CA2508953A1 - High-pressure injection proppant system - Google Patents

Abstract

A high-pressure injection proppant system for stimulating coal bed methane production preloads proppant, such as sand, into one or more high-pressure vessels, for delivery into a fluid stream, such a N2 gas stream. A screw auger arrangement meters the proppant volumes and rates into the fluid stream.
Two such vessels operationally mounted in parallel can function separately or concurrently depending on the demand for proppant in a particular formation.
The system provides for the injection of surfactants into the fluid stream to enhance the performance of the proppant, to aid in the placement of the proppant into a fracture network, and to demote proppant flowback during production and embedment. The system can be operated manualy or by computer automation to aid in the accuracy of the mixing of the fluid stream components.

Description

Agent File No. 282.2 TITLE: HIGH-PRESSURE INJECTION PROPPANT SYSTEM
s FIELD OF THE INVENTION
The present invention relates generally to systems for injecting substances into underground formations, and in particular relates to novel systems and methods of combining fluids and proppant under high-pressure, and for injection of the resultant fluid stream into formations such as coal beds.
BACKGROUND OF THE INVENTION
The Horseshoe canyon coal formations in Alberta have been difficult to stimulate for coal bed methane production. These formations have been through a plethora of conventional stimulation treatments, ranging from foams to is crosslink polymers. Due to the nature of the low reservoir pressures of these coal formations, or seams, and their sensitivity to damage by conventional stimulation fluids (defined herein as a liquid and/or gas), stimulation fluid recovery becomes almost impossible. The only other economically viable choices appear to be straight C02 or N2 gas injection. High rate N2 gas injection 2o technique is a common practice in North American coal bed methane exploited plays, and C02 is used as a flood medium.
Although using C02 gas to stimulate a formation works fine, it has certain drawbacks, including:
1. Costly treatments; and, as 2. C02 does not clean up quickly, and since water is commonly produced during stimulation, it will turn into carbonic acid which is extremely hard on surface production manifolding.

Using N2 gas works the same way all fluids do to stimulate a formation, although extremely high rates are required to create enough stress to overcome the natural formation mechanics and actually fracture, or "frac", the formation.
s Enhanced conductivity of a formation relies on the effect of hysteresis, namely when the frac faces come back together under stress, that these faces will not heal back to their original orientation. It would be desirable to use proppant (e.g.
a sand or orther suitable materials) to hold the fractured, or "fraced", faces apart as used in conventional frac theory. However, the problem with this is that N2 is so pumped as a gas and will not suspend or carry proppant as do conventional fracturing fluid systems.
What is desired therefore is a novel method of fracturing, or "fracing", a target formation (such as a coal or shale formation) using gases and proppants, and a novel system for mixing such gasses and proppants in a manner that is would result in an "impregnated" fluid stream suitable for such fracing.
Preferably, the method and system should be capable of combining N2 gas and a proppant material, such as sand, to produce a suitable fluid stream for fracing a coal formation. The method and system should further provide for introduction of surfactants to the fluid stream to further enhance the performance of the zo proppant in the target formation.

SUMMARY OF THE PRESENT INVENTION
According to the present invention, there is provided in one aspect a high-pressure injection proppant system (also referred to as "HIPS") in which proppant, such as sand, is preloaded into one or more high-pressure cylindrical s vessels, and such proppant is delivered into a fluid stream, such a N2 gas stream, via a screw auger arrangement which meters the proppant volumes and rates into the fluid stream.
In another aspect the invention provides two vessels operationally mounted in parallel which can function separately or concurrently depending on so the demand for proppant in a particular formation. When operated seperately, one vessel can be in use for fracing a formation while the other vessel is isolated, de-pressurized and reloaded with proppant via a pneumatic bulk proppant system. The other vessel is then ready for operation when the first vessel is depleted of proppant.
is In yet another aspect the invention provides for the injection of surfactants (i.e. chemicals or like substances) into the fluid stream to enhance the performance of the proppant, to aid in the placement of the proppant into the fracture network, and to demote proppant flowback during production and embedment.
2o Further, the system of the present invention can be operated manualy or by computer automation to aid in the accuracy of mixing of the components of the fluid stream.

BRIEF DESCRIPTION OF THE DRAWING FIGURES
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein:
Figure 1 is an elevational side view of a mobile carrier carrying a high s pressure injection proppant system ("HIPS") according to a preferred embodiment of the present invention, showing the pressure vessels of the system in a reclined transportation mode;
Figure 2 is a view of the system of fig.1 with the pressure vessels in an elevated operating mode;
1o Figure 3 is a plan view of the rig and system of fig.2;
Figure 4 is an elevational end view of the rig and system of fig.2;
Figure 5 shows the system of fig.4 in isolation, with the rig omitted;
Figure 6 is a view similar to fig.4, but shows an alternate embodiment of the system of the present invention, in operating mode;
is Figure 7 is an elevational side view of the system of fig.6; and, Figure 8 is a plan view of fig.6 with the front portion of the rig omitted.

LIST
OF REFERENCE
NUMBERS
IN DRAWINGS

high-pressure injection proppant system 12 trailer 14 truck s 15 hydraulic wet kit 16 axles of 12 18 wheels on 12 proppant bulk storage tank 22 low-pressure blower pump io 24 first low-pressure air line 26 second low-pressure bulk load line 28 surfactant storage and pumping assembly delivery tubing for 28 32 hydraulic lift cylinders is 34 pivots 36, 36a, 36b pressure gauges 38 densometer pressure vessels) 42 outer wall of 40 20 43 reinforced portion of 42 44 inner chamber of 40 46 first vessel inlet for proppant 48 first/top end of 40 second vessel inlet/outlet 2s 52 first vessel outlet 53 flange of 52 -s-54 screws) 56 radial inlet of 54 57 radial outlet of 54 58 motor of 54 s 60 piping arrangement 61 high-pressure fluid stream 62 first inlet of 60 64 first (Y) diverter 66 first fluid stream so 68 second fluid stream 70 venturi-type orifice 72 first outlet of 60 74 second (four way) diverter 76 first fluid sub-streams is 78 second fluid sub-stream 80 piping 82 first valves of 60 84 third (T-shaped) diverter 86 third fluid sub-streams ao 87 fourth fluid sub-streams 88 second valves 90 third valves 92 piping 94 Y-joint 2s 96 pressure vessel isolation valve 98 upstream injection port 99 downstream injection port 130 delivery line of second embodiment 140 pressure vessels) of second embodiment 142 outer wall of 140 144a first inner chamber of 140 s 144b second inner chamber of 140 144c third inner chamber of 140 145 first bottomopening of 144a 146 first vessel inlet 147 second top opening of 144a 150 second vessel inlet 152 bottom vessel outlet of 144c 154 screws) of second embodiment 158 motor of 154 160 piping arrangement of second embodiment 162 inlet 166 first fluid stream 167 Y-shaped diveter 168 second fluid stream 170 orifice zo 183 first valves 190 pressure relief valve 192 piping 196 isolation valves) DESCRIPTION OF PREFERRED EMBODIMENTS
Reference is first made to figures 1 to 3 which show a high-pressure injection proppant system, or "HIPS", (generally designated by reference numeral 10) according to a preferred embodiment of the present invention. The s system is mounted on a carrier, which in the preferred embodiment is a wheeled trailer 12 adapted to be pulled by a motorized vehicle, or truck 14. It will be understood that the carrier may take various alternate forms, namely the trailer may itself be self-propelled, the truck and trailer may form one non-detachable unit, the system may be mounted on a skid for transport between sites, or the io like. However, since the system is extremely heavy, not all carriers will be suitable for road transport as prescribed load limits for roads may be exceeded.
Hence, in the present embodiment, the 24 wheeled trailer 12 is specifically designed to remain within such load limits (i.e. is "road legal") by having three axles 16 with eight tires 18 per axle. Different axle and wheel combinations and is quantities may be equally suitable, depending on the load to be transported.
Likewise, the truck is suitably designed to haul the trailer 12, and should include a hydraulic "wet kit" 15 to power the system 10 on the trailer.
The preferred system 10 includes a proppant storage means in the form of a cone-shaped tank 20 located on the trailer 12. A relatively low-pressure 2o blower pump 22, conveniently mounted on the truck 14 close to a power source (i.e. the hydraulic wet kit 15), communicates with the tank 20 via a first low-pressure line 24. The pump 22 permits the bulk transfer of proppant from the tank 20 at the front of the trailer to the two high-pressure vessels 40 at the back of the trailer via at least one second loading line 26 (fig.2)" Although one line 26 2s may be configured for suitable delivery of proppant, each vessel has a designated line 26 in the present embodiment.
_8_ The system further includes a surfactant storage and high pressure pumping assembly 28 located on the trailer. This assembly stores one or more surfactants for injection or "misting" (via a delivery tubing generally indicated by 30) into the high-pressure fluid stream associated with the pressure vessels 40, s as will be discussed later. The pumping assembly may employ as many high-pressure surfactant pumps as required. It is noted that in alternate embodiments, the assembly may be located elsewhere than on the trailer 12, such as on another trailer, but must be capable of communicating with the fluid stream during operation for the desired misting. Likewise, the proppant storage so tank 20 may be remotely located, but in communication with the vessels 40 during operation.
The surfactant referred to herein should be a chemical or like substance for enhancing the performance of the fluid stream proppant, for aiding in the placement of the proppant into a formation's fracture network, and/or for is reducing proppant flowback during production and embedment. The proppant should be any material suitable for achieving the desired fracturing, or "fracing"
of a target formation. The preferred system of the present invention is specifically geared toward fracing a coal formation for enhancing gas production therefrom, and the desired proppant is a form of sand. The use of the terms zo "proppant", "surfactant", "front", "back" and the like is not intended to limit the present system's use or operation, nor the scope of the invention. Further, when describing the invention, all terms not defined herein have their common art-recognized meaning.
Referring now as well to fig. 4 (showing the trailer 12) and fig. 5 (omitting zs the trailer), an important aspect of the system is the arrangement at the back of the trailer which has a means for directing/diverting a high pressure fluid stream 61 into the pair of pressure vessels 40 operationally arranged in parallel, and a _g_ means for metering/feeding proppant into the fluid stream. Specifically, a piping arrangement 60 below the vessels 40 has a first inlet 62 for receiving a desired fluid. In the preferred embodiment that fluid is nitrogen gas pumped under high pressure from a nitrogen source, such as a pumper truck. A first Y-shaped s diverter 64 downstream of the inlet splits the incoming nitrogen 61 into first and second fluid streams 66, 68 respectively. An adjustable venturi-type orifice downstream of the diverter 64 is adapted to create a pressure drop, say in the range of 300 psi (or other desired amount), in the second fluid stream 68 passing therethrough. The orifice 70 should have the effect of diverting more volume of 1o fluid into the first stream than the second stream, and for maintaining a positive fluid pressure in the screws) 58, as will become apparent later. The second fluid stream 68 then proceeds under relatively lower pressure toward a first outlet 72 for discharge to a coiled tubing rig or like apparatus in communication with the target formation.
1s A second four-way diverter 74 downstream of the diverter 64 allows the first fluid stream to split again into first and second fluid sub-streams 76 and 78 respectively. Elongate piping 80 carries the second sub-stream 78 toward the top of the vessels, while the first sub-streams 76 are directed to the bottom of the vessels through respective first valves 82. If only the left vessel is operating, 2o then only the left valve 82 (as viewed in fig.5) is open for fluid entry, and the right valve 82 is closed, and visa versa. If both vessels are operating, then both valves 82 should be open. A third T-shaped diverter 84 further splits the second fluid sub-stream 78 into third fluid sub-streams 86 directed to the top of the vessels through respective second valves 88. The diverter 84 and valves 88 2s also act as a pressure equalization manifold between the vessels 40.
Further, the piping 80 and associated valves 82, 88 and 90 (discussed below) are used to equalize the fluid pressures at the top and bottom of the vessels 40, and to de-pressurize the system to atmosphere when required.
Each pressure vessel 40 is formed by an elongate cylindrical tank having relatively thick outer walls 42 (e.g. 5 inches solid steel) to accommodate the high s operating pressures (up to 9000 psi / 63 MPa or more). The walls form an elongate interior cavity or chamber 44 for holding the desired proppant. The proppant is introduced into the chamber through a first vessel inlet 46 (shown in fig.2) at a first top end 48 of the vessel. A second vessel inlet 50 is provided at the top end of each tank for entry of the respective third fluid sub-streams 86, 1o and to communicate with a respective third pressure relief valve 90 for bleeding pressure from the respective vessel to atmosphere prior to receiving proppant through the proppant inlet 46. A first vessel outlet 52 at the bottom of the vessel allows proppant and fluid to exit the vessel's chamber 44 and to encounter the first fluid sub-stream 76, and to then proceed to the proppant metering means.
It is is noted that the identifiers such a "top" and bottom" as used herein refer to the vessel in its generally vertically oriented operating position, as shown in figs 2-5, rather than when it is reclined about the pivot 34 by the hydraulic lift cylinders 32 into its generally horizontal transport position (as in fig.1 ). The vessels should be reinforced at 43 where they engage the hydraulic cylinders 32 and pivots 34.
2o The proppant metering means is defined by a high pressure sand screw 54 disposed generally perpendicularly to each vessel's longitudinal centerline and it's outlet 52. Other orientations of the screws should also be suitable.
The screw has a flanged radial inlet 56 for attachment to a respective flange 53 of the vessel outlet 52, and for receiving the proppant and fluid therefrom. A
variable 2s rate electric or other suitable motor 58 operates the screw to discharge, or meter, a desired amount of proppant through a radial screw outlet 57 into piping 92.
A
Y-shaped joint 94 allows the proppant and fluids exiting the screw 54 to enter the second fluid stream 78 prior to exiting the first outlet 72. A pressure vessel isolation valve 96 on each piping 92 upstream of the Y joint 94 operates to isolate a respective vessel from the second fluid stream 68 as desired (e.g.
when that vessel is inoperative and depressurized for proppant recharging), to prevent s fluid backflow into the vessel through the screw. Each screw may be readily removed from the system for servicing, repair, or switching to a different screw size by uncoupling the flanges 53, 56 at one end, and at the other end by uncoupling from the isolation valve 96.
The piping arrangement 60 further incorporates an "upstream" surfactant to injection port 98 at the first inlet 62 for introducing surfactants from the delivery tubing 30 into the fluid stream 61 prior to its split into the first and second fluid streams 66, 68. Such introduction may also be accomplished further downstream after the fluid and proppant have been mixed, such as at a "downstream" surfactant injection port 99 located immediately prior to the first is outlet 72. Both ports 98, 99 may also be used concurrently, and other ports may be added in the system if required.
An alternate embodiment of the present invention is shown in figures 6 to 8 where the screws 154 are located longitudinally within the pressure vessels 140. The reference numerals used in these figures are similar to those used to 2o describe the components of the system 10, with the addition of a prefix "1 ".
Each vessel has in essence three longitudinally aligned chambers. A first elongate chamber 144a is defined by the vessel's outer wall 142 for holding the proppent received through the first vessel inlet 146 via the delivery line 130. A
pressure relief valve 190 bleeds excess pressure before filling the chamber 2s 144a. A second elongate chamber 144b is longitudinally disposed within the first chamber 144a in a parallel relationship, and houses the screw 154 operated by the motor 158. The bottom end of the second chamber 144b has a first bottom opening 145 into the first chamber 144a to allow entry of the proppant. The screw raises the proppant to the opposed top end where it is discharges out of a second top opening 147 into the open end of a hollow third chamber 144c. The third chamber 144c is also located within the first chamber 144a and extends s downwardly alongside the second chamber144b and opens at a bottom vessel outlet 152 where the proppant and high-pressure fluid exit the vessel into the piping arrangement 160.
The piping arrangement 160 is similar to the piping arrangement 60 in that high pressure fluid, such as nitrogen gas, enters at the inlet 162 and is divided 1o into first and second fluid streams 166 and 168 with the aid of orifice 170. The first fluid stream is then directed to one or both vessels at the Y-shaped diverter 167 by controlling the first valves 183. The first fluid stream enters the bottom of the first chamber 144a via the second vessel inlet 150. The pressurized fluid is urged through the proppant and up the screw where it proceeds through the top is opening 147 and then down the third chamber 144c to exit the bottom outlet 152.
When the screw is activated to discharge proppent through the top opening 147, the proppant is entrained in the high-pressure fluid flow and is carried down the third chamber 144c to the outlet 152. The fluid and proppent exiting the outlet 152 proceed through piping 192 and the respective pressure vessel isolation 2o valve 196 to rejoin the second fluid stream 168 moving to the first piping outlet 172.
This system is not preferred over the first preferred embodiment for several reasons. First, for a given size of pressure vessel, the vessel 140 holds less proppent than the vessel 40 since internal volume is lost to the second and 2s third chambers 144b, 144c. Second, a longer and more costly screw must be employed in the vessel 140, and such screw is more difficult to access or remove than in the first embodiment. The screw 154 must lift proppent against gravity, whereas the negative effects of gravity are reduced in the arrangement of the preferred embodiment.
The operation and advantages of the present invention may now be better understood. For illustrative purposes it will be assumed that nitrogen and a form s of sand are to be pumped into a coal formation. In the preferred embodiment, the rig is brought to the work site in an advantageous reclined transportation mode (as in fig.1 ) to avoid road clearance limitations. The trailer's wheel configuration is also designed to make the rig "road legal", despite the extremely heavy weight of the system 10.
1o The vessels 40 and associated components are then elevated into the operating mode (fig.2) for use. If the vessel chambers 44 require charging with sand, then it is pumped from the tank 20 into at least one of the chambers via the line 26 and through respective first vessel inlet 46. An advantage of this two vessel arrangement is that fracing may commence once one vessel is charged 1s with sand. There is no need to wait for the second vessel to be filled to begin operations. Likewise, there is no need to disrupt ongoing operations once the first vessel is emptied of sand since pumping may readily switch to the second filled vessel. In the meantime, the first vessel can be refilled with sand and be ready for when the second vessel is emptied. In unusual circumstances where zo the rate and volume of sand injection requires both vessels to operate simultaneously, then operations may be disrupted periodically while the vessels are refilled.
Assuming that the left vessel 40 in fig.5 is charged and ready for operation, and the right vessel is not, then the operator should isolate the right 2s vessel by closing the first and second valves 82, 88 leading to the right vessel, as well as the respective (right side) isolation valve 96. Conversely, the first and second valves 82, 88 and the isolation valve 96 for the left vessel should be opened or activated. Once a high-pressure nitrogen stream 61 is established from a nearby nitrogen truck into the first inlet 62, the orifice 70 should provide the necessary pressure drop and split into first and second nitrogen streams 66, 68. The first stream is then further split into the first nitrogen sub-stream 76 at s the lower end of the vessel and into the third nitrogen sub-stream 86 which enters the vessel at the top. The first and second valves 82, 88 control the relative pressures of the nitrogen gas to ensure that the nitrogen moves downwardly through the sand in the chamber 44 and does not reverse to force the sand upwardly, particularly as the sand is being depleted in the vessel.
Both io gravity and the nitrogen flowing out of the vessel should urge the sand from the chamber 44 toward the screw 54. If the screw is not activated, the nitrogen should seep through the porous sand and around the stationary screw blades to escape out of the screw outlet 57. However, once the screw is activated to carry sand to the screw outlet 57, the sand should be carried in the fourth nitrogen is sub-stream 87 to the (unsanded) second nitrogen stream at the Y-joint 94, where both streams commingle and exit the first outlet 72 to a coiled tubing rig and ultimately to the coal formation.
If desired or required, surfactants may be introduced at either one or both of the upstream and downstream injection ports 98, 99. Injection at the 2o downstream port 99 avoids circulation of the surfactant through the vessels and most of the system 10. In contrast, injection into the relatively "dry"
nitrogen stream at the upstream port 98 will "wet" the sand in the vessels.
This nitrogen and sand combination, mixed potentially with one or more surfactants, should enhance the stimulation of coal deposits for improved gas 2s production over prior art methods, as discussed earlier.
It is noted that pressure gauges 36 and one or more densometers 38 are installed at selected locations in the system to monitor pressures and proppant - is -concentrations in the fluid stream exiting the system, to ensure that the desired volume and rate of proppant is being delivered to a particular formation. In particular, the gauge 36a measures the manifold inlet pressure to the screw 58, and the gauge 36b measures the manifold outlet pressure near the outlet 72. If s the exiting fluid stream is not satisfactory, then the orifice 70 and/or the various described valves and/or the speed of the screws) 58 for proppant delivery may be adjusted, either manually or preferably remotely by PLC (programmable logic controller) systems, to obtain the desired mix/values.
Further advantages of the present invention include:
so the system provides great flexibility for various pumping operations;
the system allows for a wide range of proppant density in the fluid stream;
the system can use various types of proppants;
the system's ability to mix proppant in the fluid stream, and in particular to mix sand with a N2 gas stream, provides an important means of enhancing is production of coal bed methane sales gas;
the system is cost effective to build and operate; and, the trailer 12 carrying the system 10 is "street" (i.e. weight) legal.
The above description is intended in an illustrative rather than a restrictive sense, and variations to the specific configurations described may be apparent zo to skilled persons in adapting the present invention to other specific applications.
Such variations are intended to form part of the present invention insofar as they are within the spirit and scope of the claims below. For instance, it may be possible to employ only one vessel 42, or three or more vessels 42, in the present system, but they will present certain disadvantages. If the capacity of 2s the one vessel is insufficient to treat a particular formation, then fracing operations will have to be disrupted as the vessel is refilled with proppant.
In the latter case it is believed that the third vessel would be redundant and be cost inefficient.

Claims

We claim:

1. A high-pressure injection proppant methos and system as illustrated and described herein.