The buried hill oil and gas reservoirs have become an important exploration field in China’s marine basins. The northwestern area of Shaleitian area of Bohai Bay Basin is a typical carbonate buried hill zone. Due to the lack of research on the reservoir control effect of multiple stage fractures and their related karstification, the oil and gas exploration of carbonate buried hills is restricted. This paper conducts a detailed analysis of the development characteristics of the fracture-cave system in carbonate buried hill reservoirs in the northwestern Shaleitian Uplift, and studies the reservoir control effects of fractures and karst. The results indicate that the lower Paleozoic carbonate buried hills in the northwestern area of Shaleitian Uplift belong to fracture related karst reservoirs. The reservoir space includes dissolution pores, structural fractures, and expansion pores along the structural fractures. High quality reservoirs have lithological selectivity, and fractures and dissolution pores developed in microlite crystalline dolomite and fine crystalline dolomite are better. The reservoir mainly develops three sets of fractures, with E−W and NE oriented shear fractures mainly related to two tectonic compressions during the Indosinian and Late Yanshanian. The third set of NW oriented tensile fractures is related to the intracratonic movement during the Himalayan orogeny, and compression is the main mechanism for forming high-density fractures. The later stage of extension is a necessary condition for the relaxation of fractures to form reservoir spaces. The Lower Paleozoic carbonate buried hill reservoirs have undergone three stages of karstification, which are karstification in the steady Caledonian tectonic background, karstification in the Indosinian compressive background, and fault block-horst karstification in the Yanshanian-Himalayan extensional background. In summary, the carbonate buried hill reservoirs in the northwestern Shaleitian Uplift are formed by multiple stages and multiple types of tectonic-karst processes, and the analysis of the differences in the degree of recombination in different structural parts is an important factor in understanding the reservoir formation mechanism.
| 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 |