Conditions of hydrocarbon accumulation in Ordovician low-uplift buried hill of the Tarim basin

The Tazhong area had experienced multi-stage tectonic movements,resulted in weathering denudation in lower Palaeozoic uplift,and formed buried hills in 3 stages,including 2 sets of buried hill karst reservoirs.This paper studies the development characteristics and control factors of the buried hill karst reservoirs and predicts favorable zones.Also analyzed are the source rock,reservoir-seal assemblage,migration and accumulation process in the Tazhong area.It is believed that the Ordovician karst reservoir can form a good reservoir-seal assemblage with overlying Silurian and Carboniferous shales,and its complex oil and gas transportation network involves faults,unconformity and karst system.The Ordovician buried hill reservoirs in the Tazhong low uplift had undergone complex hydrocarbon accumulation process through multiple stages;however the Himalayan structural adjustment was crucial.Potential exploration zones are predicted,including the middle and east part of the central fault horst and its northern periclinal area(Tazhong 15,16 well blocks),as well as the eastern buried hill in the Tazhong low uplift(Tazhong 1-Tazhong 5-Tazhong 48 well block).