ESP Variable Speed Drive for Wellhead Flowline Overpressure Protection
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Solution Overview
Problem
Conventional safety systems for wellhead flowlines pressurized by downhole electric submersible pumps struggle to perform fully automated proof-testing and fault diagnostics without interrupting production, relying on manual methods and requiring significant manpower, especially when dealing with high wellhead shut-in pressures exceeding 3000 psi.
Innovation Solution
A wellhead control system utilizing an ESP variable speed drive controller in conjunction with a safety logic solver and a surface emergency isolation valve, which monitors flowline pressure and adjusts the pump speed to maintain safe pressure limits during testing, enabling automated functional testing and diagnostics without shutting down the ESP.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional mechanical protection systems with thick-walled pipe are used to withstand high ESP blocked discharge pressure, then the pipeline can contain the fully-blocked pressure, but the system becomes impractical and economically unviable
Solution Approach 1:
The invention applies dynamic control by using a variable speed drive (VSD) on the ESP to actively adjust pump speed in response to flowline pressure conditions. When a blockage is detected or anticipated, the VSD reduces or stops pump operation before dangerous pressures develop, replacing the need for static over-engineered piping with dynamic operational control.
Solution Approach 2:
The system changes the operational parameters of the ESP by controlling speed and power output based on real-time pressure monitoring. The VSD modifies the pump's discharge pressure parameter dynamically, maintaining it within safe limits for the thinner-walled piping while still achieving adequate production flow rates under normal conditions.
2Ease of manufacture
If continuous monitoring and automated control systems are implemented to prevent overpressure, then safe operation can be maintained with thinner-walled pipe, but the system complexity increases
Solution Approach 1:
The variable speed drive controller performs multiple functions: it controls ESP speed for optimal production, monitors flowline pressure conditions, detects blockages, and executes safety shutdown sequences. This multi-functionality reduces the need for separate dedicated safety devices while achieving the same protective effect.
Solution Approach 2:
The system implements continuous feedback control where pressure sensors monitor flowline conditions and relay information to the VSD controller, which adjusts pump speed accordingly. This closed-loop feedback mechanism automatically maintains pressure within safe limits without requiring complex manual intervention systems.
3Reliability
If manual testing methods are used for safety system verification, then comprehensive testing can be performed, but significant manpower and time are required
Solution Approach 1:
The safety system performs self-verification through automated diagnostic routines that continuously monitor component functionality. The VSD controller automatically tests pressure sensor accuracy, valve response times, and control signal integrity without requiring external manual testing, enabling the system to verify its own safety functions during normal operation.
Solution Approach 2:
Instead of periodic manual testing that interrupts production, the system continuously monitors and verifies safety functions during normal operation. Pressure monitoring, sensor validation, and control system checks occur continuously, eliminating the need for separate testing periods while maintaining uninterrupted production.
4Productivity
If the ESP operates at high pressure to maintain production flow, then oil/gas can be lifted to surface, but the risk of overpressure in downstream flowlines increases
Solution Approach 1:
The VSD dynamically adjusts ESP operating parameters based on real-time flowline pressure conditions. When downstream blockages or pressure buildup are detected, the controller automatically reduces pump speed or shuts down the motor, preventing overpressure while maintaining optimal production rates during normal conditions.
Solution Approach 2:
The variable speed drive controller acts as an intermediary between the ESP and the flowline system, mediating the pressure transmission. It controls the energy transfer from the motor to the pump, adjusting it to match downstream capacity and prevent harmful pressure buildup while still enabling effective oil/gas lifting.
Data Source
AI summary
An ESP variable speed drive controller functions in conjunction with a safety logic solver, dedicated pressure sensors and a surface emergency isolation valve, or safety shut-off valve (SSV), to perform a full functional test of the complete wellhead flowline system. The method includes the step of using a plurality of pressure transmitters to monitor the flowline pressure during normal operations and during a full stroke test of the safety shutoff valve and adjusting the speed of the downhole ESP during the test to maintain the pipeline pressure within predetermined safe pressure limits. This wellhead flowline protection system and method utilizes the downhole ESP speed controller and an SSV to ensure that dangerous pressure levels are not reached and provides for full functional safety testing of the wellhead system. The ESP motor speed controller is used to permit functional testing and remove the pressure source from protected downstream flowline piping.