CHARACTERISTICS OF STRATIGRAPHIC OVERLAP TRAPS AND PETROLEAM PROSPECT IN THE SOUTH MARGIN OF KUQA DEPRESSION

A series of stratigraphic overlap traps were formed as a result of depositional thin out from north to south in the Jurassic and Lower Cretaceous in Kuqa Depression.Reserviors of the Jurassic traps consist of the Lower Jurassic sandstones of coastal shallow lake facies,and the cap rocks are the Middle and Upper Jurassic mudstone of marsh facies.The lower Lower Cretaceous sandstones formed the reserviors of the Lower Cretaceous traps and the mudstones of shallow deep lake facies are their cap rocks.The floor of traps consists of pre Sinian or Sinian Lower Ordovician,its blocking ability directly infleunce effectiveness of traps.The following 3 conditions may form effeetive blocking:(1)the floor is Pre Sinian;(2)floor is the Sinian Ordovician carbonates and karst of floor in the front of trap is undeveloped;(3)the floor is Sinian Ordovician carbonates with development of karst and the karst forms one part of reserviors,which is covered by the upper Cretaceous cap rocks.It was suggested that there was rich hydrocarbon resource in the Kuqa Depression,and the south margin was a hydrocarbon accumulation area migrated from the Triassic Jurassic source rocks of the depression.The stratigraphic overlap traps in the south margin of the Kuqa Depression is a favourable target for hydrocarbon exploration.