Research And Application Of Effective Driving Unit Flow Theory For Tapping The Potential Of Remaining Oil In Heterogeneous Thick Reservoir

Most of water-flooding oilfields in China have generally entered the middle and late stage of development.The long-term waterflooding development has led to serious reservoir water flooding,forming a dominant oil-water seepage channel.However,there is still a large amount of remaining oil in the reservoir.At the same time,the heterogeneity between and within the layers aggravates this contradiction,which brings great difficulty to tap the potential.In the final analysis,it is affected by the reservoir configuration(rhythm,permeability and permeability)The mechanism and distribution of fine remaining oil in the reservoir are not clear,which makes it impossible to put forward effective methods to tap potential,and the existing flow model can not provide effective theoretical support.Especially for the heterogeneous thick reservoir in Daqing Oilfield,the remaining oil reserves in high water cut period are huge,accounting for 53.7%of the remaining recoverable reserves.How to effectively tap the potential of this part of remaining oil has become an important direction to improve the crude oil production in China at present and in the future.In order to find out the oil-water distribution law of thick reservoir under different heterogeneous configuration and reveal the formation mechanism of remaining oil,based on the theoretical model of two-dimensional effective driving unit proposed by the national major special project of the 12th Five Year Plan,the injection production unit is divided into four areas based on the percolation mechanics and flow function model:type ?(high-speed flow effective drive),type?(high-speed flow effective drive),type ?(high-speed flow effective drive),type?(high-speed flow effective drive),type ?(high-speed flow effective drive)Class?(low velocity effective drive),class ?(high velocity ineffective drive)and class?(low velocity ineffective drive).By introducing two shape functions to represent the three-dimensional characteristics of heterogeneous configuration,the fusion of three-dimensional flow and three-dimensional spatial characteristics is realized.The three-dimensional effective driving unit seepage mathematical model considering gravity and the two-phase flow saturation model along the streamline direction under unsteady conditions are established,Combined with displacement experiment and numerical simulation method,the oil-water flow characteristics and saturation(streamline)variation law in injection production unit are revealed.Then,by constructing three-dimensional shape functions of rhythm,interlayer and injection production imperfect reservoirs,combined with streamline density and streamline velocity distribution,the evolution characteristics of effective driving units in reservoir displacement units with time and space under different heterogeneous configurations are characterized,The changing characteristics of water cut and oil-water saturation with the conversion of four types of effective driving units in the process of displacement are clarified,and then the remaining oil producing areas and oil-water saturation distribution rules under different heterogeneous conditions are clarified.Based on the seepage mathematical model of three-dimensional effective driving unit,a lot of numerical analysis is carried out.The results show that:(1)due to the influence of gravity and vertical heterogeneity,the effective driving range of rhythmic reservoir decreases rapidly after the formation of dominant seepage channel in high permeability layer,which leads to the generation of whole sheet remaining oil.Through the effective driving unit model,the variation range of four types of driving units in the process of water content change can be tracked,and then the different rhythmic characteristics,flow characteristics and flow characteristics can be identified The area and scale of remaining oil generation under different rhythmic gradients and reservoir thicknesses(2)The existence of interlayer changes the distribution of flow field in and between thick oil layers,resulting in the generation of sheet-like remaining oil.With the influence of interlayer extension length,interlayer inclination and other factors,the control range of driving unit also changes.Through the effective driving unit theory,the region and scale of remaining oil generation under different conditions of interlayer can be determined(3)Under the condition of injection production imperfection,the pressure balance is formed in the imperfection area to realize the effective drive,which leads to the generation of scattered remaining oil.Through the theoretical analysis of effective drive unit,the area and saturation distribution of remaining oil with the change of drive unit under the condition of imperfection of well pattern and perforation are clarified.Finally,according to the remaining oil distribution characteristics and remaining scale of six models of three types of thick oil layers in Daqing Oilfield,based on the flow field transposition method and using the three-dimensional effective driving unit seepage model,the effective potential tapping measures and specific potential tapping methods and parameter settings for three main remaining oil types of reservoirs,i.e.rhythm type,interlayer shielding type and injection production imperfect type,are proposed.According to the reservoir configuration characteristics and development status of the second block in the south,middle and west of Daqing,the whole block is divided into effective driving units,and finally 3788 driving units are divided.Then,according to the effective driving unit theory,a targeted and effective plan for tapping potential remaining oil is formulated in different regions and layers.The results show that the overall recovery of the block is increased by about 4%,The results of this study provide new theoretical guidance and technical support for further tapping the potential of remaining oil in heterogeneous thick reservoirs.