Abstract

This study was conducted to gain a more in-depth understanding of solids transport for coiled tubing workovers, cleanouts and drilling applications. Cuttings or particle transport in Coiled Tubing operations is a complex problem that is affected by numerous parameters. Predicting effective cuttings transport requires all of these parameters to be considered simultaneously. Tests were conducted to determine the effects of the following parameters:

  • Different particle size,

  • Fluid rheology, including water, gel, and multi-phase fluids,

  • Pipe eccentricity, coiled tubing positioned on the low and high side of the wellbore.

The effects of the different parameters were investigated in two different modes: the circulation mode, that involves the development of a cuttings bed or build-up of cuttings in the wellbore, and hole cleaning mode, which is cleaning out an existing cuttings bed. It will be shown that the results indicate:

  1. for the tested particle size range (0.150 – 7 mm), cleaning efficiency is partly dependant upon the particle's size,

  2. with suitable agitation, a gelledfluid is more effective for cuttings transport than water in a highly deviated wellbore,

  3. Pipe eccentricity has an effect on cuttings transport for different fluids and

  4. for complete wellbore clean-up it requires many morehole volumes than previous 'rules of thumb' would indicate.

Introduction

Drilling or wellbore cleanouts using Coiled Tubing techniques are prone to quality failures due to a lack of knowledge about solids transport. Poor transport can have a negative effect on rate of penetration (ROP) for the drilling process or on production due to flow restriction of the wellbore. Coiled Tubing can be a very cost effective technology when the overall process is well designed and executed. The highly deviated/horizontal well has placed a premium on having a reliable body of knowledge about solids transport in single and multi-phase conditions.

In our previous study1, a comprehensive experimental test of cuttings transport with single-phase and two-phase fluids was conducted. The effect of liquid/gas volume flow rate ratio, in-situ liquid velocity, ROP, inclination angle and circulation fluid properties on cuttings transport was investigated. Based on the test results a computer program was developed. In this study, the effect of particle size, fluid rheology, and pipe eccentricity on cuttings transport was further investigated. Based on these test results, an existing computer program was modified and adjusted to include these three additional parameters.

Experimental Setup

The flow loop shown in Figure 1 was used for this project. It was developed in a previous study1. This flow loop consists of a 20ft long transparent Lexanpipe with a 5 inch inner diameter to simulate the open hole and a 2–3/8" inch steel inner pipe to simulate coiled tubing. The inner pipe can be positioned on the low and the high side of the Lexan pipe for the investigation of eccentricity effects. The loop is mounted on a rigid guide rail and can be inclined at any angle in the range of 00–1100 from vertical.

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