Steam-Assisted Gravity Drainage (SAGD)

What Is Steam-Assisted Gravity Drainage (SAGD)?

Steam-assisted gravity drainage (SAGD) is a drilling technique used to extract heavy crude oil which is buried too deep or otherwise burdensome to access. Its location makes it economically inefficient to mine using traditional methods. There are several variations of the SAGD process, but Butler, McNab, and Lo developed the original in 1979. The process in use today was field tested by the Alberta Oil Sands Technology Research Authority (AOSTRA) as an efficient means of recovering difficult-to-access oil reserves.

Understanding Steam-Assisted Gravity Drainage (SAGD)

SAGD is an enhanced oil recovery (EOR) process which uses steam to extract oil from a reservoir through primary or secondary recovery techniques. EOR methods alter the chemical composition of the oil itself to make it easier to extract.

SAGD requires a pair of horizontal wells drilled from a central well pad. A horizontal well is dug at an angle of 90 degrees to a vertical bore well. This type of well has advantages over traditional vertical drilling as adjustments can allow the bit to drill in non-vertical directions. It will enable one drilling pad, or kickoff point, to explore a broader underground area.

Also known as the steam flooding process, steam generators produce steam, which travels through pipelines into the wells. As the vapor condenses into hot water, it heats the oil to make it less viscous, allowing it to flow by gravity to the bottom of the well. The oil transfers via a pipe from the producing well at the bottom to a plant for treatment.

Petroleum companies and scientists look to steam-assisted gravity drainage for its potential to prolong the life of wells in proven or probable oil fields. Proven reserves are those with a higher than 90% chance of oil recovery, and probable fields have an over 50% chance of petroleum recovery.

Modern Applications of Steam-Assisted Gravity Drainage

Canada is the largest supplier of oil to the United States, making up 56% of America's oil imports in 2019. This Canadian import is more than all oil imported from all of the Organization of Petroleum Exporting Countries (OPEC) countries combined. The majority of Canada's oil exports come from Alberta's oil sand deposits.

There are two common methods of recovering product from oil sands. The first being SAGD, which is more appropriate for the deep deposits in Alberta. The second method, more commonly known for coal recovery in the United States, is strip mining. In strip mining, the top layer of dirt and rock are removed to access the oil below. The majority of future oil production from Alberta is expected to be from SAGD harvesting.

With the rise in costs of oil production over the years and the increased demand, the replacement of traditional oil drilling rigs with non-traditional methods are why there has been a rise in SAGD recovery.

Some variations of this method are Cyclic Steam Stimulation (CSS), High-Pressure Cyclic Steam Stimulation (HPCSS), Vapor Extraction (Vapex), Enhanced Modified Steam, and Gas Push (eMSAGP). All of these methods still use steam to heat oil sand deposits for harvesting and recovering purposes.

Hazards from SAGD

These methods are not without possible geo-hazards. As reported by Inside Climate News, in 2016, four uncontrollable leaks were confirmed by the Alberta Energy Regulators at sites using high-pressure steam injection methods in Alberta's tar sands patch.

Geologists are posing that there may be risks associated with this method, specifically possible geological risks across Alberta's sands region. With these sites, in particular, there were contributing factors of natural cracks in the bedrock and salt dissolution, a process where salt water flows through rocks creating cracks and holes, which may have compounded the problem.