Fig. 1. Apparent rock strength calculated from records from worn and unworn bits.
The Payzone J simulator is being developed to help optimize drilling operations in real time. At present, the work is still experimental, and is using simulated drilling results.
Rock Strength
The J simulator has a capability to generate a drilling record that can
be output and used by another stand-alone program. This could be,
for example, a
program that deduces the rock strength from the drilling record.
The output of such a program is shown in Figure 1. This
shows the rock strength inferred from the drilling record for two bit runs
of 500 ft. For one bit run, the bit was assumed to be completely
unworn ("New") while for the other, the bit was allowed to wear from new
to about T3 condition ("With wear").
Fig. 1. Apparent rock strength calculated from records from worn and unworn bits.
When the interpretation algorithm was applied to the data set for the unworn bit, it made an accurate estimate of the rock strength. However, in the record for the bit that wore, the actual ROP was less than it would have been with an unworn bit. The result is that the interpretation algorithm estimated the rock strength to be greater than it really was.
Bit Tooth Wear
The difference between the real and estimated rock strengths is a refelection
of the state of wear of the bit teeth, so if the two records are then
compared in a second algorithm, one can make an estimate of the tooth
wear as a function of distance drilled (Figure 2).
Fig. 2. Bit tooth wear calculated from the drilling response.
The data presented above are from synthetic records generated by Payzone J, not field data. We are at present working on testing these ideas on real field data. If the work is successful, it may be possible to use the method on field records at the time they are generated. This would allow the driller to use the interpretation algorithms in real time to detect the wear of the bit as it develops.
Last update 20 March 2001.