Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B4/00—Drives for drilling, used in the borehole
  • E21B4/02—Fluid rotary type drives
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01C—ROTARY-PISTON OR OSCILLATING-PISTON MACHINES OR ENGINES
  • F01C1/00—Rotary-piston machines or engines
  • F01C1/08—Rotary-piston machines or engines of intermeshing engagement type, i.e. with engagement of co- operating members similar to that of toothed gearing
  • F01C1/10—Rotary-piston machines or engines of intermeshing engagement type, i.e. with engagement of co- operating members similar to that of toothed gearing of internal-axis type with the outer member having more teeth or tooth-equivalents, e.g. rollers, than the inner member
  • F01C1/107—Rotary-piston machines or engines of intermeshing engagement type, i.e. with engagement of co- operating members similar to that of toothed gearing of internal-axis type with the outer member having more teeth or tooth-equivalents, e.g. rollers, than the inner member with helical teeth
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C13/00—Adaptations of machines or pumps for special use, e.g. for extremely high pressures
  • F04C13/008—Pumps for submersible use, i.e. down-hole pumping
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C2/00—Rotary-piston machines or pumps
  • F04C2/08—Rotary-piston machines or pumps of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing
  • F04C2/10—Rotary-piston machines or pumps of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of internal-axis type with the outer member having more teeth or tooth-equivalents, e.g. rollers, than the inner member
  • F04C2/107—Rotary-piston machines or pumps of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of internal-axis type with the outer member having more teeth or tooth-equivalents, e.g. rollers, than the inner member with helical teeth
  • F04C2/1071—Rotary-piston machines or pumps of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of internal-axis type with the outer member having more teeth or tooth-equivalents, e.g. rollers, than the inner member with helical teeth the inner and outer member having a different number of threads and one of the two being made of elastic materials, e.g. Moineau type
  • F04C2/1073—Rotary-piston machines or pumps of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of internal-axis type with the outer member having more teeth or tooth-equivalents, e.g. rollers, than the inner member with helical teeth the inner and outer member having a different number of threads and one of the two being made of elastic materials, e.g. Moineau type where one member is stationary while the other member rotates and orbits
  • F04C2/1075—Construction of the stationary member

Definitions

• This invention relates to machine-building, more specifically, to the design and manufacturing of positive displacement hydraulic rotary machine; various embodiments of which are used for oil-field (wells) applications.
• Positive displacement motor is commonly used for directional drilling operations throughout the world and progressive cavity pump (PCP) having a similar design is widely used in artificial lift.
• PCP progressive cavity pump
• MOYNO system in reference of to the main initial business application of such machines.
• This invention is aimed to reduction of PDM/PCP performance degradation by introducing of a fixed positive clearance between the rotor and the stator and additional calibrated channels providing tolerable leakage of fluid between hydraulic chambers, allowing elastomeric coatings of the conventional system to be replaced by more resistant materials.
• SLB patented [US6241494, Demosthenis G. Pafitis, 1998] and tested some hydraulic motors with non-elastomeric stator. This type of motor operates with a clearance estimated as 0.3- 0.6 mm. With such construction, system plugging with large particles (such as LCM or Fluid Loss Materials) in some specific conditions (such as motor stall) must be solved for proper applications.
• PDM Positive Displacement Motors
• the performance of PDM depends on motor design, properties of drilling mud (density, viscosity), downhole environment condition (pressure, temperature, chemical composition of the fluid) and drilling regimes (required torque and weight on bit (WOB).
• the second application of the same hydraulic operation principle is the Progressive Cavity Pump (PCP) for lifting of production fluids from the producing formation to the surface via the production tubing.
• PCP Progressive Cavity Pump
• the rotor can be driven by submersible electric motor downhole (for deep pump) or by a surface unit rotating a rod connected to the PCP rotor (the latter variant is suitable for moderate depth).
• a Progressive Cavity Pump has several advantages in comparison with other types of pumps: it consists of two main units (rotor and stator), so it is reliable in operation, provides a steady flow rate of pumped fluid, it has easy- controllable flow rate. It is widely used for pumping of heavy oil and other high-viscosity fluids even with a high percentage of sand in the fluid. Thanks to their high performance and reliability, PCP is commonly applied for heavy oil production.
• Standard design of such hydraulic system is a combination of a metallic rotor with a helical shape and a stator with inner surface covered with elastomer material providing a tight but flexible rotor- stator contact along the contact curve throughout the motor.
• Fig. 1 shows the details of the power section 18 of PDM/PCP.
• the power section 18 generally includes the housing 22 which houses the stator 24 within which a motor rotor 26 is rotationally mounted.
• the stator 24 has a plurality of helical lobes 24a-24e, which define the corresponding number of helical cavities 24a'-24e'.
• the rotor 26 has a plurality of helical lobes 26a-26d. This figure refers to a 4-lobe rotor.
• Such systems (PDM/ PCP) are considered as positive displacement hydraulic machine: In the ideal case, the flow is proportional to rotation speed (RPM) while the torque is proportional to the differential pressure across the system.
• the prior art for design of positive displacement hydraulic machine assumes a strong positive seal called a positive interference.
• the positive interference is reduced during assembly to allow thermal expansion of the elastomer.
• the mud weight and vertical depth also must be considered as they influence the hydrostatic pressure applied to the stator' s elastomer and cause it to shrink.
• Drilling motors (such as SLB PowerpackTM ) are commonly available with different stator elastomers.
• the choice of elastomer depends on the downhole conditions. However the conditions can vary during motor operation, so it is desirable to have a stator-rotor pair which is universal for standard and challenging conditions of temperature and pressure.
• the choice of interference can be predicted by various models: for example, the Schlumberger software called PowerFit is used to calculate the desired interference fit for a PowerPackTM Steerable Motor.
• a minimal contact between two parts of helical hydraulic machine reduces friction in the rotor-stator pair, the abrasive and erosive deterioration of the surfaces, thus extending the service life of a motor or pump: this minimum gap may be imposed by a rotor guidance system, as explained in later section.
• Publication on heavy oil production methods [SPE 0059276] also emphasizes that a PCP can achieve high efficiency without "interference fit" between the rotor and stator. For pumping of fluids with a high viscosity (like heavy oil), the design based on "sloppy fit" helps to the preserve the chromed or boronized surface of a rotor.
• Such a screw pump comprising a hard rotor and hard stator exhibits a low mechanical abrasion, low erosion, while keeping the head of pump at desired level.
• the gap of several tens microns is typically recommended in publication for high- viscosity fluids.
• metal-metal pair removes the chemical-related problems of elastomer: aging by drilling fluid/production fluid, reaction with gases dissolved (H 2 S, CO 2 ), sudden decompression of the elastomer material saturated with gases after lifting of device to the surface.
• the object of this invention is to improve the design of positive displacement motors and progressive cavity pumps.
• Said object is achieved by using a positive displacement motor comprising a rotor and a stator of helical shape without elastomeric coating or liner installed with a clearance wherein said stator is hard with an elastic modulus of at least 10 times the elastic modulus of elastomers used in stators, further wherein said clearance is 0.05 - 0.5 mm.
• said rotor and/or stator are additionally covered with a wear-resistant coating.
• Said motor may comprise multiple sections comprising said rotor and said stator.
• said object can be achieved by using a positive displacement motor comprising a rotor and a stator without elastomeric coating or liner installed with a clearance wherein the lobes of said rotor have through channels hydraulically connecting the chambers formed by said lobes.
• the channels in adjacent lobes are preferably arranged not in line.
• the axis of at least part of said channels is curved.
• the diameter of said channels is 2 - 10 mm.
• the rotor surface may additionally have grooves of 5 - 10 mm width and depth of 0.5 to - 10 mm depending on operation conditions.
• one cavity has at least 2 grooves and one lobe pitch has at least two channels.
• Said motor may also comprise multiple sections comprising said rotor and said stator.
• the previously described local channels could be replaced by a spiral grooves (either in rotor or stator).
• the groove angular orientation can be either in the same or opposite direction to the component in which one is formed.
• its pitch and the number of grooves should be such that at least one opening is present in the sealing line of each cavity between the stator and rotor.
• the sealing line of each cavity has an opening for any angular position of the rotor: the opening is "apparently" moving axially during the rotor rotation, allowing the cleaning over the whole sealing length after one rotation.
• the invention relates to the oil and gas industry, in particularly, to the field of design of helical hydraulic machines.
• the design of hydraulic machine is offered with a small positive clearance between a solid rotor and solid stator.
• the size of clearance depends on the properties of fluid transported through the machine. Minimal clearance is also chosen in accordance with process of manufacturing and assembling of the rotor in the stator. Also the minimal clearance is enough for passing of most of small particulates expected in the fluid thus reducing sand plugging, abrasion and erosion caused by particle flow at high velocities.
• the flow goes through the clearance but also passes through those channels flushing the cavities while operation of the motor.
• Another alternative is to form spiral grooves in the surface of the rotor or stator.
• the lobe hole allows the flow through the pump of "cubical or spherical” large particles while the surface channels or grooves allows the flow through the pump of "flat” large particles.
• the current invention presents an improved design of a device described in the Schlumberger patent US6241494 [Demos Pafitis, 2001] claiming a principle of positive clearance for hydraulic motor with non- elastomeric stator.
• the current invention is based on this Schlumberger' s invention as a basic concept for further improvement in design and operation.
• stator of the helical machine is made of non-elastomeric material that helps to avoid the problems inherent to conventional elastomeric stators (low strength, high deformation under operational loads, aging, chemical and thermal sensitivity, gas-induced swelling, temperature expansion).
• the material for the stator manufacturing is metal, alloys, ceramic, or composite suitable for downhole conditions.
• the material for the rotor is the same or a hard material with similar temperature expansion coefficient in the operation range.
• the stator is rigid so that its elastic module is at least 10-100 times higher than in the typical elastomers used for the conventional stators.
• Special thin coating may be used on the stator (or/and rotor) to enhance their resistance to erosion and wearing.
• the device according to invention has no elastomeric elements, it can be assembled for operation at high temperatures (>140 degC).
• the rotor rotates in the stator with a prescribed and constant clearance rotor-stator.
• the said clearance is determined to be wider than the 2...3 size of particles corresponding to the top of particle size distribution in the operational fluid.
• the preferable clearance interval is from 0.05 mm - 0.5 mm.
• Fig. 1 is a cutaway view of motor/pump showing the rotor and the stator (left side).
• a cross-section taken along A-A line is shown in the right side.
• the top diagram illustrates a positive interference between a solid rotor and elastomer-coated stator (prior art design).
• Fig.2 shows another modification of prior art device with a positive clearance. The view is similar to Fig. 1.
• Fig. 3 shows the longitudinal sectional view of a stator-rotor pair according to the invention (left side) and cross-section along the A-A line (embodiment 1).
• Fig. 4 is the cross-sectional view of a rotor according to invention (embodiment 2) illustrating the allocation of drilled holes in the rotor body.
• Fig. 5 is a 3D projection of the rotor according to the invention.
• Fig. 6 is a typical operational curves for a prior art motor (elastomeric stator with positive interference depicted in Fig. 1) as well as d for solid rotor - solid stator pair with a fixed gap.
• Fig. 7 is a typical mechanical power curve as a function of pressure drop across the power section for prior art motor (elastomeric stator with positive interference) and a motor according to the invention (solid rotor - solid stator pair with a fixed gap).
• Fig. 3 shows that at the both ends of the hydraulic machine there are two additional sections 128 and 130.
• Two support sections at the ends and the hydraulic machine constitute the hydraulic section of the PDM (or PCP).
• This section can be the motor (or the pump) itself, but alternatively the downhole unit may comprise multiple sections connected together. This allows one to increase the power while, if said sections are short enough, reducing the cost of each individual section and lowering the negative effect of well curvature by providing flexible connections between said sections.
• These sections incorporate a special guiding mechanism which ensure consistent rotation and nutation of the rotor 126 inside the stator 124 and provide the support for the rotor 126 so that the rotor does not see contact with the stator within the power section between the sections 128 and 130.
• FIG. 3 shows the expected position of the rotor 126 inside the stator 124 with positive clearance along its entire perimeter. This will eliminate the friction and abrasive wearing within the poser section. Also this will decrease the filtering of the small particles since they gap for them will exist on the full round basis.
• the guiding mechanism drives the rotations of the rotor so that its rotational speed about its own axis and nutational speed about the axis of the stator are insured to be in the following relation [W. Tiraspolsky, Hydraulic Downhole Drilling Motors, Editions Technip, Paris, 1985, p. 246]: where z * is the number of lobes of the rotor.
• the guiding mechanism in the special sections 128 and 130 does not contribute to the motor performance and it is specially designed to have enhanced wearing resistance to keep the rotor in right position to the stator within the power section. This may be achieved by protecting the guiding mechanism from the main fluid and its abrasive particles passing through the motor or by use of special material or coating on the wearing surfaces of the guiding mechanism.
• Tungsten carbide can be used for the guidance system.
• the problem of plugging of the hydraulic machines is addressed by placing additional preferably round holes through the lobes of either the rotor or stator: (see Fig. 4, 5 for holes in rotor).
• the holes through the adjoining rotor lobes should not be on a straight line to ensure flushing effect (see Fig. 5).
• the axis of those holes may not be parallel to the axis of the rotor or may be curved allowing good machinability.
• Diameter of the holes is large enough to allow the passage of LCM particles (loss circulation material particles) or any other particles bigger then the clearance.
• the preferred size of transport holes is from 2 to 10 mm.
• a set of groves may be made on the surface of rotor (or stator) with typical width of 5...10 mm and depth 0.5...2 mm. As the holes the grooves may be evenly distributed along the rotor (or stator) having at least 2 grooves along the length of one helical lobe pitch of the system.
• spiral grooves can be machines either on the rotor or stator.
• the sealing area is moving on the periphery of the rotor/stator during the rotation of the rotor: each point of the rotor and stator will be covered by the sealing area during one rotation.
• the spiral can be forwards of backwards, but its pitch must accordingly adapted. With such a construction, opening in the sealing area is moving axially during the rotor rotation, allowing cleaning of the clearance.
• the holes are evenly placed along each lobe of rotor (or rotor) so that there are at least 2 holes over the lobes pitch. By such the way with running motor there will always be at least 1 channel connecting adjoining chambers.
• the holes diameter is determined (based on the large particle size) first and then the number of holes in one rotor lobe per one pitch is determined so that to achieve the summed area of all holes per each cavity to be bigger then the area of the peripheral clearance.
• Upper limit for the number of holes is determined by overall leaks area and expected motor performance (more area for the leakage means less performance for the motor).
• FIG. 4 An illustration of this concept is shown in the Fig. 4.
• the hole 100c is drilled through lobe 126c and the hole lOOd is drilled through lobe 126d.
• Relative position (angles ⁇ l and ⁇ 2) of these holes is the same for each lobe so that the in-hole and out-hole are not on the straight line along the rotor axis.
• the holes lOOd and 10Od' are neighboring along the cavity and are located on the same surface of the lobe 126d with helical pitch between them ⁇ 3 as half of stator pitch.
• Fig. 5 shows the same holes in 3D picture with expected flow pass flushing the cavity between the lobe 126a and 126d.
• This allocation of holes in lobes provides a flushing flow from one cavity to another. Additional holes induce a minor loss in the performance of a hydraulic motor, but allow sustain no-stall (no-plugging) operation in challenging conditions.
• the valve can be a "conventional" pressure limiting valve such as a ball closed by a spring against the pressure.
• a pressure limiting valve When such a pressure limiting valve is installed in the rotor by-pass central hole, it is directly submitted to the differential pressure across the motor.
• a combination of the first two said embodiments can be employed.
• the guidance systems are installed to reallocate the friction and abrasive milling from rotor-stator pair to the guidance system and provide passage of fine particles through a constant- width clearance.
• the holes in the lobe (rotor or stator) body ensure flushing for bigger particles while channels and/or spiral grooves ensure flushing for flat particles.
• the third embodiment can be added to the previous combinations to allow proper behavior during motor stalled condition, while the fluid contains a large amount of large and/or flat particles. In that case, a certain amount of flow is by-passed ou of the cavities between rotor and stator.
• the new design may be constructed by incorporating the guiding mechanism or the flushing channels or the by-pass vavle system separately or as a combination of the three solutions in one design. In any version there will be the full range of the above mentioned advantages due to the use of non-elastomeric stator that will increase the reliability of the tool.
• the disclosed device may have 2 holes of 8.5 mm in diameter per each cavity: this gives additional area of 113 mm that is about a half of leakage area in the working original prototype.
• the new design must have clearance of 0.15 mm (a half of prototype clearance).
• the area of the clearance will constitute 106 mm (i.e., less than the holes area) and most of leaks will go through the holes that will help to avoid the plugging problem.
• Fig. 6 and Fig. 7 illustrate the comparison of theoretically expected performance of new design versus conventional design of a PDM with elastomeric stator. Points on the graphs represent typical data for motor (such as SLB PowerPak A675SP4548 with normal interference fit 0,016 inches). That is a conventional PDM motor with elastomeric stator.
• the solid curves 1 are the curves approximating the experimental points of the conventional motor.
• the dashed theoretical curves 2 and 3 represent the estimations for a hydraulic motor with 2 channels of 8 mm in diameter per each cavity and the clearance 0.1mm and 0.2 mm. All the curves are plotted for the same and constant flow rate 300 gal/min (0.02 mVsec). Although the numbers on the graphs correspond to a particular motor, the shape of the curves is similar to that for all types of conventional hydraulic motors [ PowerPack Steerable Motor Handbook, Schlumberger, 2004, page 99-192].
• Fig. 7 shows the calculated performance of new design in terms of useful mechanical power.
• the effectiveness declines with the increase in the clearance, but there is an interval of pressure drop (high pressure drop), where the disclosed device is more efficient (the gap is smaller than for a motor with elastomer-covered stator).
• the curve says that the expected maximum power will stay as it was in conventional motor but stalling torque is expected to be 40% higher, so that the new motor will be able to operate in more aggressive drilling regime.
• With clearance of 0.2 mm there will always be the less power within the same range of operation but the range and the power may be increased simply by increasing the flow rate.
• Fig. 6 and Fig. 7 demonstrate that the disclosed device is less effective in operation at low differential pressure but will better fit aggressive drilling conditions when high torque is required in the same size of the tool.

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• Environmental & Geological Engineering (AREA)
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• Geochemistry & Mineralogy (AREA)
• Rotary Pumps (AREA)
• Hydraulic Motors (AREA)

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• 2008
  • 2008-05-16 CA CA2719121A patent/CA2719121C/en not_active Expired - Fee Related
  • 2008-05-16 WO PCT/RU2008/000302 patent/WO2009139658A1/en active Application Filing
  • 2008-05-16 RU RU2010151623/06A patent/RU2471076C2/ru not_active IP Right Cessation

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