Advancement in directional drilling technology has changed the way oil and gas production companies design and manage well locations and associated well site automation. Multiple wells require multiple production tanks. Environmental concerns and increasing regulation over hydrocarbon fluids stored in remote tanks require production companies to redefine or find new ways of automating wellhead control to prevent tank spills. The next generation of wireless monitoring and control products provide sophisticated monitoring capabilities and fail safe networks to address these needs. Whether automating field locations with a single well, multiple wells or remote facilities, wireless monitoring and control systems offer many advantages over hard wired systems.
The newest generation of OleumTech industrial wireless products simplifies the design, installation and commissioning of wireless automation systems. The exceptionally low power requirements of these products reduce the size of conventional solar panel applications. A remote solar site utilizing these products can be configured at half the size and cost of conventional installations. In addition, configured interval sleep mode reduces keyed radio frequency transmissions thereby reducing power consumption. The elimination of barrier boards, cable, conduit and trenching make these wireless devices ideal for rugged, remote environments where reliable performance is critical. OleumTech products discussed in this article include the self-contained WIO® LevelMate Monitor for tank measurement of oil and water levels, and the WIO® Base Unit which provides integration with the operator's "Control Device" and also provides communication and control capabilities at the wellhead. For purposes of this article, the WIO LevelMate Monitor will be referred to as the "Tank Radio", the master WIO Base Unit the "Base Radio" and the WIO Base Unit at the wellhead the "Wellhead Radio". These products integrate I/O, RF techniques, PLC platform and reliable diagnostic levels appropriate for wireless control of critical operations.
Communications of wellhead and tank data hard wired to instrumentation can become unreliable due to cable damage from trenching, grounding problems, lightning and harmonics generated by electronic drive equipment at the well pads. A typical oil and gas production site, as displayed in Figure 1 utilizes a hard wired solution. The EFM, RTU, PLC (Control Device) receives level data from the tanks and if a high level alarm occurs will shut in the wellhead or turn off the pumping unit preventing a spill. Signal cable between the tanks and the control device allows for this shutdown control. This method of emergency shutdown for tank management has been used in the industry for years.
The potential problem with signal cable is communications with the tank battery can be interrupted due to damage caused by such events as a cut cable due to trenching, a lightning strike, or corrosion depending on the age of the well. Assuming the Control Device has logic capabilities, a signal is sent to the wellhead control valve to move to the close position in the event of a high level alarm. After the damaged cable event a tank communication failure alarm is detected by the production company warning them of a possible spill condition. However, if the signal wire is damaged from the Control Device to the wellhead control valve a tank spill is possible because there is no local autonomy at the wellhead.
Typically, after a loss of communication from the tanks to the Control Device an alarm is detected by a monitoring system (SCADA) and a technician or production operator is deployed to analyze the problem. In the event of cable damage, production companies can suffer great cost due to a tank spill or loss of production because no alarm is generated under the described conditions.
Wireless systems offer a cost effective and easily installed tank monitoring and control solution for overcoming deficiencies associated with hard wire. Defining and installing a wireless tank solution is a simple process. First, define the tank measurement solution that best fits your needs. Solutions are available from a number of instrumentation companies and each option has pros and cons such as accuracy, reliability and cost. Examples of tank measurement instruments include float detection, guided radar, ultrasonic, hydrostatic and high level switch devices. Hall Effect float devices give diagnostic data in addition to level data. Radar devices provide the same function, but sometimes require more power. High level switches are inexpensive, but can fail with no diagnostic data. Tank measurement devices that offer low powered digital communications of levels, plus diagnostic information, is optimal for most wireless applications.
The self-contained, Class I, Division 1 Intrinsically Safe Tank Radio resides on top of the production tank and mounts directly to a variety of low power tank measurement devices. The Tank Radio powers up the tank measurement instrument, verifies the health of the instrument and transmits tank level data to the Control Device, thus eliminating both the power and signal cables used in hard wire applications (Figure 1). This proven technology is used in many types of fluid measuring applications including crude oil, water, diesel, kerosene, condensate and gasoline. The Tank Radio includes an integrated design that combines I/O, serial communication data acquisition, integrated lithium battery and a radio module for telemetry. Typical battery life for tank applications is 3-5 years depending on the power consumption of the tank measurement device.
One valuable feature of the Tank Radio is transmitted diagnostic data that contains extensive self-checking software that continuously verifies the instrument's health. Timed RF interval transmissions of tank level and diagnostic data are verified at the Base Radio displayed in Figure 2.
The second step in defining a wireless system is to define the requirements of the EFM, RTU, or PLC Control Device. The Base Radio, located with the Control Device, receives transmitted tank data (Figure 2). This Base Radio then provides serial communication of the collected data via RS232 or RS485 to the Control Device. Modbus master/slave RTU protocol is most commonly utilized for communication between the Base Radio and Control Device. In addition to serial communication, the Base Radio supports hard wired analog output and digital output signals representing tank levels and other process variables to the Control Device in the event a serial port is unavailable. Hard wired applications (Figure 1) require the Control Device to have additional power for the tanks signal loops while the low powered Base Radio typically uses the normal power supplied to the Control Device.
In either case, the Control Device receives diagnostic data from the tanks via the Base Radio. The Control Device can now monitor the tank levels and a count of all successful RF transmissions either by serially reading a Modbus register or programming the Base Radio to output an analog or digital representation of the tank levels to the Control Device. Tank levels can be scaled for alarming and then output a digital signal to the Control Device in the event of RF failure.
For example, if a Tank Radio is programmed to transmit data to the Base Radio every 15 minutes, a diagnostic counter register increments upon receiving a proper RF transmission. If the diagnostic register does not increment because of an RF failure, the Control Device can generate an alarm just as if the tanks were hard wired and a technician or production operator can be dispatched to diagnose the alarm condition.
In Figure 2, the Base Radio also receives data transmitted from the Wellhead Radio which is utilized for a wireless plunger lift application. The Wellhead Radio transmits data on tubing and casing pressures and the arrival sensor to the Base Radio and the Base Radio then executes the plunger lift optimization routine and transmits a command back to the Wellhead Radio to initiate the plunger operation. Data on other equipment at the well location can also be collected such as chemical injection tanks, cathodic protection or H2S gas detection. Where plunger lift is not required, pressure data can be collected to predict and enhance well performance and report on the health of well.
The Tank Radios can also simultaneously transmit data directly to the Wellhead Radio and to the Base Radio creating wireless redundancy as displayed in (Figure 3). Providing redundant communication paths enhances the reliability of the wireless monitoring and control system and effectively overcomes the shortcomings of a hard wire system. Diagnostic and PLC logic features on the Wellhead Radio monitor both paths of communication. Diagnostic registers from both the Wellhead Radio and the Base Radio are updated after each successful RF packet is transmitted. In the event the Base Radio or Control Device fails, the Tank Radio continues to transmit proper RF packets to the Wellhead Radio and prevents a false shut in. The well can continue to produce with spill prevention until a technician or production operator arrives to analyze the problem.
The Wellhead Radio, with its onboard logic capabilities can perform a variety of tasks ranging from a simple valve open/close, pump on/off control to advanced algorithms used in drive technologies. The Wellhead Radio, displayed in Figure 3, has the RF redundancy to verify that all system hardware devices are communicating correctly. However, local autonomous wellhead control independent of the wireless communications is also necessary in this critical control application. The redundant paths of the wireless communication reduce the fail factors but cannot overcome the possibility of an electronic board failure or loss of the solar power at the wellhead.
In the event the Wellhead Radio fails because of electronic component failure or loss of power, the system must failsafe correctly. If the electronic device at the wellhead fails and is unable to control the production valve or process variable an additional backup is needed. An inexpensive configurable delay relay timer meets this need. Utilizing the Wellhead Radio logic engine and digital output capabilities, the delay timer can receive a digital output that resets the shutdown relay after successful receipt of each RF packet from the Tank Radio and the Base Radio. If the Wellhead Radio is damaged or fails, the delay timer relay will not receive the timed digital output from the Wellhead Radio for reset resulting in a failsafe shutdown operation.
Advances in wireless technology and low power instrumentation are rapidly improving the reliability and capability of remote wireless systems. Production operators can proceed with confidence that their wireless monitoring and control system will provide for more efficient operations and improved safety for remote field locations.