A combination of mechanical and chemical processes can alleviate strains on water resources.
by Gabrielle Rogers-Nieman
October 26, 2015

Water is essential to oilfield operations, but limited water resources are making efficient and environmentally conscious water reuse a priority. The current challenges associated with water in the oilfield, are two-fold. Historically, the extraction of shale oil and gas through hydraulic fracturing has employed large amounts of freshwater, rationalizing source abundance and better chemical compatibilities within the bulk fluid. Today, considerable volumes of produced water result from hydraulic fracturing activity and from mature conventional oil and gas wells, which lead to complex transportation logistics and high disposal costs. Therefore, the reuse of produced and flowback water to reduce costs and address freshwater scarcity issues has been an area of increased interest within the industry, but has yet to become the standard practice in all geographical areas.

While cost-effective solutions exist to treat these waters for reuse as an alternative to freshwater, adoption by producers has been slow. Quality of produced water varies over geography as well as during a well's life cycle. Although water treatment is not a new science, reusing produced and fracture flowback water in hydraulic fracturing presents several new challenges.

One company offers water management solutions for surface and subsurface water that enhance hydrocarbon recovery while minimizing water use or production and the associated costs. Combining in-depth reservoir knowledge with decades of experience in downstream water treatment and upstream production chemistry, the company developed services that offer a suite of solutions that treat oilfield produced and flowback water for reuse. The services are designed to reduce the total cost of operations and any potential environmental impact by reducing freshwater volume requirements, truck traffic and disposal costs.

Although water treatment is not a new science, reusing produced and fracture flowback water in hydraulic fracturing presents several new challenges.Image 1. Although water treatment is not a new science, reusing produced and fracture flowback water in hydraulic fracturing presents several new challenges. (Images and graphics courtesy of Baker Hughes Inc.)

Utica Shale Case Study

One area that has experienced a dramatic increase in hydraulic fracturing activity is the Utica shale play, comprised of underlying portions of Ohio, Pennsylvania, West Virginia, New York and Quebec. To address this increase in activity and the additional stress on freshwater resources, state regulations have been put in place to control water withdrawals, as well as the disposal of flowback and produced waters and associated waste streams following hydraulic fracturing. As a result, operators are exploring new and innovative solutions to decrease freshwater use while developing energy resources. One solution is the use of alternate sources for water, such as flowback and produced water or a blend with freshwater.

For example, an operator in the Utica took the lead on environmental stewardship efforts by recycling oilfield wastewater for future completions operations. After a thorough analysis of the water, operator requirements and the task at hand, an oilfield services company designed a combination mechanical and chemical treatment process that efficiently converted the wastewater into an asset that could be reused. The treatment was designed to reduce total iron and bacteria in process waste streams, resulting in quality solids fit for the landfill and effluent water suitable for hydraulic fracturing. The operator owned a 24-hour surface water treatment facility designed to treat produced and flowback water for reuse. The facility allowed the treatment of 5,000 barrels of oilfield wastewater per day for reuse in fracturing operations, thus reducing the volumes of freshwater needed for completions.

A centralized load-in/load-out facility for the treatment of oilfield wastewater had to be implemented. The facility collected produced water, trucked from different active wellsites, that was off-loaded into an influent holding area. The process started with a chemical destabilization for the precipitation of iron. Administration of polymer followed this destabilization, and separation and clarification processes were subsequently used to remove and separate floating impurities from heavy iron precipitate, as well as for hydrocarbon removal. Cleaned produced water was then treated with a biocide as a pretreatment for reduction of bacterial content before trucking to active hydraulic fracturing sites.

Table 1

Real-time monitoring of the treatment processes throughout the facility's footprint was performed to ensure the effective reduction of iron, efficacy of biocide treatment and maintenance of the target pH range. Additionally, treated produced water samples are routinely collected for later complete water analyses in the laboratory. The results were used to provide the operator with technical recommendations on the use of the treated produced water for future drilling and completions work.

However, exorbitant disposal costs for the solid waste generated as a byproduct of the treatment process threatened the economic viability of the facility. The cost for the wet slurry disposal was twice the cost per ton of dry solids at the landfill, not including associated trucking costs. Several attempts to handle the solid waste had proven unsuccessful in removing appreciable wet slurry weight via centrifugation, and a new program was initiated to solidify the remaining volumes to reduce the landfill charge. This tactic addressed the cost associated with the landfill price categorization (wet vs. dry), but the tonnage going to the landfill was nearly the same. The service company looked for a way to remove the water content from the waste slurry to reduce solid waste tonnage by volume, which would reduce the disposal costs to the lower dry solids landfill pricing (cost per ton) and lower the volume of solids.

Introduction of one solids handling process, provided the first means to consistently reduce solid waste tonnage by recapturing water content. Today, more than 98 percent of the water volume from influent waters is being recovered, saving equivalent volumes in freshwater. Following the cleaning of produced waters, with the additional recovery of water resulting from solids processing, the operator has also benefited from the increased water volume that was recovered at no additional cost. With the implementation of this new treatment process, the operator saved more than $830,000 during an eight-month period on the cost per ton and total tonnage of solid waste disposal.

An additional benefit with the new treatment process was the reduction of total oil and grease (TOG) by 86 percent from influent waters (see Table 1). While not part of the original facility's treatment goals, this additional benefit allowed for the removal of low level TOG without changing the non-hazardous classification of the solid waste.

A surface water treatment facility for the recycling and reuse of produce and flowback water that is fully mobile, easy to maneuver and on a compact footprint can provide treatment solutions to be located in close proximity to producing wells and strategically located for upcoming well drilling or completions. This option is an obvious advantage for companies looking to reuse produced water in lieu of freshwater due to scarcity issues, and when considering exorbitant disposal costs.