In view of the increasing scarcity of energy resources, wells are being drilled to progressively greater depths for the production of liquid and gaseous hydrocarbons. Economical exploitation of these HT/HP reservoirs is possible only with the application of drilling and completion methods which do not damage the formation. Here, the reservoir-saving exposure of these deposits is an essential contribution.

The damage potential of drilling fluids and treatment fluids is usually assessed on the basis of return permeability (RP) tests. An impairment of the effective rock permeability through appropriate candidate fluids (drill in fluids, etc.) can be measured with special laboratory tests. In addition to the RP-Tests further investigations should be made to estimate the formation damage such as high-resolution digital photography, mercury porosimetry, scanning electron microscopy as well as microsection analyses.

Within the framework of the German Society for Petroleum and Coal Science and Technology a project was carried out to evaluate common formation damage test facilities and to define the “best practice” meeting the requirements of RP-measurements under borehole-like conditions. After a thorough evaluation an advanced HT/HP facility for formation damage testing was designed and built. By using of this set-up, systematic return-permeability tests were performed under dynamic conditions for temperatures up to 180 °C, for a flow pressure up to 250 bar, and a mantle pressure up to 350 bar.

This paper presents results from a study on the filtration and formation damage behaviour of drilling fluids under variation of the concentration and of the weighting material particle size distribution. Furthermore, promising results from changing dynamic and static filtration experiments are discussed.

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