Study On Identification And Distribution Of Fracture In Carboniferous Volcanic Rocks Of Chunfeng Oilfield

Chunfeng oilfield is located in the northeastern of Chepaizi area of Junggar Basin.The exploration practice and results of recent years have confirmed Carboniferous volcanic rocks is a good prospective area.The area mainly develops volcanic rocks reservoir with a large number of fractures.Fractures are mainly reservoir space and channel between pore,cave and fracture.The drilling wells for the purpose of the Carboniferous layers are less,and there are a lot of problems such as unclear types and characteristics of volcanic rock fracture,not in-depth research to fracture logging identification,unclear vertical and horizontal rules of fracture distribution.In view of the above problems,by use of core,thin sections,logging etc.this article clearly defines types of volcanic rock fracture,studies fracture logging identification,analyzes fracture parameters characteristics,then clearly defines fracture distribution rule,studies the affecting factors of fracture developing,and proposes a distribution pattern of volcanic rocks fracture.The main conclusions and achievements are follows:(1)The Carboniferous Volcanic Rocks commonly develop fracture with various types.Most of the fractures in Chunfeng oilfield belong to tectonic inclined fracture.And most of core facture have been filled with different extent by minerals.(2)The fracture identification of imaging logging shows that half filling fractures are the most,followed by filling fracture.The analyses of cross plot show that,in six volcanic rocks different types of fracture have different conventional logging response,and resistivity,acoustic,neutron,density log can be better recognition effect to different types of fractures.On the basis of Bayes discriminate analysis,the paper has been established corresponded discriminative equation to different types of factures.The paper holds that the classification accuracy is highest precision rates,with the rate up to 86.7%,and the threshold of discriminative ratio of effective fracture is 0.7.(3)The fractures are mainly medium and small,and develop high degree.The fracture dip range by 40 to 60 degrees.Relating to the local tectonics,the orientation of factures tend to mainly NNW and NNE,followed by nearly NS.(4)The evaluation plat of facture shows,within 600 meters below the surface of Carboniferous,fracture mainly developed moderately and poorly with strong heterogeneity.The fractures are commonly developed in study area.Development degree of fractures vertically tends to reduces with depth of increment,and the degree obviously relates to the fault and volcanic rock.Distribution of fracture horizontally presents intermittent striped and fragmented potato-shaped.(5)The mainly affecting factors of the facture are fault and volcanic rock.The paper shows that there are four changing characteristics of fracture special distribution range by introducing the concept of center of fracture distribution,and proposes a distribution pattern named stipe wedge center-mobile.