Tuesday 12:30-1:30 PM, February 26th
Biology and Geology Building 1053
Everybody is welcome!
By Sid Leggett, Husky Energy
Getting oil out of a reservoir is a challenge. The recovery from most reservoirs is low and it takes a lot of ingenuity and technical expertise to get a significant amount of the oil out. Primary recovery, which involves the production of oil from a reservoir by natural mechanisms, usually recovers less than 10% of the oil present. Secondary flooding of a reservoir begins with the injection of fluids, almost always water, to maintain the reservoir pressure and displace the hydrocarbons to the producing wells. This may get up to between 35 and 45% of the oil. Tertiary recovery involves adding chemicals to recover even more oil, potentially between 5 to 15% more.
This discussion is about requirements to do an Alkali/Surfactant/Polymer tertiary flood and how a particular pool in southwest Saskatchewan, the Gull Lake North Upper Shaunavon pool, met these requirements. It illustrates some of the complexities of oil pools and some of the details on how a tertiary flood functions.
The tertiary flood of the Gull Lake pool began with the injection of softened water on June 1st, 2009 followed by alkali/polymer on October 1st and full alkali/surfactant/polymer on December 1st, 2009. With oil in place reserves of 76MM bbls. (12.1MM m3), the Gull Lake ASP flood is one of the largest such floods in the world.
The middle Jurassic Upper Shaunavon Formation in the Gull Lake area is made up of shallow marine clastic and carbonate sediments deposited on a shallow marine platform at the northwest side of the Williston Basin in southwest Saskatchewan, Canada. There are two reservoirs in the Gull Lake North Upper Shaunavon oil pool – a large incised tidal channel near the top of the Upper Shaunavon Formation and several small tidal bars stratigraphically above the channel. The channel is the main reservoir for the pool and is the target for the tertiary flood.
Oil migration into the area was driven by a north-south trending hydrodynamic low. Gas associated with the oil moved structurally updip to the northwest leaving the reservoir with low GOR oil in the updip part of the channel and a water leg in the down dip part.
The Gull Lake pool met most of the requirements for an alkali/surfactant/polymer (ASP) tertiary flood – large size, lack of a gas cap, very little clay, low temperature, an intermediate API crude and a thick, high quality reservoir with no apparent permeability barriers. The only negative feature of the Gull Lake pool affecting the ASP flood is the potential for injected ASP fluid dilution from contact with the water leg for the pool.