RCD Element Design Optimization for MPD Operations

Abstract

Managed Pressure Drilling (MPD) provides ability to control and finely tune Bottom Hole Pressure (BHP) by introducing and controlling backpressure of wellbore returns. In order to maintain backpressure and for MPD to work, Rotating Control Device (RCD) has to maintain tight seal with drill pipe. In addition, RCD diverts wellbore returns away from the rig floor, thus improving safety and addressing environmental concerns associated with mud spills. RCD creates a secure seal around rotating drill pipe and tool joints using an elastomer element (RCD Element), the inner diameter of RCD element is in continuous contact with the drill string and is stressed during RIH, POOH and any other drill string movement during operations. RCD element is exposed to both internal and external changing loads and hence needs to be designed optimally to reduce nonproductive time (NPT) and conduct safe MPD operations. The present work focuses on numerical simulations to improve the RCD element functional longevity by first comparing numerical results with existing laboratory test data and followed by enhancements to RCD element shape through numerical optimization.

Firstly, laboratory tests were conducted on the RCD element with varying external pressures to estimate the axial forces on the tool joint and also, whenever possible, contact forces for the tool joint-RCD element interface. Strain gauge measurements were taken at regular intervals during the laboratory tests. The material properties for the RCD elements were obtained using standardized curve fitting methods. A detailed finite element analysis (FEA) using explicit solver was conducted; in particu lar, non-linear explicit FEA was conducted on the 2D axisymmetric RCD element geometries to simulate external pressure on the RCD element followed by upward (POOH) and downward (RIH)motion of the tool joint. The effects of fluid penetration through the RCD element were also taken into account by innovative simulation approaches to correctly mimic the physics of actual RCD operating conditions. Lastly, numerical optimization approach was utilized to obtain the best possible shape of the RCD element to improve durability of RCD.

Extensive FEA studies were conducted first to check the validity of the numerical results with laboratory testing. FEA studies predicted a good match for RCD element deformations and tool joint forces with those obtained through laboratory measurements. Simultaneously FEA studies also predicted the behavior and magnitudes of contact forces where laboratory measurements were not possible. The sealing effect and the compression behavior of the RCD element while sliding over the maximum Outside Diameter (OD) of tool joint was also correctly captured by FEA. Numerical optimization underscored the best achievable RCD element design based on operational requirements.

Since it was impractical to physically test the various topologies of the RCD element geometry, optimization through FEA was carried out with an objective of minimizing the volume and forces exerted by the tool joint during the process. This work elucidates use of advanced computational techniques for RCD element design optimization within given operating constraints.