Study On The Identification And Lithology Well Logging Models Of Carboniferous Volcanic Rocks In Chepaizi Area

Chepaizi area is located in the north-west of Junggar basin and the drilling wells which put the Carboniferous as the target layer were less,they were still in the preliminary stage at present and had a lot of problems such as lithology confusion,unclear relationship of rock electricity,the low rate of lithology identification and insufficient understanding of the horizontal distribution rules of volcanic rock.In view of the above problems,this article studied the lithology,electric property,lithological identification and distribution of the volcanic rock by extensive drilling core observation,well logging,laboratory analysis and other information.At last,it develops a logging interpretation methods and models of lithology identification and predicts the plane distribution of dominant lithology in the study area by analyzing single well lithology and even well section.The main conclusions and achievements are as follows:(1)The major rock types and lithologic characteristics have been defined of the Carboniferous in Chepaizi area.The volcanic rocks of Carboniferous consists of basic lava and intermediate lava in the study area,including lavas,clastic lava and pyroclastic rocks which totaling three categories of six major lithology: andesite,basalt,andesite basalt,basaltic brecciated lava,basaltic breccia and tuff.(2)Established a reasonable relationship between lithology and electricity,summarized the well logging response of volcanic rocks.We have observed that andesite,basalt,andesitic basalt performances for high density,high electronic resistivity,low acoustic,low neutron,and from basic to acid volcanic rock,the intensity of natural radioactivity is gradually growing.Basaltic breccia lava and basaltic breccia is characterized by high acoustic,high neutron,low gamma ray,low density,low resistivity and shows noise of imaging logging.Tuff with high gamma,high neutron,high density,high resistivity,low acoustic and imaging logging reveals as the macula densa gneissic.(3)Integrated a variety of methods to identify volcanic rocks and established mode recognition in the study area.Imaging logging data was used to divide the coring interval into four categories: lavas,clastic lavas,pyroclastic rocks and sedimentary rocks,at the same time the imaging interpretation modes of volcanic rocks was build.Then using conventional logging mode for multi-parameter crossplot to identify the composition of volcanic rocks,further refine the lithology into basaltic rocks,andesite basaltic rocks,andesitic rocks and establish the volcanic lithology identification standard.Based on the previous two-step analysis,the Fisher discriminant lithology patterns was founded.Three kinds of lithology logging identification method combined with each other,authenticated with each other to improve the recognition efficiency and accuracy.(4)Analyzed the vertical and horizontal distribution of the Carboniferous volcanic rocks.In the vertical direction,the volcanic lava and the volcanic clastic rocks appear alternately and in each layer of output,the distribution shows that volcanic rock has the characteristics of superposition of the multi period eruption cycles;on the plane,row 668 well block was dominated by the 61 fault zone,along the direction of the fault strike,the volcanic rocks was a zonal distribution,row 66 well block with the outbreak of the main activities and the volcanic rocks shows the ring belt distribution.