Classifying Coal Pores and Estimating Reservoir Parameters by Nuclear Magnetic Resonance and Mercury Intrusion Porosimetry

Abstract

The widely used coalbed methane (CBM) flow model-triple porosity/dual permeability (TPDP) model indicates that coal pores can be divided into micro-trans-pores, meso-macro-pores, and fractures, while CBM can flow via meso-macropores and fractures. The mechanism to obtain the reservoir parameters of these two flowing systems has been given little attention in the TPDP model. In this study, nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and other routine core analysis methods were conducted on nine coal samples to classify coal pore types, transform transverse relaxation time to pore radius, and estimate porosity and permeability of meso-macro-pores and fractures. Results show that the two referenced relaxation times of T 2C1 and T 2C2 , which were identified from the curves of irreducible and full water saturations obtained from NMR experiments, can classify coal pores into fractures (T 2 > T 2C2 ), meso-macro-pores (T 2C1 < T 2 < T 2C2 ), and micro-trans-pores (T 2 < T 2C1 ). The dividing point of micro-trans-pores and meso-macro-pores, which was obtained from NMR and MIP (mercury intrusion porosimetry) experiments, provided another method for transforming transverse relaxation time to pore radius. Based on the classification results and routine core analysis methods, the porosity of meso-macro-pores and fractures were calculated, and the relationship between air permeability and porosity of meso-macro-pores and fractures was finally proposed. This paper provides an effective method for obtaining the permeability and porosity of meso-macro-pores and fractures using the TPDP model to simulate the performances of CBM wells.

New characterization on the petrophysical characteristics of tight sandstone reservoirs in Yanchang Formation Ordos Basin China

“…Mohnke and Yaramanci (2008), Wang et al (2010), Li et al (2012, Cai et al (2013), Zhou et al (2013) and Ge et al (2013) analyzed pore radius distribution of various types of reservoirs using NMR methods, but they failed to intuitively describe and analyze the reservoirs' microscopic characteristics. Li et al (2008Li et al ( , 2012, Wang (2009), Yao et al (2010, Liu (2012), Mao et al (2013) and Zou et al (2013b) thought the results of pore radius distribution were consistent by contrasting NMR with mercury intrusion experiments/CT. Using NMR and other experiments contrast, Li et al (2015aLi et al ( , 2015b forecasted spaces of oil and water occurrence in the tight sandstone reservoirs.…”

Experimental Analysis of Pore and Permeability Characteristics of Coal by Low-Field NMR

“…The T 2 is linearly related to the pore size, and the geometrical fractal relation of NMR pores can be expressed as follows [13]: (16) where V c is the percentage of pore accumulation volume occupied by the total volume, %; and T 2max is the maximum transverse relaxation time, ms.…”

“…The pores corresponding to the T 2 peaks are divided into adsorption pores, seepage pores, and fissures by Yao et al [11] and Cai et al [12]. They think that the patterns of unimodal, bimodal, and multi-peak in the T 2 spectra represent different pore types and PSD, and the pore characteristics of NMR were compared with those of MIP and CT scanning [13,14].…”

Nanoscale Pore Structure Characterization and Permeability of Mudrocks and Fine-Grained Sandstones in Coal Reservoirs by Scanning Electron Microscopy, Mercury Intrusion Porosimetry, and Low-Field Nuclear Magnetic Resonance

“…At present, there are a series of experimental methods such as scanning electron microscopy (SEM) [19][20][21][22][23][24][25][26][27][28][29][30][31], mercury intrusion porosimetry (MIP) [5,[32][33][34][35][36], and low-field nuclear magnetic resonance (NMR) [35][36][37][38][39][40] which have been widely applied for qualitative and quantitative determination of pore structure characteristics of different types of reservoir rocks. Among them, high resolution SEM-based imaging techniques, for example, field emission SEM (FE-SEM) [19,20,[22][23][24][25], broad ion beam SEM (BIB-SEM) [21,27,29], and focused ion beam SEM (FIB-SEM) [26][27][28][29][30][31]41], are commonly used in the field of visualized characterization of nanoscale pore systems of tight reservoir rocks such as gas shales and fine-grained sandstones due to their high resolution imaging advantages.…”

“…Therefore, its practical application in the geophysical field has been getting more and more attention from petrophysicists and petroleum engineers [40,44]. Recently, there are also some researches which applied NMR to the investigation of the pore structure and pore related parameters of coals [35,38].…”