Saltwater has long been a byproduct of oilfield production. With the dramatic increase in unconventional plays, water management has become a significant element in oilfield economics. Fracking jobs in unconventional plays routinely put ten times as much fluid downhole as were used in conventional plays. As much as 250,000 barrels of fluid is used during completion for each well.

Saltwater and associated wastewater flows from the well as flowback and produced water. The flowback is often high volume, but varies greatly by play and even by well. It occurs during the first few weeks and months following the frack job and can be as much as 40% of the initial volume—100,000 barrels! Produced fluids flow from the formation along with hydrocarbons throughout the life of the well.

Managing well-related water

Operators are employing increasingly sophisticated management systems for fluids flowing to and from wells. The high volumes required demand reliable, consistent transport from source to well site, plus local storage and transport to well. Operators must keep careful control of the movement of fluid, particularly if it is brackish water. Tank overflows, pump failures and pipeline leaks are all unacceptable.

Fluid flowing from the well must be even more diligently managed. This fluid is typically a combination of saltwater, oil and other contaminants, none of which can be spilled or otherwise mismanaged. Operators have gone to great lengths to ensure safe and controlled saltwater disposal facilities.

Initially, these disposal facilities were focused on moving fluid from the well, through holding tanks and into the ground. Now many of them are introducing additional tank batteries for separating oil, water and contaminants. Efficient management and operational oversight is imperative.

Distributed pump control

Pumps are key components of saltwater disposal facilities, because they are the mechanism that moves the fluid between holding areas, to treatment when available and to disposal. Controlling all the pumps on site so that they work in concert is critical. So too is managing all the sensor data revealing pressures, tank  levels, flow, and motor conditions. Operators cannot afford to have tanks overflow or spill, and they need to be most efficient.

Saltwater disposal facilities commonly deploy a pump for every tank and a simple drive for every pump. One centralized PLC is then used to monitor and control all the equipment. This single interface to facility operations is a good thing, but it lacks a secondary strategy for managing individual pumps for general efficiency and in case of central failure.

If a fuse is blown or the PLC fails, the site is either down or running in hand, requiring constant intervention. This increases cost, reduces efficiency and can incur safety violations if your safeties are not set up for work in hand.

A better way to configure pump management is to put the logic and decision making where it makes sense. A 3 pump configuration should have 3 drives with built-in logic to control and protect their associated pump. A master panel then monitors and controls site conditions such as oil tank levels, settling tank level, make-up fresh water volume, lead/lag control, run hours and wear sharing. The drives tie into the master using ModBus via RS232, 485 or Ethernet, broadening the options for how you set up the master panel. If the connection to the master is lost, the drive systems can continue to do their jobs independently.

One Pump, One Motor, One Panel

With a distributed system, each pump has an associated motor and control panel. All the safeties and signals tie to that panel, making a complete unit within an overall control system. All field devices terminate in the drives, eliminating thousands of feet of wire. Communications technology makes the data from any panel accessible from wherever it is needed—at the master panel, in the office, or from a pickup down the road.

Saltwater Recycle and Reuse Economics

Some facilities already offer wastewater recycling and reuse. More will be adding these capabilities, due to key economic incentives for improving the separation process prior to disposal:

• Separated oil can be sold. First generation gravity separation yielded perhaps 0.5% oil. Now treatment systems can recover significantly more. A water management company analyzed wastewater at several disposal wells and found 2-4% oil. At $60/barrel, that amounts to $12,000 for every 10,000 barrels of wastewater with 2% oil content.

• Separated water can be reused for new fracking jobs. As much as 80% of the fluid can be reused following treatment, saving the cost of purchase and transport to the well-site.

• Separated contaminants represent a much smaller volume. Disposal wells can service a higher number of production wells as a result.

The addition of these capabilities will only increase the need for surveillance, distributed control and remote monitoring.

HPS Series Drive with Distributed Control

SPOC Automation manufactures drives that are ideally suited for use in saltwater disposal facilities. These self-contained units reduce installation costs, exposure to the elements and the cost of automation failure.

Traditional pump automation has all pump, tank and sensor controls tied to the PLC, which then directs the drive. If the PLC fails, the drive goes blind to the pump environment. Worse, if there are multiple drives controlled by a single PLC, the entire facility goes blind upon PLC failure.

SPOC Automation drive systems come pre-integrated with their own logic systems. In our experience, 80% of all pump automation and control systems use the same 8-10 signals. It is not necessary to reinvent the wheel for every project. By pre-integrating these drives and enabling communications, we can quickly establish a distributed system that can also have a master control unit.

Tank level or pressure control can be used as the control mechanism for the pump. With tank level control, the drive speeds up if the tank level is above setpoint, slows down if below the setpoint and stops if below the minimum level. With pressure control, the unit starts and stops based on tank level settings and regulates itself to the discharge pressure setpoint.

The HPS Series drive provides comprehensive control for disposal applications, controlling H-pumps, triplex and PD pumps. All standard interlocks are built-in, as is standard logic, and historical trending. Our range of drives includes the Regulator, our latest HPS drive for simple disposal applications. Our drives come SCADA ready, enabling authorized users to monitor and control them from  anywhere.