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Questions and Answers
What is one of the methods used for predicting pore pressure in high porosity/permeability formations?
What is one of the methods used for predicting pore pressure in high porosity/permeability formations?
How is SHmax calculated from wellbore breakouts according to the diagonal line from tensile fractures?
How is SHmax calculated from wellbore breakouts according to the diagonal line from tensile fractures?
Which lab method is NOT listed for estimating pore pressure in shales?
Which lab method is NOT listed for estimating pore pressure in shales?
What does effective stress consider in pore pressure measurements?
What does effective stress consider in pore pressure measurements?
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According to the content, how can seismic data contribute to pore pressure assessment?
According to the content, how can seismic data contribute to pore pressure assessment?
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What should be done to calculated pore pressures when possible?
What should be done to calculated pore pressures when possible?
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In a strike-slip faulting regime, in which direction does SHmax act as observed in deviated wells?
In a strike-slip faulting regime, in which direction does SHmax act as observed in deviated wells?
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What does the orientation of wellbore breakouts in deviated wells depend on?
What does the orientation of wellbore breakouts in deviated wells depend on?
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What type of fractures typically occur around the wellbore due to drilling in deviated wells?
What type of fractures typically occur around the wellbore due to drilling in deviated wells?
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Which factor does NOT contribute to modeling the magnitude and orientation of SHmax?
Which factor does NOT contribute to modeling the magnitude and orientation of SHmax?
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What is indicated by the angle of the breakouts with respect to the wellbore axis in deviated wells?
What is indicated by the angle of the breakouts with respect to the wellbore axis in deviated wells?
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How can stress magnitude and orientation be determined around a deviated wellbore?
How can stress magnitude and orientation be determined around a deviated wellbore?
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What equation is used to assess wellbore stability in a deviated well?
What equation is used to assess wellbore stability in a deviated well?
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What does the initial porosity (φ0) represent in the context of pore pressure prediction?
What does the initial porosity (φ0) represent in the context of pore pressure prediction?
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What is inferred when geophysical data shows abnormally high porosity at a given depth?
What is inferred when geophysical data shows abnormally high porosity at a given depth?
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What does the ratio method rely on for pore pressure predictions?
What does the ratio method rely on for pore pressure predictions?
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Which statement accurately describes the behavior of effective overburden stress with depth in hydrostatic conditions?
Which statement accurately describes the behavior of effective overburden stress with depth in hydrostatic conditions?
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Why might the ratio method lead to unphysical pore pressure calculations?
Why might the ratio method lead to unphysical pore pressure calculations?
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In Eaton's method, which parameter typically corresponds to the stress in pore pressure calculations?
In Eaton's method, which parameter typically corresponds to the stress in pore pressure calculations?
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What can lead to the need for adjusting the exponents in Eaton's method?
What can lead to the need for adjusting the exponents in Eaton's method?
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What is the acoustic formation factor represented by in the porosity equation?
What is the acoustic formation factor represented by in the porosity equation?
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What does the color red indicate regarding wellbore stability?
What does the color red indicate regarding wellbore stability?
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What is the significance of different strength scales in the wellbore breakout initiation figure?
What is the significance of different strength scales in the wellbore breakout initiation figure?
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Which statement about tensile fracture initiation is true?
Which statement about tensile fracture initiation is true?
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In the context of wellbore breakout initiation, what does a blue color signify?
In the context of wellbore breakout initiation, what does a blue color signify?
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How do the calculations for wellbore breakout initiation relate to wellbore stability?
How do the calculations for wellbore breakout initiation relate to wellbore stability?
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What factor is specifically mentioned as impacting tensile fracture initiation?
What factor is specifically mentioned as impacting tensile fracture initiation?
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What does red indicate in the context of tensile fractures?
What does red indicate in the context of tensile fractures?
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What is a key difference between wellbore breakout initiation and tensile fracture initiation?
What is a key difference between wellbore breakout initiation and tensile fracture initiation?
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How does increasing delta p affect drilling-induced tensile fractures (DITFs)?
How does increasing delta p affect drilling-induced tensile fractures (DITFs)?
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Which of the following is true regarding stress magnitudes in wellbore breakout initiation?
Which of the following is true regarding stress magnitudes in wellbore breakout initiation?
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What primarily determines the angle at which the tensile fracture forms relative to the wellbore?
What primarily determines the angle at which the tensile fracture forms relative to the wellbore?
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What happens to the range of angles over which fractures propagate when raising mud weight?
What happens to the range of angles over which fractures propagate when raising mud weight?
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What does the heavy black line in Figure 8.10 represent?
What does the heavy black line in Figure 8.10 represent?
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What is the significance of the angular span θt in the context of en echelon DITFs?
What is the significance of the angular span θt in the context of en echelon DITFs?
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What occurs when σtmin is tensile during drilling?
What occurs when σtmin is tensile during drilling?
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Which factor is NOT mentioned as influencing drilling-induced tensile fractures in the observed well?
Which factor is NOT mentioned as influencing drilling-induced tensile fractures in the observed well?
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Study Notes
SHmax from Wellbore Breakouts
- SHmax can be determined from wellbore breakouts, which are elliptical or teardrop-shaped features formed by failure of rock.
- The width of the breakout on one side of the wellbore (Wbo) is related to the maximum horizontal stress (SHmax) and the unconfined compressive strength (UCS) of the rock.
Pore Pressure Prediction
- Pore pressure is the pressure of the fluids contained within the pores of a rock.
- Estimating pore pressure is crucial for drilling operations and formation evaluation.
- Pore pressure can be predicted using various methods, depending on the formation type and available data.
- Wireline-conveyed and drill stem-conveyed pressure measurement tools directly measure pore pressure.
- Mud weights are used to estimate pore pressure by monitoring the drilling fluid density required to balance formation pressure.
Compaction Trends from Lab Measurements
- Porosity decreases with increasing effective stress, which is the difference between applied stress and pore pressure.
- The relationship between porosity and effective stress can be determined through laboratory experiments.
- This relationship can be used to estimate pore pressure from measured porosity values.
Ratio Method (Sonic and Resistivity Logs)
- This method uses the ratio of measured sonic and resistivity values to normal (reference) values to estimate pore pressure.
- The calculation requires knowledge of normal values for sonic and resistivity for the region.
- The ratio method does not explicitly consider overburden or effective stress and can sometimes result in unrealistic pore pressure predictions.
Eaton's Method
- This method uses measured resistivity and sonic logs to estimate pore pressure.
- It utilizes a relationship between pore pressure, hydrostatic pore pressure, and measured resistivity and sonic travel time.
- The exponents in the formula are often adjusted for different regions to improve accuracy.
Stress Around a Deviated Wellbore
- The stresses around a deviated wellbore are not uniform, resulting in complex stress conditions.
- The orientation of the wellbore with respect to the in-situ stress field influences the stress distribution.
- Understanding the stress distribution is critical for wellbore stability and drilling operations.
Observations from Inclined Boreholes
- Breakouts in deviated wells can be used to determine the orientation of the maximum horizontal stress (SHmax).
- Drilling-induced tensile fractures (DITFs) can also form in deviated wells.
- DITFs typically form as en-echelon pairs, which are inclined to the wellbore wall.
- The orientation and position of both DITFs and breakouts reveal information about SHmax magnitude and direction.
Wellbore Breakout Initiation Tendencies
- Wellbore breakout formation is influenced by the balance between rock strength and applied stress.
- The tendency for breakout formation is higher when rock strength is lower and stress magnitudes are higher.
- The tendency for breakout formation also depends on the wellbore angle and the direction of SHmax.
Tensile Fracture Initiation Tendencies
- Tensile fractures can form in deviated wellbores when there is a tensile stress component on the borehole wall.
- The tendency for tensile fracture formation is increased with higher mud pressures.
- The orientation and position of tensile fractures provide information about the relative magnitudes of horizontal stresses.
Field Observation on DITFs
- DITFs are observed in deviated wells and can be used to constrain the magnitude of SHmax.
- The length and orientation of DITFs are related to the difference between mud pressure and the minimum tensile stress on the borehole wall (Δp)
- This information is used to build a relationship between SHmax and Shmin.
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Description
Explore the concepts of SHmax, pore pressure prediction, and compaction trends. This quiz covers the relationships between wellbore breakouts, rock strength, and drilling operations. Test your understanding of essential geomechanical principles used in the field.