Abstract
Detailed study on the pore structure of shale oil reservoir is significantly for the exploration and development, and the conventional single pore structure measurement method cannot accurately describe the pore structure characteristics of the shale oil reservoir. In this paper, the Field Emission Scanning Electron Microscope (FESEM), low-pressure nitrogen adsorption (LP-N2A) and mercury injection porosimetry (MIP) techniques are used to comprehensive evaluate the pore structure of Chang 7 shale oil reservoir. The FESEM results show that inter pores, inner pores, organic pores and micro-cracks are developed in Chang 7 shale oil reservoir, and the pore structure can be divided into two groups from the LP-N2A and MIP. A new pore structure comprehensive evaluation method was promoted according to the connection points from the pore sizes distribution curves of LP-N2A and MIP. With this comprehensive analysis of the pore size distribution, the pore size distribution of various shale samples feature as triple-peak pattern. Due to the heterogeneity of the shale oil samples, the corresponding pore apertures of the connection points are various, and the overall pore size distribution of shale oil reservoir samples can also be divided into two types. In Group I, the size distributions exhibited a bimodal feature in a narrow range from 1.71 to 100 nm. The trimodal feature of size distributions was captured in Group II with the pore diameter ranges from 1.71 to 1426.8 nm. Group I features smaller sorting coefficient and good pore connectivity. However, the trimodal corresponds to the complex pore structure and larger sorting coefficient for Group II.
Highlights
As an essential unconventional resource, shale oil has been successfully developed in countries such as USA and Canada (Gale et al, 2007; Huang et al, 2019; Kirschbaum and Mercier, 2013; Kuhn et al, 2012; Liu et al, 2018; Ojha et al, 2017)
Various techniques were adopted for the pore structure characterization research for tight oil and gas reservoir, shale oil and gas reservoir, including scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), argon ion polishing-FESEM, focused ion beam scanning electron microscopy (FIBSEM), small-angle neutron scattering (SANS), nano-CT and quantitative analysis using mercury injection porosimetry (MIP), gas adsorption (low-pressure nitrogen adsorption (LP-N2A) and lowpressure carbon dioxide adsorption (LP-CO2A)), nuclear magnetic resonance (NMR), etc. (Clarkson et al, 2013; Gao and Li, 2015, 2016; Ji et al, 2012; Liu et al, 2018; Ma et al, 2019; Zhang et al, 2019)
The intergranular pores in Chang 7 shale oil reservoir are well developed and these pores are well connected
Summary
As an essential unconventional resource, shale oil has been successfully developed in countries such as USA and Canada (Gale et al, 2007; Huang et al, 2019; Kirschbaum and Mercier, 2013; Kuhn et al, 2012; Liu et al, 2018; Ojha et al, 2017). The detailed study on pore structure characterization of shale oil reservoir can promote the understanding and the development in shale oil fields. The unconventional reservoirs (coal seams, shale oil/gas reservoirs) commonly present complex pore type and different size, a comprehensive pore size characterization was developed by using different techniques (Cao et al, 2015; Clarkson et al, 2013; Liu et al, 2018; Okolo et al, 2015; Pan et al, 2017; Wang and Yu, 2017; Wang et al, 2014; Yang et al, 2013, 2017; Zhang et al, 2016).
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