Evaluation of Annular Pressure Losses while Casing Drilling

Abstract

Casing Drilling is an innovative drilling method wherein the well is drilled and cased simultaneously. The small annulus of Casing Drilling can create a controllable dynamic ECD (Equivalent Circulating Density). Casing Drilling technology permits the same desired ECD as conventional drilling to be achieved using a lower, but optimized, flow rate, rheological properties, and mud weight. In this paper, the frictional pressure loss during Casing Drilling operation is evaluated using Computational Fluid Dynamics. Annular pressure losses have received substantial attention in theoretical analyses, laboratory assessment and actual well measurements. Combinations of casing motion, annular eccentricities, wall roughness and fluid temperatures along the length of the annulus affect fluid flow regimes that control annular pressure losses. Current analytical solutions have limited applicability for complex conditions with pipe rotation and eccentricity. In this study, the pressure losses during Casing Drilling operation are investigated using computational fluid dynamics. The results are compared against the available analytical solution and field data. The effect of pipe rotation and eccentricity on the frictional pressure loss is investigated as well. According to the simulation results, the pipe rotation reduces the frictional pressure loss for Yield-Power-law fluid which would be beneficiary during the casing drilling operation. It is found that the pipe eccentricity has a significant effect on the ECD calculation. The industry is moving towards more challenging jobs in narrow pressure window scenarios such as deep-water and HPHT applications. Drilling with casing/liner is among the primary options to complete these sections due to strengthening effects associated with plastering the wellbore wall and also eliminating conventional drill pipe trip. Having accurate models for ECD including the effects of pipe rotation and eccentricity in the narrow annulus is essential to the success of these challenging jobs.

A Case Study: First Field Application of Fully Automated Kick Detection and Control by MPD System in Western Canada

“…Chirinos et al (2011) presented a simplified method to estimate the maximum casing pressures during MPD well control. Dokhani et al (2013) investigated annular pressure profile calculation models using computational fluid dynamics (CFD). Erge et al (2013) presented mathematical model to consider pipe rotation and buckling in BHP calculations during MPD operations.…”

Real-Time Prediction of Equivalent Circulation Density for Horizontal Wells Using Intelligent Machines

“…This can be valid in shallow wells, where temperature changes are insignificant, and hence, the rheological variations are small. Furthermore, the mathematical equations used to calculate the drilling hydraulics entail a set of assumptions such as − (i) concentric annular and circular sections, (ii) laminar and turbulent flow, where plug flow is considered as laminar flow, while transition flow is neglected, and (iii) steady-state flow, where fluid properties at any single point in the system do not change. Such potentially unrealistic assumptions cannot be fulfilled in all drilling conditions …”

“…Dokhani et al concluded that eccentricity (ϵ), which describes how off-center a pipe is in an open hole or casing, affects frictional pressure loss and hence the ECD for Herschel–Bulkley fluid.…”

“…Eccentricity reduces overall frictional pressure loss if ϵ is >0.1 and it will be neglected if ϵ is 0.8. − Moreover, Dokhani et al evaluated the effect of pipe rotations on frictional pressure loss. They observed that a drilling fluid’s apparent viscosity decreases as pipe rotation increases; hence, overall frictional loss decreases.…”

“…This phenomenon is a result of the shear-thinning properties of Herschel–Bulkley fluid . Dokhani et al also recommended considering the effect of roughness of the wellbore wall to have a more accurate estimation of drilling hydraulic calculations such as ECD.…”