Thermal Performance of Insulated Concentric Coiled Tubing (ICCT) for Continuous Steam Injection in Heavy Oil Production
Authors: Luft H.B. , Pelensky P.J. , Williams G. 
Published: December 2007

The successful production of heavy oil using the single-well steam assisted gravity drainage (SW-SAGD) process, is strongly dependent on the thermal performance of the steam injection tubing string. Insulated concentric coiled tubing (ICCTTM) has now been in use for a sufficiently long period of time that considerable experience and data has been obtained to evaluate the thermal performance of ICCT stings. This paper presents the results of thermo-fluid mechanic measurements performed by injecting steam through a full sized ICCT test spool, 200 ft in length. Laboratory measurements include internal and external tubing wall temperature, local heat flux, pressure drop, steam quality and relative thermal expansion. Results are compared with thermal conductivity measurements made with a short length ICCT heat loss test cell which was also used to help analyze the effect on ICCT thermal performance with hydrogen gas accumulated in the insulation annulus. Field measurements, performed with a twined fibre optic sensor cable strapped to the outer tubing of a full length ICCT steam injection string, are reported for the temperature profile along a portion of the ICCT string. Measured temperature profiles and other field measurements of wellhead flow conditions are compared with two-phase flow computer modeling predictions. Also presented are some recent results of the operation and performance of SW-SAGD heavy oil production wells operated by ELAN Energy Inc.

Introduction

The ongoing effort for an in-depth understanding of the fluid mechanic and thermodynamic characteristics of the new Single-Well Steam Assisted Gravity Drainage (SW-SAGD) process using Insulated Concentric Coiled Tubing (ICCTTM), which is seeing an increased application for heavy oil production by producers other than ELAN Energy Inc., requires a detailed knowledge of the thermal performance of the ICCT steam injection string and the thermo-fluid mechanic behaviour of the SW-SAGD process. The ICCT technology was first introduced to the heavy oil production industry in June of 1995 which reported some of the original thermal conductivity testing using a full sized but short length (6 ft) ICCT specimen in a specially designed heat loss test cell. In an effort to gain a more thorough understanding of the thermal performance of the full length ICCT string in service in SW-SAGD wells, a second heat loss testing apparatus was constructed which consisted of a much longer (200 ft) full sized ICCT test string which could better represent the overall thermal performance of a newly manufactured ICCT string as well as confirm the initial thermal conductivity test results.

In order to model the thermo-fluid mechanic performance of the injected steam and produced fluid flows as accurately as possible, using the computer numerical simulation routine HOWSCATTM (trademark of Essien Consulting Engineers Ltd. for Horizontal Well Steam Circulation Analysis Tool), ongoing comparisons are also being made between modeling predictions and experimental measurements obtained in the laboratory and in the field. Downhole monitoring of temperature and pressure distributions typically obtained in a SW-SAGD process, may be measured with Sensor Highway TM (trademark of Sensor Highway Ltd.) fibre optic techniques. The first results of these measurements of the temperature profile along the outer surface of the ICCT injection string are reported for a 2,465-foot portion of the ICCT which extends 1,060 ft beyond the heel into the horizontal section of the SW-SAGD wellbore.

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