Pressure maintenance by sea water injection is part of many offshore field developments. Experiences gained over the last decade in the North Sea, where there is a wide variance in the systems used, appears not to have clarified design specifications.
The paper describes various approaches to analysing water quality criteria with reference to water injection schemes and presents the philosophy of the interrelated approach of laboratory experiments, theoretical models and well injectivity predictions in relation to reservoir characteristics.
Results are presented from a laboratory and modelling investigation of permeability impairment as a function of the depth of invasion. A pore network model is described which is generated from laboratory derived pore size distribution data. Predictions of permeability from the model are compared to experimental values and good agreement is demonstrated. The incorporation into the model of particle capture mechanisms enables it to be used to predict the reduction in permeability of a core arising from injection fluids. Another modelling approach is described where the contribution of pore size to permeability is demonstrated.
Water quality experimental results are presented showing permeability profiles obtained using a multiport pressure tapped core holder which demonstrate local permeability impairment as a function of particle size and rock properties.
The results of one modelling approach is applied in the paper to the prediction of well injectivities and filtration requirements.