Reservoir Characteristics And The Oil And Gas Distribution Of Carboniferous Volcanic In Dixi Area Of Junggar Basin

The volcanic reservoirs are becoming a hot spot in oil and gas exploration with thegrowing demand of energy and the technology progress of oil and gas exploration. Thevolcanic rock types of Dixi area in Junggar basin are complex. The volcanic edifices weredistorted and deformed seriously, additionally weathering, and leaching, made the volcanicreservoir more complicated. As a result, the oil and gas distribution remained unclear,restricting the progress of oil and gas exploration of volcanics. So the reservoir characteristicsand oil and gas distribution of volcanic become the urgently need of volcanic oil and gasexploration. Integrated with methodologies of geosciences, geochemistry and geophysics, thelithology, reservoir and hydrocarbon accumulation characteristics were studied. The researchresults could be summarized as follows.There were basalt, andesite and rhyolite of volcanic lava, volcanic breccia and tuff ofpyroclastic rock, orthophyre, ivernite and granite porphyry of subvolcanic rock and volcanicsedimentary-pyroclastic rocks. The volcanic facies were subdivided into explosive facies,extrusive facies, volcanic conduit facies, subvolcanic facies and volcanic sedimentary faciesaccording to the occurrence place and the types of the volcanic.According to the idea of―point-line-surface‖, the volcanic eruption centers were firstlyforecasted by geological recognition marks. And then profiles of the volcanic edifice weredistinguished by three-dimensional seismic data. Finally, the planar distributions of volcanicconduits were forecasted by amplitude time slice, coherent time slice and trend surfaceanalysis. Then the types of the volcanic edifices were identified. The volcanic conduits ofCarboniferous ancient volcanic edifices underground in the research area generally distributedalong the faults. And a central volcanic edifice was found in the area of Dixi10well.Base on the calibrating of cores, the well logging identification process of volcanic wasset up. Additionally, the seismic data was calibrated by well loggings. The seismic facies weresubdivided into strong amplitude medium succession reflection seismic facies, weakamplitude bad succession reflection seismic facies, medium amplitude medium successionreflection seismic facies, lenticular chaotic reflection seismic facies and columnar chaoticreflection seismic facies which corresponded to effusive facies, volcanic sedimentary facies,explosive facies, subvolcanic facies and volcanic conduit facies. The macro distribution range of volcanic was predicted by the gravity and magnetic data. The plan distribution of seismicfacies was predicted by seismic facies and single well facies.Through researches on reservoir space, reservoir property and digenesis of volcanic theresults showed that the secondary solution pores and fractures were the main reservoir spacesof volcanics. Volcanic reservoir was middle porosity and low permeability. There were10kinds of diagenesises in volcanic reservoir. The diagenesises which could improve thereservoir property of volcanic were vaporization of volatile matter, condensing constriction,dissolution and weathering. And the filling of volcanic hydrotherm and buried filling were themain diagenesises which destroyed the reservoir property of volcanic. The diagenetic stageswere divided into syngenetic diagenesis stage, exodiagenesis diagenesis stage and burialdiagenesis stage. Combined with burial history, the diagenesis evolution models of explosivefacies, extrusive facies and subvolcanic facies volcanics were rebuilt. Through analyzing thecontrolling factors of the volcanic reservoir, the results showed that the volcanic facies werethe basis factors affecting the reservoir physical property. The weathering and tectonicfracturing were the keys of reservoir reforming. The explosive facies, extrusive facies, andsubvolcanic facies in the coupling region of craters-near craters and structural high werereformed strongly which reservoir physical property was better. Combined with the spatialassociation of volcanic edifice and reservoir, four kinds of volcanic reservoir geologic modelwere built. The basic and intermediate lava of peltate fissure volcanic edifice which waswidely distributed suffered from weathering and could form large area of effective reservoir.The reservoirs of pyroclastic rock, subvolcanic rock and acidic lava were of limiteddistribution. The reservoir physical property of fissure volcanic edifice was better than centralvolcanic edifice. The reservoir physical property of basic and intermediate lava andpyroclastic rock reservoirs was better than that of subvolcanic rock.Through analysis of controlling factors of volcanic oil and gas distribution, the resultsshowed that the distributions of oil and gas were controlled by the hydrocarbon depressions.Reservoir property of volcanic in the weathering and leaching zones near the unconformitywas better which controlled the vertical distributions of oil and gas. The positive structures insuccessive paleo-uplift were favorable areas of oil-gas accumulation. The deep faults were themain migration pathways of oil and gas which controlled the oil-gas accumulation. Thevolcanic rock body controlled the scale of reservoir. The volcanic hydrocarbon accumulationmodel―accumulation controlled by faults and positive structures–reservoir controlled byvolcanic body of weathered crust‖was thus established by the above mentioned.