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Frequently Asked Questions
About SWTorpedo Well Stimulation
1. How SWTorpedo well stimulation is different from Common
Explosives and Propellant Tools?
2. What is dilatancy?
3. How SWTorpedo is fielded?
4. What type of source rock will be more responsive to
SWTorpedo?
5. What are the limitations for SWTorpedo well
stimulation?
6. What types of explosives are used to assemble
SWTorpedo Tool?
7. What factors are used to determine amount of
explosives?
8. Can size or spacing of perforations limit the
applicability of SWTorpedo?
9. What is the maximum radius at which rock's
permeability will be increased?
10. What type of
fluid can be used when applying SWTorpedo?
11. When formation
pressure is low, what is the minimum of fluid column above the Tool will be required?
12. Will SWTorpedo damage
the casing?
13. Is there a chance of
losing wireline when SWTorpedo is detonated?
Answers to Frequently Asked Questions
1. How SWTorpedo well stimulation is different from Common
Explosives and Propellant Tools?
SWTorpedo Tool is conceptually different from
Propellant Tools and technologically different from Common Explosives.
· All of
Propellant Tools use the burning process (deflagration) of solid propellants or gun powders to generate gas.
Usually build-up pressure is enough to create no more than 2 of two directional vertical fractures.
Gas will be forced through the perforations in to formation. As propagation of initial fractures progress gas will
be consumed faster than propellant can generate it, as a result no new fractures can be created.
This process explained by the law of A. Griffith.
· Common Explosives
when used generate powerful impulse or wave which causes rock crashing. Its differential stress will reach a point
when it is higher than effective normal stress and main fracturing force is a force of compression.
Very often Common Explosives reduce permeability near the wellbore.
· SWTorpedo Tool
use small charges of high explosives. Multiple charges are detonated in such succession to generate tensile stresses
on a significant distance from the wellbore. Created areas of intensive tension initiate multiple radial fractures,
cause propagation of micro-fractures and rock fracturing in shear (Effect of Dilatancy) as far as ~ 54ft. from the
wellbore, resulting in increased permeability of 200% or more.
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2. What is dilatancy?
Dilatancy is a permanent deformation registered in rocks that are
subjected to non-uniform dynamic stress. It can be best explained as volume changes, porosity increases of
up to 60% and permeability increases 200% and more, due to micro-fracturing or cracking that have been measured
in laboratory experiments using core samples and in the field tests by implementing SWTorpedo well stimulation.
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3. How SWTorpedo is fielded?
· Selected
well must be prepared in the same manner as it would be for perforation. That includes: tubing and rods removal if any.
· Wireline
crew should confirm the desired depth at which SWTorpedo Tool will be detonated and mark the wireline with tape
and/or paint.
· Water
solution or other fluids used to depress the well must be pumped in to the well until its level reach the mark of at
least 90 feet above the SWTorpedo Tool.
· Reusable
torpedo's head must be attached to a cable head by the female adapter with 1 7/16 in. thread.
· Electrical
detonator must be wired and connected to a detonative cord.
· Connect
SWTorpedo to its reusable head and lower the Tool to the mark on wireline that being made earlier.
· Initiate
detonation.
· Prepare
the well for exploitation.
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4. What type of source rock will be more responsive to
SWTorpedo?
SWTorpedo proved to be successful in most of the source rocks.
Preferable Rock's and Wells Characteristics
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5. What are the limitations for SWTorpedo well
stimulation?
The limitations for SWTorpedo are:
· The depth
limit is 36,000 feet
· The
presence in the productive zone of more than 20% of highly compressible components such as clay, loam, etc
· Oil/water
contact is closer then 9 feet from the center of zone to be stimulated
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6. What types of explosives are used to assemble
SWTorpedo Tool?
To assemble SWTorpedo we use class "A" explosives such as TNT, RDX and HMX
(Made in USA). For a single Tool total of up to a 20 lb. of class "A" explosives is used.
Each charge is strategically positioned to enhance performance.
Positioning of the charges tailored to a rock's properties.
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7. What factors are used to determine amount of
explosives?
The quantity of explosive materials is determined based on the
following factors:
· required
increase of output or intake of the well
· distances
between offset wells
· size of
the interval to be stimulated
· physical
condition of the casing and bore hole
· quality
of the cement job
· dilatant
properties of the rock
· types of
the explosive materials
· individuality
of internal design of the SWTorpedo
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8. Can size or spacing of perforations limit the
applicability of SWTorpedo?
Application of SWTorpedo is NOT limited by the size or spacing of the
perforations. Due to a high speed of waves propagation bedrock will be fractured before fluid begins to move
and amount of gas generated by the Tool is minimal, so flushing effect is a secondary. Nevertheless, to create
enhanced flushing effect it is preferred to have larger size of perforated entry holes with a spacing of 4 or more
holes per foot.
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9. What is the maximum radius at which rock's
permeability will be increased?
Maximum radius of effective rock fracturing in shear is calculated and
designed for each well individually based on the pressure threshold at which dilatant fracturing would begin in
each given formation and can be extended from the wellbore up to 54 feet in each direction.
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10. What type of
fluid can be used when applying SWTorpedo?
There are no specific requirements for fluid use. Any fluid desired by
the Client such as water, brine, acid or oil can be used. It is necessary to place the Tool in the fluid in order
to transfer multiple shock waves into formation.
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11. When formation
pressure is low, what is the minimum of fluid column above the Tool will be required?
Previous experiences show that it is safe to maintain as little as 90 feet
of fluid above the Tool. Use of specially designed self distractible temporary bridges allows SWTorpedo well
stimulation technique to be applied in very shallow wells with low formation pressure.
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12. Will SWTorpedo damage
the casing?
As long as the information from the cement bond log is correct (current),
casing protection is positioned accordingly and the Tool is detonated at the desired and verified depth there will
be NO casing damage.
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13. Is there a chance of
losing wireline when SWTorpedo is detonated?
Since SWTorpedo is being used with newly designed Tool Head we experienced
NO loses or damage to a wireline.
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