The Effect Of Lake Basin Filling Evolution On Oil And Gas Accumulation In The Yanchang Formation Of The Ordos Basin

Fully studying the filling evolution process of Lake Basin and the distribution characteristics of sandstone in different sedimentary stages of Lake Basin in Ordos Basin plays an important role in predicting reservoir distribution.Based on the analysis of foreaccumulation reflection structure,migration track and logging facies,the typical seismic facies and their geological implications in Ordos Basin are studied.Firstly,the typical seismic facies of Yanchang formation are identified,four common types of foreset reflection are summarized,and their corresponding sedimentary environment and sand body distribution are studied;Secondly,the sedimentary evolution process of lacustrine basin is analyzed based on logging data;Finally,the progradational sequence is divided,the lake basin evolution model is established,and the favorable factors of oil and gas accumulation in the process of lake basin filling are studied.The results show that there are four typical progradation reflection types in Yanchang Formation of Ordos Basin,namely S-type lenticular,S-type wedge,parallel oblique wedge and tangent oblique plate.Among them,S-type lenticular reflection usually represents delta plain subfacies and delta front subfacies;S-type wedge reflection mainly develops delta front subfacies and turbidite fan;Delta deep water sedimentary model is developed in parallel oblique wedge reflection;Tangent oblique plate is mainly delta front deposition.Different progradational reflection types correspond to slope delta sedimentary stage,Delta and deep lake sedimentary stage,delta sedimentary stage and meandering river sedimentary stage respectively;The massive sandstone under deep-water gravity flow has better reservoir conditions,the close contact between sandstone and Chang-7 source rock constitutes good source and reservoir conditions,the sandstone and stable mudstone vertically constitute good reservoir cap combination,Chang-7 source rock massive sandstone mudstone forms good traps,and the reservoir forming conditions are very excellent.The study of lake basin filling evolution process can reflect the development of sedimentary facies,distribution of sand and mudstone and sediment supply in the lake basin,which is of great significance to the study of sequence framework and reservoir distribution in the lake basin.