Shale
swelling during drilling operations causes many problems
mainly related to wellbore instability. The oil-based muds (OBMs)
are very effective in controlling the swelling potential of clay-rich
shale formation, but their environmental concerns and the economic
aspects curtail their usage. In the application of water-based mud
(WBM), it is mixed with various swelling inhibitors such as inorganic
salts (KCl and NaCl), sodium silicate, polymers, and amines of various
types. The above-mentioned materials are however afflicted by some
limitations in terms of their toxicity, their effect on drilling mud
rheology, and their limited tolerance toward temperature and oil contamination.
In this study, we investigated a novel hybrid aqueous alkali alumino
silicate (AAAS) as a shale swelling inhibitor in WBM. The AAAS is
a mixture of sodium, aluminum, and silicon oxides. Experimental investigations
were carried out using a linear swell meter, hot rolling and capillary
suction timer, ζ-potential test, filtration test, and rheology
test. The application of hybrid silicate as a swelling inhibitor was
studied in two phases. In the first phase, only silicate solutions
were prepared in deionized water at various ratios (1, 2, and 5%)
and tested on sodium bentonite and shale samples containing high contents
of kaolinite clay. Further testing on commonly used inhibitors such
as KCl and sodium silicate solutions was conducted for comparative
purposes. In the second phase, different drilling mud formulations
consisting of various percentages of AAAS were mixed and tested on
original shale samples. It was observed that the novel silicate-based
mix proved to be a strong shale swelling inhibitor. Its inhibition
performance was better as compared to the sodium silicate solution
and KCl solution. It not only inhibits shale swelling but also acts
as a shale stabilizer due to its high adsorption on the shale surface,
which prevents the shale/water reactivity, makes the shale formation
stronger, and prevents caving.