Cost overruns can easily manifest during well construction because of unexpected issues including lost returns, differential sticking, and narrow pore pressure/fracture gradients. To better plan for potential overruns, operators sometimes earmark 10 to 25% of the Authorization for Expenditures (AFE) to cover the unexpected costs, which can significantly affect drilling budgets. Technical and operational risks versus the potential return on investment (ROI) are critical factors in determining whether a project will proceed.
Too often the best drilling practices used to address trouble zones are limited to a few conventional methods with a narrow range of effectiveness. Also, a lack of rock mechanics knowledge can prevent the most efficient solution being applied.
Some operators are implementing planning programs that assess and integrate the latest processes and technologies to address drilling risks up-front. Cutting-edge technologies such as managed pressure drilling methods, drilling with casing, drilling with liners, and solid expandable casing have been highly effective. Implementing proactive evaluation processes and applying the latest tools and techniques can efficiently address operational risks and trouble zones to ultimately reduce nonproductive time (NPT) and associated costs.
Employing common practices and technologies that are typically ineffective and that drive up NPT cost should be considered unacceptable. Common-sense, well-construction evaluation processes that are used with validated conventional and new technologies have proven their worth by reducing expenditures and risks—preventing the loss of wells and increasing the operator’s ROI.
This paper reviews real drilling challenges that have been encountered and the common practices that were employed to address these drilling hazards. Also this paper compares and contrasts how these same circumstances have and can be addressed much more efficiently with engineering evaluation processes that help determine the best drilling tool and/or technique to mitigate risks and reduce NPT.