Parameter uncertainty modeling of safety instrumented systems

In this study,a novel safety integrity level(SIL)determination methodology of safety instrumented systems(SISs)with parameter uncertainty is proposed by combining multistage dynamic Bayesian networks(DBNs)and Monte Carlo simulation.A multistage DBN model for SIL determination with multiple redundant cells is established.The models of function inspection test interval and function inspection test stages are alternately connected to form the multistage DBNs.The redundant cells can have different M out of N voting system architectures.An automatic modeling of conditional probability between nodes is developed.The SIL determination of SISs with parameter uncertainty is constructed by using the multistage DBNs and Monte Carlo simulation.A high-pressure SIS in the export of oil wellplatform is adopted to demonstrate the application of the proposed approach.The SIL and availability of the SIS and its subsystems are obtained.The influence of single subsystem on the SIL and availability of the SIS is studied.The influence of single redundant element on the SIL and availability of the subsystem is analyzed.A user-friendly SIL determination software with parameter uncertainty is developed on MATLAB graphical user interface.

Effect of structural parameters on the setting performance of plug slips during hydraulic fracturing

Slip is one of the most critical components for the frac plug,which would lodge into the casing and lock the frac plug in place during the setting and anchoring process.However,fracture failure of slip significantly affects the hydraulic fracturing effects and has attracted tremendous attention.In this paper,a three-dimensional contact model is applied to explore the setting process of slip.The effects of key structural parameters such as apex angle,inclination angle,and wedge angle on the contact characteristics of slip are systematically investigated.Numerical results indicate that the maximum contact stress appears at the contact area between slip tooth and the casing’s inner wall.Besides,the maximum contact stress generally increases with the increase of apex angle and inclination angle,while decrease linearly with the rise in the wedge angle.Experimental results show that the slip teeth get blunt and appear severe plastic deformation,which arises from stress concentration.Comparison of biting area indicates that the experimental results are about 21.3%larger,which still have a reasonable agreement with the numerical results.These obtained results can guide the parametric selection of plug slip and other similar components.