Enhanced Subsea Safety Critical Systems

Abstract

Description of the Material This paper describes how the Subsea Safety Critical Systems can be enhanced toprovide greater shearing pressure and volume for the Shear Rams when being usedby the Emergency Disconnect System, EDS, Deadman System, or Autoshear System. Utilizing accumulators which can be charged to 7500 psi differential pressureallows shearing pressures to approach the full working pressure of 5000 psi forthe Shear Ram Operators. Also discussed is the development of the 7500 to 5000psi stepdown regulator and other critical system components and how this systemcan be economically installed on existing Subsea Blowout Preventer (BOP)Systems. Application Some Drilling Contractors presently use 6000 to 7500 psi rated accumulators onthe BOP Stack in order to precharge on the surface to greater than 5000 psi. However, with surface Hydraulic Pressure Units (HPU), rated for 5000 psi, theycannot take advantage of the full working pressure of the accumulators. Thesubsea accumulators can be supplied with 7500 psi by several means. This paperaddresses the use of a hot line or subsea intensifier to supply the fluidpressure to the subsea accumulators. The key to having 7500 psi stored in thesubsea accumulators is to have a 7500 to 5000 psi step down regulator and othercritical components rated for 7500 psi. Results, Observations and Conclusions The 7500 to 5000 psi regulator and critical complimentary control componentshave been designed, developed, and tested for hot line use. The Isolation andDump Sub-Plate Mounted (SPM) valves have been qualified for 7500 psi serviceand the 7500 psi check valves are in the qualification process. The subseaintensifier is under testing and the results will be presented at thepresentation. Significance of Subject Matter The well construction designs for wells presently required by regulatoryrequirements are requiring larger, thicker wall, and higher yield casingstrings as well as drill pipe used in drilling and landing strings. Thesegreater strength requirements are requiring greater shearing pressures for thehigh pressure Shear Rams. Utilizing 7500 psi supply allows shear pressures togo as high as 5000 psi with a reasonable number of accumulators to supply thefluid. Background The goal of a rig's safety critical emergency system is the ability to shearpipe and safely seal the well when circumstances dictate. Two important aspects of Safety Critical BOP Systems are:BOP Components and ArrangementControl System Design, Operating Philosophy and Dedication ofAccumulators

On the rapid discharge of subsea accumulators: remarks on the normed design method and proposal of improvement

“…The effect of the surface and subsea temperatures and precharge pressure uncertainties are not to be neglected: these uncertainties, particularly relevant during typical off-shore severe operating conditions, should be included in the design sizing [20]. As the water depth increases, it is known that the delivery of a pressurized fluid become more difficult due to the effect of the hydrostatic head and pressure increase inside the accumulators: the development of the accumulator technology (to reduce the negative effect of the water depth on the volumetric efficiency) has also been analyzed [21].…”

Transient mathematical prediction and experimental verification of the charging characteristics of subsea accumulators

“…[1][2] In off-shore drilling or production, especially in deep water, accumulators are generally used as emergency power sources of safety devices, such as blowout preventer stack (BOP), 3 emergency disconnection sequenced system (EDS), 4 and lower landing string assembly (LLSA). [5][6] In order to accomplish the safety actuations, accumulator is installed on the seabed as an emergency power fluid supply source.…”