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Frequently Asked Questions
About SWTorpedo Well Services
1. How SWTorpedo well stimulation is different from Common
Explosives and Propellant Tools?
2. What is rock dilation?
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
service?
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 smaller charges of high explosives. Multiple charges are detonated in such succession to initiate multiple radial
fractures and trigger dilation at the distance from the wellbore to meet radial fractures.
Rock Dilation can be extended as far as ~ 45ft. from the wellbore, resulting in increased permeability of 700%
and higher.
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2. What is rock Dilation?
Rock Dilation 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 in
some cases more than 60% and permeability increases more than 700% due to shearing.
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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
service?
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
· Undesired water
is closer then 9 feet from the center of zone to be stimulated
· Not a limitation
but a challenge to make significant improvement when formation pressure is low.
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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 PENT, RDX and HMX .
Each charge is strategically positioned to enhance performance. Positioning of the charges and time of detonation delay
between two or three stages 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
· dilative
properties of the rock
· types of
the explosive materials been used
· 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,
movement of the fluid create a secondary flushing effect. 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 rock dilation begins in each given
formation and can be extended from the wellbore ~ 54 feet in all directions horizontally, vertical radius
is ~ 30 percent shorter.
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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, light acid, oil or diesel can be used.
Fluid around the Tool will act as a conductor that transfers shock waves to formation.
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11. When formation
pressure is low, what is the minimum of fluid column above the Tool will be required?
Low formation pressure is challenging to work with, when designing the Tool.
More field tests must be done to bring optimal results.
Previous experiences show that it is safe to maintain as little as 90 feet of fluid
above the Tool but we prefer 500ft. or more. Use of specially designed self distractible temporary bridges allows SWTorpedo
well service to be applied in very shallow wells (300ft.).
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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 No casing damage
is anticipated. Some wick casing that is used in CBM wells and the fact that most of the coals that CBM wells are drilled
in, are wick coals, makes it challenging to prevent casing rapture. When undesired water that can travel along the casing
is not an issue then created rapture will provide an additional area of exposed rock contributing to existing
perforations.
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13. Is there a chance of
losing wireline when SWTorpedo is detonated?
The Tool head is build to absorb the shock from SWTorpedo.
We have 3 different designs of the Tool head; each is used for different application. Through the development process
and field test we experienced some losses of the wireline and today the chance of loosing the cable is minimal.
For the practical reason some losses of wireline must be counted for.
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