Research On Changing Law Of Petrophysical Parameters Of Coal Reservoir In Drainage Process About Cbm Vertical Wells

It was an an important security to find out the dynamic change law of CMB well permeability in the production process for accurately predicting the gas-water production and making reasonable production system. There would be different sensitivity of reservoir permeability response in drainage, that was determined by the coal reservoir pore and fracture structure, physical characteristics, water-gas bearing characteristics, and the stress characteristics. Thus, it was decided that there was an one-sided and guiding production limitations of working in certain different parts of the scene in the experimental study on permeability variation in a particular area. To build a universal mathematical model of permeability change was important research tool to address the changes of dynamics of permeability under reservoir conditions.This paper classified the production phase based on the difference of the phase after the analysis of the coal pore fissure structure and the storage and output of the gas and water. According to the elastic plasticity, damage mechanics and the energy theory, the mathematical model of effective stress, elastic modulus, and coal matrix desorption shrinkage were set up, and their correctness were verified by the experimentl results. Combining the exploration data of Fanzhuang, the changes of the stress, elastic modulus and coal body shrinkage were calculated, and the results show that there was an increase of effective stress and matrix deformation in the entire production process with the decrease of reservoir pressure, and the range of the increase was bigger in gas-water two phase flow than the range in single-phase flow stage.Plenarily considering the negative effect from the effective stress, and the positive effect from the gas desorption on the changes of permeability in drainage, and according to Gibbs formula, Burke Heim theory, and the Kozeny-Carman equation, the permeability mathematical model of coalbed methane wells in different production stages was made, and it was validated by permeability experiment. According to the basic data, the difference of permeability changes in different stages was analysised and calculated. The results show that there was the decreases of permeability with the development of production and increase of effective stress in the single water phase, and the permeability decreases was reduced and may turn to be rebounded under the interaction of effective stress and the gas desorption with the desorption of gas in gas-water two phase flow. The main control factors of permeability variation in drainage were analysed, and the results of that the larger elastic modulus, the more increases of the permeability recovery were got. Through the study of changes of permeability in different production process the formulation of drainage system would be provided by reasonable theoretical basis.