Characteristics And Controlling Factors Of Ordovician Reservoir In Yangshuiwu Area Of Jizhong Depression

The exploration history of buried hill in the Jizhong Depression has been more than40 years.In recent years,through three-dimensional seismic exploration and fine interpretation,Huabei oilfield company discovered a series of oil and gas reservoirs in this area,which have good exploration potential in general but vary in productivity in different areas.Previous studies from this area mainly focused on the formation conditions and structural characteristics of oil and gas reservoirs,while the study on the reservoir characteristics and control factors of Ordovician strata was weak,which restricted the further exploration and development.This paper takes sedimentology,reservoir geology,and structural geology as theoretical guidance,combined with the north China platform of the Ordovician sedimentary environments and tectonic background,as well as cores,thin sections,geochemical analysis and a series of methods,the petrological,physical and reservoir spatial characteristics of the Ordovician buried hill are described..Through the analysis of diagenetic evolution process,the controlling factors of reservoir development,the following conclusions are made:(1)The Ordovician in the study area is a tidal flat deposit on the epicontinental sea,and its sedimentation is gentle,with small differences in paleomorphology.According to the characteristics of location,energy and lithology,it can be subdivided into three subfacies:the upper-tidal zone,the intertidal zone and the subtidal zone.(2)The Ordovician reservoirs in the study area are mainly distributed at the bottom of the lower section of the Fengfeng Formation,the upper part of the upper section of the Upper Majiagou Formation,the bottom of the lower section of the Upper Majiagou Formation,the top of the upper section of the Lower Majiagou Formation,the bottom of the lower section of the Lower Majiagou Formation,the middle of Liangjiashan Formation.The reservoir space is mainly secondary intercrystalline dissolution pores,tectonic fractures,dissolution fractures and intergranular dissolution pores.The reservoir lithology is mainly dolomite and dolomite limestone.The fractures are developed but mostly filled,and there are three-stage fillings can be seen under the cathode light.overall,the reservoir has an average porosity of 2.05%and an average permeability of 1.90×10~3?m~2,which is a low-porosity and low-permeability reservoir.(3)Various types of diagenesis are developed in the Ordovician in the study area,of which constructive diagenesis includes dissolution,dolomitization and tectonic disruption,and destructive diagenesis includes compaction,pressure solution,cementation and recrystallization.(4)The development of the Ordovician reservoir in the study area is controlled by three factors:sedimentation,diagenesis and tectonic.first,the microfacies beneficial to the reservoir space are mainly the dolomite flat microfacies,the limestone flat microfacies and the dolomite limestone flat microfacies in the intertidal-upper tide zone.second,the dolomitization and dissolution in the sedimentary to pene-sedimentary period and the dissolution in the supergene period are the most important diagenesis processes to improve reservoir quality.finally,the fractures generated by tectonic activities improve the reservoir performance and provide a seepage channel for dissolution.By studying the sedimentation,reservoir characteristics and controlling factors of Ordovician buried hill reservoirs in the study area,the theoretical study of the Ordovician sedimentary environment and reservoir characteristics in the study area has been enriched,which also provides a good guidance for the further exploration and development of oil and gas.