Technologies for Raising the Oil Drainage Rate with Vertical-Horizontal Well Combinations in SAGD Mode

Due to the low drainage rate and the uneven expansion of steam cavity appearing in the development of the Liaohe Oilfield which utilizes a vertical-horizontal well combination by steam assisted gravity drainage (SAGD), a horizontal-well drainage rate model was developed. It focused on a daily output equation for horizontal wells which have limited length and take into account the point effect (following the theory of R. M. Butler). With a dual-horizontal-well drainage model, and the vertical-horizontal well group was simplified as dual horizontal wells, finally, the drainage rate equation that was used for vertical well and horizontal steam injection well in SAGD. The drainage model was developed and applied to the stages of initial production and stable production. It is shown from the analysis on drainage rate equation that the drainage rate of vertical-horizontal well group SAGD is mainly controlled by the quantity of oil drainage wells and the vertical expansion height of the steam cavity. Combined with the heavy oil development practice in Liaohe Oilfield, the technical measures for increasing the drainage rate of vertical-horizontal well group SAGD were proposed. The approach involved drilling another two steam injection wells at the heel of the horizontal section and to increase the steam injection rate by 20%. Meanwhile, the best perforation position was set near the sections with low physical properties, with reperforation length of 8 m. These technical measures were applied to 6 well groups in the Liaohe Oilfield, and as a result, the daily oil production increased by different percentages. This research with field test provides the good basis for further improving the drainage rate of SAGD well groups.