Genesis of Tight Oil Reservoir in Lower Permian Fengcheng Formation in Urho Area, Junggar Basin—Evidence from the Components, Structures and Rare Earth Element

• 1、Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059

Abstract：Lower Permian Fengcheng Formation is a kind of unconventional tight oil reservoir with great exploration potentials in northwestern margin of Junggar Basin. The genesis of this type of reservoir is not clear until now, so the exploration and development benefit is confined. Researche shows that the composition of this tight oil reservoir is extremely complicated, contains not only dolomite, ferroan dolomite or ferrodolomite, tufaceous and terrigenous clast, but also complex saline minerals such as reedmergnerite, searlesite, shortite, eitelite, wegscheiderite, northupite, trona, halite and gypsum. Hydrothermal sedimentary structures and textures such as dolomite，tufaceous, complex or single saline minerals lamellar or banded, veined-network, contemporaneous deformation and eruptive breccia are widely distributed. Mineral composition of this reservoir is different from marine or continental facies"white smoke type"exhalative rock published home and abroad, but the structures and textures are accordance with them. So we classify this kind of tight oil reservoir in Fengcheng Formation to lacustrine "white smoke type" exhalative rock with special mineral composition. Research about REE show that the formation of this tight oil reservoir is closely related to contemporaneous pulsatile eruption of volcanic rocks, and the affinity between source of hydrotherm and mineral composition and andesite is strong. The Ce and Eu anomaly in Fengcheng Formation indicate that the sedimentation of hydrotherm proceeded in deep-semideep lacustrine hot brine pool with reducibility. Property of hydrotherm related to volcanic eruption is mid-low temperature, strong alkaline hot brine.

Keywords： petrology tight oil reservoir “white smoke type” exhalative rock rock components rare earth element Lower Permian Fengcheng Formation Junggar Basin