Xiong Liang, Dong Xiaoxia, Xiong Ying, et al. Types and controlling factors of tight carbonate reservoirs in the Member 1 of Permian Maokou Formation in southern Sichuan Basin[J]. Acta petrolei sinica, 2025, 46(10): 1875-1891.
Xiong Liang, Dong Xiaoxia, Xiong Ying, et al. Types and controlling factors of tight carbonate reservoirs in the Member 1 of Permian Maokou Formation in southern Sichuan Basin[J]. Acta petrolei sinica, 2025, 46(10): 1875-1891. DOI: 10.7623/syxb202510004.
Types and controlling factors of tight carbonate reservoirs in the Member 1 of Permian Maokou Formation in southern Sichuan Basin
The Member 1 of Middle Permian Maokou Formation represents the new series of strata for natural gas exploration in Sichuan Basin. Its complex lithological assemblages
heterogeneous rock fabrics and microscopic pore-facture structures pose challenges for accurately predicting high-quality reservoirs. Based on petrology
mineralogy and reservoir physical properties
this paper comprehensively investigates the types
controlling factors and spatial distribution of the Member 1 of Maokou Formation reservoirs in southern Sichuan Basin. The results show that the Member 1 of Maokou Formation can be divided into 8 sublayers from bottom to top
where three types of reservoir rocks are developed
including argillaceous (clay-rich)limestones
bioclastic packstones
and bioclastic wackestones
all characterized as low-porosity and low-permeability fracture-pore type tight carbonate reservoirs. Among these
argillaceous limestones feature a matrix microscopic pore-fracture system dominated by organic matrix pores
clay mineral (talc)pore-fractures
and grain-edge fractures
whose relatively higher porosity
permeability
and total organic carbon (TOC)contents are mainly controlled by the periodic enrichment of clay minerals and organic matters in high-frequency transgressive cycles. Argillaceous limestone has a source-reservoir integrated structure
stably and continuously distributed in the 1st
2nd
4th and 6th sublayers of Member 1 of Maokou Formation
representing the most favorable reservoirs in the Member 1 of Maokou Formation. Bioclastic packstones and bioclastic wackestones are dominated by dissolution pore-fractures
and mainly occur in the 7th and 8th sublayers. The formation of these reservoirs is controlled by penecontemporaneous dissolution in local uplift areas of the inner ramp. Although the dissolution can enhance the petrophysical properties of bioclastic packstones and bioclastic wackestones
their TOC contents are still relatively low
exhibiting a suboptimal condition for natural gas accumulation. A fracture network system was formed due to the multi-stage tectonic modifications during syndepositional to burial periods
significantly improving the accumulation/permeability capacity of tight carbonate reservoirs and providing favorable migration pathways for natural gas enrichment. For natural gas exploration in the Member 1 of Maokou Formation
the focus should be put on the area where the continuous thick argillaceous limestones (matrix pore-fracture developed zones)overlap with structural fault/fracture zones (fracture-enhanced transformation zones).
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