Abstract
Drilling re-entry wells with the highest expected production and least possible cost is always the aim of operators. The biggest challenge in gaining maximum reservoir contact when drilling with underbalanced coiled tubing drilling (UBCTD) is when it reaches lock up depths, resulting in weight transfer issues to the bit and reduced reservoir contact. Factors affecting this are formation, well profile, tortuosity, etc. These issues can be mitigated by using a rib-steered motor (RSM), with which it is possible to increase lateral reach by drilling smoother wellbores.
One technique is to thoroughly define the primary objective of the well, during the pre-planning stage, not only to increase hydrocarbon recovery, but to improve wellbore quality and minimize tortuosity which helps to achieve a greater reservoir contact. Using underbalanced coiled tubing drilling grants access to new gas-bearing formations in reservoirs that were previously by-passed or missed.
The authors present the advantages of using a 3-in. RSM compared to a 2⅞-in. conventional motor, with the help of a case study comparing all RSM and conventional motor runs. It also compares rate of penetration using RSM and 2⅞-in. conventional motor and how it affects the occurrence of lockup while drilling.
The paper also details how an underbalanced well in the Middle East for a large operator using the 3-in. RSM managed to complete the well in 24 days, some 18 days ahead of schedule for the Approval for Expenditure (AFE). The same well was also characterized by a number of drilling records that included the longest footage in a 24 hr period and the longest-ever run drilled since UBCTD was introduced. This increased performance can largely be credited to the revolutionary technology that the RSM brings to coiled tubing drilling (CTD), enabling wells to be drilled faster, with significant benefits in reach, steering ability and greater reservoir contact.
