scholarly journals Multifractal characteristics of shale and tight sandstone pore structures with nitrogen adsorption and nuclear magnetic resonance

2020 ◽  
Vol 17 (5) ◽  
pp. 1209-1220
Author(s):  
Fu-Yong Wang ◽  
Kun Yang ◽  
Yun Zai
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Specific Surface ◽  
Pore Size ◽  
Ordos Basin ◽  
Tight Sandstone ◽  
Pore Structures ◽  
Pore Size Distributions ◽  
Multifractal Spectra ◽  
Nuclear Magnetic

Abstract Based on the experiments of nitrogen gas adsorption (N2GA) and nuclear magnetic resonance (NMR), the multifractal characteristics of pore structures in shale and tight sandstone from the Chang 7 member of Triassic Yanchang Formation in Ordos Basin, NW China, are investigated. The multifractal spectra obtained from N2GA and NMR are analyzed with pore throat structure parameters. The results show that the pore size distributions obtained from N2GA and NMR are different, and the obtained multifractal characteristics vary from each other. The specific surface and total pore volume obtained by N2GA experiment have correlations with multifractal characteristics. For the core samples with the similar specific surface, the value of the deviation of multifractal spectra Rd increases with the increase in the proportion of large pores. When the proportion of macropores is small, the Rd value will increase with the increase in specific surface. The multifractal characteristics of pore structures are influenced by specific surface area, average pore size and adsorption volume measured from N2GA experiment. The multifractal characteristic parameters of tight sandstone measured from NMR spectra are larger than those of shale, which may be caused by the differences in pore size distribution and porosity of shale and tight sandstone.

Pore-Size Distributions for Organic-Shale-Reservoir Rocks From Nuclear-Magnetic-Resonance Spectra Combined With Adsorption Measurements

SPE Journal ◽  
2015 ◽  
Vol 20 (04) ◽  
pp. 824-830 ◽  
Author(s):  
Richard F. Sigal
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Pore Size ◽  
Surface Relaxation ◽  
Size Distributions ◽  
Pore Sizes ◽  
Pore Size Distributions ◽  
Shale Reservoirs ◽  
Organic Shale ◽  
Nuclear Magnetic

Summary The behavior of fluids in nanometer-scale pores can have a strong functional dependence on the pore size. In mature organic-shale reservoirs, the nuclear-magnetic-resonance (NMR) signal from methane decays by surface relaxation. The methane NMR spectrum provides an uncalibrated pore-size distribution for the pores that store methane. The distribution can be calibrated by calculating a pore-wall-surface area from a methane-Langmuir-adsorption isotherm. When this method was applied to samples from a reservoir in the dry-gas window, the pores containing methane had pore sizes that ranged from 1 to approximately 100 nm. Approximately 20–40% of the pore volume was in pores smaller than 10 nm, where deviation from bulk-fluid behavior can be significant. The samples came from two wells. The surface relaxivity for the sample from Well 2 was somewhat different from the relaxivity for the two samples from Well 1. Samples that adsorbed more methane had smaller pore sizes. This methodology to obtain pore-size distributions should be extendable to more-general organic-shale reservoirs.

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

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2359 ◽  
Author(s):  
Chaohui Lyu ◽  
Qing Wang ◽  
Zhengfu Ning ◽  
Mingqiang Chen ◽  
Mingqi Li ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Pore Size ◽  
Early Stage ◽  
Spontaneous Imbibition ◽  
Size Distributions ◽  
Pore Size Distributions ◽  
Two Samples ◽  
Tight Formations ◽  
Nuclear Magnetic

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.

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