| Baiyun sag is located in Zhu â…¡ depression of the Pearl River Mouth basin, lying in deep-water area (water depth:more than200m) in the north of South China Sea with total area more than20,000km2. It has excellent oil and gas geology condition. In the last few years, a pile of overlapped low-stand deep-water fans have been discovered with the application of sequence stratigraphy theory. Owing to the discovery of deep-water-fan system, Baiyun Sag has become the focus of deep-water oil and gas exploration. Its huge potential for oil and gas exploration has already been fully confirmed by well LW3-1-1, first deep-water (water depth:1480m) exploration well in China which obtains significant breakthrough in natural gas.In this thesis, applying theories of seismic stratigraphy, standardization of sequence stratigraphy and sedimentology, based on seismic data and constrained by well data, the author studies the distribution of frame sand bodies and sedimentary system of SB16.5on the basis of previous researchers. He uses methods like establishment of sequence stratigraphic frameworks, waveform analysis, and seismic sandstone recognition. A sort of thought and technique which can be used to establish sedimentary systems and the distribution of sedimentary facies is formed. This method is based on seismic data with the constrains of well data, and several techniques have been used as restoration of sedimentary basin prototype by line-drawing, analysis of seismic response of layers and geological properties of reflected waves by the forwarding modeling, seismic sedimentary interpretation, seismic sandstone recognition, and sandstone scanning explanation. Main progress and understanding obtained are as follows:1) The analysis of lithology in9wells shows that fine grained sediments, like mudstones and silty mudstones, are the main sedimentary in study area, politic siltstones are seconded. Siltstones and packsands only deposit in wells which are located in the continental shelf or shelf-edge belts.2) Through Establishing sequence stratigraphic frameworks and restoring sedimentary basin prototype by line-drawing, the author find that a combination of four system tracts (TST, HST, FSST, LST) is developed in both SB17.5-SB16.5and SB16.5-SB15.5sequence. And two sand bodies of different periods below and above SB16.5are recognized, one is named by165-fr (FSST) while the other one is named by1651st-1(LST).3) The analysis of wave impedances of clean mudstones and sandstones shows that two types of sandstones deposit in study area:â…¡-type sandstone whose velocity equals the velocity of mudstone and â…¢-type sandstone whose velocity is greater than the velocity of mudstone. There is no deposition of â… -type sandstone in this area, whose velocity is lesser than the velocity of mudstone.4) Through the seismic reflected wave analysis of4wells in study area, the author realizes that the top surface of1651st-1corresponds with crest and the bottom surface of1651st-1corresponds with trough in seismic sections. Furthermore, key point of recognition marks of1651st-1sand body is the bottom response, which shows as trough in seismic sections.5) The analysis of horizontal distribution of sand bodies during SB16.5period shows that165-fr sand bodies mainly distribute in continental shelf and shelf-edge areas, while1651st-1sand bodies mainly distribute in slope-break belt and slope belt, as well as the continental shelf and shelf-edge in northern areas. The whole area mainly deposits thick deep-water mudstones with silty mudstones, politic siltstones and siltstones mingled with them. Clean sandstones are less.6) Sequence SB16.5mainly develops delta-slope fan-basin fan sedimentary system in study area. Based on horizontal distribution of sand bodies and RMS amplitude map, we can find that there are clean sand bodies in river mouth bar sands and slope-fan sands, some of them can be positive reservoirs; on the contrary, clean sand bodies do not deposit in basin-fan sands and incised channel filled sands. |
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