A Laboratory Study of Thermal Oil Recovery Using Horizontal Wells

This paper reports laboratory experimental results of steam-assisted gravity drainage using horizontal wells. The results were obtained for 17°API heavy oil and light refined oil. The oil steam ratios and percentage recovery of original oil in place were measured for two different well configurations, injection well completions, and shale barrier configurations. In addition, the effect of limited steam entry was also studied using a light refined oil. The experiments were conducted in a box-shaped sand pack with five sides of steel and one side of transparent polycarbonate material to facilitate flow visualization. The results indicate that steam-assisted gravity drainage not only gives a high sweep efficiency but also gives oil steam ratios of about 0.7, indicating a high thermal efficiency for producing heavy oils. Steam-assisted gravity drainage produces heavy oil at a rate approximately three times faster than that obtained with cold oil gravity drainage. In a uniform permeability pack, initial oil production rates using horizontal injection and production wells are higher than those obtained using a vertical injector and a horizontal producer. For a vertical injector, steam injection near the pack top gave higher and faster oil recovery than steam injection near the sand pack bottom. In the case of shale barriers, a vertical injection and horizontal production scheme gives faster and higher oil recovery as compared to that obtained using a horizontal injection and production well scheme. A light refined oil was used to obtain limited entry results, where steam injection was confined to 5 to 10% of the length of a horizontal injector. This occurs when a vertically fractured zone intersects a horizontal injection well at 90°. The results indicate that limited entry does not affect total oil recovery. On the contrary, it enhances initial oil production rates. The above results indicate that steam-assisted gravity drainage is an efficient method for producing heavy oils.