Compelling factors for incorporating power automation in oilfield operations extend beyond reducing generator fuel consumption and lowering emissions. Generators powering artificial lift systems, primarily rod pumps, idle for prolonged periods due to intermittent pump cycles. Besides the inefficiencies resulting from this practice, its impact on an oil and gas operator’s ability to comply with Environmental Protection Agency (EPA)-mandated Tier 4 diesel engine emissions limits cannot be understated. Moreover, prolonged idling could expose generators to the two leading causes of failures, plugging and carbon deposit buildup.

Smoothing power fluctuations

Power automation and power-on-demand technology has been applied in various commercial and industrial processes with intermittent loads or where standby generators are needed to ensure uninterrupted power, such as hospitals. Power automation is delivering the oil field significant cost reductions in rod pump and dewatering service operations. Scalable power automation systems incorporate a hybrid battery control kit that receives a signal from the pump’s programmable logic controller (PLC) for start/stop synchronization. The automation kits also can receive signals from tank level switches, thermostat contacts and any other digital switches. Power automation systems can be found running on diesel engine-generators (gensets) in the Eagle Ford Shale and Permian Basin.

Compared to other oil fields, the high-viscosity crude produced from the Eagle Ford is better suited to lower horsepower rod pumps, requiring relatively small genset drivers with simplified battery requirements. In some instances the operator is running the rod pumps continuously on a variable speed drive or variable frequency drive (VFD) to avoid operational fluctuations. Instead of shutting down the rod pumps, the VFDs are used to minimize pump rpm from about 30 rpm to 2 rpm. This strategy helps avoid engine idling and save fuel costs to a certain extent, particularly when crude demand is low.

By eliminating idling, emissions and diesel consumption can be reduced by as much as 60%, as demonstrated with a midstream operator’s 200-hp positive displacement booster pump moving produced oil from the field by pipeline to gathering facilities. In this application a power automation package allowed the PLC on the booster pump to communicate with the generator and to automatically start/stop the power as needed. Since the booster pump only needed power about 10% of the time, the pump and the generator remained off 90% of the time.

A major producer in the Permian Basin also significantly reduced idling employing power automation. In this case diesel generators were running 24/7 and idling most of the time while serving five wells with 40-hp rod pumps operating intermittently. Formation hydrogen sulfide levels were too high at the well sites to consider using field-gas-driven generators economically. Because the producer’s goal was to reduce overall lease operating expenses, the power automation option was considered. In this instance five 60-KW diesel generators with power automation kits resulted in a $13,000-per-pump savings over a six-month span. This actually reduced annual diesel costs by 50%, or $130,000, for these five sites. Emissions also were reduced more than 50% while maximizing uptime and extending genset maintenance schedules.

Nominal loading

Upon closer examination load fluctuations seen in oilfield operations can cause generators, which are made to be loaded, to be loaded at about 50% nominal, for example, part of the day (eight to 10 hours) and less than 1% for the remainder of the day. This is a typical scenario where the operator can benefit from power automation. In other scenarios, maximum load pulling off a rod pump control panel is seen at about 1.5 amps and 120 volts. However, if there is a need to increase to 25 amps at 120 volts, there are batteries available that can scale to accomplish the increase.

Scalability is an important consideration with the evolving trend toward centralized facilities, such as with the batteries needed with gensets supporting multiple wells. In fact, power-on-demand systems are being developed for centralized tank sites supporting as many as 250 wells, requiring high startup amperage (e.g., 1,250 KW) provided by multiple gensets (e.g., five 250-KW generators). These generators are more efficient if only one is optimally loaded after a high-amperage startup and the other four are shut down rather than idling after pumping operations level out. Generators need to run at a higher load percentage; idling at low loads for long periods predicates carbon buildup and resulting emissions.

Generators used for peak shaving in oilfield operations are another compelling reason for incorporating power on demand, such as for efficiently running four generators during peak time (e.g., two hours). After peak time the other three generators are shut off while the primary generator is still running. Even the primary generator can be turned off with power drawn from battery storage. This strategy permits “hour sharing” to balance the engine hours, running the unit with the least amount of hours, prolonging engine life and reducing maintenance costs.

Mandates affecting operations Going forward, emissions reduction requirements are becoming one of the most important drivers to installing power automation. EPA-mandated Tier 4 standards require significant emissions reduction of particulate matter and nitrogen oxides. These standards govern most diesel engines used in power generation, including standby generators used intermittently and installed or located at a production site for at least 12 months. An important aspect to consider with Tier 4 is engine manufacturer’s minimum load requirements to maintain emissions. Under older Tier 3 requirements elimination of idling was merely a cost reduction option.

Considering engine inefficiencies typical of oil and gas operations, Tier 4 regeneration predicates the need to significantly reduce idling time, which is where the benefits of power automation can be realized. The industry has certainly embraced oilfield automation to reduce costs. Future applications benefiting from power automation and power on demand include transfer pumps serving tank facilities and dewatering systems. A first-time application for power automation on field-gasdriven generators in the Eagle Ford will soon go online.

Efficient options

The evolution of oilfield automation is occurring as more production operations take place outside the utility grid, predicating the need for temporary power solutions. Power companies are reluctant to build out distribution networks from their substations to new or extended oil fields because investment recovery becomes riskier at lower oil prices. For example, the utility company’s return on investment isn’t justified to make 20 MW of power available when the operator uses 2 MW for only a short period of time. Against this backdrop, automated remote power solutions are a practical option that adopts well to cost-cutting initiatives. With other automation assets like remote monitoring and PLCs on pumpjacks already commonplace in the oil field, added enhancements such as power on demand and power automation are a feasible solution for one generator or multiple generator configurations.