Diagenetic Field Analyses And Reservoir Porosity Predictions In Yuanyanggou Region Of Liaohe Western Depression

Nowadays, more and more petroleum explorations have been aiming at subtle traps andlithologic traps at deep horizon as a result of the difficult shallow-layer petroleum explorationsand the decreasing oil production rate. Nevertheless, during being buried deeply, reservoir qualitybecomes poorer and poorer when the temperature and pressure get higher and higher, anddiagenesis is one of the most important influcing factors. Therefore, explorationists are eager tomake clear not only the diagenetic condition of deep reservoirs and the distribution of high-qualityreservoirs, but also the reservoir porosities.Diagenetic field is the integrated diagenesis intensity of every space point at one time. Thediagenetic phase and diagenetic facie of any layer and any area at any time could be obtained bydiagenetic field analysis, and the distribution of high-quality reservoirs could be determined.Today's diagenetic field analysis result of Yuangyanggou Region in Liaohe Western Depressionhas been shown as follows. At deep area, the middle and bottom parts of the third member ofShahejie Formation are between middle diagenetic phase B and late diagenetic phase with poorreservoir quality and tight compaction facie. However, those parts at the slope area are betweenearly diagenetic phase A and middle diagenetic phase A with relatively good reservoir quality,whose diagenetic facies are early compaction and cementation facie, dissolution facie anddissolution and cementation facie. In addition, the top part of the third member of ShahejieFormation is between middle diagenetic phase A₁ and middle diagenetic phase A₂ at deep area,whose diagenetic facies are dissolution facie and dissolution and cementation facie. It is possibleto find hydrocarbon reservoirs there, where source rocks, reservoirs and caprocks are developed.Reservoir quality is mainly influenced and controlled by sedimentary facies and diagenesis.Considering these two factors, reservoir porosity prediction models for different sedimentaryfacies were established. And the average error ?Φ between measured porosities and predictedporosities is less than 2.5% though the average pore-filling cements of the reservoirs is 16.1%. Asthe predicting result of the third member of Shahejie Formation in Yuanyanggou Region showed,the reservoir porosities of the third middle member and the third top member of ShahejieFormation are between 4.0% and 32.0%, and most reservoirs are effective hydrocarbon reservoirsexcept some reservoirs in the South Eastern part with porosities less than 5.8%;On the side, thereservoir porosities of the third bottom member of Shahejie Formation are mainly between 3.0%and 26.0%, and the area of effective hydrocarbon reservoirs obviously decreases.The result of practical lithologic traps exploration at Well Jin1 Area displayed that it wascertainly possible to predict high-quality reservoirs and reservoir porosities through Diageneticfield analysis before drilling. The predrilling porositiy predictions of Well Jin310 have only anaverage error of 1.3%, and commecial oil and gas flow is found with an output of 40t/d.