Sensitivity Analysis of Hole Cleaning Parameters in Directional Wells

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe major differences between conventional rotary drilling and Coiled Tubing drilling are the absence of pipe rotation and the continuous circulation of drilling fluids.• In rotary drilling the circulated fluid must be selected to support the cuttings while making a connection. In slide drilling, the circulated fluids can be continuously circulated. This capability greatly aids the use of gasified fluids in underbalanced drilling. • In slide drilling, the pipe does not rotate; while in rotary drilling, the pipe rotation enhances the cuttings transport by the agitation effect due to the pipe rotation and vibration. For a typical Coiled Tubing drilling job, the challenge is achieving the circulation rate required to keep the hole clean. Current field practice is to perform frequent wiper trips.The economics of hole cleaning are crucial to the industry and therefore we seek answers to questions such as:• What is the change in the cuttings bed height when the fluids flow rates are altered? • How long does it take to clean out an existing cuttings bed?• Is there a need to remove the cuttings bed fully before resuming drilling? In this study, 600 tests were conducted and a new computer program was developed for the prediction of cuttings transport in the multi-phase system (gas+liquid+cuttings). The sensitivity of cuttings bed height with respect to liquid/gas volume flow rate ratio, in-situ liquid velocity, ROP, inclination angle and circulation fluid properties was conducted. The hole cleaning time with both circulation mode and wiper trip is also discussed. The results from the sensitivity analysis presented in this paper indicate that: i) the fraction of the circulation liquid has a significant impact on the cuttings transport in underbalanced drilling with gasified fluids, ii) among different variables, the in-situ liquid velocity is the most important variable for cuttings transport, iii) the hole cleaning time decreases non-linearly with increasing fluid circulation rate.

Flow Patterns and Minimum Suspension Velocity for Efficient Cuttings Transport in Horizontal and Deviated Wells in Coiled-Tubing Drilling

“…Li and Walker 5 presented results of their experimental study using various empirical correlations devised from their own data as well as data from other investigators. They assume that cuttings erosion follows a logarithmic expression with time.…”

“…In recent years there have been several theoretical, semitheoretical, and experimental investigations for assessing the important parameters for efficient cuttings transport in highly inclined and horizontal geometries during CTD [3][4][5][6][7][8][9] or conventional drilling, not taking into account the rotation of the inner pipe. [10][11][12][13][14] Practical recommendations were also given for optimizing hole cleaning.…”

“…13 Some authors present the data together with their own theoretical analysis, but they give very limited information on experimental parameters (e.g., rheology of fluids and cuttings concentrations). 5,6,8 The approach taken by many investigators in modeling cuttings transport for highly inclined and horizontal annuli with no innerpipe rotation is that of a two-or three-layer model. The basic model proposed for annuli is adopted from the one first proposed for solids transport in pipes by Doron et al 17 and later extended by the same authors.…”

Improved CT Well Cleanout and Milling Procedures Utilizing Only Non-Viscous Cleanout Fluids

“…In the build-up section, the solids movement is slower due to the tendency of the bed to become unstable as it accumulates solids. When the bed is unstable, the debris will slide downwards (Li and Walker 1999). Therefore, even with the right fluid, the times for solids removal are longer than expected or estimated with the conventional annular velocity calculation.…”

Hole Cleaning Performance of Water vs. Polymer-Based Fluids Under Turbulent Flow Conditions

“…Another shortcoming of these models are the coefficients involved, which mostly must be determined experimentally ( (Pilehvari, Azar et al 1999). According to (Li and Walker 1999) fluid mechanics of flow in eccentric annulus is very different than in pipes or channel flows. Local velocity near the bottom is much lower and, therefore, correlation developed for pipe and channel flow (Ramadan, Skalle et al 2003) cannot be applied to flow in the annulus.…”