The use of water-based drilling fluids to drill shale formations can cause wellbore stability problems as a result of the reaction of water with clay minerals. Examples of wellbore stability problems include shale disintegration, swelling and sloughing. Different types of clays give different types of problems. For example, when it is exposed to water, a shale sample with a high percentage of smectite tends to swell while another shale sample with a high percentage of kaolinite tends to disintegrate and disperse. Consequently, there will be higher solids loading in the wellbore. Hence, the chance to get the pipe stuck increases and the hole cleaning efficiency of drilling fluid decreases significantly.

To combat the abovementioned challenges and study the shale rock to be drilled, a series of tests should be conducted. The selection of the testing procedures and fluids to test shale samples with has been selected mainly on empirical basis involving trial and error. Molecular modeling technique can be utilized before taking the shale samples to the laboratory to provide theoretical background on the rock-fluid interactions at molecular scale. One advantage of this approach is to gain better understanding of the rock-fluid interactions from theoretical point-of-view in order to explain why one shale inhibitor works and provides adequate inhibition for one shale sample but does not work properly for another sample. The second advantage is that having insights into the potential rock-fluid interactions can guide the research to include or exclude certain types of shale inhibitors and to shorten the trial and error procedure. These advantages provide a basis upon which future drilling fluids planning can be optimized to mitigate wellbore stability issues.

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