RQD and REC in core run with different types of rock 1

[pelelo]

Hello,

When performing rock coring (rotary drilling), I was wondering how would you measure the recovery and RQD for an specific run IF there are different types of rock?.

For example, the total run is 5 feet (60 inches). The first (top) 1 ft is sandstone, then 1.5 ft limestone, then 1 ft of claystone (at the bottom). The OVERALL recovery (REC) is 3.5 /5 x 100 = 70%.

Same for the RQD. Core length > 4": 5" (sandstone), 8" (limestone) and 0" (claystone). The OVERALL RQD would be 13/60 x 100 = 22%. This would classify the rock as very poor quality (RQD < 25%). However, this RQD was based on 2 types of rocks (Sandstone + limestone).

Do you state anything special during the rock description when this situation happens?

 

[EireChch]

Typically you would just log RQD for core length. One reason being that if you have core loss, you dont know which rock it has occurred in.

 

[pelelo]

So if RQD is 20% for example, you would classify the core length as very poor?, instead of an specific rock type as being very poor?, correct?

 

[EireChch]

If you have 100% recovery you could go down the route of splitting your RQD up and applying it to different rock. but in my experience, RQD is measured on full core run lenght