Characteristics Of Carboniferous Volcanic Reservoirs In Hashan Area,Northwest Margin Of Junggar Basin

Taking the Carboniferous volcano rock revealed by the 5 wells in the Hashan area in the northwestern margin of the Junggar basin as the research target,combined with previous research results,this thesis is going to summarize its lithology and lithofacies types by using cores,cuttings and well-loggings.On this basis,the effective reservoir space types and their combination characteristics,evolution characteristics will be further generalized as well by the application of cores and thin sections observation,combined with the measured porosity and permeability data,NMR porosity data,oil saturation and plane porosity data,the dominant lithology and lithofacies types of effective reservoir in this area also will be identified.Some primary conclusions have been drawn as followed: 1.Lithology,lithofacies and the effective reservoir space typesThere are six categories & twenty-five types of igneous rocks,where the basic is the most and the secondly is the neutral;four lithofacies & nine sub-lithofacies of volcanic lithofacies,where the air-fall subfacies are the most and the secondly is the lower effusive subfacies;two categories & four sub-categories & fifteen types of effective volcanic reservoir space,and eight types of the assemblage of pore and fissure,where the secondly pore and fissure is the most,existing in the studied area.2.The dominant lithology and lithofacies types of volcanic reservoirThe air-fall subfacies have the best economic significance on the whole,the related lithology types mainly include basaltic pyroclastic rock,andesitic pyroclastic rock,dacitic pyroclastic rock,rhyolitic pyroclastic rock and composite pyroclastic rock,and then the secondary effective sudfacies are lower effusive subfacies,pyroclastic flow deposit subfacies and upper effusive subfacies,however,volcanic conduit facies and volcanogenic sedimentary facies are going to be ineffective reservoirs for their lowest measured porosity and permeability.3.The influencing factors,evolution process and development degree of reservoir spaceThe volcanic reservoir space in the studied area is affected by lithology,lithofacies and diagenesis.Its formation and evolution process can be divided into three stages & five substages.The dominant effective reservoir space is secondary pore and fissure,while effective primary pore and fissure maintain less.The interstitial dissolution pore and matrix dissolution pore in secondary pore are the best developed,which indicates the dissolution intensely improves the reservoir potentiality of the Carboniferous volcanic rock in the Hashan area.The shallow Carboniferous volcanic reservoirs have the best storage capacity in the studied area,which is related to the depth of the weathering crust in the area,and the depth that the quantity of the reserved primary pore is equal to that of the generated secondary pore occurs within the depth of the weathering crust.