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Plot The Estimated Actual Fracture Gradient Curve

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• Plot the estimated actual fracture gradient curve and the designed fracture gradient curve, which is the estimated actual fracture gradient, less allowance for well control, surge, or ECD. • Plot offset mud weight and LOT (or Formation Integrity Test) data to provide a check of the pore pressure predictions. • Start from the bottom on the mud weight curve (Point A); draw vertical line up to the designed fracture gradient curve (Point B). Point B is the initial estimated intermediate casing setting depth. The interval between Point A and Point B is the initial estimated production casing or liner interval. • Move cross to Point C from Point B at the same depth to identify the mud weight required for the depth. • Move up to Point D (must stay under the designed fracture gradient curve) to determine the surface (or intermediate casing in some offshore areas term) casing setting depth. • Move cross to Point E from Point D at the same depth to identify the mud weight required for that depth. In the case shown in the figure, there would be no requirement for casing above this depth. However, a conductor casing (or surface casing in some offshore areas term) is required to prevent wash out of shallow formation and to provide support for subsequent wellhead and to enable diverters to be installed. Certain factors apart from the pore pressure and fracture gradient are also involved in the casing depth selection process and they are: • Underground supply drinking water zones •

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