Study On Dynamic Simulation And Competition Mechanism Of Wormhole

Acidification is a commonly used means of innovation for increasing output on dense carbonate reservoir.And elaborate description of wormhole is crucial to optimum design of acidizing.The development of wormholes is directly influenced by the acid fluid injection rate,while so far the research on the corresponding relationship between the injection velocity and the dissolution pattern is not detailed enough.In this study,carbonate rock cores are selected for displacement experiments,during which effects of different injection rates on wormhole development are compared.The breakthrough volume is a key parameter in determining the optimum acidizing fluid injection rate,while the pressure drop curve is utilized to analyse the development process of wormholes.Meanwhile,nuclear magnetic resonance imaging technology is employed to analyse the core end surface and internal structure after acidification so as to identify acid dissolution types and further determine the corresponding boundary of fluid injection rates for different acid dissolution types.On the basis of the experiment,the injection velocity boundary between the wormhole and the uniform dissolution is further clarified by solving two-scale model.In addition,based on the mechanism of its competition,this paper describes the growth and expansion of the wormhole.The acid breakthrough volumes with different injection rates are calculated and compared when the hydrochloric acid concentration is 20%,which arrives the conclusion that the injection rate of 2mL/min initiates the formation of wormholes.While the numerical model results show that the injection velocity corresponding boundary of the wormhole and the uniform dissolution is 30mL/min.And the injection rate of 3~4mL/min results in the optimum acidification effect.Through the analysis of the competition between two wormholes with different distances,it is found that the main wormhole has shielding effect on associated wormhole.Under the boundary condition of inlet constant flow,outlet constant pressure and no fluid exchange around,the shielding effect increases with the decrease of two wormholes' distance and the increase of length difference.At the same time,the better the location of the associated wormhole is,the weaker the shielding effect.