Characteristics and geological properties of seismic bright spots in the Permian carbonate deposit, Changhsing Formation, Longgang Area, Northeast Sichuan Basin, China

Bright spot seismic reflections in carbonate strata are often correlated with effective reservoirs. Widely distributed bright spot reflections have been found in the Permian Changhsing Formation in the Longgang area, Northeast Sichuan Basin, China. However, there is still a lack of systematic understanding of the types, distribution, and geological origin of these bright spot reflections in the Longgang area. Integrated subsurface analysis has revealed that bright sport characteristics represent a combination of strong troughs and peaks, with thicknesses up to 30 ms of two-way time and have a shape like “a string of pearls” in the seismic section. The bright spots located in the platform margin show a NW-trending intermittent strip-like distribution, while in the open platform they are scattered. Bright spots are mainly distributed at the top of the Changhsing Formation and form in the platform margin and open platform environments. The distribution of bright spots has a good coupling with reefs and shoals located in the high paleogeographic regions of the Upper Changhsing Formation. The integrated analysis based on cores, thin sections, and geophysical data reveals that the “pearl-like” bright spots are indicators of needle-like dissolution pores, small karst caves, fracture–vug cystic caves and piebald karst fracture cave systems resulting from eogenetic karstification. Large-scale regression of sea level, which occurred at the end-Permian section, is the main control for reefs and shoals located in the exposed paleohighs suffering from eogenetic karstification. Exploration based on the location of bright spot seismic reflections may be a favorable target for hydrocarbons.