Diagenesis and Porosity Evolution of Calcareous Sandstone Reservoirs of Xu-3 Member in Western Yuanba of Northeastern Sichuan Basin, China

doi:10.19657/j.geoscience.1000-8527.2020.06.079

Abstract

Abstract:

Based on data of thin-section micropetrography, scanning electron microscopy (SEM) and physical property test, we analyzed the petrological characteristics, diagenesis, pore type and physical properties of the tight sandstone of Xu-3 Member in the western Yuanba area (northeastern Sichuan Basin). We established its diagenetic sequence and pore evolution process, which can shed light on the exploration of the Xu-3 Member tight sandstone. We show that the Xu-3 Member tight sandstone is mainly provided by the parent rocks of Longmenshan Permian and Triassic carbonate rocks, and was mainly developed in the braided river delta plain-deltaic front of medium-fine grained calcareous sandstone. Diagenesis of these sandstones includes mainly compaction and pressure dissolution, calcite cementation, recrystallization, dissolution and fracturing. The pore types include intercrystalline micropores, cracks and dissolved pores, with the porosity of 0.41% to 7.16% and permeability of 0.001,2×10^-3 to 533.59×10^-3 μm². The uniquely high-Ca content of the calcareous sandstone may have formed the typical diagenetic characteristics of strong cementation and recrystallization, but weak compaction and dissolution. The unique burial diagenesis has formed the special pores and physical properties of the calcareous sandstone. Early intensive calcite cementation may have resulted in weak compaction of calcareous sandstone, almost loss of primary pores, and weak dissolution. In the later stage, recrystallization of the muddy algae sands in the calcite chips formed many intercrystalline micropores. Average porosity of the calcareous sandstone is only 2.0%, and the physical properties are poor. The detrital particles and cement of the calcareous sandstone are mainly carbonate minerals with brittle characteristics. Under tectonic movements, cracks are readily formed which connected the pore system to communicate a large number of recrystallized micropores, intergranular dissolved pores, and residual intergranular pores.

Key words: calcareous sandstones, diagenesis, porosity evolution, recrystallization, Xu-3 Member, northeastern Sichuan Basin

CLC Number:

TE122.2

WANG Ai, ZHONG Dakang, LIU Zhongqun, WANG Wei, DU Hongquan, ZHOU Zhiheng, TANG Zicheng. Diagenesis and Porosity Evolution of Calcareous Sandstone Reservoirs of Xu-3 Member in Western Yuanba of Northeastern Sichuan Basin, China[J]. Geoscience, 2020, 34(06): 1193-1204.

Figures/Tables 20

Fig.1 Sedimentary tectonic background and stratigraphic features of the study area (after Wang Wei, 2013; Du Hongquan, 2016; Li Jun, 2016; Tang Zicheng, 2019[4,7-6,27])

Fig.2 Ternary detrital composition diagram for the Xu-3 tight sandstones from western Yuanba

Fig.3 Lithological characteristics of the Xu-3 tight sandstones from western Yuanba

Fig.4 Characteristics of compaction of the Xu-3 tight sandstones from western Yuanba

Fig.5 Burial history and thermal history of well YL28 in western Yuanba

Fig.6 Characteristics of pressure solution in the Xu-3 tight sandstones from western Yuanba

Fig.7 Characteristics of cement in the Xu-3 tight sandstones from western Yuanba

Fig.8 Distribution characteristics of calcite cement in the Xu-3 tight sandstones from western Yuanba

Fig.9 Recrystallization features of the Xu-3 tight sandstones from western Yuanba

Fig.10 Dissolution features of the Xu-3 tight sandstones from western Yuanba

Fig.11 Fracturing features of the Xu-3 tight sandstones from western Yuanba

Fig.12 Characteristics of primary pores and intercrystalline micropores in the Xu-3 tight sandstones from western Yuanba

Fig.13 Characteristics of recrystallized micropores in the Xu-3 tight sandstones from western Yuanba

Fig.14 Characteristics of dissolved pores in the Xu-3 tight sandstones from western Yuanba

Fig.15 Characteristics of fractures in the Xu-3 tight sandstones from western Yuanba

Fig.16 Porosity vs.permeability relations of the Xu-3 tight sandstones from western Yuanba

Fig.17 Diagenetic process and porosity evolution of the Xu-3 tight sandstones from western Yuanba

Table 1 Statistics of pore types and total pore ratios of the Xu-3 tight sandstones from western Yuanba

孔隙类型	残余粒间孔	晶间微孔隙	裂缝	溶蚀孔隙
平均孔隙度/%	0.04	1.4	0.3	0.3
总孔隙占比/%	2.0	68.6	14.7	14.7

Fig.18 Typical fracture development characteristics of the Xu-3 tight sandstones from western Yuanba

Fig.19 Typical pore system characteristics of the Xu-3 tight sandstones from western Yuanba

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