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Wednesday, 25 March 2009

Heavy Oil Recovery in Russia: SAGD & ES-SAGD Technologies

T.N. Nasr, Alberta Research Council

Russia has always been known as a major force for hydrocarbon production; indeed there have been times when it has bested Saudi Arabia as the globes top. It has been a market in transition recently; the pumps at the giant Soviet era fields have started to wain over the last few years and the years of underinvestment in exploration have started to take there toll. Production has fallen steadily and only recently have the exploration boundaries been pushed further in Siberia and the Russian Arctic.

With some experts predicting peak oil as early as 2030, there is more and more interest in so called "unconventional resources" such as heavy oil and bitumen. Technology in the recovery of such reserves is advancing rapidly and suddenly this huge country with depleted hydrocarbon reserves has an opportunity for the future.

So, what percentage of Russia's oil can realistically be recovered? The best sources available are from BP and the Oil and Gas Journal, but they differ by some 13 billion barrels.

The graph above makes no distinction between conventional or unconventional oil; however the USGS has speculated that the Russian Federation has roughly 13.4 billion barrels of technilcally recoverable heavy oil and 33.7 billion barrels of technically recoverable barrels of bitumen. The most promising technology being used in the heavy oil capital of the world, Canada, is Steam Assisted Gravity Drainage (SAGD)

Canadian Bitumen Resource
The Canadian bitumen deposits are almost entirely located in the province of Alberta. Three major deposits are defined as Athabasca, Cold Lake and Peace River. The average depths of the deposits are 300, 400 and 500 m, respectively. The total initial volume-in-place of bitumen is estimated to be 259.1 billion m3. This estimate could ultimately reach 400 billion m3 by the time all exploratory developments are completed. This shows that Canada has the world's largest bitumen deposits. Out of the total volume, 24 billion m3 are available for surface mining techniques. Athabasca deposit is the only deposit with surface mineable reserves. About 376 billion m3 lie too deep to be surface-mined and are exploitable by in-situ technologies. However, approximately 12%, or - 50 billion m3 of the total volume-in-place is estimated to be ultimately recovered by existing technologies. That percentage is expected to increase as more advances in recovery technologies are made. Most recently, advances made in directional drilling and measuring while drilling (MWD) technologies have facilitated development of new in-situ production technologies such as the steam assisted gravity drainage (SAGD) and Expanding Solvent-SAGD (ES-SAGD) that have significantly improved well-bore reservoir contact, sweep efficiencies, produced oil rates and reduced production costs.

The most promising thermal recovery technology is the Steam Assisted Gravity Drainage (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). Butler developed an empirical correlation for determining the oil rate from the SAGD process as a function of reservoir and oil properties. This correlation is given by the following:

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) and industry partners to test the SAGD technology. The process was tested from December 1987 to mid 1990. The UTF-Phase A project 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.

Shafts and tunnels are used for underground access of the reservoir

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 that are currently underway.

Surface accessed SAGD horizontal wells

Current developments of the SAGD process 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. A newly patented Expanding Solvent-SAGD "ES-SAGD" process has been successfully field-tested recently and has resulted in improved oil rates, OSR and lower energy and water requirements as compared to SAGD.

In the ES-SAGD concept, a hydrocarbon additive at low concentration is co-injected with steam in a gravity-dominated process, similar to the SAGD process. The hydrocarbon additive is selected in such a way that it would evaporate and condense at the same conditions as the water phase. By selecting the hydrocarbon solvent in this manner, the solvent would condense, with condensed steam, at the boundary of the steam chamber. Condensed solvent around the interface of the steam chamber dilutes the oil and in conjunction with heat, reduces its viscosity.

The ES-SAGD concept

In the example shown below, as the carbon number of the solvent additive increases, the vaporization temperature increases. Hexane has the closest vaporization temperature to the injected steam temperature (215 C at the operating pressure of 2.1 MPa) and resulted in a higher oil drainage rate. On the other hand, C8 has a vaporization temperature that exceeded the injected steam temperature and a decline in oil drainage rate is noticed as compared to Hexane.

Impact of solvent type on oil drainage

EnCana Corporation of Canada has piloted the SAGD-solvent process at its Senlac Thermal project in 2002 for heavy oil and has tested and still operating this process at its Christina Lake SAGD project for bitumen. At the Christian Lake project, conventional SAGD was operated for about 5 months followed by introduction of the SAGD-solvent for about half a year till February 2005. A significant improvement of oil production rate and SOR were observed within this short time interval. A major improvement in produced oil quality was also observed. Suncor Energy, and other oil companies, are currently testing, or planning to test, the SAGD-solvent process in the field.

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posted by The Rogtec Team @ 16:15  0 Comments

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