Stuck Up- Detection and Control
Stuck up is also one of the most common down hole problems leading to drilling complication. The problem has become more frequent and important in the light of greater number of directional wells being drilled in quest for more oil and greater recovery. Since the drill string has an unequal load distribution i.e. heavier BHA and no hole is truly vertical. A good portion of the string bears against the side of the well bore. This becomes more complicated and amplified in case of directional wells.
With such a situation prevalent down hole, if string becomes motion less even for small periods of time...
KICK WHILE TRIPPING :
When the pump is switched off, a reduction in BHP equal to annular pressure losses occurs. To prevent kick while tripping, basic requirement is that hole must be kept full of mud and the volume of mud required to fill the hole must be equal to the steel displacement of drill string pulled out. The sequence of events to a kick while making a trip-out of hole is :
• Hole remains full or does not take proper amount of mud. Whenever such situation is noticed the pipe should be run back to bottom and mud is circulated to clear the hole.
• Flow from the flow line
• Increase in pit volume
LINE UP FOR SHUT IN
When one or more positive kick signs are observed, flow check is made. In case of self-flow well can be shut-in in two ways:
a) Soft shut-in
b) Hard shut-in
SHUT IN PROCEDURES
As per API RP 59 As per following are the shut-in procedures for land/jack-up rigs & floating rigs.
- Line up for soft shut-in :
- Line up for hard shut-in :
LINE-UP FOR HARD SHUT-IN
Choke line manual valve : Open
HCR : Close
Line between HCR & Choke : Open
Remote choke : Open (partially)
Line from choke to MGS : Open
While Drilling on Land and Jack Up Rigs
SHUT IN PRESSURE INTERPRETATION
A. Shut-in Drill Pipe Pressure (SIDPP) The shut in pressure on the drill string side is the difference between the hydrostatic pressure of drilling fluid and the formation fluid pressure. When a kick enters during drilling, the drill string remains uncontaminated whereas annulus becomes contaminated with influx. If SIDPP is added to hydrostatic pressure of drilling fluid, the resultant pressure will be the pressure of the formation.
SIDPP is used to determine the kill mud weight required to balance the formation pressure by using the equation given below
Kill Mud Density (ppg) = ...
SLOW CIRCULATION RATE:
During well control operations, to avoid further entry of formation fluid it is essential to keep BHP minimum equal to formation pressure. This is done by imposing certain calculated back pressure in addition to system pressure losses on the well bore as long as old mud is in the well. Kicks have to be circulated out at slow circulation rates to ensure that the sum of this back pressure and system losses does not exceed the rating of high pressure lines and other rig equipment. Various reasons for circulating out the kicks at slow circulation rates are :-
a) To ensure that the slow circulation pressure...
TRIP MARGIN: During pulling out, upward motion of the drill string in the borehole (which is assumed to be full of mud) creates a swab pressure. This decreases BHP when pipe is in motion. One way of minimising this is to use safe tripping speeds and having close monitoring of pipe volume pulled out & mud volume pumped in to keep the hole full. Another practice to tackle the problem is to keep mud weight gradient greater than the formation pressure gradient. The resulting overbalance permits safe tripping and connection operations. This extra mud weight is called trip margin. For normal drilling operation trip margin is kept 0.2 to 0.3...
KICK It is defined as an influx or flow of formation fluid into the well-bore & can occur any time the formation fluid pressure is greater than the bottom hole pressure being exerted in the well bore.
BLOWOUT It is an uncontrolled flow of formation fluid at the surface or sub surface from the well bore. A Blow-out is the result of an uncontrolled kick.
PRIMARY WELL CONTROL During normal drilling operations the hydrostatic pressure of drilling fluid is greater than the pressure of the fluids in the formation. The maintenance of sufficient hydrostatic head exerted by drilling fluid to hold back the formation fluid...
Loss Circulation-Detection and Control
Loss of circulation or mud loss is one of the most common down hole complication encountered during drilling. This is a condition in which drilling fluid or mud is lost to subsurface formations either partially or completely. In case of partial losses there are partial returns and in case of complete losses there are no returns. The loss of circulation may result due to highly permeable and unconsolidated formations at shallow depths and in such case the losses are partial and these are known as seepage losses.
The loss of circulation at deeper depths occurs in fractures; these fractures may be...