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| Copyright © 2010 STI Engineering/ Regis Renaud ALL RIGHTS RESERVED |
This page will outline the advantages of STI's Push-in Steel Collectors over the conventional method of
large diameter drilled-in water type wells being used as a gas collector.
Large Diameter Drilled-in Collectors
Currently a 24" to 36" diameter bore hole is drilled into the waste prism. One to two tons of cuttings have to
be reburied in the landfill or disposed off-site at great cost. A 4" to 6" PVC casing is lowered into the bore
hole and the annulus is filled with several tons of gravel. The well head is connected to a 2" diameter
lateral pipe to the header. A control valve is also installed in this line to control the flow rate from the
collector. This control valve is rarely opened more than a 1/4" otherwise the well will be overdrawn and
suck in air and it could cause an underground fire.
The perforated sections of this well usually contain 4 - 1/2" holes 90 degrees from each other around the
casing and the rows are 12" apart up along the section of pipe. This restriction will be discussed later in
this paper.
Another reason a large diameter casing is used is to accommodate a pump to remove liquid from blindly
installing a well through a layer of liquid causing flooding.
2" Diameter Steel Push-in Gas Collectors
Following a PPT sounding, the log is printed out immediately. The information can assist in designing the
collector to recover the most LFG and to avoid layers of liquid that can flood collectors. This log remains as
a permanent record of the current conditions when this collector was installed and justify why a collector
was installed at this location. This data can be analyzed by anyone in the future and not have to rely on the
interpretations of a single person sitting behind a drill rig guessing at what depth the cuttings are coming
from. Also there are no gas readings from a drilled bore hole.
Typical PPT Log
PPT Cone Mandrel Pre-Punch
Following the extraction of the PPT Cone the remaining hole in the landfill is used as a guide for the 3"
diameter Mandrel to enlarge the hole to accommodate the 2" steel casing. Once the Mandrel is extracted
the 2" casing must be inserted quickly since the hole will start to consolidate within minutes. This is why
we get a very tight seal around the casing eliminating short circuiting. A vacuum can be applied to the
collector within 24 hours. Please keep in mind that no cuttings or spoils are created, therefore saving a
lot of time and costs.
Oilfield Mill Slot Screens
STI went from wire wrap screens to oilfield mill slot screens in 1999 when it was evaluated at a west coast
landfill and was found to be far superior to wire wrap screens due to its' strength and open space. Oilfield
Mill Slot screens have been used in oil wells extracting oil and gas for over 100 years.
As stated above, the large diameter wells use 4 - 1/2" diameter holes. The mill slot uses 8 - 1/8" wide
slots that are 3" long and are staggered around the casing. The best flow rate that can be achieved by any
pipe is an open ended pipe. The open space of the mill slot is equivalent to an open ended pipe every 6"
up the length of the screen section which are 5 foot joints. To achieve the same open space of a 2" pipe it
would take all of the 1/2" diameter holes in 6 !/2 feet of the 4" casing to equal the flow rate of a 2" open
ended pipe. The 1/2" holes are a built-in restriction resulting in the fact that at equal vacuum levels the
large diameter well can never extract as much gas as the push-in collector. Also remember that the large
casing is connected to a 2" lateral pipe to the header. Why spend so much money on all that large pipe
just to reduce it to 2" pipe. STI continues the 2" diameter pipe into the waste prism.
Preparing Push-in Casing Oilfield Mill Slot Screen
20 Ton Rams Completed Gas Collector
Other Attributes
The Push-in Collector has many other attributes over the drilled-in collector.
Some opponents of the push-in collectors say that they will plug up with out a gravel pack. None of the one
hundred plus push-in collectors installed by STI has ever plugged up. However, any collector installed in a
landfill has the potential to plug up, even drilled-in wells. The advantage of the steel collector is that if one
should plug up, a shot of high pressure steam will unplug and restore the collector to full operation. This
cannot be done to a PVC or HDPE well.
Based on California prices the following is a cost comparison between the 2" diameter steel push-in
collectors and larger diameter collectors. One of the controlling factors for the cost per foot is the amount
of collectors installed compared to the mobilization charges.
A 100-foot deep PPT sounding and a 2" diameter steel collector costs about $20.34 per foot.
A 100-foot deep 24" dia. bucket auger with 4" dia. PVC costs about $55.00-75.00+ per foot, depending on
the cost of cuttings disposal.
In conclusion, the PPT Profile and Push-in steel collectors are better, faster and cheaper than standard
drilled collectors.
large diameter drilled-in water type wells being used as a gas collector.
Large Diameter Drilled-in Collectors
Currently a 24" to 36" diameter bore hole is drilled into the waste prism. One to two tons of cuttings have to
be reburied in the landfill or disposed off-site at great cost. A 4" to 6" PVC casing is lowered into the bore
hole and the annulus is filled with several tons of gravel. The well head is connected to a 2" diameter
lateral pipe to the header. A control valve is also installed in this line to control the flow rate from the
collector. This control valve is rarely opened more than a 1/4" otherwise the well will be overdrawn and
suck in air and it could cause an underground fire.
The perforated sections of this well usually contain 4 - 1/2" holes 90 degrees from each other around the
casing and the rows are 12" apart up along the section of pipe. This restriction will be discussed later in
this paper.
Another reason a large diameter casing is used is to accommodate a pump to remove liquid from blindly
installing a well through a layer of liquid causing flooding.
2" Diameter Steel Push-in Gas Collectors
Following a PPT sounding, the log is printed out immediately. The information can assist in designing the
collector to recover the most LFG and to avoid layers of liquid that can flood collectors. This log remains as
a permanent record of the current conditions when this collector was installed and justify why a collector
was installed at this location. This data can be analyzed by anyone in the future and not have to rely on the
interpretations of a single person sitting behind a drill rig guessing at what depth the cuttings are coming
from. Also there are no gas readings from a drilled bore hole.
Typical PPT Log
PPT Cone Mandrel Pre-Punch
Following the extraction of the PPT Cone the remaining hole in the landfill is used as a guide for the 3"
diameter Mandrel to enlarge the hole to accommodate the 2" steel casing. Once the Mandrel is extracted
the 2" casing must be inserted quickly since the hole will start to consolidate within minutes. This is why
we get a very tight seal around the casing eliminating short circuiting. A vacuum can be applied to the
collector within 24 hours. Please keep in mind that no cuttings or spoils are created, therefore saving a
lot of time and costs.
Oilfield Mill Slot Screens
STI went from wire wrap screens to oilfield mill slot screens in 1999 when it was evaluated at a west coast
landfill and was found to be far superior to wire wrap screens due to its' strength and open space. Oilfield
Mill Slot screens have been used in oil wells extracting oil and gas for over 100 years.
As stated above, the large diameter wells use 4 - 1/2" diameter holes. The mill slot uses 8 - 1/8" wide
slots that are 3" long and are staggered around the casing. The best flow rate that can be achieved by any
pipe is an open ended pipe. The open space of the mill slot is equivalent to an open ended pipe every 6"
up the length of the screen section which are 5 foot joints. To achieve the same open space of a 2" pipe it
would take all of the 1/2" diameter holes in 6 !/2 feet of the 4" casing to equal the flow rate of a 2" open
ended pipe. The 1/2" holes are a built-in restriction resulting in the fact that at equal vacuum levels the
large diameter well can never extract as much gas as the push-in collector. Also remember that the large
casing is connected to a 2" lateral pipe to the header. Why spend so much money on all that large pipe
just to reduce it to 2" pipe. STI continues the 2" diameter pipe into the waste prism.
Preparing Push-in Casing Oilfield Mill Slot Screen
20 Ton Rams Completed Gas Collector
Other Attributes
The Push-in Collector has many other attributes over the drilled-in collector.
- An encoder attached to the push rods provide accurate depth control to within 2 centimeters,
important when working near bottom liners. - Inclinometers in the PPT cone assist in maintaining good depth control and prevents damage to
instruments. - Steel well materials can be extracted from the waste prism and reused.
- Schedule 80 pipe resists corrosion and crushing
- Lower well material costs
- Fast installation time
- Minimal Health & Safety concerns
Some opponents of the push-in collectors say that they will plug up with out a gravel pack. None of the one
hundred plus push-in collectors installed by STI has ever plugged up. However, any collector installed in a
landfill has the potential to plug up, even drilled-in wells. The advantage of the steel collector is that if one
should plug up, a shot of high pressure steam will unplug and restore the collector to full operation. This
cannot be done to a PVC or HDPE well.
Based on California prices the following is a cost comparison between the 2" diameter steel push-in
collectors and larger diameter collectors. One of the controlling factors for the cost per foot is the amount
of collectors installed compared to the mobilization charges.
A 100-foot deep PPT sounding and a 2" diameter steel collector costs about $20.34 per foot.
A 100-foot deep 24" dia. bucket auger with 4" dia. PVC costs about $55.00-75.00+ per foot, depending on
the cost of cuttings disposal.
In conclusion, the PPT Profile and Push-in steel collectors are better, faster and cheaper than standard
drilled collectors.
The third column from the left measures pore-pressure and
indicates plenty of gas pressure making this a good location for a
Push-in collector. No liquid is indicated in the log.
indicates plenty of gas pressure making this a good location for a
Push-in collector. No liquid is indicated in the log.
The cone to the right has an extra
wiper in addition to wipers inside
the red housing. This is to insure
that the inside of the rig stays a
clean and safe working space.
wiper in addition to wipers inside
the red housing. This is to insure
that the inside of the rig stays a
clean and safe working space.
