Characteristic Analysis On Extra-low Permeability Reservoir And Oil Pool For Group Chang 6 Of Jiyuan Area In Ordos Basin

The subject of the paper is Group Chang 6 of Jiyuan Area in Ordos Basin.On the basis of analysis of stratigraphic division and correlation,characteristics of tectonic,sedimentary,diagenetic and pore texture,it is summarized that the main controlling factors of reservoir and distribution of predominant reservoir in the research area.Sedimentary facies,diagenetic facies,porosity,permeability,thickness of single sand body and pore structure index were selected to evaluate the reservoir.Furthermore,On the basis of analysis of water/oil layer identification,oil reservoir assemblage and distribution,it is summarized that the main controlling factors of accumulation,oil and gas enrichment law and accumulation model,which can guide hydrocarbon exploratory development in the research area and similar low permeability reservoirs.Based on casting sections,intrusive mercury curve and logging data,it is analyzed that the features of lithological composition,porosity and permeability distribution and pore texture in the research area.The reservoir of Jiyuan area is typical of low porosity and extra-low permeability.For the evaluation of extra-low permeability reservoir,the pore structure index is introduced which takes into account five facts which are porosity,maximum intake mercury saturation,median radius,displacement pressure and sorting coefficient.It is selected that 136 samples in research area to get on the mercury experiment.According to pore structure index and mercury curves,the reservoirs are divided four types.The pore structure index is the larger,the higher the well test fluid in the appropriate intervals.The main controlling factors of the reservoirs in research area include sedimentation,secondary dissolution and deep overpressure.It is suggested that the chlorite cementation zones,secondary pore zones and overpressure zones of distributary sand bodies in the submerged delta frontier are the most favorable belts for development of reservoirs.On the basis of the coincidence of the three porosity curves which are neutron log,density log and acoustic travel time,the porosity curve index is constructed.Furthermore,the relative deep induction log and the relative acoustic travel time are introduced,and the fluid identification index is constructed.According to logging data in the research area,integrated fluid identification index and water productivity,the plate is established to identify the different reservoirs.By processing the 68 wells and comparing oil test data in the study area,the accuracy rate of the plate on water/oil layer identification is 80.9%.Through the analysis of accumulation assemblage and characteristics,there are five main control factors in Jiyuan area which are hydrocarbon source rocks,surplus pressure,sedimentation,diagenesis and tectonism.However,the main control factors have a different effect on the different layer reservoirs.Overall,from Chang 6₃ section to Chang 6₁ section,sedimentation and diagenesis have a gradually failing control,while tectonism has a gradually increasing control.The farther the distance away Chang 7 source rock,the weaker the control of source rock and surplus pressure.It is believed that there are mainly three accumulation models in the study area.One is the source rock diagenetic facies model,widely distributed in the northwest provenance.Another is the sedimentation diagenetic facies model,mainly in Chang 6₃ and Chang 6₂ section in the northeast provenance.The last one is tectonic sedimentation facies model,mainly in Chang 6₁ section in the northeast provenance.