Podcast
Questions and Answers
In a wildcat well, why is a Leak Off Test (LOT) considered the most common method for assessing formation strength below the casing shoe?
In a wildcat well, why is a Leak Off Test (LOT) considered the most common method for assessing formation strength below the casing shoe?
- It allows for real-time analysis of formation fluid composition at the surface.
- It directly measures the permeability of the formation using specialized tools.
- It provides a cost-effective and direct measurement of the fracture pressure of the formation. (correct)
- It predicts the pore pressure gradient based on offset well data.
Given a leak-off test graph, what does the point at which the pressure deviates from the linear trend line indicate?
Given a leak-off test graph, what does the point at which the pressure deviates from the linear trend line indicate?
- The hydrostatic pressure exerted by the mud column.
- The minimum pressure required to initiate fluid flow into the formation.
- The maximum pressure the formation can withstand before fracturing. (correct)
- The point at which the pump reaches its maximum pressure capacity.
A well has a casing shoe at 11,000 ft TVD with a mud weight of 14.0 ppg, and a LOT pressure of 1950 psi. If the operator decides to increase the mud weight, what is the most important consideration regarding the effect on the MAASP?
A well has a casing shoe at 11,000 ft TVD with a mud weight of 14.0 ppg, and a LOT pressure of 1950 psi. If the operator decides to increase the mud weight, what is the most important consideration regarding the effect on the MAASP?
- Increasing mud weight has no impact on MAASP as long as the LOT pressure remains constant.
- Increasing mud weight only affects the surface pressure readings and not the actual downhole pressures.
- Increasing mud weight reduces the MAASP and formation integrity, requiring a careful pressure analysis. (correct)
- Increasing mud weight always increases the MAASP proportionally, improving well control.
In a leak-off test, what could cause an operator to observe an immediate pressure drop after pumping is stopped?
In a leak-off test, what could cause an operator to observe an immediate pressure drop after pumping is stopped?
If the measured leak-off pressure is lower than expected in a newly drilled well section, what might this indicate about the formation?
If the measured leak-off pressure is lower than expected in a newly drilled well section, what might this indicate about the formation?
During a leak-off test, the pressure increases linearly with injected volume until it reaches 1200 psi, after which the curve flattens out. If the initial mud weight is 10 ppg, and the casing shoe depth is 8000 ft TVD, has the fracture gradient been exceeded?
During a leak-off test, the pressure increases linearly with injected volume until it reaches 1200 psi, after which the curve flattens out. If the initial mud weight is 10 ppg, and the casing shoe depth is 8000 ft TVD, has the fracture gradient been exceeded?
What adjustments should be made if the LOT indicates a very low fracture gradient, and drilling must continue deeper?
What adjustments should be made if the LOT indicates a very low fracture gradient, and drilling must continue deeper?
A well's LOT data indicates a narrow window between pore pressure and fracture pressure. What drilling practice would be most effective in managing this situation?
A well's LOT data indicates a narrow window between pore pressure and fracture pressure. What drilling practice would be most effective in managing this situation?
You're planning a well in a region with a known depleted reservoir. How should you modify your LOT strategy compared to drilling in a normally pressured area?
You're planning a well in a region with a known depleted reservoir. How should you modify your LOT strategy compared to drilling in a normally pressured area?
A LOT on a well shows an unexpectedly high fracture gradient. What implications does this have for future drilling operations in the area?
A LOT on a well shows an unexpectedly high fracture gradient. What implications does this have for future drilling operations in the area?
Flashcards
Leak Off Test (LOT)
Leak Off Test (LOT)
A test used on exploratory wells to measure formation strength below the casing shoe.
Leak-off Pressure
Leak-off Pressure
The point on a pressure vs. volume graph where the pressure deviates from a linear trend, indicating formation fracture.
Maximum Allowable Mud Weight
Maximum Allowable Mud Weight
The maximum mud weight that can be used without fracturing the formation.
Study Notes
- In an exploratory (wildcat) well, the formation strength below the casing shoe is normally measured using a Leak Off Test.
- Leak-off begins to occur at a pressure (at surface) of 1150-1250 psi, according to the graph provided.
- With a casing shoe depth of 11,000 feet TVD (12,250 feet MD), a mud weight of 14.0 ppg, and a leak-off test pressure of 1950 psi., the Maximum Allowable Mud Weight is 17.4 ppg.
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