| In order to study the geological controlling factors of CBM reservoir productivity of Taiyuan group in sourthern area,Qinshui Basin,this Paper using the theory of CBM geology and hydrogeology.,Based on lots of long-term produced water test data about chemical feature from CBM Wells,Rock properties analysis of limestone on The upper coal seam,drainage gas recovery data and the results of analysis of coal reservoir.Research in geological controlling factors of CBM reservoir productivity of Taiyuan group in sourthern area,Qinshui Basin by adopting the method of statistics,comparison,test and simulation.The following cognitions and conclusions were obtained:Coal seam 15 thickness Vary from one meter to six meters,Generally between two meters and four meters.Buried deep in general between 400-100 m,The gas content of coal in 10?20 m3/t,the porosity ranges from 0.38%to 9.98%,The average is 5.17%,in commonly permeability ranges from0.02x 10-3?m2 to 0.08x10-3?m2,the average is 0.044x10-3?m2,reservoir pressure is relatively low.Nuclear magnetic porosity of roof limestone ranges from 0.3678%to 2.18%,but the porosity of coal is higher.Unlike coal,T2 spectrum of Limestone has a very good continuity,connectivity of pore structure is better,but there is no obvious dividing line between bore adsorption and filtration.The beginning of drainage gas recovery,the type of water produced from CBM wells of coal seam 15 is Na-Mg-Cl,after turn into Na-HCO3-Cl,have a high salinity.Ph value decreased in the rainy season.Isotope of 8D ranges from-82 ‰ to 84.8 ‰,the scope of the isotopic hydrogen and oxygen isotopic composition within the limits of the atmospheric precipitation,so affection is serious by atmospheric precipitation.In the process of drainage gas recovery,coal seam 15 and aquifer have a good connection,accepting the aquifer recharge.Those actual drainage gas recovery data show that gas production rate is very low or no gas.When the coal seam near the fault,gas content of coal seam is very low and rock burst is serious,as the same time,the powerful ability of formation providing liquid lead to high water rate and low gas production rate.The difference between coal seam 15 and in-situ stress,rock mechanics properties of the roof rock affect the characteristics of the fracturing fractures and permeability,further affect gas production,The study found that the in-situ stress and permeability have a negative exponent relationship,The azimuth of crack by fracturing with hydraulic power Consistent with the principal compressive stress.The length of crack is proportional to the elastic modulus of coal and inversely proportional to the poisson's ratio of coal,but it shows a negative logarithmic relationship with the ratio of the lastic modulus between the roof of coal and the coal.The height of crack by fracturing with hydraulic power is inversely proportional to the ratio of the lastic modulus between the roof of coal and the coal.Using calculation module of Zone Budget in the software of Visual Modflow,predicting that the normal tonnage are 83 m3/h with 8 drain Wells in an area of 2.328 km2 on the roof of coal,The the normal tonnage in natural state is not strong.Coal seam 15 and aquifer hydraulic have little connection in the original formation condition based on the above analysis,but the coal seam and aquifer communicate with eath other by engineer operation,The output water from coal seam 15 reservoir of Taiyuan group in sourthern area,Qinshui Basin accept extraneous supply,so that effect production capacity of coalbed methane well.we are numerically simulated respectively,joining the aquifer in the upper coal seam and without aquifer,The coalbed gas well has a good productivity without aquifer,while it is bad with aquifer,That means the key geological factor is groundwater dynamic condition. |
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