Multi-Well Pad Control: RTUs vs. PLCs

Multi-Well Pad Control: RTUs vs. PLCs

Compared to RTUs, PLCs can better help reduce installation, operating and maintenance costs and handle scalable architectures required by modern well pads.

By Zack Munk, Onshore Upstream Oil & Gas business development manager, Rockwell Automation

The world’s annual energy consumption of oil and gas is projected to increase steadily from less than 200 quadrillion BTU in 2015 to nearly 250 quadrillion BTU by 2040, according to projections from the U.S. Energy Information Administration.

With demand continuing to grow, oil and gas producers will need to find new and better ways to capture energy resources. And they must do so while managing financial factors, such as dynamic pricing and production costs.

The most successful upstream producers likely will be those that embrace new technologies.

One area in which this success already is occurring is in the upstream segment of the oil and gas industry. Operators are shifting from simplistic, vertically drilled, single-well pad fields to laterally drilled, multi-well pads. These multi-well pads typically consist of anywhere from four to 12 wells, although some operators are reaching as many as 32 and even 52 wells on just one pad.

These advancements have increased efficiency in upstream production, particularly in unconventional areas. But they also place greater demands on well pad control systems. As a result, oil and gas operators, as well as their equipment suppliers, must reconsider their control-system approach for multi-well pad operations.

Control Options

For decades, the remote terminal unit (RTU) was the best control technology that could be implemented in upstream oil and gas production. It was rugged and power-conservative, and could handle the lower-bandwidth communication networks between the SCADA and the production site.

Increasingly, however, oil and gas producers have demanded more from their RTUs. And we’ve reached a point at which the modern multi-well pad, with dozens of wells per site, has pushed the limits of RTU technology to its capacity. Producers now are seeking a better solution to help them be more efficient and reduce costs.

View this free on-demand webinar from Rockwell Automation, “Rethink Your Approach to Well Pad Automation,” to learn how to increase reliability and reduce time to market.

An alternative to the RTU is the programmable logic controller (PLC). These controllers are modular and scalable and can handle a variety of communications and application support.

PLCs traditionally have not been built for inhospitable and harsh environments. They also are not a low-power-consumption device. However, modern well pads have environmentally controlled buildings and utility or generator power. This creates an ideal environment for PLCs.

Demands Exceeding Capabilities

The greater control and data-acquisition demands required in current multi-well pads now are exceeding RTUs’ capabilities. As a result, multiple RTUs often are required on these well sites to control and optimize asset performance.

Upstream producers have had success with multiple-RTU implementations, but they also have encountered challenges. For instance, multiple RTUs require oil and gas producers to maintain multiple application configurations and programs, and they must manage the communications of many RTUs on one site.

Oil and gas production workers also must have the required training and expertise to support multiple vendors’ hardware in multiple-RTU implementations. While some producers are fully staffed with the trained personnel needed to handle system maintenance, many aren’t. These producers must rely on either manufacturer support or contract-engineering support to maintain their control systems, resulting in additional maintenance overhead.

Another key challenge is “black box” RTUs. These systems are designed with specific inputs to control specific outputs. This limits flexibility for changing or upgrading systems. As a result, an oil and gas producer needs to either work with a vendor to make a change or simply keep the system as is, settling for the fact that it will not meet requirements.

Modular and Scalable

A modular and scalable PLC control architecture can address the challenges experienced with RTUs.

A modular system design means that PLCs can be configured in many different ways. This permits oil and gas operators to monitor and control a variety of field instruments. A modular PLC also supports communications for many different network types.

From a scalability standpoint, PLCs offer libraries of predeveloped and documented code that can be added quickly, as well as predeveloped upstream oil and gas libraries that can be configured on-site. This minimizes the need for a technician with specialized expertise to write new code when hardware is added. Instead, operators need only set up and configure the required data from the HMI to commission the equipment.

Remote I/O functionality is another key component of a PLC’s scalability. PLCs that offer native remote I/O functionality can save on installation costs compared to RTUs. Additionally, equipment skids can come with pre-mounted and wired I/O and instruments, making startup as simple as plugging an Ethernet cable into a switch and configuring the I/O in the controller.

Programming in the PLC environment allows program changes and the addition of I/O without needing to shut down the process. Such online editing capabilities are not available in traditional RTUs. Instead, RTUs must be taken offline to accept the changes. Such downtime is unacceptable in a modern, multi-well pad environment because it results in lost production.

In addition to online editing, PLCs can include hot-swappable hardware modules. For example, if an I/O module fails or if technicians need to add a module to a remote I/O rack, they can simply plug the module in and configure the I/O for control.

Attractive Alternative

Multi-well pads have made data and application requirements in upstream operations greater than ever. RTUs remain a feasible option, but their memory limitations, added maintenance requirements and overall higher production costs provide a strong incentive for operators to consider a better alternative.

Modular and scalable PLCs can handle the scalable architectures required by modern well pads. They also are more efficient and can help reduce installation, operating and maintenance costs.

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