Patent Grant
9752385
This application is a U.S. National Stage Application of International Application No. PCT/US2012/020929 filed Jan. 11, 2012, which is hereby incorporated by reference in its entirety.
To produce hydrocarbons (e.g., oil, gas, etc.) from a subterranean formation, wellbores may be drilled that penetrate hydrocarbon-containing portions of the subterranean formation. In traditional drilling systems, rock destruction is carried out via rotary power. This rotary power may be provided to the drill string by rotating the drill string at the surface using a rotary table. This power may also be provided by a top drive or may be provided from mud flow using a mud motor. Through these modes of power provision, traditional bits such as tri-cone, polycrystalline diamond compact (“PDC”), and diamond bits are operated at varying speeds and torques.
When using a mud motor to generate the torque for performing drilling operations, hydraulic losses along the drill string can limit the desired flow rate of mud. This in turn may reduce the hydraulic power one can apply to the mud motor to generate torque. This is especially critical for drilling systems such as Reelwell™ where the flow rates are reduced to levels approaching 30% of conventional flow rates. The dramatic drop in flow rate coupled with greater depths of drilling targeted for this technology may result in higher fluid friction during circulation and thus the need for higher circulating pressures. Such a system may impose serious limitations on the hydraulic power available to the bottom hole assembly in ultra extended reach drilling. Therefore, means of generating downhole torque on the drill bit other than from just hydraulic means via circulation along the drill string are desirable.
In addition, special modifications to positive displacement motors (PDMs) are often required to permit these systems to operate at the lower flow rates. These modifications may involve lowering the fluid volume required to drive the power section per rotation of the mud motor rotor by reducing the volume of fluid per stage section of the mud motor. At these lower flow rates, turbine motors would need to have tighter vane structures with higher blade angles and higher flow velocities across the smaller vanes to operate effectively. This may result in higher flow resistance and a greater risk of erosion from the mud flow for a given operating output torque. It is therefore desirable to develop a drilling system that creates rotational power generated from a device other than a PDM, vane, or turbine motor where hydraulic pressure would be required to generate rotational force to drill the hole.
Some specific example embodiments of the disclosure may be understood by referring, in part, to the following description and the accompanying drawings.
While embodiments of this disclosure have been depicted and described and are defined by reference to exemplary embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.
Illustrative embodiments of the present invention are described in detail herein. In the interest of clarity, not all features of an actual implementation may be described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions may be made to achieve the specific implementation goals, which may vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of the present disclosure.
In one embodiment, the present disclosure provides a pipe in pipe electric motor assembly comprising a drilling string comprising an inner pipe and an outer pipe and an electric motor, wherein the electric motor is provided with power supplied by the inner pipe and the outer pipe acting at least as conductors.
In another embodiment, the present disclosure provides a method of providing power to an electric motor comprising providing a pipe in pipe electric motor assembly comprising a drilling string comprising an inner pipe and an outer pipe and an electric motor, wherein the electric motor is provided with power supplied by the inner pipe and the outer pipe acting at least as conductors and providing power to the electric motor.
In another embodiment, the present disclosure provides a method of drilling a wellbore in a subterranean formation comprising providing a pipe in pipe electric motor assembly comprising a drilling string comprising an inner pipe and an outer pipe; an electric motor; and a drill bit, wherein the electric motor is provided with power supplied by the inner pipe and the outer pipe acting at least as conductors; providing power to the electric motor to generate rotational power; and applying the rotational power to the drill bit.
To facilitate a better understanding of the present invention, the following examples of certain embodiments are given. In no way should the following examples be read to limit, or define, the scope of the invention. Embodiments of the present disclosure may be applicable to horizontal, vertical, deviated, or otherwise nonlinear wellbores or construction boreholes such as in river crossing applications in any type of subterranean formation. Embodiments may be applicable to injection wells as well as production wells, including hydrocarbon wells.
The terms “couple” or “couples,” as used herein are intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect electrical connection via other devices and connections. The term “uphole” as used herein means along the drillstring or the hole from the distal end towards the surface, and “downhole” as used herein means along the drillstring or the hole from the surface towards the distal end.
It will be understood that the term “oil well drilling equipment” or “oil well drilling system” is not intended to limit the use of the equipment and processes described with those terms to drilling an oil well. The terms also encompass drilling natural gas wells or hydrocarbon wells in general. Further, such wells can be used for production, monitoring, or injection in relation to the recovery of hydrocarbons or other materials from the subsurface.
The present invention relates generally to well drilling and completion operations and, more particularly, to systems and methods of using electric motors to drive a drill bit.
Inner pipe (110) and outer pipe (120) may eccentric or concentric. In certain embodiments, the outer surface of inner pipe (110) may be coated with an insulating material to prevent short circuiting of the inner pipe (110) through the mud or other contact points to the outer pipe (120). In other embodiments, the inner surface of outer pipe (120) may be coated with an insulating material. Examples of insulating materials include dielectric materials. Suitable examples of dielectric materials include polyimide, a GORE™ high strength toughened fluoropolymer, nylon, TEFLON™, and ceramic coatings. In certain embodiments, only in areas sealed and protected from the drilling fluid is the bare metal of inner pipe (110) exposed to make electrical connections along the length of work string (130) to the next joint of inner pipe. Such areas may be filled with air or a non-electrically conducting fluid like oil or a conductive fluid such as water based drilling fluids so long as there is not a path for the electric current to flow from the inner pipe to the outer pipe in a short circuit manner.
In certain embodiments, stator windings (140) may be mounted in a pie wedge fashion within shell carrier (150). In certain embodiments, shell carrier (150) may be fixed within the motor housing (160) to prevent the carrier from rotating relative to the work string (130).
In certain embodiments, drive shaft magnets (180) may comprise fixed permanent magnets mounted on drive shaft (170) in such a manner as to encourage reactive torque from the varying magnetic poles created by the stator windings (140). In certain embodiments, electric motor (135) may comprise a 6 pole motor. Several variations in the number of poles and the decision on whether to couple the magnets to the drive shaft verses the housing exists as well as other forms of electric motors such as direct drive motors with a mechanical commutator drive winding arrangement and squirrel cage induction motors that do not use permanent magnets. Single phase motors are possible with the assistance of capacitors to create a pseudo second phase.
In certain embodiments, electric motor controller (190) may be positioned above the stator windings (140) to control various aspects of electric motor (135). Electric motor controller (190) can communicate in both directions with the surface through the two conductor path formed by inner pipe (110) and outer pipe (120) and through a feed through wire or wires that feed through the electric motor assembly to modules positioned below the motor such as LWD and/or MWD and steering systems.
In certain embodiments, electric motor controller (190) may be housed inside a pressure controlled cavity to protect the electronics. The electric motor controller (190) electronics may be coated with a ceramic coating to allow for the cavity to be oil filled and pressure balanced with the annulus allowing for a thinner wall to house the electronics. Advantages of filling the cavity with oil and pressure balancing with the annulus are that the wall thickness to of the electronics cavity to be maintained in a much smaller thickness since it does not have to hold back the entire pressure of the fluid column leaving more space available for the electronics and providing for better heat conduction of heat generated by the electronics to keep it within operable limits.
In certain embodiments, stator windings (140) may be encapsulated in a ceramic, rubber, or epoxy like potting. This allows the encapsulated region additional short circuit protection that would normally be relegated to the typically peek coating found on the magnet wire which can then be exposed to mud which part of the mud circulates through this region to provide cooling for the windings and power electronics as well as lubricate the mud bearings and radial bearings along the drive shaft (170).
During operation of pipe in pipe electric BHA motor assembly (100), mud may flow down annular spaces formed by inner pipe (110) and outer pipe (120). Mud and cuttings may be returned to the surface inside inner pipe (110). However, near the top of electric motor (135) this flow regime may change slightly. Flow diverters (210), which are electrically insulated from the outer drill pipe and preferably made of ceramic or metallic with a dielectric insulating coating on the outer surface, allow mud and cuttings from the annulus formed by inner pipe (110) and outer pipe (120) to enter the inner pipe while passing downward flowing mud through kidney shaped slots in flow diverter (210). Below this point, downward flowing mud may be diverted into a center bore where it passes through the inner pipe (110) electrical connection to the electric motor (135) into the motor housing (160). At this point the downward flowing mud may take two separate paths. The first path is down the center bore of drive shaft (170) and down to drill bit (220) at the bottom of the work string (130) where it exits drill bit (220) and begins its way back up the hole to the flow diverter inlet ports. The other path is through a high pressure flow restrictor (230) at the top of drive shaft (170) then through the space between the outer portion of the rotor and the inner portion of the motor housing and out through the bottom radial bearing assembly just above the shaft bit connection on the bottom of the motor housing. High pressure flow restrictor (230) may be designed to leak a certain amount of drilling fluid to flow through into the motor housing (160) to cool the stator windings (140) and to lubricate the radial and axial bearings of the electric motor (135). The high pressure flow restrictor (230) may also double as a radial bearing (240). In other embodiments, a separate radial bearing (240) may exist. Radial bearings (240) may comprise rubber marine bearings, PDC bearings or various hardened coatings like fused tungsten carbide.
High pressure flow restrictor (230) may be positioned anywhere along the either flow path as long as the flow is restricted somewhere along the path of the top of the drive shaft and the bottom of the motor housing. In certain embodiments, high pressure flow restrictor (230) may be positioned directly below the upper radial bearings (240) as it is easier to work with such a device and it also acts as a filter keeping larger solids that happen to get into the mud away from the stator windings (140) and radial bearings (240).
In other embodiments, a stator head assembly may be made out of one round bar by using machining methods like electrochemical machining, wire EDM, or electrode electro-static disgorge machine machining or even extruding the shape so that the outer diameter of stator head assembly is one solid diameter rather than 6 individual pieces. Since it may be more expensive to make the stator heads out of one bar, ideally the stator winding assembly (280) is made up of 6 pieces to reduce manufacturing costs. In the case where the stator heads are made out of one bar, the stator windings would have to be threaded through the various passages. While this may be difficult, the encapsulated coating could be injection molded into the inner area and ends. It would be desirable to still coat the stator to reduce corrosion and increase its useful life but in this case the potting material could suffice for this role. In certain embodiments, the potting material can be made of various compounds such as epoxy, ceramic based compounds, nylon or peek like polytetrafluoroethylene such as Arlon 100 from Greentweed.
In the pie wedge concept illustrated in
The stator windings (140) may be varnish, peek or other dielectric type coated magnetic wire ideally made of silver, copper, aluminum, or any conductive element, including high temperature super conductor materials. The stator windings (140) may make several wraps around the stator heads (290). Optionally, over top and embedded into the stator windings (140) may be a potting material, preferably a ceramic or more flexible high temperature epoxy. This material may be used to protect the stator windings (140) from corrosion from the mud and erosion protection, especially from fine sands that can make their way into this area.
The one or more stator heads (290) may be grooved on the outer diameter and may be keyed with the shell carrier (150) to hold the one or more stator heads (290) still from the torque generated. This torque may then carried to the motor housing (160) through additional spline grooves in the carrier housing (260) and the splines on the motor housing (160). Other ways of doing this are easy to understand by those skilled in the art.
Optionally the carrier housing (260) outer diameter and the motor housing (160) inner diameter may be slightly tapered, narrowing toward the top, to allow for a snug fit and prevent mud fines from building up between the motor housing (160) and the carrier housing (260). In this manner the winding carrier sleeve (250) may be pulled or pressed out. The top of the winding carrier sleeve (250) may have additional anti-rotation keys that engage the electronics insert and/or the additional spline grooves that engage the splines located in the motor housing (160).
In certain embodiments, the one or more stator heads (290) may be made with thin slices of the cross section shown
By using thin stamped sheets, the problems mentioned above with manufacturing costs and assembly issues may be solved while still providing for a power stator design. The thickness of each stator slice would require some modeling to optimize but a thickness of 1/16″-¼″ is a typical range. Alternately each individual stator head can be stamped out thus needing 6 stamped pieces to make 1 layer and arranged as shown in
Referring now back to
An advantage of this type of motor is that it can be controlled with solid state switches rather than using a commutator. While a commutator would work it is not ideal as it must use brushes in an electrically insulated environment, which would mean an oil filled cavity with a rotary seal for a barrier to the mud would be necessary which can be problematic for reliability and maintenance reasons if the rotary seal has to operate at high RPMs over long hours as is the case here.
Referring again back to
There are many ways to create 3-phase power from a direct current (DC) power source. A DC power source from surface or another power generation source down hole is ideal if the power has to be transmitted over great distances since the conductive mud between the inner and outer pipe creates losses in an alternating current (AC) power transmission scenario. Often power transmission lines that traverse water, especially salt water, utilize direct current in order to minimize electromagnetic radiation losses into the water surrounding the power transmission cable. Likewise in a subterranean formation there exists intervals from time to time that have a high conductivity capacity which would enhance the power losses along the pipe in pipe power transmission circuit for changes in flowing current along the pipe in pipe system. So it is a benefit to minimize current fluctuations as much as possible by utilizing a direct current rather than an alternating current to power the electric motor. That said one could use any form of electric power to drive the motor. In certain embodiments, DC power may be desirable as it may allow for easier power control of certain circuits downhole. Ideally one would want 3-phase power transmitted from surface to the motor downhole but this would mean more conductors would be required in the pipe in pipe system and this would reduce reliability and increase complexity of the pipe in pipe system to include at least 1 more conductor and realistically a 4th as a ground return would be desirable but not essential.
A generalized block diagram is shown in
In certain embodiments, the communications channel can be in direct communications with the pipe in pipe communications network or it could be communicating with a local network such as one for an MWD/LWD system or a near bit or in bit communications node or a plurality of networks and communication nodes. The processor may execute commands that are stored in a memory storage area which could be embedded in the processor itself or in separate memory elements such is memory chips like RAM or Flash RAM or a solid state hard drive or other forms of memory storage/retention devices. The memory may also used for logging performance information about the motor such as winding temperature, tool temperature, mud temperature, shaft RPM, power output, torque output, system current, voltage and power, winding current, voltage and power input, and pressure on either side of the high pressure flow restrictor to watch for signs of wash out and make sure mud is flowing through the windings to keep them cool from heat generated by resistance in the windings and bearing friction primarily. The power supply supplies power from the pipe in pipe conductors. Since the pipe in pipe conductors may be used to power everything, no connected lines are shown in
In addition batteries, rechargeable batteries, or a capacitor may be used to provide minimal power to the communications, sensors, processor and memory modules and any other desired electronic device in the tool should the power to drive the motor shut off. In this manner low power communications with the motor can continue even if there is not enough power to power the motor's electrical windings sufficiently to drill the hole. This would allow the system to stay responsive to communications and other electronic functions, such as logging data from sensors, while a connection is being made for example where maintaining power to the down hole motor is easily done is a safe manner when adding a new pipe to the string.
The use of batteries may also allow for communications and sensors to be kept alive so data exchange and commands can be performed while a connection is being made on surface or another rig operation is taking place so long as a surface connection for communications is set up and maintained. In addition communication between various network nodes in the work string may still maintained so that sensors can be monitored even if surface communications is down thus logging important data. This is especially useful when tripping out of the hole and wanting to log certain areas on the way out.
DC power may be converted to 3-phase current by the motor controller. The motor controller preferably uses solid state electronics for switching on current to windings and flipping the polarity of those windings in a manner to replicate 3-phase power from surface. Current to the 6 windings is managed in 3 pairs where the current in any pair is nearly the same at any given moment of time save for minor lag effects. The winding pairs may be opposite to each other in the motor as shown in
The phase relationships between the 3 phases may controlled by a master controller that ensures all 3 phases remain in frequency sync but 120° of separation in phase. In order to maximize power transfer to the rotor, a sinusoidal or other wave shape for the 3 phase controller may be generated to power the 3 pairs of windings. Each winding may be preferably connected in parallel, rather than in series, to reduce series resistance of the winding pairs. The windings and current flow may be timed such that each stator pole has the same orientation as its other pair. This means that the inner tip of each stator pole pair may have the same magnetic field polarity such as North, South or neutral. In embodiments where each coils is wrapped identically for each winding, each phase pair may be wired in parallel as shown in
Critical functions of the motor controller may include: (1) switch polarity directions in sync with the desired rotation direction; (2) maintain phase separation of each winding pair; (3) maintain the applied frequency and ramp the frequency up and down at acceptable rates for the motor based on changes in desired motor speed; and (4) maintain power levels to the windings to optimize torque delivery for the desired speed. Each of these functions may be accomplished by varying the supplied current or voltage, or both, to the winding pairs and/or varying the duty cycle of each wave. Alternatively, or in addition to, start up capacitors can be employed to aid the motor in ramping up in speed. These capacitors are generally switched out by the motor controller as the motor reaches about 75% of its rated speed.
It should be noted that in some embodiments, the controller may simply alter the phase of any two channels (A and B, B and C, or C and A) to change the direction of rotation of the rotor while still being able to output the same amount of torque and power to the bit. This may be significant improvement over traditional PDM motors where they can only rotate in one direction. The ability to backward rotate may have many benefits such as helping to get unstuck, undoing a rotary connection to leave a stuck fish in the hole and release the BHA, activating some other mechanical mechanism, drilling in the opposite direction using bit cutters pointing in the opposite direction, or extending a roller cone bit's life by stressing it in the opposite direction.
The motor controller may vary the power to each winding pair in a square wave or sinusoidal fashion or other cyclical wave form method such as a triangle or sawtooth wave form. In certain embodiments, a sinusoidal wave may be preferred as it is the most power efficient. Further a person of ordinary skill in the art could appreciate using varying duty cycles of each wave form to adjust overall average power delivered. In certain embodiments, the electronics may be designed with solid state switches such as variacs or relays to vary the direction of current flow through the windings from the DC source.
In one embodiment, a time varying signal may be emulated to engage the windings with square wave electrical pulses in opposite polarities. By adjusting the phase and duty cycle of each square wave, the average power consumed by the motor per rotation may be varied respectively. Such a method may be accomplished using semi-conductor based switches such as silicon controlled rectifiers (SCR), thyristors or other forms of switching devices. Other methods may include transformers for varying the power applied to the motor windings. Such transformers could include variacs, step up or step down or multi-tap transformers.
The motor driver may be a small power amplifier switch used to source enough power to turn the semi-conductor switch on and off and may also switch on or off based on logic outputs from the processor. In certain embodiments where the processor has the power to turn on and off the switches, the digital outputs or analogue outputs of the process can be attached directly to the switch control lines. Essentially the process switches between either switch pair to reverse the current through the winding pair or switches both switch pairs off when the phasing and duty cycle time deems it so.
Returning back to
The polarity of the drive shaft magnets (180) may be alternated with the North pole (N) facing out then the next magnet polarized or oriented with the South pole (S) facing out, then North again and lastly South for the four pole rotor example. A person of ordinary skill in the art would realize that the number of windings and magnets can be multiplied such as 12 stator poles and 8 rotor magnets or three stator poles and two rotor magnets. The variations will depend upon many factors but this arrangement is a good one for task at hand in trading off reliability for smoother torque delivery while ensuring the peak torque required is maintained for the motor design.
Referring now to
In certain embodiments, hall effect switches (990) may be embedded in winding carrier to monitor shaft position and RPM by observing small magnets (191) or the rotor magnet relative position on the shaft. The signal output of the hall effect switch or other type of rpm sensor is routed back to the motor control electronics where the processor can automatically measure and adjust the speed of the motor based on the sensor feedback. Other types of position sensors may also be included in the winding carrier such as proximity sensors. By monitoring the shaft position while it rotates, one can better optimize the torque delivery to the motor and watch out for pole slippage which can occur if the torque from the bit reaction of drilling exceeds the stall point off the motor or chatter which might mean one winding is applying more torque than another winding in an uneven manner and thus adjust the applied torque output of the windings to obtain as even a torque output as possible. In certain embodiments, temperature sensors may also be embedded in the carrier or adjacent to the windings. Preferably at least one temperature sensor for each winding may be used to monitor the motor temperature. Furthermore, in certain embodiments, a pressure sensor may be installed in the carrier above (192A) and below (192B) the high pressure flow restrictor (230) to monitor the performance of the flow restrictor and make sure a wash out or a plugging is not occurring and to confirm that the mud pumps are indeed on to ensure cooling of the motor.
Between the two winding and drive shaft winding sections, an optional radial bearing support (380), which may be mud lubricated, is located. An elastomeric marine bearing, roller, ball, journal or other bearing style may also be used. The stator winding carrier has spline grooves (194) to mate with motor housing splines to keep the winding carrier from rotating.
Referring now to
In certain embodiments, the electric motor may have an interface module which facilitates coupling, communication, and power transmission continuity to the surface with the drill pipe. The electric motor can be controlled from and respond to surface communications. The electric motor may have variable speed and torque capability. A gear reduction or planetary gearing in conjunction with a variable speed electric motor may be utilized to facilitate desired speed and torque output.
The electric motor may be a modular component of a bottom hole assembly or be utilized stand alone. The electric motor may be utilized to enlarge or ream the wellbore with or without drill string rotation as typically supplied from surface equipment. The electric motor may have multiple configurations to facilitate adaptability to desired rock cutting/destruction mechanisms. These configurations may include laser drilling or laser drill bit assist such as is described by Sinha et al. in SPE/IADC 102017, Polycrystalline Diamond Compact (PDC) cutting structures on fixed cutter bits, roller cone bits, pulsed electric rock drilling apparatus like the one described in US 2010/000790 by Tetra, or other rock destruction devices. In fact, the presence of the power to power and electric motor lends itself naturally to being able to supply the necessary power to drive a laser for drilling or bit drilling assistance.
Rotation for the cutting assembly may be provided by the rotation of the drill string from surface equipment or any of the following: a modular motor assembly fitted to a separate rotating cutting assembly or an integral assembly where rotation for the cutting assembly can be provided by a motor assembly or motor assemblies fitted within the single assembly. The cutting structure on the cutting assembly may have the depth of cut (ultimate diameter) powered by an independent electric motor controlling ramps or pistons. When cutting rotation is not desired the cutter assembly cutting structures may be retracted and the modular motor assembly can be commanded to shut down and if necessary the ability to rotate can be locked. Reaming could be optimized by allow the individual cylindrical reaming cutting assemblies to have power to rotate on their own arbors.
Referring now to
In one embodiment, steerable BHA stack up may be configured in accordance to
In one embodiment, a rotary steerable BHA stack up may be configured in accordance to
In one embodiment, a rotary steerable BHA stack up may be configured in accordance to
In one embodiment, a steerable BHA stack up may be configured in accordance to
In one embodiment, a rotary steerable BHA stack up may be configured in accordance to
In one embodiment, a rotary steerable BHA stack up may be configured in accordance to
Other configurations are apparent in light of this disclosure by simply moving these modules around and interconnecting them as required for hydraulic, electric power and communications needs.
The present invention is therefore well-adapted to carry out the objects and attain the ends mentioned, as well as those that are inherent therein. While the invention has been depicted, described and is defined by references to examples of the invention, such a reference does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alteration and equivalents in form and function, as will occur to those ordinarily skilled in the art having the benefit of this disclosure. The depicted and described examples are not exhaustive of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2012/020929 | 1/11/2012 | WO | 00 | 7/8/2014 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2013/105952 | 7/18/2013 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4500263 | Mohn | Feb 1985 | A |
| 4690212 | Termohlen | Sep 1987 | A |
| 4722402 | Weldon | Feb 1988 | A |
| 5400430 | Nenniger | Mar 1995 | A |
| 20110036560 | Vail et al. | Feb 2011 | A1 |
| 20130098632 | Wetzel | Apr 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 710296 | Oct 1993 | SU |
| Entry |
|---|
| Office Action issued in related Russian Application No. 2014132895 mailed on Mar. 31, 2016 (4 pages). |
| International Search Report and Written Opinion issued in related PCT Application No. PCT/US2012/020929 mailed Sep. 3, 2012, 7 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20140326509 A1 | Nov 2014 | US |
