Steam-assisted gravity drainage (SAGD) is an efficient method for super viscous oil and natural bitumen recovery. The SAGD method uses a series of pairs of injection-producing horizontal wells. The steam chambers formed above each pair of wells, reaching the top of the formation, propagate horizontally until they coalescence. As the angle of inclination of the steam chamber boundary decreases, the rate of drainage also decreases. The efficiency of a SAGD project depends strongly on bitumen-production rate, recovery factor, and cumulative steam-oil ratio (CSOR). Hence, an accurate CSOR and production rate predictions are the important task for the planning and implementation of SAGD project.
In this paper an analytical model for calculating the production rate of a horizontal well and the CSOR in the SAGD method is proposed. Verification with the results of experiments on physical models has shown that the proposed analytical model describes the SAGD process adequately. It is shown that due to non-Newtonian nature of the super viscous oils flow, the stagnant zones are formed in the inter-well space, which are not covered by the impact. The limiting angle of inclination of the steam chamber boundary at which the SAGD process terminates is obtained. The effect of the threshold pressure gradient on the horizontal well production rate and the cumulative steam oil ratio is investigated. The results of simulation showed that the threshold pressure gradient has a significant impact on the dynamics of the main indicators of the SAGD process at all stages of the steam chamber growth.
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