Atomic-Force Microscopy: A New Tool for Gas-Shale Characterization

Abstract

Summary An atomic-force microscope (AFM), a relatively new tool for studying surface characterization, can generate image features down to atomic resolution. Not only can the AFM obtain topographic images of surfaces, but it also can simultaneously identify different materials on a surface at high resolution. Since its invention in the 1980s, AFM has been used in material science and medical research, although it has not received the attention that it probably deserves in reservoir engineering. The emergence of unconventional shale-gas reservoirs, however, has opened new research frontiers for the AFM in the field of reservoir engineering. The unique capabilities of the AFM make it ideal for studying nanopores, organic materials (kerogen), minerals, and diagenetic fractures in shales. It also can be used to measure localized bulk modulus of elasticity on a surface for further implications in geophysical exploration and designing hydraulic fracturing. We introduce different AFM techniques for all these applications, along with example results.

Slip-corrected liquid permeability and its effect on hydraulic fracturing and fluid loss in shale

“…As confirmed by many researchers, pores in shale are mostly in the range of a few to hundreds of nanometers, comparable to 10-100s layers of liquid molecules [5][6][7][8][9]. Therefore, shale matrix intrinsic permeability is in the nanoDarcy (nD) range.…”

“…We present a detailed description of liquid slip flow in a shale matrix. We then present a methodology to measure the liquid slip coefficient for a shale sample using atomic force microscope (AFM) metrology [8]. Note that the concept of liquid slip [10] is similar to gas slip [7,[11][12][13][14], but the measuring methodologies, the values, and implementation in flow equations are different.…”

Characterization and Analysis of Porosity and Pore Structures

“…Atomic force microscopy (AFM) is a relatively new tool being used to characterize pores and pore features in complex rock matrices down to the atomic scale. This method cannot only be used to obtain topographic images of surfaces, but it also can simultaneously identify different materials on surfaces at high resolution (e.g., Javadpour 2009;Javadpour et al 2012). This recent interest in AFM application for rock characterization can be traced to the emergence of unconventional shale-gas reservoirs and the interest Bryan et al 2013, Heavy oil reservoir characterization using low fi eld NMR.…”

Wetting Behavior of Tight Rocks: From Core Scale to Pore Scale

“…To understand how mineralogy affects the wettability at the submicron scale, we compare the adhesion forces (F adh ) measured for different pure minerals with those measured for real heterogeneous rock surfaces by conducting atomic force microscopy (AFM) analysis. AFM analysis is used as an accurate tool at the submicron resolution (i) to visualize the pore structure on tapping mode and (ii) to measure adhesion forces between the tip of the cantilever and a solid surface on the contact mode (Basu & Sharma, 1997, 1999Drummond & Israelachvili, 2004;Javadpour et al, 2012;K. Kumar et al, 2005).…”

“…The value of adhesion or pull-off forces can be related to the surface energy (Butt et al, 2005;Schneider et al, 2003;Tormoen et al, 2004;Van Der Vegte & Hadziioannou, 1997). More details about the adhesion force measurement have been described in the literature (Javadpour et al, 2012;Karoussi et al, 2008;K. Kumar et al, 2005).…”