Downhole Alternator with Axial Fluid Passage
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Solution Overview
Problem
Existing methods for providing electrical power to downhole drilling instruments face challenges, including unreliable connections with surface power sources, limited battery life, and operational issues with downhole generators in harsh drilling environments.
Innovation Solution
A downhole alternator driven by the rotation of the drillstring or drilling sub, utilizing a rotor of coils and a stator of permanent magnets, which generates AC power without obstructing drilling fluid flow and is sealed to prevent damage, using a counterweight to ensure relative rotation and maintain operational reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a downhole generator is placed in the flow path of drilling fluid to generate power, then electrical power can be generated for downhole instruments, but the generator placement interferes with fluid flow and prevents access to the drillstring below
Solution Approach 1:
The alternator is divided into separate functional components: the stator assembly with magnets is mounted on the drilling sub while the rotor coils are mounted on the drill bit or lower section. This segmentation allows drilling fluid to flow axially through the center of the alternator without obstruction, eliminating the productivity issue while maintaining power generation capability.
Solution Approach 2:
The alternator components are arranged in an axial configuration along the drillstring rather than blocking the flow path radially. The stator and rotor are positioned to allow fluid to pass through the central axis, transforming the spatial arrangement from a flow-blocking configuration to a flow-permeable one, thus resolving the contradiction between power generation and fluid flow.
2Power
If a downhole generator is exposed to abrasive high-pressure drilling fluid, then power can be generated, but the abrasive fluid is destructive to generator moving parts and rotating seals
Solution Approach 1:
The alternator is extracted from the direct path of abrasive drilling fluid by positioning it such that fluid flows through the central axis rather than across the magnetic components. The stator and rotor are configured to minimize exposure to abrasive particles, separating the power generation function from the high-abrasion environment while maintaining operational reliability.
Solution Approach 2:
The alternator incorporates sealed housings and protective barriers that shield the magnetic components and rotating seals from direct contact with abrasive drilling fluid. These protective enclosures allow the alternator to generate power reliably while preventing abrasive particles from damaging moving parts.
3Power
If surface power sources are used with wires or cables extending through the drillstring, then electrical power can be supplied to downhole instruments, but maintaining secure connections at each joint in the rotating drillstring is difficult
Solution Approach 1:
The drillstring itself serves as the power source through the alternator that converts mechanical rotation into electrical power. This self-service approach eliminates the need for external cable connections through the drillstring joints, as each section of the drillstring generates its own power locally through the alternator mounted on the drill bit or lower section.
4Reliability
If downhole batteries are used to power downhole circuitry, then a reliable power source is provided, but the limited battery life requires periodic replacement resulting in costly downtime
Solution Approach 1:
The alternator provides continuous power generation as long as the drillstring rotates during drilling operations. Unlike batteries that deplete and require replacement, the alternator continuously converts mechanical energy from drillstring rotation into electrical power, eliminating the need for periodic battery replacement and associated downtime.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The alternator provides a reliable and long-lasting power source for downhole instruments, capable of powering drilling and telemetry circuitry efficiently, with the option to increase power output by using multiple alternators or a larger counterweight, addressing the limitations of previous power solutions.
Implementation Method 1
an alternator having a rotor made up of a series of coils that are mounted on, and spaced around the circumference of, a rotating drilling sub, and a stator made up of a multiplicity of permanent magnets also spaced around the circumference of the drilling sub... rotation of the sub, either by rotation of the drillstring or by rotation of a drill motor in the drilling sub, produces relative rotation of the rotor and stator to generate an AC electrical output
Implementation Method 2
The stator is mounted on the drilling sub by means of bearings and incorporates a counterweight that holds the rotor relatively stationary with respect to the sub and with respect to the coils
Data Source
AI summary
A downhole source of electrical power for drilling tools is driven by the rotation of a drillstring or, if the drillstring is not rotating, by the rotation of a drilling sub. The source consists of an alternator having a rotor made up of a series of coils that are mounted on, and spaced around the circumference of, a rotating drilling sub, and a stator made up of a multiplicity of permanent magnets also spaced around the circumference of the drilling sub. The stator is mounted on the drilling sub by means of bearings and incorporates a counterweight that holds the rotor relatively stationary with respect to the sub and with respect to the coils, so that rotation of the sub, either by rotation of the drillstring or by rotation of a drill motor in the drilling sub, produces relative rotation of the rotor and stator to generate an AC electrical output. The rotor and stator surround an axial fluid passage through the center of the alternator so that they do not impede the flow of the drilling fluid, and the motor is totally sealed to prevent damage to the bearings. The alternator stator is an annular permanent magnet structure which surrounds the drilling axis, and which may include two sets of rare earth disc magnets spaced axially to form an axial gap, with the counterweight holding the magnets stationary with respect to the alternator coils. The coil structure is also annular and also surrounds the drilling axis, with the coil structure preferably including two sets of offset coils positioned to rotate in the gap between the permanent magnets. The two sets of coils make up a two-phase system; if desired, a single set of coils may be used to provide a single-phase system.