Causes:
1. Differential Sticky
1) May happen during well control situation, weight up mud not too much, keep monitoring casing pressure; consider Drillers Method first. Even take consideration of rotating drill string with Annular BOP closed.
2) Underground Blowout: When it occurs, the flow rate of formation fluid can be very high. The high flow rate can held pipe against the side of hole to cause stuck. Never drill beyond your kick tolerance.
3) Keep moving pipe (May still got circulation)
4) Stuck Force = Differential Pressure * Stuck Area * Coefficient of Friction
2. Formation Stuck
1) Geopressured
2) Reactive , (Gumbo)
3) Unconsolidated
4) Mobile
- Sloughing Shale: Term used to identify the deterioration of shale due to hydration. The solution is a chemical one: Salt water muds with Sodium ions(), Calcium ions() and Potassium ion().
- Salt Creep ()When thick sections of salt must be drilled, it behaves as a very viscous liquid and will flow into the drilled hole. Anytime salt creep occurs, spotting or circulation of fresh water across the creeping section will rectify the problem. Fresh water will dissolve salt and enlarge hole. So it is recommended that an under saturated () mud be used for drilling psuedoplastic salt. Oil mud does nothing at this situation.
5) Fractured/ Faulted
- Natural Angle of Repose of Granular FormationsAnthracite coal () and older, dehydrated () shales is a common formation to exhibit this behavior. When this happen, rounder pieces caving may come across shakers. Immediate Action: 1. Asbestos fibers (), fibrous materials () can be added to drilling fluid to make a stronger filter cake, to plaster off the face of the zone.2. It is generally time dependent, consideration should be given to maximizing penetration rate through the zone to the next casing point and getting casing set.3. If item 2 is not possible, cement grouting () can also be selected.
3. Mechanical Stuck
1) Key Seating (Stiffer BHA)
2) Well bore Geometry
- Crooked HoleUtilizing Stiffer () BHAs will minimize tendency of changing hole direction. This is especially true in highly dipping beds () which have a tendency to form ledges. ()
- Mud ring: It is a decrease in hole diameter caused by a build up clay material or filter cake. Utilizing low fluid loss (high temperature/ high pressure value), inhibited mud will minimize or even eliminate creation of mud rings.
3) Undergauge hole (Whenever a bit is undergage by as much as 2/16, the hole should be reamed back to bottom with the next bit prior to drill new hole, especially during abrasive () formations.)
4) Hole Cleaning/ Pack-off Bridging
- Insufficient Hole Cleaning: Annular velocity of mud is the most important factor in annular cuttings transport;When water base muds are in use, turbulent flow will increase hole erosion. Care must be taken in mud selection to minimize and eliminate erosion; For water muds, high viscosity laminar flow will be the recommended. For oil muds, low viscosity, turbulent flow will be best; Mud density increases, the cutting transportation increase. Mud Yield Point increases, the cutting transportation increase; Monitor Yield Point for best control of water muds. Monitor Low Shear Rate Stresses (6rpm) for best control of oil muds.
- Hole cave-inFractured chalk () or broken caprock () over a salt dome () or dehydrated shales () are possible examples of this mechanism.
- Inclined Hole InstabilityAs well are directionally drilled, the wellbore will no longer run parallel to the axis of major stress (overburden), and wellbore instability can result. Solution is to increase mud weight to the point where stability is restored. So pore pressure calculations and casing point selection are both important.
5) Cementing Problem: Flash Set, Long rat hole, Cement Chunks
- Immediate reciprocate and rotate pipe is recommended action.
- Consideration should also be given to spot acid in the broken cement to soluble () it. Strength and type of acid to spot should be carefully considered as acid also acts on steel tubulars.
6) Casing Problem
7) Junk in Hole (Part of bit, drill string: Jamming of tubulars might happen all at once.)Note, Mechanic jars are pre-set at jar shop.
