PROCEEDINGS, Thirty-Eighth Workshop on Geothermal Reservoir Engineering
Stanford University, Stanford, California, February 11-13, 2013
SGP-TR-198
PERFORMANCE EVALUATION OF DEEPENED WELLS 420DA AND 517DA IN THE
LEYTE GEOTHERMAL PRODUCTION FIELD, PHILIPPINES
Rowena N. Abapo, Marie Hazel B. Colo, Romeo P. Andrino, Edwin H. Alcober
Energy Development Corporation
Julia Vargas cor. Meralco Ave., Ortigas Center
Pasig City, Philippines, 1605, Philippines
e-mail: [email protected]
ABSTRACT
The Leyte Geothermal Production Field (LGPF),
located in central eastern Philippines, is a key
contributor of geothermal power since its operation in
1997. To enhance steam field production, two
shallow wells, 420D and 517, were drilled in 2004
with depths of 1200 m and 1700 m respectively. On
completion, these wells were poised to meet the
steam requirements of the power plants in LGPF
contributing a combined output of 4MWe. Well
420D has been producing since 2004 until it
collapsed in June 2007 but was revived through
vertical clearing discharge. When 420D reached
minimal output in November 2010, well was
evaluated for deepening with acidizing. This was
implemented in May 2011 resulting to a gain of
8MWe. Successful deepening of the initially high
enthalpy well 420D was achieved by tapping both the
shallow two-phase and deep liquid zones of the
reservoir resulting to a medium enthalpy discharge.
The well also intersected more the Mahiao East Fault
and a new structure Litid South Fault in the openhole
section providing additional production. On the other
hand, 517 was evaluated for re-entry/deepening in
July 2011 to increase production and clear the
mineral deposits, although output has been stable
since 2008. The minimal increase of 1.6MWe in the
post-deepening output of 517DA was expected due to
the shallower than programmed total depth cleared
and the inability to maximize the target East Fault
Line. The LGPF Experience in wells 420DA and
517DA highlighted the importance of the productive
structures to be intersected, the well’s downhole
temperature, enthalpy range, setting depth of the
production casing shoe and the length of the
openhole section to ensure the improved performance
of shallow wells upon deepening. Tapping both the
shallow two-phase and deep liquid zones of the
reservoir resulting to a medium enthalpy discharge
has contributed to the improved performance of the
deepened wells.
BACKGROUND
Upper Mahiao and Malitbog sectors aims to enhance
steam field production, hence two (2) shallow wells
(W420D and W517) were drilled. W420D was
drilled as an intermediate depth well targeted towards
the bottom northwest section of W415D while W517
was drilled shallow to tap the shallow feed zones of
Malitbog. W420D was spudded on July 1, 2004 and
was completed on August 2, 2004 while W517 was
spudded on July 2, 2004 and was completed on
August 2, 2004. W420D tapped the shallow steam
zone of the reservoir for production and cased-off
Litid North fault which acts as a conduit for
injection/condensate returns. In addition, 420D aims
to avail the permeability associated with Kapakuhan
fault. W517 on the other hand, was drilled to tap the
liquid reservoir and target solely the East Fault line.
Post drilling tests showed that W420D obtained a
modest injectivity index of 18-24li/s-MPa and -3 to -
7 skin suggesting no wellbore damage. W517
obtained an injectivity index of 13.9li/s-MPa with a
skin of -3 to -5 which also suggest no wellbore.
W517 had been on continuous production since its
cut-in on November 2004 until it produced minimal
output of 1.6MWe in August 2010 that made it a
candidate for re-entry/deepening. W420D was cut-in
on October 2004 and well had been on continuous
production until it collapsed in June 2007 due to
injection returns based on gas chemistry. It may also
have been influenced by silica deposition, blockage
and interference from 423D re-entry. Well was
revived through clearing discharge and its ouput
recovered to 1.4MWe. Recurrence of the gradual
decline in output prompted the recommendation to
re-enter/deepen the well.
Figure 1: Location map of W420D
Figure 2: Location map of W517
DEEPENED WELLS
Well 420D deepening W420D was originally designed to be sidetracked
from the original total depth of the well at
1200mMD. However, the liner retrieval operation
recovered only 221 m of the slotted liners and not the
entire length. Hence, the sidetrack point was revised
from 1200 to 932mMD. W420D attained the target
depth of 2300mMD without major problems
encountered during drilling/deepening.
W420D data and profile
The well is a shallow in-fill production well drilled to
augment the steam supply for the steamline
interconnection (SLI) that diverts steam from Upper
Mahiao sector the Malitbog and Mahanagdong
sectors. The well’s output has been influenced by
silica deposition. Well ejected considerable scales
(98% amorphous silica) when it was revived through
vertical clearing discharge in November 2007 after
collapsing in June 2007. It subsequently recovered its
output of 1.4MWe. Silica deposition, caused by
extensive boiling of the silica-saturated brine returns
is still observed as evidenced by the recurrence of the
gradual decline in output to 0.6MWe as of July2010.
Another clearing discharge was conducted on
April2009 but was not able to recover the well’s
output. This may indicate that silica deposition is not
only within the wellbore but could also be within the
formation. W420D output is expected to decline
further as high enthalpy wells are prone to silica
deposition.
Figure 3: Well profile of W420D (pre-deepening)
Figure 4: Well profile of W420DA (post-deepening)
Figure 5 shows the W420DA fluid chemistry trend.
Clres level increased to 10,000ppm-12,000ppm while
420DA
517DAA
Tqtz increased to 285°C. C02TD is stable at 500
mmol/100mol after the deepening.
Figure 5: W420DA Chemistry
Well517 deepening
Well 517 target depth was supposed to be at
2700mMD. However, due to recurring high torque
and increasing pick-up weight, well was completed at
a shallower depth. During deepening, well was
sidetracked through the 9-5/8” production casing
between 1031 and 1037mMD. The 7” TOL was set at
997mMD, while the 7” BOL was squatted at the
bottom. Circulation losses encountered between 1439
and 1512mMD. Drilling blind down to total depth
had caused poor hole cleaning resulting to recurring
tight holes, obstructions, fill and stuck pipes. In the 8-
1/2” hole, the well track bit walked within the East
Fault Line at 1249mMD and further made a positive
walk between 1278mMD and 2013mMD of
Kadluman Fault. A low drilling penetration rates of
1.9mph was observed during at 2436-2430mMD,
thus the hole was prematurely bottomed out at
2430mMD.
W517 data and profile
W517 was a shallow vertical well at pad 511 of the
Malitbog sector. It was drilled to a total depth of
1700mMD. The well has an output of 2.7MWe but
due to reservoir pressure drawdown, the well’s output
significantly decreased to 1.6MWe. The re-entry
sidetracking and deepening of the well was
considered as M & R well owing to the limited areas
of expansion in the Malitbog Sector (Bien, 2011).
The well was drilled to supply steam to the Malitbog
power plant and tap the liquid phase of the reservoir
existing at deeper levels below -435mRSL for
production and to intersect the permeability
associated with East Fault Line. W517 output is
relatively stable since 2008 at 1.6-1.8MWe.
Figure 6: Reservoir Process affecting 517
Slight decline in its output was observed as compared
to its earlier discharge in 2005 which can be
attributed to the effect of injection returns as
confirmed by the positive tracer responses from
injection wells. The re-entry was recommended to
recover its output and clear the hole of mineral
deposits.
Figure 7: Well profile of W517(pre-deepening)
Figure 8: Well profile of W517DA(post-deepening)
Figure 6 shows the W517DA fluid chemistry trend.
Clres level is still lower compared to its pre-deepening
level while Tqtz increased to 260°C.
Figure 6: W517DA Chemistry
COMPLETION TEST DATA
W420D completion test results (Table 1) show that
major permeable zones are located at 850-970mMD
before and after the deepening. The major zone at
W517 is at 1600mMD (Table 2) although this is not
apparent after the deepening.
Table 1: W420D Pre and Post-deepening output
Well Data Pre-
deepening
Post-
deepening
Max Measured Temp °C 279 (1200mMD)
281 (2000mMD)
Injectivity Index (li/s-MPa) 18.2 – 24.1 133
Kh (da-m) 1.6 23.5
Major Permeable
Zone,mMD
850-900 950-970
Table 2: W517 Pre and Post-deepening output
Well Data Pre-
deepening
Post-
deepening
Max Measured Temp °C 245 (1690mMD)
246 (2200mMD)
Injectivity Index (li/s-MPa) 13.9 48
Kh (da-m) 2.88 - 3.68 3.17
Major Permeable
Zone,mMD
1600 -
Measured downhole temperatures of the two wells
(Table 1 and 2) are above 220°C. Well 420DA
(Kh=23.5da-m) showed better permeability than
W517DA (Kh=3.2da-m). Furthermore, W420DA had
better acceptance with an injectivity index of
133li/s/MPa compared to the 48li/s/MPa injectivity
index of W517DA.
DEEPENED WELLS PERFORMANCE
The pre-deepening outputs of wells 420D and 517 are
presented in Tables 3 and 4. The output of W420D
significantly increased after the deepening from 1.6
to to 9.0MWe (June 2011). There was a similar but
not as significant an increase in the output of 517
after the deepening from 1.6 to 3.0 MWe.
Table 3: W420D Pre and Post deepening output
Well Data
Pre-
deepening
Post-
deepening
%
Output
Increase
WHP (MPag) 1.5 1.4
500%
MF (kg/s) 4.3 24.2
H (kJ/kg) 2611 2368
SF (kg/s) 3.9 19.1
MWe 1.6 8.0
lrmd/lgpf/rna 3jul12
W420D Output vs Time
2004 2006 2008 2010 2012 2014
1800
2200
2600
3000
H(kJ/kg)
2004 2006 2008 2010 2012 2014
0
1
2
3
WHP
(MPag)
2004 2006 2008 2010 2012 2014
0
510
152025
SteamFlow
(kg/s)
2004 2006 2008 2010 2012 2014
010
2030
4050
MassFlow
(kg/s)
2004 2006 2008 2010 2012 2014
0
5
10
15
20
WaterFlow
(kg/s)
420DA
Figure 7: W420DA pre and post-deepening
output
Table 4: W517 Pre and Post-deepening output
Well Data
Pre-
deepening
Post-
deepening
%
Output
Increase
WHP (MPag) 1.22 1.34
188%
MF (kg/s) 21.1 35.2
H (kJ/kg) 1106 1156
SF (kg/s) 3.3 6.3
MWe 1.6 3.0
Figure 8: W517DA pre and post- deepening
output
The significant increase in the W420Da post-
deepening output maybe attributed to the successful
deepening to its target depth. The well was also able
to intersect additional structures, i.e. Kapakuhan,
Mahiao East and Litid South. Improvement in the
well’s injectivity index from 24 to 133li/s-MPa
suggests enhanced permeability and acceptance. The
well’s downhole temperature is also relatively high
from 279°C (pre-deepening) to 281°C (post-
deepening), which also contributed to the well’s
performance given the high enthalpy nature of its
discharge.
Figure 8: W420D pre- deepening temperature
Figure 9: W420DA post- deepening temperature
The minimal increase in the 517DA post-deepening
output was due to its premature completion at a
shallower depth (2430mMD). Hence, the target East
Fault line at 2700mMD was not bottomed out.
Bitwalking at the fault plane did not contribute much
to the well’s output. No significant improvement in
the well’s temperature was observed (245°C to
lrmd/lgpf/rna 15nov11
W517DA Output vs Time
2004 2006 2008 2010 2012
1000
1200
1400
1600
1800
H(kJ/kg)
2004 2006 2008 2010 2012
0
1
2
3
WHP
(MPag)
2004 2006 2008 2010 2012
0
5
10
15
SteamFlow
(kg/s)
DR = 0.02MWe/mo
2004 2006 2008 2010 2012
10
20
30
40
MassFlow
(kg/s)
2004 2006 2008 2010 2012
10
15
20
25
30
WaterFlow
(kg/s)
517DA
246°C) and its post-deepening condition may have
affected the well’s output. With the well deeper, there
could be more contribution from the liquid zone as
evidenced by the increasing water flow during TFT
measurements. There was a significant increase in
injectivity index from 13.9 to 48li/s-MPa.
Figure10: W517 pre- deepening temperature
Figure11: W517DA post- deepening temperature
SUMMARY
Well 420DA has tapped both the upper two-phase
and deep liquid zones of the reservoir resulting to a
medium enthalpy discharge. The well has also
intersected more the Mahiao East Fault and a new
structure Litid South Fault in the openhole section
providing additional mass inflow for production.
W51DA improved its post-deepening output from 1.6
to 3MWe. A higher liquid fraction in the discharge
resulted from the deepening.
For future deepening of shallow wells it is
recommended to consider the prolific structures to be
intersected, high downhole temperature, high
enthalpy, dry well and the reservoir condition in
evaluating candidate wells for deepening to produce
significant results. Application of new technologies
to enhance the well permeability and productivity can
also be evaluated.
REFERENCES
Bien, O. C., (2011), "Geological Report of Well
420DA, Pad 407, Tongonan Geothermal
Production Field, Leyte. Energy Development
Corporation” (unpublished)
Bien, O. C., (2011), "Geological Report of Well
420DA, Pad 407, Tongonan Geothermal
Production Field, Leyte. Energy Development
Corporation” (unpublished)