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The study of diagenesis of shale is an important part of the analysis of diagenesis system, pore structure and formation overpressure. Based on the data of X-ray diffraction, logging curve and measured porosity, the transformation amount of clay minerals in the hinterland of Junggar Basin was quantitatively analyzed. Combined with temperature, logging curve and porosity, the diagenetic evolution stage of shale was determined, and the mechanism of overpressure development was discussed. The study shows that the diagenetic evolution of shale in the hinterland of Junggar Basin can be divided into three stages. At the dominant stage of mechanical compaction from 0 m to 2 400 m, the clay mineral content in this stage is mainly affected by sediment sources, and the content and conversion amount have little change. The porosity calculated by acoustic logging is slightly larger than that calculated by density logging. The sonic time difference (AC), density (DEN) and compensated neutron (CNL) curves all decrease, while the resistivity (RT) curves increase. From 2 400 m to 4 200 m, during the transition stage between chemical compaction and mechanical compaction, illite-montmorillonite mixed layer began to transform into illite and chlorite, and the porosity calculated by density logging is equivalent to that calculated by acoustic logging. The curve of AC, DEN and CNL decreases slowly, and the RT curve slightly reverses. Below 4 200 m, in the dominant stage of chemical compaction, clay minerals begin to transform in large quantities, and feldspar begins to dissolve in large quantities. With the increase of depth, temperature and pressure gradually increase. When the temperature reaches about 120 ℃, kaolinite transforms into illite, and the content of potassium feldspar drops to almost 0%. The porosity calculated by density logging slightly deviates from the normal evolution trend, while the porosity calculated by sonic logging significantly deviates from the normal evolution trend, and the AC, DEN, CNL and RT curves all invert. Chemical compaction is one of the main causes of overpressure in the study area.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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