Applications
- Depth Matching between cased-hole and open-hole logs
- Pick up radioactive anomalies caused by saline water invasion
- Pick up radioactive anomalies caused by water invasion or radioactive tracers
Sample Logs
Tool Schematic
Mathematical Model
| GR = (1-\phi_e) \cdot GR_{m} + \phi_e \cdot s_w \cdot GR_w |
where GR_w is natural gamma radioactivity of formation water and GR_m is natural gamma radioactivity of rocks:
| GR_m = \sum_i GR_{mi} V_{mi}/V |
where
GR_{mi} | natural gamma radioactivity of i-th mineral |
V_{mi}/V | volume share occupied by i-th mineral |
Tool Schematic
The typical GR values for popular minerals is brought on Table 1.
| Table 1. GR values for popular minerals | ||
| Rock Type | GR, API | |
| 1 | Halite (NaCl) | 0 |
| 2 | Coal | 0 |
| 3 | Limestone | 5 – 10 |
| 4 | Sandstone | 10 – 20 |
| 5 | Dolomite | 10 – 20 |
| 6 | Shale | 80 – 140 |
| 7 | Mica | 100 – 170 |
| 8 | Silvite (KCl) | 500 |
See also
Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics / Reservoir Data Logs (RDL) @model / Lithology Log Interpretation @model