Electricity generation within a downhole drilling motor

A progressing cavity-type drilling motor having an electrical generator disposed within the rotor of the drilling motor. In some embodiments, the electrical generator produces electrical energy from a flow of drilling fluid through a bore in the rotor. In other embodiments, the electrical generator produces electrical energy by harnessing the kinetic energy of the rotor as the drilling motor is used to drill into a formation. The electrical energy generated by the generator can be stored or used to power sensors, actuators, control systems, and other downhole equipment.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a U.S. National Stage Application of International Application No. PCT/US2014/055092 filed Sep. 11, 2014, which is incorporated herein by reference in its entirety for all purposes.

BACKGROUND

The present disclosure relates generally to electrical power generation during drilling operations.

Modern drilling operations commonly implement various pieces of downhole equipment that require electrical power. For example, sensors, control boards, drives, and logging tools are just some of the many pieces of common downhole electrical equipment.

Despite the pervasiveness of downhole electrical equipment, supplying power to the downhole equipment continues to challenge drilling operators. Increasingly deeper wellbores and increasingly harsher downhole conditions make direct connections to surface power sources challenging. Further, the duration of many drilling operations exceed the life of battery systems, requiring the replacement of batteries mid-operation. Because such replacement may require removal and rerunning of the drill string, it is costly, time-consuming, and risks damage to the wellbore.

In light of these issues there is a need for downhole power generation system for supplying electrical power to downhole equipment.

DETAILED DESCRIPTION

The present disclosure relates generally to wellbore operations and, more particularly, to downhole drilling motors with integrated electrical generators.

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 in any type of subterranean formation. Embodiments may be applicable to injection wells as well as production wells, including hydrocarbon wells. Devices and methods in accordance with certain embodiments may be used in one or more of wireline, measurement-while-drilling (MWD) logging-while-drilling (LWD) operations and well bore drilling and reaming tools.

FIG. 1depicts a conventional downhole drilling system100including a drill rig102, a drill string104and a positive displacement motor (PDM)106coupled to a drill bit108. PDM106forms part of a collection of downhole tools, equipment, and components disposed at the end of the drill string104and commonly referred to as the bottomhole assembly (BHA).

The PDM106generally includes a hydraulic drive110, a bent housing112for steering the PDM106, a bearing pack114, and a drive shaft116coupled to the drill bit108. During operation, drilling fluid is pumped from the rig102into the drill string104. The hydraulic drive110converts the hydraulic energy of the pressurized drilling fluid into torsional and rotational energy that is transmitted by the driveshaft116to the drill bit108. The drill bit108is forced into the formation by the weight of the drill string104, commonly referred to as weight-on-bit (WOB), so that as the drill bit108is rotated, it removes material from the formation, creating a wellbore118. The drilling fluid sent through the drill string104exits from ports in the drill hit108and returns to the surface via an annulus120defined by the wellbore118and the drill string104. In addition to powering the hydraulic drive110, the drilling fluid cools the various BHA components and carries formation cuttings to the surface.

As depicted inFIG. 2, a PDM200includes a hydraulic drive202. The hydraulic drive202is a progressing cavity drive that includes a helically lobed rotor204disposed within a stator206. When installed, the rotor204is eccentric relative to the stator206. Because of this eccentricity, a universal joint, constant-velocity (CV) joint, or similar joint capable of negating the eccentric motion of the rotor204may be used to couple the rotor204to the drive shaft. In accordance with conventional progressing cavity drives, the helically lobed rotor204is typically a metallic material and may be plated with chrome or a similar wear or corrosion resistant coating. The stator206is also commonly created from a metallic tube lined with a helically lobed elastomeric insert208.

The rotor204defines a set of rotor lobes that intermesh with a set of stator lobes defined by the stator206and the elastomeric insert208. The rotor204typically has one fewer lobe than the stator206such that when the rotor204is assembled with the stator206a series of cavities are formed between the rotor204and the stator206. Each cavity is sealed from adjacent cavities by interference seals formed between the elastomeric insert208and the rotor204.

During operation of the hydraulic drive202, drilling fluid is pumped under pressure into one end of the hydraulic drive where it fills a first set of cavities between the stator206and the rotor204. A pressure differential across adjacent cavities forces the rotor204to rotate relative to the stator206. As the rotor204rotates inside the stator206, adjacent cavities are opened and filled with fluid. As this rotation and filling process repeats in a continuous manner, the fluid flows progressively down the length of the hydraulic drive202, and continues to drive the rotation of the rotor204.

Progressing cavity drives, such as hydraulic drive202, typically have an operational range limited by flow and pressure. If pressure or flow is too low, the forces generated by the fluid may not be sufficient to turn the rotor. On the other hand, if pressure or flow is too high, the seals between the stator and rotor may be overcome, causing the motor to stall and potentially damaging components of the PDM.

The demand for drilling fluid during drilling operations may exceed the operational range of the hydraulic drive. For example, optimum cooling of drilling components or optimum cleaning of the wellbore may require a constant flow of drilling fluid beyond the operational range. In other instances, the heightened fluid demand may be intermittent, such as an occasional increase in fluid to perform a sweep of the wellbore.

To prevent damage to the hydraulic drive202due to drilling fluid demand that exceeds the operational range of the hydraulic drive202, the hydraulic drive202may include one or more bypasses. Bypasses provide additional flow paths for drilling fluid, thereby reducing the flow and pressure within the hydraulic drive202and avoiding potential stalls. A bypass may provide a flow path that circumvents the hydraulic drive completely or, as depicted inFIG. 2, a bypass bore214may run through the center of the helically lobed rotor204.

In embodiments discussed in more detail below, the fluid flow or mass flow through the bypass bore214drives a generator for generating electrical power for downhole equipment. In other embodiments, the bypass bore214or a partial bore in the rotor provides a location for generators that produce power based on movement of the rotor204including such as shock loads, vibrations, and changes in acceleration.

One embodiment for generating power from flow through a bypass bore is depicted inFIG. 3.FIG. 3shows a hydraulic drive300including a primary stator302and a primary rotor304. A bypass bore306runs through the primary rotor304and provides a flow path for drilling fluids. Disposed within the bypass bore306is a drive used to convert the fluid flow into mechanical energy. Specifically, the drive is a turbine308which converts the fluid flow into rotational energy. For purposes of this embodiment, the turbine308may be a reaction turbine, an impulse turbine, or a design with characteristics of both reaction and impulse turbines. Similarly, the number and design of the turbine's blades or “buckets” may vary.

As fluid flows through the bypass bore306, the turbine308rotates, turning a shaft310. The shaft310in turn drives a generator312which converts the rotation of the shaft310into electrical energy. The generator312generally includes a generator rotor318and a generator stator320, rotation of the rotor318within the stator320causing power to be generated by the generator312.

The characteristics of the generator312may vary. For example, the number of generator poles and windings may be varied based on the specific power generation needs of a given application. In addition, various magnetic fields required for operation of the generator may be created by one or more permanent magnets or electromagnets, or a combination of permanent and electromagnets.

FIG. 3also includes a nozzle314for regulating flow through the bypass bore306. In any embodiment, the nozzle314may be a jet nozzle for increasing the velocity of the drilling fluid as it enters the bypass bore306. Alternatively, the nozzle may act as a restrictor, limiting the amount of flow through the bypass bore306and ensuring that sufficient flow and pressure are achieved between the primary rotor304and primary stator302for operation of the hydraulic drive300.

Although nozzle314is depicted inFIG. 3as a static jet nozzle, the nozzle may be variable and capable of dynamically changing the amount of fluid permitted to flow through the bypass bore306. For example, in some embodiments, the nozzle may include a spring-biased valve that remains closed until sufficient hydrostatic pressure to operate the hydraulic drive is achieved. Examples of spring-based nozzles that may be used to control flow through the bypass bore can be found in U.S. Pat. No. 7,757,781 to Hay et al. In addition to spring-based nozzles, the nozzle may be electrically or hydraulically actuated and may use power generated by the generator312for actuation and control.

FIG. 4depicts a hydraulic drive400in which the means for converting the fluid flow into mechanical energy is an impeller408. Similar to the previous turbine embodiment, the impeller408converts energy from fluid flowing through the hydraulic drive into rotational energy and can be any suitable impeller design known in the art. Hydraulic drive400also includes a generator412.

As depicted inFIG. 4, the generator412may be a self-contained generator with the generator stator and rotor enclosed in a housing. Alternatively, as previously depicted inFIG. 3, the generator312may be configured such that the generator stator320is mounted on an inside surface of the primary rotor304.

FIG. 5A-Bdepict another embodiment of a hydraulic drive500in which a secondary progressing cavity drive508is disposed within the primary rotor504and drives a generator520. The secondary progressing cavity drive508includes a secondary helically lobed rotor512and a secondary stator510. In the embodiment depicted inFIG. 5A, the secondary stator510is an elastomer stator having an internal surface with a series of helical lobes. In another embodiment depicted inFIG. 5B, a secondary stator514is formed by applying an elastomer layer to a base structure. The elastomer layer and base structure combine to create an internal surface with a series of helical lobes. The base structure may be formed as part of the primary rotor504or may be a separate component inserted into the primary rotor504.

InFIGS. 5A-B, the secondary helically lobed rotor512is disposed within the secondary stator510,514forming cavities between the lobes of the secondary stator and the secondary rotor512. As drilling fluid enters the hydraulic drive500, the fluid flows through the passages between the secondary stator510,514and the secondary rotor512, rotating the secondary rotor relative to secondary stator510,514and driving the generator520.

The above embodiments are intended only to illustrate some structures suitable as drives for a generator. Embodiments may include any drive suitable for converting the energy of the fluid flowing through the primary rotor bore into mechanical energy for running an electrical generator. Although the above embodiments each include drives that rotate about an axis substantially parallel to a longitudinal axis of the rotor and bypass, other embodiments may include arrangements in which the axis of rotation of the drive is substantially perpendicular to the longitudinal axis. By way of example, such embodiments may include drives based on vane motors, gear motors, or peristaltic motors.

Embodiments may also include generators that rely on reciprocating motion instead of rotational motion to generate electricity. For example, the generator may include a magnet that reciprocates through a wire coil to generate electricity. To obtain linear motion for the generator, a drive based on a linear reciprocating piston pump or rotating barrel-cam design may be used.

Electricity may also be generated by converting the kinetic energy of the flowing fluid into electrical energy by way of the piezoelectric effect. Piezoelectric materials produce electric charge when stress is applied to them and may be used in a device to produce electrical power from a flowing fluid. Specifically, the flowing fluid may be diverted to apply varying threes to a piezoelectric member, thereby generating electricity. One such device that may be used in an embodiment of the present invention is described in U.S. Pat. No. 6,011,346 to Buchanan et al.

In other embodiments, power may be generated by using magnetorestrictive materials. When strain is induced in a magnetorestrictive material, a corresponding change in a magnetic field about the material occurs. The change of the magnetic field can then be used to induce current in a conductor, producing electricity. One such device that may be incorporated into an embodiment of the present invention is described in PCT/US Application No. 2012/027898 to Hay, et al.

FIG. 6is a schematic illustration of a hydraulic drive600in which electrical energy is produced by harnessing the kinetic energy of the hydraulic drive600. During drilling operations, the hydraulic drive600experiences forces in the form of shock loading and vibrations due to, among other things, interactions between the drill bit and formation, interactions between the BHA and the formation, and operation of other downhole drilling tools. The hydraulic drive600may also experience periods of acceleration or deceleration due to changes in formation resistance, changes in the flow rate of drilling fluid, changes to the drill string rotational speed, and other factors.

To harness changes in the movement of the drive600caused by these forces, a kinetic generator612may be disposed within the hydraulic drive600. The kinetic generator612is coupled to the hydraulic drive600such that at least some of the forces experienced by the hydraulic drive600are transmitted to the kinetic generator612. The kinetic generator612may include a flywheel, oscillating weight, cantilevered beam, or other structure that moves in response to forces experienced by the hydraulic drive600and that in turn is used to drive the kinetic generator612.

The electrical power produced by the various embodiments in this disclosure may be used to power various tools and downhole equipment. The following examples are not intended to limit the scope of this disclosure, but are only meant to illustrate some of the wide range of downhole equipment that may be powered using the system disclosed herein. In any embodiment, the electrical power may be used to power sensors for measuring parameters of the drilling unit such as WOB, drill bit revolutions-per-minute, torque, differential pressures between various components, and vibration or shock. The electrical power may also be used for measuring parameters of the wellbore or formation such as pressure, temperature, or resistivity, or to actuate pieces of downhole equipment such as control valves or ports.

Any embodiment may include power electronics for processing the generated power to meet the specific power requirements of the downhole equipment. For example, the power electronics may include a rectifier for converting alternating current to direct current. The power electronics may also include one or more regulators or transformers for regulating or modifying voltage. A battery or other power storage medium for storing the generated power may also be included to provide backup up power or power for use when the drilling motor is not in operation. The power electronics may be located within the rotor. For example, power electronics package316inFIG. 3is shown as being located within rotor304. In other embodiments, the power electronics may be located in a different section of the PDM or BHA and electrically connected to the in-rotor generator.

Although numerous characteristics and advantages of embodiments of the present invention have been set forth in the foregoing description and accompanying figures, this description is illustrative only. Changes to details regarding structure and arrangement that are not specifically included in this description may nevertheless be within the full extent indicated by the claims.