Experimental Investigation on the Characteristic Mobilization and Remaining Oil Distribution under CO 2 Huff-n-Puff of Chang 7 Continental Shale Oil

Jianhong Zhu, Junbin Chen, Xiaoming Wang, Lingyi Fan and Xiangrong Nie
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Jianhong Zhu: College of Petroleum Engineering, Xi’an Shiyou University, Xi’an 710065, China
Junbin Chen: College of Petroleum Engineering, Xi’an Shiyou University, Xi’an 710065, China
Xiaoming Wang: College of Petroleum Engineering, Xi’an Shiyou University, Xi’an 710065, China
Lingyi Fan: College of Petroleum Engineering, Xi’an Shiyou University, Xi’an 710065, China
Xiangrong Nie: College of Petroleum Engineering, Xi’an Shiyou University, Xi’an 710065, China

Energies, 2021, vol. 14, issue 10, 1-18

Abstract: The Chang 7 continental shale oil reservoir is tight. The recovery factor is extremely low, the remaining oil is very high, and injecting water to improve oil recovery effectiveness is too hard. Therefore, in this paper, physical simulation experiments of CO 2 huff-n-puff shale oil and NMR tests were conducted to study the cycle numbers and permeability on the recovery degree, as well as the characteristics of shale oil mobilization and the remaining oil micro distribution. The results showed that the cumulative oil recovery factors (ORFs) gradually increased in the natural logarithmic form, the single cycle ORFs decreased rapidly in exponential form with the huff-n-puff cycle number, and the biggest economic cycle numbers were between approximately 3 and 5. Furthermore, the higher the permeability, the higher the ORF, but the difference of ORF decreased between the two experimental samples with the cycles. In addition, the gap of production and recovery degree was large between the different scale pores, the ORF of macropores was 6–8 times that of micropores, and the final remaining oil was mainly distributed in the micropores, accounting for 82.29% of the total amount; meanwhile, the macropores comprised less than 0.5%. In the process of huff-n-puff, CO 2 flowed into macropores, mesopores, and smallpores under the pressure differential effect, but a small amount of CO 2 slowly diffused into micropores, resulting in the ORF of the former with more free oil being higher and the ORF of micropores with more adsorbed oil being lower. Therefore, promoting a better contact and reaction between CO 2 and shale oil of micropores is one of the key ways to effectively develop the Chang 7 continental shale oil and enhance oil recovery.

Keywords: CO 2 huff-n-puff; oil recovery factor; remaining oil distribution; NMR; pore scale (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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