Diagenesis Researches And Favorable Reservoir Predictions In The Damintun Depression

As the data collected from all over the world shows, one-third of oil and gas distributes inthe reservoir buried deeper than 3500 meters underground approximately . With the burial depthincreased , the reservoir characters become worse and worse until there is no commercial valueto exploit . Thus it is necessary for geologists urgently to know the diagenesis states in the deepburied reservoirs and the areas where favorable reservoirs developed in the deep horizonsexploration . We attempt to predict the areas favorable reservoirs developed in the horizontalorientation in the middle and deep horizons of Damintun depression in Bohaiwan basin , thenenrich and perfect the exploration technology of sandstone and conglomerate in the subtlereservoir ulteriorly by studies on diagenesis and evaluating methods of oil and gas reservoirs .As the results of the diagenesis researches show , the Tertiary reservoirs composed ofclastic rock in the Damintun depression can be divided into the early diagenetic stages and themiddle diagenetic stages , aggregately five subphases . It can be divided dominantly into fourdiagenetic facies , the early compaction and cementation , dissolution , dissolution and partialrecementation , strong compaction diagenetic facies . Three high porosity zones are developedin the vertical orientation . They almost occurre in the sandstones of channels , floodplains ,delta plains , branch channels and channel mouth bars of the delta fronts , fan-delta plains andfan-delta fronts , little in alluvial fan and shallow lake . According to the analysis of the factorsof the high porosity zones formation , we believe that the first high porosity zone formed bydissolution of meteoric waters and organic acids , the second one formed by dissolution oforganic acids , and the third one formed by dissolution of organic acids and dehydration of clayminerals .According to the evaluating methods of oil and gas reservoirs in PetroChina, the reservoirsof the Member 3 submember 4 of the Shahejie Formation are divided into 4 types . The areasdeveloped favorable and the relatively favorable reservoirs are blocked out by superposing thediagenetic facies map on the microfacies map . It's suggested that we should seek the traps anddo further explorations and researches in the areas .