Horizontal sections drilled in conditions that require high mud densities to prevent wellbore collapse are very challenging from both drilling engineering and drilling fluid management point of views. Due to drilling complications, nonaqueous fluids (NAFs) are the best suitable drilling fluids of choice for drilling complex and long horizontal sections. From the other side, as nonacid soluble weighting materials cannot be used while drilling some reservoir sections, which are completed with open screens in open hole, using calcium carbonate is the most economical and best preferred acid soluble/nondamaging option to formulate these fluids.
When the density requirements reach above 90 lb/ft3 (12 lb/gal) while using calcium carbonate in the NAFs, fluid formulations exhibit high rheological values due to excessive solids. High solids loading and improper fluids engineering in these high-density ranges lead to hole instability and differential sticking issues in addition to extreme difficulties in managing completions screens runs. These challenges can severely limit the well depth or increase the operation time, impacting profitability of whole project; failing to tackle even one of them could result in catastrophic failure.
To overcome above associated challenges, a flexible novel flat rheology invert emulsion system formulation was introduced, which was customized for sustaining high solids loading while maintaining its signature flat-rheology profile. This system uses new technology emulsifier and rheology modifier package for achieving flat-rheology independent of temperature and pressure changes. The fluid formulation was implemented in the area by loading the mud system with more than 330 pounds per barrel of calcium carbonate for reaching densities up to 99 lb/ft3 (13.25 lb/gal).
This paper will present a comprehensive overview of novel technology, the steps taken from planning to execution, the overall performance-based results, the cost effectiveness of the new solution, and the challenges during implementation. The troubleshooting steps taken are also discussed for all the challenges that occurred while drilling.