Petroleum Science HD402 HDI-2 HDI 050 4050 4100 he sandstone 15 Fig. l Profile section of the Carboniferous reservoir in Hade 4 Oilfield south to north and even pinches out. The biggest The saturation pressure is far below the stratigraphic thickness of a single well drilled is 29.0m. The Donghe pressure, and the gap between the stratigraphic pressure sandstone trap is a compound trap controlled by the and the saturation pressure is large, so it belongs with low-amplitude anticline and the Donghe sandstone an unsaturated oil reservoi pinch-out line, and consists of two relativel independent crests, namely HD4 crest and HD1-2 crest, 2. Key technical problem and philosophy of (shown in Fig. 2). The crest is at an altitude of-4090.0m, research the structural trap amplitude being 34.5m. The trap is mall, but its oil-containing area is 136 km, relatively The exploration of the Donghe sandstone subtle big. The type of the reservoir is of chiefly medium and reservoir in Hade 4 oil field is confronted with three key high porosity and permeability. The porosity is between technical problems: The first is the accurate 12%-24%, averaged 15.65%. The permeability zone discrimination of the Donghe sandstone pinch-out lines the second is the variable speed mapping of low- amplitude structure; and the third is the establishment of the tilting water-oil contact and the analysis of its genesis for an accurate calculation of its oil containing range There are some major problems arising in both the study of accurate structure and the horizontal prediction of the reservoir as follows: (1) The structural amplitude of Hade 4 oilfield is below 34m, the burial depth of the target layer measures over 5,050m and is located under the igneous velocity anomaly body. No obvious structure appears in the to map; only a broad and gentle nose uplift can be seen causing great difficulty in speed research and variable (2) The project is located in an eluvial soil-cover area in a big desert, and the shooting and reception conditions are relatively poor. In addition, the target layer is also buried deep, and the thickness of the Fig. 2 Top tectonic map of the Carboniferous thin reservoir is small (the biggest thickness is below 30m) sand layer and the Donghe sandstone reservoir so, in the condition of existing seismic data resolution, in Hade 4 Oilfield it is difficult to directly recognize the Donghe sandstone <1-2000×103μum2, averaged126.51×103μm2. The reservoir and its pinch- out point resistivity of the reservoir is low, so a reservoir of an (3)The Donghe sandstone overlapped the formatio ly resistivity is developed the lowest of the Silurian deposited sand-shale alternating layers at ivity being 0. 50Q2m, consistent with the layer of angular unconformity hickness and physical water. The reservoir has a pressure coefficient of property itself has the feature of a horizontal 1. 10-1. 11, and belongs to a normal pressure system. heterogeneity. Additionally, the attitude of the C1994-2007ChinaAcademicJournalElectronicPublishingHouse.Allrightsreservedhttp://www.cnki.net36 Petroleum Science 2004 Fig.1 Profile section of the Carboniferous reservoir in Hade 4 Oilfield south to north and even pinches out. The biggest thickness of a single well drilled is 29.0m. The Donghe sandstone trap is a compound trap controlled by the low-amplitude anticline and the Donghe sandstone pinch-out line, and consists of two relatively independent crests, namely HD4 crest and HD1-2 crest, (shown in Fig.2). The crest is at an altitude of-4090.0m, the structural trap amplitude being 34.5m. The trap is small, but its oil-containing area is 136 km2 , relatively big. The type of the reservoir is of chiefly medium and high porosity and permeability. The porosity is between 12%~24%, averaged 15.65%. The permeability zone is Fig. 2 Top tectonic map of the Carboniferous thin sand layer and the Donghe sandstone reservoir in Hade 4 Oilfield <1~2000×10-3μm 2 , averaged 126.51 × 10-3 μ m 2 . The resistivity of the reservoir is low, so a reservoir of an extremely low resistivity is developed, the lowest resistivity being 0.50Ωm, consistent with the layer of water. The reservoir has a pressure coefficient of 1.10~1.11, and belongs to a normal pressure system. The saturation pressure is far below the stratigraphic pressure, and the gap between the stratigraphic pressure and the saturation pressure is large, so it belongs with an unsaturated oil reservoir. 2. Key technical problem and philosophy of research The exploration of the Donghe sandstone subtle reservoir in Hade 4 oil field is confronted with three key technical problems: The first is the accurate discrimination of the Donghe sandstone pinch-out lines; the second is the variable speed mapping of low￾amplitude structure; and the third is the establishment of the tilting water-oil contact and the analysis of its genesis for an accurate calculation of its oil containing range. There are some major problems arising in both the study of accurate structure and the horizontal prediction of the reservoir as follows: (1) The structural amplitude of Hade 4 oilfield is below 34m, the burial depth of the target layer measures over 5,050m and is located under the igneous velocity anomaly body. No obvious structure appears in the T0 map; only a broad and gentle nose uplift can be seen, causing great difficulty in speed research and variable￾speed spatial correction. (2) The project is located in an eluvial soil-cover area in a big desert, and the shooting and reception conditions are relatively poor. In addition, the target layer is also buried deep, and the thickness of the reservoir is small (the biggest thickness is below 30m), so, in the condition of existing seismic data resolution, it is difficult to directly recognize the Donghe sandstone reservoir and its pinch-out point. (3) The Donghe sandstone overlapped the formation of the Silurian deposited sand-shale alternating layers at angular unconformity. Its thickness and physical property itself has the feature of a horizontal heterogeneity. Additionally, the attitude of the