Abstract:
During the process of formation evolution, different types of energy are accumulated in different phase substances of coal reservoir. To clarify the changes in the state of different phases of substances with energy changes and its impact on the development of coalbed methane. Firstly, the elastic deformation potential energy density formula and the equivalent spring model were used to calculate the elastic potential energy of the coal matrix and the maximum reduction of the crack opening. Then, the Langmuir isothermal equation and ideal gas isothermal expansion work formula were used to calculate the expansion energy of absorbed coal bed methane under isothermal condition. Later, the Navier Stokes equation was used to analyze coal bed water pressure energy, gravitational potential energy and kinetic energy. Finally, to analyze the main factors affecting coal permeability, the permeability test with helium, methane and deionized water was carried out. The energy conversion and matter state changes of every phase substances in the whole process of coal bed methane development were comprehensively analyzed. Four adjacent CBM well groups with similar geological conditions but different energy characteristics in Zhengzhuang block were selected, combining the respective output characteristics and the energy characteristics of local coal reservoir, the impact of coal reservoir energy on coal bed methane development was discussed in details. The results show that after the energy balance of the system is broken, the coal rock releases elastic potential energy through expansion, which causes the crack opening to decrease. Adsorbed coal bed methane is power source of coal bed methane production, which releases expansion energy through desorption and expansion, while continuing to invade the flow space of coal bed water. The reduction of crack opening will hinder the connection between coal bed water pressure energy and the expansion energy of adsorbed coal bed methane, so that the latter will no longer change with the change of the former. The studies indicate that the greater the coal bed water pressure energy of the coal bed, the stronger the water production potential of the coal reservoir. The greater the expansion energy of adsorbed coal bed methane, the more beneficial the coal bed methane production. The smaller the elastic potential energy and the maximum reduction of the crack opening of the coal matrix, the more conducive to the development of coal bed methane. The influence of coal matrix deformation on fluid productive is not obvious, but the mode of fluid migration and mass transfer efficiency is. There are differences in the energy carried by coal reservoir in a small area, and these differences have a significant impact on the production of CBM wells. Coal reservoir energy is the key to the evaluation of coal bed methane development.