Reservoir Diagenesis Characteristic Of The Upper Es₄ In Shengtuo-Lijin Area Of Dongying Depression

The paper has studied on the reservoir petrography,diagenesis features of the Upper Es4 in Shengtuo-Lijin area of Dongying depression using core,thin section,logging,welllogging,and combined with basin numerical simulation model and fluid inclusions data.In the end,we summarized the diagenetic evolution sequence and diagenetic facies and analyzed the heterogeneities of various features in different sequences and different sedimentary facies zones.Through the thin section examination we concluded that the study area is composed of feldspathic lithic sandstone and lithic arkose sandstone,the rock debris are composed of crystallized rock,intermediate-acid magmatite,limestone,dolomite,mudstone,and it's characterized by crystallized rock.The detrital composition is characterized by its low compositional maturity,and it's value increased with the increase of transportation distance.The diagenesises are complicated in the study area,which is characterized by multi-stages of cementation and dissolution.The porosity type is mainly composed of secondary porosity.Through the calculation of diagenetic parameters,we concluded that the mid-fan has higher compaction rate and intergranular dissolution intensity,the inner-fan and the terminal-fan have higher cementation rate;the hanging wall's reservoir has lower compaction rate,and the eastern part of the hanging wall's reservoir has lower cementation rate than the foot wall's reservoir,and the western part of the hanging wall's reservoir has higher cementation rate while the intergranular dissolution intensity is lower than the foot wall's reservoir.Through the examination of fluid inclusions' homogenization temperature,we concluded that the study area experienced one low maturity hydrocarbon expulsion(dongying period)and one high maturity hydrocarbon expulsion(guantao period-nowadays).Combined with basin numerical simulation model and fluid inclusions data,we concluded that the reservoir of Upper Es4 has experienced the diagenetic environment with early alkaline(48Ma-43.5Ma)— early acid(43.5Ma-24.6Ma)— late alkaline(24.6Ma-14Ma)—late acid(14Ma-0Ma).The reservoir is determined in the middle of diagenesis A stage and mid-diagenesis A2 in most area;the eogenetic diagenetic alterations include clays cementation,and dolomite-contained matrix recrystallization and calcite cementation,while the mesogenetic alterations include ferro-calcite and ferro-dolomite cementation,quartz overgrowths and so on.The study area's reservoir is composed of 5 diagenetic facies.The hanging wall of the study area's best reservoir are SQ4 and SQ2,and the foot wall of the study area's best reservoir are SQ4 and SQ2.In the sandstones which are porous cemented,the middle part of the sandstones have experienced acid-alkaline alternation completely,and have the best reservoir quality.The inferior-medium compaction strong dissolution diagenetic facies and the medium-strong compaction inferior dissolution bitumen-filling diagenetic facies are mainly distributed in the mid-fan subfacies,which have the best reservoir quality because of the strong activity of later acid fluid.The inferior compaction inferior dissolution matrix-filling diagenetic facies and inferior-medium compaction ferro-carbonate strong cementation diagenetic facies are mainly distributed in the inner-fan and the terminal-fan,and their reservoir quality is worse.The pattern of diagenetic facies evolution from the inner-fan to the terminal-fan is the main cause of the difference of reservoir quality.