Research And Application Of Ultra-low Permeability Reservoirs Time-varying Numerical Simulation Considering Natural Fractures

H field belongs to ultra-low permeability reservoir and it has been in the stage of high water-cut.During the development of waterflooding,injected water will break through seriously in a certain direction and develop dominant channels.The phenomenon of flooding is serious with poor sweep efficiency and low oil recovery.Theoretical research and mine production practice show that the physical properties of ultra-low permeability reservoirs which have lots of natural fractures will change during reservoir development.Therefore,considering the characteristics of natural fractures and the change of reservoir physical properties,identifying dominant channels and describing their spatial development characteristics are of great practical significance for oilfields to stabilize oil and control water,adjust parameters of injection and production and exploit the remaining oil.This paper takes the H oil reservoir as an example,using water flooding experiments,mercury injection experiments,scanning electron microscopy,thin slice analysis,well test interpretation and other technical means to study the main laws of reservoir physical property changes during the water injection development of ultra-low permeability reservoirs.For reservoirs with good physical properties,the physical properties of the reservoirs tend to become better in the course of waterflood development;reservoirs with poor physical properties will tend to deteriorate during waterflood development.Comprehensive application of core,seismic and well logging data,through surface outcrops,FMI imaging logging,comprehensive consideration of lithology,sedimentary microfacies,faults,construction of three-dimensional fine geological model considering natural fractures.Based on the three-dimensional fine geological model,synthetically considering the changes of reservoir physical properties during the waterflooding development and the effects of natural fractures and fracturing fractures,the equivalent continuous medium theory was used to form a reservoir numerical simulation method that takes into account the time-varying nature of reservoir properties.Applying the time-varying streamline numerical simulation to obtain the distribution of injection-production flow lines at different time steps in the study area,and calculating the distribution coefficient of injection wells to identify the dominant channels.The dominant flow field is mainly along the fracture direction and the source direction.Based on the numerical simulation of reservoirs with time-varying considerations of reservoir properties,inter-well connectivity method,and flow field method were used to quantitatively identify the dominant channels.Based on geology,fractures,production dynamics,and dynamic monitoring data,as well as reservoir numerical simulation studies that take into account the time-varying effects of natural fracture reservoirs,a comprehensive evaluation index system for the dominant channels of ultra-low permeability reservoirs was established and application of neural network algorithm to compile dominant channel identification software suitable for ultra-low permeability reservoirs.Combined with sedimentary facies,water absorption profiles,and tracer monitoring data,the spatial distribution of dominant channels in ultra-low permeability reservoirs is described.The predominant channels in the plane mainly develop along the direction of fractures and material sources,and the dominant channels are mostly developed in positive rhythms in the longitudinal direction.