In recent years, monitoring of the subsea BOP in order to keep track of movements, loads, and fatigue accumulation on subsea wellheads has been performed. On the Norwegian Continental Shelf, more than 50% of the semisubmersible drilling rigs have equipment for measuring the motion and load on the subsea BOP. A typical setup is to have motion sensors installed and calculate the loads on the lower part of the BOP and the subsea structure from indirect methods where knowledge of system parameters such as tension, weights and drag coefficients is used to establish the loads. Direct measurement of the load using strain gauges or LVDT's has proven challenging due to time consuming installation, fragile measurement equipment, and difficulties finding suitable areas to mount the sensors.

The objective of this paper is to present a novel sensor technology that allows for accurate measurement of strains in a wide measuring range. In contrast to existing measuring equipment this new sensor technology enables a compact, robust, and easy to install strain sensor. The new sensor is small enough to be mounted behind the bolts/ nuts on an 18 ¾″ BOP flange neck. The sensors can be used to increase the accuracy and reduce unnecessary conservatism in the measured wellhead loads. This can again reduce the need for expensive load reducing measures or disconnects.

This paper will present the core principles of the new strain sensor. Laboratory tests showing the performance and accuracy of the sensor will be shown, and the benefits of this sensor versus existing technologies will be demonstrated.

The introduction of this new sensor enables direct measurement of the loading on the subsea wellhead system. The new measuring process will be presented and compared with the traditional indirect measurement process. This comparison will illustrate where in the measuring process increased accuracy and reduced conservatism can be achieved, and then quantifying the improvements.

Further, the paper will present results from use of the sensor in actual measurement campaigns from drilling operations in harsh environment on the Norwegian Continental Shelf.

The paper will present the findings from the first measuring campaigns using this new sensor technology. The measured results will be compared with the traditional indirect measurement method and the improvement, in terms of reduced conservatism and increased accuracy, will be shown. Then finally, the consequence in terms of reduction on measured extreme and fatigue load, will be presented.

This paper will show how new sensor technology can be used to obtain more accurate and less conservative measurements of the loading on a subsea wellhead system in order to reduce the need for expensive load reducing measures.

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