Study About Tracer Concentration Model Under Step-by-step Regulation In Fractured Low Permeability Reservoir

As an effective measure of governing water channeling in fractured low permeability reservoir,step-by-step regulation can effectively reduce percolation ab ility of fracture bands with high permeability,expand the spread range of injected water and enhance the water-flooding effect.However,in the process of step-by-step regulation,it is far from enough to only use the injection pressure and dynamic changes of production to adjust parameters under step-by-step regulation in real time.In order to achieve the dynamic monitoring and predict the effect of step-by-step regulation,taking the regulation to injected water channeling in fractured low permeability reservoir of the East Yan Chang superficial layer belonging to the Ordos Basin as an example,this paper raises the tracer monitoring technology under step-by-step regulation.By analyzing characteristic of reservoir matrix porosity and fracture static-dynamic state,fine-grained sedimentation,strong compaction,cementation and diagenesis are clarified as root causes of tight reservoir.At the same time,natural fractures are developed in the reservoir because of bedding fractures formed by sedimentation a nd diagenetic fractures by rupturing.Finally,fractured low permeability reservoir is formed in study area.By analyzing characteristic of water-flooding layer in different fracture systems and corresponding tracer typical curves,according to the shape of tracer curve after step-by-step regulation,it is clarified that the process of step-by-step regulation in the fractured low permeability reservoir is the equivalent conversion among different water channeling fracture systems.Meanwhile,three patterns in the tracer curve named as single-peak,multi-peak and wide plate are built.Based on the characteristic of three fracture systems,tracer physical models under different grades of step-by-step regulation are abstracted and built.According to the hypothesis conditions,based on one-dimensional convection and diffusion theory,tracer mathematical models corresponding to three patterns are deduced.And the sensibility of parameters such as number of fracture bands,equivalent diameter,number of tube and length of the migration is analyzed.Using genetic algorithm to invert and fit tracer concentration curves belonging to C25 well group in oil field of the East Yan C hang,it turned out that three tracer interpretation models can explain well the dynamic variation rule of main parameters under step-by-step regulation in fractured low permeability reservoir.So,this study can provide theoretical basis for the mechanism of step-by-step regulation,parameter optimization and the establishment of time domain tracer technology between wells.