关键词: 超深层碎屑岩, 岩性油气藏, 潜山内幕, 临河坳陷, 河套盆地

Abstract: In recent years, the breakthrough in efficient hydrocarbon exploration and discovery of large-scale reserves have been achieved in Linhe depression, Hetao Basin. The short period since exploration and discovery and low prospecting degree indicate great exploration potential and a broad exploration prospect. The discovered petroleum resources are dominated by structural reservoirs. Hydrocarbon accumulation begins to occur in the new fields such as ultra-deep clastic rock, lithology, and interior metamorphic rock buried hill, showing good exploration potential. The research shows as follows. (1) The ultra-deep clastic rocks of Linhe depression boast favorable reservoir forming conditions such as good reservoir properties (maximum porosity of 18.2 % ), high formation pressure coefficient (from 1.50 to 2.15), developed gypsum salt rock, and favorable seal conditions. The risk exploration wells, Well Hetan1 and Well Longhua1, show the trend of hydrocarbon accumulation and good exploration potential of ultra-deep oil-gas reservoirs, and it is predicted that the area of favorable oil-gas bearing region is over 200 km², and the resources amount to 2×10⁸t. (2) The large material source sedimentary system developed in Linhe depression is characterized with NW- and NNW-trending deposition, which is obliquely intersected with the current fault and structural belt trending (NE), thus providing important conditions for the formation of large-scale lithologic and structural-lithologic oil-gas reservoirs far away from the large tectonic area; the area of the favorable oil-gas region is predicted to be 800 km², and the resources amount from 3×10⁸ t to 4×10⁸t. (3) In the large metamorphic rock buried hill zones such as Jilantai area and Nalin Lake of Linhe depression, the hydrocarbon accumulation conditions are similar as those in Liaohe depression, characterized with diversified mineral compositions of metamorphic rocks, interbeded brittle minerals, and wide oil-source connection window (greater than 2 000 m). The weathering crusts in Jilantai area and Nalin Lake have evolved into massive reservoirs, of which the interior development has layered reflection features, thus providing favorable conditions for quasi-lamellar oil-gas reservoirs. Moreover, the reservoir distribution area is wide and up to 300 km², and the hydrocarbon resource is predicted to be 1×10⁸ t to 2×10⁸t, showing great exploration potential. Through studying the hydrocarbon accumulation conditions, mode as well as favorable oil and gas distribution areas in the above new fields, it will vigorously prompt the continuous exploration and discovery and largely increase reserve and production in Linhe depression, Hetao Basin. Additionally, it is of vital reference significance for the research of hydrocarbon exploration in similar basins in Huhe depression and the peripheral area of Ordos Basin.

Key words: ultra-deep clastic rocks, lithologic reservoirs, inner buried hill, Linhe depression, Hetao Basin