| Recently, a great exploration breakthrough has been made in shoal porous reservoir of Maokou Formation in
northern Sichuan Basin. Based on the latest drilling and seismic data, the stratigraphy, sedimentology and geochemistry of
Maokou Formation in northern Sichuan Basin has been studied. The results show that：(1) The slope facies is developed in
Maokou Formation of Well JG1, which confirms the differentiation of platform and trough occurring in mid-late stage of
member-2 to late stage of member-3 of Maokou Formation. (2) The middle and upper part of member-2 of Maokou
Formation develops the lower slope subfacies, which is mainly composed of grey-black micrite limestone and silty
limestone, with storm deposits, silicon interlayer and lamellation developed. The storm deposition sequences that can be
recognized mainly include combination of erosion surface and biodetritus bedding, combination of biodetritus bedding and
graded bedding, combination of erosion surface and biodetritus bedding and horizontal bedding, combination of erosion
surface and gravel bedding. The member-2 of Maokou Formation develops upper slope subfacies, which consists of
bioclastic micritic limestone and micrite bioclast limestone reflecting low-energy sedimentary environment, and the
paleontology is a combination of shallow water organisms, with sediment structure of biological burrows and imbricated
bedding developed. (3) The slope facies in the northern Sichuan Basin constitutes a continuous shallow sedimentary
sequence in the vertical direction, and spreads along the Jiange-Langzhong line in a northwest direction. The slope and
platform margin form the progradational sedimentary model of rimmed platform. (4) Organic geochemical analysis shows
that the lower slope subfacies have a high abundance of organic carbon, among which tempestite is the best with TOC up
to 15%, which has high-quality hydrocarbon generation potential. The study clarifies the period and plane position of
platform and trough differentiation, and provids support for expanding the exploration of shoal porous reservoir of
Maokou Formation. The discovery of high-quality hydrocarbon source rock in the lower slope subfacies can contribute to
establish a variety of reservoir formation mode in the Maokou Formation, which is of great significance to evaluate the
resource potential of the Maokou Formation in northern Sichuan Basin. |
