The Source Area and Sedimentary Pattern of Gaoqing Sand Bodies in Dongying Depression

Gaoqing sandbody is a well-known massive sandbody of Es 3 in southwest Dongying depression. It is more than 400 thick with an area of over 160 km 2. Gaoqing sandbody provides excellent space for oil accumulation because it overlies the main source rock of Boxing subdepression. Nevertheless, twenty years′ drilling and exploration of the sandbody has failed to find enough oil in it. The indeterminate source rock seems to be the most important factor affecting the exploration work. Based on previous studies and exploration data available, this paper has studied the depositional characteristics of Gaoqing sandbody in such aspects as regional sedimentation, seismic facies, distribution of the sandbody, lithofacies and sedimentary micro-characteristics. A study of sedimentary characte-ristics of southwestern Qingcheng convex has revealed that Qingcheng convex was a subwater convex and received deposition in Palaeogene. Due to the uplift of the convex caused by Dongying movement at the end of Palaeogene, it was denuded with some remnant sediments of Palaeogene remaining at the northern gentle slope and some progradational deposition at the southern gentle slope. It is concluded that the oil source of Gaoqing sandbody is the Luxi uplifted belt instead of the Qingcheng uplifted belt, which developed a complex made up of several progradational leafy sandbodies and litho-leafy sandbodies. The sedimentary characteristics and pattern of the sandbody are also summed up. According to the results of the study and the practical work, the authors have put forward some new viewpoints. It is believed that the corner of the sandbody is a favorable position where little litho-reservoirs and litho-structural reservoirs are accumulated, that the mudstone facies part of the front delta tends to form subtle turbidite litho-reservoirs, and that the oil source of the Zhenglizhuang sandbody, i.e., the thick sandbody of Es 2 in this region, is the southern Luxi uplifted belt, because Gaoqing convex seems to be a subwater upland in Palaeogene. The results of the study have practical reference value in search for subtle litho-reservoirs, which constitute the main goals in the exploration work of eastern China.