PETE 411
Well Drilling
Lesson 6
Drilling Structures
1
Types of Drilling Structures
 Conventional Rotary Rig for drilling
on Land
 Alternate Drilling Structures
 Structures for deep Water or
Arctic Drilling
 Hydrogen Sulfide and RULE 36
2
Homework
Read:
Applied Drilling Engineering, Ch.5 (bits)
HW #3: Posted
(due Sept. 18, 2002)
Find HW #3 and Lessons at:
http://pumpjack.tamu.edu/~juvkam-wold/
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Standard Derrick - Engines close to derrick - Mechanical Transmission 4
700 hp ENGINE
COMPOUND
700 hp ENGINE
700 hp ENGINE
5
Drilling Structures:
 Conventional Land Rig
 Jack-up Rig
 Drillship
 Semisubmersible
 Jacket Platform
 Gravel Island
 Ice Island
 Guyed Tower
 Tension Leg Platform
 Spar Platform
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Pile-founded
steel jacket
platform
Cost increases
rapidly with depth
Bending moments
Natural Frequency
Mud Line
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~100 sec nat.frequency
(waves ~ 6-10 sec)
Pivot at bottom
(problem)
Buoyed tower concept of 1970
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1983
1,000 ft
of water
FAIRLEAD
200 TON CLUMP WEIGHTS
Principal features of the Lena guyed tower
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High ice forces
Weak soild
Shallow water
~1,000 ft dia.
Arctic drilling structure - Ice Island
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Spar Platform in Transit
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Spar
Platform
Installed
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Rule 36 - TRC
Protection of the General Public from the
Effects of H2S
Applicable if H2S Concentration > 100 ppm
Point of Escape
Radius of Exposure
 Operator must determine the H2S Concentration
 and the Potential Flow Rate
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H2S
Determination of Radius of Exposure
The 100 ppm radius of exposure (in ft)
R100  [1.589 (Mole fract ion H 2 in gas mi xture) Q] 0.6258
R100= dist. from source where H2S conc. = 100 ppm
Q = source strength = open flow potential, SCFD
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H2S
 Determination of Radius of Exposure
 The 500 ppm radius of exposure (in ft)
R 500  [0.4546 (Mole Fraction H 2S) Q]
0.6258
R500= dist. from source where H2S conc. = 500 ppm
Q = source strength = open flow potential, SCFD
 These are the Pasquill - Gifford Equations
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Example
A well that is about to be drilled is estimated
to have an open flow potential of 5 million
SCFD. Based on other wells in the field it is
estimated that the H2S mole fraction in the
gas mixture will be 0.1.
Calculate the radius of exposure to H2S
concentrations of 500 ppm and 100 ppm.
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Example
R500  [0.4546 (Mole Fract ion H 2S) Q]
 [0.4546(0.1)(5 * 10 )]
6
0.6258
0.6258
= 2,250 ft
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Example
R100  [1.589 (Mole Fract ion H 2S)Q]
0.6258
 [1.589(0.1)5 * 10 ]
6 0.6258
= 4,924 ft
ppm
500
100
R500
R100
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To Determine Q
 Use open flow potential
 Where insufficient data exist
for calculating
R100
(100 ppm radius):
 Assume R100= 3,000 ft
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Storage Tanks for Production
 If H2S conc. > 500 ppm
(i) Post warning sign within 50’ of
facility
(ii) Fencing is required in populated
area
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Storage Tanks for Production
 In general, If R500 > 50 ft:
(i) Post warning signs on access roads
(ii) Post marker signs at public crossing
e.g.
Poison Gas
and
Caution
in Black and Yellow colors
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Need Contingency Plan if:
(i) R100 > 50 ft
• and includes public area other than public
road
100 ppm can cause throat irritation in < 1 hr
(ii) or R500 > 50 ft
• and includes public road
500 ppm can cause unconsciousness in < 2 min
death in ~1/2 hr
(iii) or R100 > 3,000 ft
{600 ppm can cause death after a few minutes}
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The Contingency Plan
 Must provide for action of alerting and
protecting the public following accidental
release of a potentially hazardous volume
of H2S.
 Plan must include (names and) phone
numbers of people to be notified…e.g.
•
•
•
•
Supervisor
Hospital and Fire Dept./ Sheriff or Police
District Railroad Commission etc.
Local Residents
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Drilling Provision:
If R100  3,000 ft, we also need to:
(i) Maintain protective breathing equipment
at the well site
(ii) Install and maintain automatic H2S
detection and alarm equipment
(iii) Provide means for flaring the gas
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Drilling Provision
(iv) Provide remote control of BOP and choke
equipment - at safe distance
(v) DST of H2S zones only during daylight
(vi) Notify railroad commission prior to
performing such DST
etc.
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If R100  3,000 ft
• Provide training for personnel
• Submit certificate of compliance
(with all the rules)
30 days prior to commencement of
drilling or WO
Certificate must be approved before
commencing activities
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If R100  3,000 ft
 Altered conditions may require submittal
of amended certificate
 Certificates are non-transferable
 Completion reports for new wells must
include the H2S conc. of the gas if in
excess of 100 ppm
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What is Buoyancy?
Buoyancy is the net effect of all the pressure
forces acting on a submerged body.
The buoyancy force is equal to the weight
of fluid displaced.
For example, a one-cubic-ft rock submerged
in a tank containing water would
experience a buoyancy force equal to the
weight of 1 cu. ft of water, i.e., 62.4 lbf.
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The End
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