Steam-assisted gravity drainage

Tar Sands Canadian tar sands either are strip-mined and extracted with hot water or employ steam-assisted gravity drainage (SAGD) for in situ recovery of heavy oil (bitumen). The bitumen is processed into naphtha, kerosine, and gasoline fractions (which are hydrotreated), in addition to gas (which is recovered). Current production of syncrude from Canadian tar sands is about 113,000 T/d (790,000 B/d) with expected increases to about 190,000 T/d (1.7 MB/d) by 2010. 

ZLD is used in steam-assisted gravity drainage (SAGD) facUities in areas where adequate disposal weUs are too far from the central processing facUity [14]. However, the thermal unit had problems handling non-volatile organic compounds (humic acids and asphaltenes) that build up in the evaporator/crystaUiser and contaminate the salt cake. The facUity in Alberta, Canada had to instaU a second MVR unit making the process very... 

SAGD (steam-assisted gravity drainage) produced water has a high level of sihca (200— 300 mg/1), and soluble organics, mostly humic acid and asphaltenes. The TDS is typically <20,000 mg/1. 

FIGURE 17.11 Steam-assisted gravity drainage for in situ extraction of steam-heated bitumen from a sandstone formation. 

Gates, I.D. (2007) Oil phase viscosity behaviour in expanding-solvent steam-assisted gravity drainage. Journal of Petroleum Science and Engineering, 59 (1-2), 123-134. 

Owing to the wide use of steam-assisted gravity drainage (SAGD) in heavy-oil production, Canada became one of the world s top ten hydrocarbon-producing countries. Heavy-oil recovery by steam injection requires two to five toimes of steam per tonne of recovered oil [2-4]. After 20% of the heavy oil in place has been recovered from a reservoir, most of the steam energy is wasted to heating the water contained therein, and the profitability of production decreases by a factor of at least 2 [3, 4]. 

We call the movement of reservoir fluid driven by gas pressure through pores and cracks from the injection to the production well pressure drainage. Unlike in steam-assisted gravity drainage, both intensity and direction of pressure drainage can be controlled. For instance, it can be directed upwards when BM reaction occurs in the lower horizontal well (see Fig. 2). 

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