Enhancing oil and gas operations — SCADA via satellite

Oil and gas operations are located in unforgiving environments, from the blistering cold of the arctic to the scorching heat of the desert and the storm conditions out on the open sea. To sustain secure operating conditions in these remote areas, reliable communication is vital to the end user.

Supervisory control and data acquisition

Supervisory control and data acquisition (SCADA) describes a computer-based system that manages mission-critical process applications on the ‘factory floor’. These applications are frequently critical for health, safety and the environment. Telemetry is often used in combination with SCADA, being the process by which data is collected and actions are performed remotely via a suitable transmission medium. In the context of this article, the telemetry medium is a satellite communications solution.

SCADA in oil and gas operations

SCADA is not limited to a particular aspect of oil and gas operations. Applications can be found in upstream areas such as well monitoring, downstream in areas such as pipeline operations, in trade by managing the fiscal metering/custody transfer operations and logistics in applications such as inventory management of tank storage facilities.

Selecting a satellite communication solution — factors to consider

Security

When selecting a satellite communications solution, there are numerous factors that must be considered. Enterprise applications such as email, internet access, telephony and videoconferencing are tied into the public communications infrastructure. Due to security and reliability considerations it is considered best practice to isolate mission-critical SCADA communications infrastructure from public networks.

Dedicated satellite communications network solutions tailored for the SCADA applications environment offer greater security against hacker attacks and virus infestation which mainly target computers that are connected to the internet and are running office applications.

Reliability

Due to the mission-critical nature of most SCADA operations, a reliable communication solution is of utmost importance. The satellite communications industry is mature with a proven track record, with satellite transponder availability typically in the 99.99 percentile range — a number far superior to that of terrestrial networks. A miniature satellite hub, such as those developed by TSAT, can be deployed at the end user’s SCADA control centre. Data to and from the remote terminal units (RTUs) are piped directly into the SCADA system. There is no vulnerable terrestrial back-channel from a communication service provider’s facility, which can cause the entire network to crash if cut during public works.

Figure 1: A satellite SCADA network

To increase the reliability of a satellite hub, it is frequently deployed in a redundant/load sharing configuration. This ensures that the hub is available more than 100% of the time, making it far from the weakest link in the communication chain.

Types of connectivity

Contrary to business-related communications, which take place randomly, SCADA communication is quite predictable. It is a continuous process, where the SCADA application polls the RTUs at regular intervals. The outgoing poll request is a short datagram (packet) containing as few as 10 bytes. The returned data from the RTUs are also in a datagram format with the message size being from 10 to 250 bytes. One could easily assume that a satellite solution based on dial-up connectivity such as Inmarsat, Iridium or Globalstar would be ideal for this application environment. Since SCADA is not just data collection, but also entails control, you simply don’t want the system to encounter a busy connection. What is needed is a system that provides an ‘always on’ type of connection, commonly referred to as leased line connectivity.

Solutions such as those provided by TSAT support both circuit switched (leased line and multi drop) and packet switched (TCP/IP and X.25) applications concurrently.

Recurring communications cost

Since a typical SCADA application will run for at least 10 years, the cost to operate a satellite communication solution can become astronomical unless the correct solution is carefully selected. There are several commercial operators in the market that provide leased line connectivity to the oil and gas business. These operators have a business model not unlike that of the mobile phone companies in that they sell or lease inexpensive satellite terminals, although clients are then tied to using their service exclusively. The service is metered, ie, you pay for the amount of data being transmitted to and from each terminal.

To make satellite communications an attractive alternative for SCADA applications, a solution is needed that utilises bandwidth effectively and provides the lowest operating cost. Since the typical SCADA RTU transmits at low data rates (from 2400-9600 bps), a typical satellite SCADA network should be able to operate with as little as 50 kHz bandwidth.

Using fixed stationary satellites, having K_u-band (12-18 GHz) or C-band (4-8 GHz) transponders, the end user is able to select the satellite operator that has the best coverage and the best price. It is not unusual to see correctly configured networks having recurring monthly communications costs of less than US$1000 for the entire network.

Dedicated network VSAT shared hub services are being promoted for the SCADA applications environment. With this type of solution, multiple customers share the same frequency spectrum. From a security perspective this may not be a desired solution. Furthermore, data to and from the RTUs are routed through the service provider’s hub facility. In most cases, the connection to the service provider’s hub is through a leased line. The cost for this line can be staggering, since in many cases the connection will be going to a different city, state and, in some cases, even a different country. To eliminate the terrestrial back-channel, the service provider may offer an alternative method of connection called a ‘double-hop’.

Figure 2: Antenna with main unit

This ‘double-hop’involves the installation of a satellite terminal at the end user’s SCADA control centre. With this arrangement the data has to travel from the SCADA centre up to the satellite, down to the hub, back up to the satellite and finally down to the remote terminal. The return reply from the RTU makes the same trip in reverse. The implication of this ‘double-hop’ is greater latency, which may not be acceptable for time sensitive control applications.

By using a central hub, such as those provided by TSAT, the data is connected directly into the SCADA computer without any terrestrial back haul or ‘double-hop’.

Communication protocols

Some service providers only support IP-based application traffic. In reality, most of the SCADA world deals with legacy hardware that is based on asynchronous RS232 serial communication protocols. To further complicate matters, a typical SCADA communications network may include RTUs from several manufacturers each utilising their own set of communication protocols. Also, older RTUs generally do not have report by exception capabilities (RBE) which increases a SCADA system’s responsiveness to real-time events. Some satellite equipment providers, such as TSAT, support multiple communication protocols concurrently, and have developed protocol drivers to enable RBE functionality. Apart from gaining the desired responsiveness, an additional benefit is the resultant drop in traffic over the satellite link which effectively increases the throughput of the network. Throughput increases of up to 150% have been realised in this way.

End-user control

Since no two SCADA systems are alike, it is imperative that the implemented solution provides enough flexibility to allow the end user to optimise the network design to suit the requirements of a given application, such as being able to logically group RTUs to a specific serial port on the SCADA systems front end processor, assign bandwidth resources to individual RTUs or group of RTUs to optimise system performance, and to define the optimal satellite link access scheme for the application.

The satellite network should provide a network management system (NMS) that makes configuration, system management and support easy for the non-satellite professional SCADA engineer.

Utility-grade equipment

Most SCADA applications involve placing the satellite terminals in harsh environments. The low-cost satellite terminals targeting the small office/home office (SOHO) market are designed to operate in a sheltered environment. These terminals are also designed to operate from a 110-240 VAC mains supply. SCADA requirements necessitate the use of satellite terminals with rugged mechanical enclosures and designed for the utility applications environment where power is in short supply. Along pipelines in remote areas there may not be any main supply at all and the RTU has to operate from a solar-powered battery supply. Solar panel arrays are quite expensive and if the satellite terminals draw a lot of power, large arrays and battery banks will be required. Most satellite terminals continuously draw more than 40 W, so it is important to use a terminal such as TSAT that can reduce the power consumption to less than 0.2 W when not transmitting.

Australian Satellite Services
www.ascs.com.au