Diagenesis And Reservoir Evaluation In Ⅻ Sand Group Of The Third Member Of Qingshankou Formation, Daqingzi Oilfield, Songliao Basin

Daqingzi Oilfield contains profuse petroleum resources, but diagenesisand diagenetic facies which play the key roles in the formation anddistribution of reservoirs are not only focal points but also difficultpoints currently. Especially, the research to the diagenetic facies isinadequate. Based on former studies, using cores, well logging andmodern laboratory analysis materials, along with new technologies andtheories of geology and laboratory assay, pore types，heterogeneity andcontrolling factors of reservoir quality have been analyzed. Collectiveevaluation to sandstone reservoirs in the study interval has been madeon the basis of reservoir quality and single well reservoir evaluation.Lithology could mainly be interpreted as Lithic Arokose and a sort ofFeldsparthic Litharenite, of which both component maturity and structuralmaturity were low, according to the statistic analysis results of coresample sections from Ⅻ sand group of the third member. Sandstonereservoirs of the study area have undergone complicated diagenesistransformations such as consolidation, cementation, dissolution,replacement, etc. Sandstone reservoirs from Ⅻ sand group of the thirdmember could be deduced as being in the middle diagenetic phase A,according to organic substance maturity, clay mineral types andtransformation, relative content of smectite in illite-montmorillonitemixed-layers, evolution properties of pores, and the combination,distribution, evolution as well as the forming order of some authigenicminerals.The study interval could be characterized by mixed type property which contained both primary pores and secondary pores, according toobservations on casting sections and SEM methods. The major pore typesare inter particle pore, dissolved inner particle pore and mold pore,while the first type is most common. There are also some fissure poresand a small amount of extraordinary big pores. Six diagenetic facies-compaction diagenetic facies, carbonate-cementation facies, unstablecomponents dissolution facies, siliceouscementation facies, albitediagenetic facies and fracture diagenetic facies.-diagenesis facies-havebeen identified based on diagenetic phases, diagenetic types androck-forming mineral microscopical analysis. Diagenesis processesimpacting the quality of a reservoir contain consolidation, cementationand dissolution, since only the third process of the three favors thephysical properties of a reservoir by improving the porosity. A smallarea of secondary pores was inferred to exist between1890m to1920munder the sea level. The reservoir was evaluated based on the researchof diagenetic facies and diagenetic evolution, by combining regionaldistribution of sedimentary system, the distribution and evolution ofreservoirs, heterogeneity of porosity and permeability. The horizontaldistribution of reservoir layers was dominated prominently by sedimentaryfacies according to the analysis of the horizontal distribution figureof small layer reservoir evaluation. Especially,38,39and40smalllayers have fine reserving capability.