Drilling And Completion For Steam-assisted Gravity Drainage (SAGD) Operations
Authors: Nzekwu Ben 
Published: March 2010

My contribution to this journal issue, the theme of which is Advances in Drilling and Completion, is on the placement and application of horizontal wells for secondary production of light to medium crude oils and the primary recovery of heavy oil and bitumen. Drilling, well completion and production are complex operations determined by geological factors and technological considerations. The perspective I present in this brief review is that of an exploitation engineer with respect to how recent advances in drilling and completion facilitate and enhance the SAGD process. Innovative techniques and engineering decisions for precise drilling of horizontal wells are important in the effectiveness and efficiency of SAGD-based recovery schemes. Pairs of horizontal wells are maintained parallel in drilling through the use of magnetic guidance tools. There are multi-lateral completions, re-entry, under-balanced drilling, and the application of coiled tubing. Completion methods include the use of sand screen devices, gas lift, jet pumps and production lifting with sumps using pilot holes.

Horizontal Wells and SAGD
SAGD, as a primary or improved recovery technique, has evolved rapidly over the last decade. Its growth has been in tandem with the acceptance and implementation of horizontal wells. The technology is environmentally friendly and cost effective for lifting heavy oils and bitumen which are ordinarily immobile in reservoirs. Steam is injected and oil is recovered from a large zone around a horizontal well, with advantage taken of natural forces that favour counter-current gravitational movements of steam, condensates and reservoir fluids. Under gravity, mobilized oil continuously drains into a horizontal well to be moved to the surface. Various types of reservoirs can be accommodated, at different levels of pressure and maturity. The technology has been demonstrated on small scales in the laboratory of Dr. Roger Butler and in AOSTRA's Underground Test Facility. Field tests are in progress. As with any new technology, the transfer from the laboratory to the field has its trials and tribulation. Poorly planned and xecuted tests under field conditions can conceal the true potential of the scheme. The requirement for diligent planning, well-trained staff and field operators " accurately" implementing the design programs cannot be over emphasized.

Considerations for SAGO

Well Configurations
There are at present three major arrangements of the horizontal wells in exploiting SAGD. The basic involves two wells drilled one above the other. The lower well, or producer, is located at the base of the formation. The other well, the steam injector, is located several metres above and parallel to the producer. A more recently developed scheme involves the use of a single well with dual tubing strings. Steam is injected from the surface through the one tube to exit at the toe of the well. Along the horizontal part mobilized fluids and condensates drain into the liner to be lifted through the production tubing from the heel to the surface.