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- The simple gamma ray log and the spectral gamma ray log.
- The GR log detects responses from in-situ radioactive elements within the formation; thorium, potassium and uranium.
- The simple GR log shows the combined effect of all these elements while the spectral GR log shows their individual effects.
- Used to calculate the volume of shale present within the formation.
- Possible errors include:
- reduced response due to increased compton scattering from the accumulation of drilling mud in caved in sections of the well.
- counted for by running caliper logs simultaneous to GR logs, and utilising charts published by mud logging companies which correct for borehole size, with mud property consideration
- the use od radioactive mud additives increases the response to the GR logs as they pass through the drilling fluid, and if the mud invade the formation then the tool will read a higher than normal formation response
- counted for by utilising charts published by mud logging companies with mud property consideration

3. mechanical, spontaneous, induced


Using the SP log we can determine the formation layers (LHS - sands, RHS - shale). Differences between oil and water in potential clean sand zones is determined by the resistivity log (large

difference between tracks - formation water, small differnece (high res) - oil).