| Baiyinchagan depression is a secondary tectonic unit of chuanjing sag,which is located in the east of Erlian basin.Because of the study area's complex sedimentary environment and system,mixed formation lithology,unclear rock-electricity relationship character and ambiguous stratigraphic correlation markers,different opinions have been reported regarding the recognition of the study area's sedimentary system.Wengte area's Tenggeer formation 1st lower segment has been considered the target formation.Based on core observation assay results,well drilling and logging data,combined with geology theory,this paper carries out the study on target formation's stratigraphic classification and correlation,sedimentary facies and sandbody distribution.Under the control of sedimentary cycle and secondary cycle,based on the standard well and marker bed,Tenggeer formation can be divided into three segments,and each of them has three sandgroups.Tenggeer 1st lower section(TX1 ? TX2 ? TX3)'s sedimentary facies and sand body distribution is the main research object of the paper.Based on previous ideas on sediment source,by using analysis of clastic consituents and heavy mineral combination method,it is confirmed that Wengte area's sediment source is located in the southeast slope of the basin.Comparedto previous study,the sediment source has changed from the southwest to the southeast.Due to the low formation water salinity,which leads to the unclear rock-electricity relationship character of spontaneous potential curve,the target formation of the research area's lithology and sedimentary facies can't be identified byspontaneous potential curve.Although Natural gamma curve's rock-electricity relationship is basically clear,it may fail in some situation.Therefore,logging faciesanalysis and sandbody identification have been finished byusing Natural gama curve mainly,caliper curve and interval transit time curve minorly.Rock's color,composition,particle size,psephicity,sorting feature,sedimentary structure,Characteristics of probability accumulation curves have been studied to find that there are three kinds of sedimentary systems in total: proluvial fan,formed by lake basin margin's flood current which comes from southern basin;fandelta,which is formed by enter-lake sediments;braided river delta,which is formed by southeastern river.Although there is three kinds of sedimentary system,themain kind is braided river delta,the main sub facies is delta front.The mainsedimentary micro-facies are underwater distributary channel,floodplain mat appearance sand,frontal sheet sand and shunt flume bay.Wengte area is near the sediment source,lake basin margin's slope is large.When the rivers entered the lake,its speed decreased rapidly,the sediments accumulated quickly,clastic material mechanical differentiation is weak,terrible separation between sandstone and mudstone,mixed lithology formation(shaly sand and sandy mudstone)developed.The lithology and rock-electricity relationship is socomplex that the identification of sandstone and mudstone is really difficult.It is not rigorous to identify sandtone only by means of GR curve half-side pointmethod,in some well section,some logging curves are contradictory to each other.For example,Natural gama curve's amplitude abnormal increases that the lithology should be sandstone while the corresponding caliper curves reveals theenlargement of hole diameter;Natural gama curve's amplitude abnormal increases while the value of interval transit time curve enlarges at the same time,its value can even exceed the mudstone's.After analysing the rock-electricity relationship character,the well section which is similar to the above ones have been analysed,its lithology is mainly mudstone,sandy mudstone,shaly sand,and all of them are ineffective reservoirs.In order to identify effective reservoir accurately and reject sandwich,during this study,a set of comprehensive logging curves have been combined and used to increase the accuracy of identification of mixed lithology sandstone. |
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