CBM Enrichment Rules Of Eastern Ordors Basin And Controlling Mechanism

Ordos Basin has abundant CBM,and it is one of the hot CBM exploration and development area,but rare studies have been done on the enrichment rules of the CBM.Based on the analysis of the drilling data,outcrop,well logging,gas,water and core samples,the CBM accumulation rules controlled by sedimentary system,the hydrodynamic characters and its influence on the CBM,the ground stress and its domination on the coal bed permeability,the CBM generation mechanism became more clear.It has been found that the sedimentary system controlled coal accumulation,coal quality,coal top and bottom combined types,and the aquifer develop characters,so the deposit process basically dominates the material base of the CBM generation,accumulation and preservation.The distribution of the aquifer,the coal bed porosity and permeability,the water and gas production and their chemical characters all show that the hydrodynamic conditions of the north area are more active than the south,and vertically,for Shanxi Formation,it is stronger than Taiyuan Formation to the north of Sanjiao area,while in Sanjiao-Jixian area it is opposite.Different hydrodynamic characters affect the coal bed methane accumulation,to the south of Baode area,the weak-stagnant hydrodynamic conditions is favorable for the high rank coalbed methane accumulation;the active hydrodynamic environment and the good sealing conditions are significant of the secondary biogas generation and accumulation for the low-mid rank coal in Baode and the area to the north of Baode.The ground stress calculating model of the Daning-Jixian area was established according to well testing data.The study shows that burial depth of coal layers less than 800m are in the tensional stress field,so the fracture are developed,the permeability of the coal bed normally higher than 0.5×10-3?m2,while the layers that deeper than 1200m are in the compressive stress field,and the permeability is lower than 0.1×10-3?m2,for the layers between 800m and 1200m,the coal bed permeability are within 0.1?0.5×10-3?m2,the coal bed are in the transition zone.The fractured-developed area with high permeability should be focused on for CBM exploration and development.To make clear the CBM generation of the study area,the components and stable isotopes of the wellhead CBM samples of Baode area were analyzed.The results support that the coalbed methane of this area has both the thermal and biogenic generation characters,in the main is thermal genesis,secondary is biogenic origin as supplement in late period,and the biogenic generating process is CO2 reduction.Further more,the geologic conditions also proved that this area is favorable for the biogenetic gas generation.Based on this mechanism,Hequ and Zhungeerqi blocks were judged to be the potential area with biogenic CBM.The CBM resource in place with burial depth less than 1500m is 0.205 TCM within 13.5×10km2 gas bearing area.The evaluation index system was set up based on the preferred 11 geologic parameters and 10 target areas were evaluated,among which,Baode,Sanjiao-Liulin,Daning-Jixian,Hancheng and south Yanchuan blocks were optimized to be type ? which are the best for CBM exploration and development,and north Shilou,Hequ,Zhugeerqi,LinXian-xingxian,and Heyang-Chengcheng blocks are type ? for CBM exploration.