Reservoir Characteristics And Controlling Factors Analyzing Of Low Porosity,Low Permeability Sand Reservoir,Jiyuan In Ordos

It is observed that low permeability reservoir characteristics and controlling factors are unclear in Triassic Yanchang formation in Ordos Basin Jiyuan region.In response to this issue,resolution sequence stratigraphy,sedimentary facies and diagenesis studies are carried out in the research area by a comprehensive analysis of outcrop,rock core,well logging and laboratory analysis data,based on high-accuracy sequence stratigraphy,modern sedimentology and reservoir geology theories.Five levels of Yanchang formation's high-accuracy sequence stratigraphic framework have been established in the research area and spatial and temporal evolution of key sequence stratigraphic framework,depositional systems,micro-reservoir and control factors have been analyzed.A forecast of favorable reservoir zone of the research area is conducted on the basis of the above studies.The main findings and conclusions are stated below.This study clarifies the characteristics and structure of each sequence boundary of Yanchang Formation in Jiyuan Area.It identifies one second-order sequence,five third-order sequences,17 fourth-order sequences,and 36 fifth-order high accuracy sequences.The third-order sequence is characterized by the incise waterway unconformity.Based on the logging,drilling,and rock core data,the initial and maximum transgressive surfaces are recognized,and the sequences are divided into lowstand,transgressive,and highstand system tracts.To analyze reservoir characteristics and diagenesis,high accuracy chorostratigraphy contrasting frameworks are set up and meandering deltas,lakes,other depositional systems and 13 genetic units are identified.The disertation also illustrates the genesis,structure and distribution of the depositional systems,and analyzes the major depositional systems,and their filling and evolution patterns in the sequence framework.In these sequences,the majority of lowstand system tract is strong progradational delta,while highstand system tract is mainly occupied by slow progradational delta and transgressive system tract by delta front and lacustrine clay deposits.Based on the reservoir data of different sedimentary units,it is concluded that the reservoir sandstone in the study area has the following characteristics:mainly fine sandstone,medium-good sorting,medium roundness,cemented porous,variety of fillings,low porosity and very-low to ultra-low permeability.In accordance with the diagenetic mechanism,Compaction,pressolution,cementation,denutation and metasomasis diagenesis are identified.and the relationship among base level cycling,micro sedimentary facies differentiating and diagenetic transformations are studied.Different diagenetic naming schemes are proposed according to the various daigenesis in the several layers.The study indicates that the prospecting zones are a favorable target of "sandstone depositional unit + sandstone with relatively large granule and good physical property + constructive diagenesis".