Method and system for density correction for geophysical well logging inside drilling rods
A method and system for estimating density of material surrounding a borehole in mineral exploration, the method including inserting a tool into a drilling rod located within a borehole, the tool having a gamma radiation source and at least one sensor; raising the tool within the drilling rod; receiving gamma count readings at the at least one sensor; sending the gamma count readings to a computing device; and removing effects of the drilling rod from the gamma count readings at the computing device to calculate a density of material surrounding the borehole.
1. A method for estimating density of material surrounding a borehole in mineral exploration, the method comprising:
inserting a tool into a drilling rod located within a borehole, the tool having a gamma radiation source and at least one sensor;
raising the tool within the drilling rod;
receiving gamma count readings at the at least one sensor;
sending the gamma count readings to a computing device; and
calculating, via the computing device, an estimated density ρ of the material surrounding the borehole, wherein the estimated density ρ of the material surrounding the borehole is calculated based on:
ρ=ρ 1 −h (ρ 1 −ρ h )/ x
where ρ 1 is a density based on readings at the sensor, h is a wall thickness of the drilling rod, ρ h is a density of the drilling rod, and x is the distance between the gamma radiation source and the sensor.
2. The method of claim 1 , wherein the tool is raised at a predetermined rate.
3. The method of claim 1 , wherein the raising is done utilizing a pulley system connected to a drilling tower.
4. The method of claim 1 , further comprising calibrating the tool by running the tool through the borehole a second time after the drilling rod has been removed from the borehole.
5. The method of claim 1 , wherein the radiation source is selected to provide unique readings for a lithology of the borehole.
6. The method of claim 1 , further comprising defining a confidence range for densities based on lithological information and drilling rod compensation.
7. The method of claim 1 , wherein the tool has a single sensor.
8. A non-transitory computer readable medium for storing instructions which, when executed by a processor of a computing device, are configured to:
receive gamma count readings from a sensor of a tool, the tool having a gamma ray source and being raised in a drilling rod within a borehole;
determine a combined density from the gamma count readings; and
calculate an estimated density ρ of the material surrounding the borehole, wherein the estimated density ρ of the material surrounding the borehole is calculated based on:
ρ=ρ 1 −h (ρ 1 −ρ h )/ x
where ρ 1 is a density based on readings at the sensor, h is a wall thickness of the drilling rod, ρ h is a density of the drilling rod, and x is the distance between the gamma ray source and the sensor.
9. The non-transitory computer readable medium of claim 8 , wherein the tool has a single sensor, the instructions being further configured to compensate for density readings based on the counting values read by the sensor.
10. The non-transitory computer readable medium of claim 8 , wherein the instructions are further configured to calibrate density measurements for the tool by receiving gamma counts from running the tool through the borehole a second time after the drilling rod has been removed from the borehole.
11. The non-transitory computer readable medium of claim 8 , wherein the instructions are further configured to define a confidence range for densities based on lithological information and drilling rod compensation.