Sedimentary Sequence Study About Cretaceous Strata In Yanji Basin

Situated in autonomic county of Korea, Jilin province, Yanji basin is regarded as an out-basin belonging to Daqing oil field. It was proved that oil and gas had been formulated in Yanji basin, because people had found oil-rich stone and natural gas during geological survey in 1977 around the monuments of eastern and western Liyan, Zhixin town, Yanji county, the plan of oil prospecting had been performed discontinuously in Yanji basin since 1977 because of that finding. Now, 28 wells had been established in Yanji basin. Although prospected appearance of oil and gas had been showed in several wells, we finally find with regret that there are a lot of problems we cannot answer and we have not found an availed trap so far. As a result, in order to look for covert oil and gas reservoir as the first task, we need a further research in Yanji basin, the effective method of looking for fine exploring area of oil and gas is that we should adopt sedimentary study in Yanji basin.Various kinds of comprehensive theories and methods can be applied in this paper, such as sequence stratigrapy, sedimentology, seismic stratigraphy, petroleum geology, geochemistry, reservoir geology, and resources evaluation. Beginning with establishment of sequence framework, strata division and strata contrast, we principally study the feature of Cretaceous strata sequence, the typicality of sediment, the situation and rule of sedimentary facies in vertical and transverse direction, the law of source-reservoir-seal combination, and the assessment of favorable oil and gas reservoir. We ultimately offer useful and valuable theories which could be applied for prospecting for oil and gas reason in Yanji basin.According to the comprehensive data of drilling, logging and log and combining the work performed by predecessors, we initiatory consider that Cretaceous strata units of 28 wells in Yanji basin controlled by tectonic movement of Yenshan can be divided into 2 second-order sequences and 14 third-order sequences. One second-order sequence comprise Quanshuicun Group and Dalazi Group, and another Longjing Group. After elaborating on those third-order sequences, we establish Cretaceous strata framework. In light of the tectonic movement during Cretaceous period, the evolution of sedimentary facies and the contrast of sedimentary sequence in Yanji basin, we sum up the law about litho-facies, palaeo-geography and think the Cretaceous history of sedimentary evolution and palaeo-geography can be divided into three units: expanding phase, developing phase and thrinking phase.Mainly depending on theories of sequence stratigraphy, we conclude Cretaceous strata characteristic of source-reservoir-cap rock assembling, and offer the valuation of potential oil and gas reservoir. The tendency of three potential prospecting areas are Chaoyangchuan, neighborhood of Yanji city, and Dexin.