*4.4. Physical Properties*

The Chepaizi Uplift, where the Hong-Che Fault Zone is located, is one of the oldest uplifts in the Junggar Basin. The Carboniferous has been exposed to the surface for a long period and has been subjected to weathering and leaching, which gradually transformed the Carboniferous volcanic rocks into favorable reservoirs. Judging from the current cast thin section analysis data from the Che 210 well block in the Hong-Che Fault Zone, the reservoir space mainly consists of secondary dissolved pores and micro fractures, while no primary pores are found, which indicate that weathering and leaching determined the reservoir capacity of the area. According to the relationship between the porosity and permeability data of the actual core analyses in this area and distance from the weathering crust, the vertical zonation characteristics of the weathering crust at the top of the Carboniferous are obvious: The thickness of the soil layer is approximately 0–30 m, the lithology is mainly weathered residual soil, which was formed by weathering and rock erosion, and the regional distribution is relatively stable, therefore, it can function as a regional cap rock. The leached zone is 30–350 m. The reservoir physical properties are good, the average porosity is 7.42%, and the average permeability is 0.071 mD. This is the main reservoir in this area. Based on the current evaluation results, the oil layer mainly developed in the leached zone. Depths of 350–700 m represent the disintegration zone. Compared with the corrosion zone, the reservoir permeability of the disintegration zone is similar to that of the corrosion zone but the porosities are quite di fferent, with an average porosity of 5.07% and average permeability of 0.143 mD. The reservoirs in the disintegration zone are mainly dry layers, which are partially water bearing but not active. The parent rock zone is below 700 m, its reservoir physical properties are poor, its average porosity is 1.60%, and its average permeability is 0.032 mD, which is a lower threshold in this area (Figure 14).

**Figure 14.** The stratigraphic section of the Che 210 well block.

Vertically, the degree of development of dissolution pores and microfractures in the Carboniferous reservoirs in the Che 210 well block was clearly a ffected by di fferences in weathering and leaching. The reservoirs with the best physical properties mainly developed in the leached zone, which is 30–350 m from the top of the Carboniferous. Meanwhile, oil production tests and production tests in this area further indicate that the oil reservoirs are distributed within a range of 350 m below the upper boundary of the Carboniferous. This indicates that the physical reservoir properties control the vertical distribution ranges of the reservoirs.

#### **5. Reservoir Formation Model**

The crude oil in the Carboniferous reservoir in the Hong-Che Fault Zone mainly comes from the source rocks of Permian Fengcheng Formation and Lower Wuerhe Formation in the Shawan Depression. Since the Permian, this area has been in a structural pattern of high in the west and low in the east for a long period and has become a favorable area directionally for the migration of oil and gas, which was generated in the Shawan Depression. The oil and gas first migrated along the faults and then moved upward (westward) with the unconformity as the migration channel. The oil and gas mainly migrated along a spatial channel, which consisted of faults-unconformities and entered the trap in the hanging wall from the oil-generating area of the footwall of the Hong-Che fault [52–59]. Oil and gas migrated vertically through faults, laterally along unconformities, gradually migrated to higher parts, and accumulated in the stratigraphic traps of volcanic weathering bodies. The reservoir formation model is as follows (Figure 15).

**Figure 15.** Hydrocarbon accumulation model of Carboniferous in the Hong-Che Fault Zone (adapted from [21]).
