Sedimentary Characteristics Of M Formation Of Lower Cretaceous In Block A,Alberta Basin,Canada

This paper is based on the data of the M Formation of Lower Cretaceous in Block A of Alberta Basin,Canada.The study is guided by theories of sedimentology,well logs geology,and seismic.Responding to the issue about the types and spatial types of sedimentary facies in the study area are not known.On the basis of macro depositional setting,micro sedimentary features,and sedimentary patterns of the study area have been established.At the same time,the areal characteristics of lithology,well log facies and seismic facies have been studied.The evolution and areal distribution characteristics of sedimentary facies have been revealed in different periods.Through the comprehensive analysis,the spatial and plane distribution of sedimentary facies in the study area was characterized.It provides a reliable geological basis for the exploration and development in the study area.The study concludes the following,1.According to the characteristics of lithology,sedimentary structure,trace fossil composition,occurrence and distribution,three trace fossils assemblages can be divided,and the sedimentary environment represented by each trace fossil assemblage was analyzed.It is believed that Scoyenia appears in the shallow lakes with low energy,Planolites appears in the deeper shallow lakes or closed lakes with relative calm water and poor oxygen conditions,Cylindrichnus appears in lakeside and estuary.2.The study area is a typical meandering river deposition in a tidal environment,which may be located in a relatively curved part of the inner estuary system.The result shows that point bar,channel lag,flood plain,abandoned channel are the main microfacies in the study area.The tidal affected point bars provides an optimal oil sand reservoir.3.According to the analysis of the core and sedimentary facies,a complete point bar consists of six types of lithofacies in the study area,including Breccia,Sandstone,Sandy_IHS,Muddy_IHS,Mudplug and Mudstone.The Muddy_IHS and Mudplug finger into the lower sandstone.The proportion of Muddy_IHS and Mudplug is gradually increasing in the direction from the point bar to the abandoned channel.The abandoned channel is one of the important signs of the end of a single-stage point bar.4.According to typical seismic facies attribute spatial and plane distribution analysis,the location,shape and range of the channel in the study area can be described more accurately.It is believed that meandering river was developed in Asm2,and abandoned channel was developed in Asm3.5.By integration of lithofacies,logging facies,and seismic facies,the study area of M Formation could be the inner part of estuary,close to the continental part,it is dominated continental runoff and less affected by tides.The sand bodies in Asm2 are distributed in central and northeastern part,the channel and point bar are developed;and the sand bodies in Asm3 are distributed in central and northern part,the abandoned channel and point bar are developed.The study area is gradually evolved towards the estuary with the strengthening of transgression.