Coal Reservoir Modeling And Prediction Of Favorable Development Blocks In Zhengzhuang Block

The Permian Shanxi formation No.3 coal seam in the Zhengzhuang field,southern Qinshui basin,is a key target production seam for coalbed methane(CBM).Based on multi-attributes seismic interpretation 3D geological modeling techniques,this thesis investigated the characteristics of subtle structures of No.3 coal seam,forecasted the distributions of several key CBM reservoir physical properties,and finally optimized the most favorable target area for further CBM development in the Zhengzhuang field.The following achievements were obtained.Multi-attributes seismic interpretation technique was used to interpret the tectonic structure of the top and bottom surfaces of the No.3 coal seam.The structure-oriented filtering technique and key seismic attributes(variance,curvature,chaos,ant-tracking)extract technique were used to improve the accuracy of structure interpretation and the positioning of the structural top and bottom of the No.3 coal seam.With the help of these comprehensive interpretation technologies,totally 493 faults and 21 collapse columns were identified in No.3 coal seam of the Zhengzhuang field.Several key structural curvature properties were used to predict the distribution of coal texture of the No.3 coal seam.The curvature of the top surface of No.3 coal seam was calculated and used for characterization of the subtle structures.It was found that there is a correlation between the curvature properties and the content of deformed coal in No.3 coal seam.Among the curvature properties,the Gaussian curvature and shape index were chosen to fit with the data of coal texture,and as a result,a model was founded to predict the thickness of undeformed,cataclastic,and granulated coals.The results indicate that the cataclastic coal is widely distributed throughout the whole field and has a maximum in the middle of the field.Meanwhile the undeformed and granulated coals are mainly distributed in the southwest,and the north of the study area,respectively.The 3D geological modeling of the No.3 CBM reservoir was performed using the commercial Petrel software.In the 3D geological model,the buried depth and the thickness of No.3 coal seam were firstly evaluated.After that,lithofacies modeling and petrophysical modeling were done by gridding the founded structure model.Then the distribution of coal gangue were evaluated using sequential indicator simulation method,and the distributions of porosity,permeability and gas content was predicated using lithofacies modeling and Gaussian random function simulation.The results show that the distribution of porosity and gas content were controlled by the coal gangues.The porosity of No.3 coal seam is of 0.64%-12.82%,with average of 4.52%.The gas content ranges from 11.3-30.8m~3/t,averaging 23.1m~3/t.The permeability ranges from 0.05 md to 0.39 md,averaging 0.14 md.The permeability model shows that the buried depth and deformed coal content have an effect on permeability.The distribution of the CBM production favorable area in the Zhengzhuang field was evaluated by considering seven key geological factors.Firstly,the correlation degrees between gas production rate and the seven factors were calculated by way of gray relational grading.Then the evaluation parameter(E)was calculated,and used to classify the CBM reservoir.Finally,the Zhengzhuang field was divided into four types of CBM reservoir: the favorable zones(0.75?E<1),sub-favorable zones(0.5?E<0.75),unfavorable zones(0.25?E<0.5)and most unfavorable zones(0?E<0.25).