A simple model for predicting the internal and external filtration during produced water re-injection using field data from Grane well G-32.

Abstract

Produced water re-injection is a method for managing the produced water in an environmentally friendly way by injecting produced water into a porous formation. This is also a method of maintaining the reservoir pressure. Contaminations in the injected water will reduce the injectivity by plugging the porous media around the borehole and by creating an external filter cake, effectively reducing the porosity and permeability. The first stage of injectivity decline is internal filtration, and is when solids get deposited in the area close to the borehole. The second stage is external filtration, and this is when particles no longer penetrate into the formation, but start forming an external filter cake The thesis presents a model for the impedance, which is the inverse of the injectivity, that takes into account the internal and external filtration. This model is tested using field data from Grane well G-32. Grane has a high porosity and high permeability sandstone, and injection was done without fracturing the reservoir. The model uses cumulative injected volume as the variable instead of pore volumes injected which similar models are based on. An alternative way of determining the filtration coefficient is chosen because results from laboratory tests are unavailable The model gives a good correlation with field data from Grane, and realistic value are back calculated using the model with some uncertainty. The alternative way of determining the filtration coefficient gives a low estimate, and indicates that laboratory experiments should be done in order to test the model further.