Why electric submersible pump (ESP) optimisation starts with motor control

Electrical Submersible Pumps (ESPs) are a key element in the artificial lift systems used to increase the flow of fluids from oil wells when natural reservoir pressure is insufficient. This is a dynamic application, not a steady-state load, unlike standard industrial processes. ESP systems operate under continuously changing conditions including declining reservoir pressure, variable gas content, producing solids, changing fluid properties, and eventually fluctuating load demand. The pump motor is required to operate across a wide range of speeds and loads, often under unstable conditions. From the perspective of the variable speed drive (VSD) that controls the motor, the challenge is clear – delivering consistent performance in an inconsistent environment.

Motor control defines system stability in ESP applications. The drive is more than a speed control device; its embedded control logic determines smooth start and acceleration behavior, stable operation during load variations, response to supply and load disturbances, process changes and balance between protection and production continuity. Application-specific control programs are designed to improve usability, enhance safe operation, protect equipment, and support production optimisation, all based on accumulated field experience.

Permanent magnet (PM) motors are being increasingly adopted in ESP applications to improve efficiency and performance. This presents challenges related to precise and robust startup, synchronisation, efficiency, management of regenerative behavior during backspin conditions and stable control across varying operating conditions, which requires advanced drive control. Industry developments confirm that successful implementation of PM motors depends not only on the motor itself, but on robust control, monitoring, and protection.

The backspin challenge

Backspin occurs when the pump stops and the fluid column drives the system into reverse rotation. Several factors influence the magnitude of ESP backspin torque and the resulting rotational speed. These include reservoir and well conditions, the fluid properties, the height, and load of the fluid column, as well as the design and construction of the pump itself. Together, these variables define how the ESP system behaves during shutdown and how aggressively it may rotate in reverse, which in turn directly impacts the complexity and risk associated with restarting the ESP safely.

For the ESP system this is not simply a transient event. It introduces uncontrolled reverse motion, mechanical stress on the downhole equipment, and significant uncertainty during restart. In practice, improper handling of backspin can lead to unstable restarts, increased wear of mechanical components, and a higher probability of trips and shutdowns. The situation becomes particularly critical when attempting to restart the ESP while it is still rotating in reverse.

Backspin is not only a mechanical phenomenon, but a critical motor control challenge. The drive must be able to detect the rotational condition of the motor, prevent unsafe restart attempts, and manage controlled synchronisation before torque is applied. Ensuring that the restart occurs under stable and controlled conditions is essential, not only to protect the equipment, but also to maintain production continuity.

Under certain conditions, the backspin duration can be significantly extended, leading to increased non-productive time. Waiting for the fluid column to naturally descend before restarting is neither efficient nor practical. This makes the ability to safely start the ESP while it is still in a backspin condition not just an option, but a necessity.

Restarting and underload

ESP systems can experience difficulties in sustaining operations or achieving a successful restart due to downhole mechanical challenges. This is often caused by solids present in the fluid, or harsh operating conditions, which can increase torque demand and eventually lead to a full stall if the pump becomes stuck or triggers an overload trip. In such situations, restarting the ESP is no longer a straightforward process.

Instead, preparing the system for a successful restart requires dedicated motor control capabilities within the drive, including specific functions designed to release the pump in a controlled manner. Managing this recovery phase effectively is essential to restore operation while minimising additional mechanical stress and avoiding repeated trip conditions.

In contrast, ESP operation under underload conditions presents a different set of challenges that can also impact system performance, efficiency, and reliability. It can negatively affect downhole pump and motor cooling efficiency, as the motor relies on fluid flow for proper heat dissipation. In addition, persistent underload conditions may indicate mechanical issues such as broken shafts or partial loss of pump stages, which can lead to long-term degradation or permanent failure if not properly addressed.

Gas locks

Not all underload scenarios are associated with mechanical failure. In many wells, particularly those with high gas content, gas locks can significantly affect ESP performance and create underload conditions. This is especially evident in installations where gas separation or handling equipment is limited or not present. In such cases, the pump may lose its ability to effectively lift fluid, resulting in unstable operation and reduced production efficiency.

Tracking and managing these conditions requires advanced motor control capabilities within the drive to continuously monitor operating parameters and adapt motor behaviour accordingly. This enables the drive to support the ESP in overcoming gas lock conditions and maintaining stable operation.

Advanced application-specific control solutions

To address the evolving requirements in ESP applications, motor control solutions have progressively moved from generic control approaches toward application-driven solutions, incorporating dedicated functionalities tailored specifically for ESP systems. One example is the Submersible Motor Control Program (SMC) implemented within ABB’s ACS880 drive platform.

At its core, SMC is focused on delivering application-oriented motor control that ensures stable performance across a wide operating range while integrating protection functions that are closely aligned with actual process conditions. At the same time, it supports a simplified and robust system architecture, reducing overall complexity without compromising performance or reliability. Key application-driven functions with SMC include:

• Kick-start & acceleration assistance: this uses current-boost-based start functions to provide sufficient torque for the PM motor at low speeds, enabling reliable startup and smooth acceleration under high load conditions without losing synchronisation.
• Energy optimiser mode: this automatically optimises motor current using a Maximum-Torque-Per-Ampere (MTPA) approach, improving power factor and energy efficiency especially at partial loads compared to conventional scalar control.
• Backspin speed observer: a sensor-less observer detects motor speed and direction during backspin, enabling safe startup by avoiding operation against reverse rotation. This prevents torque reversal, reduces the risk of trips, and minimises mechanical stress.
• Flying start: this allows the ESP to restart in a backspin condition by synchronising with the motor’s speed and direction. This ensures smooth restart in the correct direction while avoiding mechanical stress and high inrush currents.
• Pump impeller cleaning: controlled motion sequences are applied to safely remove solids buildup in pump stages, restoring performance while reducing the risk of stall, instability, mechanical failure, and downtime.
• Gas lock and underload protection: the SMC detects gas lock conditions and dynamically adapts motor behaviour to restore flow, stabilising operation and reducing manual intervention in gas wells.
• Production optimisation (PID control): built-in PID control continuously adjusts the motor speed based on process feedback, maintaining optimal operating conditions and maximising production efficiency.

• Automatic restart: this function enables the ESP to recover quickly from transient trips by automatically restarting the drive under actual operating conditions.

Intelligent motor control makes the difference

Through intelligent motor control it is possible to transform ESP challenges into controllable outcomes that define stability, protection and performance in dynamic oilfield conditions.

Click here for more information about ABB’s artificial lift solutions.

Author bio

Motaz Hassan has over 22 years of experience in the oil and gas industry, Artificial Lift. He is passionate about driving innovation and business growth through Artificial Lift Systems, Variable Speed Drives (VSD), Automation, Motors, and Controls.

Currently serving as Global Application Manager – Artificial Lift Solutions at ABB, he leads global application strategies, portfolio development, technical sales support, and business development initiatives focused on delivering value to oil operators, OEMs, and industry partners worldwide.

Read the article online at: https://www.oilfieldtechnology.com/special-reports/01092026/why-electric-submersible-pump-esp-optimisation-starts-with-motor-control/