Geomechanics Improves Drilling Operations and Reduces Non-Productive Times (NPT) in Kilo Field, Offshore Northwest Java

Ong, See Hong (Baker Hughes) | Power, William L. (Baker Hughes) | Sitio, Aprianto (Baker Hughes) | Tanjung, Erwindo (PERTAMINA Hulu Energy)

OnePetro 

Abstract Recent drilling of moderately to highly deviated development wells in the Kilo Field has proven to be extremely challenging. Numerous lost-time incidents including stuck pipe, pack-off, and difficulties in running casing were experienced, particularly when drilling through the Main-Massive Formation. Earlier analyses pointed to mud material quality issues, but drilling performance benchmarking with other nearby fields ruled out this explanation. Faced with continually high NPTs, a geomechanical study was initiated to mitigate the wellbore instability problems. The recommendations arising from the comprehensive geomechanical and drilling experience analyses have been implemented to improve performance during subsequent development drilling. The field-wide geomechanical model indicates the Kilo Field is characterized by a state of stress that is transitional between a normal and strike-slip faulting regimes. The combination of relatively large differential stress and relatively weak rocks means the field is potentially subject to stress-induced wellbore instability problems. However, observations of numerous time-dependent failures imply secondary influences must also be considered to arrive at possible remediation strategies. A systematic ranking process has been developed to delineate the primary causal mechanism of wellbore instability. This process suggests that the major contributor to the time-dependent deterioration process is rising pore pressure caused by the invasion of drilling fluid into micro-fractured formations, and then exacerbated by less-than-optimal drilling practices. This finding, together with the improved geomechanical understanding of the Kilo Field, provides the basis for optimizing mud weights and wellbore trajectories as well as formulating appropriate drilling strategies to maintain the mud hydrostatic support (overbalance) in future drilling. The finding also highlights the importance of integrating geomechanics with drilling practices when developing strategies to mitigate unstable hole problems. This paper presents a comprehensive, ordered workflow that integrates the disparate data available in a mature field to identify the most likely causative mechanisms of the time-delayed wellbore instabilities. This knowledge was then used to develop strategies for optimizing future drilling operations in the Kilo Field.

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