Comprehensive Logging Evaluation Of Coalbed Methane Reservoirs In Shenfu Block

In this article,we choose Shenfu block as the research target,which is a typical mediumrank coal block.Combining the geological environment and geophysical logging response,a comprehensive evaluation method,including logging evaluation of industrial components,coal rank,physical properties,gas content,water content and coal texture,as well as researches on controlling factors of favorable CBM seams is established based on conventional logging,NMR logging,array acoustic logging,FMI logging and core test data.Statistical models are established to evaluate the coal quality in this area by analyzing the correlation between industrial components and logging response.Combining with geological environment of this block,No.8+9 coal seams are better than No.4+5 coal seams.Theory of logging response in different coal ranks is analyzed in detail,especially the response of neutron porosity(CNL)logging and photoelectric absorption cross section index(Pe)logging.Based on the in-situ situation of this block,a CNL-Pe cross plot is made to identify the coal rank.Results of three CBM wells show the effectiveness of this approach.And the standard chart for identifying different ranks of coal is established based on the logging response theory.Physical properties of coal are difficult to evaluate precisely because of the dual-pore texture,including matrix pores and fracture pores.In this article,matrix porosity is evaluated based on coal core analysis.Fracture porosity is evaluated based on dual-lateral logging data.And permeability is evaluated by conventional logging,NMR logging and array acoustic logging.In light of the accumulation mechanisms,coalbed gas in this area is mainly adsorbed gas,and free gas in some CBM wells.Gas content is evaluated by statistical model or Langmuir equations.Gas content of free gas is evaluated by difference method,porosity model,or array acoustic logging method.After analyzing the necessity and feasibility of evaluating water-bearing properties,we establish an index IWB based on Archie equations to evaluate water-bearing property.And a case study based on water production data of some producing block show the effectiveness of this index.By analyzing the response of coal texture in logging curves,another index ICT is established based on borehole diameter curve(CAL)to evaluate coal texture.The comparison between coal core analysis results and the evaluation results show the capability of this index.In the part of predicting gas production capability,first we analyze the effect of different factors on it.And combining research experience,five controlling factors of favorable coal seams are extracted in this block,including effective thickness,gas-bearing property,waterbearing property,coal texture and coal texture.After applying evaluation methods into wells in this area,the response of these controlling factors is used to evaluate the properties of different coal seams and predict favorable seams of different wells.