Coalbed Methane Occurrence And Target Areas Optimization In Xingjiashe,Gujiao Block

Gujiao Block locates near Taiyuan City,which is the capital city of Shanxi Province.It is abundant in Coalbed Methane(CBM)resources,but remians a relatively low level of exploration and development on CBM.Therefore we selected the CBM from Xingjiashe area in Gujiao Block as the study object of this paper.On the basis of the previous analytical materials of exploration and development on coal seams and CBM,we conducted a comprehensive study on CBM from Xingjiashe area in Gujiao Block,including the geological background of CBM,hydrocarbon and physical properties of coal reservoir and the controlling factors on accumulation and preservation.Finally,by using the analytical hierarchy fuzzy mathematics method,we have optimized target area in Xingjiashe area,which provided important guidance on CBM exploration.Xingjiashe area in Gujiao Block is a Carboniferous-Permian coalbed methane field.The geological tectonic structures are relatively simple,with syncline as the main structure and rare faults.The main coal seams are No.2 coal seam of Shanxi group,and No.8 and No.9 coal seam of Taiyuan group.The coal seam thickness is medium and the continuity is well.The coal seam occurrence condition is good with buried depth all below 1000 m.The water content of coal seams is very low in common,and mudstone water resisting layer is widely developed(No.9 coal seam),showing good hydrogeological conditions.The preservation condition of CBM is medium,and the physical conditions are good,which is favorable for CBM development in Xingjiashe area.We suggest that the burial depth of coal seam has a certain beneficial influence on the increase of gas content.No obvious correlation between gas content and coal thickness is observed.As one of escaping channel for CBM,normal faults have significant negative effect on gas content,which decreases around the normal fault.It is indicated that the volcanic activity has a significant positive effect on CBM gas content and generally controls the distribution pattern of CBM in this area.Based on the analytical hierarchy fuzzy mathematics method,we have established a three-level evaluation model on target area optimization of CBM exploration.Favorable area with high accumulation and production for CBM is the primary evaluation index(U).The secondary indicators are resources conditions,saving conditions,development conditions.The third-level indicators include eight different parameters,such as coal thickness,gas content,coal rank,roof-floor lithology,permeability and so on.According to the result,the I class favorable area of No.2 coalbed methane is near the 2-2 well which is first class area.The I class favorable area of No.8 coalbed methane locates along the well of GJ01 to GJ07 and C26 in the west.The overall situation of No.9 coalbed methane is not very good without I class favorable area and the II class favorable area can be taken into consideration.