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Energies 2018, 11(9), 2359; https://doi.org/10.3390/en11092359

Investigation on the Application of NMR to Spontaneous Imbibition Recovery of Tight Sandstones: An Experimental Study

1
State Key Laboratory of Petroleum Resources and Prospecting in China University of Petroleum, Beijing 102249, China
2
Ministry of Education Key Laboratory of Petroleum Engineering in China University of Petroleum, Beijing 102249, China
3
Hubei Subsurface Multi-Scale Imaging Key Laboratory, Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China
*
Authors to whom correspondence should be addressed.
Received: 1 August 2018 / Revised: 1 September 2018 / Accepted: 5 September 2018 / Published: 6 September 2018
(This article belongs to the Special Issue Flow and Transport Properties of Unconventional Reservoirs 2018)
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Abstract

In this paper, the nuclear magnetic resonance (NMR) technique is applied to exploring the spontaneous imbibition mechanism in tight sandstones under all face open (AFO) boundary conditions, which will benefit a better understanding of spontaneous imbibition during the development of oil & gas in tight formations. The advantages of nuclear magnetic resonance imaging (NMRI) and NMR T2 are used to define the distribution of remaining oil, evaluate the effect of micro structures on imbibition and predict imbibition recovery. NMR T2 results show that pore size distributions around two peaks are not only the main oil distributions under saturated condition but also fall within the main imbibition distributions range. Spontaneous imbibition mainly occurs in the first 6 h and then slows down and even ceases. The oil signals in tiny pores stabilize during the early stage of imbibition while the oil signal in large pores keeps fluctuating during the late stage of imbibition. NMRI results demonstrate that spontaneous imbibition is a replacement process starting slowly from the boundaries to the center under AFO and ending with oil-water mixing. Furthermore, the wetting phase can invade the whole core in the first 6 h, which is identical with the main period of imbibition occurring according to NMR T2 results. Factors influencing the history of oil distribution and saturation differ at different periods, while it is dominated by capillary imbibition at the early stage and allocated by diffusion at later time. Two imbibition recovery curves calculated by NMRI and NMR T2 are basically consistent, while there still exists some deviations between them as a result of the resolutions of NMRI and NMR T2. In addition, the heterogeneity of pore size distributions in the two samples aggravates this discrepancy. The work in this paper should prove of great help to better understand the process of the spontaneous imbibition, not only at the macroscopic level but also at the microscopic level, which is significant for oil/gas recovery in tight formations. View Full-Text
Keywords: tight sandstones; spontaneous imbibition; remaining oil distributions; imbibition front; imbibition recovery; NMR tight sandstones; spontaneous imbibition; remaining oil distributions; imbibition front; imbibition recovery; NMR
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Lyu, C.; Wang, Q.; Ning, Z.; Chen, M.; Li, M.; Chen, Z.; Xia, Y. Investigation on the Application of NMR to Spontaneous Imbibition Recovery of Tight Sandstones: An Experimental Study. Energies 2018, 11, 2359.

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