Geologic Modeling Technology And Application In Coalbed Methane

Coalbed methane is a kind of unconventional gas with self-generation and self-preservation in coal and is absorbed by coal.Compared with conventional gas,there are many differences in geological genesis and reservoir characteristics.Due to so many specialties,it is important to build precise geological model showing the geologic and development characteristics of the coal,and this kind of model has great significance to predict the advantageous coal reservoir,decide reasonable well-types and optimize well pattern arrangement.According to the features of medium-rank coalbed methane with numerous stone bands,isochronous stratigraphy framework for coal was built and the vertical and horizontal characteristics of coal were analyzed.Combined with the outcrop geographic information,structure interpretation was done.The controlled points were added in the areas where there have no wells and seismic,thus the structure map can be more consistent to the actual geological condition and the structure interpretation technology for coal was summarized based on wells,seismic and outcrop geographic information.By using of the cross plot between core analysis density and ash content,cut-off value of 2.0 g/cm3 for coal was obtained,combined with the method of "half amplitude point" of density log,coal can be interpreted accurately,and the burial depth and thickness can be gotten,the coal quality can be evaluated and the interburden can be determined.As for the characteristic for medium-rank coal in which cleat develops very much,the cleat distribution and orientation were studied,through history matching,cleat permeability can be gotten which can reflect the production characteristics of coalbed methane.Based on the production data which were matched very well,the relationship between cleat permeability and burial depth can be built,and the combination between static data and dynamic data are realized for reservoir characterization.In studying area,coal has a high ash content which has a big influence on the gas content,after analyzing the fault,mines,burial depth and lithology which can affect the gas content,the workflow of quality control for gas content was formed.Through the calibration of core and log,a series of relationship can be gained among density,ash content,burial depth and gas content,of course the gas content in situation can be obtained,the malpractice for calculating resource was overcome which used the dry ash free gas content or air dry gas content before,it is a great progress.By use of the technology of three dimension geologic modeling,integrating the results of stratigraphy correlation,structure interpretation,log interpretation,cleat permeability and gas content into the geologic model,coal seam distribution was simulated in three dimension space by means of Sequential Indicator Simulation method after fine structure model was built;the density model controlled by coal facies was simulated by use of Sequential Gaussian Simulation method;the distribution rules of gas content was gotten based on the nonlinear relationship between burial depth and gas content;cleat permeability model was built in view of the relationship between burial depth and cleat permeability from good fitting data;fine model in medium-rank coalbed methane was built which can reflect reservoir characteristics in detail.Based on the geology model,gas initially in place(GIIP)was calculated,and the uncertainty for the sensitive parameters was analyzed,it shows that coal facies has big influence on GIIP,the range of GIIP in different scale can be gotten to reduce the risk.In three dimension geologic model,according to the following conditions:permeability is more than 0.08 mD,burial depth is in 100-650 m and ash content is lower than 55%,integrated these three conditions,the accumulative net coal thickness of F coal measure can be calculated,thickness of 20 m is chosen to draw the favorable area,and four advantageous zones were drawn.The four successful fractured wells are in these zones.In the application of medium-rank coalbed methane in F coal measure in B area of A country,many problems are solved compared with previous study,such as large thickness for modeling unit,net coal thickness and gas content with given constant values in one region,no geological model reflecting permeability changes,etc.Three dimension geologic modeling technology is summarized to study medium-rank coalbed methane integrated multi-information.