Chemical Equilibrium Models: Their Use in Simulating the Injection of Incompatible Waters

Summary One of the problems encountered in waterflooding projects is scale formation caused by chemical incompatibility between potential injection waters and reservoir brine. Chemical compatibility evaluation through laboratory experiments on cores at reservoir conditions is of limited value because only first-contact phenomena are reproduced. A numerical model is presented that couples a reservoir-fluid-flow/thermal-equilibrium simulator with a chemical-equilibrium computer code. This model, AGIPS, enables us to calculate the evolution in time of the amount of scale formed at any point in the reservoir and inside the wells when changes occur in the temperature of the injected water and when the injection water mixes with reservoir brine. Moreover, the model calculates temperature and pressure profiles in the reservoir, together with their evolution in time, taking into account the permeability reduction caused by scale formation. Results are presented for the chemical-equilibrium code validation by matching experimental data on scale formation in mixtures of incompatible waters. An example is also given of the use of AGIPS in simulating a five-spot waterflood where incompatible water is injected.