Abstract

Mobil Oil Indonesia has successfully drilled and completed two horizontal wells, C-II-18 and C-III-12 during 1991 in the Arun field, North Sumatra, Indonesia.

The objective of these wells was to increase gas deliverability and improve condensate to gas ratio (CGR) by completing the wells bare-foot with a 6"hole in the condensate-rich lower section of the Arun Limestone. At a later date, Mobil has the option to exploit the portion of Arun limestone in the build section behind the 7" liner to increase total gas deliverability. Early production results from both wells indicate gas and condensate rates significantly higher than comparable standard Arun wells with 40°-50° inclination.

The biggest challenge in horizontal drilling was high circulating temperature, in excess of 300°F, in the Arun limestone which caused MWD tools to fail in the 6" horizontal hole in C-II-18. The 6" horizontal hole on both wells adopted conventional rotary BHA's. Undergauge string stabilizers were employed as needed to maintain or increase hole angle. Directional data in the 6" hole was obtained by running magnetic multishot surveys (MMS). The well path was kept within an 80 ft interval window in the horizontal section. Azimuth control was maintained by lining up the target at entry and holding course by employing PDC bits with minimal walk tendency. Differential pressure sticking, key seating and lost circulation risks were other challenges in horizontal drilling. These were significantly reduced by employing a 7" liner in the build section to the start of horizontal portion of the hole.