| The Wangjiagang area is located in the east of the southern slope of the Dongying Depression and is an important oilfield area in the Dongying Depression.The upper part of the fourth member of the Shahejie Formation is a lacustrine carbonate rock with complex oil and gas distribution.In order to reduce the exploration and development costs and clarify the sedimentary laws,the sedimentary facies of the lacustrine carbonate rocks and favorable reservoirs in the fourth member of the Shahejie Formation in the study area were studied.Based on the geochemical indicators such as carbon and oxygen isotope characteristics,trace elements,and sporopollen,the sedimentary environment elements such as paleo-sedimentary background,paleoclimate,paleo-salinity,and ancient material source were analyzed.The study found that the evolution of sedimentary environment in the upper part of the 4th member of the Shahejie Formation was divided into three stages: In the first stage of the low-level domain,the climate was arid and hot with high salinity and abundant terrigenous debris.During the second phase of the invasion of the lake,the water body quickly deepened,the ancient climate changed from arid and hot to warm and humid,the ancient salinity was low,and the source of the ancient material was reduced in two directions.During the period of low three-stage high horizon,paleo-salinity in the paleoclimate is relatively stable with small changes,which is favorable for the development of lacustrine carbonate rocks.Through the identification of more than 150 microscopic thin sections in the study area,the main rock types in the study area were divided into composition-structure,mainly including: micritic limestone,granular limestone,mixed rock and other rock types.The logging lithology in the study area is interpreted as undifferentiated limestone or dolomite,and the lithology accuracy is not enough.Therefore,the gray correlation method is used to identify the core types of rock wells,and the lithology-electricity is established using the well logging data in the study area.The standard identification template identified a total of 22 major lacustrine carbonate rock types.After inspection of the thin sheet data,the recognition effect is better.Combined with the characteristics of lithologic combination,sedimentary structure,logging characteristics,and phase sequence,the lacustrine carbonate rocks in the study area were divided into four types of lithofacies: the combination of grain-micrite limestone and dolomite limestone interbed,muddy argillaceous limestone combination,mixed layer system combination.The characteristics of the lithofacies distribution and the depositional environment it represents are summarized.Based on the petrological characteristics of the 12 wells in the study area,the division of petrofacies and the analysis of single well profiles,combined with the regional sedimentary background in the study area,the main sedimentary facies of the upper submember of the Fourth Member of the Shajiajie Formation in Wangjiagang were summarized.According to the distribution characteristics,it was determined that the upper sub-segment of the Shahejie Formation in the study area is a carbonate beach-bain facies deposit,and four sedimentary microfacies,ie,limestone beach,cloud-rock beach,grain beach,and mixed beach are mainly developed.Based on the study of major types of reservoir space and main controlling factors in the study area,combined with test oil test production and pore permeability data,the prediction of the favorable facies zone in the study area is divided into three ca tegories.Among them,grain beach and Yunyan Beach are the better reservoir areas,followed by limestone beach.Based on the above research,favorable exploration target areas were proposed. |
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