Fine tuning PDC bits for 'sedimentary interbeds' in deepwater

Typical 4,5 and 6 bladed large cutter (16-25mm cutter)PDC bits drill deepwater claystone with little issues at optimal and often contrained ROP (due to LWD data acquisition requirements).

As soon as silt/sand/limestone content increases however it's often like hitting a brick wall where to further avoid instantaneous doglegs or washouts above or to drill through etc significant time is lost to drill the non claystone sequences.
Later on and perhaps more importantly 'wellbore quality defects' are shown when it is more than common to hang up during trips or with logging tools etc at these interfaces.

When weight is applied on these sequences high dyanmic and vibrational effect also often/frequently result damaging bit, risking other drillstring and/or wellbore asurance issues. What results and the then smarter option is to cut back on weight, and take the ROP hit so as not to compromise on hole quality. 

Indeed in severe interbeds and/or well cemented stringers I have seen bits pulled in more than one region as they failed to drill through.

What can/is being done is terms of fine tuning these bits to drill through these challenges/issue more effctively/efficiently is the topic of this discussion?

What has/is being done to address this, what success, lessons have are being learned?

Regards.

1 Answer(s)

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