Tudy On Depositional System Of N1s2 Formation In Chunguang Block, Junggar Basin

Sedimentary system is a three-dimensional bodies caused in the process of the relevant sedimentary environmental and interconnected sedimentation, which plays an important role in researching on oil and gas geology, reservoir prediction and traps and so on Chepaizi uplift locates on the western swell of Junggar Basin. Since pai-2 well drill commercial oil in neogene Shawan Formation on February 2005, multiple lithologic hydrocarbon reservoirs have been discovered in Shawan formation and established the spring field. But the later deployment of multi-port wells successively defeated or not achieved the ideal effect. The main reason is that we do not know enough about the region lacking the effective combination of seismic data and geologic rule.For the phenomena and problems above, this article, taking the second section of the Shawan formation in the spring block as an example, using sequence stratigraphy, seismic stratigraphy and sediment geology theory as the nstruction, on the basis of well logging, drilling and seismic data, will research sedimentary system in the studied area, mainly including the sequence stratigraphic framework, sand body identification and distribution analysis and the research of sedimentary system, etc. Main progress and understanding obtained are as follows:(1) The second section of the Shawan Formation is a complete set of T-R sequence. The composite surface of subearial unconformable surface and the maximum regressive surface form the sequence interface. There is maximum flooding surfaces in the sequence. Transgressive system tract(TST) is under the maximum flooding surfaces and is piled in the style of retrogradation; Regressive system tract(RST) is above the maximum flooding surfaces and is piled in the style of progradation.(2) The sandstone in the second section of the Shawan Formation is mainlyⅠstyle, and the thickness of single sand body is small(less than 10m).Because of that, the sandstone displays a lower right tilted symmetry waveform on the seismic section(negative polarity), and the amplitude wear off gradually until disappeare from the center to the lateral pinchout.(3) There are nine sets of sand groups in the second section of the Shawan Formation, The first three sets lie in TST, which in the northwest appeare fan-shaped, and in the south or southeast appeare stripe-shaped or fan-shaped. The rest six sets of sand groups lie in RST, which overall appeare stripe-shaped in the early stage and fan-shaped later. The 7nd to 9nd sets of sand groups exist only in the south area.(4) The study area is divided into bulge, littoral shelf, and lake sub-sag three sedimentary tectonic units and mainly develop braided river delta, beach bar and subaqueous fan three types of sedimentary facies. Braided river delta locates in the north, beach bar in the middle, and subaqueous fan in deep water area in the south. Provenance come from the north bulge structure high, mainly the north west one in the TST period and the north(east) one added in the to the RST period.(5) There are braided river delta-lake sedimentary systems in second section of the Shawan Formation. The former is situated on the transition district of land to lake area, the later is fully developed in lake area and including beach bar and underwater fan sedimentary type.