Similar Material Proportioning and Preparation of Ductile Surrounding Rocks for Simulating In Situ Coalbed methane Production from Tectonically Deformed Coals

The permeability and mechanical characteristics of ductile rocks surrounding coals were determined using samples from the roofs and floors of the #5 and #10 coalbeds in the Yangliu coal mine. This mine is in the Huaibei mining district, which is a typical tectonically deformed coal development area in China. The orthogonal test scheme involved five factors and four levels, and it was designed to measure the permeability and mechanical characteristics of similar materials by comprehensively considering the proportions and formation conditions. The effects of sand-binder ratio, gypsum-talc powder ratio, water-solid proportion, moulding pressure and moulding time on compressive strength, elastic modulus and permeability of similar materials were studied by comprehensive equilibrium method. The results show that the compressive strength and elastic modulus of similar materials were negatively correlated with the sand-binder ratio, but positively correlated with the gypsum-talc powder ratio, water-solid proportion and moulding pressure. Permeability was positively correlated with the sand-binder ratio, negatively correlated with moulding pressure, and has no significant relationship with gypsum-talc powder ratio and water-solid proportion. The moulding time has the least effect on the permeability and mechanical properties of similar materials. The optimal ratios determined are as follows: an aggregate to cement mass ratio of 1:1, a gypsum to talc powder mass ratio of 1:1, and a deionised water to total solid material ratio of 25%. In the preparation of similar materials, the optimal moulding pressure is 16.26 MPa, while the optimal moulding time is 6 h. This study provides the optimization of raw materials, the proportioning plan and the preparation method of roof and floor similar materials for large-scale indoor simulation experiments, and promotes the development of coalbed methane in tectonically deformed coal areas.

Automated summary

The permeability and mechanical characteristics of ductile rocks surrounding coals were studied, and the optimal ratios and preparation conditions of similar materials were determined. These findings provide a foundation for large-scale simulation experiments and promote the development of coalbed methane.