Volcanic Eruption Environment And Reservoir Significance Of Late Paleozoic In The Junggar Basin

The Late Paleozoic volcanic rocks are widely distributed in Junggar Basin,which is closely related to oil and gas reservoirs and the potential of development should not be underestimated.The volcanic rocks are dominated by subaerial eruptions,and underwater volcanic rocks have been discovered successively.However,the identification marks of the two and their reservoir significance need further study and comparison.Based on the previous research results,in the study area,Lithology,lithofacies and reservoir space classification scheme have been concluded by profile survey,measurement of volcanic edifice,rock-mineral determination,casting slice and geochemistry,then the environment and mode of volcanic eruption and the influence on reservoir are studied.Primary understanding and the conclusions are as follow:1.Lithology and lithofacies characteristicsLithology and lithofacies classification schemes have been identified.The cocanic rocks of Late Paleozoic in Junggar Basin have been divided into 4 genetic types,33 specific lithology,and 4 types,14sub-facies.2.Identification of eruption environmentThis paper presents a comparison of environmental characteristics of volcanic eruption in the study area.The scheme is divided into two levels: the main method and the auxiliary method:Characteristic lithologic type,lithologic combination,characteristic structure,alteration characteristics,features of occurrence,pore characteristics and Lithofacies characteristics,color of the rock,development scale and Fossil assemblage.3.Establishment of volcanic eruption patternThe central eruption model of two eruptive environments,land and underwater,has been established.The subaerial volcanic edifice is formed by magma moving along the volcanic channel to the earth's surface and directly contacting the air,volcano neck subfacies for the center zone,and the external eruption outbreak appear alternating,the plane distribution is mostly concentric,and no particular rock type.Underwater volcanoes are formed by the movement of magma along volcanic channels and contact with water,the internal subfacies of the intrusive facies are centered,and the whole is in a dome shape,and is covered by the outer subfacies of the intrusive facies,and it is obvious that there are some special rock types,such as perlite,lithophysa rhyolite and bentonite.4.Reservoir space type and combination characteristicsThis paper sums up the division of volcanic reservoir space in the study area.The scheme is divided into 2genetic types,20 kinds of reservoir space,and 10 types of reservoir space combination are determined: Stomata type,fracture type,pore type,stomata + fracture type,stomata + dissolution pore type,fracture + devitrification pore type,pillow packing type,stomata + secondary pore + fracture type,intergranular pore + dissolution pore + fracture type and dissolution pore + fracture type.5.Influence of eruption environment on reservoirThere are many types of reservoir space,stomatal type combination is very common,and Columnar joints,layered cleavage fractures,dissolution pores are more developed,these factors will enhance reservoir performance in the subaerial eruption environment.The porosity is not developed,the fissures are filled and the strong alteration will reduce the reservoir performance,but devitrification,lava ball/pillow pore-fracture and the potential effects of organic matter on volcanic rocks will enhance reservoir performance in the subaqueous eruption environment.On the whole,the reservoir performance of subaerial eruption environment is better than that of underwater eruption environment.