Sedimentary System Analysis Of Zhujiang Formation In The Northern Slope Of Baiyun Sag

The Baiyun sag in the northen of Zhujiang basin has become the largest oil and gas resources base in China. Because the Baiyun sag in the south of the Zhujiang Basin has enough source and preservation conditions. the Baiyun Sag and its surrounding area has very good oil and gas reservoir forming conditions.All the Conditions make Baiyun sag become one of the most potential exploration areas.Because a lot of source has been found in the Zhujiang Formation.SO, based on the Zhujiang Formation in the Northern Slope of Baiyun Sag as the research object,it can be guiding significance for the entire Zhujiang basin study in the future.In the paper, we use the research method is combined considering of continental sequence stratigraphy, sedimentology and seismic sedimentology, and the effect on the deposition. The integrated use of a variety of geological, seismic, well logging, core informations, through combination analysis and prediction, the sequence stratigraphic of Zhujiang Formation established. Then by studying the spatial distribution relationship and configuration of the sedimentary system, the sedimentary facies model can be determinedFirst, based on core observation, lithologic facies developed twelve petrographic facies and seven lithofacies. Based on petrographical assemblage, sedimentary structures, and logging data, a comprehensive analysis of a single well sedimentary facies that the Zhujiang Formation in the Northern Slope of Baiyun Sag mainly developed foure subphase and seven microfacies. Summed up the logging facies and logging corresponding feature.Secondly,This study focus on chronotaxy of IODP1148 and Zhujiang basin with the help of continuous coring, which can truly reflect the change of sea-level in Oligocene to miocene and have better guidance to the sequence research of Zhujiang basin. By using regional paleontology data, this study makes foraminiferal abundance another tool to divide boundary of sequence and maximum flooding surface. The study finds uplap、downlap、toplap、truncation and the like unconformity characters combine with sequence and tract system divided by single well, with the help of seismic data over 170 thousand square kilometers in Zhujiang basin which can conclude that there are six three-grade sequence interfaces:SB23.8、SB21、SB18、SB17.5、SB17.1、 SB16.5,and five three-grade sequences:NSQ1、NSQ2、NSQ3、NSQ4、NSQ5.Based on the analysis of sedimentary facies,combined with the seismic attributes (RMS、Avg inst freq) and strata slice, fluvial-aeolian dunes-lacustrine depositional system research has done in the sequence stratigraphic framework through the methods of point (single well)-line (connecting-well)-surface(plane). It is suggested that in NSQ1 (23.8-21Ma), small area of oblique progradation can be seen from south of Southern Panyu Low Uplift to Baiyun Sag, which reflect a progradational delta deposition。In the highstand system tracts, the delta deposition grow on the shelf margins as the high rate of relative sea level falling。where on the northern slope of Baiyun Sag, south of Panyu Low Uplift, lowstand fans, and slope fans and progradational wedge (lowstand delta) can be identified。In NSQ2 (21-18.5Ma) lowstand wedge or lowstand delta, as well as transgressional delta, can be identified in the PY34, PY35 borefild of northern slope of Baiyun Sag. In NSQ3(18Ma-17.5Ma), as the low rate of relative sea level falling, the sedimentary supply is not sufficient because of the interception of the near sediment souce area, therefore the shelf edge delta do not develop. In the sequence NSQ4 (17.5-17Ma), the sedimentary facies is mainly littoral facies and bathyal facies, and the main deposits is mudstone. But In the sequence NSQ5 (17-16.5Ma), the shelf edge delta grows, which can be identified from the parallel to sub-parallel seismic reflection and the increasing quantities of standstone.Finally, the paper fine characterizes plane distribution and the internal structure features of Sedimentary System, Sums up Depositional model of system combination on the North Slope Zhujiang Formation in Baiyun Depression; forecasts advantageous facies of Depositional system combination on North Slope Zhujiang Formation in Baiyun Depression, believes NSQ1 delta front has river mouth bar, far bar and sheet sand deposition, due to the rising sea levels, advantageous area of transition changes from the delta front to the shallow continental shelf.Delta front develops sandstone with relatively good physical properties and is a good reservoir; the shallow shelf mudstone is an excellent caprock. NSQ2 sequence, on the one hand is the deposition of the delta front which phase sequence of overlying relationship and lithological variation are similar to NSQ1, except that their development range is significantly increased, due to the gradual rise in sea level; On the other hand, advantageous reservoir area are developed in the thick marine shales of the gravity flow deposits which type is widely distributed in the shelf break belt and has good reservoir properties; and because it is developed in a thick layer of mudstone, Reservoir and cap combination is more favorable. In NSQ3 period, the advantageous reservoir area is a re-deposition of tidal sand ridges (or shelf sand ridges) which pre-deposited delta front sand transformed by the latter part of the flow trend. During this NSQ4 period the advantageous area is consistent with the previous layer sequence.As sea level gradually decreases, delta-continental interaction shelf zone and onshore-continental interaction shelf are slightly southward migrated. In NSQ5 period, with the continued decline in sea level and shrinking carbonate platform, at 17.1-16.5Ma, the delta-continental interaction shelf is the favorable area.