asx announcement 14 january 2009, page-16

Hi geojac,

Answers to questions:

1. Theres always a certain amount of vibration going on downhole with a drill string. To minimise this you endeavour to stabilise the bottom section of the drill string (Bottom Hole Assembly or BHA)with stabilisers or roller reamers. You also generally want to design your BHA so the string is in tension while youre drilling. Optimising drilling parameters....particularly string rotation speed can also help minimise downhole vibration. Many companies run downhole motors which allow you to turn the drill string at a slower speed as the motor is driving the bit not the string.
2. How do strings get stuck? There are many mechanisms that can lead to a stuck string. Bad hole cleaning can lead to packing off around bit and/or BHA. The formation can be overpressured and pinch in on your drill string. The same can happen when drilling formations containing high swelling clays with water based mud systems. The formation may mechanically fall apart and pack off the BHA if its tectonically stressed. Fractures and faults can sometimes cause problems..this could possibly be the issue with Savina-1. Lots of possible causes.
3. working a stuck string free? You basicallyt pull on it and try to get it to turn. If you havent got full circulation then you try and re-establish circulation by various means (in extreme cases you perforate your BHA and circulate via same). The string can be rotated in both directions but if youre stuck you need to be careful you dont apply too much torque and exceed the make up torque of the drillpipe connections....you'll then back off your drill string and be in a bigger mess. Most operators run jars in their BHA. Jars are hydraulic subs that store energy which can be released as an up and down jarring motion.

As already stated the most important thing is to keep a handle on costs and benfits of what youre doing. When you reach the point where sidetracking becomes the most cost effective option then thats what must be done. The better operators have a forward plan in place as soon as they get stuck. The amateurs keep yanking away for weeks without any consideration to cost effectiveness of the operation and end up with a very expensive hole in the ground.