Characterization And Effectiveness Evaluation On The Carboniferous Volcanic Reservoir Spaces In The North Of Chepaizi Area

The Chepaizi area is located in the north-west edge of Junggar basin.Industrial oil flow has been discovered in the Carboniferous volcanic rocks.At present,the exploration degree of Carboniferous is very low in the north of Chepaizi area.Especially,the type of rocks in the reservoir is not clearly known,the type,the combination and the distribution of the reservoir spaces are not clear,the effective reservoir space identification is difficult,which seriously hinders the exploration and development process of the oil field.Aiming at these problems,the core,lab analysis,well logging as well as dynamic performance are utilized to classify the types of igneous rock,furthermore,the storage space and combination type,features discrimination,distribution,heterogeneity and effectiveness of pore space are studied with the help of rock mechanical lab test.The main results and understandings are illustrated as follows:(1)The rock type and features in the study area are illustrated herein that,there are totally three types of igneous rocks: the volcanic lava rock,volcanic-clastic rock and volcanic clastic-lava rock,which are characterized by 6 most developed rocks,such as basalt,andesite,andesitic basalt,basaltic breccia lava,basaltic breccia,and volcanic tuff rock.(2)Three types of reservoir spaces are identified,they are pores,vugs and cracks,and there are nine small classes.It is thought that there are mainly 5 combinations of reservoir spaces,that is,isolated pores,connected pores,fractures,fractures-pores,pores-fractures-vugs.The physical properties of pores-fractures-vugs' combination are best,while the physical properties of isolated pores are the worst.(3)The lithologic,vertical and areal distribution rule of storage space is revealed so as to construct the 4 storage space combination,that is,isolated,multiple superimposed,cyclic superimposed and transitional modes,and then the 3D models of lithology,pores and vugs,fractures and combinations of reservoir spaces are established in the study area.The lithology,the physical property of the matrix and the combinations of various types of reservoir spaces are defined in the three-dimensional space,and the geometric shape of the fractures in three dimensional space is depicted.(4)The method to quantitatively characterize the heterogeneity of storage space in the volcanic rocks is established.The heterogeneity composite index is calculated based on the parameters of rock structure,fracture,erosion and rock property,therefore the evaluation criteria for the heterogeneity of the reservoir spaces of volcanic rock are established.Pointed out that the pores-fractures-vugs' combined heterogeneity is the strongest,the heterogeneity of connected pores,fractures,fractures-pores combination are strong,and the heterogeneity of the isolated pores is weak.(5)The concept of pore effectiveness coefficient and logging curve variation range are proposed to construct the evaluation criteria for the effectiveness of the storage space.The three combinations of reservoir spaces which are related to the fracture have better effectiveness,and it can also form a certain quantity of crude oil accumulation in the space combination of the connected pores.Then,4 oil storage modes are constructed as net,pearl,tree root and fracture-surface.It is thought that the key to locate the oil is to search for the fracture developed zones and vug developed zones.