| With the increasing demand of global energy and the sharp drop of conventional resources,unconventional oil and gas reservoirs,represented by tight oil reservoirs,are increasingly emphasized by oilfield developers.Different from the tight sand reservoirs,tight sandstone conglomerate reservoirs are lithologic oil-gas reservoirs.During the deposition process,multi stage of sedimentary fan body overlaps with a lower maturity degree of rock particles,and particles with different sizes are mixed,so the sorting of the tight sandstone conglomerate reservoir is poor.And under a variety of diagenesis process,the contact relationship between particles is tighter and the rock microstructure is complex,which makes it difficult to evaluate and explore the tight sandstone conglomerate reservoirs.Predecessors have conducted extensive research works on tight sandstone conglomerate reservoirs in the analysis of sedimentary and diagenetic characteristics,analysis of main controlling factors of reservoir accumulation,division of rock physical phase,and reservoir prediction.However,due to the strong heterogeneity of pore structures in tight sandstone conglomerate reservoirs and the law of the characteristic of the electrical properties and fluid distribution is unclear,the evaluation method of the pore structure and saturation in the tight sandstone conglomerate reservoirs is necessary to be studied furter.In order to improve the evaluation accuracy of the tight sandstone conglomerate reservoir,based on the analysis of rock physics experiments,combined with sedimentation and diagenesis,this paper makes clear the main affect factors of pore-throat structure and saturation of the tight sandstone conglomerate reservoir firstly,and then proposes a new model for evaluating pore structure and saturation.Thesis research achieved the following results and cognition.(1)The lithology of the tight sandstone conglomerate reservoir rock can be divided according to the grain size,and fine-grained conglomerate and small conglomerate are the main lithologies,the lithologies with the best oiliness are gritstone and fine-grained conglomerate.This paper brought in artificial intelligence method to identify the lithology of the tight sandstone conglomerate reservoirs,and used well logging data to complete a point-by-point lithology identification through the programming based on the FORWARD platform,which can decrease the reservoir heterogeneity caused by lithology and give a good base for the tight sandstone conglomerate reservoir evaluation.(2)Existing characterization techniques have their own advantages and disadvantages in evaluating the pore structure of tight sandstone conglomerate reservoirs.High-pressure mercury intrusion can characterize the micro-pore information of the reservoir rocks,but it can't distinguish pore and throat information.Constant-pressure mercury injection can separate the pore and throat information,but due to the maximum mercury-injection pressure limit,the pore throat information with a radius less than 0.119?m cannot be reflected.The pore throat radius distribution of the saturated T2 spectrum after the pore-throat correction is wider,but the original nuclear magnetic T2 spectrum reflects the hydrogen information of the rock fluid,which needs to be converted to the pore-throat distribution curves according to the conversion coefficient.Although the cast thin section and scanning electron microscope can intuitively characterize the pore structure characteristics of the rocks,but it can't directly extract the pore structure characterization parameters.Studying the advantages of constant velocity mercury injection,high pressure mercury injection,and nuclear magnetic resonance in evaluating the distribution of the pore throat radius,the ffull-scale throat radius distribution curve of tight sandstone conglomerate reservoirs was reconstructed,and the rock pore throat distribution characterized by the reconstructed curves is more comprehensive and accurate.(3)The main controlling factors affecting the pore structure of tight sandstone conglomerate reservoir rocks are diagenesis and lithology.The effect of compaction,cementation and filling on the pore structure of the tight sandstone conglomerate reservoirs are obviously damaged.The smaller the reservoir rock grain,the higher the content of the inter-grain pore and the better the pore structure of the reservoir rocks.This paper brought in the rate of compaction,the rate of cementing and the rate of micro-porosity to express the strength of the influence of diagenesis on the pore structure.Combined with the correlation between the pore structural characterization parameters and diagenetic strength parameters,the sensitive parameters of the pore structural characterization about the diagenesis were extracted,and a quantitative evaluation model of the pore structure was established by multi-parameter fitting.Based on the lithology identification technology and the analysis of the pore structure effects of sedimentary and diagenetic processes,the type of pore structure of reservoir rock was classified into type ?,?,and ? from good to bad.(4)The results of the rock electrical experiments show that the electrical parameters of the reservoir rock show a significant nonlinear relationship with each other,and the traditional Archie formula is not suitable to evaluate the saturation of the tight sandstone conglomerate reservoir.The study identified that the main controlling factors affecting the saturation evaluation of tight sandstone conglomerate reservoirs are pore throat structure,wettability,and lithology.Combined with rock electricity experiments,the values of rock electrical parameters for different lithologies were determined,and saturation was calculated according to different lithologies.At the same time,a cementation index model was established based on the parallel conducting mechanism of rock with NMR logging.The calculation model of cementation index considering the influence of pore structure was established by introducing the tortuosity and the parameters of pore cross section shape.Combined with the SDR model of nuclear magnetic resonance,the calculation model of the saturation index of tight rock conglomerate reservoirs was deduced by introducing pore cross section shape under different wetting environments.(5)Based on comprehensive application of the pore structure and saturation evaluation methods,the integrated quality of the test reservoirs of tight sandstone conglomerate reservoirs was evaluated by using porosity,pore structure parameters,pore structure types,oil saturation,and lithology as comprehensive evaluation criteria.Twenty-five wells and thirty-five test intervals were used to evaluate the application effect,and the rate of conformity was 87%,which proved that the research method of the paper had a good adaptability for the evaluation of tight rock conglomerate reservoirs.Through the studies of experiments and theories in this paper,the characteristic of pore-throat structure and rock electrical of tight sandstone conglomerate reservoirs have been clarified.Meanwhile,the main influencing factors of pore throat structure and saturation in tight sandstone conglomerate reservoirs have been revealed.Combining geological analysis and rock physics experiment results,a set of qualitative and quantitative evaluation methods for pore-throat structure of tight sandstone conglomerate reservoirs have been established.Also,the new calculation methods for saturation exponent n and cementation index m are established based on considering the influencing factors,which improves the calculation accuracy of oil saturation in tight sandstone conglomerate reservoirs and has realized the refined evaluation of the tight sandstone conglomerate reservoirs. |
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