The Characteristics and the Accumulation Mechanism of Complex Reservoirs in the Hanilcatam Area,Tarim Basin

In recent years,with new discoveries,the Hanilcatam area in the Tabei uplift of the Tarim basin is becoming an important oil exploration zone.The area is rich in oil and gas resources.The main exploration target in this area is Ordovician carbonate rock.The high heterogeneity of fractured vug reservoir,including the complexity of distribution of hydrocarbon and water,various types of oil reservoirs,changeable fluid properties and uniform oil-water interface,brings many difficulties to exploration of this area.This paper discussed the origin of hydrocarbon and the process of hydrocarbon filling and accumulation by analyzing oil,gas and water samples,investigating well logging and summarizing geological data and seismic data.According to our researches,we believed: the hydrocarbon originated mainly from middle-upper Ordovician source rocks and its accumulation period was in the late Hercynian(Late Permian);the complexity of oil and gas was controlled by the seals of the late Hercynian.The reservoirs of the buried hill area in the north undergone intense biodegradations due to denudation of its overlying cover to form non-saturated reservoirs and their oils became heavy to ultra-heavy oils.But in the south,the reservoirs were deeply buried beneath the cap rocks with no degradation,therefore,they were mainly weak volatile oil reservoirs and produced normal oil.The reservoirs have experienced continuous deep burying processes since the late Hercynian,and the original characteristics of the reservoir fluids was such preserved.On the basis of this conclusion,we expect more explorations of normal oil and light oil to be employed in the deep-buried south region.