Abstract: There are various reasons for subeconomic wells in oil and gas exploration, including the problems of geology, engineering and management, among which the most common problem is geology. The lack of oil and gas accumulation in the lost well H drilled for natural gas in the Dengying Formation (pre-Cambrian) in the western Sichuan Basin was considered using geochemical tools, which include the optical analysis of bitumen and homogenization temperatures and gas compositions of fluid inclusions in dolomites filled in the dissolved fractures and pores. Oil accumulation in the well H area was normal from the Middle Triassic to the Early Jurassic. Bitumen was oxidized and washed by flowing waters in the period of oil cracking to gas from the Middle Jurassic to Cretaceous. As a result, there was no natural gas accumulation in the well H anticlinal area since the anticline was tilted and cut by a fault. The well H anticline was restored again during neotectonics in the Cenozoic, but there was no gas charging in the anticline because no gas was generated from oil-cracking or source rocks. Therefore, the well H was dry. Structures or traps with normal oil charging and normal gas charging and neotectonic stability are potential targets for gas exploration in the Dengying Formation in the Sichuan Basin.