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A common issue encountered by drilling engineers during drilling operation in oil and gas industries is that simple water-based muds are not suitable for deeper depth and certain clay-swelling formations. Another option as to increasing the density of the drilling mud which brings about an increase in filtration loss, additives may be added to improve the fluid properties. This paper aims on determining the effectiveness of common salts, sodium chloride (NaCl) and potassium chloride (KCl), and haematite on the rheological properties of optimized carboxymethyl cellulose (CMC)–bentonite and partially hydrolyzed polyacrylamide (PHPA)–bentonite muds. Both CMC and PHPA polymer act as fluid loss-reducing agents and viscosifiers for normal bentonite water-based mud. The mud is further enhanced to counter certain swelling formations such as shale through the addition of NaCl and KCl. These salts inhibit the shale formation from swelling through its ions by entering the lattice of the drilling mud or formation instead of the water ions. Haematite, on the other hand, basically functions to increase mud density and acts as a substitute for barite. The effect of haematite on drilling fluid was studied because it gives higher degree of rheological parameters and increases density as compared to barite. So, an optimized concentration of additives was determined for both CMC–bentonite and PHPA–bentonite mud systems, respectively. Three grams of KCl and 3 g haematite were used for CMC–bentonite mud, while 3 g KCl and 1 g haematite were added into PHPA–bentonite mud. Both these muds have shown swelling reduction as compared to those without the use of additives. Moreover, they exhibited Herschel–Bulkley fluid behaviour according to the power law model where their ‘ n ’ value was less than 1, while their yield points were more than zero. Since shale sloughing is a major problem faced during drilling operation, it leads to major complications in drilling. So, finally, both the formulated drilling fluids are tested to analyse their effect in shale formations by static immersion test. The shale rock was collected from Champhai District of Mizoram. Both the formulated muds exhibited great results as swelling in shale rock was reduced for both muds and optimum rheological values were maintained.

journal of petroleum exploration and production technology

The effect of salts and haematite on carboxymethyl cellulose–bentonite and partially hydrolyzed polyacrylamide–bentonite muds for an effective drilling in shale formations