Research On Diagenesis And Sweet Spot Prediction Of Fuyu Oil Layer In Zhongxin-Qianguonan Area

The reservoir quality of Fuyu oil layer in Zhongxin-Qianguonan area is relatively different,low permeability and ultra-low permeability reservoir developed at the same time,diagenesis has significant impaction on the reservoir quality.Therefore,based on microcosmic experiment,combined with core analysis test data,logging and oil test data,with the study of reservoir characteristics,we carried out the study of diagenesis and diagenetic facies,analyzing the main control factors of sweet spot development,predicting the distribution of sweet spot reservoir.This paper made the following findings:(1)The reservoir is composed of feldspathic litharenite and lithic arkose.The reservoir quality is poor,primary pores are the main parts of porosity,and dissolution pores improve reservoir quality.The ultra-low permeability area developed ultra-low permeability reservoir,with high displacement pressure and poor pore-throat connectivity.The low permeability area developed low to ultra-low permeability reservoir,with low displacement pressure and relatively good pore-throat connectivity.The forth layer of sand group ? and the fifth layer of sand group ? are in relatively good quality.(2)The reservoir is strongly affected by compaction,the compaction is the main factor of porosity reduction,the reduction of porosity by compaction is higher in ultra-low permeability reservoir than it in low permeability reservoir.The main types of cements are siliceous and carbonate,and the main clay minerals are I/S mixed-layer and illite.Dissolution has slight effect on the improvement of porosity,the reservoir is in A period of the middle diagenetic stage,the diagenetic sequence is compaction-early calcite cementation-early siliceous cementation-feldspar dissolution – ferrocalcite cementation-ankerite cementation-pyrite cementation.(3)With the help of quantitative parameters as the compaction rate,the cementation rate and the improvement of dissolution and their corresponding limits,we found five diagenetic types: fine sandstone with strong compaction and weak cementation and weak dissolution diagenetic facies,fine sandstone with strong compaction and medium cementation and weak dissolution diagenetic facies,fine sandstone with medium compaction and strong cementation and weak dissolution diagenetic facies,fine sandstone with medium compaction and medium cementation and medium dissolution diagenetic facies,siltstone with strong compaction and medium cementation and weak dissolution diagenetic facies.According to the logging value,We identified diagenetic facies on well and profile as well as plane.(4)Based on lithofacies factor and diagenetic facies,we found that the reservoir is mainly composed of fine sandstone and siltstone,fine sandstone has relatively good property.Compaction is the main effect of the ultra-low permeability reservoir while deposition factor is the main effects of the low permeability reservoir.The content of carbonate cement is higher in the sandstone and mudstone boundary.Dissolution strength is related to the distance from the fault.(5)According to relevance between diagenetic facies and oiliness,combined with sand body type and size,the reservoirs are divided into five kinds,then we predicted the sweet spot reservoir of the forth layer of sand group?.The type?reservoir is the sweet spot reservoir,mainly in Qianguonan area,developing fine sandstone with medium compaction and medium cementation and medium dissolution diagenetic facies.