Study Of Sedimentary Facies Characteristic Of Cambrian-Ordovician In Awati Fault Depression And Its Surrounding Region

Awati fault depression lies in west of north depression in Tarim Basin, is about 30 thousands km2. Its surrounding aera includes Ke Ping uplift, Ba Chu uplift, Shun Tuo Guo Le uplift, Sha Xi uplift and Ku Che depression. The study aera has several features, including great depth, little structure, little exploration well for the bed of interest, and abundant hydrocarbon, so the study of sedimentary facies characteristics of the Cambrian-Ordovician is very important.On the base of outcrop exploration, making synthetic seismogram and horizon calibration, seismic interpretation for digital section and regional paper-section, the outcrop stratigraphic column, regional correlation section of strata for bed of interest, strata isopach map, original basin section, seismic facies map, sedimentary facies map, oil and gas comprehensive evaluation map etc, were compiled, about 31. The sedimentary facies characteristics and relationships between sedimentary facies characteristics and hydrocarbon in Awati fault depression and its surrounding aera were systematical studied. The results and cognitions are as follows:(1) During Early Cambrian, there is a platform sedimentary environment in study aera; During Middle Cambrian, the difference of sedimentary environment is great. The study area includes ocean trough, embayment in north and west of Awati fault depression (normal and brackish marine sedimentary environment, consisting of intraplatform basin and passageway of ocean current), restricted platform in south of research region, evaporate platform and lagoon.(2) During Late Cambrian-Middle Ordovician, sedimentary structure setup is relatively steady in the study area, and sedimentary environment is inherited. There are three lithofacies zones in the study area. The rolling slope and ocean trough lie in the northwest of Awati fault depression. To southeast, there are the open platform and shallow water platform. The reef-bank lies in the platform margin break.(3) During Late Ordovician, there are ocean trough, slope (lower, middle, up slope), open sea continental shelf from northwest to southeast; lime mud mound or reef-bank can develop in uplifted area on the edge of ocean trough, break in the intraslope, and break between Awati fault depression and Manjiaer depression; The volcanic rock mainly developed in Abei Block and Shunbei Block, and a little part distributed in other area.(4) In the view of sedimentary evolution, the ocean trough in the northwest of Awati fault depression, which instructs conspicuous source rock, begins to develop from Middle Cambrian and dies out at the end of Late Ordovician. It is at its best during Early Ordovician.(5) The reef-bank, developed in the break of intraslope and platform margin of Ordovician system, instructs favorable reservoir bed.