A Theoretical Investigation into Fines Migration and Injectivity Decline due to Hydrodynamic Effects
Caruso, N. A.
Engineering Honours Degree, 2012
University of Adelaide
Fines migration is a wide spread physics mechanism of formation damage in oilfields. In particular, a significant injectivity decline due to fines mobilisation and straining has been widely reported. A predictive mathematical model for injectivity impairment due to fines migration, which permits optimisation of the injection, is not available in contemporary literature.
The physics of fines mobilisation, migration and straining were analysed during water injection into an oilfield, in order to predict injectivity decline. An analytical model was developed accounting for fines detachment, migration and straining, with subsequent permeability decline. The model may be used for injectivity forecasting at the well scale. The modelling describes fines mobilisation near to the well, their migration, straining and even re-attachment far away from the well.
An explicit formula for injectivity decline permits the planning of well stimulation. It may also predict whether higher injection rates would improve or worsen the injectivity. A formula for the radius of the damaged zone permits determining the amount of acid during acidising and depth of holes during re-perforation. Explicit expressions for attached and strained fines concentrations resulted in exact formulae for injectivity index versus time. The typical size of the damaged zone is 1-3 m. Injectivity decreases quickly at the beginning of injection and stabilises with time. Typically, the injectivity decreases 1.5-4 times.