The use of water-based drilling fluids to drill shale formations causes wellbore stability problems as a result of the reaction of water with clay minerals. When it comes in contact with water, clay starts to react, swell and/or disperse leading to shale disintegration and sloughing. Consequently, tight hole might develop and/or higher solids loading in the wellbore might be experienced and, hence, the chance to get stuck pipe increases and the hole cleaning efficiency of drilling fluid decreases significantly.
This paper describes the experimental work conducted on four shale samples to assess clay-fluid interactions and shale stabilization. After conducting mineralogical analysis using X-ray diffraction, shale inhibition tests including dispersion and swelling tests were carried out using de-ionized water, 5% potassium chloride brine and 5% Polyamines solution. The work has been extended to cover different pure clay samples: sodium montmorillonite, illite and illite smectite mixed layer.
Cation exchange capacity results showed high reactivity in sodium montmorillonite and illite-smectite mixed layer as they are more willing to exchange cations and adsorb water at natural conditions. Similarly, shale samples with higher concentration of smectite and illite-smectite showed higher CEC values. Dispersion results showed that shale recovery percentages varied from 30.8% for shale sample dominated by kaolinite to 98.65% for those with low kaolinite content. For the high kaolinite sample, the recovery percentage jumped from 30.8% to 59% with potassium chloride and eventually to 85.5% when the polyamine solution was used. When the samples were tested in the swell meter, results showed higher swelling percentage values for those samples with higher smectite content followed by illite while two samples showed no potential swelling as they have low clay content of less than 15%.