In the Steam Assisted Gravity Drainage (SAGD) process, the pre-heat is a very important step in the successful development of the steam chamber. The pre-heat period lasts months and is deemed complete when the temperature between the injector and producer is high enough to establish hydraulic communication. A uniform pre-heat along the wellbore is crucial to achieve steam chamber conformance throughout the life of the well pair. The efficiency of the pre-heat can be affected by several factors, with completion type being one of the most important among them. The objective of this study is to evaluate the impact of this factor on thermal efficiency during the pre-heat phase of the SAGD process.
In this study, the completion practices in five major SAGD projects in Alberta, Canada (Suncor's Firebag and Mckay River, Cenovus' Christina Lake and Foster Creek, and ConocoPhillip's Surmont) were evaluated. The critical factor used to determine the efficiency of any completion type in the pre-heat process is the heat loss and heat exchange along the producer and injector wellbores and the completion components. This variation in thermal efficiency results from factors such as concentric versus eccentric dual tubing completion, and tubular size, length and configuration.
The results of the study provide a comparison of different completion practices in the five major SAGD operations in Canada. The simulation modeling of the process, along with field experience and observations, helped to understand the impact of counter-current heat exchange and heat loss in concentric versus eccentric completions. Also, the results were used to quantitatively evaluate the impact that vacuum insulated tubing has on delivering energy to the reservoir and its associated thermal efficiency during the pre-heat process.
This paper is aimed at providing a better understanding of the impact of different completion methods on thermal efficiency during the pre-heat period in the SAGD process. The study also incorporated actual field performance of the 5 major SAGD projects available in the public domain and AER reports.