrows A.

Description

Strata Fracturing Apparatus and Method
The present invention relates to a strata-fracturing apparatus and a method of fracturing strata, and is concerned particularly with pumping apparatus for a hydraulic fracturing system.
Hydraulic fracturing, more commonly referred to as "fracking", is a technique for extracting gas and oil from rock formations, typically shale formations, deep underground. The method involves drilling a well initially vertically downwards, until the shale formation is reached, and then substantially horizontally into the formation itself. Fluid and some particulates are then injected into the formation at high pressure to shatter the shale and thereby to release the gas from small pockets therein. The gas is then forced up through the well bore along with the fluid, where it is captured. Figure 1 shows schematically a fracking operation beneath ground. A ground level is indicated generally at 10 and a subterranean shale formation is shown at 12. A well head 14 is connected to a pumping apparatus 16 and a supply of fracking, or stimulant, fluid is shown at 18. A well casing 20 extends vertically down into the shale 12 and then horizontally along the formation. A region in which the shale is fractured, to liberate gases and oil, is indicated at 12a. The fluid pressures required to "stimulate" the formation in this way are considerable: typically 12500 psi and the surface pumps are therefore very powerful. Typically reciprocating pumps are used, which are noisy. Often the location of the pumping apparatus is close to a residential area, where the noise levels are unacceptable, as are the emissions from the diesel engines that drive the pumps.
Gear changes are also necessary which cause shock pulses that can lead to wear and damage of the pumps.
Embodiments of the present invention aim to provide pumping apparatus that addresses at least some of the aforementioned disadvantages with the existing apparatus and methods .
According to one aspect of the present invention, there is provided apparatus for pumping a stimulant fluid in a hydraulic fracturing system, the apparatus comprising an engine and a pressure converter arranged in use to be driven by the engine at a first pressure, and to pump stimulant fluid at a second, higher pressure.
The pressure converter preferably comprises a hydraulic power unit. The hydraulic power unit may comprise at least one loading actuator and at least one displacement actuator, connected to the loading actuator by a beam so that in use force is transmitted from the or each loading actuator to the or each displacement actuator through the beam.
In a preferred arrangement, the hydraulic power unit comprises a reciprocating intensifier. Preferably the apparatus also comprises a hydraulic control module for supplying hydraulic fluid to the pressure converter . In a preferred arrangement the engine comprises a gas turbine engine.
The apparatus may include additive supply means arranged in use to introduce an additive into the stimulating fluid downstream of an output of the pressure converter.
The invention also provides a method of hydraulically fracturing a subterranean formation, the method comprising pumping pressurised stimulant fluid to the formation with a pressure converter driven by an engine.
Preferably the method includes using a reciprocating intensifier as the pressure converter. In a preferred arrangement the method includes driving the pressure converter using a gas turbine engine.
Preferably the method comprises introducing an additive into the stimulant fluid downstream of an output of the pressure intensifier. The additive may comprise a proppant .
According to another aspect of the present invention, there is provided a method of introducing a proppant into a well, for a hydraulic fracturing system, the method comprising introducing the proppant into a pump for pumping stimulant fluid into the well, wherein the proppant is supplied to the pump from a reservoir via at least one inlet valve and is expelled from the pump together with stimulant fluid via at least one outlet valve.
In a preferred arrangement the method comprises drawing the proppant into a cylinder from the reservoir during an induction stroke of a piston in the cylinder and pushing the proppant together with stimulant fluid into a well bore during a pressure stroke of the piston. The proppant may comprise pellets or capsules or bags or proppant. The pellets or capsules or bags may be soluble. The pellets or capsules or bags may comprise an additive in addition to the proppant. The additive may comprise a lubricant .
The method may comprise introducing proppant into a well bore in pellet or capsule or bag form, and causing the pellet or capsule or bag to dissolve at a down well structure .
According to another aspect of the present invention there is provided a proppant for a hydraulic fracturing method, the proppant comprising an aggregate material in a pellet, capsule or bag form, wherein the pellet, capsule or bag is soluble and is arranged to dissolve to release the proppant .
The invention may include any combination of the features or limitations referred to herein, except such a combination of features as are mutually exclusive, or mutually inconsistent. A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows schematically a hydraulic fracturing system;
Figure 2 shows schematically in plan view a pumping apparatus for a hydraulic fracturing system, according to an embodiment of the present invention;
Figure 3 shows schematically the apparatus of Figure 2 in side view;
Figure 4 shows schematically the apparatus of Figures 2 and 3 in end view;
Figure 5 illustrates schematically a control apparatus of an intensifier part of the apparatus of Figures 2-4; Figure 6 shows schematically a control apparatus of a second embodiment;
Figure 7 shows schematically a first embodiment of proppant injector in accordance with the present invention;
Figure 8 shows a second embodiment of proppant injector in accordance with the present invention; and
Figures 9 to 12 show, schematically, a sequence of steps for charging and discharging proppant into a line from a pump, according to an embodiment of the present invention. Turning to Figure 2, this shows in plan view a pair of identical pumping modules, generally at 100. Each one comprises a gas turbine engine 112, having an input attenuator 112a and a discharge attenuator 112b, driving a hydraulic power unit in the form of a reciprocating pressure intensifier 114 via hydraulic lines 116, as will be described later. The intensifier 114 multiplies the pressure applied by displacement actuators 118.
Figures 3 and 4 show the pumping modules respectively in side view and end view. A reservoir of hydraulic fluid is indicated at 120. In Figure 3 it can be seen that the intensifier 114 is configured at a 45 degree angle to the horizontal. This is for economy of space aboard a truck (not shown) that is used to deliver the apparatus to the site .
Figure 5 shows schematically at 200 a control system for the intensifier of Figures 2-4. A pair of primary hydraulic loading actuators 210 translate load via a loading beam 212 into two pairs of displacement actuators 21 . The primary hydraulic loading actuators 210 are arranged in diametric opposition and are arranged to move in the direction of arrows A in a reciprocating manner. The displacement actuators are used to displace stimulation fluid in a wellbore (not shown) for the fracturing of subterranean strata. Two sets of displacement actuators are used, again in diametric opposition in an alternating cycle, and moving in a reciprocating manner in the directions of arrows A.
The loading beam 212 transfers load from the primary loading actuator 210 to opposed displacement actuators 214 and also resets the previous displacement actuators for the next stroke.
A hydraulic control module 216 supplies pressurised hydraulic fluid alternately to the opposed primary actuators 210, and a hydraulic power module 218 provides hydraulic energy to the control module 216.
Discharge check valves 220 prevent the backflo of pressurised fracturing fluids into the displacement actuators 214, and intake check valves 222 prevent the backflow of pressurised fracturing fluids into the intake line . The valves are all controlled electronically and the reciprocating action of the bifurcated intensifier provides a self-resetting effect in which one set of displacement actuators re-charge with stimulation fluid during discharge by the other set.
Figure 6 shows schematically the control arrangements for an alternative embodiment, in which sand, as a proppant, is added to the stimulant fluid. A proppant is usually used in a hydraulic fracturing process to keep open the tiny fractures induced in the formation, thus allowing more of the trapped gas to escape. Various proppants are used, but one common substance is silica sand. With prior known pumps, a problem arises if the sand is drawn into the pumping apparatus. This is because the sand will act as an abradant, and will cause wear in the seals and valves leading eventually to a loss of pressure. In the embodiment shown in Figure 6 this problem is addressed by introducing the sand downstream of the output from the displacement actuators. In Figure 6 the features that are identical with those in Figure 5 have been given the same reference numerals. In addition, four proppant injectors, or sand dosing units 300 are connected downstream of the discharge check valves 220 of the displacement actuators 214. Using automated ball valves 310, the sand dosing unit 300 charges with sand 312 after stimulant fluid has been drawn into the displacement actuator. Then, during the pressurised pump discharge stroke of the displacement actuator, the sand is discharged into the line to mix with the stimulant fluid. The ball valve is sufficiently robust to withstand the pressure in the discharge, and the sand is never drawn into the charging stroke of the displacement actuator.
The embodiments of the invention described above provide a reliable pumping apparatus that moves more slowly than previously considered pumps, and so is more stable, less noisy and less prone to damage. It also weighs less and so is easier to transport, and when coupled with the gas turbine engine produces less pollution than other pumps.
Turning to Figure7, this shows in more detail a first embodiment of proppant dosing device 400, for injecting proppant into a pressurised stimulant-intake portion of a pumping system. The dosing device comprises a hopper 402 for containing a reservoir of proppant 404 and a valve 406 which controls communication between the hopper and an inlet line 408 leading to the pump (not shown) . The inlet line 408 carries stimulant fluid to the pump in use and the proppant becomes mixed with the stimulant at the dosing device. A control module M controls the position of valve 406, so that the valve can move between a first position, shown in the drawing, in which the proppant is isolated from the line 408, and a second position {not shown) in which the proppant is connected to the inlet line, and in which position the stimulant becomes dosed with proppant. Arrows B indicate the directions in which the valve moves between the two positions.
Figure 8 shows an alternative embodiment of proppant dosing device 500. A proppant supply line 502 supplies proppant 504 under pressure in the direction of Arrow C. A gate 506, operated by a hydraulic actuator 506a in the directions of Arrows D controls access of the proppant 504 into a pressurised stimulant line 508 downstream of the pump (not shown) . In contrast with previously considered pumping systems for hydraulic fracturing, in which small pistons have a short stroke and operate at high speed, the pumping apparatus described herein can be said to be a "high volume - low velocity" pump, in that large pistons are travelling very slowly, which reduces noise and also wear.
As a consequence the valves operate more slowly, and open more fully, as compared with previously considered pumping systems. This makes them less susceptible to wear from proppant contamination. This allows that the proppant can be introduced directly into the pump, which would be very damaging to previously considered pumps. Figures 9-12 show four stages in the action of the pump, in which proppant is introduced directly into the pump along with the stimulant fluid.
Turning to Figure 9, this shows a start position of the pump. A displacement unit is shown generally at 600, and comprises a cylinder 602 and a piston 604 which reciprocates within it in the direction of Arrow E. A discharge valve 606 is controlled by a discharge valve actuator 608 to discharge stimulant and proppant to a line 610 leading to the well (not shown) . The stimulant fluid is drawn in via a valve that is omitted from this drawing for reasons of clarity.
Proppant 612 is held in a reservoir 614 and is allowed into the cylinder by inlet valve 616 under the control of actuator 618.
In Figure 9 the inlet valve is closed, the outlet valve is closed and the cylinder is poised at the start of its withdrawal.
Figure 10 shows the cylinder moving backwards in the direction of Arrow F. The inlet valve is open and proppant 612 is drawn into the cylinder 602. The outlet valve remains closed. In Figure 11 the piston 604 is fully withdrawn and is about to return in the direction of Arrow G. The cylinder 602 is fully charged with proppant. The inlet valve 616 is closed and the outlet valve 606 is open to the line 610.
In Figure 12 the piston 604 has moved fully forward to push the proppant and stimulant into the line 610 through the open outlet valve 606. The inlet valve 616 is now closed. The proppant itself, usually in the form of natural aggregate such as sand, could alternatively be delivered in the form of soluble pellets or capsules, or even soluble bags. The palletisation or bagging would prevent the contamination of the injection system by proppant.
The size and/or content of the capsules and the properties of the proppant carried could be selected according to the nature of the strata or rock formation being developed. Thus the density of the stimulant fluid could be tailored to suit the formation.
The rate of dissolution of the pellets/capsules could be selected so as to control the point at which the proppant is released. Alternatively or in addition the pellets could be dissolved by a targeted solvent or the dissolution could be initiated by a catalyst, for example when a predetermined pressure has been reached or after a sufficient quantity of proppant has been transferred to the end of the wellbore.
The pellets or capsules may also incorporate additives, such as wellbore lubricants. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the applicant claims protection in respect of any patentable feature or combination of features referred to herein, and/or shown in the drawings, whether or not particular emphasis has been placed thereon.

Claims

1. Apparatus for pumping a stimulant fluid in a hydraulic fracturing system, the apparatus comprising an engine and a pressure converter arranged in use to be driven by the engine at a first pressure, and to pump stimulant fluid at a second, higher pressure.
2. Apparatus according to Claim 1, wherein the pressure converter comprises a hydraulic power unit.
3. Apparatus according to Claim 2, wherein the hydraulic power unit comprises at least one loading actuator and at least one displacement actuator, connected to the loading actuator by a beam so that in use force is transmitted from the or each loading actuator to the or each displacement actuator through the beam.
4. Apparatus according to Claim 2 or Claim 3, wherein the hydraulic power unit comprises a reciprocating intensifier.
5. Apparatus according to any of Claims 1 to 4, comprising a hydraulic control module for supplying hydraulic fluid to the pressure converter.
6. Apparatus according to any of the preceding claims, wherein the engine comprises a gas turbine engine.
7. Apparatus according to any of the preceding claims, wherein the apparatus includes additive supply means arranged in use to introduce an additive into the stimulating fluid downstream of an output of the pressure converter .
8. A method of hydraulically fracturing a subterranean formation, the method comprising pumping pressurised stimulant fluid to the formation with a pressure converter driven by an engine.
9. A method according to Claim 8, wherein the method includes using a reciprocating intensifier as the pressure converter .
10, A method according to Claim 8 or 9, wherein the method includes driving the pressure converter using a gas turbine engine .
11. A method according to any of Claims 8 to 10, comprising introducing an additive into the stimulant fluid downstream of an output of the pressure intensifier.
12. A method according to Claim 11, wherein the additive is a proppant.
13. A method of introducing a proppant into a well, for a hydraulic fracturing system, the method comprising introducing the proppant into a pump for pumping stimulant fluid into the well, wherein the proppant is supplied to the pump from a reservoir via at least one inlet valve and is expelled from the pump together with stimulant fluid via at least one outlet valve.
14. A method according to Claim 13, comprising drawing the proppant into a cylinder from the reservoir during an induction stroke of a piston in the cylinder and pushing the proppant together with stimulant fluid into a well bore during a pressure stroke of the piston.
15. A method according to Claim 13 or Claim 14, wherein the proppant comprises pellets or capsules or bags or proppant. The pellets or capsules or bags may be soluble. The pellets or capsules or bags may comprise an additive in addition to the proppant .
16. A method according to Claim 15, wherein the additive comprises a lubricant.
17. A method according to any of Claims 13 to 16, wherein the method comprises introducing proppant into a well bore in pellet or capsule or bag form, and causing the pellet or capsule or bag to dissolve at a down well structure.
18. A proppant for a hydraulic fracturing method, the proppant comprising an aggregate material in a pellet, capsule or bag form, wherein the pellet, capsule or bag is soluble and is arranged to dissolve to release the proppant.
PCT/GB2016/051872 2015-06-24 2016-06-23 Strata fracturing apparatus and method WO2016207631A1 (en)

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GB1511096.8A GB2539683A (en) 2015-06-24 2015-06-24 Strata fracturing apparatus and method

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