Using BIB-SEM Imaging for Permeability Prediction in Heterogeneous Shales

Abstract

Organic-rich shale samples from a lacustrine sedimentary sequence of the Newark Basin (New Jersey, USA) are investigated by combining Broad Ion Beam polishing with Scanning Electron Microscopy (BIB-SEM). We model permeability from this 2D data and compare our results with measured petrophysical properties. Three samples with total organic carbon (TOC) contents ranging from 0.7% to 2.9% and permeabilities ranging from 4 to 160 nD are selected. Pore space is imaged at high resolution (at 20,000x magnification) and segmented from representative BIB-SEM maps. Modeled permeabilities, derived using the capillary tube model (CTM) on segmented pores, range from 2.3 nD to 310 nD and are relatively close to measured intrinsic permeabilities. SEM-visible porosities range from 0.1% to 1.8% increasing with TOC, in agreement with our measurements. The CTM predicts permeability correctly within one order of magnitude. The results of this work demonstrate the potential of 2D BIB-SEM for calculating transport properties of heterogeneous shales.

Full-Scale Pore and Microfracture Characterization of Deep Coal Reservoirs: A Case Study of the Benxi Formation Coal in the Daning–Jixian Block, China

“…The characteristics of coal reservoirs, such as adsorbability, gas-bearing capacity, and permeability, are related to the development degree and structural characteris-tics of pores and fractures [53][54][55]. In this paper, a formula similar to that of Sinn et al is used to calculate the deep coal reservoir permeability [56]. An ideal capillary bundle is assumed, and laminar flow through a cylindrical pipe is described by combining Darcy's law and the Hagen-Poiseuille equation to express permeability.…”

“…Based on LT-N 2 GA, the LP-CO 2 GA method, and the high-pressure MIP method, the pore characteristics (PV, SSA, and pore diameter) of the coal samples can be quantitatively characterized; thus, the porosity corresponding to each pore can be calculated. Combined with the pore radius (r), the absolute permeability of a single pore can be further calculated (K 1 ) [56]:…”

“…Based on micro-CT scanning and three-dimensional reconstruction technology, we quantitatively characterize the volume of microfractures and the total volume of coal samples after three-dimensional reconstruction, calculate the pore (fracture) clearance (∅) corresponding to each microfracture, and then combine the microfracture width (ω) to further calculate the absolute permeability (K 1 ) of each microfracture [56]:…”

“…where ∅ i is the microfracture degree of the ith microfracture and τ is the tortuosity of microfractures. In this study, τ = 10 was used for calculation [56,57], and K i is the absolute permeability of the ith microfracture. K is the calculated total fracture permeability of the coal sample.…”