Minimizing downtime and maximizing uptime hinges upon a steady stream of timely, complete, and reliable information. The dynamic nature of subsea operations demands accurate and dependable data to assure safety, optimize production, and maintain technical and mechanical workings. Subsea well complexities require integration of all parts to work as a whole, which often limits equipment selection or prohibits upgrading existing infrastructure. Typically, establishing the subsea infrastructure narrows options for monitoring and managing data because of protocol configurations. Simply put, all parts – technical and mechanical – need common formatting rules to relay and exchange messages.

Easing these data-transfer constraints was the premise behind a subsea production system that increases expansion options and enables combining incompatible systems or retrofitting a variety of designs into existing operations. Modular in design, this electrohydraulic system uses open standards that enable multiplex control, monitoring, and shutdown functions for all major tree manufacturers.

Multiple lines of communication opened
The subsea system employs an open communication controller (OCC) functioning like an intelligent digital modem, providing a flexible and robust link between topside and subsea devices. It also uses native protocols for connectivity. Traditionally, openness is obtained by converting all protocols into one common format and then transmitting through the single protocol to the surface. Although effective, this approach is inflexible, imposing barriers for ad hoc maintenance requirements for instrumentation. The OCC’s protocol independence can integrate with all major subsea tree manufacturers and interface with all third-party subsea devices. Each protocol can be transmitted transparently so third-party surface applications can communicate directly with their instruments using their native format combined with high data rates on multidrop topographies ideal for instrument maintenance activities.

Because the system uses an open architecture, it supports multiple interface standards such as Serial and Ethernet, providing compliance for open standards such as intelligent well interface standardization (IWIS) and transmission control protocol/Internet protocol. Flexible configuration via an in-built web client enables any topside port to be connected to any subsea port.

To manage the flow of information, open database standards can disseminate information from all subsea devices to real-time, operational, and historic databases. Manual input capabilities allow the operator to supplement or annotate the database with additional information. In this age of global links at the touch of a button, access to data is not limited by location. Connectivity to any subsea installation is possible through the Internet using any standard web browser. The interface for applications to talk directly to end devices is supplied by a topside master control station. A single topside unit can communicate with multiple subsea units sharing a single communication line. Weatherford’s system enables communication between the subsea network and the surface equipment through power lines or fiber optics depending on conditions, circumstances, and needs.

Data control facilitated
An offshore project in Indonesia recently used Weatherford’s subsea control system to produce nine wells via a subsea development, floating production unit (FPU), and nearby pipeline. The logistics of the project required communicating with the nine wells in four fields at water depths from 312 to 689 ft (95 to 210 m). The closest field lies 2.8 miles (4.5 km) from the FPU. The most distant field lies 16.9 miles (27 km) away. The parameters fall into the production system’s communication reach of up to 62.5 miles (100 km). Reserves from the four fields are estimated at 1 Tcf of recoverable gas. A robust production control and communication system was needed to withstand dynamic plate tectonics and consistently deliver reliable and accurate data because the area is prone to seismic and volcanic activity.

The first phase of the project developed five slots of a six-well cluster, commingling the production gases from each well and measuring flow rates using manifold-mounted wet gas flowmeters. Control of these five wells was facilitated from a single umbilical. Four additional trees positioned during the second phase were controlled from a separate umbilical installed during the first phase.

Subsea control modules (SCMs), which house an OCC and dual subsea electronic modules (SEMs), have full multiplexed control and monitoring of the subsea trees and instrumentation, downhole hydraulically operated valves, and the manifold wet gas flowmeters. The dual-redundant SEM design incorporates separate signal and power lines into independent canisters within the SCM. Each redundant power and signal line is interconnected and monitored by the redundant SEM. Failure of either SEM, either communications line, or either power line does not affect the availability of the other system components.

open-communication control, Weatherford

The open-communication control (OCC) system enables operators to connect with virtually all subsea tree instruments and peripheral devices. (Image courtesy of Weatherford International Ltd.)

The open platform and intelligent nature of the technology actively determines the optimum operating frequencies to maximize performance over subsea cables. Digital adaptation to external noise, cable construction, and other environmental factors enables high-reliability communication speeds of up to 390 kbps. Eleven hydraulic functions are available to each tree from the respective SCMs installed with a remotely operated vehicle (ROV). In shallower waters, these systems can be diver-installed. In very deep water, running tools or funnels are available with ROV assistance. The SCM design for this application does not require a running tool, so a variety of vessels can be deployed for future interventions or upgrades.

North Sea communications upgraded
With the OCC’s open architecture, the system can share the existing subsea network, which prevents replacing the infrastructure for updating or adding new instrumentation. A major operator faced that situation in the North Sea when 32 subsea-completed wells needed additional gauges. The wells originally were equipped with four electric pressure-temperature downhole gauges per well when the field came onstream in 1999. In 2007, the operator determined production objectives required eight gauges per well.

Expanding the number of gauges per well to optimize production presented several challenges. The system in place did not have built-in expandability, the existing control module did not have room for a new downhole communications card, and the newly selected card – an IWIS card – was not compatible with the existing control system. To compound this upgrade challenge, the existing number of communication wires in the umbilical and on the seafloor already was at capacity.

The retrofit capability of the SCM made it the logical choice to facilitate adding gauges because it could integrate with existing infrastructure and was compatible with the IWIS card. It also provides the means for further upgrades. Capitalizing on the multiplex control feature enabled the SCM to use the existing communication wires. Multiplex communication on the power lines provided the communication channels for the required number of gauges in the wells. The redundancy gained with the additional pressure-temperature gauges provided the data resolution needed for more detailed analysis. In addition to seamlessly integrating the system to facilitate additional data, communication speed increased from 1.2 kbits/second to 390 kbits/second.