Comparison of Pore Fractal Characteristics Between Marine and Continental Shales

Abstract

Fractal characterization offers a quantitative evaluation on the heterogeneity of pore structure which greatly affects gas adsorption and transportation in shales. To compare the fractal characteristics between marine and continental shales, nine samples from the Lower Silurian Longmaxi formation in the Sichuan basin and nine from the Middle Jurassic Dameigou formation in the Qaidam basin were collected. Reservoir properties and fractal dimensions were characterized for all the collected samples. In this study, fractal dimensions were originated ¶ Corresponding author. This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 4.0 (CC-BY) License. Further distribution of this work is permitted, provided the original work is properly cited. 1840016-1Fractals 2018.26. Downloaded from www.worldscientific.com by 13.66.222.141 on 06/19/19. Re-use and distribution is strictly not permitted, except for Open Access articles. J. Liu et al.from the Frenkel-Halsey-Hill (FHH) model with N 2 adsorption data. Compared to continental shale, marine shale has greater values of quartz content, porosity, specific surface area and total pore volume but lower level of clay minerals content, permeability, average pore diameter and methane adsorption capacity. The quartz in marine shale is mostly associated with biogenic origin, while that in continental shale is mainly due to terrigenous debris. The N 2 adsorption-desorption isotherms exhibit that marine shale has fewer inkbottle-shaped pores but more plate-like and slit-shaped pores than continental shale. Two fractal dimensions (D 1 and D 2 ) were obtained at P/P o of 0-0.5 and 0.5-1. The dimension D 2 is commonly greater than D 1 , suggesting that larger pores (diameter >∼ 4 nm) have more complex structures than small pores (diameter <∼ 4 nm). The fractal dimensions (both D 1 and D 2 ) positively correlate to clay minerals content, specific surface area and methane adsorption capacity, but have negative relationships with porosity, permeability and average pore diameter. The fractal dimensions increase proportionally with the increasing quartz content in marine shale but have no obvious correlation with that in continental shale. The dimension D 1 is correlative to the TOC content and permeability of marine shale at a similar degree with dimension D 2 , while the dimension D 1 is more sensitive to those of continental shale than dimension D 2 . Compared with dimension D 2 , for two shales, dimension D 1 is better associated with the content of clay minerals but has worse correlations with the specific surface area and average pore diameter.

Pore Structure Petrophysical Characterization of the Upper Cretaceous Oil Shale from the Songliao Basin (NE China) Using Low-Field NMR

“…Because of the sedimentary, diagenesis, and tectonism, shale is usually characterized as strong heterogeneity and thus contains various pore types [37,38]. As verified by Yao et al [25], NMR T 2 amplitude is able to indicate the pore type and morphology.…”

“…is phenomenon indicates that the S/V distribution is able to be clarified as two patterns, that is, peaked at ∼2 nm − 1 (Pattern A) and peaked at ∼20 nm − 1 (Pattern B), based on Figure 9 and equation (5). As for the Basically, in shale samples, pores with smaller S/V benefit to adsorb fluid, while pores with bigger S/V are helpful for the storage-free fluid [38]. us, the NMR-based approach for the S/V measurement is conducive to filter the favorable target for shale oil exploration because free oil (rather than adsorbed oil) is potentially the most producible component of tight shale reservoirs [43].…”

Experimental Investigation into the Effects of Fracturing Fluid-Shale Interaction on Pore Structure and Wettability

“…The increase in the 3 Geofluids value of D from 2 to 3 represents an increase in the irregularity and complexity of the pores. K has different values when P/P 0 < 0:5 and P/P 0 > 0:5, corresponding to two different D values: D 1 and D 2 [46,53]. According to previous studies, P/P 0 < 0:5 and P/P 0 > 0:5 represent the adsorption process within the pores with PD < 4 nm and PD > 4 nm, respectively [46,54].…”

An Introduction to Fractal-Based Approaches in Unconventional Reservoirs — Part I

“…The fractal dimensions of pore-throat structures were calculated and its influences on the physical properties of sandstone samples were 9 and Biyang Depression of Henan Oilfield by Jijun Li et al 10 The controlling factors for fractal dimensions, including pore morphology, total organic carbon content, and mineral content, were analyzed accordingly. To compare the fractal characteristics between marine and continental shales, Liu et al 11 also characterized the reservoir properties and fractal dimensions of 18 shale samples. Weiming Wang et al 12 studied the morphological characteristics and size distribution of nanoscale pores in the volcanic rocks of the Haerjiawu Formation using the results of low temperature nitrogen adsorption experiments and fractal geometry theory.…”