Developing a Retrieval System for Subsea Sensors and Transmitters

Abstract Operators are facing increased complexity in their subsea operations with up to 1,500 subsea sensors and transmitters installed each year [1]. Whereas the retrieval of topside sensors has proved to be very successful delivering significant cost savings, operators face maintenance difficulties and costly subsea interventions in upgrading and replacing subsea sensors. This paper will look at how subsea technology has evolved to enable operators to retrieve subsea sensors, allowing them to better maintain existing instruments, replace failed ones and install improved versions. Such developments can save customers millions of dollars by reducing the cost and time required to maintain subsea assets. The paper will look at the challenges Roxar faced in developing the first industry-wide subsea sensor retrieval system utilizing an ROV (Remotely Operated Vehicle) and which was evaluated by a consortium that includes BP, Chevron, Shell, Total and Statoil. The paper will also examine the key elements of the system including the ROV tool and the Hydraulic & Control System, which enables the ROV to control the retrieval tool. Testing results and applications will also be referenced. The paper will interest all operators looking to optimize their subsea equipment and address a challenge commonly faced by everyone in the deepwater offshore production industry. Introduction - The Market Need As oil and gas companies in Brazil and elsewhere continue to pursue complicated and costly exploration in deep and remote waters while, at the same time, looking to optimize production, there is an increased demand for better data and intelligence on operating conditions subsea and downhole. Whereas a single production field may have 20 to 30 operating wells, with more than 40 production trees and manifolds, each of these assets can have anywhere from five to 15 monitoring sensors mounted with up to 1,500 subsea sensors and transmitters installed each year. Such instrumentation measures pressure, temperature, and sand erosion or corrosion, and is retrieved from trees, manifolds and other process systems. Furthermore with a predicted annual deepwater spending to reach US$35 billion by 2014 [2], the deployment of these sensors is only likely to increase. It is these sensors that provide operators with increased visibility to production variables, early indications of degrading asset health, and early warnings of impending abnormal situations. As intelligent sensor usage increases and production environments become more complex and remote, the demand for easier ways to maintain these assets becomes paramount to improved reliability and lower operating costs. A December 2009 Emerson survey [3] of subsea specialists, for example, found reliability to be the most important criteria in subsea installations today (see figure 1) with a further 89% welcoming a system that could retrieve instrumentation during production.