In drilling and well completion, "Known-Unknown" refers to a method for managing uncertainty and risk during the drilling and completion process. It's a way of identifying and analyzing potential unknowns that could impact the project's success.

Here's a breakdown:

Known: This refers to factors that are well-understood and predictable. These could include things like:

• Geological data: Existing well logs, seismic surveys, and other geological information.
• Well design parameters: Target depth, casing sizes, and drilling mud properties.
• Equipment specifications: Drilling rig capabilities, drill pipe dimensions, and tool types.

Unknown: This refers to factors that are uncertain or potentially unpredictable. These could include things like:

• Formation properties: Reservoir pressure, permeability, and fluid type.
• Geomechanical risks: Fault zones, potential wellbore instability, and abnormal pressures.
• Operational risks: Equipment failures, weather delays, and unforeseen logistical challenges.

The Known-Unknown framework helps to:

1. Identify potential risks: By systematically categorizing information as known or unknown, engineers and operators can better understand potential threats to the project.
2. Develop mitigation strategies: For each identified unknown, a plan can be developed to address the potential risk. This might involve acquiring more data, implementing contingency plans, or employing specialized techniques.
3. Improve decision-making: By having a clear understanding of the known and unknown factors, stakeholders can make more informed decisions about drilling and completion activities.

Example:

Imagine a drilling operation targeting a shale formation. The known factors might include the well design, geological data from nearby wells, and equipment specifications. However, the unknown factors could include:

• Reservoir pressure: Is the formation over-pressured or under-pressured?
• Fracture network: How extensive and interconnected are the fractures within the shale?
• Fluid type: Is it oil, gas, or a mixture?

By addressing these unknowns through data acquisition, modeling, and contingency planning, the operator can improve the chances of a successful drilling and completion operation.

In summary, the Known-Unknown approach is a valuable tool for managing risk and uncertainty in drilling and well completion. It encourages a proactive approach to identifying potential problems and developing strategies to mitigate them.