Abstract: The Hexiwu buried-hill zone is a major hydrocarbon accumulation in the Langgu sag in northern Jizhong depression, where no new breakthrough has been made since three small Ordovician buried-hill reservoirs (Bieguzhuang, Liuqiying, Liuqiying West) were discovered in the south during the early exploration stage. Pertinent and deep study was conducted on the structure and reservoir characteristics that constrains the hydrocarbon accumulation in the Ordovician heterogeneous carbonate buried-hill reservoir, as well as reservoir stimulation and other major techniques. Through the merged 3D seismic prestack depth migration (PSDM) processing and precise structure interpretation, the zonal structure framework was ascertained, and accordingly the Yangshuiwu buried-hill structure comprising three local highs was discovered. Analysis was made on the Ordovician sedimentary facies and reservoir characteristics, indicating that the dolomite flat and dolomitic lime flat are favorable sedimentary facies belts within the study area, and the reservoir development is jointly controlled by rock type, fracture distribution and karstifcation. The dolomite serves as major reservoir. Through the study of hydrocarbon supply conditions, tectonic evolution and its control on hydrocarbon accumulation, and reservoir-cap rock assemblage, a new model of massive-laminar complex buried-hill accumulation was established for the Ordovician carbonate heterogeneous reservoir within the Hexiwu buried-hill zone. Guided by the new study results, a risk exploration well, Antan 1X, was deployed at the structure high in the west of Yangshuiwu buried-hill. This well revealed a high yield of 40.89×10⁴m³ gas and 71.16 m³ oil per day in the Ordovician reservoir, marking a signifcant breakthrough in ultra-deep and ultra-high temperature Ordovician buried-hill exploration in the north of Jizhong depression. Moreover, the practice exhibits the promising exploration prospect in this domain.

Key words: ultra-deep and ultra-high temperature buried-hill, exploration breakthrough, Langgu sag, Ordovician, Yangshuiwu buried-hill