Classification And Evaluation Of ? Oil Group Of N₁-N₂¹ Reservoir In Gaskule Oilfield

The study stratum is the ? oil group of N1-N21 reservoir in Gaskule oilfield,the southwestern Qaidam basin.The VII oil group has multiple and thin interbedded layers.The reservoir is of high heterogeneity,difficult to develop.Therefore,it is urgent to carry out the study of reservoir classification and evaluation to serve the further exploration and development.Based on the theories of sedimentary petrology and reservoir geology,stratigraphic correlation,sedimentary microfacies and reservoir characteristics which includes petrological features,pore structure characteristic and physical properties have been studied by the way of comprehensively analyzing core data,logging data,seismic and chemical test data.On the basis of reservoir fundamental research,it has been furtherly reached the reservoir classification and evaluation.The reservoir types spatial distribution are illustrated by the three-dimensional geological model in order to guide the production-increasing work of dominant reservoir in the middle and late period of oilfield development.The VII oil group is divided into 4 sand groups,10 small layers and 20 single layers.It has been known that the source materials came from the northwest.The geological background is delta front of braided river,which is based on the regional lake regression.Sedimentary subfacies can be furtherly divided into some microfacies,that is underwater distributary channels,tributary bays and river mouth bars.The reservoir petrology types include lithic feldspar sandstone and feldspathic lithic sandstone.The reservoir space mainly consists of intergranular pore,which is irregular distribution.The main types of throat are pore-shrinking throat and neck-shrinking throat.The sand body of VII oil group belongs to a medium porosity and medium permeability reservoir,with the feature of strong heterogeneity.On the basis of determining the low limits of effective reservoir physical properties,using machine learning clustering algorithm,under the constraints of sedimentary microfacies and reservoir characteristics,the reservoir classification criteria are established by selecting porosity,permeability,FZI and PZI parameters,thus the reservoir is divided into three types.Research suggests that sedimentary facies control reservoir distribution.The first and second types of reservoirs are dominant reservoirs,which mainly distribute in underwater distributary channels and river mouth bar.The third type of reservoir is in poor quality,mainly distributes in thin sands between rivers.According to the comprehensive geological research,a three-dimensional geological model of VII oil group in N1-N21 reservoir of Gaskule oilfield have been identified.And the spatial distribution law of reservoir types and reservoir attributes in the study area also can be obtained.