Combined Technology of Weak Gel Flooding assisting Thermal Huff and Puff Enhances Oil Recovery for Offshore Heavy Oil Field

Abstract

Abstract South part of NN reservoir, locating at Bohai Bay of China, has geology characteristics of flat structure, complex oil-water contact system. The formation oil viscosity reaches as high as 413~741mPa•s. At initial production stage, daily oil of vertical well and horizontal well reached 21m3/d and 35m3/d, respectively. Due to complex oil-water relationship and high formation oil viscosity, oil production rate of whole reservoir decreased from 0.6% to 0.3% after one year. Combinatorial development techniques including thermal huff-puff and weak gel flooding have been optimized for further enhancing oil recovery. Considering the platform space limit, thermal huff-puff uses multiple thermal fluid(nitrogen, dioxide, hot water) instead of conventional steam. Twelve new horizon wells have been carried out in the pure oil zone for thermal huff-puff pilot. Until now, there have been twelve wells which completing the first cycle huff-puff, and six wells have completed the second cycle. Meanwhile, in order to keep the formation pressure and reduce the channeling risk, selected three high water-cut production wells were changed into injection wells for weak gel flooding pilot. After carried out combinatorial development techniques, the rate of oil production of whole reservoir has increased from 0.3% to 0.7%. Thermal huff-puff heated oil during the huff process then decreases the formation oil viscosity, and finally increasing the production ability of horizon wells in the puff process. Compared with natural energy production, peak oil production and periodic oil production of thermal production respectively increases to 3 times and 1.6 times in the first cycle. Weak gel flooding increases viscosity of the injected fluid and reduces the difference of water-oil mobility ratio, the average resistance coefficient of three injection wells reaches as high as 1.74. Around the three injection wells, there are nine wells increasing the oil production, and incremental oil production for single well has reached 0.45×104m3~2.12×104m3 in the past few years. Also, there is a positive synergistic effect between thermal huff-puff and weak gel flooding. The artesian flow days of one thermal well extends 76 days in the help of weak gel flooding. Our experiences show that such combinatorial development techniques are effective for enhancing oil recovery of heavy oil fields and meet the demand of high speed development for offshore oil fields.