SAGD

Steam Assisted Gravity

Drainage (SAGD):

A New Oil Producton Technology

for Heavy Oil and Bitumens

T.N. Nasr, Alberta Research Council, Calgary, CanadaIntroduction

The capacity of world heavy oil and oil sands has been estimated

to be as much as that of the world’s total discovered light

and medium crude oils in place. Over 90% of the world’s heavy oil

and oil sands are deposited in Canada and Venezuela. Up to 90%

of Canada’s estimated reserves could be recovered by in-situ operations

and 10% by surface mining. As the resources available for

conventional crude in Canada continue to decline, further development

of heavy oil and oil sands recovery technologies is critical

in meeting Canada’s present and future energy requirements.

Most recently, advances made in directional drilling and measuring

while drilling (MWD) technologies have facilitated development

of new in-situ production technologies such as Steam Assisted

Gravity Drainage (SAGD) and combined SAGD-solvent processes.

These processes have significantly improved well-bore reservoir

contact and sweep efficiencies as well as reduced production costs.SAGD Oil Recovery Technology

Western Canada has large reserves of heavy crude oil and

bitumen. However, most of these reserves cannot be produced by

conventional recovery methods. Specialized techniques are therefore

required to produce these heavy oils. Recent thermal oil

recovery technology developments at the Alberta Research

Council (ARC) have focused on SAGD and SAGD-solvent r techno

processes.

The most promising thermal recovery technology is the SAGD

process. In this process, two horizontal wells separated by a

vertical distance are placed near the bottom of the formation. The

top horizontal well is used to inject steam, which rises forming a

large steam chamber above the well, and the bottom well is used

to collect the produced liquids (formation water, condensate, and

oil). The rising steam condenses on the boundary of the chamber,

heating and entraining the oil to the production well. The process

leads to a high recovery and high oil rate at economic oil-to-steam

ratios (OSR).

The Underground Test Facility (UTF-Phase A) at Fort

McMurray, Alberta, Canada was constructed in 1985 by the Alberta

Oil Sands Technology and Research Authority (AOSTRA) to test

the concept of SAGD. The process was tested from December 1987

to mid-1990. The UTF-Phase Aproject was the first successful field

demonstration of the SAGD process. In addition to proving the

concept of SAGD, it also provided operational know-how, which is

critical to its successful commercial application.

Following the success of the UTF Phase A project, 500 m long

horizontal wells have been used in subsequent phases to further

test the commercial viability of the SAGD process. In addition, a

number of field pilots are in progress in other heavy oil reservoirs

in western Canada (Alberta and Saskatchewan), and around the

world. These pilots tested the use of surface-accessed horizontal

wells and extended SAGD applications to problem reservoirs.

These reservoirs often have lower permeabilities, are deeper, have

bottom water transition zones, with initial gas-saturated “live” oil

and top water / gas caps. In Alberta, the success of these pilots has

led to a number of commercial SAGD projects currently underway.

Current developments of the SAGD process at ARC are aimed

at improving oil rates, OSR, reducing energy and minimizing

water disposal requirements. In addition to SAGD, progress has

been made in the development of combined steam-solvent injection

processes, a novel approach for combining the benefits of

steam and solvents in the recovery of heavy oil and bitumen has

been undertaken. A newly patented Expanding Solvent-SAGD

“ES-SAGD” process has been successfully field-tested and has

resulted in improved oil rates, OSR and lower energy and water

requirements as compared to conventional SAGD.