| The Wutonggou formation reservoir in Shaqiu 5 well region is generally a kinds of extra-low permeability conglomerate reservoir,which has following characteristics include to serious heterogeneity,large pressure differences in between oil layers,general water channeling for oil wells and poor development effect by injection water etc.Especially the water channeling reasons and water flooded models currently have not all unified viewpoint,above reasons become the technical problems which restrict the improvement of reservoir development.In year 2008,five adjustment wells have been implemented,and the production results show that the research results of remaining oil distribution are large differences with previous knowledge,that is what the oil wells are high water content when they start production and resulting in stagnant state of reservoir adjustment development.Therefore,it become very important and difficult to determine water channeling types and distribution models of remaining oil of extra-low permeability conglomerate reservoir for improving development effect.In this research paper,the following subjects include to reservoir geology,development geology and fluid mechanics theory are selected as theoretical direction to solve development problems of extra-low permeability reservoir.Firstly,the development characteristics of extra-low permeability reservoir in early period are analyzed with general low permeability reservoir.The core samples analysis show that the Wutonggou formation reservoir in Shaqiu 5 well region is extra-low permeability reservoir,but the percent 64.7 of oil wells have natural industrial production capacity,the percent 73 of oil wells can have production effect by water injection method within 1 year,and the injection pressure of the percent 41 of water injection wells are 0 MPa in wellhead after water injection of half year.Combined with test well characteristics of oil wells in early development to determine finally that the Wutonggou formation reservoir in Shaqiu 5 well region must have double kinds of pore system,the extra-low permeability pore system is the main pore type,but a small part of high permeability pore system also exit in reservoir and this part of high permeability pore system lead to abnormal development characteristics in early reservoir development.For these high permeability pore system,they may be the fractures inside reservoir and also may be the high permeability thin layers or high permeability strips.However,the fractures inside reservoir are mainly vertical fracture or fracture side without filling according to core descriptions,above kinds of facture are closing state under formation.Furthermore,the effective ratio,water channeling ratio and cumulative oil production of single well of oil wells for every directions are close in Wutonggou formation reservoir in Shaqiu 5 well region,these development characteristics are not accord with water channeling rules caused by artificial fractures.In addition,according to the production and injection profile data,the displacing effect between layers is basic balance,so the water channeling reason is not caused by single layer breakthrough.Based on above analysis,the high permeability strips inside reservoir are clearly determined to water channeling type.The corresponding relations between water absorption of 181 layers of 25 wells in early development and lithology are researched in Shaqiu 5 well region,and the research results show that the water absorption ability of ? type conglomerate is obviously stronger than lithologies,thus the ? type conglomerate with cementation loose is firstly determined as water channeling.The following well logging parameters such as true resistivity,acoustic and nature gamma are selected to establish log identification standard of water channeling,then 5 aspect evidences confirm that the water channeling is the core factor which influence water flooding and water channeling of extra-low permeability reservoir.Compare with reservoir pore structure between ? type conglomerate and other lithologies,the water channeling shows following characteristics such as the most low displacement pressure,the maximum average capillary radius,rough degree curve and the most low homogeneous coefficient.The relationship between water channeling thickness and water channeling types of oil well are what the oil wells in water channeling well region are mainly strongest water flooding and fast water flooding and the oil wells in no water channeling well region are not mainly production effect.The relationship between water channeling thickness and injection pressure are what the injection pressure of water injection wells is low in thick water channeling well region and the injection pressure is high in thin water channeling well region.The relationship between drilling water channeling of straight wells and resistivity decline range of oil layers are what the resistivity decline range is about 6 ?·m when the water channeling is development and connectivity,the resistivity decline range is about 2?3 ?·m when the water channeling is development and no connectivity between wells and the resistivity decline range is about 1 ?·m when the water channeling is no development.The relationship between drilling water channeling of horizontal wells and water content are what the water content of horizontal well is high when the water channeling is development and connectivity between wells,the water content of horizontal well is middle when the water channeling is development and no connectivity between wells and the water content of horizontal well is low when the water channeling is no development.The water channeling is considered as a kind of flow unit to analyze its distribution characteristics.Based on analysis of 29 cross well profiles,81 water channelings in 5 layers are identified,in which the number of water channeling with larger than 0.5km2 is totally 7,the number of water channeling between 0.2km2 and 0.5km2 is totally 11,the number with smaller 0.2km2 is totally 63.On the plane,the distributions of water channelings and oil layers have high consistency.Vertically,the distribution location of water channeling is mainly in middle-low section of oil layer and the percent of water channeling thickness to oil layer thickness is about 20%.The original oil saturation of reservoir is accurately restored by use of established models and oil saturation changing index is used to evaluate water flooded degree.The water flooding mode and water channeling development has obvious relevance which is show following aspects:(1)the water flooding degree is middle-low when reservoir is no drilling water channeling;(2)the whole water flooding degree is middle-high when reservoir is drilling water channeling;(3)the water flooding degree of water channeling development is high when reservoir is drilling water channeling;(4)the percent of high water flooding thickness to reservoir thickness is about 13.2%,the other thickness is middle-low water flooding degree and this state is coincide with overall recovery percent of reserves which number is 14.29%;(5)the percent of middle-low water flooding thickness with no water channeling development to reservoir thickness is about 36.8%,the percent of middle-low water flooding thickness with water channeling development which deduct water channeling thickness to reservoir thickness is about 50%.Based on above analysis,the remaining oil with the reservoir of water channeling development is also the important goal of next reservoir adjustment.Although the distribution range of water channeling is very wide and its number is also more,the percent of water channeling thickness to oil layer thickness is just only 20%?24%.Therefore,the water channeling can be effectively avoided to perforation and production through the optimization of horizontal well structure,it is feasible that implementing reservoir adjustment by use of horizontal well. |
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