Summary
Steam-assisted gravity drainage (SAGD) has been used to develop the "super heavy" oil reservoirs in PetroChina Xinjiang Oilfield Branch. These reservoirs have a very high oil viscosity that can reach more than 50,000 cp at 50°C. Moreover, owing to their continental deposit origin, these reservoirs have a low porosity and a low permeability, as well as frequent and heterogeneous occurrence of mud/shale stringers within. Because of these challenging reservoir qualities, the conventional steam circulation SAGD startup process takes 10 to 12 months before the SAGD well pair can be switched to production. A geomechanical dilation mechanism is used to startup the SAGD production with outstanding success. As a result, dilation startup has recently become the routine start-up process in Xinjiang's SAGD production.
This paper describes further improvement in dilation startup by injecting a unique catalyst to evoke the in-situ catalytic aquathermolysis mechanism. The reservoir is first dilated to form a high-porosity and high-permeability conduit connecting the SAGD well pair. The catalyst is then injected into these newly created pore spaces, contacting the heavy oil in large volume, and helping reduce in-situ oil viscosity. This technology has been applied on more than 10 SAGD well pairs and excellent field results were generated in terms of reduced steam use, shortened steam circulation time, and increased initial oil production. This paper presents this integrated chemical geomechanics technology with relevant laboratory test and field results supporting the description.
