158 / 2022-02-27 20:23:17

Establishment of retrograde fan delta sedimentary model of Upper Urho Formation in Junggar Basin and discovery of large stratigraphic lithologic traps

Fan delta, Sedimentary model, lithologic traps, Upper Urho Formation, Junggra Basin

In recent years, major oil and gas discoveries have been archived in the Upper Permian Upper Urho Formation (P₃w) in major petroliferous sag of Junggar Basin, including Mahu Sag, Fukang sag and Shawan Sag. The sedimentary system and sedimentary evolution of Upper Urho Formation are studied through field outcrop, core, drilling and logging data. The results show that: ① Upper Urho Formation mainly developed fan delta sedimentary system. The lithology gradually becomes thinner from bottom to top, reflecting the sedimentary characteristics of lake transgression. The sand body regress and overlap each other to provenance area. ② The distribution of fan body is controlled by sedimentary paleo-channel and paleo-provenance, and the fan body is divided by paleo-uplift. Ten fan delta sedimentary bodies are developed in the Upper Urho Formation of the Junggar Basin. ③ The sedimentary model of retrograde fan delta of Upper Urho Formation is established. This mode has revealed following geological laws：slope break control sand distribution; fan delta plain dense conglomerate and lacustrine mudstone control the forming of the lithologic trap. Conglomerate with poor mud matrix developed in fan delta front control good reservoir. It is pointed out that the sand body developed in the channel between paleo-uplift can form effective lithologic traps. The sedimentary model of retrograde fan delta can provide geological basis for further oil and gas exploration and reference for oil and gas exploration in areas with similar background.