Reservoir Charateristics And Favorable Reservoir Evaluation On The Upper Sub-member Of The First Member Of Liushagang Formation In Weizhou 11-7N Oilfield And Surrounding Area

Weizhou 11-7N Oil Field with surrounding area is one of oil-rich blocks in Weixinan Depression in Beibuwan Basin.Liushagang Formation is one of important oil-gas-bearing intervals.The depression is a half graben-like structure characterized as "northern fault besides southern stratigraphic overlap".Liu 1 upper sub-member controlled by structural belt of fault No.1 has several unsolved problems as following:(a)The relationship among sedimentary systems is not equivocal;(b)The regularity of sand distribution and the vertical superimposed relationship are not clear;(c)The regular pattern of sedimentary microfacies distribution is indeterminate.Therefore,in this paper,guided by Reservoir Sedimentology,Sequence Stratigraphy,Seismic Sedimentology and related theories,I intensively studied the reservoir sedimentary characteristics of Liu 1 upper sub-member in Weizhou 11-7N Oil Field and surrounding area based on comprehensive application of core,logging,seismic and chemical analysis data etc.,leading to the conclusions and cognitions as following:1.Through the detailed observation and description of the core,I summarize the main sedimentary structure features of Liu 1 upper sub-member in Weizhou 11-7N oilfield and the surrounding area and determine sedimentary facies types,which are belonged to the normal delta front deposition and turbidite fan deposition.The main microfacies conclude underwater distributary channel,underwater interdistributary bay,mouth bar,sheet sand,side lobe of turbidite fan.2.Based on comprehensive application of core,logging and seismic data,the high resolution sequence stratigraphy theory,I found the stratigraphic frame of the study area combining well and seismic.And Liu 1 upper sub-member is divided into one long-term base level cycle(a descending half cycle),five middle-term base level cycles(three descending half cycles,2 rising half cycles).3.The tectonic pattern of the study area is "one uplift and two sags",which controls the distribution of sedimentary system.There are two normal delta front facies deposition in the west,where the provenance directions are respectively NW,SSW.There is one turbidite fan deposition in the east,where the sediments come from the east.Influenced by varied base level,sedimentary source recharge,eastern and northern contemporaneous faults and other factors,the sand bodis mainly consists of middle and thin sandstones with a broader distribution,which become the main reservoir of Liu 1 upper sub-member in the study area.4.In lithology,the reservoirs in Weizhou 11-7N oilfield and the surrounding area are mainly based on lithic quartz sandstone and quartz sandstone.It is common to see quartz particles secondary enlargement.Feldspar grains contain solution and leaching.Reservoir space mainly includes primary intergranular pore and intergranular dissolved pore.The characteristics of pore and throat are as following:(a)The distribution of pores is relatively uniform;(b)The throat is comparatively wide;(c)The quite big pore;(d)Relatively well connected pores.5.According to the analysis hierarchy process and comprehensive and quantitative reservoir evaluation,selection of porosity,shale content,sand content,sedimentary facies,GR as evaluation parameters,All the reservoirs of each sedimentary unit in Liu 1 upper sub-member in Weizhou 11-7N oilfield and surrounding area are conducted comprehensive and quantitative reservoir evaluation.The result shows that the reservoirs of Liu 1 upper sub-member in the study area are divided into 4 different types respectively with obvious characteristics,which are related to the distribution of sedimentary facies.