The results of isotope dating of illite in hydrocarbon reservoirs and testing results of saturation pressure and homogenization temperature of fluid inclusion indicate that natural gas reservoirs in Duoqiaobai area of Dongpu depression can be mainly divided into two mega-stages;The first stage is about 30.4-18.4Ma corresponding to the early sedimentary stage of Dongying-Guantao Formation

the chief formation stage of natural gas reservoirs. The most of this stage is in correspondence with the erosion stage of 27-17Ma which is favorable for the formation of natural gas reservoirs due to the reduction of erosion stratum pressure. The second stage is equivalent to the Quaternary(since 2Ma)

this stage is on one hand for adjustment of the formed natural gas reservoirs

on the other hand for continuously injection of the secondary crop gas. The characteristics of formation of natural gas reservoirs in Duqiaobai area of Dongpu depression is in general with the newer of layer

the later of gas reservoirs forming and the older of layer

the earlier of gas reservoirs forming. The formation stage of natural gas reservoirs in Duqiaobai area is earlier in comparison with that in Qiaokou and Baimiao area.