Lower Cretaceous volcanic rocks that contain major natural fractures are the main natural gas reservoirs in the deep Xujiaweizi depression of the northern Songliao Basin in China. Natural fractures are mainly tectonic fractures, in addition to some shrinkage, dissolution, and cryptoexplosive fractures. Analyzing various sources of data revealed that fractures are generally better developed in the rhyolites and trachytes of the crater and near-crater group. Also, tectonic fractures are developed to a higher degree in the hanging wall of faults, with the degree of development decreasing with increasing distance from the fault planes. More than 85% of these fractures are found to be unfilled and, when connected by pores, provide the main effective storage volume for these volcanic reservoirs (up to ∼75%). Natural gas production is closely related to the linear density (P10) of unfilled tectonic fractures and the angle between the orientation of unfilled tectonic fracture and the corresponding direction of the maximum horizontal stress component. The results show that natural gas production is elevated when the average P10 exceeds 2 m−1, and the average included angle is less than 30°. Finally, it was concluded that within the study area, unfilled tectonic fractures of near east-west strikes, which have smaller included angles (<30°) with respect to the maximum horizontal stress direction, are under minimal compressive stresses and make the best fluid-flow pathways in the reservoir.

中文翻译：

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松辽盆地徐家围子凹陷致密气火山岩储层天然裂缝及其对产量的影响

松辽盆地北部徐家围子坳陷深部以含天然裂缝的下白垩统火山岩为主。天然裂缝主要是构造裂缝，此外还有一些收缩、溶蚀和隐爆裂缝。对各种数据来源的分析表明，在陨石坑和陨石坑附近群的流纹岩和粗面岩中，裂缝通常更发育。此外，断层上盘构造裂缝发育程度较高，随着距断层面距离的增加，构造裂缝的发育程度逐渐降低。发现这些裂缝中超过 85% 未被填充，当通过孔隙连接时，为这些火山岩储层提供了主要的有效存储量（高达 75%）。天然气产量与未充填构造裂缝的线密度（P10）以及未充填构造裂缝的取向与最大水平应力分量对应方向的夹角密切相关。结果表明，当平均P10超过2 m-1，平均夹角小于30°时，天然气产量增加。最后得出结论，在研究区内，近东西走向的未充填构造裂缝与最大水平应力方向夹角较小（<30°），受压应力最小，流动性最好。 - 水库中的流动路径。