PERFORMANCE OF HORIZONTAL-VERTICAL COMBINATIONS FOR STEAMFLOODING BOTTOM WATER FORMATIONS

In Alberta and Saskatchewan, many heavy oil formations have a communicating high water saturation zone, which makes the use of conventional oil recovery methods unattractive. Often, attempts to produce such marginal oil reservoirs result in excessive water production due to coning and steam migration into the bottom water zone. Water-flooding is ineffective because of the high mobility ratio of water to heavy oil. This paper discusses recovery strategies and reservoir situations under which a steamflood can be conducted efficiently. A heavy oil reservoir in Saskatchewan was selected as the prototype for the scaled model steamflooding experiments. Four combinations of vertical and horizontal wells (injectors and producers) and two bottom water thickness were used. In one series of runs, the use of a small volume of solvent with steam was examined, with a view to divert steam early from the water zone. The results showed that the horizontal injector-horizontal producer combination recovered 68% of the oil in the presence of 10% thickness of high water saturation. In the absence of bottom water, the horizontal combination was only slightly better than vertical wells. With thicker bottom water zones (50% of model thickness), the oil recovery fell about 20% in all four cases. A 10% PV solvent slug injected ahead of steam improved oil recovery by only 5%. Guidelines are offered for steamflooding similar heavy oil reservoirs.