Pipe Rotation and Hole Cleaning in an Eccentric Annulus

Abstract

The drilling community generally believes that pipe rotation helps hole cleaning during both drilling and cementing. However, there has been a lack of reliable calculations to describe the effect and application in engineering and design and deployment. This paper discusses the effect of pipe rotation on velocity profile and pressure drop in concentric and eccentric annulus during the axial flow of non-Newtonian fluid. The calculations are applied to the design of hole cleaning during drilling and cementing. In the absence of reliable calculations one can only guess the impact of pipe rotation on hole cleaning. This work gives an engineer the tool to design for improved hole cleaning and hence save time and money during well construction and production. Pipe rotation is all the more important in an eccentric annulus to remove the drill cuttings and the gelled drilling fluid from the narrow annulus. This is because in an eccentric annulus, in the absence of pipe rotation, the fluid flows preferentially through the wider annulus. The pipe rotation speed (i.e., the RPM) required to move the gelled drilling fluid and the drill cuttings in various annulus configurations and eccentricities are presented. The results discussed in this paper can be applied for effective hole cleaning during drilling and cementing, which should save non- productive time (NPT) during drilling and cementing and also reduce remedial and intervention costs during well production. Introduction A number of studies on the hydraulic effects of drill pipe rotation have been performed over the years1,2,3. In these studies, the authors observed that drillstring rotation served to lower pressure drop and Equivalent Circulating Density (ECD). Others studied the effects of drillstring rotation in Newtonian fluids from a theoretical perspective and concluded rotation had a significant effect on pressure drop, especially in smaller diameter gaps through which fluid was moving in laminar flow4. Several studies were later conducted in support of slim hole drilling efforts. In these studies, it was found that the rotating drillstring can produce large increases in pressure drop and ECD5,6,7. Finally with the use of pressure-while-drilling (PWD) tools in hydraulic studies8,9,10, a positive link between pipe rotation speed and increasing annular pressure drop was clearly seen. To summarize, industry researchers now generally agree on the positive relationship between drillstring rotation speed and annular pressure drop. Given the link between annular pressure drop and velocity, the relationship between annular point velocity and drillstring rotation speed exists. In an earlier paper11a rigorous engineering method was discussed to determine pipe rotation effects on axial flow for concentric pipe geometry. The effects of pipe rotation on pressure drop and local velocities were presented. The work discussed in this paper expands the previous work to include the effect of drillstring eccentricity. The effects of pipe rotation on pressure drop at different eccentricities are discussed. The effects of rotation on local velocity profiles across the annular gap are shown using the maximum level of drillstring eccentricity used in this paper. The combined effects of rotation and eccentricity on hole cleaning also are discussed.

Modified Yield Power‐Law fluid flow in narrow annuli with inner rotating pipe

“…A similar event is reported in previous studies. [41] For instance, in Figure 13c, the peak axial velocities for v ¼ 0 rpm and v ¼ 300 are respectively 0.01U b and 0.264U b representing about 2540 % increase in velocity. This huge improvement resulting from increasing v will effectively enhance cuttings bed removal in highly inclined wellbores.…”

Improving drilling hydraulics estimations-a case study

“…Owing to the chaotic nature of fluid particle movement in turbulent flow, it is extremely difficult to arrive at an exact analytical method for determining pressure losses (Rabia 1985). To resolve the issue, simplification of friction factor equation is essential.…”

“…Blasius equation is a simple equation commonly used in drilling sources to find the Darcy friction factor in turbulent pressure drop (see Blasius 1913), and this was later used and cited by Schlumberger (1984); Rabia (1985), and Moore (1986). This equation is popular as it only depends on the Reynolds number and is independent of roughness.…”

PDC Bit Hydraulic & Mud Rheological simulation to model pressure drop across Bit

“…This brings about effective cuttings removal as the cuttings are removed as fast as they are generated [4]. Flow rate of mud has significant positive effect on cuttings removal away from PDC bit [5][6][7][8][9]. Increasing the annular velocity by increasing the flow rate decreases the cuttings bed height significantly.…”