The worldwide energy sector has accelerated the development of its unconventional oil and gas resources through increased use of horizontal drilling and hydraulic fracturing practices. Water is an essential element in the fracturing process and the recycling or reuse of spent water can dramatically reduce costs. The volume of water required to fracture a well varies, but it generally ranges from one million gallons to five million gallons. Operators face difficult challenges securing water sources for their operations, especially already dry regions. Furthermore, the management of waste water associated with hydraulic fracturing has an environmental impact and associated cost.
The development of technology to recycle and reuse this water is now becoming critical and Anguil has integrated solutions to help. We have developed an effective water recycling system that allows well operators to safely reuse water without jeopardizing well output.
WATER RECYCLE AND REUSE
Water generated during drilling, well completion, and production is categorized either as flowback or produced water. Flowback water is the initial fluid produced after hydraulic fracturing and is typically recovered during the first six weeks of well production. The flowback water characteristics stem from the initial source water, the natural formation brine, fracturing fluid additives, proppants, and drilling fluids. Generally, 20-40% of the fracturing fluid volume is recovered as flowback. Produced water is the water which naturally exists within shale formation and is recovered concurrently with oil and gas. After the initial flowback period, produced water resembles the characteristics of the formation brine. The volume recovery rate of produced water is lower in comparison to the flowback, but occurs over the decades of a well’s lifetime. Currently, the majority of flowback and produced water is disposed of in salt water disposal wells.
Recycling and reuse of flowback and/or produced water reduces fresh water demand and the associated costs of water purchase, transportation, and disposal. In contrast to the usual practice of complete disposal, a portion of the flowback is treated for reuse either onsite or at an adjacent well. The primary economic benefit from recycling is a significant reduction in the number of truck loads required to ship fresh water to the well site and the flowback water offsite. Environmental benefits include reduced reliance on and competition for fresh water sources, a reduced carbon footprint from trucking, and less stress on the local infrastructure.
Treatment requirements for flowback and produced water are normally established by the company performing the well completion. Knowledge of the fracture fluid employed is required when considering the recycling methodology in order to identify the required treatment characteristics. Two common fracturing fluids are slick water and gels. Slickwater is normally used for natural gas production, whereas gels are often deployed for oil field development.
ANGUIL’S FRAC WATER REUSE SYSTEM
Since there is a wide variation in flowback and produced water quality in oil and gas fields, Anguil Aqua Systems is presently focused on the treatment of flowback and/or produced water from natural gas wells.
Previously, the high levels of Total Dissolved Solids (TDS) in produced water were thought to render it unusable. However, well service companies have demonstrated that moderate TDS levels in recycled water do not impact well production capacity. Hence our solution is to focus on the minimization of Total Suspended Solids (TSS) and, overall reduction of bacteria and other contaminants affecting the fracturing fluid additives.
Of the many approaches to the minimization of TSS, the Anguil solution is a ballasted flocculation system. Similar systems have been successfully employed to treat drinking water as well as municipal and industrial waste waters containing many of the same contaminants found in flowback and produced waters.
The diagram below depicts the flow pattern for the clarification process. In the first tank, the raw water or influent is combined with a coagulant, commonly ferrous sulfate, ferric sulfate, ferric chloride, or alum. The coagulated influent then passes into the flocculation tank where a polymer and a ballast material such as microsand, iron oxides, or chemically enhanced sludge is added. Coagulation and sedimentation times are reduced by the addition of chemical additives and the ballast material. After ballast and polymer additions, the flocculated water then proceeds to the third tank where additional mixing occurs, allowing the floc to coalesce into larger precipitates. The matured, flocculated water proceeds to the clarification tank where the floc is separated from the water by passing through plate or tube settlers. Clarified water then exits from the top of the system.
Settled floc and ballast material are collected and pumped to the ballast recovery unit where the ballast is separated from the waste solids. The waste solids are sent to disposal and the recovered ballast is returned to the first flocculation tank. We can provide treatment systems which help improve injection facilities operations and maintenance, reducing injection pressures and minimizing acid jobs by keeping your wells from fouling. Furthermore, our solutions include treatment options to enhance your oil recovery and treat for hydrogen sulfide control.
As a member of the Gas Processors Suppliers Association, Anguil is heavily invested in industry’s success and future. Countless air pollution control installations at natural gas processing and petroleum refining sites gives us the necessary knowledge to address your water treatment needs safely, effectively and within your demanding production schedules.
- Reuse of Flowback and Produced Water: Physical and chemical treatment system that reduces suspended solids to acceptable reuse standards for hydraulic fracturing.
- Mobile Precipitation: A system easily deployed on site, allowing treatment for multi-well completions, or transport to a nearby well.
- High Contaminant Removal: Total Suspended Solids (TSS), turbidity, oil/grease, color, and bacteria.
- Chemical Coagulation: A wide range of available coagulants and polymers allows customization to site specific needs.
- Automated Chemical Feed System: Treatment begins with proper dosing of chemicals to precipitate dissolved contaminants. The Frac Water Reuse System incorporates chemical metering pumps, day tanks and pH instrumentation to ensure treatment objectives are being achieved.
- Lower Costs: Ballasted clarification allows for smaller equipment footprint, reduced power consumption, and reasonable chemical use. Recovery and reuse of ballast material lowers consumable costs.
- Short Term Lease Agreements: Flexibility to only pay for water recycling system during peak water demand.
- Customized Service and Project Management Contracts: Anguil personnel can be contracted to provide continuous service and/or operation of the entire water recycling system.
Many chemical and petroleum companies use batch reactors to make their products. These reactors typically have vents which are opened and closed during emptying, filling, mixing, heating or cooling and other steps of the production process. The gases coming from these vents must be controlled under most government regulations. Often the emissions produced are inert (little or no oxygen) streams with relatively low flow and high concentration of Volatile Organic Compounds (VOCs). In this case, the company was operating several reactors that required venting for depressurizing, filling and mixing. The process flow rate was less than 50 SCFM (80.25 Nm3/hr) and was essentially all light hydrocarbons such as methane, ethane and propane, with some halogenated hydrocarbons.
There are two oxidation strategies for this type of process stream, the first is to dilute the process vent with fresh air. This strategy provides oxygen for combustion and reduces the Lower Explosive Limit (LEL) below 50%, using a conventional oxidizer system. The National Fire Protection Association (NFPA) and FM Global guidelines suggest facilities keep vent collection systems airstreams below the 50% LEL for safety reasons. Because of the high BTU (British Thermal Unit) content of the process vent in this application, it would have required a high volume of fresh air to achieve the necessary LEL condition which would have dramatically increased operating expenses and raised safety concerns.
While the above scheme is sometimes acceptable, Anguil implemented a different, safer strategy for this application. Instead of diluting the process vent with fresh air, designers kept the process stream inert, sending it directly through a burner port of a Direct Fired Thermal Oxidizer (DFTO). Essentially this allowed the combustion device to use the high BTU content as fuel for oxidation.
Once the DFTO is brought up to operating temperature with natural gas, the inert process gases are directed to the burner. During normal system operation, the VOC-laden process vent will fuel the pollution control device. During periods of low process flow or low energy content, supplemental fuel is added to the burner, natural gas in this case, to maintain operating temperature of 1400-1600°F (760°C-870°C) in the oxidizer combustion chamber. A minimum of one second residence time at these temperatures ensures a destruction efficiency of 99%+. An oxygen meter in the exhaust stack ensures that sufficient oxygen was present for complete destruction of the VOCs.
A soft refractory lining inside the oxidizer lets the operator start and stop the system without risk of refractory failure that can occur with other designs. This also allows them to shut down the oxidizer during substantial periods of process downtime without negatively affecting the longevity of the equipment.
For inert gases that contain no halogens or sulfur compounds the hot, purified, gas will be released to atmosphere from the combustion chamber or possibly sent to a heat exchanger for energy recovery. This particular application contained halogenated compounds, therefore the hot exhaust gases leaving the DFTO are directed into a hastelloy quench where they are cooled down before entering a packed bed scrubber.
The recirculation with a caustic solution inside the scrubber removes HCl (Hydrochloric Acid) and HBr (Hydrobromic acid). The scrubbed gases are then pulled into an Induced Draft fan and finally out an exhaust stack. An induced draft fan is used with halogenated streams so that there is no potential for corrosive gases escaping to atmosphere. Any leakage of acid gases will result in substantial risk to equipment longevity and to personnel. These scrubbing systems provide 99%+ removal of the acid gases prior to discharge to the atmosphere.
With these acid gases there is also a potential for corrosion of the oxidizer shell behind the insulation if the metal temperature is below the acid dew point. To prevent that from occurring, the oxidizer is designed with an external shroud to keep the carbon steel shell at a temperature above the acid gas dew point, avoiding corrosion concerns.
The Anguil System has a complete control system with communication capability to DCS (Distributed Control Systems) systems and modems for remote monitoring / diagnostics. These controls provide for automatic purge, system heat-up and a wide range of operating conditions. Magnetic driven scrubber recirculation pumps and scrubber controls are also provided for automatic operation without personnel adjustments.