Research Of Sedimentary Micro Facies Of Chang6₃Formation In Huanxian Area

The study objective of the topic is to find out the characteristics of sedimentary facies and microfacies of Chang63Formation,establish sedimentation model,predict favorable facies belt and sand belt, and then understand the evolution process of Erdos Basin better,provide guiding significance for seeking benificial hydrocarbon accumulation zone,and provide basis for evaluation deployment and productivity construction.On the basic theory of sedimentology,according to the characteristics of sedimentary cycles in studing area,the paper researches stratigraphic division and contrast work all over the region on the wealth geologic and geophysical prospecting data of study area,cobining with the former’s research data;from the core observation and description detailed,combined with logging data,to study marker bed,and then to analyzes single well facies and divide sedimentary microfacies all region,conduct joint-well sedimentary microfacies’s contrast and build the database of sedimentary microfacies;then to analyzes sandbody distribution rule and the characteristics of sedimentary microfacies’s distribution,compilate each layer’s sand content contour map and sedimentary microfacies’s distribution;then make full use of analysis and laboratory data, cobining with the former’s understanding,do detailed study of this area’s material source,and last analyzes the sedimentary evolution characteristics of each layer,establish the sedimentation model of study area.By dissecting the entirety characteristics of sequence stratagraphic of Yanchang Formation6section in Huanxian area in depth,we find that stratagraphic cycles of Yanchang Formation6section is very clear in the area,there are severel complete fine-coarse-fine sedimentary cycles from bottom up,from it we can divide Chang6to three sand group;in Chang63Formation,we also can identify severel fine-coarse-fine anti-positive sedimentary cycles in the second level,from this,we can divide Chang63to another three small sand group as Chang631, Chang632, Chang633from bottom up.we have made fine stratigraphic correlation via unity the contrast marker bed, and redefined stratigraphic division of Yanchang Formation6section in Huanxian area.Based on the classical deposition theory,and to fully digest the previous research in this area,it is thought that the Yanchang Formation6section in this area is a set of development of delta-front—deep lake sedimentary system by the core observation and description of38well(footage is458.45m),combined with113well logging data and analysis of laboratory data.We also do research in the types and characteristics of sedimentary microfacies in depth,identified2facies,3subfacies and10microfacies.The2facies include delta and lake facies.The3subfacies include delta-front,prodelta and deep lake.The10microfacies include the underwater distributary channel, channel mouth bar,distal bar,interbranch channel facies, prodelta clay, sandy debrite flow, turbidity current, fluidized sediment flow, slump and deep lake mud sedimentary microfacies.By the dividing of single well analysis and sedimentary microfacies,we get the value of sand content of each layer in Yanchang Formation6section, compilate each layer’s sand content contour map, and then do study of regularity of sandbody distribution; then compilate each period’s sedimentary microfacies’s distribution map, also do research in sedimentary microfacies’s distribution characteristics. The results show that delta-front subfacies develops in the area of western,northern and east-northern, in which, the most development is the underwater distributary channel microfacies which distributied in a strip shape, secondly is the interbranch channel microfacies,the last is the mouth bar microfacies, generally it distributies in the front end of the underwater distributary channel microfacies; The outer edge of the delta-front is connect with the prodelta, it develops prodelta clay;In front of the prodelta is the sedimentary area of deep lake,in addition to the deep lake mud microfacies,the more is gravity flow,in which the most is sandy debrite flow microfacies,mostly distributied in the main channel,then is the turbidite microfacies, generally it distributies in the front edge of the main channel and deep lake mud microfacies.On the basis of careful analysis of the former’s research achievements about the characteristics of the study area’s antient bottom shape,and then do preliminary snalysis of the area in Huanxian from the5main aspects:the distributed characteristics of sandstone grain size,the characteristics of sandstone’s light mineral component, the characteristics of sandstone’s heavy mineral assemblage, the characteristics of sedimentary facies’s pattern, the distributed characteristics of sandbody, it shows that the most important material source of the study area is the western, secondly becomes east-northern and northern,it also points out the route of some area’s detrital material to the basin.From the detailed analysis of the distributed characteristics and the evolution rule of the sedimentary microfacies of the study area’s3layers,it indicates that:during the depositional period of Chang633, in the delta-front sedimentary area, the most development is the underwater distributary channel microfacies which distributied in strip shape or in piece, the mouth bar microfacies is less. In the area of gravity flow,the square measure in the area of sandy debrite flow is more than the area of turbidit,and mostly distributied in the main channel; during the depositional period of Chang632, the square measure of the underwater distributary channel in the delta-front subfacies is slightly reduced,but the mouth bar microfacies increases correspondly. The sandy debrite flow microfacies develops more in the area of gravity flow; during the depositional period of Chang63’, the square measure of the mouth bar develops a little more in the delta-front area. In the gravity flow of deep lake, the growth rate of the turbidit’area exceeds the sandy debrite flow microfacies’; during each secondary period of Chang63, the direction of material source has not changed, the most important material source of the study area is the western, secondly becomes east-northern and northern,it also points out the route of detrital material to the basin throughs the channel of the prodelta from shallow water to deep water area.