To produce heavy crude oil and natural bitumen, thermal recovery methods have been commonly used. According to PJSC TATNEFT, for fourteen years of development of heavy oil fields, more than 45 million tons of steam at temperature of more than 200°C has been injected into subsurface formations. One of the most effective technologies for producing ultra-viscous crude oil and natural bitumen is the steam assisted gravity drainage (SAGD) process. To ensure high efficiency and safety of the SAGD technology, an operator must control the SAGD process and perform a large bulk of chemical-analytical and other types of analyses of produced fluids. The paper discusses possible negative aftereffects of SAGD termination following the lengthy period of steam injection. In SAGD, the injected steam serves the two purposes: fills the void space left by the heavy oil, and maintains the temperature in the steam chamber. The latter purpose is very important, since cooling of the steam chamber may lead to decrease of the reservoir pressure and the abrupt steam condensation, which, in its turn, may result in pay rock deformation, extensive land surface subsidence, behind-the-casing flows, contamination of the overlying formations, including aquifers. Obtaining analytical estimates of the steam mass to maintain the steam chamber temperature is an important tool of the SAGD process control, along with the 3D thermohydrodynamic modeling. The authors present an analytical technique to separate the injected steam into the steam mass to maintain the steam chamber temperature and the steam mass to provide the steam chamber growth. The technique is based on the material balance equation and the estimate of the steam-condensate mixture density in reservoir conditions.
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