Research On Low Permeability Reservoirs Characteristics And Favorable Reservoirs Prediction Of The Middle Es₃,Daluhu Oilfield

Low permeability reservoir is affected by sedimentary,diagenetic and tectonism.In research,because of its complicated genesis and reservoir heterogeneity strong,it is difficult to predict the favorable reservoir and going against the high efficiency development of the low permeability reservoir.This study analysised distribution and evolution of sedimentary facies and the evolution law of diagenetic and reservoir spatial under the control of lithofacies on the base of summarizing the types of lithofacies and their combination patterns,concluding the main controlling factors of different reservoir ‘dessert' and distribution of favorable reservoirs.Following conclusions are got.(1)The study area is located in the deep-semi-deep lake and belongs to hyperpycnal flows controlled by flood influx which transports sediments to the front of delta in the northern of Luxi Uplift.The depositional model on “inner fan-middle fan-outer fan” was constructed.The inner fan mainly develops the main water channel and subsea natural barrier,and the middle fan develops the braided channel,inter-channel,and sand dam,and the outer fan develops the leaf.12 lithofacies has been recognized and are further classified into 5 categories lithofacies combination patterns in this paper,according to the cores and the development of hyperpycnal flows.(2)Based on the study of sedimentary facies,we further research the diagenesis,diagenetic facies and reservoir characteristics.The results show that compaction,dissolution and cementification are the most.Combined with the types of lithofacies and diagenesis,we quantitatively calculate diagenesis intensity and synthetically name diagenetic facies.Finally,we divided eight diagenetic facies: snail fossil-feldspar strong dissolution-calcite strong cementation diagenetic facies,gravel-feldspar strong dissolution-strong compaction diagenetic facies,medium-coarse sand feldspar and calcite strong dissolution-medium compaction diagenetic facies,medium-coarse sand-feldspar strong dissolution-strong compaction diagenetic facies,medium-fine sand-feldspar and calcite strong dissolution-medium compaction diagenetic facies,medium-fine sand-feldspar medium dissolution-calcite strong cement-medium compaction diagenetic facies,muddy siltstone-mixed base filling compacted compact diagenetic facies,argillaceous sandstone-high plastic cuttings strong compaction diagenetic facies.The first six of them are the main diagenetic facies types in the study area.(3)Combined with mercury injection data,casting sheet and scanning electron microscope data,the pore structure of reservoir is divided into 6 categories on the base of the research on pore and throat.Type I is mainly distributed in medium-coarse sand feldspar and calcite strong dissolution-medium compaction diagenetic facies.Type II is mainly distributed in mediumcoarse sand-feldspar strong dissolution-strong compaction diagenetic facies.Type III is mainly distributed in medium-coarse sand-feldspar strong dissolution-strong compaction diagenetic facies.Type IV is mainly distributed in gravel-feldspar strong dissolution-strong compaction diagenetic facies.Type V is mainly distributed in medium-fine sand-feldspar medium dissolution-calcite strong cement-medium compaction diagenetic facies and snail fossil-feldspar strong dissolution-calcite strong cementation diagenetic facies.Type VI is mainly distributed in muddy siltstone-mixed base filling compacted compact diagenetic facies,argillaceous sandstone-high plastic cuttings strong compaction diagenetic facies.(4)Most of the fractures in the study area are high angle and full to semi-filling.Under the influence of the fault zone,dolomite strong cementation diagenetic facies can not be effective reservoir in the surrounding rock.(5)The origin of low permeability reservoir was analyzed from three aspects:sedimentation,diagenesis and structure.I to IV reservoir are the main oil and gas development areas and mainly distributed in gravel-feldspar strong dissolution-strong compaction diagenetic facies,medium-coarse sand feldspar and calcite strong dissolution-medium compaction diagenetic facies,medium-coarse sand-feldspar strong dissolution-strong compaction diagenetic facies,medium-fine sand-feldspar and calcite strong dissolution-medium compaction diagenetic facies of braided channel,inter-channel and sand dam.