鄂尔多斯盆地ZR106区块长6段致密砂岩储层地质特征OA

The Chang 6 member of the Yanchang Formation in the Ordos Basin is one of the key horizons for continental tight oil development in China.This study focuses on the Chang 6 member in the ZR106 block of the Longfang area.Based on data from cores,casting thin sections,scanning electron microscopy(SEM),mercury intrusion porosimetry,and well logging,a systematic investigation was conducted on the petrology,reservoir physical properties,and pore structure characteristics of the tight sandstone reservoirs in the study area.On this basis,the types and characteristics of diagenesis were analyzed in detail,and their influence on reservoir development and evolution was further discussed.The results show that the sand bodies in the Chang 6 member of the study area are mainly controlled by sandy debris flows and turbidite channels.The reservoirs are primarily composed of feldspathic sandstones,with occurrences of lithic feldspathic sandstones.The feldspathic sandstones can be categorized into three types:pure sandstones,mixed sandstones,and transitional sandstones.The Chang 6 reservoirs in the study area are characterized by generally low porosity and ultra-low permeability,forming typical tight reservoirs.Their pore systems exhibit a combination of secondary dissolution pores and residual primary intergranular pores,along with the development of a small number of microfractures.The pore structures of the reservoirs can be classified into four distinct types.Compaction and cementation in the Chang 6 reservoirs have a destructive effect,reducing porosity,whereas dissolution plays a constructive role by enhancing and preserving porosity.The presence of chlorite coatings,acting as a"protective shell"is a key microscopic indicator for distinguishing high-quality reservoirs from tight zones.The Chang 6 sandstones in the study area are currently at the middle diagenetic stage A,and intensive dissolution is the critical factor for improving reservoir quality.