Steam assisted gravity drainage ("SAGD") wells require precise separation between the producer/injector well pair if efficient drainage is to occur. The high-accuracy downhole surveying required to drill the well pair is achieved through the use of active magnetic ranging. The two predominant active magnetic ranging systems utilized for the majority of the SAGD wells drilled to date are the Magnetic Guidance Tool (MGT ™) and the Rotating Magnet Ranging Service (RMRS ™). As of this writing, there have been over 200 SAGD well pairs drilled in Alberta, Saskatchewan, Wyoming, California, and Venezuela. The majority of these wells, approximately 95%, have been drilled with the use of the MGT. This paper will provide a comprehensive comparison between the two active ranging systems. The focus of the discussion will be on data transmission efficiency, survey data quality, ease of operation, and the various methods for ranging tool deployment. Each system will be compared to the other with respect to its advantages and disadvantages for re-drill operation and for measuring horizontal proximity to observation wells. The primary purpose of this paper is to provide a comparison of the two technologies, based upon field experience, and show how each system compares in the SAGD drilling environment. The paper will also discuss how incorporating Electro- Magnetic (EM) telemetry technology into the drilling operation has resulted in the largest single contribution to improved total drilling efficiency in SAGD operations.
In June 1993, Amoco Canada drilled the first-ever SAGD well pair from surface using the Magnetic Guidance Tool at Wolf Lake1, Northern Alberta. Since that time, over 200 well pairs have been drilled worldwide, with the majority in Alberta and Saskatchewan. The MGT and the RMRS are the only two systems that been able to consistently demonstrate the ability to meet the precise tolerances and operational efficiencies required in these types of wells. While other systems have been tried, active magnetic ranging systems have risen to the forefront in terms of accuracy, simplicity, commercial availability and data repeatability. Active ranging systems have proven to be successful in both drilling and re-drilling SAGD well pairs and ranging to observation wells and well intersections. Each system has specific application advantages and disadvantages. Only specific SAGD applications will be discussed in this paper. In 1993 when the Wolf Lake SAGD pair was being planned, the concepts of both MGT and RMRS existed. The MGT was initially chosen over the RMRS because of its simplicity of theory and ease of development. The MGT has been utilized to drill over 95% of the SAGD well pairs in existence.
The experience that Vector Magnetics and Sperry-Sun gained in drilling SAGD well pairs provided the knowledge base upon which the RMRS was conceived, developed, and tested. Sperry-Sun was involved in the initial testing of the RMRS. MGT data obtained from the initial test runs provided the data comparisons necessary to test, improve, and commercialize the RMRS.
Within the last two years, EM telemetry has been improved and adapted to SAGD applications.