Performance of electric submersible pumps (ESP) used for heavy oil extraction in low-pressure SAGD projects can be impaired because of high temperature of the produced fluids and the gas phase formed at the pump inlet. The answer to the problem is the technology for two-stage lifting. An intermediate casing string with a plugged-back end and openings cut at a specified depth is run in hole. An ESP with an enclosed submersible motor is conveyed into the intermediate casing on a tubing string. The diluted heavy oil enters the intermediate casing-production casing annulus, and rises to the openings in the intermediate casing below the flowing level in hole. As the formation fluid rises towards the flowing level, the pressure decreases, facilitating, thus, water vaporization. The temperature of the fluid also decreases with pressure decline. A certain amount of water is vaporized and rises to surface to enter the outgoing gas line. Because of energy consumed in the process of phase inversion, the temperature of the produced fluid decreases. The cooled-down fluid enters the intermediate casing-production casing annulus through the openings, goes downwards through the submersible motor housing to cool the motor to the ESP inlet, and then, through the tubing string, to oil gathering line. The separated gas goes through the annulus to the outgoing gas line. The density of the well fluid increases with the resultant increase of fluid pressure at the pump inlet.
Decrease of the fluid temperature and increase of the fluid pressure at the pump inlet creates downhole pressure-and-temperature conditions preventing boiling of water in ESP cavities when bottomhole pressure drops. This improves the ESP performance and the overall economics of the oil production process. The additional advantage is associated with decreased rate of salt precipitation in downhole pumping equipment.
The technology was successfully tested in two wells of the Ashalchinskoye heavy oil field in conditions of low bottomhole pressure and the fluid temperature close to the temperature of inversion. The technology is able to improve the performance of artificially-lifted shallow horizontal SAGD-wells: to attain multiple increase of oil production rate and to decrease steam-oil ratio.
References
1. Takhautdinov Sh.F., Sabirov R.K., Ibragimov N.G. et al., Sozdanie i promyshlennoe vnedrenie kompleksa tekhnologiy razrabotki mestorozhdeniy sverkhvyazkikh neftey (The creation and implementation of technology complex for heavy oil deposits development), Kazan': Fen Publ., 2011, 142 p.
2. Akhmadishin F.F., Stroitel'stvo skvazhin s gorizontal'nym okonchaniem na malye glubiny dlya dobychi vysokovyazkoy nefti i prirodnykh bitumov metodom parogravitatsionnogo drenazha (Construction of wells with horizontal completion at shallow depths for extraction of heavy oil and natural bitumen using SAGD method): thesis of candidate of technical science, Bugul'ma, 2016.
3. Ageev Sh.R., Grigoryan E.E, Matvienko G.P., Rossiyskie ustanovki lopastnykh nasosov dlya dobychi nefti i ikh primenenie (Russian vane-type pumps units for oil production and their application), Perm': Press-Master Publ., 2007, 648 p.
4. Kisman K.E., Artificial lift – A major unresolved issue for SAGD, Journal of Canadian Petroleum Technology, 2003, V. 42, no. 8, pp. 39–45.
