Braided River Delta Reservoir Characteristic In Rifted Basin

Chengbei low fault block is located the low break zone between Chengning uplift and Qikou sag.Sha 2 member is in the transformation area of rifted basin to depression basin whose hydrocarbon reservoir is mainly deep lithologic and structural-lithologic.The reservoir is mainly ultra-low permeability which is hard to exploit.So it is important to research reservoir character and its controlling factor.Based on sedimentation and reservoir geology,the research system of "multidisciplinary and hierarchical stripping" is built combined with development geology,seismic inversion,well testing date,stochastic simulation and document searching.The system start to recognize microfacies distribution and evolution feature and define the favorable member.According to sand scale and its validity,dry sand and extra thin reservoir are removed and then reservoir is left.Reservoir character is studied and classified combined with development date and define the high quality reservoir.Finally,the high quality reservoir is fine characterized.The mode of transformation of rifted basin to depression basin is established after the recognition of sedimentary environment and microfacies.Braided river delta front and submarine fan are developed at the same time in the early of Sha 2 member.Braided river delta front whose microfacies includes underwater distributary channel,mouth bar,front sheet,interdistributary and distal bar is widely distributed in the middle of Sha 2 member.Finally,it mainly develop lacustrine facies.According to the major sand of inversion,favorable microfacies and member are defined and sand distribution is fine characterized considering sedimentary evolution.Sha 2 member in Chengbei low fault block is on the stage of reservoir evaluation to early development stage so that accumulation is the main research point,and pearmeability as well as heterogeneity are secondary.The feature of reservoir accumulation included that most reservoir is thin and mid-low porosity rock,whose pore is secondary intergranular and intragranular space which is filled with calcite,dolomite and mud.The surface porosity is between 4 and 10 percentage and oil saturation is 39.7 percentage on average,whose shale content is high.The permeability feature indicated that reservoir is mainly ultra-low,low and extra-low following,partly being tight reservoir whose pore throat is mainly mid-little which diameter usually below 10 um.The heterogeneity included that the coefficient of variation is big,the interbed of which is plenty and its scale is smaller.The method of double factors regression analysis is built based on reservoir feature,static parameter and development date,which refer to testing as classification criteria.Firstly,this method choose classification parameter and make them standardization.Secondly,testing production and physical property are analyzed to find their correlation and physical property distribution area is defined according to oil field flow potential.As a result,reservoir is classified into ?,?,? and ?,which high quality reservoir include ?and ?.The reservoir type in Sha 2 member of Chengbei low fault block is mainly ? and high quality reservoir is pretty scarce.Large high production reservoir is hard to developed.