Introduction
1. Geological setting
Fig. 1. (a) Locations of the study area, (b) Deyang-Anyue Rift and Central Sichuan paleouplift and (c) composite stratigraphic column of Sinian-Cambrian in the Sichuan Basin. |
2. Types and structural features of platform margins of the Dengying Formation
Table 1. Structural features of different types of platform margins in Dengying Formation of the Deyang-Anyue Rift and its periphery |
Type | Slope gradient | High-energy zone position | Typical lithofacies and assemblage | Logging response features | Seismic facies features |
---|---|---|---|---|---|
Single-stage fault- controlled type | ≥45° | Upthrown wall of the fault | Mound-shoal complex, assemblage of thin algal arenaceous dolomite and algal laminated dolomite. | GR is about 12 API; resistivity is characterized by serrated middle-high value. | Mounded or annular shape, low frequency, medium-weak amplitude reflection. |
Multi-stage fault- controlled type | 10°-45° | High position of the faulted horst | Mound-shoal complex, assemblage of thick algal agglomerate dolomite, algal arenaceous dolomite and algal dolomite. | GR is about 6 API; resistivity is smaller in the middle and larger in the upper and lower. | Mounded shape, low frequency, chaotic weak reflection. |
Gentle slope type | ≤1° | Neritic zone of Deng 2 Member slope | Granular shoal, assemblage of thick sparry arenaceous dolomite and thin algal laminated dolomite. | GR is about 4 API; resistivity is smaller in the middle and larger in the upper and lower. | Low-gentle mounded shape, medium-low frequency, intermittent medium-weak reflection. |
Overlapping type | 20°-45° | Rift margins of Deng 2 and Deng 4 members | Algal mound and mound-shoal complex, assemblage of thick algal dolomite with algal stromatolitic and algal lamina structure and thin algal arenaceous dolomite. | GR is about 9 API; resistivity is smaller in the middle and larger in the upper and lower. | Tower shape, medium- low frequency, blank or chaotic weak reflection. |
Fig. 2. Seismic sections of different types of platform margins in Dengying Formation of the Deyang-Anyue Rift and its periphery, Sichuan Basin (see section locations in |
2.1. Structural features of single-stage fault-controlled platform margin
2.2. Structural features of multi-stage fault-controlled platform margin
Fig. 3. Composite histogram of sedimentary facies in typical wells of different types of platform margins in Dengying Formation of the Deyang-Anyue Rift and its periphery, Sichuan Basin (GR—Gamma ray; Rlld—resistivity of deep laterolog; Rlls—resistivity of shallow laterolog). |
Fig. 4. Sedimentary features of different types of platform margins in Dengying Formation in typical wells of the Deyang-Anyue Rift and its periphery, Sichuan Basin. (a) Well Pengtan-1, 5779.10 m, Deng 2 Member, algal agglomerate dolomite, with well-developed karst caves; (b) Well Zhongjiang-2, 6553.40 m, sparry arenaceous dolomite, with well-developed pinholes; (c) Well Pengtan-1, 5782.65 m, Deng 2 Member, grape-like dolomite, karst vugs are filled with lace-like multi-stage dolomite, cast thin section (−); (d) Well Pengtan-1, 5731.56 m, Deng 2 Member, sparry algal arenaceous dolomite, cast thin section (−); (e) Well Pengshen-2, 7791.95 m, Deng 4 Member, algal agglomerate dolomite, with well-developed vugs; (f) Well Pengshen-1, 7262.35 m, Deng 4 Member, algal arenaceous dolomite, with well-developed bedding vugs; (g) Well Jiaotan-1, 5621.50 mm, Deng 4 Member, sparry arenaceous dolomite, cast thin section (−); (h) Well Pengshen-2, 7789.50 m, Deng 4 Member, algal agglomerate dolomite, cast thin section (−); (i) Well Zi-1, 4029.20 m, Deng 2 Member, grape-like dolomite; (j) Well Zitan-1, 4934.20 m, Deng 2 Member, sparry algal arenaceous dolomite, with well-developed pinholes; (k) Well Zi-2, 4015.26 m, Deng 2 Member, sparry arenaceous dolomite, cast thin section (−); (l) Well Wei-117, Deng 2 Member, 3968.21 m, sparry algal arenaceous dolomite, cast thin section (−); (m) Well Gaoshi-1, 4975.20 m, Deng 4 Member, algal stromatolitic dolomite, with well-developed vugs; (n) Well Gaoshi-1, 4968.40 m, Deng 4 Member, algal laminated dolomite; (o) Well Gaoshi-6, 5352.62 m, Deng 2 Member, micritic and sparry algal arenaceous dolomite, cast thin section (−); (p) Well Gaoshi-1, 4987.21 m, Deng 4 Member, foamy sponge dolomite, cast thin section (−). |
2.3. Structural features of gentle slope platform margin
2.4. Structural features of overlapping platform margin
3. Seismic facies and distribution of platform margins
3.1. Seismic facies features of platform margins
Fig. 5. Seismic facies features of different types of sedimentary facies in the Dengying Formation of the Deyang-Anyue Rift and its periphery, Sichuan Basin (see the profile location in |
Fig. 6. Comparison of seismic sections of different sedimentary facies and different types of platform margins in the Dengying Formation of Deyang-Anyue Rift and its periphery, Sichuan Basin (The section locations are shown in |
3.2. Distribution of platform margins
Fig. 7. Residual thickness map of Sinian in the Sichuan Basin. |
Fig. 8. (a) Distribution of different types of platform margins and (b) sedimentary facies of Dengying Formation in the large-scale Central Sichuan study area, Sichuan Basin. |
4. Reservoir physical properties and hydrocarbon enrichment model of mound-shoal complexes in platform margin belt
4.1. Reservoir physical properties of mound-shoal complexes
Table 2. Reservoir physical properties of platform margin mound-shoal facies in Dengying Formation of the Deyang- Anyue Rift and its periphery, Sichuan Basin |
Types of platform margins | Distribution region | Reservoir of Deng 4 Member | Reservoir of Deng 2 Member | ||||
---|---|---|---|---|---|---|---|
Thickness/m | Porosity/% | Plane porosity/% | Thickness/m | Porosity/% | Plane porosity/% | ||
Single-stage fault-controlled type | Weiyuan East- Gaoshiti West | 40-50 | 1.2 | 2.0 | |||
Multi-stage fault-controlled type | Penglai-Yanting | 100-170 | 3.6 | 3.6 | 100-265 | 3.5 | 5.3 |
Gentle slope type | Ziyang-Weiyuan | 20-65 | 5.7 | 8.1 | |||
Overlapping type | Gao-Mo | 25-70 | 3.2 | 6.0 | 60-100 | 3.0 | 2.9-3.2 |
4.2. Hydrocarbon enrichment model in the platform margin belt
Fig. 9. Composite evaluation maps of the platform margin belts of Dengying Formation in large-scale Sichuan study area, Sichuan Basin. (a) Overlapping map of thickness of Lower Cambrian source rocks and platform margin belts in Sichuan Basin; (b) Overlapping map of paleo-structures on Sinian top before the deposition of Permian and platform margin belts in Sichuan Basin; (c) Overlapping map of paleo-structures on Sinian top before the deposition of Jurassic and platform margin belts in Sichuan Basin; (d) Overlapping map of current structures on Sinian top and platform margin belts in Sichuan Basin. |
Fig. 10. Sections of hydrocarbon accumulation models in various types of platform margins of Dengying Formation in the Deyang-Anyue Rift and its periphery, Sichuan Basin (the locations are shown in |
Fig. 11. Composite evaluation maps of Penglai-Zhongjiang Block in the Sichuan Basin. |