Title: PETE 689 UBD
1PETE 689 - UBD
- Lesson 15
- Special Considerations
- Read UDM - Chapter 6
2Special Considerations
- Safety in UBD
- Regulatory Requirements
- Environmental Issues
- Directional Drilling
3Special Considerations
- Percussion Drilling
- High Pressure Drilling
- Cementing
- Formation Evaluation
4Safety in UBD
- Since significantly greater volumes of oil and
gas are produced in underbalanced drilling
(compared to overbalanced drilling), and because
these products are highly combustible,
considerable attention must be paid to safety
procedures. - Produced fluids must be handled safely.
5Hydrogen Sulfide
- Provide necessary notice of the proposed
operations and hazards. - Provide adequate training.
- Special Safety equipment, such as sensors,
warning alarms, wind socks, concentration
measuring devices, portable and fixed air
breathing respirators.
6Hydrogen Sulfide
- An H2S emergency contingency plan with the site
specific information and detailed procedures. - Hydrogen sulfide resistant materials and
training. - Pressure surface separation vessels and auxiliary
vacuum degassing equipment to isolate all
personnel from possible exposure to this
poisonous gas.
7Flaring Gas
- Adequate sized flare lines, leading to properly
positioned flare stacks, equipped with automatic
flame igniters, are essential. - Take wind direction into consideration.
- Height may need adjustment.
- Flare lines must be properly anchored.
8Separation and Storage
- Liquid hydrocarbon separation and storage
facilities must be - positioned remotely
- provide adequate storage volume
- proper manifolding for transfer to sales.
9Training
- Personnel training must be provided.
- Written procedures must be provided.
- Redundancy in critical man power must be
provided. - Redundancy in choke manifold.
- Emergency ingress and egress must be provided.
10Downhole Fires
- Air drilling can lead to downhole fires and
corrosion.
11Drilling with Natural Gas
- Surface fires can be a problem.
- Prepare for proper handling of hydrocarbon gasses
at the surface. - Guidelines can be found in
- API RP 500B
- National Fire Protection Association (NFPA) 70
- NFPAA 496
12Backflow
- Drillstrings need floats to prevent flow back up
the drillstring. - Placement of drillstring floats is important for
operational and safety reasons.
13Well Control
- No standards for testing of RH and RBOP has been
developed.
14Equipment
- Operational and equipment testing procedures must
be established. - Operations should not continue if pressures
exceed the maximum limits established. - In flowdrilling, emphasis is placed on monitoring
pressure while drilling, tripping, and stripping,
in addition to early kick detection.
15Equipment
- To develop testing procedures, prepare a detailed
BOP and manifolding flow diagrams that show
step-by-step testing for system parts. - Test BOPs when installed, each time they are
reinstalled, once each week, and following
repairs.
16Equipment
- Regularly inspect and monitor surface equipment.
- Stop flowdrilling when H2S is detected.
- Inspect mud/gas separators at least daily.
- Inspect diverter rubber elements several times a
day. - Check diverter alignment with the rotary.
- Develop contingency plans.
17Regulatory Requirements
- In planning an UB well, always check with local,
state, or federal agency governing the wells
location for the latest regulations.
18Canada
- Interim Directive ID 94-3, from the Energy
Resources Conservation Board provides the most
detailed regulations in North America. - Mandates strict enforcement of
- BOP system configuration.
- Tripping procedures.
- Well control certification of key personnel.
19United Kingdom
- The Department of Trade and Industry sets
specific requirements and regulations pertinent
to the drilling and completion of underbalanced
wells. - Authority has be delegated to the Health and
Safety Executive to review operators plans, and
to grant or deny permits for proposed work.
20United States
- In the United States, a survey of the primary oil
and gas producing states indicated that there
were no special regulations written specifically
for UBD. In most cases, the existing regulations
could be broadly interpreted to cover UBD.
21Issues to Consider
- Be certain that the BOP stack, with a
- diverter System
- permits drilling to proceed while
- controlling annular pressure.
- allows connections to be made either
- with the well flowing or shut-in.
- allows tripping of the drillstring under
- pressure to change bits or bottomhole assemblies.
22Issues to Consider
- provides for backup annular control in case of
failure of the diverter. - provides for a choke manifold arrangement which
allows annular pressure to be varied so that it
will not exceed related working pressure of the
equipment. - Provides a mean to bleed-off pressure or to kill
the well, independent of the diverter system. - Provides a means to quickly and safely shut-in
the well.
23Issues to Consider
- Use string float(s) and fire float(s), if air is
used. - If sour gas is present, drillpipe protection and
blind shear rams are needed. - Kill fluid is needed.
- Casing integrity needs to be guaranteed and full
length cementing should be implemented as
regulated. - Surface equipment spacing needs to adhere to
appropriate regulations.
24Issues to Consider
- Flaring must follow appropriate regulations.
- Appropriate separator equipment should be used,
as required. - Provide adequate provision for storage of
produced fluids. - Crews need to be appropriately certified and
trained. - Monitoring and alarms are essential for H2S
environments. - Adhere to all safety regulations.
25Environmental Issues
- Regulations vary significantly from
state-to-state, and country-to-country. - Check applicable regulations carefully.
26Land and Water Pollution
- UBD provides some environmental benefits (closed
loop systems, less drilling mud, etc), but
produces more formation fluids than conventional. - Oil coated cuttings must be disposed of properly.
27Air Pollution Considerations
- Burning hydrocarbons during drilling can become
an environmental concern. - Know regulations on air pollution.
- Dust during air drilling can be a problem.
28Produced Water Disposal
- Produced water must be disposed of.
- Disposal operations can include
- Disposal into surface water drainage systems.
- Reinjection.
- Approved land disposal
- Overboard offshore disposal
- Reserve pits
29Directional Drilling
- There is no reason why directional wells cannot
be undertaken with UBD. - However, compressible fluids can complicate
directional drilling.
30Directional Drilling (Complications)
- Conventional downhole motor life is shorter, and
conventional motors are not as efficient. - Conventional MWD systems do not work with
compressible fluids. - Hole cleaning can be a problem with angles gt50 deg
31Directional Drilling (Complications)
- The horizontal section length is reduced due to
increased drag. - Not all formations and lithologies are suitable
for drilling with dry gas, moist or foam.
32Bottomhole Assemblies
- Main issues for directional drilling
underbalanced are similar to those for
conventional directional drilling - Directional control.
- Surveying.
- Hole cleaning.
- Drillstring friction.
33Bottomhole Assemblies
- BHA is designed to control direction and angle.
- The deviation tendency is a function of the
stiffness of the assembly.
34Three Types of BHAs
- Building assemblies
- Dropping assemblies
- Holding assemblies
35Building Assemblies
36Dropping Assemblies
37Holding Assemblies
38Downhole Motors
- Conventional mud motors can be run with
compressible fluids, but there are disadvantages.
39Conventional Mud Motors Disadvantages
- Designed to run with low volumetric flow rates
and high pressure drops. Leads to high inlet
pressures and low efficiency with compressible
fluids. - Compressible fluids can lead to motor stall.
- High inlet pressure results in high energy stored
in the drillstring above the motor.
40Conventional Mud Motors Disadvantages
- Volume to clean the hole with air drilling is
three times greater than the recommended flow
rate for the conventional mud motor. - Mud motors are hydrostatic, they can use only the
displacement work, and not the expansion work of
the compressed air.
41Mud Motors
- Mud motors have been developed for use with
compressible fluids. - Advantages
- Boosters are not needed.
- Efficiency is improved.
- Motors do not stall as easily.
- Overspeed is less likely.
- Can be used with compressible and slightly
compressible fluids.
42Surveying
- Conventional MWD signals cannot be sent up
compressible fluids. - Electromagnetic MWD (EMWD) tools are being
developed. - Steering tools are still available.
43Hole Cleaning
- Hole cleaning is more difficult in highly
deviated wells. - A rule-of-thumb is that for adequate hole
cleaning in horizontal wells, a volumetric rate
of 2.5 times greater than a vertical well is
necessary.
44Torque and Drag
- Friction coefficient in an air-drilled hole can
be three to four times than expected in
mud-filled hole.
45Horizontal Section Length
- Additional torque and drag can lessen the
achievable horizontal displacement of high angle
and horizontal wells.
46Lithology and Target Constraints
- Lithologies that can be drilled with air are
limited. Younger less consolidated rocks are
usually not good candidates for air. - Directional wells sometimes must be drilled
overbalanced to prevent wellbore collapse.
47Percussion Drilling
- In percussion drilling, rock is broken by causing
the bit to repeatedly strike the workfront,
without imparting any significant shearing
component to its action. - A hammer tool is used in the BHA.
- Normally only used with dry gas, mist, and foam
drilling.
48Background
ROP for three different percussion tools with 8
to 8½-inch solid-head bits in Sierra White
Granite, For a WOB of 5,000 lbf. The flow rate
was between 600 and 1,100 scfm for each hammer
(after Finger, 1984 26)
49Approximation of ROP
- Assume that the MSE Co
- Determine the hammer manufacturers power output
value. The penetration rate is related to the
rocks unconfined compressive strength, the
hammer power output and the hole area by
50Approximation of ROP
ROP 2.5210 6 H / (Co Dh2)
ROP rate of penetration (ft/hr) H hammer power
output (hp) Co unconfined compressive strength,
(psi) Dh hole diameter (inches)
51Equipment
Flat-bottom bits, used in conjunction with an air
percussion hammer (anon)
52Equipment
Internally ported hammer and a flat-bottom bit
(anon)
53Equipment
Components of an externally ported hammer (anon)
54FPB/HT (flat-bottomed percussion bit/hammer tool)
tandem recommended WOB Versus hole size (after
Whiteley and England, 1986 30)
Recommended Weight on Bit (lbf)
Bit Diameter (inches)
55Hole Cleaning
- Pratt modified Angels minimum velocity by
- Using a revised air prediction module inside the
drillstring where the friction factor was
calibrated from actual measurements. - Exit boundary conditions were modified as an
input parameter and exit chip velocity was fixed
at zero. - The influence of the BHA and changing hole size
were incorporated. - Chip size change was built into the model.
56Gauge Wear
Diamond-Enhanced Insert (after Reinsvold, et al.,
1988 31)
57Smooth Hole?
Spiral hole drilled with an industrial hammer and
a flat-bottomed bit (after Pratt, 1989 29)
58Smooth Hole?
Ledges drilled with an industrial hammer and a
flat-bottomed bit (after Pratt, 1989 29)
59Summary
- Maintain proper WOB.
- Rotate as slowly.
- Provide an air bypass.
- Deep the threads clean and use recommended
lubricants. - Dope the pins only.
- Never run on junk.
60Summary
- When changing out bits, make sure that the new
bit is no more than 0.25 in larger than the old. - Stabilize as required.
- Monitor compressors.
- Blow the hole clean.
61High Pressure Drilling
- Special attention should be given to high surface
pressures because of the additional force
required to trip pipe. - Stringent safety considerations are required.
62Flowdrilling in High Pressured Formations
- The use of CT drilling is increasing with high
pressure flowdrilling. - Surface well control equipment must be rated
based on maximum anticipated conditions. - RBOPs should replace rotating heads.
63Coiled Tubing Drilling Design Criteria
- Select the CT size, hole size, drilling fluid,
and BHA. - Calculate the reel weight and size.
- Calculate the tubing forces and stresses. Do not
let them exceed 80 of the yield strength, and
the minimum WOB can be provided at TD.
64Coiled Tubing Drilling Design Criteria
- 4. In vertical wells.
- Dmax (sy) / ( 4.245 - 0.06493Wdf )
- Dmax maximum depth (feet)
- Wdf drilling fluid weight (ppg)
- sy yield stress (psi)
- 5. In Deviated wells.
- Ensure that the injector can supply the necessary
push/pull.
65Coiled Tubing Drilling Design Criteria
- 5. In Deviated wells.
- Ensure that the injector can supply the necessary
push/pull. - Calculate the drilling fluid pressure drop in the
CT, BHA and annulus at 100 motor flow capacity
and determine the absolute pressure in the CT
during drilling. - Asses torsional limitations. The downhole
motor-stall torque should not be longer than the
maximum working torque for the CT.
66Coiled Tubing Drilling Design Criteria
- 5. In Deviated wells.
- Calculate the fatigue life of the pipe.
- Asses any hydraulic limits . Consider hole
cleaning in vertical, inclined , and horizontal
wellbores. - Be sure that directional control is possible.
67Cementing
- Extremely light cement can be used to
- Provide primary cementing in formations with low
fracture pressures. - Cure lost circulation in cavernous vugs.
- Squeeze depleted zones.
- Zonal isolation.
- Heat Insulation.
68Properties of Foamed Cement
- Will the strength be adequate and will the sheath
be destroyed by perforating? - Compressive strength of foamed cement is
generally higher than a comparable non-foamed
cement of the same density. - Will there be gas migration through the cement
itself? - Will the bond be different than for conventional
cements?
69Systems with Low Density Particulate Matter
- Cement companies have additive in which the HSP
of the cement can be reduced. - Example is hollow glass micro spheres.
70Design Considerations
- Foam quality.
- PVT behavior.
- Cement system.
- Free water.
- Backpressure.
- Permeability.
- Compressive strength.
- Fluid Loss.
71Formation Evaluation
72Evaluation of Formation Fluids While Drilling
- Evaluation of formation fluids during UBD is more
accurate than conventional. - Qualitative and Quantitative information can be
obtained or inferred.
73Evaluation with Logging Tools
- Gamma Ray. For formation or bed definition (e.g.
distinguishing sands from shales). - Spectra Gamma ray. Quantitative definition of the
gamma ray spectrum to define clay content, clay
and mineral type, and to aid in fracture
detection. - Epithermal Neutron. To identify porosity of
liquid-filled zones. - Induction Resistivity. To help distinguish
hydrocarbons from saline formation water and to
help quantify the water saturation.
74Evaluation with Logging Tools
- High Resolution Density. To quantify porosity.
- Temperature. To indicate liquid level in the
borehole and to delineate zones where fluids are
actually being produced. - Production. Production logs, such as borehole
spinners, cam help to quantify the relative
amount of production from each interval. - Nuclear Magnetic Resonance. To help quantify the
permeability of formations.
75MWD
- If a compressible fluid is used, conventional mud
pulse telemetry tools cannot be used. - Electromagnetic devices can.
76Coring Underbalanced
- Reducing coring fluid invasion allows for careful
determinations of formation properties where
wettability alteration has been minimized.
77Permeability and Deliverability Assessments
- Effective monitoring of production rates permits
real-time decisions regarding changes in drilling
depth, wellbore orientation, and overall section
length.
78THE END