Because of the volume and quality of water required for hydraulic fracturing operations, water recycling and treatment is an essential component of oil shale development. Drilling operators must focus on ways to reuse the produced and flowback water generated during the process of releasing natural gas, an increasingly important energy resource in the U.S. In the Fayetteville Shale, a more than 300-million-year-old geological formation that stretches across Arkansas, one oil company recycles more than 90% of its produced water and has been successfully using a mobile mixed oxidant solution (MOS) onsite chemical generation system with remote monitoring to safely and cost-effectively treat more than 2 million barrels of flowback and produced water since 2013.
Economic, environmental and operational demands challenge oil and gas drilling operators to produce consistent results in a highly regulated and competitive environment. In the Fayetteville Shale, where produced water bacteria counts regularly can exceed 107 colony-forming units (cfu) per mL, finding a low-cost water disinfection solution to reliably treat high volumes of water and achieve a superior bacterial kill was paramount. Without the right disinfection, the growth of excessive microbial populations found in produced water can cause corrosion and “souring” of the drilling well.
In Fayetteville, a heavy sulfate-reducing bacteria (SRB) growth was generating high concentrations of hydrogen sulfide, a known and not uncommon toxic and corrosive byproduct of bacteria accumulations in produced water. Drilling operators initially used chlorine dioxide to address the issue. While chlorine dioxide demonstrates an effective kill rate, its disinfection chemistry could not prevent a future outbreak of bacteria because it is so quickly dispersed due to off-gassing. The three-chemical process of chlorine dioxide treatment also requires extensive equipment, safety concerns and highly trained personnel.
When chlorine dioxide failed to achieve long-lasting effectiveness, the drilling operator switched to a mobile MOS treatment unit with remote monitoring in a “hub and spoke” arrangement, where produced and flowback water is safely held for treatment in retention ponds and then transported a short distance to be reused at the fracturing site. The mobile water treatment system is a completely self-contained onsite chemical generating system that automatically treats high-volume water of fluctuating quality.
The MIOX Blackwater mobile water treatment system uses electrolysis to produce MOS in a 9-by-40-ft trailer. Delivered sodium chloride liquid brine and city water flow into an electrolytic cell, where they are exposed to electricity to create a blend of sodium hypochlorite and hydrogen peroxide. This solution eliminates SRB and acid-producing bacteria that can lower production and foul wellbores. In the Fayetteville Shale, the process has reduced the 10 million SRBs regularly seen to less than 1 cfu per mL of fluid. Because the technology operates with salt, water and electricity, there are virtually no health, safety, spill or environmental concerns on site.
Because water treatment in a natural gas fracturing operation often is situated in a remote location, the Fayetteville Shale Blackwater mobile water treatment system runs continuously without onsite staff or crew providing physical oversight. Instead, the system’s programmable logic controller is configured with remote monitoring that allows operators and service technicians to view the activity of the system through highly secure Internet access. Using tightly controlled security on existing Internet networks, oil company personnel can view the same screen that is on the MOS generator from their computers or phones down the road or across the country. The screen provides a “fingerprint” of the system, with all available parameters—incoming water temperature and cell current, for example—to reveal the state of the system. This access gives operators peace of mind that the system is running successfully without interruption, and allows technicians to analyze data and track operating trends that can improve system performance.
Wireless communication also alerts personnel if system parameters are outside the norm. At the Fayetteville Shale operation, where feedwater to the MOS generator is supplied by the local municipality, the city water was shut off for an extended period of time, likely due to maintenance. As engineered, the system went into safe mode, attempting to reboot every 45 minutes. When the water did not come back on after the first attempted reboot, the system e-mailed drilling site operational personnel and the manufacturer’s service technicians. In this way, manufacturing personnel were able to proactively support the needs of their client’s water treatment system. The city eventually turned the water back on with minimal disruption to water recycling operations.
If a system requires troubleshooting, response time can be critically important for operations that rely on equipment that is constantly running. In addition to fast and cost-effective troubleshooting, remote monitoring alerts technicians and operators when the unit needs standard maintenance, and also e-mails a daily system status update.
An MOS mobile system automatically treats fluctuating water quality on demand, within a small footprint, using only brine, water and electricity. Cost breakdown on fluid types demonstrates that the MOS system is economical, ranging from about 2 cents per barrel for treating a blend of fresh and produced water, to about 10 cents per barrel for “extreme demand” fluid.