Significance of Rock Mineral Composition On Rock Mechanical Properties And Brittleness Evaluation of Roof And Floor of Broken Soft Coal Seam

Abstract

Fracture of coal structure and low permeability were the main reasons for the “difficult to released gas” in broken soft coal seam. Exploration of horizontal well coalbed gas technology of roof and floor of broken soft coal seam provided a new technical way for coalbed gas development in broken soft coal seam. In this paper, taking Xinxie -1 drilling as an example, the evaluation method of fractured reservoirs in roof and floor of broken soft coal seam was improved. By systematic studied on mineralogy, petrology and engineering mechanics characteristics of top and bottom plates in broken soft coal seam, the influence of rock mineral composition on the rock mechanics properties of the roof and floor of coal seam was explored. In addition, By used correlation analysis and grey relational analysis, a brittle evaluation method of coal seam top and bottom plates based on mineral composition was established. The research results showed that: ①The main components of rock minerals in the top and bottom plates of broken soft coal seam were quartz and clay minerals, followed by plagioclase, siderite and pyrite. The main types of rock cementation were quartz enlargement and siderite cementation, and the pore damage caused by cementation was much greater than that of compaction; ②With the increased of rock particle size, compressive strength (CS) and elastic modulus (E) showed a gradual increase trend, Poisson's ratio (μ) showed a gradual decrease trend, other rock mechanical parameters had no obvious changes. The difference of mineral composition and cementation type was the key factor cause abnormal mechanical properties of rocks; ③Compared with clay minerals, the change of brittle mineral content such as quartz, plagioclase and siderite in rocks were sensitive to the mechanical properties of rocks. The sensitive minerals of compressive strength, shear strength, elastic modulus and softening coefficient were quartz, the sensitive minerals of compressive strength were plagioclase and siderite, and the sensitive minerals of Poisson's ratio are quartz and clay; ④The calculation results of the established mineral weight analysis method were more realistic. It could be concluded that the roof of 13-1 coal, 11-2 coal, 9-2 coal and 4-2 coal seams were more inclined to form fracture network during fracturing, which had guiding significance for the optimization of fracturing horizon.

Recognition Algorithm of AE Signal of Rock Fracture Based on Multiscale 1DCNN-BLSTM

“…With the increase of brittle mineral content in the rock mass, various fracture modes and multiple fracture planes appear, and fracture behavior and acoustic emission phenomena occur in many areas. It can be seen that the brittleness of rock mass has an important infuence on the fracture form of rock mass [4][5][6]. When the content of brittle minerals reaches 50%, the internal cracks of the rock become reticular after fracturing, and the rock has reached the fracturing state [4].…”