Sequence Stratigraphy Study Of Shizigou And Qigequan Formation In North Slope Of Sanhu Depression, Qaidam Basin

This topic was based on a collecting of56wells data including logging data, coredata, seismic data and other information in North Slope of Sanhu depression, QaidamBasin. Using the theory of high-resolution sequence stratigraphy, the sequencedivision works have been carried out in the whole region. On the basis of single wellsequence division, using phase analysis method, the conversion relationship betweengeological facies, logging facies and seismic facies was established. In addition,combining with provenance analysis and seismic inversion technique, the sedimentaryfacies plan and three favorable target positions were finally described.There are6sequence boundaries in the Shizigou formation of Neogene system inNorth Slope of Sanhu depression. Each one has a significant difference on structuralcharacteristic. Onlap on top of SB1(sequence boundary1), SB5and SB6showobviously water-transgression; the upper and lower strata beside the SB2interfacehave a wide variation on the reflected wave characteristics; there are feebletruncations on SB3and SB4also. With all mention above, Shizigou formation isdivided into5sequences and10system tracts.The sedimentary facies types in Shizigou and Qigequan formation includedelta-front, lake, shallow lake and semi-deep lake deposition. Provenance is fromTaijinaier, Tuofengshan and Yanhu direction. Single-deck sandstone in the lacustrineexpansion system tract (LEST) is thin, while it can also be good reservoir oncondition that sand sheet or beach-bar exists. Mudstone in the top of lake expansionsystem tract(EST) is good source rock and seal. Sand body in lacustrine wrinklesystem tract (LWST) including delta and shallow lake sand is abundant and can befavorable reservoir.The innovation of this study is the delta-front sand identification in Taijinaier,Tuofengshan and Yanhu direction. The evidence is as follows:(1) water-escapestructure is typical of the delta-front sandbar;(2) the larger plant debris fossil mustcome from delta deposit;(3)wavy cross-stratification is not unique to the shallow lakesand, it is also the characteristic of delta-front;(4) sand thickness trend to be thinnerfrom lake basin margin to the center, and sand/stratum value is greater than20%,which are the typical characteristics of delta-front;(5) progradation configuration andthe delta-front turbidity sand have been found.With three possible lithologic traps favorable exploration areas are found in Shizigou formation:(1) Taijinaier delta front sand body and nose structure compositetrap;(2) the Tuofengshan delta front sand body and constructed slopes composite trap;(3) the delta-front turbidity sand to the west of Seshen11Well.