Many of the problems associated with the use of water based fluids in drilling and completion operations are caused by incompatibilities between the fluids and the shales. Such incompatibilities may result in washouts, increased drilling costs (solids handling, rig time, dilution fluids), shale sloughing during the drilling operation and after displacements to completion fluids or during gravel packing. One of the most important factors leading to an undesired result (either a premature screenout, thus a potential sand control failure, or a higher skin) in water-packing of open holes is the presence of reactive shales in the interval to be gravel packed. Although there is a substantial amount of literature on shale inhibition with water-based drilling fluids, the importance of shale inhibition and the problems associated with shale reactivity during gravel packing remain largely unexplored. Furthermore, shale inhibitor selection often relies purely on a comparison of the results from bottle roll tests using shale samples in candidate fluid/inhibitor pairs (drilling or completion fluid) and on tests measuring degree of shale swelling. While these tests are highly functional, they can only provide information on the relative performance of fluids, and their relevance to gravel packing is questionable, as these tests do not simulate the conditions experienced during such treatments. This paper presents guidelines on selection methodology of shale inhibitors for use in gravel packing applications based on the data available in our respective companies, including a comparison of results from conventional bottle roll tests to those from flow through predrilled holes in shale core samples. Recommendations are made depending on brine typeand density, type of shale, temperature, fluid exposure history, as well as environmental considerations.
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