The Ordovician in Ordos basin had been deposited in a "three uplifts-two saddles-two depressions" paleotectonic framework.The three uplifts were horizontally distributed as the letter "L" and together controlled the sedimentary facies of Ordovician and the regional distributions of different types of reservoirs.The main reservoir types in Ordovician include sub-salt reservoirs in the eastern depression

residuum karst reservoir on the slope zone of the palaeohigh

dolomite reservoirs in the 4th member of Majiagou Formation on the saddle of the palaeohigh

Middle Ordovician gravity flow reservoirs in the western part of the palaeohigh

and bioherm or reef reservoirs on the southern slope zone of the palaeohigh.Among these reservoir types

the residuum karst reservoirs are the most favorable

and the large Jingbian gas field has been discovered in this reservoir type.Based on analysis of reservoir characteristics and hydrocarbon migration and accumulation

it is believed that the other 4 types of reservoirs still have relatively large exploration potentials

though no substantial progress has been made in exploration

thus they would be the key frontiers for exploration in the Lower Paleozoic in Ordos basin.