How to Efficiently Remove Sand From Deviated Wellbores With a Solids Transport Simulator and a Coiled Tubing Cleanout Tool
Authors: Li J. , Walker S. , Aitken B. 
Published: December 2007

Several cleanout operations have been developed over the years. One of the most common operations is running in with coiled tubing (CT) and circulating the solids out with a liquid or multi-phase fluid. Solids tend to settle and form an equilibrium bed on the low side of the wellbore. This problem is exasperated by the eccentric annular flow path created with CT in deviated wellbores. Fluids with adequate solids suspension properties tend to have poor solids re-entrainment abilities once a stationary bed has formed. Current approaches to remove the solids bed involve using higher flow rates, or seeking out exotic and costly fluids, neither of which ensures complete fill removal in every case.

Due to the complexity of the phenomena, a description of how the parameters affect solids transport can prove to be very challenging, especially when one or more of the variables is changed during an operation. In order to develop a computer model to predict solids transport behavior in deviated wellbores and ensure efficient hole cleaning, various comprehensive flow-loop test results have been collected since 19951–3. A computer simulator was developed based on the collected data. The computer model provides a practical means to evaluate the solids transport considering downhole conditions.

In this paper some of the important test results are summarized and discussed. The general structure and features used to develop the simulator are described. By considering jet orientation and tripping speeds, an operation can be optimized to remove solids with near 100% efficiency. A special cleanout tool with that can switch between forward and backward facing jets has been developed. Some field trials were completed to test the validity of the solids transport model, cleanout tool, and to demonstrate how to optimize a sand cleanout in a deviated wellbore.

Introduction

Typically a CT cleanout job starts after establishing circulation at the top of fill. One then penetrates into the solids some distance prior to pulling the CT back in a wiper trip. Depending on the job type, a single or multiple wiper trips may be required to clean the hole. In order to clean the hole in a cost-effective way, the field engineer has to analyze and predict the solids transport and solids distribution along the wellbore during the operation and to estimate the time needed to clean the hole. Due to limited pump flow rates and no pipe rotation with CT, some of solids may never be cleaned out of the hole no matter how much time is spent flushing the wellbore with clean fluids.

Solids transport is affected by many variables and the complexity of the phenomena presents challenges to the field engineer whose trying to determine how the parameters affect solids transport even when one or more than one of the variables is changed during an operation. Most of the previous solids transport studies in the oil industry mainly focused on finding the minimum critical velocity in the wellbore annulus for conventional rotary drilling with mud fluids. The studies lack information related to solids transport with two-phase fluids and the prediction of the hole-cleaning time. There is no previously published information related to the solids transport with the wiper trip.

In our previous studies1–3, a comprehensive experimental test of solids transport for both the stationary circulation and the wiper trip was conducted. The effect of multi-phase flow, rate of penetration (ROP), deviation angle, circulation fluid properties, particle size, fluid rheology, pipe eccentricity, wiper trip speed and nozzle type on solids transport was investigated.