Deployment	Borehole
Log Name	GR
Measured Property	Intensity of natural gamma ray emission from surroundings rocks
Sensor Type	Scintillation counter
Units
SI	R /s
Oil Metric	μ R /hr = 2.8 ·10^-10R /s
Oil Field	GAPI = 4.2^·10^-10R /s = 1.5^μ R /hr

* – for scintillation detectors

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

$\begin{array}{l}\displaystyle GR = (1-\phi_e) \cdot GR_{m} + \phi_e \cdot s_w \cdot GR_w\end{array}$

where $\begin{array}{l}GR_w\end{array}$ is natural gamma radioactivity of formation water and $\begin{array}{l}GR_m\end{array}$ is natural gamma radioactivity of rocks:

$\begin{array}{l}\displaystyle GR_m = \sum_i GR_{mi}\end{array}$

where $\begin{array}{l}GR_{mi}\end{array}$ natural gamma radioactivity of i-th mineral.

The graphic image of different shales volume models is brought on Fig. 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

Page tree

Applications

Sample Logs

Tool Schematic

Mathematical Model

See also

Page tree

Gamma Ray (GR) Logging Tool

Applications

Sample Logs

Tool Schematic

Mathematical Model

See also