Abstract：

The depleted tight oil reservoir in Xinjiang has low oil recovery, high residual oil content, and as the reservoir has
moderate water sensitivity, water injection is difficult and has poor yield. In order to improve the degree of recovery of the tight reservoir, a simulation experiment of CO2 huff and puff was carried out to study the effects of the huff and puff injection period, production pressure, and permeability on the huff and puff. The pore size range was also analyzed by NMR. The results show that with the increase of the number of huff and puff cycles, the cycle recovery rate and cumulative recovery rate decreased and the huff and puff effect was worse. The lower the production pressure, the higher the cumulative recovery rate. The higher the permeability, the lower the production gas ratio, the higher the cycle recovery and the better the throughput effect. After eight huff and puff cycles, the cumulative recovery increased 16%~34%, about five to eight times that of the depletion recovery, but the main contribution of recovery is in the first five cycles, accounting for 83.0% to 91.7% of the total increase in recovery. Compared with the small pore, the crude oil in the large pore is first produced. In the first huff and puff cycle, the oil production in the pores radius is lager than pore radius value corresponding 50 ms on the T2 spectrum accounted for 49.00%~73.66% of the total oil output. With the increase of huff and puff cycle, the oil production of the pore radius value corresponding 10 ~ 50 ms and 1 ~ 10 ms on the T2 spectrum take the dominant role in turn. In summary, after the depletion of the tight oil reservoir by standard methods, the injection of CO2 by huff and puff can significantly improve the degree of reservoir recovery, but the number of huff and puff cycles should be limited to within five.

Key words：tight oil formation; CO2 huff and puff; MMP; cycle of huff and puff; gas-oil ratio; NMR

Received： 2017-05-16

Corresponding Authors： cupysl@126.com

Cite this article：MA Quanzheng, YANG Shenglai, CHEN Hao, WANG Lu, QIAN Kun, MENG Zhan, LEI Hao, WANG Zhilin. Effect and influencing factors of CO2 huff and puff in a tight oil reservoir—Taking the Lucaogou formation in the Xinjiang Jimsar sag as an example. Petroleum Science Bulletin, 2018, 04: 434-445.

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