Low volumes of quartz cement in deeply buried Fulmar Formation sandstones explained by a low effective stress burial history

Oye, Olakunle J.; Aplin, Andrew C.; Orland, Ian J.; Valley, John W.

doi:10.1016/j.geoen.2022.211383

Cited by 1 publication

(1 citation statement)

References 33 publications

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“…Not only are the minerals in a rock complex and variable, , but also the different cementation states may have a significant effect on its various properties. , In view of different diagenetic facies that had different petrology, diagenesis, and physical properties, , these characteristics directly determine the size of rock mechanics parameters (including compressive strength, Poisson’s ratio, and elastic modulus) and the reasonable evaluation of rock brittleness . It is of great significance to the effective prediction of formation fracture pressure and the evaluation of wellbore stability during coalbed methane development.…”

Section: Introductionmentioning

confidence: 99%

Influence of Mineral Composition on Rock Mechanics Properties and Brittleness Evaluation of Surrounding Rocks in Soft Coal Seams

Wu,

Li,

et al. 2023

ACS Omega

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The structural fracture of the coal seam with its low permeability is the dominant reason for the "difficult gas out" of the broken soft coal seam. The brittleness of the roof and floor rock stratum of the broken soft coal seam has a significant effect on the fracture extension pressure of the surrounding rock after casing perforation and hydraulic fracturing of the horizontal well for coalbed methane (CBM). In this paper, 15 rock samples were scientifically collected from the roof and floor of the main mining coal seam of the Early Permian coal-bearing series in the Xinxie-1 well of the Huainan Coalfield in Anhui Province, China. On the basis of mineral composition analysis of these samples, the influence of mineral composition on the mechanics properties of the rock at the roof and floor of the coal seam was investigated. The correlation analysis and gray correlation analysis were adopted to construct an evaluation method for the brittleness of the rock at the roof and floor of the coal seam based on the mineral content. The results indicated that the most significant compositions of the minerals in the rock at the roof and floor of the broken soft coal seam were quartz and clay minerals. The most significant types of rock cementation are quartz agglomeration and rhodochrosite cementation. Pore destruction as a result of cementation was much greater than that of compaction. In comparison to clay minerals, the variation in the content of brittle minerals such as quartz, plagioclase, and siderite in the rock showed more sensitivity to the mechanics properties of the rock. The more sensitive minerals for compressive strength (CS), shear strength (SS), modulus of elasticity (E), softening coefficient (K), and Poisson's ratio (μ) are quartz, those for tensile strength (TS) are plagioclase and siderite, and those for Poisson's ratio are clay minerals. Based on the established mineral content weighting analysis method, it was calculated that the brittleness index (BI) of the rocks at the roof of the 13-1, 11-2, 9-2, and 4-2 coal seams was larger, which was advantageous for the formation of longer fracturing crack networks. This is theoretical guidance for the optimization of horizontal well fracturing design in the deep coal beds of the Huainan Coalfield.

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