What is the n value in borehole log?
Standard Penetration Resistance (“N” value) The number of blows by a 63.6kg hammer dropped 760 mm to drive a 50 mm diameter open sampler attached to “A” drill rods for a distance of 300 mm after an initial penetration of 150 mm.
How do you read a well log?
Follow the Ko Ko Rules:
- Tight non-reservoir: Right-Right-Right-Right.
- Shale: Right-Right-Right-Left.
- Low porosity (tight) reservoir: Left-Right-Right-Right.
- Water bearing reservoir: Left-Left-Left-Left.
- Oil bearing reservoir: Left-Right-Left-Left.
- Gas reservoir: Left-Right-Left-Right.
What is bore log chart?
A borehole log is a record or graph of the sensor output (e.g., gamma ray count rate) plotted on the horizontal axis versus depth on the vertical axis.
How do you measure the depth of boring?
Introduction to Depth of Boring: At the depth equal to two times the width of foundation, this stress is about 10%. Considering the effect of stress felt, the boring should be always taken to a depth at least equal to one and half times of the foundation width below the base of the foundation.
How is SPT calculated?
SPT N value for cohesive soils with r 2 as 0.998 is represented by following equation.
- C = – 2.2049 + 6.484N (r^{2} = 0.998) (1)
- C = – 16.5 + 2.15N (r^{2} = 0.998) (2)
- \varphi = 7N\, \left( {r^{2} = 0.998}\, \right);for\, N \le 4. (3)
- \varphi = 27.12 + 0.2857N\, \left( {r^{2} = 0.998} \right);\,for \,N = 4 to 50. (4)
What does high SPT N value mean?
2.9. SPT (N) value in sandy soils indicates the friction angle in sandy soils and in clay soils indicates the stiffness of the clay stratum.
What is well log interpretation?
Well logs present a concise, detailed plot of formation parameters versus depth. From these plots, interpreters can identify lithologies, differentiate between porous and nonporous rock and quickly recognize pay zones in subsurface formations.
How do you read porosity logs?
To obtain porosity, read the value directly from the log. If the log is recorded in limestone units and the formation you wish to evaluate is sandstone or dolomite, then correct the log value by using the appropriate chart in a log interpretation chartbook.
What is RL in borehole?
Relative level in surveying refers to equating elevations of survey points with reference to a common assumed datum. It is a vertical distance between survey point and adopted datum plane. Thus it is considered as the base elevation which is used as reference to reckon heights or depths of other important places.
What is the minimum depth of a borehole?
Except in the case of very dense materials or bedrock, the minimum depth of borehole is 6m. Drill a borehole at least 3m into bedrock. For dense, coarse-grained soil and very stiff clays, extend boring depth up to a range of 5-6m to corroborate that soil layer thickness is sufficient.
What is the maximum depth of a borehole?
Water table lies at a depth generally less than 20 m, and the maximum depth of boreholes rarely exceeds 60 m.
What is a good N value for soil?
Correlation with soil mechanical properties
| Relative density | SPT N value | Bulk density (kg/m3) |
|---|---|---|
| Loose | 5 – 10 | 1 530 – 2 000 |
| Medium | 11 – 30 | 1 750 – 2 100 |
| Dense | 31 – 50 | 1 750 – 2 245 |
| Very dense | > 50 | > 2 100 |
What is N value in soil report?
The measured N-value (blows/0.3 m) is the so-called standard penetration resistance of the soil. The penetration resistance is influenced by the stress conditions at the depth of the test.
What does SPT N60 mean?
N60 is what a safety hammer (cathead and rope) N value is estimated to be uncorrected. An auto hammer is estimated to be about 80% efficient. 1.333 times more than a safety hammer.
What is DT in well logging?
DT. Short-spacing delay time ( t) µs/ft.
What is RT in well logging?
Rw= Resistivity of formation water. Rmf= Resistivity of mud filtrate. Rt= Resistivity of uninvaded zone.