John N. McEwen
Shell Canada Ltd.
Calgary
A third-party supervisory control and data acquisition (scada) software package, it's modules and utilities, can be used as a platform for scada development in a wide variety of situations.
The IRIS 75000 scada software package, from Datap Systems of Calgary, enabled Shell Canada Ltd. (SCL) to develop a complete retrofit system for its Burnt Timber natural gas complex in Alberta while maintaining internal staffing levels at a minimum.
In 1989, not only was Burnt Timber's system replaced, but also developed was the Jumping Pound gas complex located east of Calgary, and the Virginia Hills oil complex north of Edmonton. The preceding and other smaller projects were implemented with a total average staff count of 1 0 for the year.
Now that the majority of new systems are in place, staffing levels are maintained at lower levels. This could only be achieved if commonality between systems is strictly maintained from the operating system right through to the core scada product.
Software package enhancements, modifications, and bug fixes are made by the computer software vendor only.
SCL does not have any source code for the basic scada package, which keeps responsibility focused back with the vendor.
Because the scada software product was fairly new, many problems were encountered early on with functionality and bugs. To deal with these, a strict software reporting and tracking scheme was put in place which the vendor and both parties adhered to it at all times.
CHOOSING THE SYSTEM
In late 1986, the computer assisted operations (CAO) group decided to utilize a third-party package for new field scada systems and replace existing ones where economically viable. Up to then, HP1000 (Series E & F) hardware technology had been used in seven SCL oil and gas fields. This hardware, according to the vendor, was a discontinued line with reliability and serviceability eventually becoming an issue.
The scada software had been jointly developed with Shell Oil Co. (SOC) up until 1980. Independent development paths then ensued due to differing operational requirements.
The software eventually became outdated, while becoming increasingly difficult to modify and maintain.
Because of its nature, many day-to-day changes had to be made by the CAO group and then ported out to a field system. This contributed to the ever-increasing backlog of field maintenance requests.
The manpower-intensive nature of the older HP1000 scada systems was becoming a deterrent for system justification in new fields. Specifically, the Clearwater and Panther fields in Burnt Timber were to come on stream in 1988 and 1989, respectively, and the Virginia Hills oil field (enhanced oil recovery) in late 1989.
SCADA PLATFORM SELECTION
A strategic review, conducted in 1986, evaluated six approaches to scada, using decision-analysis techniques.
the alternatives were as follows:
- Deferred action or status quo
- In-house upgrade
- In-house rewrite
- Contracted or systems house rewrite
- Modify SOC's system
- Third-party package.
Various attributes were analyzed, including initial software development and hardware costs, long-term over-life costs (15 years) for software and hardware, field requirements, and support factors.
All this indicated SCL should be moving towards a new generation of scada hardware and software, making use of a third-party package if possible.
The scada products of 65 potential vendors were evaluated via telephone interviews. A second and more extensive telephone interview was conducted, based on technical and functional capabilities; ten vendors remained. Eventually five finalists emerged.
Based on the functional and data processing requirements, Datap Systems of Calgary was selected. The IRIS 75000 scada package from Datap is based on ESCA Corp.'s real-time data base product, HABITAT, which runs on the DEC VAX/VMS suite of computers. Datap provides scada functionality as an OEM user of HABITAT.
PLATFORM DEVELOPMENT
Once the decision was made to use Datap's scada package, a contract had to be negotiated to define the various levels of functionality required.
The CAO group wrote a statement of requirements (SOR) which defined the required changes to Datap's scada software. Each item of this SOR was evaluated by Datap as to it's fit with Datap's own development plans. Most requirements were accepted or slightly modified.
One key design factor identified in the scada review material and discussions was the need to accept the basic package design as is. Without this mind set, third-party package benefits would have been difficult to achieve.
Another major design consideration was the template concept. For example, applications such as metering, choke-valve control, and emergency shutdown would be used in every installation.
The final major consideration was the user's familiarization of IRIS 75000. Initial product walk-throughs with operators and technicians from fields to be retrofitted were conducted. This was key to the definition of enhancement requests and facilitated a sense of product ownership which in turn helped gain acceptance of the template concept.
In 1987, a project execution plan (PEP) was defined which set out project activities, the accountabilities and schedules which covered the completion of the IRIS 75000 Version 1.1 platform, and its implementation in the first retrofit field, the Waterton gas complex in southern Alberta.
All of the preceding was completed on time and within budget by mid-1988. As a result of this exercise, the CAO group and Datap learned much about what was useful and what features should be added, deleted, and altered.
The next release of IRIS was version 2.0. This was to be implemented in 1989 in three fields: Jumping Pound gas complex Virginia Hills oil field, and the Burnt Timber gas complex.
BURNT TIMBER GAS COMPLEX
The Burnt Timber gas complex is located about 100 km northwest of Calgary in the central Alberta foothills. Shell Canada is the major owner and operator of the complex which includes the Burnt Timber gas plant, three compressor stations, and operations for five fields south and two fields north of the region (Fig. 1).
The major fields include Burnt Timber and Panther River in the south, and Limestone and Clearwater in the north. These fields were discovered between the mid-1950s and the mid-1970s, with production first starting in 1970. The gas from these fields contains from 1 to 30% hydrogen sulfide and is produced from about 50 wells.
The raw sour gas from the south is processed by the Burnt Timber gas plant while gas from north fields is handled by a nearby non-Shell gas plant. A single day's production from the complex is enough to heat 250,000 homes in southern Alberta.
All of the wells and compressor stations are in remote areas where it can take up to 1 hr for an operator to drive between wells.
To drive from the most southerly well to the most northerly well can take 4 hr or more depending on the weather conditions.
It is the remote monitoring and control that substantially reduces the amount of check-out time, provides current data on the well's operation, and gives the ability to control the well as product demand changes or in meeting an emergency situation.
Safety of operation from an environmental and personal level is a key principle for the use of a scada system within Shell Canada.
SYSTEM HARDWARE
Due to the complexity of the fields, remoteness, and the need to keep scanning up-time to a maximum, it was decided that a high availability scada system should be put in place.
A redundant system in a master/standby mode was selected, specifically a DEC MIRA MicroVAX 3600. This system contains two separate and independent computers. One is designated the master and runs the scada application. The other is designated the standby and waits to take over when the master fails or is taken down.
Each has its own operating system, memory, and mass storage devices. A hardware /software "watchdog" function monitors the master computer to detect failures and initiate the switch-over process. Switch modules are used to transfer input/output (I/O) lines to the standby system.
This particular hardware /software combination is classified as a "warm" standby system. The master has been set up to transfer relevant scada information to the standby once per hour, and the actual time involved in a fail-over is about 10 min.
Thus, the system is unavailable for only a few minutes and is up to date to within the last hour. This was deemed sufficient from an operational viewpoint.
Independent front-end processors (Simpact) are used on each System to scan from, and control to, the various programmable logic controllers (PLC) and remote terminal units (RTU) in the many fields.
These Simpact processors, based on PDP-11 technology, currently communicate with three protocols: Modbus, Allen Bradley, and a generic Shell protocol. The first two are used for PLCs while the latter is used for many different types of RTUs.
In Burnt Timber, Vascon 100 and Hydril RTU protocols are used. Information gathered by the Simpact processor is then forwarded onto the data base in the scada application. This is a report-by-exception process whereby the Simpact retains the last value scanned and a maximum deviation value, as configured by the field personnel. This exception reporting cuts down dramatically on the number of interrupts hitting the scada VAX computer.
The scada configuration has been designed to handle two types of terminal support. This includes the Aydin 4100 console and the Aydin emulation using ESCA's PC17 software product running on an IBM PC or compatible (Fig. 2).
The graphics used in both products are character graphics supporting a display of 42 lines by 80 character. The Aydin 41 00 is basically a WYSE PC with a custom graphics board, custom software, and a 19-in. monitor. Its keyboard layout has been expanded to include a custom 48-function keyboard which is configurable by Shell.
Custom graphics characters have been generated and are displayed via the installation of a character chip in each Aydin 4100. The 48-function keys are also supported via PC17 on an ordinary keyboard, but are accessed by using combination keystrokes.
A total of 13 Aydins exist in the field, along with two spare units. Field staff also have the ability to dial in from home using their own personal computers. This is very useful during off hours when field staff are not on site.
Communication within the complex is based mostly on a light route microwave system called the SR500 system. Due to the complexity of terrain and distances involved, this system proved more economical than buried cable or a complex network of UHF radios, although cable and radios are used in areas of difficult terrain.
The scada system uses the microwave system for scanning, operator console, and printer functions, distributed throughout the complex. It's architecture is based on a star-like structure with all routing information passing through a central station located in the nearest town. Five repeater stations and six out-stations are necessary to provide total field coverage.
In one instance, three microwave hops are required to get data from the field office scada computer to the central microwave station, and then another four hops out to a particular gas field, for a total of seven hops.
SYSTEM SOFTWARE
The IRIS 75000 software package is a third-party scada system designed to run on DEC's VAX range of computers under the VMS operating system. IRIS 75000 is developed by Datap Systems of Calgary and is layered upon the real-time data base tool, HABITAT (Fig. 3).
The real-time data base contains a current image of the field status and is kept up-to-date continuously by the data acquisition subsystem. Basic data processing functions include status and multistatus points, analogs, meter (accumulator) points, set points, and controls, all with the appropriate alarming and thresholding.
Alarming features include flexible definition of points to be alarmed, alarm frequency and delay thresholding, alarm lockout and suppression, and alarm reduction. Other features of the package include:
- A derivation package providing decision making and conditional logic capability that can issue controls or trigger tasks
- Basic scheduler package with wide functional applicability
- Man/machine interface
- Data base builder/editor
- Event archiving and logging capability to maintain history of events
- Trend package for sampling of select data and subsequent graphical/tabular display
- Special applications such as trouble tickets and electronic mail
- Dual computer configuration support.
In the IRIS software, a main menu exists which gives user access to all of the functions required by field staff. Many overview schematics of the field have been created which are organized hierarchically to go from macro to micro views. These schematics are the main avenue for traversing through the system.
On every schematic or display, there are reserved areas. One of these displays, the first-alert zone, is used to convey knowledge on most recent alarms. Another reserved region of the display, shows log information of the three most recent significant activities on the system. The full log system can also be easily viewed if desired.
One of the most critical features related to safety is the emergency shut down (ESD) menu. Via this display, an operator can shut down each well or compressor station in an orderly fashion in case of emergency.
Other security measures include the definition of numerous security levels which are assigned to each user of the system. Each level permits only certain functions to be performed on the system. Along with this is an assigned area of responsibility. Because the complex is so large, only certain operators are permitted to control their designated fields.
The system also reports on the velocity of gas in the pipelines. This is used in monitoring potential corrosion-related problems.
User-written applications can be incorporated into the IRIS product by using the fundamentals of the HABITAT real-time data base tool. One such application developed by Shell is a metering package. This subsystem scans for oil/gas flow rates, pressures, and temperatures, and then integrates them over time to determine a volume for the day.
The calculations, American Gas Association AGA3 and AGA8, incorporate gas composition figures to convert from operating conditions to standard temperature and pressure. This adjusted rate is mathematically integrated over time to give a produced volume for the day.
Metering is written in Fortran and uses HABITAT subroutines to access the associated data base.
Shell has also developed a central system used to collect scada data from field systems. The central operations production data (COPD) data base provides a centralized (Calgary) system of data collection where corporate systems and individual clients can obtain raw field production data without having to duplicate communication and data-gathering systems.
Data are sent daily from the field scada systems to the COPD MicroVAX 11 to reside on an Oracle data base for up to 60 days. These data are automatically transmitted monthly or on request from this machine to various corporate data bases for automatic report generation and long-term retention.
Facilities are available for ad-hoc retrievals of field data. The type of data sent includes temperatures, pressures, flow rates, and some mechanical information.
SYSTEM PREPARATION
Before the project could begin, a set of formal project design and control documents needed to be completed. The first was a design basis memorandum which provided the foundation for all project design, development, and implementation decisions.
The second was the PEP which identified the complete set of project activities, the accountabilities and schedules.
From the estimations provided by the PEP, two authority for expenditure (AFE) documents were raised. A capital AFE for tracking hardware costs and an operating and maintenance AFE for tracking development and software expenditures.
The DEC MIRA 3600 was delivered to Datap Systems of Calgary in the fall of 1988 for testing of the IRIS scada software. It was then delivered to Shell Canada in December of that year for development to begin on the Burnt Timber system.
SYSTEM DEVELOPMENT
Actual development of the scada system began in January 1989 on the MIRA, temporarily located in Shell's Calgary offices. This initially involved further testing of the software in a MIRA environment.
Local expertise for supporting the DEC MIRA system and the IRIS scada software in this fail-over mode was deemed to be initially low. This was recognized by the vendors and after 2 months, improved substantially.
Once the fail-over mechanism was fully tested and understood, actual development began on Burnt Timber's system. After the core product was installed, the system was readied for final delivery to Burnt Timber's field office in May 1989. This involved a day's worth of system preparation by DEC, delivery over 2 days, and final set-up over another 2 days.
This complex system required much cabling in the back panels, and great care was taken to get it right.
The scada application development took place on a field-by-field basis. The new gas fields coming on stream, Panther and Clearwater, were done first. The remaining fields, already under scada surveillance by the older HP systems, were implemented next.
To model 50 wells and three compressor stations, approximately 6,000 status, multistatus, analogs, set points, and controls were configured into the IRIS data base. Roughly 250 additional custom displays also had to be incorporated into the system. Along with this went all the associated communication and polling information into respective data bases.
A total of 13 Aydin consoles were required throughout the complex. These were located in the field office, compressor stations, gas plants, and one in the nearest community.
Printers were also located with each Aydin. Communication baud rates range from 300 to 4,800 for scanning purposes, 2,400 for printers, and from 9,600 to 19,200 for Aydins. The remote dial-ups are served by 2,400 lines.
The typical scan rate used is 1 min, with demand scan functionality being operator or circumstance driven.
While in the master/standby mode, the MIRA copies critical information from master to standby once per hour. The average fail-over time is 10 min. The system will fail-over whenever certain hardware or software problems are detected, or whenever back-ups are performed. A full system backup is performed once per month, with save cases of critical data being captured to tape every night.
The commissioning stage involved the check-out of every point and control in the system. This was very time consuming since it usually involved one to two crews of two field staff tripping alarms or altering values on the end-devices of each well or facility.
The development staff back at the field office would then verify, via radio, the activity on the scada system. All safety-related points and controls were tested first.
The Panther and Clearwater fields were new, so their points could be tested before actually bringing wells on line. The remaining fields, which were already being monitored via the older HP scada system, had to have strings of RTUs swung onto the new system at a time.
This usually required an increased work load in a short period of time to ensure that the wells could be operated safely on the new scada system.
For the Panther and Clearwater well sites, PLCs were used as RTUs. This permitted easier commissioning since the PLC could be brought into the field office, hooked up to the MIRA VAX and then checked out.
At the site, only the connection between PLC and the end devices had to be verified. This substantially reduced the amount of checkout time. The PLCs, once in place, could also handle local ESD and process control functions.
The training of staff was coordinated in the field to hit every shift crew. Approximately 15 days were required where Aydin consoles were set up in a classroom environment. Up to four Aydins were used to accommodate no more than ten people at a time.
The project was completed by early December 1989 at a total cost of U.S. $615,000 against a budget of $650,000.
The direct, up-front involvement of operations staff (users), including the participation of a liaison, assisted in the definition and acceptance of the system. Both the field and plant operations groups are very pleased with the platform-based application. Because of the third-party nature of the system, whereby one accepts what they get, a small portion of the way they do business had to be altered. This has not caused any detrimental effects.
Having the complete set of project documentation in place and reviewed by team members prior to actual project development greatly assisted the staff in meeting its targets.
The template concept has been accepted by the fields and was necessary to maintain reasonable support levels as more systems were installed. The operators now have more control over their own system which helps to instil a sense of ownership.
The next challenge is to allow the operators systematically to do more of their own modifications which traditionally have been handled by the central scada support group. The advantages of commonality between systems must be weighed against individual operator maintenance which could potentially move systems further away from the common core. This must be carefully managed to be successful.
BIBLIOGRAPHY
- Dixon, D.W., Light Route Micro wave Network for the Burnt Timber Gas Complex" Entelec '91, Houston, Mar. 3-6, 1991.
- Sandercook, T.G., "Quality Management--A Partnership in Excellence," Entelec '91, Houston, Mar. 3-6, 1991.
Copyright 1991 Oil & Gas Journal. All Rights Reserved.
