地质科技通报 (May 2022)
Experimental study on EOR of offshore heavy oil reservoir in high-ultra-high water cut stage
Abstract
To explore the mechanism of enhancing the recovery degree of remaining oil in heavy oil reservoir with different liquid extraction methods in high and ultra-high water cut stage, a displacement experiment of heavy oil reservoirs in marine sandstone under different extraction methods and crude oil viscosity was designed.One dimensional displacement simulation experiment was carried out by constructing interior long core physics to study the effects of different liquid extraction methods and crude oil viscosity on EOR in high and ultra-high water cut stage.Then, the distribution of remaining oil under different water injection methods was studied by combining nuclear magnetic resonance imaging with T2 spectrum. The research shows that the recovery degree for the 100 mPa·s crude oil can be increased by about 11% compared with constant low-speed drive.Taking the water cut is more than 99% as a termination condition for displacement completion, the recovery degree of oil reservoir in high water cut stage is the highest through multiple amplitude control and liquid extraction. When it reaches ultra-high water cut stage for core low-speed water flooding, the core saturation showing in NMR image decreases obviously. With the progress of displacement, porosity component decreases gradually, that is, remaining oil decreases gradually.Compared withone large liquid extraction, multiple liquid extraction shows better effect on the production degree of different pore sizes than during the high water cut stage. Micropores, pores and mesopores are affected with different degrees, and the overall recovery degree is increased by 17.01%. The development of small and medium pores results in the increase of recovery degree by 13.31%, accounting for 78.2%of the increase range.In the ultra-high water cut stage, the dominant seepage channels are easily formed under the condition of both one large liquid extraction and multiple liquid extraction, and the oil recovery degree of multiple liquid extraction is 9.2% higher than that of one large liquid extraction. Under different liquid extraction methods, the medium pore makes main contribution to improve the recovery degree, accounting for 97.2% of the increase range, and the sweep degree of micro pore wave is the smallest. The research results indicate that multiple amplitude control and liquid extraction technology can provide technical support for EOR of heavy oil reservoir in high and ultra-high water cut stage.
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