Investigating the Meso‐Mechanical Anisotropy and Fracture Surface Roughness of Continental Shale

Abstract

Continental shale is abundant with unconventional oil and gas and has considerable prospect for exploitation. However, due to deposited environment differences, continental shale presents unique characteristics in terms of structure and mineralogy compared to marine shale. The mechanical property is elemental parameter for reservoir production, but relevant studies of continental shale are rarely reported. In this study, several groups of mesoscale (0.1–10 mm) uniaxial compression tests were conducted on continental shale with various bedding angles, sourced from the Yanchang Formation in the southern Ordos Basin, China. A new integrated real‐time loading‐observation‐acquisition system, specifically, a miniature tensile instrument‐light microscope (MTI‐LM) system, was utilized, which allowed us to visualize the failure process and simultaneously record the stress‐strain curves, providing snapshots for investigation of fracture initiation, propagation, and fracture surface features. The results demonstrate that as the bedding angle relative to the maximum compression direction increases, the uniaxial compressive strength (σc) and the percentage of bedding‐parallel fractures (Fp) fluctuate reversely, namely, higher σc corresponds to lower Fp. Additionally, a good consistency is revealed among the variations of σc, failure time and fracture surface roughness with bedding angles, suggesting stronger shale having rougher fracture surfaces and longer failure time at a certain loading rate. The meso‐mechanical anisotropy of shales is supposed to have an origin in heterogeneous component and microtexture, as indicated by different bridges connecting the opposite facies of fractures. The findings help reveal the mechanism underlying mechanical anisotropy and facilitate fracability evaluation of shallow shale gas reservoir.

Rough Surface Effect on CO2 Displacement at the Nanoscale

“…In shale nanopores, rough surface morphology is typically similar to the random wave simulated in this study. The sharpness of the transition between concave and convex of the rough surface is influenced by the lithofacies of shale . For instance, siliceous shale (containing a large amount of quartz) often has a much sharper surface than calcareous shale (containing a large amount of carbonates).…”

Anisotropic Characterization of Mechanical Behavior and Fracture Morphology in Marine and Continental Shales under Uniaxial Compression: A Comparative Analysis

“…(2) Acoustic emission method , uncovers the development of cracks within the shale, with the bedding plane affecting not only the fracturing mechanism but also the energy release rate of fractures. (3) Real-time visualization both in two and three dimensions: Huang et al used a two-dimensional optical microscope for real-time observations, finding strong anisotropy in crack initiation, propagation, and failure modes. The uniaxial compressive strength and the degree of stratified excavation display opposing trends with increasing bedding angles.…”

“…Additionally, some researchers have examined the effect of varying temperatures on shale anisotropy. However, it should be noted that, with the exception of Huang et al, which explicitly mentioned the use of CS, most studies did not specify the sedimentary facies of shale under investigation. Upon further examination, the names and sedimentary phases of the shale in these studies are listed in Table S1 in the Supporting Information.…”

Comparative Study of Marine and Lacustrine Shale Reservoirs from the Viewpoint of Rock Mechanics

“…Moreover, most of the previous research mainly focused on the mineral composition, pore structure, sedimentary environment, and geochemical feature. Our knowledge about the mechanical properties of lacustrine shale is still very lacking. , …”

“…Our knowledge about the mechanical properties of lacustrine shale is still very lacking. 3,20 Based on the successful experience of marine shale gas development, is it feasible to simply copy it to lacustrine shale? If not, what is the correct way?…”