| Author's Name: YIN Changhai1, 2, SHI Jiangbo1, 2, TAN Xiucheng3, WANG Xiandong1, 2, TIAN Xiaobin1, 2,
JU Linbo1, 2, WEI Yulin1, 2, WANG Haiyan1, 2, TAN Wancang1, 2,
XIAO Di3, LI Minglong3, YANG Wenjie3 |
| The Middle Permian Maokou Formation is an important stratigraphic series for increasing reserves and
production in Sichuan Basin. The preliminary exploration mainly focused on the limestone fissure type reservoirs related to
the weathered crust at the top of the Maokou Formation. In recent years, with the breakthrough of a series of high-yield
wells in the central Sichuan region, the significant exploration potential in dolomite of the Maokou Member 2 has been
demonstrated, including the intraplatform shoal dolomite reservoir of the lower member of Permian Maokou Member 2 in
Hechuan - Tongnan area, while the strong reservoir heterogeneity restricts the further exploration. Based on core and thin
section observation, physical property experiments and geochemical analysis, the basic characteristics of dolomite reservoir
of the lower submember of Maokou Member 2 in Hechuan-Tongnan area are systematically analyzed, and the genesis and
formation mechanism of dolomite reservoir are discussed. The results show that the dolomite reservoir of lower submember
of Maokou Member 2 consists of pinhole dolomite and vuggy dolomite, and the reservoir space is characterized by
intercrystal (dissolved) pore, karst cave and fracture as the main seepage channel. The reservoir type is mainly fracturevuggy
reservoir, and secondly fracture-pore reservoir. The average porosity and permeability of pinhole dolomite of the full
diameter sample are 2.50% and 0.806×10-3 μm2,and these of vuggy dolomite are 4.32% and 1.047×10-3 μm2. Combined with
previous sedimentation and diagenesis research, it is considered that the high energy shoal facies is material base for
reservoir development and multi-stage karstification is the key for the formation of high quality reservoir.
Penecontemporaneous dolomitization is the key to reservoir space preservation by enhancing the compaction resistance of
rocks. The late hydrothermal dolomitization of Maokou Formation related with the Dongwu Movement (Emei taphrogenesis
in the upper-Yangtze region) in the late Middle Permian is dominated by cementing and filling early pores, which reduces
the reservoir performance of dolomite. This study provides a basis for predicting the distribution zone of high-quality
reservoirs in Maokou Formation. |
