Abstract:

The exploration and development practice has suggested that the volcanic rocks of the Huoshiling formation in the Chaganhua subsag of the Changling fault depression are distinct in rock types and lithologic assemblages from typical volcanoclastic rocks. Core samples and thin sections from the Huoshiling formation volcanic rocks reveal unique structures such as volcanic ash balls and quench-fractured breccia, with generally poor reservoir physical properties. Typical hummocky envelopes of volcanic edifice cannot be identified. All these phenomena indicate a potential unique eruption environment in this area. By analyzing seismic reflection characteristics, core descriptions, thin section features, and laboratory test results, typical indicators of the eruption environments were identified. Combining lithologic assemblages from existing wells and the regional tectonic setting, a volcanic eruption and deposition model for this area was established. The study reveals that the volcanic rocks in this area experienced three periods of eruption in onshore, land-water and underwater environments, respectively. Underwater volcanic rocks exhibit low aspect ratio, and is often in wide and gentle shield shape, with poorly developed primary pores, but developed dissolution and devitrification pores. The overall reservoir space is dominated by medium to small pores. The onshore volcanic rock strata are selected as exploration targets due to developed pores and good rock physical properties.

Key words: Changling fault depression, Chaganhua subsag, Huoshiling formation, volcanic reservoir, lithologic assemblage, eruption environment, identification indicator, reservoir space