Distribution pattern and exploration prospect of Longwangmiao Fm reservoirs in the Leshan-Longnüsi Paleouplift, Sichuan Basin

The Longwangmiao Fm gas pool was found in 2012 in Moxi area in Leshan-Longnüsi Paleouplift, central Sichuan Basin. Previous geological studies showed that the Lower Cambrian Longwangmiao Fm reservoir is mainly pore type reservoir of grain shoal facies, locally superimposed by the vuggy reservoir formed by Caledonian karstification, and the distribution of the reservoir has a critical control effect on the gas pool there. Therefore, the reservoir prediction in this area follows the approach of “looking for the overlap of shoal facies, karst, bright spots, and traps”. First, the favorable facies boundary and karstification effect range are defined based on sedimentary facies; on the basis of precise correlation of the top and bottom horizons of the reservoir, the favorable development area of the reservoir was then predicted according to the seismic response characteristics of “bright spots” of the Longwangmiao Fm reservoir; finally, favorable exploration areas were selected according to the effective configuration of reservoir and trap. Due to the horizontal change in reservoir and lithology, Longwangmiao Fm top has no uniform interface features on the seismic profile, making it difficult to trace. In the actual interpretation process, the underlying reference horizon is sought out first, then the bottom boundary of Longwangmiao Fm is correlated, and finally its top boundary is correlated. The prediction results indicated that the Longwangmiao reservoir distributes in band shape in a wide range around the Paleouplift; and the exploration prospects mainly involve three domains: lithologic-stratigraphic traps near the pinchout line of Longwangmiao Fm; lithologic traps formed by isolated shoal body; and structural and lithologic traps at the north flank of the Paleouplift.