It is a well-established practice in the oil and gas industry to capture daily non-productive time (NPT) resulting from unscheduled events during drilling campaigns. Annually, the cost estimate of non-productive time (NPT) is about 31 percent of the total cost of drilling per well in the study area. Geologic Non-Productive Time (GNPT) caused by geological related subsurface events constitute major part of NPT. In most cases, GNPT is not usually tracked and or decoupled from NPT and this has made it difficult to focus efforts on with a view to proffering solutions to their occurrences. The objective of this study is to identify, measure, track and analyze underlying causes of GNPT in order to minimize or prevent financial losses and potential damages (tangible & intangible) associated with these events. The methodology used in this study includes integration of subsurface cuttings and geological features, formation evaluation challenges and observed drilling events to define twelve major subsurface events that were grouped into four GNPT categories. The categories are: (1) well flow, (2) lost circulation, (3) wellbore instability and (4) Subsurface evaluation. These events were tracked with the corresponding cost and rig time implications for wells drilled within the selected time frame. Fifty wells were drilled between 2015 to 2017 in our study area, and GNPT occurred in seventeen wells costing millions of dollars. From our analysis of the tracked GNPT over this period, the GNPT big hitters were found to be wellbore instability and lost circulation issues. The result of this study led to concerted efforts at reducing the GNPT in the drilling operations by focusing diligently on tackling the identified GNPT big hitters in 2017 through deployment of more accurate pore pressure, fracture gradient, wellbore stability modeling and most importantly, adopting effective communication strategies among the subsurface and drilling teams. This study aided in identifying, preventing and controlling the big hitters' events, thus reducing drilling incidents and overall well costs.

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