The Formation Mechanism of High Efficient Reservoir Chang 8 in Fuxian Area of Ordos Basin

The Chang 8 Reservoir in Fuxian Area of Ordos Basin was controlled by the sedimentation and diagenesis.It had the chatacters of fine particle size and low maturity,it was a compacted sandstone reservoir with local development high-efficiency reservoir.Based on observation of drilling cores,core thin section,scanning electron microscopy,energy spectral analysis and back scatter and so on,in combination with well logging data,an integrated study is performed,it indicates that the major control factors of high-efficiency reservoir Chang 8 include:reservoir property is better with the increase of grain size,and the property of fine sand is better than aleurolite;a amount of mudstone,biotite and carbonatite have obvious effect on reservoir property;the best reservoir property is developmed in subaquatic distributary channels of the delta fronts,mouth bar takes the second place;high-efficiency reservoirs have a relationship with the thickness of sandbody;the property of reservoir where rim chlorite cement is developed is better than that of poor rim chlorite.