Study On Dynamic Variation Character Of Coal Reservior Characteristic Under The Condition Of Multi-well Development

There are so many factors influencing the large-scale development of coalbed methane,of which the key factors include reservoir pressure,saturation as well as permeability.In this paper,the dynamic characteristics of coal reservoir parameters under the condition of large-scale development are studied with Hancheng mining area as the research object.The paper starts with the pressure drop characteristics of a single well to get an idea of factors that can affect the pressure propagation,and further experiments the pressure drop under various well spacing conditions from knowning of the impact of interwell interference on reservoir pressure drop and gets an ultimate optimization of 350m-spacing triangular well pattern.Based on the performance data of 35 wells,a gas-water differentiation theory was put forward taking into consideration different structures wells of WL1 well group locate in,and the numerical model established by commercial software CMG to do the verification indicates that natural gas after desorption will migrates to the higher part of structure to cause a gas saturation growth and hence results in an uneven gas-water saturation in different structural locations.This paper concludes that buoyancy explains much of gas saturation difference,an crutial part of gas-water differentiation theory,and brings the original mathematical model of coalbed methane seepage an improvement.Based on the control mechanism of permeability variation,considering the effects of effective stress,matrix shrinkage and Klingenberg effect on permeability,a piecewise mathematical model conforming to unsaturated coalbed gas reservoirs permeability characteristics in China was established.A simulation based on performance data of 7wells and related resevoir parameters along with a sensitivity analysis suggests that effective stress and matrix shrinkage are the most important two factors that cause permeability change,and influence of the Klingenberg effect is limited in the period of lower-pressure extraction,study also show that the dynamic characteristic of permeability are influenced by the combination of mechanical parameters of coal,Langmuir volume strain,critical desorption pressure and Langmuir pressure constant of coal rock,and most strongly influenced by the mechanical parameters of rock and Langmuir volume strain.