Abstract
Santan is a mature gas field in East Kalimantan, Indonesia, where infill wells are being drilled to increase production rates. A crowded offshore platform in the Santan Field increases well trajectory complexity and presents a heightened risk of wellbore collision issues. The high number of wells on this directional pad in the shallow water drilling environment results in densely populated existing conductor pipe. Thorough drilling assessments and anti-collision directional drilling mitigation practices are key to successfully executing safe and reliable drilling operations.
To further mitigate the likelihood of a well control situation resulting from a collision with a neighboring conductor or casing, a 17.5 in. IADC Classification 115 Steel Tooth (ST) rolling cone bit with special heel technology was utilized in the Santan field. This is the first time this technology has been applied in Asia Pacific. The ST bit employs continuous disk shaped heel rows on all three cones rather than conventional ST chisel shaped heel row teeth which have multiple sharp cutting edges. The special disk heel rows are designed to deflect off casing in the event of a collision in order to minimize damage to conductor or casing.
The use of the special disk heel technology bit has yielded positive results to date. The bits have successfully and safely drilled in a critical zone where the center-to-center distance between slots was as low as 1m. The drilling performance and well trajectory targets were achieved. Reduced drilling parameters were used as per anti-collision and lost circulation practices, however, the overall rate of penetration (ROP) and directional behavior with the special disk heel bit was similar to conventional ST bits used in offset wells without collision risks. Turn and build rates of up to 4.8°/100 ft were achieved on a bent motor bottomhole assembly, while the average distance to the plan at the end of the section was only 10.59 ft. A series of laboratory casing collision tests was conducted during the development of the special disk heel bit which demonstrated a 75-80% reduction in casing collision damage as compared to a conventional IADC 115 ST bit. Overall, this technology minimizes the detrimental effects should a collision occur, without sacrificing ROP or steerability performance.
The special disk heel ST bit has proven to cause significantly less damage to casing from a collision event than any other bit type – ST, tungsten carbide insert (TCI), or PDC bits, while still providing excellent ROP and steerability in soft formation, shallow water applications. This technology allows operators to more confidently place additional wellbores in crowded offshore template environments for greater field development from a single platform.
