Cost Effective Deepwater Well Construction— A Case for Managed Pressure Drilling With Casing

Abstract

Abstract Engineers now face increasing challenge of drilling in Ultra Deepwater environments which form the cornerstone of future field developments. The deepwater environments are characterised by complex temperature profiles and geological features such as High Pressure-High Temperature (HP-HT) with very narrow pore pressure-fracture pressure window; Shallow unconsolidated reservoirs with very high overburden; Combination of ‘'flexible" lithologies. In these environments the use of overbalanced drilling techniques becomes difficult as the tolerance between formation pressure, wellbore pressure and the pressure at which the formation will fracture becomes very small. This can lead to severe drilling problems with attendant increase in drilling costs to possible loss of well control itself. These deepwater environments can benefit from Managed Pressure Drilling (MPD) when effectively combined with casing drilling technique but its uptake has been rather slow. For the industry to develop a managed pressure drilling capability that will allow today's generation of complex wells to be drilled safely with casing, it is necessary to develop models that will accurately simulate the MPD process and to embed these models within an easy to use, intuitive well design package for pre-planning and as a real time tool to monitor, diagnose and optimise downhole operations and provide forward simulations based on rig and downhole data. This paper presents the unique algorithms developed to simulate the MPD process and to analyse the effects of soft issues on the wellbore flow and pressure regimes and impact on torque/drag. The algorithms developed have been validated with live well data including pump rates, fluid properties and especially PWD and pump pressure data. The predictions and actual data have been found to be in very close agreement. The results of algorithm validation are presented to illustrate how the simulator can be utilised for real time design as well as process optimisation especially for casing drilling versus standard drillstring scenario. Highlights of the effects of the complex relationships between eccentricity, rotation and fluid rheology at bottom hole and riser conditions are also presented to illustrate the drilling process optimisation. The paper is concluded with guidelines on MPD operating windows for different scenarios and a brief description of the system architecture of the MPD Simulator – The MPDEEP.