In the oil and gas industry, hydraulic fracturing (fracking) along with horizontal drilling are perhaps the most significant achievements in terms of both engineering and innovation. These achievements enable producers to maximize returns from each well. As a result, the number of hydraulically fractured shale oil and gas wells continue to increase.
Hydraulic fracturing is the high-pressure injection of water, sand, and chemicals that fracture shale deposits deep underground to help free trapped oil and gas.
Hydraulic fracturing is a very water intensive process, using an estimated 3 to 5 million gallons of Frac fluid per individual well with water accounting for over 90% of the solution. However, fracking leaves billions of gallons of wastewater every year and regulations are in place that require Frac fluid to be collected and disposed of in an approved manner. While some companies reuse the wastewater from Frac ponds/tanks, others utilize water treatment facilities.
Frac ponds are convenient and affordable, making for a very appealing solution. Unfortunately, they do have a downside. Frac ponds can overflow during strong rains, leading to environmental consequences and potential fines. Also, frac pond liners can leak causing environmental concerns as well as the potential to not have enough fluid for the next Frac job. Therefore, monitoring Frac pond level is critical.
Fortunately, like most of the measurement challenges faced in the industry, OleumTech offers a variety of solutions available to meet the requirements of the application.
The ultimate decision is based on the number of Frac ponds in the operation, the distance between the ponds, the communications infrastructure and the platform/software the data is intended to be viewed on. With one of the most comprehensive product portfolios on the market, OleumTech can solve the challenge with a number of products including wireless gateways, self-contained wireless transmitters, I/O modules or any combination thereof.
Regardless of the product used, the preferred sensor for the application is a submersible hydrostatic level sensor, as shown to the right (with a wireless transmitter). Not only are the sensors extremely accurate but they are functional in any Frac pond shape, configuration or size. The sensor is attached to a long cable and could be tossed into the pond to rest on the bottom.
The sensor operates by measuring the hydrostatic pressure (or head pressure), exerted by the water where 1 PSI equals approximately 27.7 inches of water. Most Frac pond applications utilize a 0-5 psi sensor, providing level measurement in Frac ponds up to a depth of approximately 138.5 inches, or 11.5 feet. However, the sensors are available in higher pressure ranges to accommodate deeper Frac ponds. Atmospheric conditions affecting barometric pressure can impact the integrity of the hydrostatic pressure readings. Therefore, OleumTech recommends only using a hydrostatic pressure sensor with an integral vent tube in the cable to correct for barometric/atmospheric pressure changes.
In this scenario, which is very common, level measurement is required for a single Frac pond. As mentioned above, the submersible hydrostatic level sensor will be utilized. The hydrostatic sensor produces an analog output.
Therefore, the device it connects to must have an analog input. More often than not, and OleumTech DH1 Gateway (Base Unit) is used. The DH1 Gateway has onboard I/O, including four analog inputs that can easily accommodate the analog output generated from the sensor.
As depicted in the image above, the DH1 is mounted in an enclosure and the hydrostatic sensor rests on the bottom of the Frac pond. The sensor is supplied with a weight kit to keep the sensor in place.
Given that Frac ponds are usually in isolated, remote areas, some type of communications solution is also required to get the data back to a Supervisory Control and Data Acquisition (SCADA) Host. A variety of methods can be used including cell modems, satellite modems, a private radio network, or if another OleumTech network exist in the area, the DH1 is compatible over the air with other OleumTech gateways and the data can be peered.
Power for these systems is generally provided by solar panel and rechargeable battery. Of course, the battery and solar panel is sized appropriately for the power requirements of the DH1 and the communications solution used. With power in place, the DH1 is then connected to a serial port of the third-party communications solution. Typically, the third-party communications solution will have an associated static IP address and a port number will be assigned to the serial port.
From an operational perspective, the DH1 is continually reading the analog signal of the hydrostatic sensor. In the case where third-party communications is used, the DH1 acts as a Modbus slave and is given a Modbus ID when configured. At the desired frequency, the SCADA host will poll the IP address and port number the DH1 is connected to. The poll request will also include the Modbus ID along with the specific Modbus register(s) to retrieve the Frac pond level.
In this scenario, which is also very common, level measurement is required from multiple Frac ponds. The recommended solution will vary based on a number of factors, including the desired frequency of measurements, distance between Frac ponds, and RF line of sight. Regardless, the core of the application with respect to the hydrostatic sensor, Gateway communications, and SCADA polling architecture are identical to that described above.
In the case where there are multiple Frac ponds in the same in general area (all < 1.4 miles with clear line of sight to the DH1), self-contained, battery-powered hydrostatic wireless transmitters can be used. These transmitters are offered with an LCD display (WT-LL5) for those operators wanting local indication and without an LCD display (SM-HP1) where local indication is not desired.
The Frac Pond site with the best cell coverage will be selected to be the location of the enclosure, Base Unit, Cell/Satellite Modem, etc. and will be an identical setup as Scenario 1 above. However, for each additional Frac Pond, a wireless Hydrostatic Pressure Transmitter (up to 63 transmitters can communicate to one DH1 Base Unit) will be installed with a Hydrostatic Pressure sensor.
Every user-defined time interval (i.e. 5 minutes), the Wireless Transmitter will wake up, power the sensor, allow it to stabilize, take the reading and transmit the data to the DH1 Base Unit. The Modbus register map will be dynamically created based on the number of sensors added to the OleumTech network. Regardless, the SCADA host will poll the DH1 and function as described above in scenario 1.
In this scenario, there will be times when the distances between Frac ponds are more than the range of the standard wireless hydrostatic transmitter. One solution is the use of OleumTech’s IO MAX (WT-MX1) pictured to the right. The IO MAX offers a completely self-contained package and optional solar panel with a rechargeable battery pack.
The other advantage of the IO MAX is that the 900 MHz option has 10 times the output power as the standard wireless hydrostatic transmitter for even greater range. The wireless hydrostatic transmitter has an output power of 10 mW whereas the IO MAX has an output power of 100 mW.
Even with the increased output power of the IO MAX, there will still be Frac ponds that are distance challenged. The OleumTech gateways have an output power of 1 W and when used with high gain directional antennas, can achieve up to a 40-mile range with clear line of sight. As mentioned above, the OleumTech gateways are compatible over the air and have the ability to peer data. Therefore, when assets are geographically dispersed, a hybrid solution is recommended as any combination of standard wireless hydrostatic transmitters, IO MAX’s, and gateways can be used as shown below. This, by far, offers the most flexibility for a given Frac pond application.
In March of 2017, OleumTech announced a partnership with Sigfox. To date, OleumTech has released over 150 products into the Sigfox ecosystem. These products include a Sigfox Ready wireless hydrostatic transmitter with an LCD display (SFX-LH11). This is a sensor to cloud solution and while the sensor and transmitter essentially work the same, the architecture is much different than that described above.
As depicted in the image below, the transmitter communicates directly to Sigfox base stations and data is retrieved directly from the cloud without any additional communications infrastructure or network buildout. Of course, there are monthly charges associated with using this public network approach. However, in volume, the costs are negligible and could be as low as $1/year/site. The solution becomes very attractive for Frac pond monitoring but is only available in areas where Sigfox has coverage.
As the number of hydraulically fractured wells continue to increase along with associated regulations and legislation, wastewater will continue to be a priority, including the use of Frac ponds. As illustrated above, OleumTech offers a variety of solutions to monitor Frac pond level.
This application story was contributed by OleumTech. For more information or to customize a solution for your operation, please contact either your OleumTech representative or OleumTech directly at 1.949.305.9009 or by email firstname.lastname@example.org.