Analysis Oil And Gas Accumulation Conditions In Tanan Sag Of Erlian Basin

Erlian basin is an important production base of Huabei oil field,which consisted with more than 50 small and scattered independent sags.The new discoveries and oil production improvement mainly rely on the several sags ' exploration.Tanan Sag is one of Erlian basin,which is expected to achieve new and more reservior.The early exploration of Tanan Sag has made some discoveries,but subsequent 7 drill wells,such as Ta4,Ta6x and Tall,are all missed.There is no real breakthrough on economies and large scale reserves implement for many years.In this paper,aiming at the low degree of prospecting in Tanan Sag,more in-depth analysis of reservoir forming conditions has been carried out,and several conclusions are as following:1?Integrated with single well analysis and well-seismic profiles combination,the sequence stratigraphy framework of Tanan sag has been built.According to the several key unconformities and major transgressive surfaces,2 tectonic sequences has been divided in Lower Cretaceous,that is rift and after-rift depression sequences.3 3rd-order sequences have been recognized in the rift tectonic sequence,which are respectively corresponding to the Formation of Aersan(K1ba),First Member of Teng(klbtl)and Second Member of Teng(klbt2).2?There mainly developed fan delta,subaqueous fan and lacustrine deposit in Tanan sag.Clastic mainly came from both sides along the short axis direction.During the K1ba deposition,fan delta developed on both sides of the sag,and vertical or oblique interfilled with fluvial-delta deposit from the long axis on the central structural belt in the sag.During the First Member of Teng period(kl btl),with the lake-level rise and lacustrine area expanded,subaqueous fan and fan delta developed along the both sides.The distributed channels of fan delta front are the favorable sedimentary bodies.3?Tanan sag is a half graben tectonic pattern with rift at west and onlap at east.Half graben developed with regular exercise,faults formed in early rift period re-active later and lead to different depression subsidence.Structural units can be subdivided into the eastern sag belt,central structural zone,western sag belt and slope belt.The eastern slope belt and the central structural belt has good oil accumulating background.4?According to the oil and gas accumulation study,two layers of mature source rock distribution and effective thickness of klba and klbtl have been revealed,and the objective evidence of grood oil source condition near the eastern trough has been showed.The wedge-like sandbody of fan delta front at the middle of K1ba Formation has good reservoir properties.T8 unconformity surface is the major oil and gas migration channel and the hydrocarbon migration distance is short in Tanan Sag,so it is possible to form accumulation pool at the top of Klba Formation.3 target drilling wells have been proposed in the following exploitation.