Historically Total E&P Indonesie, operating offshore East Kalimantan (Indonesia), has used a 12 to 14% KCl/polymer water-based drilling fluid to drill the intermediate hole section. Excessive hole washouts requiring significant cement volumes to properly cement the casing have been noted. Another drawback to the standard KCl/polymer system is that general hole conditions related to torque/drag and excessive time tripping in and out have affected overall efficiency. Additionally, with the necessity to maintain mud density not greater than 1.15 SG (9.6 lb/gal) for this intermediate section, significantly large dilution rates have been required while drilling with the KCl/polymer system. There was a need to improve the drilling fluid which led to the successful introduction of a novel polyamine clay hydration suppressant as a KCl alternative in this area.
Novel polyamine at 2 vol% has been used as alternative to 12 to 14 wt% of KCl. The polyamine significantly improved the clay/shale inhibition with a noticeable improvement in cuttings integrity observed across the shale shakers. Seawater with 5 to 8 wt% of sodium chloride (NaCl) was used as the base fluid for the system. The system was easy to engineer and easy to maintain at rigsite. A combination of xanthan gum and polyanionic cellulose (PAC) was used to provide the required rheology and fluid loss control in the system. There was no specific addition and handling of mixing facilities for this system.
After initial trials on 3 wells, the decision was made to replace the KCl/polymer system with this new inhibitive system as the “fluid of choice” for water-based drilling fluid sections. The system has now been selected as an alternative to KCl in offshore operations East Kalimantan, Indonesia.
To date, a total of 15 surface and intermediate sections of 12 wells have been drilled, cased and cemented successfully in Offshore East Kalimantan, Indonesia using this novel polyamine system. Dilution rates were significantly reduced by about ⅔ as compared to dilutions rates using the KCl/polymer system.