| Junggar basin is a multi-layer system, multi-source sag and source-reservoir-cap assemblage of petroliferous basin. Mahu depression, which located in the central depression of Junggar basin, is the one of the most favorable hydrocarbon generation sag of Junggar basin. With the Permian and Carboniferous multiple source rocks, previous researchers found a series of reservoirs and oilfields, such as Wuerhe reservoir of 530 wells in Karamay oilfield, Eight zone of Wuerhe reservoir, nine zone of Carboniferous reservoir, Wuerhe oilfield, Fengcheng oilfield, Mabei oilfield in the west slope and the Kepai fault belt on the plate.In this study, we focused on the area that located in the central western Mahu slope area, with less oil and gas wells have been drilled. Ma18 (high yield) and Ma 6 wells are located in the edge of this area.Using the knowledge and methods of Geophysics, Sequence stratigraphy, Sedimentology, Reservoir Geology, this paper systematically studied and evaluated lithologic reservoirs of the Triassic Baikouquan Formation in the Mahu Western area, Junggar Basin with the aid of the combination of processing and interpretation. The main results are achieved as follows:(1)Compared with conventional 3D data, high-density wide-azimuth 3D-seimic data has advantage in the signal to noise ratio, resolution, amplitude and imaging accuracy, which laid a solid foundation for the identification of microfracture, sedimentary facies, identification of lithologic stratigraphic traps and prediction of high-quality reservoirs in the Mahu slope area. Based on high-density wide-azimuth data, azimuthal curvature fusion and pre-stack inversions are an effective technique to improve the identification accuracy of small faults in slope area and to achieve high-quality reservoir prediction of Fan-delta-type sandstone and conglomerate.(2)The main objective sequence stratigraphic framework was established by combining the wellbore and seismic data. It was found that the angle unconformable contact between T1b-P3w and P3w-P2w, and the P2w was truncated from east to west, P3w was truncated from south to north, The characteristics of the stratigraphic distribution in the south-north trending strike-off, the T1b full-scale stable deposition and gradual thinning from north to south.(3)Through the fine structure and fracture characteristics study, we found that each objective layer is southeast dipping monoclinic tectonic background, locally developed two dimensions of a inheritance of low amplitude nose convex belt, and along with this two low amplitude nose convex, there are two Indosinian and Yanshanian active fault zones. Affected by structural slope break and low amplitude nose salient belts, the strata are generally steep in the west, broad in the middle and steep in the east.(4)According to the study of sequence and sedimentary facies, the main target layer of the study area is the fan-delta deposition with multi-stage water system tract superimposed, the early deposition of the upper water into the system tract and the mudstone cap layer of the late deposition of water into the system tract to form a better reservoir-cap assemblage; Controlled by sedimentary background on plane, favorable reservoir are mainly developed in fan-delta front subfacies, The main sedimentary was underwater distributary channel sand which controlled by valley landforms, usually was gray sandstone and conglomerate with higher maturity and better physical properties.(5) Reservoir study suggested that Mahu western area has the characteristic of the lower producing oil, the upper storing oil, fracture communicating more oil source, low-amplitude nose convex belt controlling oil-gas accumulation, fan-delta front subfacies controlling oil-gas scale, reservoir physical properties and high pressure development degree controlling oil-gas production capacity. |
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