Patent Application
20130255941
This invention relates to treating produced water and flowback water. More particularly, it relates to recycling produced water and flowback water from oil and gas operations using a mobile water treatment facility.
Hydraulic fracturing has significantly increased access to and production of oil and natural gas in various locations throughout the United States. Shale deposits approximately two miles deep can be accessed by drilling vertically and then horizontally to the shale deposit that contains oil and/or natural gas once the vertical well bore has been drilled. The drilling operation is then redirected horizontally and subsequently drilled one to two miles through the center of the shale deposit. Once the well bore is drilled, the horizontal portion is perforated using explosive charges staged along the horizontal well bore.
After the well bore has been perforated, a significant amount of water (for example, up to 5,000,000 gallons) carrying chemicals, sand, ceramic beads, and gels are injected at very high pressure to create fissures in the shale deposit. These fissures are propped open by the sand and ceramic beads. This allows gas and oil to be released from the fissures. Following injection of the liquid, approximately 20% of the liquid returns to the surface in the first 7 to 14 days. This water (known as “flowback water”) has concentrations of organics (oil and grease), metals (iron and manganese), scalants (calcium and sulfates) and salts. After the initial discharge of flowback water, the well continues to produce oil and “produced water” which is similar in composition to flowback water, but higher in concentration of salts.
Well drillers often import water from fresh water sources in 120 barrel tanker trucks (approximately 5,000 gallon capacity). Because of the weight of trucks and the fragile road conditions, trucks are often only allowed to transport at 50% load capacity. While distance from water source to well site varies, one-way trips in excess of 30 miles are not uncommon. There can also be significant wait time when both loading and unloading the trucks. A typical hydraulic fracturing operation consumes 4 million gallons of water or 1,600 to 2,000 tanker trucks at 50% capacity.
Once the well has been drilled and hydraulically fractured, flowback is produced at the well, and is about 20% of the input volume. The flowback water (and later, the produced water) is typically collected and transported offsite to an injection well (e.g., disposal well), typically 30 or more miles away. In addition to wells created by fracturing, other oil and gas wells also release produced water. The flowback water and produced water are generally not treated prior to transportation, and thus, are filled with contaminants, making transportation more hazardous. Prior to putting the flowback and produced water into the injection well, the water is often treated with biocides and scale inhibitors so that the water does not clog or contaminate the disposal well site. This current model is expensive, as trucking costs are currently approximately $135 per hour, significant transportation is destructive of existing roads, and transporting the water is potentially dangerous because of traffic incidents and the potential of hazardous spills.
Embodiments of the present invention include a system and method for treatment of both flowback and produced water at the wellhead of oil and gas operations so that the treated water may be used by the drillers to drill new wells, for capping or shutting in a well, etc., thus reducing the amount of fresh water required at wells. The system and method include a mobile treatment facility that may be transported to a well site. After water flows through the mobile treatment system, it may be suitable for reuse in a future hydraulic fracturing operation. This will significantly reduce or eliminate the usual transportation of contaminated liquids to an injection well or remote treatment facility. The system may have selected reaction tank sizes to minimize inefficient chemical usage. The system may be automated so that each step begins when fluid is present in a given tank and stops when fluid is no longer present in a given tank. The system may be decanted prior to transporting it so that contaminated water is not transported or disposed of. The system may include dynamic chemical usage controls to adjust feed rates of chemicals for the tanks based on the flow rate of the water through the system.
a-7f are schematic drawings of a stirrer according to an embodiment of the present invention.
Embodiments of the present invention include a mobile treatment facility for the treatment of flowback or produced water at or near the wellhead of oil and gas operations so that the treated water may be used by the drillers to drill new wells, for capping or shutting in a well, etc., thus reducing the amount of fresh water required at wellheads. The mobile treatment facility may be trailer mounted (i.e., it may be built in a trailer), and thus, it may be easily moved from one site to another. The treatment facility includes tanks that remove undesirable contaminants (e.g., organics, metals, scalants, salts, and radionuclides). The tanks may be sized to provide controlled retention time for each step of the contaminant removal process, thereby reducing chemical usage. The system may also be automated and include dynamic chemical usage controls. That is, each step begins when fluid is present in a given tank and stops when fluid is no longer present in a given tank. Furthermore, the chemical usage may be monitored by a controller that adjusts chemical feed rates based on the water flow rate, contaminants, and other variables for more efficient use of chemicals.
As shown schematically in
The mobile treatment facility may be built to suit individual user needs. That is, the flowback and produced water may have particular contaminants or contaminant levels that warrant modifying a standard system to more efficiently process the water. Alternatively, while one particular treatment process is described, any suitable water treatment process may be used. Additionally, the facility may be scalable to accommodate larger or smaller flows. While any size facility may be utilized for any project, a facility that is configured for a particular flow may be more efficient. In one embodiment, as shown in
In embodiments of the invention, water may be continually transferred from one tank to another. The rate at which the water is transferred to subsequent tanks is based on the flow rate in the system and the sizes of the tanks. The flow rate is substantially controlled by the influent pump 10. That is, the treatment train is controlled by gravity after an initial charge by the influent pump 10. For example, each tank has an inlet (and thus a level) that is slightly lower than the level of the previous tank. As such, the level of the first tank is higher than the level of the last tank and the tanks gradually empty from one tank to the subsequent tank. Based on the time it takes the reactions and/or separations to occur, it is estimated that water exiting a given tank has been fully treated by that tank. For example, a given amount of water may spend 5-25 minutes in a given tank, which may be sufficient time to treat the water. The flow rate, chemical feed rates, and mixing rates may be adjusted so that the water is properly treated in each tank so that water exiting a given tank has been fully treated by that tank.
An influent pump 10 takes the water (e.g., flowback, produced, or other water) from an inlet 11 and pumps it to the system of tanks and filters. The first tank 20 may be an oil water separator that uses gravity separation to separate the oil and water. As shown in
The second tank 30 may be used to dissolve residual oils and polymers (e.g., gels), including those used in hydraulic fracturing. To do so, the water and an effective amount of a poly-breaker and an oil scavenger may be added to the tank via one or more chemical feeds 38 and mixed at a relatively fast speed using the motor 36 to operate the mixer 37. The poly-breaker and oil scavenger may include a phosphoric acid and sodium phosphate. The poly-breaker may include, for example, orthophosphoric acid, and may be WT-810 (a poly-breaker sold by ProTreat Technology Corporation, Golden, Colo.). The oil scavenger may be any suitable oil scavenger, such as WT-802 manufactured by ProTreat Technology Corporation. These materials assist to break down oils and gels in the water after the oil water separator. The second tank 30 may also soften the water using any suitable known chemical. For example, a softener may include calcium carbonate and crystalline silica. The softener could be WT-875 sold by ProTreat Technology Corporation. The treated water from the second tank 30 is then transferred to the third tank 40 via pipes. As stated above, based on the flow rate, mixing rate, and chemical feed rate, it is estimated that the majority of the water exiting the second tank has been treated by the chemicals in the second tank.
In the third tank 40, the pH of the water is raised. To do so, the water and an effective amount of a base, such as KOH, NaOH, or hydrated lime slurry, are mixed at a relatively fast speed. The pH is raised to 9 to 13. In some embodiments, the pH is raised to about 10 to 11. Calcium carbonate may also be added to the water in the third tank. The chemicals may be pumped into the tank via one or more chemical feeds 48 and mixed via the mixer 47. A pH meter 44 may be present to measure the pH of the tank. A suitable chemical additive could be WT-820 sold by ProTreat Technology Corporation. The treated water from the third tank 40 is then transferred the fourth tank 50 via pipes. As stated above, based on the flow rate, mixing rate, and chemical feed rate, it is estimated that the majority of the water exiting the third tank has been treated by the chemicals in the third tank.
In the fourth tank 50, an effective amount of one or more coagulants, such as an inorganic coagulant or an organic coagulant, are added. Suitable inorganic coagulants include aluminum-based compounds and iron-based compounds such as aluminum chlorohydrate (ACH), polyaluminum chloride, aluminum sulfate, polyaluminum chloride sulfate, polyaluminum silicate sulfate, ferric sulfate, ferric chloride, and ferrous sulfate. Suitable organic coagulants include polyamines, polydiallyldimethyl ammonium chloride cationic polymers (polyDADMACS), and epi-DMA (epichlorohydrin/dimethyl amine copolymers (sometimes referred to as epi-DMA amines or epi-amines)). A suitable coagulant is WT-830 sold by ProTreat Technology Corporation. The coagulant may be added via the chemical feed 58. The coagulant is mixed into the water at a relatively fast speed using a motor 56 to turn the mixer 57. The coagulants combine with dissolved solids and organics in the water. The treated water from the fourth tank 50 is then transferred to the fifth tank 60 via pipes. As stated above, based on the flow rate, mixing rate, and chemical feed rate, it is estimated that the majority of the water exiting the fourth tank has been treated by the chemicals in the fourth tank.
The fifth tank 60 may be used to create or grow flocculent. To do so, an effective amount of polymers, such as cationic polymers, anionic polymers, or non-ionic polymers are added to the water while being mixed (using the motor 66 to operate the mixer 67) at a relatively slow speed. Any suitable polymers may be used, including cationic polymers such as copolymers of acrylamide and DMAEM (dimethyl-aminoethyl-methacrylate) or copolymers of acrylamide and DADMAC, or Mannich amines; anionic polymers such as polyacrylates or copolymers of acrylamide and acrylate; or non-ionic polymers such as polyacrylamides. A suitable polymer (or polymer mixture) for the fifth tank is WT-842 sold by ProTreat Technology Corporation. The polymers are added via the chemical feed 68, and contaminants in the water combine with the polymers to build larger polymer chins to form flocculent that may be precipitated out of the system. The water with flocculent is then transferred from the fifth tank 60 to the sixth tank 70 via pipes. As stated above, based on the flow rate, mixing rate, and chemical feed rate, it is estimated that the majority of the water exiting the fifth tank has been treated by the chemicals in the fifth tank.
In the sixth tank 70, the flocculent is removed from the water. The sixth tank may be a cone shaped tank, and the flocculent may settle at the bottom of the cone. The sixth tank may be mixed (using a motor 76 to operate a mixer 77) at a relatively slow speed at the bottom of the tank. For example, the sixth tank may be mixed at about 1 rpm or less so that the flocculent is stirred to prevent excessive coagulation but not agitated so much that the flocculent is excessively broken down. As shown in
In the seventh tank 80, the pH of the water is lowered. To do so, an effective amount of an acid, such as HCl, is mixed with the water at a relatively fast speed using a motor 86 to operate a mixer 87. The acid additive could be WT-860 sold by ProTreat Technology Corporation. The pH is lowered to any suitable pH. In some embodiments, the pH is lowered to about 6 to 8. In some embodiments, the pH is lowered to about 7. A pH meter 84b may be used to monitor the pH of the tank. In addition, a biocide may be added to the seventh tank 80 to kill any bacteria still remaining in the water. Suitable biocides include Busan 1058 (e.g., a mixture including tetrahydro-3,5-dimethyl-2H-1,3,5-thiadiazine-2-thion and sodium hydroxide), Onyxide 200 Preservative (e.g., a mixture of 1,3,5-triazine-1,3,5(2H,4H,6H)-triethanol and water), chlorine, and sodium hypochlorite. The acid and biocide may be added via chemical feeds 88. A level indicator 84a may also be present in the seventh tank. As stated above, based on the flow rate, mixing rate, and chemical feed rate, it is estimated that the majority of the water exiting the seventh tank has been treated by the chemicals in the seventh tank.
The effluent pump 12 takes water from the seventh tank 80 and directs it to one or more filters 90 designed to remove any remaining particulate including any remaining flocculent particles. The filters may be any suitable filter, such as a fiber bag-type filter. For example, a fiber bag-type particulate filter may be used having pore sizes of about 0.1 to 1 microns. However, any suitable filters with any suitable pore size may be used. Prior to exiting the system, the water may be run through one or more meters or sensors. For example, in some embodiments, a flow meter may be present at the outlet to determine the flow rate of the system. In other embodiments, a turbidity meter 96 may be used to determine the clarity of the effluent before the effluent exits the system. The processed water then exits the outlet 13 of the facility. The processed water is generally visibly clear (i.e., it has low turbidity) and may then be used in various applications, such as new drilling or fracturing processes, to plug wells, etc.
While the above described process is one suitable treatment method and sequence, any suitable treatment method and sequence may be used.
Each tank may include a variety of motors, monitors, sensors, valves, chemical storage areas, chemical feeds, and vents. For instance, as shown schematically in
One or more tanks may also include one or more chemical feeds 38. Chemicals that are added to the tank may be stored in the control room 3, storage area 4, or any other suitable area. A feed 38 may feed chemicals from their storage area to the tank. For example, as shown in
Each tank may also include a vent 29, 39. The vent may be a one-way air vent that allows pressurized gas to exit the tank. In some embodiments, the vent is permanently open and a blower 92, external to the tank, is activated periodically to vent the tanks. In still other embodiments, the vent is permanently open and the blower 92 runs continuously during operation of the system to create a negative pressure system to evacuate all gasses produced in the tanks. The blower 92 may vent the gasses directly to the atmosphere or it may trap the gasses, as necessary.
In the above described embodiment, seven tanks are used in sequence in order to process flowback, produced, or other water. In some conventional water treatment systems, each tank is the same size. In such a system, the maximum flow rate is determined by the tank with the longest retention time requirement, and thus all other tanks would be oversized. Such a system may thereby require inefficient chemical usage. However, in embodiments of the present invention, the reaction tanks are sized to provide controlled retention time for each step of the process. That is, given constant flow throughout the system, tank size must vary to conduct the proper chemical reaction at each step. As such, the tanks are sized to improve efficiency and chemical usage. For example, as shown in
In some embodiments, the facility may be automated. As shown in
The controller 100 may be used to control the startup sequence, run sequence, pause sequence, decant sequence, sleep sequence, wait sequence, and general operation of the system. When the system is switched from standby to running, the influent pump 10 is activated and the controller will determine the appropriate action to take after evaluating various criteria. For example, the level of the first and seventh tanks may be evaluated and the flow rate through the system may be evaluated. If the flow rate (as measured at the end of the system) is below a set amount and/or the first and seventh tanks show low fill levels, the system will initiate the startup sequence. On the other hand, if the tank levels are above the set amount and the flow rate is sufficient, the system will initiate a resume sequence. In the startup sequence, the influent pump 10 is initiated by the controller 100. As water fills the tank, it begins to fill the pipe between the first tank 20 and the second tank 30. After the water in the first tank 20 is filled to a sufficient level, treated water begins to spill into and fill the second tank via the pipe. Once sufficient water has been transferred from the first tank 20 into the second tank 30, i.e., beyond the low level indicator (as measured by sensor 32), the second tank 30 is activated. When the second tank 30 is activated, the motor 36 is turned on to activate the mixer 37. In addition, the chemical feed 38 is activated such that chemicals are added. That is, a chemical feed pump is activated which pumps chemicals from a storage area through the chemical feed 38 into the tank. As water fills the second tank 30, it begins to fill the pipe between the second tank 30 and the third tank 40. After the water in the second tank 30 is filled to a sufficient level, treated water begins to spill into and fill the third tank 40. Once sufficient water has been transferred from the second tank 30 into the third tank 40, i.e., beyond the low level indicator, the third tank 40 is activated. When the third tank 40 is activated, the motor is turned on to activate the mixer. In addition, the chemical feed is activated such that chemicals are added. This process continues until all tanks are active. Once all tanks are active, the system is in run mode and the effluent pump 12 is used to control the rate the effluent exits the seventh tank to ensure that the levels in the tanks are such that the gravity system is able to operate.
If the flow rate, as measured at the end of the system, is lower than a preset amount, the chemical feed for the activated tanks remains on at a constant rate throughout operation of the system. If the flow level is at or above a preset amount, the chemical feed of each tank is controlled by the controller 100 to maximize the efficiency of the system. That is, the rate at which the chemicals are added by the chemical feeds are varied to provide effective amounts of chemicals, thereby improving chemical usage and optimally processing the water. In some embodiments, the chemical feeds in most tanks, i.e., the first, second, and fourth through sixth tanks are controlled based on the flow rate as measured by the flow rate meter 97 at the end of the system, while the chemical feeds in the third and seventh tanks are controlled based on the pH levels in the tank (using a pH meter). However, the chemical feeds may be controlled based on any number of variables in a given tank or in the system, including turbidity levels as measured by a turbidity meter 96.
The controller 100 may also have a standby setting. In the standby setting, the pumps, motors, and chemical feeds are stopped and all operations ceased. The controller 100 may also have a sleep sequence in which, the mixer motors remain on at a relatively slow rate to prevent excessive settling. In a wake sequence, after the system has been on standby or non-operational, the mixer motors may be started to agitate the contents of the tanks so that the system may be ready to run.
The controller may also have a decant sequence. When operations cease for a period of time, the mobile treatment system needs to be moved, or tanks need to be examined or repaired, the system may be put into a decant sequence. That is, in some alternative embodiments, each tank is pumped out individually to clear out the system, producing contaminated water in various stages of decontamination. However, in embodiments of the present invention, the decant sequence is utilized to substantially flush out the system to produce treated water. Each tank may have an additional valve near the bottom of the tank that leads to decant piping. For example, as shown in
In the decant sequence, the influent pump 10 is stopped and the decant pump 14 is started. The decant outlet valve 25b to empty the first tank and the decant inlet valve 35a to fill the second tank is open. Once a low level meter 22 on the first tank shows that the first tank is empty (or below a set point), the decant outlet valve 25b to empty the first tank and decant inlet valve 35a to fill the second tank is closed. The second tank is then operated. The decant outlet valve 35b to empty the second tank and the decant inlet valve 45a to fill the third tank is open. Once a low level meter 32 on the second tank shows that the second tank is empty (or below a set point), the decant outlet valve 35b to empty the second tank and the decant inlet valve 45a to fill the third tank is closed. The third tank is then operated. The decant outlet valve 45b to empty the third tank and the decant inlet valve 55a to fill the fourth tank is then open. The process is repeated for each tank until the low level meter of the seventh tank is activated. However, the decant pump 14 is not used after the sixth tank. At that point, the system uses gravity to move the water from the sixth tank to the seventh tank. A decant inlet valve 85a may be opened which lowers the level at which water is transferred from the sixth tank to the seventh tank, allowing the sixth tank to more fully drain. In addition, during operation of the decant sequence the effluent pump 12 is run to expel water from the seventh tank. After the decant sequence has been completed, the system is placed into standby. By using the decant sequence, the water in the system may be decontaminated prior to moving, stopping, or working on the system. As such, in embodiments of the present invention, when the decant sequence is initiated, the water in the system is pumped through the system, thereby producing water that is substantially decontaminated. Accordingly, when the system needs to be evacuated (e.g., for moving the system, cleaning the system, etc.), treated water is produced, thereby reducing the amount of waste that must be handled at the site.
The controller 100 may also dynamically control the chemical insertion rate for each tank. That is, the controller 100 may adjust the chemical insertion rate for a given tank based on the flow rate, pH level, or other criteria to optimize the chemical insertion rate for a given tank. For example, the controller monitors and tracks given parameters for the system, e.g., flow rate, or a tank, e.g., pH, and a process optimization algorithm in the controller adjusts the chemical feed rate (or chemical addition rate) of a chemical feed of a given tank based on the parameters while monitoring the effect on the product water quality or another variable. Thereby, the controller may dynamically control chemical usage of the system to maximize efficiency and to adequately sense and respond to changing contaminants. As shown in
In addition to controlling the water processing of the system, the controller 100 may also be programmed or configured to operate other aspects of the system. For example, in some embodiments, the controller 100 may be programmed to set off an alarm when a toxic gas or fire is detected in the system by either the detectors, or it may be programmed to set off an alarm if there is a system error as detected by the sensors or detectors in the tanks or the water processing compartment. In some embodiments, for example, the controller 100 may be programmed to notify the user when chemical supplies for a given tank are running low or empty.
The sensors and monitors of each tank, as well as the variety of sensors present in the water processing compartment and monitoring compartment, may be monitored and/or recorded. That is, the sensors and monitors of each tank, as well as the detectors and measurement devices in the water processing portion of the system may transmit (either via wires or wirelessly) data to the monitoring compartment 3 or to an off-site location. For example, in some embodiments, a plurality of controllers in the monitoring compartment are connected to a computer located in the monitoring compartment. The computer may be configured to wireless transmit data (e.g., over the interne) so that the system may be monitored and controlled from another location. A user may then analyze the data (for example, using a computer at another location) and modify the operational parameters of the system, as necessary. For example, while the system may include a process optimization algorithm to dynamically adjust chemical addition rates, a user may determine that despite the dynamic control, usage is still not optimal. As such, the user may adjust the process optimization algorithm to further optimize chemical usage. In some embodiments, the controller 100 may be configured or programmed to provide continuous analytical data to provide historical trending and statistics regarding the input and output of the facility. A data processing unit, such as a computer, may then be used to analyze and report the data.
Although the present invention has been described and illustrated in respect to exemplary embodiments, it is to be understood that it is not to be so limited, since changes and modifications may be made therein which are within the full intended scope of this invention as hereinafter claimed.
This application claims priority to and the benefit of U.S. Provisional Application No. 61/617,013, filed on Mar. 28, 2012 in the U.S. Patent and Trademark Office, the entire content of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61617013 | Mar 2012 | US |
