Depositional Architecture Research On Chang6Oil Formation In Yuan 284 Block,Hua Qing Oilfield

Delta deposits are widely developed in Chang 6 oil formation of Yanchang Formation in Ordos Basin,which has great potential for exploitation and development.The strong heterogeneity within the reservoir leads to the problems of rapid production decline and large yield difference among different blocks.Therefore,the key to improve the development effect is to study the internal architecuture of the reservoir carefully.Taking Yuan284 Block of Huaqing Oilfield as an example,this paper aims to establish an accurate isochronal stratigraphic framework,clarify the type of sedimentary facies and characteristics of sedimentary microfacies,anatomy the architecture of different hierarchical sandbodies and establish a 3D architecture model in the study area.This goal is accomplished by comprehensive analysis of core,logging and seismic data.The results show that:?1?The stratigraphic pattern of the study area is prograditional type.The thickness of the stratum decreases from NE to SW,and the overall progradational dip angle is0.48°.The slope break zone developed in the northeastern part of the study area,with an inclination of 1.8 degrees.?2?The study area is a deeper water lobe-shaped delta deposits with four types of sedimentary microfacies:distributary channel,mouth bar,overbank and interdistributary bay.The mechanism of sediment flow includes traction flow and gravity flow,and the major mechanism is traction flow.The gravity flow deposits are characterized by the existence at the bottom of mouth bar sands.?3?A hierarchy for architecture of deeper lobe-shaped delta has been established,which includes delta system subsequence(5^th grade),lobe systems(6^th grade),lobe complex(7^thgrade),single lobe(8^th grade)and accretion sandbodies in single lobe(9^th grade).?4?For compound lobe systems in sub-layers,the sandbody is sheet-shaped in the plan and progradational-superimposed vertically.There are three patterns in lobe system in single layers,including sheet-shaped,proximate sheet-shaped and lobe-shaped patterns,and there are two vertical superposition pattern including progradational and additional patterns.A single lobe is lobe-shaped and tongue-shaped in plane views and it looks like a"bottom flat and top convex"shape in profie views.The thickness of one single lobe is about 5.0?7.0m,with an average of 5.84m.The width of a single lobe is about950?2800m,with an average of 1850m.There is a good linear positive correlation between the width and maximum thickness of single lobe.There are 12 vertical superposition patterns and 6 lateral traction patterns among single lobe.?5?The thickness of single foreset layer in a single lobe is about 0.2?1.0 m,and its dip angle is about 0.62?0.8°along the source direction,and the foreset layer can extends as far as about 500?800m,while the width of foreset layer is about 700?1500m and foreset layer is uphill-arched cross the source direction.