Study On Buried Hill Reservoir And Its Hydrocarbon Accumulation Conditions In The Beach Area Of Liaohe Rifted-basin

The buried hill reservoirs has become one of the most important fields of hydrocarbonexploration in China. At present, many buried hills of Liaohe rifted-basin including Xinglongtai,Shuguang, Dongshengpu, Qijia etc, have gone into production, and the hydrocarbon exploration inburied hill has showed good prospects. The beach area of Liaohe rifted-basin is the extending partfrom land to sea and resembles the land part in the tectonic frame and evolution. Based on explorationand development practical experience and research results accumulated during past decades, this paperstudied three buried hill belts of the beach area in Liaohe rifted-basin. Through the multidisciplinarycomprehensive research by combining geology, well logging and geophysics, this paper aims to guidethe further hydrocarbon exploration for buried hills in this area.Firstly, through regional stratigraphic correlation and analysis of frequency spectrums, ages ofburied hills and relative location of several wells of drilling buried hill are determined. For the firsttime, we confirm that carbonate and clastic buried hill of Haiyue buried hill belt belongs to Sinian-Lower Paleozoic, Haiyue metamorphic buffed hill belongs to Archean Anshan group of EasternLiaoning type, Huludao metamorphic buried hill belongs to Archean Jianping group of WesternLiaoning type, and carbonate buried hill of Yannan buried hill belt belongs to Lower Paleozoic, andvolcanic buried hill of it belongs to Mesozoic lower-Cretaceous Xiaoling group. Tectoniccharacteristics of buried hills show that three buried hill belts in this area are horst buried hillsrestrained by two normal faults of contrary proneness and NE stretch. They belOng to tectonic-corrosive buffed hills caused by two synthetical geologic effects of weathering and tectonic movement.Secondly, by using many advanced methods and techniques including finite element inversionmethod, 5700 Imaging of log (FMI), artificial neural network, fracture identifying by log, predictionof fracture by seismic attribute etc, this paper studies and predicts the development and distribution offractures in buried hills. Particularly, by using 5700 Imaging of log (FMI), this paper discovers thatweathering net fracture occurs on the surface of carbonate buried hill of Hainan 20 in Haiyue buriedhill belt. It exists a weathering crust with a thickness of about 30 meters. Three types of reservoirspace including weathering crust, tectonic fractures and corrosive pore are identified in this paper. Thecharacteristics of developing and effecting factors of them are also determined. Weathering crustmainly occurs at the top of buried hill, which had continuously undergone weathering and erosion.Tectonic fractures mainly occurs in the area of concentrative tensional stress, the degree of fracturedeveloping is controlled by regionally main faults. Corrosive pores are often formed in carbonatereservoirs, and related to dissolving of acidic water compressed from source rock.This paper also studies the forming conditions of buried hill reservoirs. The buried hills in this area are closed to hydrocarbon generating depression with a large scale of source rocks and highresources abundances. Reservoir rocks have many types of lithologies and spaces. The reservoir rocksare overlain by compact Paleogene lacustrine mudstone and Mesozoic clastic rocks with highthickness and good homogeneity. Main faults can serve as favourable hydrocarbon migrationpathways, because they have long extending distance, great fault displacement, and formed earlier andmoved periodically. Degree of hydrocarbon filling gets to normal hydrocarbon column. Reservoir-forming collocation of buried hills is characterized by "early rising, intermidiate buried depth, latefixing". Therefore, the formation conditions of buried hill are better.Finally, this paper comprehensively evaluates the buried hill traps and chooses favorableexploration goals. Consequently we discover four typeâ… traps, seven typeâ…¡traps, six typeâ…¢traps,and two typeâ…£traps, and point out short-term and long-term prospecting goals. In this paper,preliminary analysis of dynamic system of petroleum accumulation in the beach area is performed forthe first time. We conclude that Hainan 20 buried hill reservoir belongs to exotic-source, half-sealpetroleum accumulation dynamic system and make a summary of hydrocarbon concentration rules ofburied hills.