Guantao formation in Du84 block, Liaohe oilfield is a typical massive block extra-heavy oil pool with top-water. The oil viscosity is very high and the formation thickness is great. Bitumen shell with 3~4m thickness exist between the top-water layer and oil column. If the bitumen is dissolved when heating in the steam injection recovery process, the top-water will flow down. Moreover, the field production showed that conventional steam stimulation recovery with vertical well is poor. New methods and technologies have to be researched and tested to improve the oil recovery, decrease operation cost and enhances economic efficiency.
Numerical simulation results showed that the reservoir can be developed efficiently by implementing Steam Assisted Gravity Drainage (SAGD) process using existing vertical well and horizontal wells to be drilled following steam stimulation. To avoiding top water going down, the new well completion methods have to apply, and the upper portion of the formation in the steam injector shouldn't be perforated. If the viscosity of the bitumen shell is greater than 500×104mPa.s, the 20m thickness of upper portion shouldn't be perforated to inhibit the top-water effectively. If the viscosity of the bitumen shell is 50~200×104mPa.s, the thickness of upper portion not perforated should be more than 30m to inhibit the top-water effectively. At the same time, the results also showed that the heat communication between the wells is an important factor to control the top-water. The SAGD process can be implemented only when heat communication is established by steam stimulation in order to inhibit the top-water.
Introduction
China has abundant super-heavy oil resource, Which is mainly distributed, in Liaohe Oilfield, Karamay Oilfield of Xinjiang and Shengli Oilfield. Up to now, about 200million tons of super-heavy oil reserves has been gone into production. But for the super-heavy oil reservoirs with top water, it is first time to be developed with steam injection.
For Super-heavy oil, its main property is very high viscosity, so its mobility is very poor or there is no mobility at all in formation. Therefore, the technical challenge encountered in Super-heavy oil recovery is how to reduce oil viscosity and increase its mobility. As we known, steam injection recovery has been the most effective technology for heavy oil, but for Super-heavy oil reservoir, the good recovery performance can't be achieved only through conventional steam injection method. The field production showed that the cycle period was short, with only two month generally, oil production and oil/steam ratio per cycle were low, and the oil rate decline dramatically, so the final economic profit was poor. Therefore, the effective recovery technologies have to be researched and tested to further improve the steam injection recovery(1). In the meantime, how to control the top-water is also a new technology. There is no experience about developing the Super-heavy oil reservoir with the top-water in the world. Therefore, controlling the top-water is one of the technical challenges to develop the reservoir.
Using the exiting vertical wells, Steam Assisted Gravity Drainage (SAGD) process(2) through combination of vertical and horizontal well(3) can enhance the oil recovery further. The new well completion methods that the upper portion of the formation in the steam injector shouldn't be perforated have to apply, in order to avoid top water going down, and the heat communication between the wells is an important factor to control the top-water. The SAGD process can be implemented only when heat communication is established by steam stimulation in order to inhibit the top-water.
