Mechanism and Application of Improving Heavy Oil Recovery Greatly by Solvent and Foam Assisted Steam Flooding

摘要

The annual production reached 47. 5 million tons in 2012 in Shengli oilfield, almost 96% of which was produced by CSS with low recovery factor of only 18. 8% . Steam flooding as the main EOR technique isn't available for the heavy oil in Shengli oilfield because of the following challenges: (1) the deeply buried depth of reservoirs (more than 1300m) results in low steam quality at bottom hole. (2) high formation pressure makes steam zone narrower and hot water and condensation zone wider. (3) the severe heterogeneity of reservoir causes steam channeling. To improve greatly recovery factor after CSS, a solvent and foam assisted steam flooding (SFASF) pilot was carried out in Gudao Block 2 heavy oil reservoir. The oil production rate of small well spacing pilot increased from 20t/d to a peak of 101t/d, water cut decreased from 89% to 74. 6% , and the recovery factor will be raised by 21. 8% and up to 57. 7% during SFASF. The mechanism of SFASF was investigated. In order to reduce the steam channeling and improve steam uniform driving, N2 and foam agent were injected periodically during steam flooding. A new foam agent was developed, of which the resistance factor can always keep more than 20 under residual oil saturation at 300°C. In order to improve displacement efficiency at hot water and condensation zone, A new anionic solvent was developed and injected during steam flooding so as to decrease oil-water interfacial tension and residual oil saturation. The solvent can make IFT up to 10~(-3) mN/m at 300°C. Moreover, optimum concentration of foam agent and solvent of SFASF is about 0. 5% and 0. 3% respectively and steam flooding is continuous with one month chemical system plug after three month interval. In order to get better effects high steam quality boiler by superheat, equal dryness distributing and high efficiency wellbore insulation technology were developed. Combining heat with chemical is a trend to improve greatly heavy oil reservoirs recovery factor and the SFASF technique is available for more than 0. 174 trillion tons oil reserve in Shengli oilfield.