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: abapo.rn@energy.com.ph

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)