Multi-Plunger Pump Drive Control for Cavitation-Limited Fracturing
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Solution Overview
Problem
Hydraulic fracturing pumps often suffer from cavitation and damage due to operating at speeds above the critical speed, which is exacerbated by diesel-powered transmissions with multiple gears that exceed safe operating limits, leading to inefficiencies and reduced pump rates.
Innovation Solution
Implementing a multi-plunger hydraulic fracturing system powered by electric or hydraulic motors with planetary gear trains and variable frequency drives to maintain pump speeds at or below critical limits, using multiple motors to distribute power and prevent overspeeding, and incorporating speed reduction gearboxes to achieve desired pump rates while minimizing cavitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If diesel-powered transmissions with multiple gears are used to increase pump speed, then pump rate increases, but pump cavitation and damage occur due to operation above critical speed
Solution Approach 1:
The pump system is divided into multiple independent plungers (e.g., 5, 7, or 9 plungers) driven by a common crankshaft. This segmentation allows the pump to maintain high productivity through multiple simultaneous strokes while keeping each plunger's speed within critical limits, preventing cavitation and damage.
Solution Approach 2:
The invention changes the operational parameters by using variable frequency drives to precisely control motor speeds, ensuring operation at or below critical speeds. Additionally, the stroke length and bore sizes are optimized to achieve desired pump rates without exceeding critical plunger speeds, resolving the contradiction between productivity and reliability.
2Productivity
If transmission speed is increased to compensate for offline pumps, then pump rate is maintained, but pump cavitation occurs due to exceeding critical speed
Solution Approach 1:
Variable frequency drives provide precise speed control with feedback mechanisms that monitor and adjust motor speeds to maintain operation at or below critical speeds. This feedback system ensures that even when compensating for offline pumps, the remaining plungers operate within safe speed ranges, preventing cavitation while maintaining productivity.
Solution Approach 2:
The system uses dynamically adjustable stroke lengths and bore sizes that can be optimized for different operating conditions. This dynamic configuration allows the pump to maintain high productivity across varying numbers of operational plungers without exceeding critical speeds, thereby preventing cavitation.
3Reliability
If slower pump speeds are used to prevent cavitation, then pump damage is reduced, but pump rate and efficiency decrease
Solution Approach 1:
Multiple plungers are merged into a single pump system, sharing the total productivity requirement. Each plunger operates at or below critical speed to prevent cavitation, while the combined output of multiple plungers achieves the desired high pump rate, thus maintaining both reliability and productivity.
Solution Approach 2:
The pump system uses composite design elements including optimized bore sizes and stroke lengths that combine to achieve high productivity. The composite configuration of multiple plungers with varying parameters allows the system to operate at lower individual speeds while maintaining high overall pump rates, preventing cavitation without sacrificing productivity.
4Reliability
If multiple electric or hydraulic motors with planetary gear trains are used to control pump speed, then cavitation is prevented, but device complexity increases
Solution Approach 1:
The planetary gear train serves multiple functions: it reduces motor speed to appropriate pump speeds, provides torque multiplication, and enables precise speed control through variable frequency drives. This multi-functionality reduces the need for additional separate components, managing complexity while achieving cavitation prevention.
Solution Approach 2:
Planetary gear trains act as intermediaries between the high-speed motors and the pump mechanism, transforming motor output to appropriate pump speeds. This intermediary mechanism allows the use of high-speed efficient motors while maintaining pump operation below critical speeds, preventing cavitation without directly coupling motors to plungers.
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
This configuration effectively prevents pump cavitation and damage, maintains efficient fluid transfer, and extends the life of pump components by ensuring operation within safe speed ranges, even when compensating for offline pumps, while allowing for slight overspeed as a safety margin.
Implementation Method 1
a planetary gear train having a plurality of input pinion gears in rotational contact with each of the plurality of motors
Implementation Method 2
the formation of vacuum bubbles as a result of fluid being accelerated too fast through the pump. A heightened speed of operation creates low pressure within the pumps, creating vacuum bubbles. As the pump plungers retract, the vacuum bubbles implode, causing damage (cavitation) to the pump and engine systems.
Data Source
AI summary
A hydraulic fracturing system for fracturing a subterranean formation is described according to various embodiments. In an embodiment, the system can include a multi-plunger hydraulic fracturing pump fluidly connected to a well associated with the subterranean formation, the multi-plunger pump configured to pump fluid into a wellbore associated with the well at a high pressure so that the fluid passes from the wellbore into the subterranean formation and fractures the subterranean formation. In an embodiment, a plurality of motors can be positioned to power the multi-plunger pump, and a planetary gear train can have a plurality of pinion gears in rotational contact with each of the plurality of motors. In an embodiment, a gear ratio of the planetary gear train and a speed at which the plurality of motors operates can be selected so as to limit a maximum pump speed associated with the multi-plunger pump.