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The oil and gas industry tends to seek integrated solutions that provide the full range of topside to subsea equipment and facilities down to the reservoir including installation, monitoring and life-of-field services. The subsea control system plays an important role as the binding element between subsea elements like subsea trees, manifolds, boosting and compression pumps in subsea production systems. The seamless integration of the production control system with the pump control system is the key for the success of providing an integrated solution from topside to subsea. The most efficient way is to incorporate and merge field proven know-how of pump and production control systems based on existing technologies and accommodate it for future needs. The benefits for the customer are reduced CAPEX and significant technical advantages, being only one interface to the distributed control system (DCS), a minimum quantity of installation and workover tools, less topside and subsea equipment for distribution and control and testing equipment, a fully integrated field monitoring system and field proven components consisting of the best technologies the market is able to provide. Depending on the project requirement a unified or integrated controls can be realized as an integration of the topside control units by adding the pump control to an existing production control system or vice versa. For new projects a full integration can be achieved from topside to subsea from system to board level. For full integration, common building blocks from the same subsea control module (SCM) product family are being used. Core components from existing technologies have been thoroughly evaluated and selected to form the basis for the new pump control SCM which completes the SCM family. With the introduction of the single-unit integrated controls SCM into the SCM family, a wide range of SCMs with a unified interface without losing the knowledge and experience made over years of operation can now be offered. The integration also facilitates the usage of online life-of-field services for pump and production controls in an integrated approach. This paper addresses the key benefits and the functionality of this technology.
Abstract Today's subsea control systems generate vast amounts of data that can be used to help increase productivity, integrity, and safety of the subsea production system, however the key question is; is all of the available data being fully utilized for this purpose? In majority of cases, the answer is sadly no. This paper will illustrate how remote condition and performance monitoring of the subsea production system enables a predictive, condition based maintenance instead of reactive maintenance. Condition and performance monitoring takes all subsea process and housekeeping data in real time; processes and integrates it with mathematical models in order to identify the equipment's condition. In addition, technical condition indices (0-100% values) are assigned to rapidly detect deterioration and aggregate equipments to provide an overall system condition. The solution is essential to be combined with experienced engineering support for consideration of equipment's criticality, past experience and equipment's operating philosophy. Monitoring production has historically been the operators’ main focus - knowing that a well produces and how a reservoir performs are arguably more important than knowing the integrity of the subsea equipment. This narrow focus, however has led to a down prioritization of equipment related data and a number of maintenance planning and integrity issues. Condition and performance monitoring provides a solution for operators to fully utilize available subsea and topside data in order to increase productivity and minimize downtime. This paper illustrates the benefits of condition and performance monitoring which enables proactive and predictive maintenance by providing operators with an early warning when the equipment starts to decline while still in operation, thus providing time for corrective action to be planned with minimal disruption to production. With the capability of remote surveillance and utilization of existing instrumentations and equipments, condition and performance monitoring solution can conveniently be implemented on both new and mature fields. Field case studies will be shared to illustrate how condition and performance monitoring solutions have been successfully implemented in previous projects.
The subsea production control system installed on 3 wells in Mobil North Sea Ltd's. Beryl Field have each logged five or more full years of service. This paper describes the control system employed and reviews the operational history.
The Beryl Field, an 80 square mile block 95 miles southeast of the Shetland Islands, was licensed in 1971 by the British government to a group of producing oil companies with Mobil North Sea Limited acting as the operator. Principal development of the field was designed around the use of a Condeep platform structure. This platform supports well drilling, production processing, oil platform supports well drilling, production processing, oil storage and tanker loading facilities. After installation of the platform in 1975, the field discovery well, 9/13-1, was completed and produced to the platform using a SEAL Intermediate System single wet tree. This well was brought on stream in mid-1976 and provided a good basis for development of future subsea wells.
In 1977, Mobil initiated a program to complete three previously drilled delineation wells. Hardware selection previously drilled delineation wells. Hardware selection consisted of Cameron Iron Works completion equipment and "Plain Jane" subsea trees along with Hydril control systems. Two wells were completed and connected to the platform in late-1978. The third well was brought on-stream in late-1979.
CONTROL SYSTEM REVIEW
The overriding characteristics in selection of the Beryl control system was 100% availability. That is, except for interruption of production because of other platform or downhole conditions, the primary objective of the control system was to available at all times. The reliability of existing control system components was enhanced by the use of both redundancy and back-up control capability. This, combined with ease of maintainability and field servicing were prime considerations in the control system chosen for the Beryl field.
The surface portion of the control system consists of a dual microprocessor based master station located on the Beryl Alpha platform along with a sequence system control panel and hydraulic power unit. This equipment is utilized panel and hydraulic power unit. This equipment is utilized to control the three subsea wells. Figure 1 depicts the system block diagram including surface hardware and that required for one subsea tree.
Each subsea tree includes three control pods. Two of these, redundant electrohydraulic (EH) control pods, house solenoid and hydraulically piloted valves in oil-filled, pressure balanced containers. Electronics are housed in a pressure balanced containers. Electronics are housed in a one-atmosphere enclosure located atop the hydraulic section of each pod. This pod serves as a back-up pod to the electrohydraulic pods. All pods are diver retrievable and field repairable.
Control system connection to the platform is via separate electric and hydraulic umbilicals. Operation of a tree in the EH mode requires both umbilicals to be functional; however, operation in the sequenced back-up mode only requires use of the hydraulic umbilical. Loss of the hydraulic umbilical causes all control valves, EH and sequence controlled, to return to their failsafe state resulting in well shut-in.
SURFACE EQUIPMENT Master Station
The dual microprocessor master station is the focal point for all control operations. Associated with the master point for all control operations. Associated with the master station is a master display panel incorporating control pushbuttons, status indicators and alarm readouts. pushbuttons, status indicators and alarm readouts. Each single microprocessor master station contains memory, processing modules, input/output modules and communication modems necessary for stand-alone control of the entire system. Them microprocessor module assembles all messages to be transmitted to the EH pods and receives all data from the pods. It establishes monitoring and command priorities, and generates and checks the transmission priorities, and generates and checks the transmission signals.
It IS not sufficient merely to speclfy the rellablllty or avallablllty of a system, there are differing requirements for the topsldes and the subsea elements It 1s well known that rellablllty data for electronic components exlsts, but for other components, such as subsea mateable connectors, not enough reliable data exlsts For these components additional crlterla should be specified to ensure that reliability is addressed during selection It IS tradltlonal for a reliability study to be carrled out during the detaled design phase A reliability study alone is not sufficient, t may be'closing the gate after the horse has bolted'' The quantitative specification of rehability, avalabllity and mantanability, before contract award, is the key to ensuring that the system design will be adequate