Abstract: Based on comprehensive study of outcrops, fossils, drilling data and well logging, shallow lacustrine facies, instead of unitary fluvial facies, were recognized in the sandstone-bearing sequence of upper Guantou Formabion， in Gudao oilfield. The shallow lacustrine deposits are special in that the lake topography is smooth, lake surface is wide, water body is very shallow. Lake level changes are frequent influenced by mainly the corresponding climate changes. Deposit mainly are alternative mostlyred mudstone and grey mudstone which showing oxidizing and reducing environment. Sedimentary features show that sedimentary structure generally occur in shallow lakes and creature genesis structure growing, waterplane rise→decline depositoinal cycle obviously. Through taking the observation of core hole, describe and analyse lab test, five microfacies(water channel, sand flat, mixed flat, mud flat and marsh) can be distinguished, established the sedimentary model of Ng1+2 sand sets in Gudao oilfield.

Key words: Gudao oilfield, Guantao Formation, Ng1+2 sand sets, shallow lakes, sedimentary model