Study On Heterogeneity Of Meandering River Reservoir Of The Minghuazhen Formation In The Gangxi Oilfield

The Gangxi oilfield is the key development area of the Dagang Oilfield.The reservoir sand body of the Gangxi oilfield is stably distributed in a large range from northeast to southwest,and the thickness of single sand layer is 5～20m.Due to the wide distribution of argillaceous interlayer formed by sand body lateral deposition,the heterogeneity in the reservoir layer is very strong,so it is imperative to study the reservoir heterogeneity.On the basis of literature research,combined with the statistical reservoir data of the Minghuazhen Formation in the Gangxi oilfield,the reservoir heterogeneity was studied from the macro and micro perspectives.For the main controlling factors of reservoir heterogeneity(sedimentary microfacies type,permeability,sand body thickness,permeability variation coefficient,breakthrough coefficient and grade difference),the entropy weight method was used to calculate the comprehensive evaluation index of heterogeneity and predict the reservoir heterogeneity in this area.The research shows that:(1)the fine strata of the Minghuazhen Formation in the Gangxi oilfield are divided into three oil-bearing groups including,Ming I,Ming II and Ming III,22 small layers and 60 single sand layers;(2)The provenance of the Minghuazhen Formation in the Gangxi oilfield is NE-SW trending,developing meandering river sedimentary deposition,mainly including sedimentary microfacies such as point bar,abandoned river channel,late river channel and crevasse fan;(3)The interlayers mainly include argillaceous interlayers,with few physical interlayers and calcareous interlayers.Positive rhythm and compound positive rhythm are the most common rhythms of permeability;(4)The interlayers are stably developed and thick.The heterogeneity of the three oil-bearing groups is strong,and the Ming III is the strongest;(5)The distribution of sand bodies on the plane is stable,mainly banded and flaky.The physical property distribution is seriously affected by sedimentary microfacies.The physical properties of point dams are good,and the physical properties of abandoned channels are poor;(6)The reservoirs are mainly composed of fine sandstones,and sub angular and sub circular are the main rounding types with medium to good sorting.Point contact is the main intergranular contact type,with a small amount of line point and point line contact.The cement type is mainly argillaceous and iron dolomite cementation;(7)Sedimentary microfacies control the distribution of heterogeneity.The areas with good physical properties has weak heterogeneity while those with poor physical properties has strong heterogeneity.