Objective With the continuous breakthroughs in oil and gas exploration and development technology, shale oil is expected to become an important replacement for traditional petroleum resources.It is of great significance for the exploration and development of shale oil laminae to clarify the development characteristics of shale laminae, quantitative characterization of pore structure, occurrence characteristics of shale oil and oil-bearing properties. Methods The organic-rich shale of the Chang 7 member of Yanchang Formation in the southeastern Ordos Basin was studied for its development characteristics, reservoir performance and the oiliness of different shale types. Thin section observation, scanning electron microscopy and high-pressure mercury intrusion and nitrogen adsorption were used to classify the types of shale laminae and clarify the diagnostic properties of oil-bearing shale. Results Laminae are developed in silty mudstone, argillaceous siltstone, siltstone, black shale and tuff in the study area. These were found to be macroscopically divided into three types: thick laminated shale (The thickness is between 1-10 cm), medium-thickness laminated shale (The thickness is between 1 mm~1 cm), and thin laminated shale (The thickness is less than 1 mm). Felsic minerals (27.7%-79.0%) and clay minerals (12.0%-63.0%) dominate the mineral composition of the Chang 7 shale laminae, with a small content of carbonate minerals (3.2%-27.0%). Microscopically, depending on the mineral composition, the shale occurs in four layer units (Silty, argillaceous, organic-rich and tuff laminae) and two layer combinations(Combination of highly siliceous laminae and high clay laminae.). Silty laminae have rich pore types, good reservoir physical properties, good pore connectivity, high oil saturation, accounting for 46% of the whole, and good oil-bearing properties; argillaceous and organic-rich laminae have medium physical properties and poor pore connectivity, oil saturation accounts for 32% and 22% of the whole, and the oil-bearing property is poor; The reservoir physical properties and oil-bearing properties of tuff laminae are the worst, and there are few pore structures with good reservoir properties in the study area. The high-clay laminae combination has more nanopores and micropores with small pore size, which have medium reservoir performance and poor oil-bearing properties. The highly siliceous laminae combination has a range of pore sizes and good reservoir performance, and would provide more reservoir space for oil migration and good oil-bearing. Conclusions The combination of silty laminae and highly siliceous laminae is significantly superior to the other laminae types in terms of reservoir space, reservoir performance and oil content. These findings provide an important reference for shale oil evaluation.
| 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 |