Positive Displacement Metering System for Oil and Gas Wells
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Solution Overview
Problem
Existing chemical injection systems for oil and gas wells, particularly undersea wells, face challenges with accurate metering and contamination resistance, as they are prone to clogging and require frequent maintenance, especially when dealing with low flow rates and varying fluid properties.
Innovation Solution
A positive displacement fluid metering system that measures the time required for a free piston to move within a cylinder, using a four-way valve to adjust flow rates and incorporate a cleaning cycle to clear obstructions, with a shear seal gate type valve construction for reliable operation with high-pressure, contaminated fluids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If orifice metering is used for flow control, then flow rate adjustment is achieved, but the system becomes subject to clogging and filming
Solution Approach 1:
The patent replaces traditional orifice-based mechanical metering with a positive displacement piston system that uses volumetric displacement to measure and control flow. The piston moves a known volume per stroke, eliminating the need for small orifices that are prone to clogging. Flow rate is controlled by adjusting the number of strokes per minute and the displacement volume, providing reliable operation with contaminated fluids.
Solution Approach 2:
The system changes the fundamental parameter for flow control from pressure-driven orifice flow to positive displacement volumetric flow. By measuring piston stroke volume and frequency, the system achieves flow control without relying on small orifices, thereby maintaining reliability while enabling flow rate adjustment through parameter changes in displacement volume and stroke frequency.
2Measurement precision
If small orifices are used for metering, then precise flow control is achieved, but the system becomes susceptible to clogging from particulate contamination
Solution Approach 1:
The patent replaces orifice-based precision metering with a positive displacement piston system that achieves precision through volumetric measurement. The piston displaces a known volume of fluid per stroke, and flow rate is calculated from stroke volume and frequency. This eliminates small orifices entirely, providing precise metering without susceptibility to particulate clogging.
Solution Approach 2:
The piston acts as an intermediary between the fluid source and the measurement system. Instead of measuring flow through a restrictive orifice that can clog, the piston indirectly measures flow by counting strokes and knowing the displacement volume per stroke. This intermediary mechanism provides precise measurement while being immune to particulate contamination.
3Reliability
If filters are installed in the chemical injection line, then clogging is prevented, but system reliability decreases and maintenance requirements increase
Solution Approach 1:
The patent eliminates the need for filters by replacing orifice-based metering with positive displacement piston metering. Since the system does not rely on small orifices that can clog, filters become unnecessary, reducing system complexity and maintenance requirements while maintaining reliability through the inherently clog-resistant piston mechanism.
4Reliability
If multiple subsea wells require individual injection systems, then each well receives dedicated chemical treatment, but capital costs and system complexity increase
Solution Approach 1:
The patent describes a system where a single chemical injection system with a multi-position valve can serve multiple subsea wells. The valve can be positioned to direct chemical flow to different wells, allowing one injection system to perform the function of multiple dedicated systems. This reduces capital costs and system complexity while maintaining the ability to provide dedicated chemical treatment to each well as needed.
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 system provides precise and reliable flow control, immune to clogging and changes in fluid properties, enabling accurate metering over a wide range of flow rates and reducing maintenance needs, with the ability to measure flow rates from 1 GPD to over 3000 GPD without recalibration.
Implementation Method 1
A positive displacement metering system measures the time required for a free piston (or other fluid barrier) in a cylinder (or other metering body) of known dimensions to move to move a certain distance and thereby determine an average flow rate
Implementation Method 2
The controller selectively adjusts a variable valve opening to adjust flow rate, switch between the first and second positions
Implementation Method 3
with a shear seal gate type valve construction for reliable operation with high-pressure, contaminated fluids
Data Source
AI summary
A positive displacement metering system measures the rate of travel of a free piston in a cylinder of known volume to determine the flow rate of a fluid out of the cylinder. The system may also measure and record the inlet and outlet pressures or the differential pressure between the fluid inlet and outlet. The control program positions a four-way valve which may function as an adjustable metering orifice in response to the measured flow rate and/or changes in the inlet and outlet pressures to achieve the desired flow rate. At the end of each stroke, the four-way valve is repositioned to reverse fluid flow through the metering cylinder. The system may revise the valve position settings for both forward and reverse strokes based on the measured time required for a full stroke of the piston within the cylinder at a certain valve position or a measured rate of movement of the free piston.