Technology Drives Monitoring Trends

By Terry Miller
Fisher Controls International, Inc.

Advanced monitoring and control equipment designed to enhance flow measurements on remote, unmanned natural gas wells, gathering systems, and transmission lines is contributing to increased production efficiency and producers' profitability. Use of this type of equipment, linked by almost any popular communications method to a host computer, improves manpower utilization, enables faster corrective action in case of problems, produces greater yields, and documents compliance with government regulations. As a result, remote monitoring and control is growing rapidly, especially among independent producers.

According to information from the Independent Petroleum Association of America, 30,000 total gas wells were automated at the end of 1995. The benefits of automation are stimulating the installation of monitoring and control equipment (RTUs and flow computers) on some 8,200 additional wells each year, and improved economics has broadened the field of candidates for automation to more than 50 percent of the 296,000 operating wells in North America by the end of 1995.

This growth is the product of several significant technology-driven trends that have reduced the life-cycle cost and improved the profitability of gas production automation:

• easier installation, integration, and operation of equipment

• greater control over well operation with improved reliability

• increased profitability from automated wells

• faster and less expensive communications from remote sites.

Easier Installation & Use

One of the major reasons many independent producers have been hesitant to invest in remote monitoring and control was their concern over the complexity of the electronics-based equipment. Now, increasing interest by the independents is due in large part to recognition of this problem by leading manufacturers and their efforts to make products that are easier to install and operate. Many producers want to do their own installation, programming, and maintenance. This is now possible with compact, turnkey units that give good results when taken directly from the shipping crate, connected to the meter run, and turned on. In addition, downloadable programs are available for changing a unit's operating values to achieve specific objectives.

You don't have to be a computer programmer to customize today's units to perform specific control functions. If a user wants to base some calculations on certain measured inputs in order to have the unit make a well-head flow adjustment, it should not be difficult for a maintenance technician to do the necessary work through a user-friendly interface. Some RTUs and flow computers, for example, are equipped with advanced function sequence tables (FSTs) that facilitate customization.

Most manufacturers are also working to make their units easier to integrate with a customer's existing automation system.

Remote Control

The increasing sophistication of field units is making possible greater control over well operation. Thus, we now have "flow computers", which are RTUs with differential and static pressure transmitters integrated into them. Flow computers are able to take the measurement information provided by metering devices and transmitters, along with user-entered inputs, and produce an accurate and reliable record of the gas quantities that have passed through the measurement point.

The addition of flow control allows the producer to take advantage of spot markets and maintain control over nominations by increasing or decreasing production accordingly without having to send an employee out to the site. The improving economics of remote monitoring and control is another reason why more and more flow computers are being installed on moderate yield wells.

Flow computers are highly reliable today, a result of the increasing use of surface mounted electronic components, which are better able to withstand exposure to the wide range of temperatures, dust, and vibration encountered in gas production fields. They also tend to be less expensive to purchase and maintain than their predecessors.

Improved Economics

While high performance monitoring and control equipment can be expensive and represents a cost that some producers may feel they can avoid, the fact is that over the long-term, remote monitoring and control reduces operating costs and improves a producer's profitability. A number of factors contribute. More accurate measurements, tighter flow control, and faster response to changing conditions result in greater yields, and that in itself improves the producer's bottom line. In addition, timely reporting of field conditions helps reduce the number of visits to the site by field service personnel, but when the equipment sounds an alarm remotely, personnel can be dispatched quickly to rectify the situation. Also, data obtained and stored by this equipment provides the audit trail, event and alarm logs, and other information needed for the documentation required by customers and mandated by government regulations.

In addition to these general benefits, a number of costs associated with remote monitoring and control equipment are decreasing due to advanced electronics technology. For one thing, all the components are assembled into one compact, easy-to-install package. These rugged, self-sustaining units contain field connections, central processing unit, memory, and communications equipment. They are easier for the smaller independent companies to purchase and install.

Lower overall power consumption is another important economic factor resulting from the use of advanced electronics that are smaller and require less power. At the same time, computations are becoming faster as more equipment makes use of 32-bit processors. When evaluating equipment, prospective buyers should consider overall performance and installed cost of the unit.

Still another economic consideration is the ease of field maintenance and upgrades. Users can exchange equipment, reconfigure a new unit, add input/output (I/O), and bring it back on line quickly without calling on the manufacturer. It is also possible to store all the configuration information in a safe place so that it can be downloaded when needed.

In this regard, it is very important for producers to have solid support from the suppliers of both hardware and software to ensure smooth, reliable operation of a remote gas monitoring and control system. Support can be in the form of technical advice, proven gas field applications, training of maintenance personnel, and local manufacturer's representatives who can answer questions and provide a variety of customer services.

One thing should be clear. The up-front cost is not the best measure of value with this equipment. Factors such as accuracy, reliability, ease of use, flexibility, application of open standards, supplier support, and potential for increased productivity should also be considered when evaluating the true cost of owning a remote electronic measurement, monitoring, and control system.

Advanced Communications

Another area of dramatic cost improvement is in the communication of data between RTUs and the host computer. Communications via digital cellular phone networks are faster and can be less expensive, especially for smaller independent producers because they don't have to install expensive private communications systems. They simply utilize the existing cellular system without the large capital outlay necessary for other methods of communication from remote sites. As cellular coverage becomes more widespread, this will be an increasingly popular method of communicating, further expanding the use of monitoring and control equipment.

Cellular Digital Packet Data (CDPD) is currently being used in a successful cellular communications application between a host computer in Oklahoma City and RTUs in the gas fields of western Oklahoma. The cellular carrier is charging a flat rate for communications, modem, antenna, and necessary coax cable. Ultimately, CDPD charges will be by the byte of data sent, estimated to be in the range of $15 per the first 100 kilobyte with lower rates for additional 100 kilobytes.

For areas without good cellular coverage, an alternative communications system may soon be available employing low orbit earth satellites. This advanced technology should work very well, but initial costs may not be competitive with conventional communication methods.

Lightning Protection

Direct lightning strikes can seriously damage most electronics equipment. However, catastrophic damage resulting from the electromagnetic interference (EMI) and radio frequency interference (RFI) caused by nearby strikes can be prevented or reduced. If the monitoring and control unit is isolated from the meter tube and provided with its own local ground, the effect of indirect hits is minimized. Other methods have been tried, experience has shown this approach to work best.

Additional lightning protection is also necessary for I/O signals and communications connections. This can be achieved with gas discharge tubes and metal oxide varistors (MOVs), ensuring continuous operations under harsh conditions.

A State-of-the-Art System

A large independent producer operates a sophisticated natural gas measurement and control system in the Hugoton Gas Field, which is regulated by the State of Kansas. The recently installed system comprises flow measurement, valve control, solar power with battery backup, and radio communication to a host system of multiple personal computers running Intellution software. The remote equipment will also accommodate future interfaces to other on-site equipment such as salt water tank level instrumentation, pumping unit control, and well compressor status.

This system incorporates sophisticated modeling logic that balances the desired flow from the wells so overall flow to each compressor remains constant for any given period. Market information is used by the host to set start times, duration of flows, and flow rates. This data is downloaded to each field device which then operates independently for up to one month, resulting in increased total flow from the field by optimizing throughput for each compressor.

Daily operations reports from the field units are automatically communicated to field personnel each morning, allowing them to quickly correct problems that could reduce output. This is especially critical in winter when low temperatures can cause taps to freeze, making it difficult to keep pumping units and field compressors on line at a time when demand and prices are highest. Utilization of operating data has resulted in increased overall flow and improved flow balance from the field. While specific numbers have not been released, a 2 to 3 percent flow increase is probable due to faster solution of potential problems.

Accurate control and automated adjustment for pressure changes have also had a positive impact on productivity. Prior to automated control, operators shut off some wells before reaching desired production levels because they would not return to the site soon enough to prevent excess production. Field automation now achieves target production with much greater precision, and valves are continually adjusted to obtain the desired flow rate as pipeline and well pressures change.

Short-term production gains are achieved as market changes and opportunities are identified by increasing or decreasing production for the spot market. Using the flow control features of the system, a new field flow rate and control strategy can be operating within minutes after being downloaded from the host.

In addition, operating costs have been reduced. One field operator is now responsible for about 50 percent more sites, and the company has been able to add wells without increasing field personnel. This producer is also reported to have reduced contract services for well monitoring by $60,000 per month.

Future Issues

Just as open architecture is the choice for most new industrial control systems, open, non-proprietary systems are expected to prevail for remote gas monitoring and control. Buyers should beware of proprietary systems which may quickly become dinosaurs. Prospective buyers should ask, "If I buy a proprietary host package and later want to install RTUs from another manufacturer, how expensive will that be?"

Host computer software should facilitate communications with all types of field equipment as well as other computer systems within the company. Intellution is one example of open software that can communicate with any RTU.

Communications protocols are another area where an open standard should be embraced. The commonly used MODBUS protocol has been modified many times in an attempt to make it serve these applications, and many of the larger companies have adopted their own private communications protocols. Just as the process industries have standardized on the Fieldbus protocol, this industry needs a standard protocol. A standards committee should be established as soon as possible to address this need.

Conclusion

Gas monitoring and control has come a long way from the days of chart recorders. Advanced electronics devices and telemetry have brought knowledge of field operating conditions to the home office, allowing greater, more timely control over individual wells for increased productivity and profitability. As more and more wells are automated, these benefits will spread throughout the natural gas industry.