Surveillance system innovations
Gregor Deans, Amin Amin, Kunal Dutta-Roy,
Schlumberger
The industry’s new advances in surveillance systems have allowed innovative ways to monitor subsea systems and production operations extending from the sandface to the host facilities. This enables productivity optimization through closed loop actions based on factual real-time information.
Combining real-time data acquired from subsea monitoring systems with modeled and historical data, expert analysis and real-time productivity optimization tools provide the necessary information for detailed analysis of production and hardware performance. This information allows interventions and production operations to be planned more efficiently, thereby reducing downtime, production loss, and operating expenses.
In the last few years, the industry has dramatically increased the number of intelligent seabed and downhole monitoring devices in the subsea industry with the introduction and acceptance of multiphase flow metering, fiber optic temperature and flow sensors, intelligent well flow control devices, and similar systems. E&P companies have launched a number of initiatives to develop smart-field technologies, infrastructures, data visualization, and analysis applications.
Digital oilfield
In 2002, Cambridge Energy Research Associates (CERA) began a study into the digital oilfield of the future (DOFF), interviewing over 150 industry experts. CERA also pursued studies on the technologies available and the operator needs and business drivers. The CERA study detailed a number of fundamental capabilities that were key in the implementation of the DOFF, including full monitoring of the asset from reservoir to process, the ability to view data remotely, improved tools for data analysis and visualization, and more advanced and reliable monitoring and control systems.
The DOFF study identified four main drivers for increasing value:
• Enhanced recovery
• Lower operating costs
• Increased daily production
• Reduction in capital costs
For subsea fields, improved subsea design and advanced surveillance can lead to two distinct cost savings:
• Increase in production through the use of intelligent wells, reservoir and subsea modeling, and other advances
• Reduced intervention costs and deferred production, by the reduction or prediction of equipment failure
Well intervention
Current PCS are designed primarily for tree and downhole safety valve control and to monitor the pressure and temperature at the wellhead - a usage that has not changed significantly in the last 10-15 years.
Most wells require intervention during their life spans. Operator well interventions could be installing or servicing control valves, changing gas lift valves, production logging, pulling failed tubing, removing scale or paraffins, perforating new sections, or squeezing cement into perforations to shut off water flow to extend the productive lives of wells and provide additional well and reservoir data. However, subsea interventions are not performed routinely, because their associated costs and risks are considered prohibitive. Because of the lack of routine intervention, an operator’s subsea well overall production performance is estimated at 75% of a comparable land or platform well.
Subsea limitations
The industry recognizes the inherent limitations of today’s subsea production control systems (PCS) that restrict the availability of high frequency data, production, and equipment diagnostic data, for analysis on the hosting facility or onshore.
These limitations include:
• Low data rates for subsea sensors due to the legacy modem technology used by current PCS
• Lack of diagnostic data (fast loop data) due to the low data rates
• Lack of transparency as data acquired from seabed and downhole sensors is collected by the subsea control system processor over a local master/slave communications link and then passed to the surface along with the tree valve and production data
The industry's solution to the problem is to separate the production and surveillance functionality on the seabed.
• Lack of plug and play with subsea PCS sys-tems where subsea sensor data and subsea to-surface communications are routed through the processor in the PCS subsea control module (SCM). This limitation is being partly addressed by the ongoing intelligent well interface standardization (IWIS) initiative
• The low data rates and lack of communications management often result in the required sensor data being queued and/or delayed
• Limited expandability because current PCS are designed for purpose, which is primarily tree valve control
• Downhole and seabed control and monitoring equipment must be defined early in project development due to the limited expandability of PCS systems.
Solution
The industry’s solution to the problem is to separate the production and surveillance functionality on the seabed. This would allow the PCS to perform all production control functions such as tree and downhole valve control and production safety related monitoring and control, e.g., emergency well shutdowns. All monitoring equipment, except production safety related equipment, would be routed through a separate surveillance system.
The system consists of a stand-alone subsea electronics module mounted on the tree or manifold which provides a high bandwidth communications link to surface allowing additional sensors to be added subsea. This communication link to surface can be over dedicated fiber optic or electrical lines in the umbilical or by optical multiplexing using the existing PCS fiber optic communication lines.
The two major advantages of separate surveillance and control systems are that the operation of the surveillance system does not necessarily affect the existing infrastructure and that it can be retrieved without interrupting production.
The introduction of high bandwidth subsea to surface surveillance systems such as the Schlumberger Subsea Monitoring and Control (SMC) system can result in a significant increase in the amount of production and equipment data available to the operator on the platform/FPSO and onshore.
The SMC surveillance system provides a local, managed communications network on the seabed and is also IWIS compliant; so instrumentation and control modules can interact seamlessly reducing interface engineering, testing and costs.
Early involvement in the development and eventual adoption of these standards is essential for the integrated sensor-to-engineer process and the uptake of the DOFF within the industry.
The CERA group identified that the trends in the technology toward an industrial Ethernet-based system providing advanced alarming, device-to-device distributed communications, robustness, and lower cost sensors will lead to appreciably better systems. The use of these networked solutions would provide higher reliability, built-in redundancy and improved monitoring of facilities.
The SMC system provides the subsea TCP/IP network, which brings this functionality subsea and links the subsea sensors to the platform or FPSO network and then linked to an onshore network. This connectivity allows remote configuration of subsea equipment from onshore but more importantly links the onshore engineer to the field.
Also, this system allows the development of a data flow from sensor to an onshore operations center (OOC) or onshore support center (OSC), identifying and reducing interfaces and complexity while providing open and expandable system architecture for future sensors and analysis software. The CERA group identified the benefits of the DOFF and the onshore centers as providing:
• Reduction and discontinuation of manual data gathering and input tasks
• Emphasis on “visit-by-exception” to resolve equipment and production issues
• Flexible staffing based more closely on consulting models where each knowledge worker is assigned to two or more project or asset teams
• Centralized off-site monitoring.
Wellsite data gathering
Due to the increase in real-time data at the wellsite, an offshore-to-onshore data management system is needed to handle the transfer of the production data to the operator and/or service company onshore database.
The transmission of the data onshore allows visualization and analytical tools to be employed, thereby reducing the volume of data and providing information and event notification that is relevant to the engineer. This includes the calculation of productivity index from measured data and associated models, predictive alarming, and the use of decision-making tools such as chemical injection optimization, system performance monitoring, and the detection of events and trend violations by raising red-flag failures with an associated severity level.
Offshore data gathering systems such as the Schlumberger WellSite Interface (WSI) system allow data to be collected from multiple wellsite acquisition systems over both serial and Ethernet communication links and from direct I/O e.g. 4-20mA signals from local sensors. The data is then packaged into Wellsite Information Transfer Mark-up Language (WITSML) files.
These (WITSML) files are delivered either to a local or remote operator database and, if required, an onshore externally hosted database. A web-based user interface allows the onshore engineer to browse the acquisition systems connected to the offshore WSI remotely and select the data points he wishes to pass onshore.
Data transfer and security
Currently, the industry standard WITSML data format is primarily for drilling data; however, there is an ongoing initiative guided by the Petrochemical Open Standards Consortium (POSC) group to develop similar data schemes for production data.
The industry’s ability to send the data securely is essential especially when sensitive production data is involved. A company’s use of the Hypertext Transfer Protocol over Secure Socket Layer (HTTPS) protocol for encryption when passing the WITSML data files onshore provides a level of data security.
The system applications must also be made to operate locally at the wellsite or within the onshore center and provide validated event detection and notification in areas, such as monitoring of subsea equipment conditions and flow assurance attributes in pipelines and risers. These tools can be integrated into OOCs to allow an engineer to launch analysis tools directly from the operations center interface when an event is detected.
Condition monitoring tool
With the availability of data management tools to allow the transfer of real-time subsea data to onshore support or operations centers, the operator often finds himself provided with large quantities of raw data but little information of what the data indicates or context to allow operational decisions to be made. Tools must be designed to reduce the quantity of data presented while increasing the information provided to the operator.
Advanced software decision tools are required that would provide condition monitoring of subsea production and equipment using real-time data. This would reduce the quantity of data to process and provide the operator with immediate recommendations to improve production while reducing possible equipment failure. These tools must be designed to provide the operator with useful, qualified production and equipment event information even in subsea fields where non-validated or missing data due to failed sensors may exist.
Rather than provide a complete control loop process i.e. monitor, analyze and control, the goal of these tools is to monitor, analyze , provide alerts and remediation recommendations to the engineer who needs them, whether through a visualization tool, historian interface or email, with all the necessary data to make the appropriate and informed decision. The email or report can contain contextual data as well as schematics, process and instrumentation diagrams, etc. to provide the engineer with all the data required to analyze the event. The tool can also be linked to an operators messaging, support or maintenance ticketing application in order to provide the appropriate engineer with the timely information to manage the event.
Interfaces and Standards
In 2002 the custody of the WITSML specifications was transferred to the POSC group who are involved in the initial development of the specifications of a mark-up language for production data called WITSML Production. It is anticipated that this will become the standard for data exchange for production data from the wellsite. Additionally, another ongoing project maintained by the POSC group called ProductionML (or ProdML) is designed to develop a standard for the delivery of production reports.
Early involvement in the development and eventual adoption of these standards is essential for the integrated sensor-to-engineer process and the uptake of the DOFF within the industry.
As these technologies become proven through field trials and permanent installations, it is now the responsibility of the subsea community to assess the cost/benefits, and be more aggressive towards the adoption of subsea reservoir/production surveillance systems in tandem with the more traditional tree-centric control systems.•
Editors Note: This a summary of the “Advances in Subsea Events Monitoring and Data Analysis Systems” paper presented at the DOT Conference & Exhibition in Vitoria, Brazil, Nov. 8-10, 2005.
