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

Yanqi Basin stretches across the Kuruktag and the South Tianshan Moutain fold belt, which is confirmed to be one of the medium and small sized petroliferous basin in western China. Since the discover of the Yancan 1 well in 1994, four petroliferous blocks- Baozhong, Baobei, Ben butu and Eastern Ben butu have been explored successively. In order to get the successive exploration blocks, the breakthroughs of exploration of non-convex traps are badly needed at present.In the light of Drilling data and seismic data, Yancan 1 and Cheng 1 that drilling out Ba daowan formation are mainly considered and also sequences division are completed, moreover,the seismic profiles of six in-lines and five cross lines which go through the Bohu depression are uesd to recovering prototype basin. Based on the seismic data and under the restrictions of drilling data, seismic and sedimentary facies of each sequence in Ba daowan formation are recognized on the basis of previous research , according to the division of drilling sequences and the reflect termination of seismic profiles, as well as the packing style of the formation in the process of Line Drawing,and then define the favorable reservoir facies.Main achieved cognitions are as follows:(1) It is divided into three sequences in Ba daowan formation ,then compiled seismic and sedimentary facies figures of each sequence ,according to the division of drilling sequence and the reflect termination of seismic profiles, combining with the layer packing styles ;(2) 7 seismic reflectance signature are summarized to according to the reflection of Badaowan formation. Moreover,the sedimentary environments can be obtained through these reflection feature. The medium amplitude,medium frequency,relatively continuous reflection generally reflect the progradation process of the deposit which may develop single sand body, are formed at late stage of high level.(3)The depositional system of alluvial fan, braid river, braid river delta and lacustrine facies are mainly developed at the early stage of Ba daowan formation.,while developed meandering river and meandering river delta at the late stage,The grit of main stream channel,fan-delta,delta plain in each sequence of Ba daowan formation have distributed continuously,the sand-mud ratio is so high as to be no value for exploration;(4)Isolated sand body is very probably developed between the basinward dipping progradation of sandstone and mudstone interbedded,which deposit during the period of forced regression, consequently formed subtle lithologic trap. This system tract is extensively developed in each sequence of Ba daowan formation.