Study Of Sedimentary Systems In Sangonghe Formation In Bohu Depression, Yanqi Basin

Yanqi Basin across Kuruktag above the fold belt and the South Tianshan fold belt, surrounded by mountains, is a major axis was NWW basin to extend the diamond. Study area is the Bohu depression with area of 5400km2. Bohu depression in focus in the north recession with area of 3100km2. Reservoirs have been found are anticline reservoir, non-anticline trap exploration despite get some progress, but not yet made a breakthrough in commercial value. Now an urgent need of non-anticlinal traps oil and gas exploration breakthrough in order to obtain oil and gas exploration blocks replaced. Sangonghe formation is the main layer, but this did not find the value of the reservoir with exploration. So through study of sedimentary systems in Sangonghe formation,hoping to find a favorable exploration target.By use of Drilling data and seismic data and used the six seismic profiles to recover prototype basin. Based on the seismic data and under the restrictions of drilling data, seismic and sedimentary facies of each sequence in Sangonghe 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 two sequences in Sangonghe formation, ccording to the division of drilling sequence and the reflect termination of seismic profiles, combining with the layer packing styles.(2)The analysises of seismic facies confirm:①It is characterized by medium amplitude irregular reflection which has relatively steady amplitude, extremely poor lateral continuity and bedded at the boarder of the basin, reflects that the source are relatively close and the deposits etreamly poor sorted, are gravelly mud confusion accumulate.②while characterized by low frequence high amplitude reflection at the western region of interest and also Baolang-Sumu structural belt.③The seismic facies of weak-high amplitude,medium–high frequency ,parallel and continuously reflection, generally represent of shore-shallow lacustrine depositional environment,interpret as mud containing grit and silt.④And the seismic facies of weak amplitude,neatly,clearly reflection are main distributed at the center of the sag, inferred as semi-deep lake facies mudstone stratum clip a set of homogeneous, relatively high continuity finesandstone and siltstone.(3)The sedimentary graphs of the two sequence of Sangonghe formation indicate:①It mainly develop alluvial fan, braided rivebraided rive delta and lacustrine facies(shore-shallow lacustrine,semi-deep lake)depositional system;②The sand body of main stream channel,braided river-delta,delta plain .etc which distribute pieces-link,are overtop sand-shale ratio and have no exploration value;③The progradation of sandstone and mudstone interbedded,which deposited during the Low stand delta stage,are very likely develop single sand body,and thereby formed subtle lithologic trap.This system tract are inordinately developed inside of the two sequence of Sangonghe formation.