Evaluation Of Coalbed Methane Favorable Target Area In Dacheng Based On A Joint Inversion Of Seismic And Well Log

Dacheng coalfield is located in Langfang,Hebei province,where is east to Tianjin,southeast to Cangzhou,west Baoding.The detailed work collected geology,seismic,logging data and other related information of dacheng area and analysis the main controlling factors of the coal-bed gas reservoirs.Using of wave impedance well-seismic joint inversion method,it can carry out the quantitative forecast to 5 and 10 coal seam thickness,coal seam roof and floor lithology,porosity and permeability of coal seam,coal quality,and coal pore water.Finally,the work evaluated the favorable target area and made concludes,that were the following results and understanding:Through analysis of geological factors of Dacheng region:(1)the basic geological conditions of coalbed methane exploration and development in the study area:good material base of the coalbed methane in the development of coal seam.The coal and rock maceral was high.High content of lens of mass points itself can generate large amounts of gas,at the same time,develop cracks and pores.Is was advantageous to the gas adsorption,and benefited to the enrichment of coalbed methane.The coal phase of Dacheng area is mainly the forest peat bog development zone.The large coal seam thickness and the stable distribution were advantageous zone of the coal bed methane production.(2)in general,coal reservoir macroscopic fracture and microscopic pore characteristics development regularity were not strong in Dacheng area.The overall trend was that the cleat of 5 coal group and fracture pore were developed,at the same time,the 10 coal group had undeveloped cleat,filling serious,but the matrix pore development,and poor pore connectivity.The low permeability of coal reservoir in this area,which was typical of low permeability reservoir,would be difficult to develop.(3)the better preservation conditions of the coal seam gas reservoirs:The top floor of the coal seam was mostly of mud or carbon mud rock.The breakthrough pressure was high,and had the good sealing ability.Vertically it was divided into three sets of independent hydrodynamic system.Among them,the environment of carboniferous-Permian strata was weak alternating hydrogeological.Formation water was given priority to with pore water which seepage from the high place to the lower part(from east to west).The confined water was favor to the preservation of coalbed methane.The coal-bed gas reservoirs of Dacheng area was basic finalized in the late tertiary.However,in the process of structural movement,faulting development was adverse to the coalbed methane preservation,at the result of the loss of coalbed methane.By comprehensive utilization of coal seismic exploration data,drilling data,and geophysical well logging data,th seismic and logging data joint inversion basic realized quantitative prediction of the coal thickness,coal seam roof and floor lithology,porosity and permeability of coal seam,coal quality and coal pore aquosity.Based on the inversion results,the total amount of the coal bed methane resources was 302.6 x 108m~3.Calculated by 50%,the methane gas was 151.3 by 108m~3.Finally,through quantitative evaluation,three coal-bed methane exploration areas in the northwest,central and southeast regions were selected.Among them,the northwest block,especially edge,was the most favorable exploration target area,which manifested high evolution degree of coal and rock,coal thickness,good preservation condition,shallow depth,and higher coalbed methane content.