Researches Of The Gravity Flow Depositions In Lake Basin And Reservoir Characteristics Of Chang6Reservoir In Huachi Area, Ordos Basin

Chang6reservoir of Yanchang Formation in Huachi area is high constructivedevelopmental stages of deltas, and it widely developted many gravity flowdepositions in deep-water fan. It developed thick massive sand bodies and thesandstone has large scale, and distribution of sand bodies is stable. The reservoirproperties are well, and the oil saturation is high. For this feature, based onsedimentological analysis, we combined with the core data, logging information andlaboratory analysis and so on, and rearshed the gravity flow sedimentary and reservoircharacteristics of Chang6reservoir in deep-water fan in lake basin in Huachi area.We found it develop slump, sandy debris flows and turbidite which are three kinds ofgravity flow types. They have different genetic mechanisms and sedimentarycharacteristics, and different combinations of types of distribution in inner fan, middlefan, outer fan of lake sediments. Combined with gravity flow within the basindepositional model, Chang6reservoir is divided into three small layers what isstudied, and the spatial distribution of gravity flow deposits are described by twoaspects characterize from gravity flow sedimentary facies and the sand body ofgravity flow. It found that gravity flow is well-developed in Chang63reservoir insemi-deep section of the lake environment, and sandy debris flow deposited sand ofthe three gravity flow deposits is thicker.By some analysis and testing of conventional sheet, casting sheet, scanningelectron microscopy, spectrum, we had analyzed the rock composition, particle size,interstitial material type and content, and rearched the reservoir characteristics ofChang6reservoir in Huachi region. The study found that sandstone reservoir ofChang6reservoir in Huachi region is affected by the nature of parent rock greater, asa whole they have this feature that compositional maturity is low, and texturalmaturity is medium–low. The major rock types include lithic feldspathic sandstone, and mineral composition is unstable, and the content of feldspar is relatively high.Interstitial material include mainly water mica, kaolinite, chlorite (film), calcareouscementation and siliceous cementation, and the main pore types include intergranularpores, intragranular dissolved pore, moldic pores. In the matter statistically, thecorrelation of porosity and permeability is good, and they are controlled by sand. Thephysical property of reservoir was northeast-southwest to stripped distribution. As awhole it shows that the northern physical property is good, and the southern physicalproperty is poor, and western physical property is better than the eastern physicalproperty.According to comprehensive research of gravity flow sedimentary characteristicsand reservoir characteristics, summarized the two factors which can control reservoirs:one factor is gravity flow type; other factor is diagenesis. Gravity flow deposits affectthe reservoir from three aspects:(1) Different types of gravity flow deposits determinedifferent rock types;(2) Porosity and permeability of deposited sandstone in differenttypes of gravity flow have large difference;(3) Different gravity flow deposits havedifferent control functions to reservoir properties. Different diagenesis have alsodifferent effects to Chang6reservoir of Yanchang Formation in Huachi region：constructive effects and destructive effects. Summing up the different styles ofdiagenesis affect the reservoirs of Huachi area, it can be divided into two aspects:(1)It exists positive correlation between the content of chlorite film with primary porosity,and plane porosity of reservoir in areas where the content of chlorite has a high rate oflevels is high;(2) It exists a correlation between the level of content of feldspar withintra-grain pores in the same sand belt.The results not only has important theoretical significance, but also has importantpractical significance for deepening the research of gravity flow in deep-water fan inthis area and efficient development of the gas resources in deep-water fan of Chang6Chang6reservoir in Huachi area.