Abstract: Multiple episodes of volcanic eruptions lead to the development of multiple layers of weathering crust vertically in tuff buried hill. Geochemical, petrologic and logging data jointly demonstrate the existence of multiple episodes of weathering crust in the tuff buried hill. For well Ha-31, weathering crusts were developed at 1062 ~ 1080 m and 1165 ~ 1179 m and show K, Na, Ca leaching, larger CIA index, smaller S / A index, and relatively rich Al, Fe, Mn, P, etc content which are in accordance with the response to conventional well logging. Additionally, for singe well in logging, it shows some degree of cyclicity vertically, and this kind of cyclicity can be correlated among multi-wells. Moreover, tuffs originated from different eruption periods show different structures, composition, and sizes. From above, we can conclude that tuffs were formed in multiple episodes and multiple weathered crusts were developed vertically. The effects of multiple episodes of paleo-weathering crusts of tuff buried hills on hydrocarbon accumulation include vertical reservoir of zonal distribution , weathering crust reservoirs (late weathering crusts) and inner buried reservoirs (early weathering crusts) with vertical overlay, and complex hydrocarbon accumulation mode. The proposition of multiple episodes of tuff weathering crust related reservoirs extends the volcanic hill exploration depth and provides a theoretical basis for volcanic rocks inner buried hill exploration.

Key words: Tuff, Weathering crust, tuff buried hill, Hydrocarbon accumulation effect, Erlian Basin