Simultaneously modelling steam flow and heat transfer in vertical and horizontal wellbores during SAGD cyclic pre-heating stage

Steam-assisted-gravity-drainage (SAGD) is currently an effective technology for heavy oil recovery. The pre-heating stage is important to affect the overall process of SAGD development. In this paper, flow and heat transfer model in vertical well section and horizontal well section and thermal connectivity judgment model during cyclic pre-heating stage were established. Model calculation results are in good agreement with actual measurement results. The effects of steam injection rate and steam quality on the distribution of steam parameters along the whole wellbore and the distribution of heat transfer were compared. Besides, the optimization of steam injection parameter combination was provided. Ultimately, the effect of horizontal well spacing on pre-heating thermal connectivity was discussed. The results show that: With the increase of steam injection rate and steam injection quality, the pressure and temperature drop of the fluid increase. Wellhead required steam injection pressure and temperature increases and even superheated steam appear with the increase of steam injection rate and steam injection quality. The position where the pre-heating backflow turns from wet steam to subcooled water gradually shifts to the wellhead. With the increase of steam injection rate and steam injection quality, the heat transfer between annulus and reservoir decreases, but the uniformity of pre-heating in the horizontal section increases. The time required for cyclic pre-heating to form thermal communication between double wells increases significantly as the horizontal well spacing increases. To simultaneously integrate the uniformity and economy of pre-heating on the oilfield site, the steam injection quality at the heel end of the horizontal section of 0.7, the steam injection rate of 80 t/d, and the horizontal well spacing of 5 m were recommended.