| Based on the basic geological data and actual production data,by means of theoretical analysis,experimental test and numerical simulation,the law of coalbed methane production and productivity control factors were studied.The results showed that:The main coal bearing strata in the study area are Permian Shanxi formation and Carboniferous Taiyuan formation,target coal seam 3# coal is located in Shanxi group.Due to the influence of multi period tectonic movement,there are some differences in the degree of structural development in the study area.Structural coal identification based on logging curves,the study area is mainly composed of transitional structural coal,the thickness of tectonic coal shows the characteristics of "thick in the east and thin in the west" in the region.Based on the study of the basic parameters and reservoir forming characteristics of 3# coal reservoir in the study area,we know that,the coalbed methane reservoir in the study area has the characteristics of huge resource potential,complex reservoir forming process,low permeability,low pressure and good preservation condition.According to the productivity characteristics of 185 coalbed methane wells,the relationship between productivity and geological factors is studied,the results show that the CBM production capacity in the study area is constrained by factors such as the pressure ratio,gas content,coal seam depth,geostress,tectonic site and structural complexity of the study area,leading to coal-bed methane production in the region to show the "South high north low" distribution characteristics.The characteristics of coalbed methane production capacity decline show that,the higher the gas content of coalbed methane,the longer the duration of coalbed methane production and the later decline;Generally,when the degree of recovery is greater than 30%,the gas well production capacity begins to decrease,with the increase of the degree of production,the greater the rate of decline,reservoir pressure is an important cause of productivity,According to the simulation results of the propagation distance and velocity of the pressure drop funnel in different time periods in the production process,the coalbed methane production curve is divided into three stages: The first stage of the reservoir energy is high,coalbed methane production power enough,combined with the early mining,high abundance of resources,coal-bed methane output was a rapid rise in the stage;The second stage pressure drop funnel is not obvious,the pressure propagation is slow,the reservoir energy is reduced,the coalbed methane output power is reduced,and the production capacity is rapidly decreasing;The characteristics of the third stage reservoir pressure drop funnel are basically stable.The decrease of the abundance of resources leads to the decrease of the coalbed methane production capacity with the new rate of decline,which is the stage of production capacity reduction.Based on the understanding of the influencing factors of coalbed methane production capacity,the factors were quantitatively analyzed by gray correlation analysis,The effects of gas content,average sand ratio,porosity,total liquid volume,coal thickness,coal seam depth,tectonic curvature and joint density on coalbed methane production capacity were determined.The weighted values of single well productivity of CBM in the study area were calculated by combining the correlation data between the production area data and the gray correlation method.Thus realizing the comprehensive evaluation of the effect of coalbed methane development in the region.The results show that the difference of the development effect of coalbed methane in different areas of Fanzhuang block is obvious,The overall appearance of the "West good East bad,South good north bad" pattern,the development of the optimal area in the south of the block,high-yield wells are distributed here,Single well average daily gas production is mainly between 1000 ~ 6000m~3/d,an average of 2300m~3/d. |
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