Reservoir characteristics and main controlling factors of the Longwangmiao Formation in the Moxi area, central Sichuan Basin, China

摘要

Longwangmiao Formation in the Lower Cambrian is one of the key petroleum systems in Sichuan Basin. Especially with the great breakthrough of the Longwangmiao Formation in the central Sichuan Basin, it shows a giant exploration potential. Using various data and approaches including core and petrographical analysis, petrophysical properties, SEM, and cathodoluminescence emission, the reservoir characteristics and the main controlling factors of the Longwangmiao Formation (in the Moxi area) are evaluated. This study shows that the reservoir of the Longwangmiao Formation developed very well. It is mainly composed of dolarenite and fine crystalline dolostone. The most dominant pore types are dissolved enlarged intergranular and intercrystalline pores or vugs. The reservoir properties of the Longwangmiao Formation were varying respectively, from 0.5 to 12 % and 0.001 to 1000 mD. The main reservoir controlling factors are deposition, diagenesis, and tectonism. Deposition laid a foundation to reservoir development, especially the intraplatform shoals deposited in an environment with relatively high energy and platform flat located in the highland with low energy. In the early Cambrian Longwangmiao period, two episodes of transgression and regression process had occurred, and reservoir intervals are developed in the end of each episode. Meanwhile, diagenetic alterations are keys to reservoir evolution; three kinds of dissolution played an effective role in the generation and development of the pore system. Compaction and cementation caused many damages to the reservoir porosity. Fractures caused by structural breakages can improve the reservoir permeability and provide fluid migration pathways to the late dissolution, which formed solution-enlarged fractures as reservoir and percolation spaces.