Mechanisms and Influence Factors of Downhole Electrical Heating-Assisted Steam-Assisted Gravity Drainage Production

Approximately 70% steam-assisted gravity drainage (SAGD) wellpairs have entered into the production phase in China, while due to the fluvial sedimentation environment with strong reservoir heterogeneity, only 53% of the horizontal well section develops a steam chamber. In order to massively recover the bypassed oil and expand the steam chamber along the horizontal section, downhole electrical heating was proposed, and its mechanisms of high temperature-induced rock mechanics change and influence factors are investigated in this study using laboratory experiments and electrical steam hybrid numerical simulation. It is found that the electrical heating-assisted SAGD has four key mechanisms, namely, localized temperature elevation, development of a fixed point steam chamber, localized oil gravity drainage, and petrophysical property improvement. The influence factors include the static and operational factors, in which the permeability ratio is the primary factor for choosing SAGD wellpairs, while the steam injection rate, steam chamber operational pressure, injector and producer pressure difference, adjacent SAGD steam chamber pressure differential, heater surface temperature, and electrical heating period integrally influence the incremental production performance. Through carefully modifying the parameters, the typical SAGD wellpair steam chamber could expand from 67 to 100% along the horizontal section, with an incremental oil rate of 3-5 m³/day, and the cumulative steam/oil ratio decreases from 6.67 to 4.17. The downhole electrical heating is particularly efficient in improving steam chamber conformance in heterogeneous reservoirs and also has significant potential in similar reservoirs developed by horizontal wells.