Download - SPE-RGCE Case studies
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INTRODUCTION
Aim of this study is to reduce the drillingcost in ultra deep water by usingmodified second and third generation
rigs other than fourth and fifthgeneration.
This study focuses how to reduce the
environmental pollution in deepwaterconfigurations in case of riser failure.
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STUDY FIELD
Block = Donggaladeepwater block,
OffshoreMahakam straight,
Indonesia.
Rig type = second and
third generation(jack up rig)
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Drilling data
Total Depth = 13,000 ft
Water Depth = 6,000 ft
Well plan Conductor casing= 13 3/8 inch
Surface casing = 11 inch
Intermediate casing = 9 5/8 inch
Production casing = 7 inch
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PROBLEM IN THE WELL
Surface casing had to be set higherthan planned to avoid penetrationinto the shallow gas zone.
Well plan need to be changed
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OPTIONS AND THEIR
LIMITATIONS Option 1:drilling ahead and setting the 95/8-in. casing
followed by the 7-in. casing string.
Problems: After setting the 7-in. casing string higher than
was called for in the well plan, had to drilldeeper using smaller casing sizes.
The smaller hole would have to be drilled usingslim hole tools, which would have presented thedifficulty of a smaller internal diameter at TD
Difficulty in logging and testing for formationevaluation
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Option 2:
To plug and abandon the well andcontinue exploration in a different
areaOption 3:
To start with a larger conventional
casing size to maintain adequate holesize in the target zone.
Limitation: Require more rig size capacity
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SOLUTION :EXPANDABLE
OPEN HOLE LINER A 1,300-ft string of 95/8113/4-in. solid
expandable open hole liner was run to
depth and set at 9,400 ft. Liner expansion was performed with
hydraulic pressure up the liner.
As each stand of drill pipe was removedfrom the hole, the pressure was bled off,and the stand was broken out andracked back in the derrick.
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The process of reconnecting the topdrive and resuming upward expansionwas repeated until the entire liner had
been expanded and sealed
The liner was pressure tested to 1,000psi for 30 minutes.
The expansion cone was then pulledout of hole, and the float shoe wasdrilled out.
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RESULT:
Installation of an expandable linerenabled to get back on the originalwell plan and
Reached the target zone withadequate wellbore size.
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PROBLEM 2
Fear of environmental pollution dueto riser failure in the surface stackBOP
Loss of mud in the ocean floor.
High cost of drilling per well
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OPTIONS & THEIR
LIMITATIONS Option 1: Use of subsurface BOP stack to prevent
riser failure and use of low pressure riser
Limitation: Require fifth generation drilling rig (drill
ship) with the typical day rate increase upto 2oo,000 $/day
Option 2: Use of surface stack BOP and high
pressure riser Limitation: More chance for riser failure
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SOLUTION : ENVIRONMENTALSAFEGUARD SUBSEA SHUTOFFVALVE
Offers a practical means of
disconnection in an emergency. Capability to shear, seal, and
disconnect from the seabed;
In an unplanned disconnect, therelease of mud from the riser intothe sea is reduced by nearly 60%.
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RESULT
The implications of using thistechnology combination extendbeyond project cost; operators cannow reach ultra deepwater targetsusing a wellbore size that waspreviously possible only by use of
subsea-BOP technology.
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ADVANTAGE
Use of a high-pressure riser as opposed toa low-pressure riser used with fourth- andfifth-generation rigs.
Lower mobilization costs. Significant reduction in day rates.
Less fuel consumption.
Reduced mud volume.
Lower bit costs based on smaller holesize.
Reduced casing cost as a result ofeliminating a number of strings.
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