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2 Acta Geophysica

2 2023

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Prediction of coalbed methane content based on seismic identification of key geological parameters: a case in a study area, Southern Qinshui Basin

Liu Jing, Chang Suoliang, Zhang Sheng, Li Yanrong, Hao Yaju, He Guoxian, He You, Liu Bo

Acta Geophysica

2023

Vol. 71, no. 6

2645--2662

The coalbed methane content (CMC) is an important parameter to evaluate the degree of coalbed methane enrichment, and also an important reservoir parameter to calculate coalbed methane resources, productivity prediction and reservoir simulation. Accurately identifying the distribution of CMC is crucial to the exploration of CBM. In this study, we developed a prediction method for the CMC distribution via seismic techniques identification of key geological parameters such as structure, coal thickness and sedimentation. Firstly, the geological factors that control the generation and preservation of CBM in the study area are quantitatively characterized by using five parameters: surface (X1), residual (X2), dip (X3), coal thickness (X4) and the ratio of sand to mud (X5). Secondly, the geological parameters are extracted by seismic structure interpretation and inversion prediction technology. Thirdly, the key geological parameters of CMC are screened out by grey correlation analysis. Finally, the functional relationship of CMC and the key geological parameters is established to predict the CMC distribution. The method is applied to the CMC distribution prediction of two coal seams of a study area in the southern Qinshui Basin, China. Results show that different coal seams differ in key geological parameters of CMC, resulting in various CMC distribution laws. The CMC prediction method based on the key geological factors can effectively delineate the CBM enrichment area in the study area, providing important reference for the CBM exploration and development.

Precise time‑depth conversion of coal measure strata based on velocity splicing: a case application in Qinshui basin

Zhang Qifan, Chang Suoliang, Zhang Sheng, Zhao Lipeng, Shi Xiaohong, Guo Chunsheng, Yu Guangming, Liu Jing, Liu Bo

Acta Geophysica

2023

Vol. 71, no. 4

1729--1746

Transforming seismic data from the time domain to the depth domain is a very important step when using 3D seismic exploration to guide the exploration and development of coalbed methane (CBM). However, the conventional time-depth conversion method has difficulty meeting the control accuracy requirements of CBM development based on horizontal well technology when the 3D seismic data in a mining area are old. Therefore, a precise time-depth conversion method was found to improving the accuracy of time-depth conversion, which is based on the splicing of seismic inversion velocity and poststack migration velocity. The first step of this method is obtaining the standard layers in the time domain by precise interpretation of seismic data. Then, the inversion velocity and poststack migration velocity are spliced to obtain the complete interval velocity volume of the study area, and the results are corrected. The next step is the prediction of the coal seam floor elevation based on the spliced velocity, and the predicted coal seam floor elevation is corrected by borehole data. Finally, the mesh is between standard layers in the depth domain to obtain the 3D data volume in the depth domain. The method was applied to the time-depth conversion of 3D seismic data in the Yangquan X study area. The results show that the relative error between the predicted results and the borehole data of No. 3, No. 8 and No. 15 coal seam is only 0.72% through the validation of the reserved boreholes, indicating that the method is effective. This study provides a precise method of time-depth conversion for seismic data when there is only poststack seismic data in the mining area, which can not only improve the interpretation accuracy of standard layers but can also improve the prediction accuracy of other layers between standard layers, which can better guide the well location arrangement of coalfield and CBM.