Favorable reservoir analysis of Emeishan basalt in Zhougongshan area of southwest Sichuan Province

The Zhougong 2 well that drilled Emeishan basalt of Zhougongshan structure in Ya'an area of western Sichuan is a typical well in basalt gas reservoirs, whose core is relatively long, fairly complete and close to the high-yield well Zhougong 1 well. Based on the petrological characteristics, the combination of macroscopic and microscopic phenomena and starting with the core, electrical, physical, and microscopic characteristics of Emeishan basalt reservoir in Zhougong 2 well core, the authors summarized its petrological characteristics, porosity type, fluid features and the distribution in the longitudinal direction in comparison with production intervals of Zhougong 1 well. The results show that the favorable reservoirs of basalt are distributed in two intervals in southwest Sichuan: one is the weathering crust, which is extensively developed at the top with the thickness of a few meters, and the other is the amygdale-rich brecciated basalt in the upper part of the cycle. The second type of reservoir has well-developed asphalt associated with quartz and extensive dissolved pores, caves and cracks, but with less permeability; the majority of its efficiency reservoir space was generated by the secondary actions. The good matching relationship between tectonism in the dormant period of eruption and the weathering and dissolution is of great importance. The open system was generally quite easily formed by the aggregation of later period tectonic cracks and joint fissures perpendicular to the bedding, and this may also be the main factor that has undermined the gas reservoir storage conditions of Zhougong 2 well.