A general coupled kinetic adsorption/precipitation transport model for scale inhibitor retention in porous media: I. Model formulation

The application of scale inhibitors to prevent mineral scale formation downhole is performed routinely in the oil industry in chemical "squeeze" treatments in water producing wells. The retention of scale inhibitor (SI) within the formation is central to a squeeze treatment having a long lifetime. Scale inhibitors are retained within porous media by the two main mechanisms of "adsorption" (G) and "precipitation" (?). There is not complete agreement in the literature about when we should use one mechanistic description or another. Field observations are not sufficiently accurate to distinguish between different retention models/mechanisms and a detailed analysis of a given retention mechanism requires carefully designed laboratory experiments at "field relevant" conditions. In previous experimental and modelling work (SPE 114108), we have demonstrated for static (equilibrium) "apparent adsorption" tests where the system exhibits either (a) adsorption only or (b) it is in the coupled adsorption/precipitation (G/?) regime. Results from an extensive series of "apparent adsorption" experimental measurements were presented for various mineral separates to illustrate these points. In addition to experiments, we must also have well developed models which can describe these retention processes both for equilibrium G/? cases and also for kinetic flowing situations where the processes are not at equilibrium. That is, a complete model of SI retention must have (i) an equilibrium description of the coupled G/? process (SPE 114108); (ii) a kinetic model of coupled G/? which correctly limits to the equilibrium case (i.e. the kinetics must be consistent with the equilibrium G/? model as t ? 8); (iii) the full kinetic G/? model must then be embedded in a transport model for flow through porous media. In this paper, the two tasks in (ii) and (iii) are carried out; a fully cononsistent coupled G/? is developed and then incorporated into a transport model (a 1D core flood simulator) and a number of example simulations are carried out. In the related Paper II (SPE 130703), the application of this coupled model in a sensitivity study of field squeeze treatments is described. © 2010, Society of Petroleum Engineers.