Understanding Fluid Displacement in Extended-Reach Drilled Wells

Abstract

This paper explores the fluid displacement of extended-reach drilled (ERD) wells in relation to density hierarchy. Historically, less emphasis has been placed on the proper density hierarchy for the fluid train in ERD wells because the wells are horizontal. Through sensitivity analysis, the significance of fluid density differences is demonstrated. Fluid displacement in ERD wells is different from conventional wells. Various factors influence fluid displacement in primary cementing, including rheology and density differences between fluids. Rheological differences affect fluid displacement by changing the fluid velocity profile in the mixed zone, whereas density differences affect fluid displacement through additional gravitational force on the fluids. Gravity does not affect the way rheological differences impact the fluid profiles. Unlike rheological differences, the direction of gravitational forces with reference to the flow direction is perpendicular for an ERD well compared to a conventional well (vertical or deviated); thus, the resulting flow pattern exclusively resulting from density differences is not similar between the two well configurations. A new finite-volume-based three-dimensional (3D) displacement model was used to understand the effect of the key characteristic (density) of fluid displacement in ERD wells. The model is capable of accurately capturing the rheological behavior of the fluids using a best-fit rheological model and features time-dependent fluid evolution in both the pipe and annulus under the influence of pipe rotation and reciprocation. This work presents a comprehensive sensitivity analysis for the effects of density differences between successive fluids in ERD well configurations and their interaction with other parameters, such as rheology differences, fluid velocities, and pipe movement. This paper augments the current industry understanding of density hierarchy in ERD well scenarios and also includes case studies comparing predicted cement placement to that of cement bond logs (CBLs) in ERD wells.