Water Treatment Technologies
Chlorine Dioxide (ClO2)
ClO2 is a selective oxidizer used as a biocide on frac jobs (replaces conventional biocides and other oxidizers) and kills within seconds, compared to hours for conventional biocides. Conventional biocide applications typically treat on-the-fly after the working tanks as the fluid is being pumped downhole (usually between 0.3-1.0 GPT). Water is not completely sterilized before being pumped downhole and mixes with formation brine, subsequently reducing biocide ppm (likely below kill threshold), bacteria are exposed to new/additional resources, and are given a perfect environment of darkness and heat to repair/regenerate eventually souring and contaminating the formation.
Dangers of Untreated Bacteria in Stored Water
Oilfield bacteria are present everywhere water can be found. Left untreated, bacteria populations can result in operational issues through the upstream and midstream production environment. If injected downhole, microorganisms (bacteria) in the water will survive and thrive, resulting in microbial proliferation and biofilm build-up. This leads to well plugging, reduced flow, reduced recovery, and reduced production. Other costly issue include:
Microbial-Influenced Corrosion (MIC), which can also cause flooding and other expensive operational losses such as loss of production, down time and production pipe replacement.
Microbial-Influenced Souring (MIS), which causes the generation of H2S gas, and is both a corrosion and a human health hazard.
Bio slime/sludge produced from bacteria will also cause interface issues and cause severe emulsions in separation vessels. Emulsion Problems / Oil Carryover § Iron sulfide is a byproduct of bacteria generated H2S. Iron sulfide becomes oil-coated very easily and will foul anything and everything from formation to tank batteries. Iron sulfide will cause interface fouling/emulsions in separators and gun barrels causing separation issues and oil carryover.
EPA REGISTERED BIOCIDE
ClO2 is an EPA registered biocide that is considered eco-friendly at the treating rates (0.8ppm going downhole). This is beneficial to the operator’s frac disclosures.
ClO2 is not affected by pH, organics, or minerals found in frac fluid.
ClO2 is only known biocide to kill bacterial spores. Shalestone’s goal is to sterilize fluids before they are pumped downhole, limiting the chances of souring, or contaminating the formation.
ZERO NEGATIVE IMPACT
Water that has been treated with ClO2 can be used without negative impacts to hydraulic fracturing fluids, the producing formation or downhole equipment.
This chemistry also acts as a oxidizing agent for iron sulfide (FeS) and Hydrogen sulfide (H2S), helping to control issues related to corrosion and equipment fouling.
Through a complex reaction, it oxidizes soluble Fe2 to Fe3, which is non-soluble in water and will precipitate. So, although ClO2 doesn’t remove the iron, it alters its state to a form that can be removed through filtration or settling.
Advantages of ClO2
Our Approach - Safety First
The Shalestone unit produces ClO2 in water as an aqueous solution on-site and injects into our injection ports with our custom header system.
Some water treatment companies use semi-batch applications that may require safety precautions related to transportation and storage of ClO2. ClO2 for oilfield surface operations should not be shipped to the site due to environmental and health hazards – it must be generated near the point of application, then injected immediately into larger quantities of water. The gas is generated onsite via a mobile or permanently mounted generator using water and either a two-precursor (acid, sodium chlorite) or a three-precursor (sodium hypochlorite, hydrochloric acid, sodium chlorite) system.
All Shalestone units have many safety shutdowns and sensors designed to make chlorine dioxide generation much safer.
A Science Based Approach
The Shaleshok2 unit is a 14” ADOX™ Inline Generator set up as a turnkey system that offers ease of installation and startup. This system is designed to produce 3000 PPD of chlorine dioxide. The generator is based on a vacuum eductor which provides the motive force to pull the chemicals into the reaction zone. The production rate can be adjusted via the 4-20mA plant flow signal and operator or SCADA entered dose. This generator is on a stainless-steel skid and connected to a single application point. The efficiency of the generator is optimized using trusted technology. It utilizes a PLC control system with a 10” touchscreen HMI for visual feedback of generator operations and local operator interface. The system will require 240 vac / 3 φ / 60 Hz / 30 amps for electrical power provided by Shalestone via generator.
The Shaleshok2 unit has a built-in redundancy system.
The system is automated based on flow and ORP readings. Our technicians trend output data that can be seen in real-time by the oil and gas operator and on-site Shalestone operators.
It has a bleach analyzer to adjust the bleach accordingly based on efficacy of the bleach.
The reactor is connected directly to the header to eliminate large quantities of highly concentrate ClO2 in the unit.
The operator room is separate from the pump eliminated noise and exposure risk. The operator should not have to access the except for manual testing.
The unit has adequate outside lighting, eliminating the need for an additional light plant.
ClO2 and H2S monitors are in the unit for added safety shutdown.
Shalestone always tests the influent and effluent stream of the water transfer lines before and after the point of Chlorine Dioxide injection.
Treated water sample testing is conducted at every stage during the process. Shalestone technicians take water samples at the header and working tanks and run chlorine dioxide levels with a Palin testing device (not a color metric test).
ORP Tests water in the water transfer line downstream of injection for oxidation levels and automatically adjusts chemical rates based on determined set point. ORP is the truest and most accurate way to measure the effectiveness of the ClO2. This gives our operators assurances we are maintaining a safe and effective level of ClO2.
Levels are monitored on screens where the service operator has complete control at their fingertips.
The units are equipped with control panels with automatic monitoring during treatment to determine the required injection of ClO2.