Introduction
1. Overview of geological exploration
Fig. 1. Tectonic unit division and stratigraphy of the eastern segment of Fukang fault zone. (a) Location of the study area in Junggar Basin; (b) Planar structural map of the study area; (c) SN-trending section of the eastern segment of Fukang fault zone; (d) Composite stratigraphic column of the study area. N—Neogene; E—Paleogene; J—Jurassic; T—Triassic; P3wt— Upper Permian Wutonggou Formation; P2h—Middle Permian Hongyanchi Formation; P2l—Middle Permian Lucaogou Formation; P2jj—Middle Permian Jingjingzigou Formation |
2. Basic geological conditions of hydrocarbon accumulation
2.1. Source rock
Table 1. Geochemical parameters of the source rock in Permian Lucaogou Formation in southeast margin of Eastern Junggar region |
Structural Zone | Well/ Outcrop | Depth | TOC/% | S1+S2/ (mg·g−1) | Chloroform bitumen “A”/‰ | HI/ (mg·g−1) | Type | Tmax /°C | Ro/% |
---|---|---|---|---|---|---|---|---|---|
Hanging wall of the Fukang fault zone | XJC1 | 410-650* | 1.93* | 28.00* | 0.06* | 463.0* | I, II1 (mainly Type II1) | 460-480 | 1.71 |
ZY4 | 0.94 | ||||||||
Dalongkou | 17.83 | 113.50 | 463.0 | 440 | 0.60-0.70 | ||||
Santai uplift | Ergonghe | 11.17 | 94.50 | 840.0 | 447-449 | ||||
Jinan Sag | ZY2 | 170-478 | 1.93* | 0.06* | 0.65-0.90* | ||||
BC1 | 432-452* | ||||||||
ST1 | 5.20 | 37.60 | 0.60 | 379.0 | II1 | 436-445 | 0.60-0.75 | ||
S101 | 6.80 | 45.70 | 341.0 | II1 | |||||
Jimsar Sag | J3301 | 150-330 | 3.82 | 20.00 | 1.15 | 391.0 | II1 | 418-447 | 0.91 |
J35 | 2.03 | 7.10 | 7.10 | 287.0 | II2 | 428-454 | |||
J174 | 6.11 | 15.23 | 0.16 | 313.7 | II1 | 436-460 | 0.87 |
Note: *Data sourced from Reference [14]. |
2.2. Reservoirs
Fig. 2. Microscopic characteristics of casting thin sections of Permian reservoir in Jinan Sag. (a) Well Sa-101, 3043.6 m, Jingjingzigou Formation, feldspathic lithic sandstone, mainly composed of volcanic debris under plane-polarizerd light (the same below); (b) Well Sa-4, 2399.6 m, Jingjingzigou Formation, secondary dissolution pores of feldspar, lithic and zeolite cements; (c) Well Sa-4, 2399.6 m, Jingjingzigou Formation, dissolution pores are filled with chlorite; (d) Well Sa-104, 3432.7 m, Jingjingzigou Formation, particles are mainly in point-line contact; (e) Well Sa-104, 3435.7 m, Jingjingzigou Formation, pores are filled with ferroan calcite cements; (f) Well Sa-103, 3356.2 m, Jingjingzigou Formation, crude oil disseminates chlorite and lithic dissolution pores; (g) Well Tai-701, 3090.4 m, Wutonggou Formation, dominated by glutenite and medium-fine grained lithic sandstone, with intergranular pores and intragranular dissolution pores; (h) Well Tai-701, 3090.4 m, Wutonggou Formation, structural cracks; (i) Well Sa-3, 3326.3 m, Lucaogou Formation, structural cracks. |
2.3. Caprock
Fig. 3. Chromatograph-mass spectrogram of crude oil in Jingjingzigou Formation and source rock in Lucaogou Formation in Well Satan-1. |
2.4. Source-reservoir-caprock assemblage
3. Sub-source hydrocarbon accumulation
3.1. Source of oil and gas
Table 2. Geochemical parameters of crude oil and source rock in Jinan Sag |
Well | Formation | Sample | δ13C/ ‰ | Pr/Ph | (C21+C22)/ (C28+C29) |
---|---|---|---|---|---|
ST1 | P2jj | Crude oil | −32.36 | 1.26 | 2.55 |
S101 | P2jj | Oil-soaked fine sandstone | −32.60 | 1.31 | 4.02 |
ST1 | P2l | Grey-black mudstone | −29.80 | 1.02 | 2.86 |
Fig. 4. Relationship between dominant peak wavelength and red-green entropy of Permian oil inclusions in Jinan Sag. |
3.2. Fluid inclusions in reservoirs and hydrocarbon accumulation stages
Table 3. Capture pressure of oil inclusions and homogenization temperature and salinity of associated brine inclusions in Jingjingzigou Formation, Jinan Sag |
Well | Inclusion type | Host mineral | Homogenization temperature/°C | Freezing point/°C | Salinity/ % | Capture pressure/MPa | Stage |
---|---|---|---|---|---|---|---|
Sa-4, Sa-101, Sa-103, Sa-104 | Brine inclusion associated with oil inclusion | Quartz overgrowth edge and quartz crack | 50.1-71.9 | −4.8 | 7.9 | 12.4 | I |
−5.0 | 7.6 | ||||||
Quartz crack and calcite cement | 76.0-86.8 | −8.5 | 12.3 | 29.2 | II | ||
−6.8 | 10.2 | ||||||
Quartz crack and calcite cement | 89.9-98.7 | −0.3 | 0.5 | 32.6 | Ⅲ |
Fig. 5. Microphotos, homogenization temperature and fluorescence spectra of inclusions in Jingjingzigou Formation in Jinan Sag. (a) Well Sa-101, 3255.9 m, showing a group of blue-green oil inclusions under fluorescence; (b) Well Sa-4, 3221.3 m, showing blue oil inclusions under fluorescence; (c) Well Sa-4, 3221.3 m, showing yellow oil inclusions under fluorescence; (d) Well Sa-4, 3221.3 m, showing yellow-green oil inclusions under fluorescence; (e) Well Sa-101, 3255.9 m. The homogenization temperature of oil inclusions is 59.0 °C, and that of brine inclusions is 67.6 °C; (f) Well Sa-4, 3221.3 m, the homogenization temperature of oil inclusions is 62.2 °C, and that of brine inclusions is 86.3 °C and 88.6 °C, respectively; (g) Well Sa-4, 3221.3 m, the homogenization temperature of oil inclusions is 64.1 °C, and that of brine inclusions is 77.7 °C and 79.8 °C, respectively; (h) Well Sa-4, 3221.3 m, the homogenization temperature of brine inclusions is 96.7 °C and 97.6 °C, respectively; (i) Well Sa-101, 3255.9 m, the main peak wavelength of the blue-green fluorescent oil inclusion is 493 nm; (j) Well Sa-4, 3221.3 m, the main peak wavelength of the blue fluorescent oil inclusion is 452 nm; (k) Well Sa-4, 3221.3 m, the main peak wavelength of the yellow fluorescent oil inclusion is 568 nm; (l) Well Sa-4, 3221.3 m, the main peak wavelength of the yellow-green fluorescent oil inclusion is 535 nm. |
Fig. 6. Reservoir burial-thermal histories and hydrocarbon accumulation stages in Well Satan-1 and Well Xinjican-1. J1s—Lower Jurassic Sangonghe Formation; J1b—Lower Jurassic Badaowan Formation; T3—Upper Triassic; T2—Middle Triassic; T1—Lower Triassic; T1j—Lower Triassic Jiucaiyuan Formation. |
3.3. Hydrocarbon charging, migration and accumulation
3.3.1. Direction of oil migration and accumulation during key hydrocarbon accumulation stages
Table 4. Maturity of source rock in the Lucaogou Formation and Permian crude oil in Jinan region |
Location | Profile/ Well | Source rock | Ts/(Ts+Tm) of crude oil | ||
---|---|---|---|---|---|
Ro/% | Tmax/ °C | Ts/ (Ts+Tm) | |||
Central and western parts | Ergonghe profile | 447- 449 | |||
Well JN1 | 0.25 | ||||
Well T701 | 0.82 | 442 | 0.20 | 0.18 | |
NE part | Well ST1 | 0.60-0.75 | 436 | 0.07 | 0.22 |
3.3.2. Driving force for oil charging
Fig. 7. Relationships between oil saturation and capillary radius of Jingjingzigou reservoir in Jinan Sag. |
3.3.3. Pathways for oil migration
Fig. 8. Microfractures and oil inclusions captured inside of Jingjingzigou Formation reservoir. (a) Well Sa-104, 3437.9 m, cracks crossing quartz can be observed under plane-polarized light; (b) Well Sa-104, 3437.9 m, a large amount of yellow oil inclusions can be observed in cracks crossing quartz under fluorescence; (c) Well Sa-4, 2399.6 m, cracks crossing quartz can be observed under lane-polarized light; (d) Well Sa-4, 2399.6 m, a large amount of blue oil inclusions can be observed in cracks crossing quartz under fluorescence. |
3.4. Evolution and models of hydrocarbon accumulation
3.4.1. Evolution of hydrocarbon accumulation
3.4.1.1. Early hydrocarbon accumulation through long-distance migration
Fig. 9. Schematic diagram of hydrocarbon accumulation and evolution in Jinan sag. |
3.4.1.2. Middle hydrocarbon accumulation by mixing crude oil charging
3.4.1.3. Late hydrocarbon enrichment in structural highs by short-distance charging
3.4.2. Models of hydrocarbon accumulation
Fig. 10. Sub-source hydrocarbon accumulation model in EW direction in Jinan Sag. |