Seismic rock physics characteristics of water-rich roof sandstone in the Shendong mining area
Water enrichment in roof sandstones affects the mining safety of coalbeds.In order to improve the interpretation accuracy and reliability,the authors have taken the water-rich roof sandstone of the 1-2 coalbed of Zhiluo Formation in the Shendong mining area as an example and studied its petrophysical characteristics and seismic interpretation methods,incorporating X-ray powder diffraction analysis,wireline-log constrained petrophysical modeling,and cross-plot analysis.The results show that the mineral composition of the sandstone is complex and mainly includes quartz(35.6％),calcite(28.5％),kaolinite(19.1％),albite(11.0％),and illite(5.8％).Following the proposed rock physical modeling strategy,the modeled P-wave velocity and density of water-saturated roof sandstone are consistent with the corresponding measured wireline logs.These consistencies have mutually verified the proposed rock physical modeling strategy and the wireline logging.With the strategy,one can use the modeled petrophysical parameters to analyze the porosity variations and water-saturation states.Generally,both porosity and water-saturation states significantly affect the petrophysical parameters.Seismic velocities,moduli,impedances,and density gradually decrease with increasing porosity,while velocity and modulus ratios show opposite trends.In the low porosity range(＜0.1),seismic velocity,moduli,and impedances vary rapidly with porosity change,while velocity and modulus ratios change slowly.In contrast,the variation trends in the high porosity range(＞0.2)are completely different.The petrophysical parameters under the water-saturated state have higher magnitudes and variation ranges than the dry state.Among all petrophysical parameters,acoustic impedances and velocity ratio are probably the preferred parameters for analyzing roof sandstone.In the P-wave impedance vs.velocity ratio cross-plot,the scattered points of roof sandstone are distributed in radial partitions,and the interpretation template made from the cross-plot can quantitatively and simultaneously interpret the porosity variation and water-saturation states.The research results can provide parameter support and theoretical guidance for analyzing petrophysical characteristics and water-rich interpretation of coalbed roof sandstones.
万方数据
维普
