Design and Performance Evaluation of an Ultradeepwater Subsea Blowout Preventer Control System Using Shape Memory Alloy Actuators

Abstract

Abstract As drilling moves to ultradeepwater, conventional blowout preventers (BOP) actuation technologies based on full or partial hydraulics are unable to meet the API standard for control system response times because of long hydraulic fluid communication path between an offshore platform and a BOP stack on the sea floor. Now that an ultradeepwater subsea blowout preventer (SSBOP) control system using shape memory alloy actuators has been demonstrated in the laboratory, several practical issues can be addressed. The experimental device uses nitinol smart alloy material (SMA). It can be actuated by electrical heating, thereby replacing hydraulic actuation and hydraulic lines with electric cables. Alternatively, the SMA actuator system can be activated by chemical heating. With significantly fewer components, the SMA system will dramatically reduce total cost and will increase operation reliability. The new device can easily be retrofitted to existing conventional subsea control system thus enabling other methods to be used as a backup. Most importantly, the innovative all-electric BOP will provide a much faster response than its hydraulic counterpart and will improve safety for subsea drilling. The BOP actuator uses strands of SMA wires to achieve large force and large displacement in a remarkably small space. Experimental results demonstrate that the BOP can be activated and fully closed in less than 15 seconds. This paper considers chemical and thermal energy sources as alternatives to electricity and ways to trigger an automatic mechanism. Additionally, a model is used to calculate the SMA length and diameter that will be required to provide sufficient force for different types and diameters of BOP rams (blind, pipe, or shear) or the annular BOP, and the energy requirements in each case. The model also addresses the range of pressures and temperatures that can be handled. Simple guidelines are presented along with practical field examples for different types of BOP hook ups. Introduction As drilling moves from land to offshore, to deepwater, and to ultradeepwater, blowout preventers (BOP) inevitably are challenged to act faster and more reliably in severe ocean conditions. Ultradeepwater rigs require a faster and more sophisticated control system for the subsea BOP (SSBOP) that connects the riser and the wellhead thousands feet down from the surface. API RP16E1 mandates that an annular SSBOP shuts down within 60 seconds and a ram SSBOP closes in 45 seconds or less. Norsok standard2 response time for closing subsea rams is 30 seconds except for annuli above 20″, which has up to 45 seconds to close. The industry's preference is to close wells as soon as possible.