Proper selection of reservoir drilling fluids (RDF) or drill-in fluids can minimize formation damage and maximise well productivity or injectivity. Typically, fluid selection involves pre-screening of fluid candidates followed by laboratory return permeability testing of a selected few. However, as the fluids often have different fluid loss and return permeability properties, the final decision as to which fluid to use is often arbitrary. These difficulties stem from the fact that there is no recognised method for comparing formation damage potential of fluids with different fluid loss and return permeability profiles and the lack of valid models for upscaling laboratory data to field skin factors.
In a recently finished EU project, a methodology was developed to bridge the gap between the laboratory measured data and field skin factors, so laboratory fluid loss and return permeability data can be interpreted in field skin terms. This will help the fluid engineers to select the least damaging fluid for their application. The methodology makes it possible to compare laboratory results obtained under different test conditions, and to estimate skin factors for different reservoir sections from a single return permeability test. This functionality is very useful for calculating the productivity of complex reservoirs with anisotropy and heterogeneity.
For correct upscaling of return permeability to field skin, both the fluid loss and return permeability profiles are required. This paper recommends dynamic fluid loss for return permeability testing. This paper also recommends a slight change to routine formation damage test procedures to obtain the return permeability profile necessary for upscaling. Detailed laboratory data analysis techniques to generate input parameters for the developed models are also reported.
The above mentioned methodology has been built into a simulator in Microsoft Excel with a user friendly interface.