Study On The Sedimentary Systems Of The Badaowan Formation In Bohu Depression Of Yanqi Basin

Yanqi Basin locates in the east of the South Tianshan Mountain tectonic structure, which is the Meso-cenozoic sedimentary basin.Bohu is a Meso-Cenozoic overlaying depression in the south basin,which is the Mesozoic Jurassic depositional center. The hydrocarbon resources estimated results finished in the recent years suggest that, the resource of this basin is huge, while the exploration degree is low. The fields found are mainly anticline structure reservoirs at present. The most important of exploration assignment is to find non-anticline traps which replace the old ones. Badaowan formation lithologic trap is one of the most beneficial exploration targets. Thus , it is significant to make clear its sedimentary system.On the basis of previous researches, this paper takes the current well in Yanqi Basin as precondition, the seismic data as basis. Firstly synthetic seismograms and well picks seismic demarcation of 15 representative wells are launched. And then the correspond relationship between lithology and seismic facies is concluded. On the basis above, the Badaowan formation (sequence boundary sb1~sb4) and tectonic close interpretation are launched on 2D seismic data of the whole district. The correspond relationship between seismic facies and sedimentary facies is studied on the basic of sequence statigraphy framework built by line dawing and sequence statigraphy standard theory. Finally, the Badaowan formation sedimentary system in study area is analyzed integrally. Through the above works, the main results and views obtained are as follow:The seismic facies-sedimentary facies and sedimentary system of the 3 sequences in Badaowan formation are analyzed under the sequence statigraphy framework built by our team, and the key view obtained includes:1) provenance: generally divided into northwest, northeast and south 3 provenance area and 12 provenances2) river system and fan- delta distribution: 3 river systems are developed mainly, including NWâ†'SE river system, NEâ†'SW system, and Sâ†'N system. The northeast and northwest river systems flow by north depression, and then the end flow into the south depression. While the south river system restrict in the south depression only.3) sedimentary facies types: alluvial fans(offshore alluvial fans and subsea alluvial fans ), delta(braided river delta, meandering river delta and fan delta), turbidite fan( deep-water turbidite fan of delta frontage and deep-water turbidite sand-body of offshore alluvial fan frontage), deep lake-offshore lake swamp( deep lake-semideep lake, offshore lake and offshore swamp can be divided roughly) etc.4) sedimentary system: generally the Jurassic sedimentary in this basin is divided into alluvial fan-delta-turbidite fan sedimentary system and lake facies system 2 styles. The different depositional period and different geographic location, the sedimentary systems developed are various.5) faceis controlled factors: the common rule of tectonic controls basin and basin control deposition is coincided. The east to west vertical pressure and northwest to southeast, northeast to southwest compresso shear, 3 tectonic belt control absolutely provenance, river, sedimentary facies and system.