Clay instability problems in the reservoir zones can create risks with costly consequences for completion operations. Some sandstone reservoir rocks contain significant amounts of interstitial clay within the pore system. Clays are also present in reservoirs with interbedding shale and sandstone. Swelling and dispersion of these clay minerals in the reservoir can affect wellbore integrity, induce formation damage, reduce gravel pack permeability, plug screens, and cause failures in the completion tools and assemblies.

In many situations completion brines can provide some degree of inhibition, some reservoirs require more effective and permanent treatments to control reactive clays. Numerous products are available for clay inhibition, but a majority of them were primarily developed for drilling fluids. Organic additives for clay inhibition used extensively in drilling fluids have been transferred into the completion brine technologies to provide effective solutions in reservoirs with a high potential for clay instability. Chemical compatibility is a critical factor in the selection of additives for completion brine.

This paper will present the results of a study conducted with monovalent and divalent brines treated with different types of organic clay inhibitors. Compatibility tests will show the cases where inhibitor additives are compatible with multiple types of brines. Other cases present strong chemical incompatibilities between specific brines and specific organic inhibitors. Discussion of the chemistry of organic clay inhibitors and their chemical interactions with brines will be presented. Discussion of the chemical interaction causing incompatibilities will be presented and associated with the effects of brine properties (pH, density, and composition). Furthermore, different rock-fluid interaction tests using actual reservoir formation samples are presented to show the performance of some of the most common organic clay inhibitors in completion brines. The data presented can be used as a guideline to select compatible clay inhibitors according to the brine properties.

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