USER MANUAL Doc.No: WI4200 Rev.No: 6.00 24h on-call support: +47 51951170
AST FUNCTION The Anti Stick-slip Tool (AST) stabilizes drilling torque originating from the bit through a direct mechanical process where excess torque causes the tool to contract along internal helical splines. This contraction will effectively decrease the weight on bit (WOB) and prevent further accumulation of torque. An internal spring is energized in the process and will cause the tool to extend thereby increasing WOB when drilling torque decreases. This process ensures continuous efficient drilling is maintained and destructive torsional vibrations ( stick-slip) are limited. The stroke of the tool is sufficient to provide the desired effect without affecting depth tracking. The mean weight on bit is controlled from surface and no changes are necessary to normal drilling procedures. This also allows the tool to be used without the need for an on-site specialist. The illustration shows how the AST will contract to reduce WOB in case of excess torque from a sticky formation layer. LIMITATIONS AST Page 2 of 6
BHA CONFIGURATION: The AST tool is typically placed in the BHA immediately above the non-magnetic portion and below any roller-reamer or stabiliser fitted at this. DO NOT position the AST in a string transition area e.g. between collars and HWDP. Avoid having the tool placed between stiffer BHA components. With Under-Reamer, the AST is placed above the reamer and should be spaced out by a flex pipe, collar or pony collar to limit sideforces on the AST. HANDLING The unit is robust and cannot be damaged by standard pipe-handling equipment. However under no circumstances should any handling tools or equipment be used on chromed surface of the telescopic extension (Illustration A). Protective transport clamps (yellow) are fitted to some toolsizes.(illustration B) Remove the clamp in the rotary - before use and put back on when the tool is laid out. Illustration A Illustration B Protective clamp (all elastomer) CAUTION 1: The tool can compress and rotate slightly if weight is applied during handling in the rotary table NOTE 1: There is no need for a safety/protective clamp on the tool. Note however Caution 1 AST Page 3 of 6
DRILLING: No particular steps are necessary when drilling with AST with the exception of the cautions and notes detailed in this manual. The normal procedure to start drilling is establishing a good off bottom torque reading and then carefully lower the bit to bottom applying weight to increase torque to the desired level. NOTE 2: When drilling vertical wells, the bit RPM should be 120 RPM or higher to ensure optimal AST performance, ensuring that the bit is lifted from bottom faster than the string above the AST is moving down. If there is considerable friction above the AST, the required RPM for optimal operation may be lower than 120. NOTE 3: In boreholes with high contrast between dynamic and static friction, standing harmonic oscillations in the BHA can develop. Although unable to absorb these oscillations the AST tool will still act to eliminate any bit induced spikes. AST Page 4 of 6
AST TOOL (RIG) CHECKS A surface check should be performed if re-running the AST is considered. The AST should be replaced regardless if the next run will take tool past 200 rotating hours. The AST should also be replaced for reasons mentioned under Lay-out Procedures (next page) or if other dynamic BHA components are replaced for the same reasons. An example of a dynamic component is the RSS (Rotary Steerable System). Surface Acceptance Check Procedure 1. Seals and surfaces: a. Wipe the polished section of the mandrel dry and watch for oil / mud leakage. b. Check that there is no mechanical damage on the polished section that will damage the seals. Junk damage, transport damage, etc. c. If there is leaking oil or mud or damage, the tool must be laid out. 2. Internal wear a. Remove slips and have the BHA hanging from the elevators. b. Draw a line using a sharp marker pen across the telescopic interface. c. If available, fit back on the protective transport clamp that came with the tool. d. Apply CHAIN TONGS above and below the polished section. Hold the tool body (uppermost tong) still and move the lower CHAIN TONGS in opposite directions to determine the free play or backlash. *) e. Measure the movement of the mark starting from the REFERENCE LINE on the protective clamp into the green and red sectors. Alternatively measure the play in millimetres and compare to the Acceptance Table below. f. If no play is observed (tool seized) or if the play enters red sector and is outside the limit stated in the Acceptance Table, the tool must be laid out. *) Maximum force required to perform the wear check is about 125 lbs (55 kg) on a 3 (1m) chain tong. AST Page 5 of 6
Acceptance Table; Spline wear Tool size: Maximum play 4 ¾! 2mm 6 ¾! 2mm 8 ¼! 4mm 9! 3mm 9 ½! 5mm Downhole Check It is possible to check the mechanical integrity of the AST (and other tools in the upper BHA) in abnormal situations, such as when working a stuck BHA or having no drilling progress. This is done by comparing downhole RPM from the MWD / RSS tool with surface RPM. If the average downhole RPM is the same as the surface reading, the AST and all other components between the two measuring points have their mechanical integrity intact. Lay-out Procedure The maximum rotating hours (as per IADC report) on an AST tool are 200. In practical terms, the tool should be laid out prior to a run that will result in accumulated rotating hours beyond 200. In cases where a tool has been subjected to abnormal conditions, e.g. excessive jarring, drilling for a considerable time with a ringed out or under gauged bit or damaged under-reamer, high sand or solids content in the mud, then the AST may have suffered accelerated wear and should be laid out sooner. AST Page 6 of 6