Before Halliburton introduced its Acid on the Fly (AOF) blending system, pre-blended acid product was moved and processed several times, originating from the vendor and moving to a facility storage tank, a blend tank, transport and finally to a job site poly tank for storage. This translated into many round trips to location and multiple transfer points.

“This blend-and-batch method led to the acid being mixed several days before it was pumped in a treatment,” said Leonard Case, Halliburton’s product manager of equipment systems for production enhancement. “After delivery to location and storage in tanks, the blended acid solution would have to be recirculated to ensure that various additives such as the corrosion inhibitor are evenly distributed in the blend. After the treatment, any remaining pre-blended material would then have to be properly disposed of. Corrosion inhibitor has a limited life, so if the job is delayed indefinitely, the entire blend would need to be removed from location and properly disposed of.”

The AOF system helps improve the acidizing process by delivering a precisely controlled acid blend downhole, enabling collection of a blended sample any time during the treatment and allowing modification of the acidizing treatment at any time. In addition, the system improves personnel safety and eliminates disposal issues since unblended materials can be placed back into inventory.

The system’s computer-based monitoring provides quality control and helps ensure the designed acid blend is delivered downhole. The ability to modify the treatment at any time means that if, for example, a problem arises due to hydrofluoric acid creating unexpected formation damage, the treatment can be stopped or the acid blend quickly changed to hydrochloric acid. The computer and electrical system are backed up by manual controls for fail-safe performance.

The system won the stimulation category of Hart Energy’s 2009 Meritorious Awards for Engineering Innovation. Since then, the system has been deployed via mobile units in California and Mexico, and similar technology has been deployed on several of Halliburton’s stimulation vessels operating globally. “The location footprint has been reduced by more than 75%, and spills and location leaks have been reduced because of reduced physical connections required,” Case said. “Blends are freshly blended, reducing prep time with increased quality of the blends and no wasted product.”

Halliburton has made several improvements to the system since its introduction. Using raw acid storage tanks with solar-powered vapor scrubbers modified one blender’s manifold and pumps to handle high pump blending rates into the 20 bbl/min range. A majority of the improvements have targeted increasing the reliability of the components. “An offshore version is now being offered and is currently installed on several stimulation vessels operating globally in areas such as Angola, the Arabian Gulf, the Gulf of Mexico, Hos Saylor and the Falcon Tide,” Case said. “The next Gulf of Mexico boat will also have an acid blender, as will the next stimulation boat for Brazil.”

The system has not been eclipsed by newer technology since its introduction, with the industry appearing to be focusing on materials instead of on advancements in controls, components and overall systems, Case said.

Currently, Halliburton is working to verify real-time cool-down computer models with memory gauges run on actual jobs. “With this information we are confident that once we reach certain injection rates, we can reduce corrosion inhibitor concentrations on the fly, creating savings for the customer while improving well performance,” Case said.

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