Coalbed Methane System And Superposition Of Laochang Block In Eastern Yunnan,China

There are many coal seams in the Upper Permian Longtan Formation of Laochang block.Therefore,Superposed CBM system may be developed.In view of the characteristics of coalbed methane reservoir formation,it is necessary to develop targeted development technology and technical programs.For this reason,the paper,fully extracting geological information of coalbed methane from coalfield exploration data,combining with the experimental results of CBM exploration & development and the experimental data of samples,studies the superposed CBM system in Laochang block and achieves a series of research knowledge.Based on sedimentological and logging response markers,the Longtan Formation is divided into four third-order sequences(SQ1~SQ4).Among them,SQ1 is basically absent in the study area.Taking typical boreholes as objects,the superposed characteristics of coal-bed methane system in Longtan Formation are analyzed from three aspects of apparent reservoir pressure,coal-bed gas content and porosity & permeability distribution.It is found that the vertical distribution of CBM system corresponds well with the sequence stratigraphic framework.This paper establishes a comprehensive evaluation method system for the sealing property of key strata and judges the sealing of faults and key strata combining the geological basis of modern tectonic stress field and superposed characteristics of coalbed methane system.According to the logging identification results,two key formation groups are identified in Longtan Formation.On this basis,the Longtan Formation is divided into three CBM systems,considering the vertical variation rule of coalbed methane content and pressure coefficient,and their lateral variation rule and geological influencing factors are revealed.The superposed index "F" is established to evaluate the overlapping degree of CBM system in this paper.It is suggested that "F=0.5" can be used as a basis for judging whether the upper and lower adjacent CBM systems are independent.The results show that dividing line is the north-west boundary of the fourth survey area in Laochang block.Near the Southeast direction,the three CBM systems of Longtan Formation are independent for each other.But their,near the northwest direction,are closely related to each other and belong to the same gas-bearing system.