BEFORE THE OIL AND GAS CONSERVATION COMMISSION
OF THE STATE OF
* * *
IN
THE MATTER OF THE APPLICATION OF )
PUBLIC SERVICE COMPANY OF
FOR AN ORDER AUTHORIZING THE CLOSURE )
OF THE
GAS
STORAGE FACILITY IN
COUNTY,
APPLICATION
The Applicant, Public Service Company of
William C. Uding, P.E.
Gas Storage Projects Director
Xcel Energy Services Inc.
Telephone: (303) 571-7383
and
James
D. Albright, Esq.
Assistant
General Counsel
Xcel
Energy Services Inc.
Telephone: (303)
294-2753
WHEREFORE, Public Service respectfully requests
that this matter be set for hearing by the Commission; that notice thereof be
given as required by law; and that upon such hearing the Commission issue an
order granting this Application and issuing a certificate of closure for the
Leyden Facility as requested herein.
Public Service further requests that the Commission in its order grant
such other provisions as the Commission may find to be necessary or desirable
in the matter.
Dated this 3rd day of March, 2003.
Respectfully submitted,
By:
James D. Albright, #18685
Assistant General Counsel
Xcel Energy Services Inc.
Tel.:
(303) 294-2753
Fax:
(303) 294-2988
and
Gorsuch Kirgis LLP
G. Donohue Kane, #11346
Tel. (303)
376-5000
Fax: (303)
376-5001
ATTORNEYS
FOR PUBLIC SERVICE
COMPANY
OF
Verification
STATE OF
) ss.
CITY AND
William C. Uding, of
lawful age, being first duly sworn upon oath, deposes and says that he is Gas
Storage Projects Director for Xcel Energy Services Inc., agent for Public
Service Company of Colorado, that he has read the foregoing Application,
including the Closure Plan attached as Exhibit A thereto, and that the matters
therein contained are true to the best of his knowledge, information and
belief.
William
C. Uding
Subscribed and sworn to before me this 3rd day
of March, 2003.
Witness my hand and official seal.
My
commission expires: _______________________________.
Notary
Public
( S E A L )
CLOSURE PLAN
FOR THE
Public Service Company of
I. Overview and Summary of Closure Plan
II. Background and Description of the
A. Background
B. The
C. The
Decision to Close the
D. Gas
Migration and Leakage of Storage Gas From the
III.
Water Flooding of the Caverns and Removal of Storage Gas
IV. Conversion
of Certain Gas and Water Wells to Water Storage Operation
V. Abandonment
of Gas Injection/Withdrawal Wells
VI. Abandonment
of Shaft Seal Systems
VII. Abandonment
of Observation Wells
VIII. Abandonment
of Gathering Lines and Above Ground Facilities
IX. Monitoring
During Closure
X. Post
Closure Monitoring
Public Service Company of Colorado
Colorado Oil and Gas Conservation Commission
I. Overview and Summary of Closure Plan
II. Background and Description of the Leyden Facility
I.
Overview and Summary of Closure Plan
IV.
Conversion of Certain Gas and
Water Wells to Water Storage Operation
V.
Abandonment of Gas Injection/Withdrawal Wells
VI.
Abandonment of Shaft Seal Systems
VII.
Abandonment of Observation Wells
VIII.
Abandonment of Gathering Pipelines and Removal of Above Ground
Facilities
I. Overview and Summary of Closure Plan
13.
The purpose of this document is to set
forth Public Service Company of
14.
15.
Although dependent largely on the
availability of sufficient quantities of water for flooding the underground
storage caverns, Public Service estimates that the closure process will take
approximately two and one-half years from the date of commencement of water
flooding, which currently is planned to occur in mid-2003. Therefore, by the end of calendar year 2005,
it is anticipated that the facility will be closed as a natural gas storage
facility and the only remaining activities conducted by Public Service at the
site will be post-closure monitoring and the subsequent abandonment of
monitoring wells.
16.
17.
In order to put into context the details
of the Company’s proposed Closure Plan, the following section provides a
background and description of the Leyden
Facility. The remaining sections of this
Closure Plan discuss in greater detail the closure procedures summarized above.
II. Background and Description of the
A. Background
The underground
storage of natural gas is common, with over 400 underground gas storage
facilities operating in the
The Leyden Facility was initially developed in 1958-1959 and
was placed into operation by Public Service in 1960. Since 1960, Public Service has operated the
abandoned coal workings of the
In 1960, upon
Public Service’s application in Cause No. 146, the Colorado Oil and Gas
Conservation Commission (“Commission”) approved the Leyden
Facility pursuant to its authority under C.R.S. § 34-64-104. In accordance with the approved project,
Public Service was authorized to store natural gas in the
18.
B. The
The Leyden Facility consists of an underground gas storage
field and the
The Leyden
Coal Mine operated for approximately 47 years from 1903 to 1950. At the time of its conversion to natural gas
storage operations in 1960, the Leyden Facility was
located distant from any community with the exception of the tiny town of
19.
Referring to Appendix A, the green shaded
area of the map shows the extent of the natural gas storage leases, which
includes some minor ownership of land purchased by the Company. The rough black line just inside the green
shading is the extent of the known coal mining activity underground. About 6 million tons of coal were removed
from the mine during its production, or less than 50 percent of the coal
located in the mine, leaving a void of about 150 million cubic feet. The lease property extends about 500 feet
from the perimeter of the mine cavern in most areas, except for portion on the
north side.
There are 14 gas
injection/withdrawal wells and 20 observation and water wells on the
The shafts that
were constructed and used during the coal mining era to remove the coal are
shown on the map in Appendix A as bold black squares with x’s
in their center. These shafts were
sealed in the early 1960’s as a critical element of the storage seal, and have
been remained sealed to the present day.
A photograph of a typical shaft seal site is contained in Appendix B to
the Closure Plan.
20.
The gas gathering system is comprised of
steel and plastic piping that is largely buried on the leased property and in
public rights of way. These lines vary
in size from 24-inch to 4-inch diameter.
21. The Leyden
Station is located on a 6.7-acre tract of Company-owned property in Section 25,
just east of the gas storage area on the north side of
22.
The Leyden
Facility operates by injecting natural gas into the underground space left
after coal mining. These cavern spaces
have almost entirely collapsed, leaving an underground “rubble pile” of rock
that supports the overlying rock formations.
Due to the gradual nature of the collapse, there is no danger from
subsidence at the surface over this facility.
The void created by the original coal removal process is still present
in the rubble although not anywhere as spacious as the “rooms” in the coal
mine. Additionally, some of the
sandstones within the
In 1958, before
Public Service began gas storage activities, the rubble pile voids and the
sandstone pores were full of water.
These void spaces, where water can effectively be drained by gravity to
a sump area or removed by pumping, are the primary areas within the storage
reservoir where Public Service historically has stored natural gas. Gas is also stored in sandstone pockets, or
lenses, located above and on either side of the mine cavern. Sandstone is porous and permeable and capable
of holding natural gas. The geologic
formation of the storage facility where all this occurs is the Cretaceous Lower
Laramie formation. This overlies the Fox
Hills sandstone and the Pierre Shale.
The
The cap rock is a 400-foot thick layer
composite of impervious clays, claystones, and
siltstones separating the storage reservoir from the surface. From core samples recovered during early well
drilling, Public Service determined that the
23.
The sandstones of the
Public Service
has a wastewater discharge permit
(Permit No. CO-0001279) issued by the Colorado Water Quality Control
Division for wastewater discharges from the Leyden
Facility into Leyden Creek. The permitted outfalls are: the discharge from Water Well No. 12;
overflow from the livestock-watering pond that receives water from Well No. 21;
discharge from the Leyden Knockout Tank; and
discharge from the Retention Pond, including discharges into livestock watering
pond.
C. The Decision to Close the
On
In recent
years, the Leyden Facility has come under intense
public scrutiny due to a series of events concerning natural gas
migration. These events include a 1998
jury verdict in a Jefferson County District Court civil action brought against
Public Service, which found that Leyden storage gas
had migrated on to an adjacent landowner’s property, and the release of
information concerning a new observation well, Well No. 36, which discovered
storage gas about 175 feet from the mine cavern, but within Company-owned
property. The reaction in the press and
by governmental officials, local landowners, developers and environmental
groups to this information caused Public Service to re-evaluate the continued
viability of
24.
25.
D. Gas Migration and Leakage of Storage Gas From
the
26.
27.
Public Service believes that to the
extent any gas migration has ever occurred from the Leyden
Facility, such migration could only have occurred through sandstone lenses in
communication with the mine caverns.
While any such migration is virtually impossible to quantify with any
degree of accuracy, at the end of the closure procedures proposed herein any
such migrated gas will be at native pressures and pose no threat to safety or
the environment greater than the coal bed methane gas already present in the
underlying formations in the area. In addition,
Public Service firmly believes that, based on the characteristics of the Upper
Laramie, the only way storage gas could ever leak to the surface in sufficient
quantities to be recognized as such is through artificial penetrations, such as
boreholes, through the cap rock. There
have been a few isolated instances of storage gas leaking to the surface over
the 40-plus year life of the facility.
But it is important to note that in each case the cause was, in fact, a
borehole. The leaks were found by Public
Service during leakage surveys, and they were all promptly repaired.
The first of
these leaks was found in the Barbara Gulch area as bubbles under ice in
1964. The source was traced back to an
abandoned water well extending from below the mine level. The well’s casing was removed and new casing
installed. This borehole is now operated
as observation Well No. 17.
28.
In the mid 1970’s, gas bubbling was
observed inside the concrete liner of shaft seal no. 2. It was found that this gas bubbling was
associated with pumping water from the east workings from water well nos. 7 and
13. In response, Public Service
discontinued pumping from these wells to allow the standing water in this area
of the mine to cover the bottom of shaft no. 2.
Another borehole
that was found leaking to the surface was discovered during a surface leakage
survey that is a part of a regular effort by the field operators. In December 1979, a surface leak of storage
gas was located on the northeast edge of the field. Again, a drill rig was brought in to the
location of the gas and began drilling.
An unplugged core hole from the mining era was found shortly after
drilling began. This hole was cleaned to
bottom, around 500 feet, and casing was cemented in the hole. This is now operated as observation well no.
23.
To Public
Service's knowledge, no gas from the storage facility has ever escaped to the
surface except through man-made holes punched through the cap rock as
explained. Otherwise, the cap rock seal
has been one hundred percent effective.
Public Service
employs several methods for monitoring gas leakage at the Leyden
Facility. First, each well is visited
and inspected not less than once per week.
Second, a walking survey with gas detection equipment is performed on a
regular basis over the storage field area and the buried gas gathering
piping. An annual inspection of the gas
storage area is also performed from a helicopter by looking for stressed or
dead vegetation. Finally, permanent soil
vapor extraction points have been installed around the southeast perimeter of
the storage area. Samples from these
monitor points are collected and analyzed in a laboratory for hydrocarbon gas
content.
In 1999, Public
Service drilled an observation well, Well No. 36, in which it discovered the
existence of storage gas in a Lower Laramie sandstone about 775 feet below
ground level outside the perimeter of the mine cavern. The most likely path of the gas found in Well
No. 36 is through fractures in the
III. Water
Flooding of the Caverns and Removal of Storage Gas
29.
During the early engineering design work
of the facility closure process, Public Service concluded that flooding of the
abandoned mine workings with water was the most efficient and effective means to
extract the remaining recoverable storage gas and retire the gas storage
reservoir. Injection of water is
necessary to displace the gas volumetrically in the mine cavern. Water flooding would also return the property
as nearly as practical to its condition before gas storage operations
commenced. Although the underlying Fox
Hills aquifer would fill the underground caverns eventually through natural
water flow, it was determined that this natural water flooding process would
take approximately 40 years, and would require Public Service to retain gas
storage rights and remain on the leased property during this period. It was therefore concluded that an external
supply of water would need to be secured to facilitate the flooding
operations. An estimated 2100 acre-feet
of water would be required to accomplish this.
Due to federal Environmental Protection Agency regulations, it was also
concluded that the water supply should be potable.
30.
31.
In mid-2001, Public Service and the City
of
32.
As a result, an agreement was consummated
between Public Service and the City providing for the City to supply a quantity
of water sufficient to flood the caverns, the termination of Public Service's
rights under existing gas storage leases (including one lease where the City
had acquired the landowner's interests),the City's acquisition of new rights
and construction of facilities to conduct water storage operations, Public
Service's conveyance of certain wells and equipment useful for the City's water
storage operations, and the conveyance of an option (and funds) for the City to
purchase a 102-acre parcel of land adjacent to the Leyden
site.This Agreement was approved by the Arvada City
Council on January 27, 2003, and was fully executed on January 28, 2003. The Agreement with the City is subject to
Public Service obtaining approval of its Closure Plan from the Commission. A copy of the Agreement between the Public
Service and the City is attached to this Closure Plan as Appendix F.
The last injections
of natural gas by Public Service into the Leyden
Facility for gas storage occurred on
In accordance
with the Agreement with the City of
IV. Conversion
of Certain Gas and Water Wells to Water Storage Operation
Several of the
existing wells at the Leyden Facility will be used
for the injection of water and later transferred to the City of
Well #4 is
currently a gas withdrawal well on the north end of the west cavern. This well will be used to recover gas that is
displaced as water floods the caverns.
At the time water reaches the 10¾-inch casing shoe of this well, 5145
feet above sea level elevation, gas recovery will be complete. A temporary plug will be set in the bottom of
the 10¾-inch casing in order to fill the casing to surface with water. The well will be logged to verify good cement
bond and a gas detection log will be run.
If gas is found, the area will be perforated for possible additional gas
recovery or venting. Following that, the
perforations would be cement squeezed, the temporary plug would be removed and
the well transferred to the City for use in its water storage operation.
Well #5 is an
east cavern gas withdrawal well. It is
the structurally highest well in the east cavern. This well will be used to recover the gas
being displaced as the cavern is flooded with water. When the injected water level reaches the
7-inch casing shoe located at 5144 feet above sea level, gas recovery will be
complete. A temporary plug will be set
in the bottom of the 7-inch casing in order to fill the casing to surface with
water. The well will be logged to verify
good cement bond and a gas detection log will be run. If gas is found, the area will be perforated
for possible additional gas recovery or venting. Following that, the perforations would be
cement squeezed, the temporary plug would be removed and the well transferred
to the City for use in its water storage operations.
An east cavern well, Well #7, was drilled
and operated as a water production well.
It historically had been a marginal producer, having a poor connection
to the cavern area. This well was
recently worked over to improve its capacity as a water injection well. A 7-inch liner was installed in the well down
through a previously open hole section below the cemented casing. A 1.66-inch tubing string and down hole
pressure gauge were also set during that workover. Its use as a water injector will be evaluated
at the time water is available for injection.
This well would then be transferred to the City for use in its water
storage operations.
A west cavern
well, #12, has been the primary water withdrawal well. It will be used as the primary water
injection well. This well currently has
a submersible pump and 3½-inch tubing for water production. The pump and tubing will be removed to aid in
the injection process. This well also
has an existing 1.66-inch tubing string and down hole pressure gauge used for
monitoring. The 1.66-inch string and the
down hole gauge will remain in place to monitor the injection process. Following injection, the well will be
transferred to the City for use in its water storage operation.
Well
#19, West Cavern
Well #19 is a
gas withdrawal well in the west cavern.
A 7-inch liner is set through the cavern level in this well. When the injected water level reaches the
9⅝-inch casing shoe at 5050 feet above sea level elevation, gas recovery
will be completed. A temporary plug will
be set in the bottom of the 7-inch liner in order to fill the casing to surface
with water. The well will be logged to
verify good cement bond and a gas detection log will be run. If gas is found, the area will be perforated
for possible additional gas recovery or venting. Following that, the perforations would be
cement squeezed, the temporary plug would be removed and the well transferred
to the City for use in its water storage operations.
Well #21 is
currently a water withdrawal well that produces water from the west
cavern. This well and pumping equipment
will be transferred to the City in its current condition.
Well #30,West
Cavern
V. Abandonment of Gas Injection/Withdrawal
Wells
The remaining gas injection/withdrawal
wells, Wells #3, #14, #15, #16, #18, #22, #25, #26 and #29, will be plugged and
abandoned following these general procedures.
The injected water level will be allowed to reach above the production
casing shoe and a permanent plug will be set.
The well bore will be filled with water and a cement bond log and gas
detection log will be run. Copies of
these logs will be forwarded to the Commission Staff. If inadequate cement or gas accumulations are
suspected from these logging results, a remedial action such as a cement
squeeze on a poor bond zone or perforating and evaluating a logged gas show
will be conducted. If gas zones are
found in this manner, the gas will be recovered into the gathering system or
vented as appropriate. The well would
then be abandoned according to the prevailing rules of the Commission. The surface equipment and fencing will be
removed and the site reclaimed according to the lease agreements and Commission
standards. The Commission’s Rules and
Regulation govern the abandonment of gas storage wells. In accordance with these rules, the Company
will formally file its notice of intent with the Commission to plug each
individual well, prior to any abandonment.
This notice of intent would contain information regarding the design,
procedures and materials to be used in the plugging operations. After the Commission approves or modifies the
procedure, the field plugging operations will be conducted and the Commission
will be notified by means of a Subsequent Report of Abandonment.
VI. Abandonment of Shaft
Seal Systems
The shaft seal
systems refer to the four original mine shafts that were used to extract the
coal during the mining operations from 1903 to 1950. These shafts, which are about 10 feet by
twelve feet on the surface, were originally vertical rectangular openings that
extended from the surface to coal seams.
During the conversion of the facility for gas storage, these shafts were
reopened and cleaned out to bottom. A
sealing mechanism was constructed in each of the shafts to contain the gas
pressure during storage. Roughly
described from bottom to top, the seal consists of a concrete plug that was
poured in the mined cavern section up into the shaft itself. Refer to Appendix B for a photograph of one
of the shaft seals. A coarse fill
material, (gravel), then fills the shaft to above the water level that was
present in the mine during this shaft work in 1961. This condition describes shafts #3 and
#4. Shafts #1 and #2 were only cleaned
out to the level of the standing water in the shafts at that time. Workers then entered the shaft down to the
level of this fill to enlarge the diameter of a short section of each shaft by
a few feet. Another, or upper, concrete
plug was then poured in this enlarged shaft area, typically 20~30 feet in
height. Above this upper plug is the mud
section that varies from 50 feet to 123
feet, depending on the shaft. The
mud section is clean gravel and 9.0 pound per gallon drilling mud. On top of the mud section is a short filter
section, (sand), followed by a compacted clay fill section. Bank run gravel then fills the shafts to the
surface. The shafts all have concrete
liners from the surface to varying depths from 50 feet to 144 feet, and each is
equipped with a metal cap with service entrances. A well from the surface of each shaft extends
down to the mud section. Drilling mud
has been circulated on a regular basis at each location in order to suspend the
mud solids and additional mud is added as necessary. The head created by this column of mud has
been kept above storage pressures through out the facility’s operating history.
The proposed
procedure for abandoning these shaft seal system is as follows. The shafts will continue to be maintained as
they were during normal operation until the gas pressure in the caverns falls
below 40 psig. When the cavern pressure
is less than 40 psig, the circulation procedure will change and, as additional
fluid is needed, only fresh water will be added instead of the 9.0#/gal
mud. If a shaft then circulates only the
fresh water, the circulation and addition of water will be discontinued. If the presence of gas is noted in the shafts
above the mud section, the remedial action would be to add fresh water and
reinstate the regular circulation schedule.
If this effort were not successful, mud would then be added and
circulated. At the time the injected
water level in the caverns stands as high as the bottom of the mud section in
each shaft, that shaft’s mud circulating well could then be plugged and
abandoned per normal Commission rules regarding abandonment of wells.
VII. Abandonment of Observation Wells
The Leyden Facility includes 17 wells that are classified as
observation wells. These wells provide a
variety of data such as the monitoring of water levels in formations both above
and below the storage zone, monitoring of repairs made to boreholes found
during the storage operation, such as Wells #17 and #23, wells drilled for the
purpose of improving the geologic description of the area, and wells that were
unsuccessful as gas injection/withdrawal wells.
The following provides a well-by-well description of the current
disposition and plans for these wells.
This well was
the first well drilled in the field and was planned as a gas
injection-withdrawal well. It was
unsuccessful for that purpose as it encountered an unmined
coal pillar. It was plugged and
abandoned in 1969 although the surface equipment is still in place. The surface equipment will be removed and the
well site reclaimed. This work can be
performed at any time during the closure process.
The #2 well was
also drilled as a gas withdrawal well.
It too found unmined coal instead of cavern
and has been used as observation since that time. A cast iron plug will be set in the bottom of
the well, the well bore displaced with water and cement bond log and gas
detection log will be run. Poor cement
and/or gas accumulations behind casing will be evaluated and remedied if
found. The well would then be plugged
and abandoned according to current Commission rules and the surface
reclaimed. The abandonment work on this
well could be done at anytime during the closure process.
Wells #10 and
#11 are observation wells over the mined areas of the east and west caverns,
respectively. These wells are about 400
feet deep and monitor a water zone of the Upper Laramie Formation that is shown
to be hydraulically isolated from the
Well #13 was
originally drilled and operated as a water production well from the east
cavern. This well was a marginal water
producer and pumping was discontinued in the early 1970’s after the east cavern
was pumped down for gas storage operations.
The east cavern, having been mined earlier and somewhat higher in the stratigraphic section, does not have the water influx
problems as the newer and lower west cavern.
This well was recently reworked to correct casing problems. The cavern level was plugged and an upper
zone of the
These wells are
the result of a repair made to a disused water well that was found to be
leaking gas to the surface in the early 1960s.
The original well bore was believed to be a coal exploration core hole
that penetrated the Laramie Fox Hills aquifer.
The rancher then used it for stock water while it flowed to
surface. A short time after gas storage
operations began, bubbles were found under ice in the adjacent Barbara
Gulch. A drill rig was used to reenter
the borehole, remove the old casing and set and cement the new casing. Difficulties during the workover
caused the abandonment of the first reentry.
The rig was moved over a couple feet and a new well was started to
reenter the original hole. Both
wellheads are still in place and are referred to as #17a and #17b. The #17b well monitors the
This well was
drilled in the mid 1970’s to observe an apparent problem with the east cavern
shaft sealing systems. When the east
cavern water was pumped down to a level that exposed the shaft bottoms to the
storage gas, leakage occurred up the #2 shaft.
This well was drilled and used to monitor this problem. Pumping was discontinued from the east cavern
and the shaft bottoms where again submerged.
This remedied the leakage from the #2 shaft. The #20 well will be plugged and abandoned
according to Commission rules and the lease agreements after the #1 and #2
Shaft Seal systems have been abandoned.
Well #23 was
drilled in 1981 to repair an old coal exploration core hole that was found to
be leaking to surface. The leak was
found during one of the regular surface surveys that were used to search for
leaks. A drill rig was moved over the
spot of gas leakage and the core hole was cleaned out and casing was set. Located over the north edge of the east
cavern, this well will be plugged and abandoned according to Commission rules
after the water injection in the east cavern is completed.
This well,
located above the west cavern, was drilled to enhance the understanding of the
geology of the cap rock at the
This well,
located above the west cavern, was drilled in 1990 to evaluate a shallow gas
charged formation that was encountered while drilling wells #25 and #26. The gas charged zone was encountered at 137
feet G.L. The well was completed in the
zone and a gas sample taken from the well.
The gas was confirmed to be storage gas, which probably entered the sand
from casing leaks on Well #15 and #16 which had been repaired earlier in the
year. The well is monitored weekly and
no significant pressure change has occurred from the initial 15 psig well head
pressure. After wells #15 and #16 have
been plugged this well will be blown down and plugged and abandoned according
to Commission rules and the lease agreements.
This well,
located above the east cavern, was drilled in 1990 to investigate a potential
leak in well #3 and #5. The only gas
that was encountered was at a depth of 474 feet G.L., which was well below the
suspected leaks in wells #3 and #5. A
sample of the gas from the zone at 474 feet G.L. was analyzed and it was
determined that the gas was naturally occurring formation gas. This well could be plugged and abandoned at
anytime during the closure process according to the prevailing Commission rules
and lease agreements.
This well,
located north of the cavern, was drilled in 1993 to ensure that the gas storage
operation was not having a significant negative impact on the Fox Hills or
other major aquifers. While drilling
down to the Fox Hills, gas was encountered at 661 feet G.L. The well was completed and tested. Gas analysis confirmed that this was storage
gas. A down hole pressure gauge was
installed to monitor the pressure in the Fox Hills and a gas meter was
installed to monitor the volume of gas being vented. Monitoring will continue until water
injection into the caverns is completed and no significant volume of gas is
being vented. This well will then be
plugged and abandoned according to Commission rules and the lease agreements.
Well #32 was
drilled in 1995, north of the cavern to define the northern extent of a shallow
gas charged sand found in well #31. No
gas was encountered in this well. This
well could be plugged and abandoned at anytime during the closure process
according to the prevailing Commission rules and lease agreements.
This well was
drilled in 1999 north of the cavern in an investigation of the landowner’s
claim of migrated storage gas. The well
was not perforated or otherwise completed.
This well could be plugged and abandoned at anytime during the closure
process according to the prevailing Commission rules and lease agreements.
VIII. Abandonment of Gathering Pipelines and
Removal of Above Ground Facilities
As part of the
Closure Plan for the Leyden Facility, Public Service
plans to abandon in place all gathering pipelines upstream of an existing valve
located in
The abandoned
lines will be cut away at the “K” valve and at each well connect. The pipelines will then be purged with an
inert gas to remove any natural gas.
Following the purge, the lines will be sealed with either a flat plate,
a cap or the ends filled with slurry.
The pipelines will then be abandoned in place.
33.
Facilities that are above ground such as
valve sets, separators and pipe clean out sets, will be removed and the surface
will be reclaimed.
IX. Monitoring During Closure
During the
closure process, Public Service will continue the monitoring activities that it
currently has in place. Public Service
conducts three different monitoring procedures over and around the storage
facility, as follows:
Public Service
inspects all of its wells visually at least once per week. On an annual basis, the buried gas gathering
lines are surveyed by walking with gas detection equipment (FID). An overland walking survey of the storage
cavern is also conducted in the same manner.
These practices will continue until after the caverns have been flooded
with water, gas recovery is completed and the wells are abandoned or
transferred to the City of
In early 2000,
Public Service installed 17 shallow soil gas monitoring wells around the south
and east boundaries of the storage field.
Following the initial 3 sampling rounds, testing has been done on a
quarterly basis for a total of 11 rounds since inception. Public Service plans to continue this testing
until the storage caverns have been flooded with water, the gas recovery is
completed and the wells are abandoned or transferred to the City of
Pubic Service
uses several deep observation wells to monitor various aspects of the gas
storage facility. Locations above,
around and below the storage area yield a variety of information about the
formations and the surrounding hydrology.
These observation wells are described below.
Wells
#10 & #11
These wells are
located above the east and west caverns respectively and are completed in the
Well
#33
This observation
well is located on Public Service fee property.
Well #33, located in the
Well
#36
Well #36 is
located Public Service fee property on the south side of the field within the
current buffer zone around the mined cavern.
This well is dually completed, one zone monitoring a Lower Laramie sand
at a depth of 782-789 feet below ground level.
This sand was found to contain storage gas during drilling
operations. The Foxhills
sand is also completed in this and is mechanically isolated from the
X. Post Closure Monitoring
Two wells, #33
and #36, along with their monitoring systems will be kept operational for 24
months beyond the date of completed water injection into cavern space. Additionally, the soil gas testing from the
existing locations south of
[1] “Coal Mine Methane Storage in Abandoned Mines,” EPA Coalbed Methane Outreach Program Technical Options Series (July 1998). A copy of the EPA paper may be accessed through the following weblink: www.epa.gov/coalbed/pdf/stu001.pdf.