Reservoir Geology Of Xishanchang 2 Waterflood Development Zone In Ordos Basin

Xishan Chang-2 Water Injection Development Zone is Located in the middle of northern Shaanxi slope of Ordos Basin,As a low porosity and low permeability reservoir with strong heterogeneity,Research Area Chang-2 Oil-bearing Bed serves as the main oil-bearing bed in this area.At present,the reservoir has entered the middle and late stage of reservoir development,and faces the problems of low formation pressure and high water cut in the development process.In order to further classify and evaluate the reservoir,divide the favorable development area,and provide strong support for the subsequent adjustment and development plan.On the basis of a large number of basic data and test and analysis results,guided by the theories of oil and gas reservoir geology,structural geology,sedimentary petrology and other disciplines,this paper carried out a fine description and classification evaluation of Chang 2 reservoir in the study area,and made the following achievements and understandings:Chang-2 Oil-bearing Bed is divided into five beds:Chang-2₁¹,Chang-2₁²,Chang-2₁³,Chang-2₂¹and Chang-2₂²Sub-layers and Chang-2³Oil-bearing Subgroup,and each bed is relatively stable in thickness;Chang-2₁³,Chang-2₂¹and Chang-2₂²Sub-layers are of monoclinic structure high in east and low in west,with small nose uplift developed locally,which is beneficial to oil and gas accumulation,and each bed has certain inheritance.The Research Area belongs to delta plain subfacies sediments,mainly developing distributary channel,swamp and onshore natural levee microfacies.Chang-2₁³Bed is dominated by swamp and onshore natural levee microfacies,Chang-2₂¹and Chang-2₂²Sub-layers are dominated by branch channel microfacies;the lithology of reservoir is dominated by arkose,the interstitial material is mainly chlorite,and the mineral cementation type is mainly porous cementation,with low composition maturity and the largest proportion of fine sand.At present,the diagenetic stage of the target strata in the study area is A transitional stage from late diagenetic stage A to late diagenetic stage B,which is accompanied by strong diagenesis such as compaction,cementation,metasomatism and dissolution from the initial sedimentation to the present,with an important impact on the physical properties of the reservoir;the average porosity of Chang-2₁³,Chang-2₂¹and Chang-2₂²Sub-layers is 11.84%,12.54%and 12.06%respectively,and the average permeability is 5.86 x10^-3μm²,7.54 x10^-3μm²and 6.26 x10^-3μm²respectively,with good correlation between porosity and permeability.In the Research Area,Chang-2₁³Sub-layers enjoys weak intra-layer heterogeneity and Chang-2₂¹and Chang-2₂²Sub-layers enjoys strong intra-layer heterogeneity;The Research Area enjoys strong inter-layer and plane heterogeneity;the sensitivity of reservoir is:moderately strong water sensitivity,moderately weak velocity sensitivity,moderately strong salt sensitivity,weak alkali sensitivity and acid-free sensitivity.On the basis of the analysis results of the lithologic characteristics,sedimentary characteristics and reservoir characteristics of the target layer,and referring to the previous reservoir classification methods,Chang-2 Reservoir in this area is divided into four types,among which the most Class II Reservoir and Class III Reservoir are developed,with large sand body thickness,contiguous distribution,and relatively good physical properties and oil-bearing property.Class IV Reservoir is mainly distributed in Chang-2₁³Sub-layer,with basically scattered narrow strip distribution in Chang-2₂¹and Chang-2₂²Sub-layers,and this kind of reservoir is not of great development value.Class I Reservoir is basically undeveloped.