30 Questions
Which pressure must be greater than the least principal stress in the formation to initiate a fracture in the borehole wall?
The hydrostatic pressure of the drilling fluid
What is the direction in which fractures will propagate when the pressure in the borehole exceeds the least of the stresses within the rock structure?
Perpendicular to the least principal stress
What is the primary well control barrier that cannot be achieved if the formation breaks down and mud losses occur?
Borehole stability
What is the condition that can lead to formation fluid influx?
BHP > F.F.P.
What is the term used to describe the pressure of the drilling fluid column?
Formation fracture pressure
What is the consequence of the formation breaking down when the borehole pressure exceeds the least principal stress?
Mud losses can occur
What is the main purpose of conducting LOT and FBT tests?
To identify the weakest part of the wellbore
When is LOT and FBT testing carried out?
Immediately after setting and cementing the casing
What is done to avoid the drillbit getting stuck in the openhole during the LOT and FBT tests?
Pull the drillbit back into the casing shoe
What is generally used to close the BOPs during LOT and FBT testing?
Pipe ram
Why is pressure applied by pumping a small amount of mud into the well at surface during LOT and FBT testing?
To measure pressure response in the well
What is assumed about the weakest part of the wellbore in LOT and FBT tests?
It is just below the casing shoe
What is the purpose of calculating the equivalent circulating density (ECD)?
To get a true representation of the pressure acting against the formation at the bottom of the well
What contributes to the additional pressure at the bottom of the borehole when the drilling fluid is circulating?
The frictional pressure required to pump the fluid up the annulus
In the given example, what was the true vertical depth of the casing shoe?
5010 ft
What was the surface pressure at leak off in the given example?
940 psi
What is the calculated maximum mud weight for the next section to be drilled in the given example?
13.3 ppg
What was the mud weight used to conduct the leak off test in the given example?
10.2 ppg
What is the primary purpose of a leak off test (LOT)?
To determine the maximum pressure the open formation can withstand before fracturing
When is a leak off test typically conducted?
After drilling out of a new casing shoe
How is the leak off pressure determined during a LOT?
By observing the pressure at which fluid begins to leak into the formation
What is the primary use of the leak off pressure determined from a LOT?
To establish the upper limit for the mud weight
During a LOT, when is the operation typically terminated?
When the pressure stops increasing linearly
Which of the following is NOT mentioned as a method to calculate fracture pressure?
The Bourgoyne and Young Method
What is the primary purpose of the Formation Integrity Test (FIT)?
To determine the maximum pressure the formation can withstand
If fluid begins to leak off into the formation during a FIT, what does it indicate?
It is not safe to drill the next section with the current parameters
What is the Leak Off Pressure (LOP) used for?
To determine the maximum allowable pressure on the formation below the shoe
What is the Maximum Allowable Annular Surface Pressure (MAASP) calculated from?
The Leak Off Pressure (LOP)
How is the maximum allowable mud weight for the next hole section determined?
From the Leak Off Pressure (LOP) calculations
What safety factor is typically subtracted from the allowable mud weight?
0.5 ppg (0.026 psi/ft)
Learn about the conditions when formation fluid influx can occur and how formation breakdown can lead to mud losses and hinder primary well control. Explore the three principal stresses in formations that determine fracture occurrence under borehole pressure.
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