Construction of a logging interpretation model for coal structure from multi-coal seams area

The coal structure is the key constraint for the optimization of the main production layer and the optimal combination of the production layer in the exploration and development of multi-coal coal-bed methane ( CBM). It is especially important to accurately identify the coal structure. Most logging interpretation models have been established for the interpretation of a single thick coal seam. There are few studies on multi-coal areas with many coal seams and thin seams. Taking the multi-coal strata in the Yuwang block of Yunnan province as an example,this paper proposes a method for constructing the logging interpretation model of coal structure in multiple coal seams. Firstly,the coal seam structure geological strength index (GSI) was assigned a value. Through the core coring analysis,the coal structure of multi-coal samples is specifically classified,and the geological strength factor GSI is assigned to quantify the core coal structure. Secondly,the Pearson correlation analysis was conducted. Longitudinal and lateral correlation matrix analysis was performed using multiple logging curves to screen the most relevant natural gamma (GR),density (DEN),caliper (CAL) and deep lateral resistivity (RD) curves. Thirdly,Cluster was verified. The K-means clustering method based on nested K-means algorithm is used to verify the coal structure and extract the relevant laws. Finally,the coal struc- ture logging interpretation model was built. After the validity verification is completed,the logging interpretation model is constructed to identify the coal seam structure of the multi-coal,and the coal structure index obtained by the model calculation is used to accurately identify the coal structure. The calculation model is used to identify the vertical and planar coal structure in the middle and northern coal seams of the Yuwang block. In the vertical direction,the coal structure of the multi-coal coal seam is changed from simple to complex,and the class III coal is gradually increasing. On the plane,the coal structures of the seven coal seams in the upper main coal seam are mainly class II coal,and the coal structure near the YW-05 well is better. It is mainly class I coal,followed by the southeast. The coal structure in the northeast is poor,and it is close to class III coal. The 19 coal seams in the lower main coal seam are mainly class II coal,but there is a small amount of class III coal in the southwest. The class I coal is mainly distributed near the YW-05 well,and the rest is mainly class II coal. The recognition result has high accuracy,and the logging curve re- quired by the model is easy to be obtained. The model is simple and easy to be calculated,and can support the actual demand of multi-coal CBM exploration and development.