Research On Sequence Stratigraphy And Sedimentary System Of The Cretaceous Napo Formation T And U Members In Blocks 14 And 17,North-Central Oriente Basin,Ecuador

With low amplitude structure,abundant oil and gas resources,blocks 14 and 17are located in the north-central Oriente basin,Ecuador.Logging data showed that sandstone developed in Napo formation T and U members has a large number of oil and gas shows.However,because of the weak basic geological data and the low level of research,exploration and development of the Cretaceous Napo formation T-U members has been greatly affected.Systematically research on sequence stratigraphy and sedimentary system is one of the key ways to solve the problem of the exploration and development of Napo formation T-Umembersin blocks 14 and 17.This study applies theories of sequence stratigraphy and sedimentology to carry out the study on sequence stratigraphy and sandbody distributions of Cretaceous Napo formation T-U interval of blocks 14 and 17.Isochronous sequence stratigraphic framework of Hollin and Napo T-U interval in the study area has been built.Sedimentary microfacies have been analyzed.Sedimentary model has been established.Distribution and evolution of sedimentary facies have been analyzed.And reservoirs have been evaluated.On the basis of comparative study about typical single wells and connected wells‘profiles of the study area,two-dimensional seismic sequence stratigraphic interpretation,core observation and well logging analysis,Napo formation T&U intervals can be divided into two 3^rd order sequences.Sequence 1 is roughly equivalent to LWR?T?SS+UPR?T?SS+MID?NAPO?SH+B?LS.And sequence 2 is roughly equivalent to LWR?U?SS+UPR?U?SS+A?LS.On the basis of core facies,logging facies,and palaeontological data analysis,types of sedimentary facies(subfacies and microfacies)in the study area are identified.Barrier coast facies mainly developed during the depositional time of LWR?T?SS and LWR?U?SS.During the depositional time of LWR?T?SS and LWR?U?SS Barrier island,tidal channel-flood tidal delta,lagoon,sand flat,mixed flat,mud flat and storm deposits developed.Shelf facies mainly developed during the depositional time of UPR?T?SS,MID?NAPO?SH,B?LS,UPR?U?SS,and A?LS.During the depositional time of UPR?T?SS and UPR?U?SS,glauconite sandstone and quartz arenite mainly developed.During the depositional time of MID?NAPO?SH,shelf mud mainly developed.And during the depositional time of B?LS and A?LS,packstone mainly developed.On the basis of types of sedimentary facies(subfacies and microfacies)for systems tract analysis,combined with integrated logging and core facies analysis,distribution and evolution of sedimentary facies for each reservoir has been analyzed.It showed that the complete shelf-barrier coast sedimentary system developed.Based on the analysis of source rocks,reservoir conditions,sedimentary microfacies types,hydrocarbon migration conditions,cap rocks and traps conditions,reservoirs in the study area developing in various sedimentary systems have been evaluated and ranked,and favorable reservoirs plane distribution of each reservoir have also been predicted.According to the descending order,the favorable sandbodies for oil and gas storage are sandbodies of tidal channel-flood tidal delta,barrier island,coast,tidal flat,and lagoon shoal and mixed flat.