The Effect of the Initial Rock Permeability on the Extent of Injectivity Reduction Due to Brine Injection Through Fractured Formation

Abstract

The injectivity reduction with time is an important aspect in designing water, injection projects. One of the main factors that affect the injectivity, due to particle invasion, is the matrix initial permeability. This factor had been experimentally investigated and evaluated by many researchers, hut all of their experimental works were based on linear core flow tests. However, in some field injection projects, there was a much less reduction in the injectivity with time than what was predicted by the experimental models. This incompatibility was related to the induction OS fractures caused by injection at a pressure higher than the formation fracturing pressure. This study was conducted to investigate experimentally the effect of the matrix initial permeability oil the extent of injectivity reduction caused by brine injection through a rock matrix with a single fracture. The injected brine contained solid particles less than 6 mum or less than 20 mum in size at a concentration of 9 mg/l. The early results show experimentally the huge difference in the injectivity reduction extent between flow tests carried out with closed and open fracture injection. Then, the results are presented as an injectivity index at a certain injected pore volume versus initial permeability. The slope of this relation is called reduction rate. This I ate was evaluated for different cases. For the case of brine suspensions that contain small particles, the reduction rate of the injectivity index due to initial permeability variation in the case of open fracture tests was much less than that of the closed fracture tests. For the case of fracture injection of the large particles suspensions, the reduction rate was threefold higher than that of the small particles suspension. This proves that the particle sire factor, has all important role in determining the extent of the initial rock permeability effect on the injectivity index in fracture injection.