Natural fractures in rocks cause drilling mud losses and wellbore stability problems. A recently developed "double porosity model" can make drilling safer and. Forecast wellbore stability to avoid drilling-related failures. Many drilling-related failures are caused by unstable boreholes, whether these are caused by lost circulation, poor hole cleaning, or stuck BHA and casing. Predicting wellbore stability. Once a geomechanical model has been developed that quantifies the principal stress magnitudes and orientations  ‎Overview · ‎Predicting failure in wells · ‎Casing seat selection · ‎Validating the.


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  • Improving Wellbore Stability

The same criterion should be used both to determine the magnitudes of well bore stability in-situ stresses and to calibrate stability models to improve predictions. Defining the mud window at a single depth Loosely speaking, the mud window can be defined as the range of equivalent densities or pressures that avoid drilling problems.

The lower bound is the mud weight required to well bore stability excessive wellbore failure as a function of orientation Fig.

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Similar figures can be developed to describe the well bore stability of lost circulationwhich defines the upper bound of the mud window Fig.

The mud window at a given depth Fig. Notice that the lost circulation pressure can be a function of wellbore orientation.


This is because it depends on the fracture initiation pressure and the pressure required to propagate the fracture away from the near wellbore as well as on the pressure required to propagate the fracture in the far field. However, the lost circulation pressure Fig.

This is because to generate a well bore stability circulation event, the wellbore pressure must be large enough to do three things: Create a fracture at the borehole wall Propagate that fracture through the near-wellbore stress concentration Extend the fracture against well bore stability least principal far-field stress The far-field stress, of course, is constant, and so the fracture propagation pressure is essentially independent of wellbore orientation.

GEO ExPro - Improving Wellbore Stability

However, the initiation well bore stability link-up pressures are strong functions of wellbore orientation. Thus, it can be helpful to choose a wellbore orientation on the basis of maximizing the lost circulation pressure to reach a drilling objective in a low-mud window environment.


In this environment, wells that must be drilled to the NW or SE at this depth should have as small a deviation from vertical as possible. Establishing a minimum safe mud weight What is the criterion used well bore stability establish the minimum safe mud weight?


Clearly, it is well bore stability that will minimize the risk of complete hole collapse. But additional factors can influence this value, including: The volume of cuttings The inclination of the well The position around the well of the breakouts.

The cuttings volume and well inclination are important because of hole-cleaning issues. The larger the cuttings volume per unit hole length, the better hole cleaning needs to be. And, because hole cleaning is easier in vertical wells than in deviated wells, vertical wells can accommodate larger amounts of failure.

well bore stability

Increases in pumping rate and carrying capacity, or reduced penetration rates, can mitigate the risk associated with excessive cuttings volumes.

Because in deviated wells there is considerable pipe contact with the top and bottom of the well, breakouts in these locations are likely to be more problematic than breakouts on well bore stability sides of the hole.

However, if the well needs to well bore stability steered, breakouts on its sides may adversely affect directional control.

Wellbore Stability: A Critical Review and Introduction to DEM - OnePetro

These wellbore stability analysis requires a geomechanical model constructed from one or more offset well bore stability geomechanical models. Stress magnitudes are calculated using the calibrated parameters from the offset wells for required wellbore trajectories.

Additionally, uncertainty analysis of the wellbore stability assessment using Monte Carlo Simulation can also be undertaken.