Major breakthroughs have been achieved in gas exploration in the Ordovician Majiagou Formation in Yanchang exploration area.These discoveries show that the development and distribution of gas-bearing layers have a close relationship with the furrow erosion palaeogeomorphology on top of the Ordovician.By using such techniques such as fine subdivision and correlation of the Majiagou Formation

thickness mapping of the Benxi Formation on the unconformity

forward modeling-based identification of eroded furrows on seismic section

and seismic inversion

we mapped the paleogeology of the pre-Upper Paleozoic and recognized two NW-SE trending eroded furrows on top of the Ordovician.The comprehensive analysis of the paleogeomorphogloic map and wave impedance map shows that the distribution of favorable reservoirs with low wave impedance in the Ordovician is consistent with the locations of erosion furrows and the eroded slopes on both sides.Moreover

it is also consistent with the locations of wells that produce gas from the Ordovician and that have favorable oil/gas shows.The research indicates that favorable reservoirs occur near Y112 well in Ganquan area

Y113-Y101 wells in the northwest of the study area and Y118-Y119-Y108 wells in central of the study area.These areas should be the major target areas for further exploration of the Ordovieian.