Characteristics And Desorption Difference Of High Rank Coal Reservoirs In The South Of Qinshui Basin

It is of great significance to study the characteristics and desorption difference of high rank coal reservoirs in the south of Qinshui Basin for the scientific and efficient development of coalbed methane.Based on the data arrangement and analysis,geological investigation,experimental simulation and data test of Fanzhuang,Zhengzhuang,Changzhi and Anze blocks in the south of Qinshui Basin,this paper studies the development characteristics of the difference of the critical desorption pressure of the high-order coal reservoirs in different blocks,clarifies the main reasons for the development of the difference of the critical desorption pressure in different blocks,and discusses the geological and engineering control factors.It provides theoretical support for the formulation of efficient development policies and the selection of technological parameters for reservoir reconstruction in different blocks.The results show that the natural water loss rate of the fresh coal sample is relatively low in the study area.Under the saturated humidity,the coal sample can fully absorb the water in the pores,and the occurrence phase of the coal seam water is mainly free water.The moisture test of dry samples shows that some of the water in coal pores is difficult to be discharged.Under the same particle size and different humidity,the higher the humidity,the easier the coal powder is to absorb water.The ability of coal powder with different particle size to absorb water is related to its particle size and the air humidity.The contact angle of coal and rock in the study area is mostly less than 90 degrees,which has strong hydrophilicity for formation water and is favorable for capillary water absorption of coal.The high rank coal reservoir has strong hydrophilicity,and the water in the pores is difficult to release in the natural state,which affects the drainage and pressure reduction of coalbed methane.After water injection of high rank coal in different areas and different properties,the initial desorption rate slows down,but the influence degree of coal rocks in different areas and different properties is quite different.The water content of coal seam restrains the desorption rate of methane at the initial stage,but with the continuous desorption of methane,the adsorbed methane can be desorbed after the water in coal and rock fractures is gradually discharged,and the desorption amount will not be reduced.The theoretical critical desorption pressure of most wells in Fanzhuang block is higher than the measured value by more than 1MPa,but some wells are close to the two values or the former is low;the theoretical critical desorption pressure of Zhengzhuang block is generally higher than the measured value by about 2MPa;the theoretical and measured desorption pressure of Qinnan East block is basically the same;the measured critical desorption pressure of Anze block is higher than the theoretical value.The main control factor of the difference between the measured critical desorption pressure and the theoretical critical desorption pressure is the coal structure,which determines the three types of desorption differences.There are 47 figures,21 tables and 81 references in this paper.