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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.

Use of the subsurface for energy resources (enhanced geothermal systems, conventional and unconventional hydrocarbons), or for storage of waste (CO2, radioactive), requires the prediction of how fluids and the fractured porous rock mass interact. The GREAT cell (Geo-Reservoir Experimental Analogue Technology) is designed to recreate subsurface conditions in the laboratory to a depth of 3.5 km on 200 mm diameter rock samples containing fracture networks, thereby enabling these predictions to be validated. The cell represents an important new development in experimental technology, uniquely creating a truly polyaxial rotatable stress field, facilitating fluid flow through samples, and employing state of the art fibre optic strain sensing, capable of thousands of detailed measurements per hour. The cell’s mechanical and hydraulic operation is demonstrated by applying multiple continuous orientations of principal stress to a homogeneous benchmark sample, and to a fractured sample with a dipole borehole fluid fracture flow experiment, with backpressure. Sample strain for multiple stress orientations is compared to numerical simulations validating the operation of the cell. Fracture permeability as a function of the direction and magnitude of the stress field is presented. Such experiments were not possible to date using current state of the art geotechnical equipment.

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