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More recent developments in SAGD
Steam Assisted Gravity Drainage

by Franklin L. Foster, Ph.D.

[This article made possible thanks to the co-operation and financial support of the
 Petroleum Society of CIM, Lloydminster Heavy Oil Section]

In the second half of 2006, Husky Energy's Tucker Thermal Project near Cold Lake began production. It is expected the project will produce 30,000 barrels per day of bitumen and 90,000 barrels per day of steam.  Over the projected 30 year life of the plant, some 350 million barrels of bitumen will be produced.

Steam Assisted Gravity Drainage is at the heart of the project, assisted by several recent developments.  The producing wells are 32 well pairs situated on only three well pads.  This greatly reduces the surface impact of the project on the environment.  From the well pads, the wells are directionally drilled to a depth of about 450 meters and then the wellbores go horizontally through the oil bearing sand for approximately 700 meters.  The pay zone, in the Clearwater Formation, consists of a layer of sand 30 to 50 meters thick and so is ideally suited for SAGD.

A well pair, in the pay zone, consists of two well bores, one above the other, running parallel with each other only three to seven meters apart over the entire 700 meter horizon.  Each of these 32 well pairs are approximately 100 meters apart in the pay zone.  Steam is continuously injected into the upper wellbore.  A steam chamber forms, heating the bitumen and enabling it to flow.  Gravity pulls the bitumen down into the lower horizontal well.  Oil, water, and particulate matter are produced through this wellbore to the surface.

Another recent advance is in electronic instrumentation.  Sensors are placed at both the well heel (where the wellbore changes to horizontal) and the well toe (the far end of the wellbore).  The sensors must be able to perform at high accuracy under high temperature conditions for a life span of 10 years.  These sensors allow for the monitoring of temperature, pressure and other important information about conditions in the reservoir, especially pressure, and this allows the oil to be produced without surface pumps but instead relying on controlling the pressure below which is in the range of 3,300 kilopascals.

The demand for 90,000 bbl/day of steam introduces the issue of water use.  Earlier applications of SAGD, and other recovery methods using steam, put a high demand on water.  Use of surface water became controversial as water table levels were lowered.  Other possible sources of water include fresh ground water (also controversial) and saline ground water.  A 6 month license has been granted to use surface water during startup; however all produced water at the Tucker Project will be processed to make steam.  The Tucker Thermal Project will use more than 7 million cubic meters of water per year.  Of that volume, 1.7 million cubic meters of brackish water will be sourced from the McMurray Formation which underlies the Clearwater Formation which contains the bitumen.  The Tucker Plant will include equipment to desalinize and soften the produced water for use in the five 280 million BTU/hour steam generators on site.  About 90% of the steam generated will be reinjected into the reservoir or used on site for heating.

The produced fluids are initially processed in a free water knockout vessel, followed by a treater where the remainder of the water is removed from the oil, and then on to the usual settling and sales tanks.  From the sales tanks, the bitumen is blended with diluent for transport by pipeline to the Husky Energy Upgrader in Lloydminster. 

The Tucker Lake Project already promises to be a success and Husky Energy will follow it with the Sunrise Thermal Project.  Such projects, with drilling budgets alone of more than $75 million and overall project costs of over $500 million are an important reason why the oil and gas industry accounts for more than 82% of the economic activity in northeastern Alberta.  In addition, the 30,000 barrels per day of petroleum will make its contribution to meeting the energy needs of today's world.

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Information Sources:
Husky Energy
National Energy Board
Alberta Economic Commission
Pembina Institute

However, responsibility for the contents of the above article is entirely that of the author.