COMPLETION METHODS COMPARATIVE OF GAS … METHODS COMPARATIVE OF GAS PRODUCER WELLS IN NATURALLY...

COMPLETION METHODS COMPARATIVE OF GAS PRODUCER WELLS IN NATURALLY FRACTURED RESERVOIRS

Authors: María Elena Barboza, Luis González, Miguel La Cruz

CONTENT

. INTRODUCTION 4

2. GEOLOGICAL MODEL 5

2.1 Structural Model 5

2.2 Strength Regime 6

2.2.1 Presence of Fractures 6

2.3 Stratigraphy 7

3. ROCK PROPERTIES 8

4. RESERVOIR CHARACTERISTICS 10

4.1 Fluids 10

4.2 Pressures 11

5. DRILLED WELLS 13

5.1 Well SIP-2X 13

5.1.1 Perforating phase 13

5.1.2 Petrophysical Evaluation 13

5.1.3 Mechanical Completion 14

5.1.4 Production Evaluation 16

5.2 Well SIP-3X 20

5.2.1 Perforating phase 20

5.2.2 Petrophysical Evaluation 21

5.2.3 Mechanical Completion 22

5.2.4 Hydraulic Fracture 25

5.2.5 Production Evaluation 29

6. RESULTS ANALYSIS 33

7. CONCLUSIONS 36

8. BIBLIOGRAPHY 36

2

FIGURES

Page

1. Sipororo Structure 5

2. General trend of natural fractures, Sipororo Field 6

3. Stratigraphic column of the Barrancas Area 8 4. Stratigraphic section, SIP-3X - SIP-3X 9 5. Bottom Hole Pressure behavior taken with RCI in well SIP-2X 12 6. Electrical Logs and Casings Schedule of well SIP-2X 15 7. Mechanical completion, well SIP-2X 15

8. Isochronal test interpretation. Well SIP-2X 18

9. IPR Analysis and AOF calculation. Well SIP-2X 19

10. Well SIP-3X. Cement Log in Gobernador Formation 23

11. Well SIP-3X. Casings schedule and Electrical Logs 24

12. Well SIP-3X. Mechanical completion 24

13. Well SIP-3X. Observed behavior during the Minifrac Test 27

14. Well SIP-3X. Temperature Log before and after the Minifrac Test 28

15. Well SIP-3X. Fracturing Process 28

16. Nodal Analysis of Flow after Flow Test, Gobernador Formation 30

17. Production Log Results, Gobernador Formation. Well SIP-3X 31

18. Nodal Analysis of Isochronal Test, well SIP-3X 32

19. Well SIP-3X. Interpretation results of the Isochronal Test 33

3

TABLES

Page

1. Fracture Analysis, Gobernador Formation. Wells SIP-2X and SIP-3X 7

2. Compositional Analysis. Surface sample taken during the Isochronal test.

Well SIP-2X. 10

3. Pressures measured with RCI (Reservoir Characterization Instrument) in

well SIP-2X 12

4. Hydrostatic Pressure of the Mud vs. Reservoir Pressure. Well SIP-2X 13

5. Petrophysical Evaluation Summary. Well SIP-2X 14

6. Isochronal test summary. Well SIP-2X 16

7. Production Log Summary, well SIP-2X 20

8. Mud Hydrostatic Pressure vs. Reservoir Pressure. Well SIP-3X 21

9. Petrophysical Evaluation Summary. Well SIP-3X 21

10. Pressures and Temperatures measured with MDT, well SIP-3X 22

11. Flow after Flow Test, Gobernador Formation, well SIP-3X 29

12. Production Log Results, Gobernador Formation, well SIP-3X 31

13. Well SIP-3X. Modified Isochronal test summary 32

14. Well SIP-3X. Isochronal test interpretation 33

4

1. INTRODUCTION Drilling wells in naturally fractured reservoirs leads to high formation damage (high

skin values). Fractures could be plugged and/or sealed due to drilling fluids loss

and its additives during drilling and completion works, as well as by cement, which

will locate itself preferably in highly conductive fractures. An adequate design of

the perforation work and well schedule completion contributes to minimize

formation damage.

The purpose of this paper is to show the gained experience from two completion

techniques in two wells of the Sipororo field located in Barrancas area, in which

the reservoirs have mixed lithologies of sandstones and limestones with low

porosity and a permeability matrix connected with natural fractures. The first well,

SIP-2X, was drilled with Oil Base Mud (OBM), with a light overbalance and

completed open hole with a pre-perforated casing, avoiding formation damage due

to cementing job. The second well, SIP-3X, due to severe circulation loss, was

completed with a cemented casing to allow a hydraulic fracturing job and to be

able to communicate the well with the non damaged zone of the reservoir, through

the mud additives to control mud losses and the cement. In both cases excellent

productivity results were obtained, showing less formation damage for the

hydraulic fractured well.

The analyses were based on the available information of the Gobernador

Formation, since this is the one with the best petrophysical and productive

characteristics. The following parameters were compared: performance during

drilling phase, lithology, petrophysical properties of the rock, strength regime,

presence of fractures, isochronal test results. It was found that both the high

presence of natural fractures and the hydraulic fracturing job contributed to

increase the productivity of the well SIP-3X, located in the area with the poorer

matrix rock properties compared to the area where the well SIP-2X is located.

5

2. GEOLOGICAL MODEL 2.1 STRUCTURAL MODEL

• The Sipororo Structure is an elongated anticline aligned in direction NE-

SW, limited by two semi-parallel faults with direction NE-SW, one of them

located to the NW and the other one located al SE, converging at the end of

the structure, as well as the deeper levels.

• The fault limiting the structure to the Southeast, which was originated by a

tectonic inversion process, is characterized by a twisted trace, oriented SW-

NE, which dips to the NE with high angular values in its upper part and with

lower angular values towards the bottom.

• The faults slanting the above mentioned, with throws between 200 ft and

500 ft, cut the structure and divide it into three main blocks identified as

SIP-1, SIP-2 and SIP-3 (Figure 1)

Figure 1 Sipororo Structure.

6

2.2 STRENGTH REGIME

The structure is basically the result of compression in direction WNW-ESE,

responsible for the lifting of the Andes Range, which originates at the same time

dextral course movements along Boconó Fault. This regime, which is responsible

for the structure generation, is the predominat one observed in the Maracaibo and

Barinas-Apure Basins.

2.2.1 Presence of Fractures Studies over natural fractures performed in several wells of the area, reveal the

presence of a high number of fractures distributed in at least three sets with

different orientations (Figure 2):

• N 45º E. Phase I Fractures, show white calcite as the filling mineral in all the

cases.

• N 290º E. Phase II Fractures, which are usually filled with white calcite.

• N 315º E. Phase III Fractures. Mainly, this fractures don’t show filling

minerals, and are generally open.

The Filling mineral is mostly calcite and quartz in a very small amount.

Figure 2. General trend of natural fractures. Sipororo Field. (Mikel Erquiaga, 2002)

7

Images from Microresistivity and Acoustic Logs of wells SIP-2X and SIP-3X show

the following result for the Gobernador Formation (Table 1):

Well

Formation TOP (ft)

BASE (ft)

Semi Open Fractures

Open Fractures

Dip Direction Induced Fractures

SIP-2X Gobernador 8410 8541 - 2 65° NE 7

SIP-3X

Gobernador 8810 9115 66

without discrimination

60°-70° NE

55°-65° N-NE

50°-60° NW

5

Table 1 Fracture Analysis, Gobernador Formation. Wells SIP-2X and SIP-3X

2.3 STRATIGRAPHY In the Barrancas Area, the stratigraphic column is formed, from recent to older, by

Formations: Río Yuca, Parángula, Pagüey, Masparrito, Gobernador, Burguita,

Navay, Escandalosa, Aguardiente and Igneous-Metamorphic Basament (Figure 3). The main objective is the Gobernador Formation followed by the Escandalosa

Formation.

8

Formación LitologíaEstratigrafía

Río Yuca-

Parangula

CR

ETA

CIC

O

BASAMENTO ++++++++++++++++++++++++++++++++++++

ROCA MADRE

SELLO

SELLO

Período

o

Agu

a rdi

ente

75.0

105

Campaniense

Cenomaniense

Albiense

80.0

16.2

Registros

P A

L E

O G

E N

O

SB 44 Ma ?

SB-94 Ma

Sistema Petro lero

Turoniense

Maastrichtiense

Esca

ndal

osa

Nav

ay

Burguita

INFE

RIO

RSU

PER

IOR

E O

C

E

N

O

M

E

D

I O

MIO

CEN

O

MED

IO

42.0

49.070.0

Mbro La Morita

Mbro Quevedo

Mbro Caliza ‘O’ Informal

Arenas P-R

Gobernador

Masparrito

T ?

RESERVORIO

?

RESERVORIO ?

SB-87 Ma

Reg

istro

en

esca

la, e

spes

or m

edid

o en

los

pozo

s La

Yuc

a y

Sip

oror

o-1X

= 1

700’

Espe

sor e

n la

col

umna

muy

dis

min

uido

. Esp

esor

real

= 25

00-6

500’

E

spes

or re

al=

500

-900

0’

SELLO

RESERVORIO

?

Pagü

ey

RESERVORIO

?

RESERVORIO ?

Mbro Caliza Informal

Mbro Arenisca Informal

Figure 3. Stratigraphic Column of the Barrancas Area.

3 ROCK PROPERTIES Gobernador’s lithology is made up of light gray, beige and brown sandstones.

Quartz grains are white, from medium size to coarse and moderatedly sorted;

matrix is shaly and occasionally calcareous. It contains inter-stratified layers of

9

light gray compact limonite. Studies of reservoir properties include direct

measurements of core plugs, basic electric logs (neutron-density and sonic) and

special logs (Magnetic Resonance, Reservoir Characterization Instrument).

Thickness: In the structure a variable total thickness is presented because there

are incised valleys, from about 427 feet in the well SIP-3X decreasing up to 131

feet in the well SIP-2X (Figure 4).

TD 10639.20 ft

Sip-3x

MD gr

GR.EDIT (gAPI)0.0 350.0

resist

AF90 (ohm.m)0.2 2000.0

AT90_houst (ohm.m)0.2 2000.0

TVDTVD

markerFormation Tops Panel

Masparrito_O - 7782.92 ft�

Gobernador_O - 7950.43 ft�

Burguita_O - 8378.34 ft�

TD 9681.94 ft

SIP-2X

GR

GR (gAPI)0.0 300.0

TVD resist

M2R6:AWS (ohm.m)0.2 2000.0

marker

Masparrito_O

Gobernador_O

Disc_Paleoceno_OBurguita_O

0 5000m m

ft ft

SIP-3X-X

9200

9000

8800

8600

9200

9000

8800

8600

88008700860085008400830082008100

Sección EstratigráficaSIP-3X SIP-2XTD 10639.20 ft

Sip-3x

MD gr


resist

AF90 (ohm.m)0.2 2000.0

AT90_houst (ohm.m)0.2 2000.0

TVDTVD





TD 9681.94 ft

SIP-2X

GR

GR (gAPI)0.0 300.0

TVD resist

M2R6:AWS (ohm.m)0.2 2000.0

marker

Masparrito_O

Gobernador_O


0 5000m m

ft ft

SIP-3X-X

9200

9000

8800

8600

9200

9000

8800

8600

88008700860085008400830082008100

Sección EstratigráficaSIP-3X SIP-2X

Fm. Gobernador

TD 10639.20 ft

Sip-3x

MD gr


resist

AF90 (ohm.m)0.2 2000.0

AT90_houst (ohm.m)0.2 2000.0

TVDTVD





TD 9681.94 ft

SIP-2X

GR

GR (gAPI)0.0 300.0

TVD resist

M2R6:AWS (ohm.m)0.2 2000.0

marker

Masparrito_O

Gobernador_O


0 5000m m

ft ft

SIP-3X-X

9200

9000

8800

8600

9200

9000

8800

8600

88008700860085008400830082008100

Sección EstratigráficaSIP-3X SIP-2XTD 10639.20 ft

Sip-3x

MD gr


resist

AF90 (ohm.m)0.2 2000.0

AT90_houst (ohm.m)0.2 2000.0

TVDTVD





TD 9681.94 ft

SIP-2X

GR

GR (gAPI)0.0 300.0

TVD resist

M2R6:AWS (ohm.m)0.2 2000.0

marker

Masparrito_O

Gobernador_O


0 5000m m

ft ft

SIP-3X-X

9200

9000

8800

8600

9200

9000

8800

8600

88008700860085008400830082008100

Sección EstratigráficaSIP-3X SIP-2X

Fm. Gobernador

Figure 4 Stratigraphic Section, SIP-3X - SIP-2X.

Mineralogy: 75% quartz, 15% clays, 5% de pyrite and a fraction of feldspar,

calcite and siderite that represent the remaining 5%. With reference to the shaly

fraction (15%), the most abundant are the illite and the inter-stratified illite-smectite;

the other species are practically absent, except for caolinite, which represents 20-

40% in the upper half of the stratum, and it is less than 5% in the remaining part.

Diagenesis: The most important diagenetic processes are quartz overgrown,

compaction and precipitation of clay minerals in the pore space.

Fm. Masparrito

10

Petrophysical Properties:

In general, porosity is low with values that oscillate from 1% to 12%, with an

average value of 6%, and a notorious increase of the average porosity toward the

base of the Formation.

The permeability is 0.02 to 25 md. The highest average values are in the mid to

lower portion although the maximum values (which are punctual) are observed

towards the top.

4 RESERVOIR CHARACTERISTICS

4.1 FLUIDS

In well SIP-2X, two samples of bottom hole fluids were taken with RCI (Reservoir

Characterization Instrument) before running the completion in the well. The

samples of surface fluids taken during the Isochronal test were subjected to PVT

analysis. In all the samples, there was a high content of Methane (94.5%), and

similar percentages of CO2 (3.35%) and Ethane (1%) (Table 2).

Compound Gas from Separator

Wellstream

% Mole % Mole % Weight CO2 Carbon Dioxide 3,35 3,35 8,33

N2 Nitrogen 0,46 0,46 0,73

C1 Methane 94,50 94,42 85,67

C2 Ethane 1,01 1,01 1,72

C3 Propane 0,26 0,26 0,65

iC4 i-Buthane 0,09 0,09 0,30

nC4 n-Buthane 0,08 0,08 0,26

iC5 i-Penthane 0,05 0,05 0,21

nC5 n-Penthan 0,03 0,03 0,12

C6 Hexane 0,04 0,04 0,20

C7 Heptane 0,07 0,07 0,38

C8 Octane 0,05 0,05 0,33

C9 Nonane 0,01 0,01 0,11

C10 Decane 0,00 0,01 0,06

Table 2. Compositional Analysis. Surface sample taken during the Isochronal Test. Well SIP-2X.

11

The low concentration of heavy elements (C7+ <1%), as well as the high GLR

registered in the tests allows us to conclude that it is a non associated gas

reservoir (GLR> 15.000 SCFD/BLPD and% C7 <5%).

The fluids samples taken during the isochronal test of well SIP-2X, were taken in

the test separator operating at 913 psig and 166°F and re-combined to a GLR of

478.14 MSCF/SB.

The dew point was measured at reservoir conditions (3353 psi). When carrying out

pressure depletion at constant temperature and volume, non significant volumes of

liquid are obtained, this corroborates the existence of a dry gas and gives an idea

of the recovery efficiency of the gas in the reservoir during the depletion process.

The compressibility factor, Z, was 0.954 and the viscosity of the gas was 0.0205

cp at the dew point.

The liquid phase, condensates, is 43.4° API gravity at standard conditions (14.7

psia y 60°F).

4.2 PRESSURES While the electrical logs were run in well SIP-2X, samples of pressure and

temperature were taken and are shown in Table 3 and Figure 5. SIP-2X

TVDPunto Depth Depth SS Hidrostatica BU final Temperatura

(PIES) (PIES) (Lpc) (lpc) (° F) TVDFALSO FALSO FALSO FALSO FALSO FALSO

2 8369 7615 5041 4455 254 Masparrito 81743 8404 7650 5066 4458 256

FALSO FALSO FALSO FALSO FALSO FALSO A Gobernador 83235 8448 7694 5094 4460,7 258

FALSO FALSO FALSO FALSO FALSO FALSO Quevedo 8783FALSO FALSO FALSO FALSO FALSO FALSOFALSO FALSO FALSO FALSO FALSO FALSO La Morita 8867FALSO FALSO FALSO FALSO FALSO FALSOFALSO FALSO FALSO FALSO FALSO FALSO Caliza "O" 8917FALSO FALSO FALSO FALSO FALSO FALSOFALSO FALSO FALSO FALSO FALSO FALSO Are Escandalosa 8996FALSO FALSO FALSO FALSO FALSO FALSOFALSO FALSO FALSO FALSO FALSO FALSO Aguardiente 9311

15 9120 8366 5466 4518 277FALSO FALSO FALSO FALSO FALSO FALSO Are Aguardiente 9440

17 9141 8387 5481 4520 28018 9154 8400 5487 4520 280 Basamento 9490

FALSO FALSO FALSO FALSO FALSOFALSO FALSO FALSO FALSO FALSO TD 9585

Topes Geologicos

Table 3 Pressures measured with RCI (Reservoir Characterization Instrument) in well SIP-2X.

12

Presion vs Profundidad

y = 0,0825x + 3764,9R2 = 1

4400

4420

4440

4460

4480

4500

4520

4540

4560

4580

4600

8000 8200 8400 8600 8800 9000 9200 9400pies

psi

Grad Press

Lineal (Grad Press)

Figure 5 Bottom Hole Pressures behavior taken with RCI in well SIP-2X

It is observed that the pressure in the Gobernador Formation is 4455 psi at 8369

feet TVD with a temperature of 254 °F.

In the well SIP-3X similar pressures were measured at lower depths in the

Gobernador Formation, 4456 lpc at 8970 feet, which represent a difference of

approximately 50 psi at the same reference level. This difference in pressures

cannot be attributed to the drainage from well SIP-2X due to the distance and to

the multiple faults that separate them.

5 DRILLED WELLS 5.1 WELL SIP-2X

5.1.1 Drilling Phase The well SIP-2X is an exploratory well drilled in Block SIP-2 of the Sipororo Field

to a total depth of 9681 feet MD.

13

While drilling there were no problems with circulation losses. Initially, there was a

gas blow out as a consequence of perforating near balance between the mud

density, of 10.4 lpg, and the formation pressure. Then, the mud density was

progressively increased to 11.3 ppg to the final depth to control the entrance of

gas, without circulation losses. Table 4 shows the comparison between the

hydrostatic pressure of the mud and the pressure of the reservoir.

Depth (feet)

Density (lpg)

Hydrostatic Pressure (lpc)

Reservoir Pressure (lpc)

∆P (lpc)

8369 11.2 4874 4455 419

8404 11.2 4894 4458 436

8448 11.2 4920 4461 459 Table 4 Hydrostatic Pressure of the Mud vs. Reservoir Pressure. Well SIP-2X

5.1.2 Petrophysical Evaluation

The petrophysical evaluation of the reservoir has been complicated, due to the

lithological variation of the horizons which have intercalations of limestone, sandy

limestone, and calcareous sand, tiny and smaller layer of silty shale, calcareous

shale and silt. These affect mainly the porosity calculations, because the bulk

density varies from one horizon to another and it also presents gradations inside

the same horizon.

The salinity of the produced water is of 1200 ppm, with a resistivity of 4.1 ohm.m at

25 °C. Formation Top Bottom Top Bottom Gross NetPay PHIT PHIE MPHS Sw VClay PERM

MD MD TVD TVD TVD TVD Φ N/D Φ MRIL K

Fm. Masparrito. 8.262,0 8.410,0 8.176,0 8.322,6 147,1 8,9 0,067 0,053 0,056 0,45 0,06 0,579

Fm. Gobernador. 8.410,0 8.541,5 8.322,6 8.453,0 130,9 75,4 0,087 0,070 0,059 0,27 0,03 25,65

Fm. Navay/ Fm.

Burgüita 8.541,5 9.008,0 8.453,0 8.916,2 463,6 24,8 0,111 0,080 0,051 0,48 0,11 25,1

Fm. Escandalosa.

Mbro. Calizas de la ‘O’ 9.008,0 9.088,0 8.916,2 8.995,6 79,9 5,0 0,073 0,068 0,036 0,23 0,03 4,76

Fm. Escandalosa.

Mbro. Areniscas de E. 9.088,0 9.404,0 8.995,6 9.309,5 314,3 91,4 0,107 0,078 0,088 0,41 0,13 15,32

Fm. Aguardiente

Mbro. Calizas de A. 9.404,0 9.534,0 9.309,5 9.438,6 129,6 0,0 0,000 0,000 0,000 1,00 0,00 0,0

Fm. Aguardiente

Mbro. Arenisca de A. 9.534,0 9.584,0 9.438,6 9.488,3 50,2 0,0 0,000 0,000 0,000 1,00 0,00 0,0

Total (Gob+Esc) 672,2 180,6 0,096 0,073 0,073 0,35 0,08 18,6

Total 1315,3 205,5 0,098 0,074 0,070 0,36 0,086 19,4

Table 5. Petrophysical Evaluation Summary. Well SIP-2X

14

5.1.3 Mechanical Completion The well was completed open hole, with a pre-perforated liner (12 HPP; 5/8”), just

as it was originally planned, taking into consideration that this system eliminates

the damage that can be caused to the reservoir if the traditional completion, with

cemented casing, was used.

Figures 6 & 7 show the Electrical Log and the Casing Schedule as well as the

mechanical completion of well SIP-2X.

Río Yuca ParángulaRío Yuca Parángula

Pagüey Sup. / Medio


Pagüey Medio

Pagüey Medio

Pagüey Inferior

Pagüey Inferior

GobernadorEscandalosaAguardiente


Hoyo 26” @ 1735’

Rev. 20” @ 1641’

Hoyo 17 1/2” @ 4370’

Rev. 13 3/8” @ 4363’

Hoyo 12 1/4” @ 8285’

Rev. 9 5/8” @ 8274’

Inducción / Dual LaterologRayos GammaAcústico Dipolar Cáliper 6 Brazos Orientado

Inducción / Rayos Gamma / G Espectral / Acústico DipolarDensidad / NeutrónCáliper 6 Brazos Orientado/Earth Imagen (modo Dip Log)

Inducción / Rayos Gamma XMAC Acústico Dipolar CruzadoDensidad / NeutrónCáliper 6 Brazos Orientado/Dip Log

Liner Perforado 7”

Hoyo 8 ½” @ 9.681’

1. Rayos Gamma / Resist. Alta / Gamma Ray Espectral/ Densidad /Neutrón 2. XMAC Acústico Dipolar X3. Cáliper 6 Brazos Orientado / Imagen Resistiva & Acústica4. Resonancia Magnética 5. Puntos de Presión con RCI / Muestras de Fluido.6. Testigos Rotados RCORD7. Registro Sísmico (VSP)

Río Yuca ParángulaRío Yuca Parángula



Pagüey Medio

Pagüey Medio

Pagüey Inferior

Pagüey Inferior



Hoyo 26” @ 1735’

Rev. 20” @ 1641’

Hoyo 17 1/2” @ 4370’

Rev. 13 3/8” @ 4363’

Hoyo 12 1/4” @ 8285’

Rev. 9 5/8” @ 8274’

Inducción / Dual LaterologRayos GammaAcústico Dipolar Cáliper 6 Brazos Orientado

Inducción / Rayos Gamma / G Espectral / Acústico DipolarDensidad / NeutrónCáliper 6 Brazos Orientado/Earth Imagen (modo Dip Log)

Inducción / Rayos Gamma XMAC Acústico Dipolar CruzadoDensidad / NeutrónCáliper 6 Brazos Orientado/Dip Log

Liner Perforado 7”

Hoyo 8 ½” @ 9.681’

1. Rayos Gamma / Resist. Alta / Gamma Ray Espectral/ Densidad /Neutrón 2. XMAC Acústico Dipolar X3. Cáliper 6 Brazos Orientado / Imagen Resistiva & Acústica4. Resonancia Magnética 5. Puntos de Presión con RCI / Muestras de Fluido.6. Testigos Rotados RCORD7. Registro Sísmico (VSP)

Figure 6. Electrical Logs and Casing Schedule. Well SIP-2X.

15

Revestidor 9-5/8” @ 8274’

TD: 9681 MD

Packer 9-5/8”X 6” + 7-5/8”Mill Out Extension + Cross Over Hunting Boss Box + 6” Seal Bore Extension + Cross Over New Van Box

7”.

Liner perforado 12 HPP DESDE’ 8286’-9638 MD

Long. Total: 8100’-9679 MD

Packer hidráulico de Producción 9-5/8” x 3-1/2” @ 7982’

SSV (TRM-4 with 2.813’ nipleprofile @ 331.5’

Sliding Sleeve CS-3U @ 7932’

Flow Control Valve TLFC-HB @ 8015’

3-1/2” SGM for PQG-GC Dual Gauge (Tubing reading gaugeswith T connector) @ 8050 MD

Revestidor 9-5/8” @ 8274’

TD: 9681 MD

Packer 9-5/8”X 6” + 7-5/8”Mill Out Extension + Cross Over Hunting Boss Box + 6” Seal Bore Extension + Cross Over New Van Box

7”.

Liner perforado 12 HPP DESDE’ 8286’-9638 MD

Long. Total: 8100’-9679 MD

Packer hidráulico de Producción 9-5/8” x 3-1/2” @ 7982’

SSV (TRM-4 with 2.813’ nipleprofile @ 331.5’

Sliding Sleeve CS-3U @ 7932’

Flow Control Valve TLFC-HB @ 8015’

3-1/2” SGM for PQG-GC Dual Gauge (Tubing reading gaugeswith T connector) @ 8050 MD

Figure 7. Mechanical Completion. Well SIP-2X

5.1.4 Production Evaluation An isochronal test was carried out with the purpose of measuring the capacity of

production of the well, which covered the following steps:

• A cleanup period was completed during 32,7 hrs. The closure time after the

initial cleaning period was of 50.1 hrs.

• The well was closed at the bottom, and a pressure build up was observed

during 50,3 hrs. Final pressure: 4425 lpca. Temperature: 256 °F (124 °C) @

8050.

• A modified isochronal test was carried out with chokes of ¼”; ½”; ¾” and a

stabilized flow with a choke of 7/8", Maximum rate: 34,9 MMSCFD, well

head pressure of 2360 lpc (Table 6).

• During the last flow PVT samples were taken.

• At the end of the isochronal test the well was closed to observe the

pressure build up, which had lasted 320 hrs.

16

• A Production Log (PLT) was run, after cleaning with Coiled Tubing due to

an obstruction in the completion at 8769 feet, above the Member Arenas P-

R of the Escandalosa Formation. It indicated that, during the isochronal

test, the Gobernador Formation was producing by itself.

Table 6 Isochronal Test Summary. Well SIP-2X.

For the results interpretation of the test, the software Saphir by Kappa Engineering

was used to model the reservoir as two layers, with storage and damage, and with

parallel faults limiting the reservoir (Fig. 8).

A very important factor to keep in mind is casing in the well, it makes the test

difficult to interpret. In this case, the model that represents the pressure and flows

measured during the test represent only the production from Gobernador.

The obtained parameters show a layer of very good primary permeability,

apparently damaged, while the area of low permeability would not show damage

and its vertical contribution to the area of better permeability would be very small.

CAMPO : BARRANCASPOZO:SIPORORO-2X FORMACION: Gobernador / Navay / Escandalosa / AguardienteINTERVALOS: 8274'-9681'

Reductor1/4" 1/2" 3/4" 7/8"

Tiempo por Reductor (hrs) 4,00 4,00 4,00 12,00Fecha Inicio : 23 Nov 19:37 23 Nov 03:25 23 Nov 11:11 23 Nov 19:33

Fecha Final : 23 Nov 22:47 23 Nov 06:55 23 Nov 14:51 24 Nov 6:50Tiempo Acumulado Prueba Horas 3,17 3,50 3,50 11,25

Caudal de Líquido bpd 0,00 0,00 5,00 96,00Gravedad del Petróleo º API N/A N/A 43,50Caudal de Gas MMscf/d 6,00 19,89 29,80 34,90Volumen de Gas Quemado MMscf 0,80 2,91 4,52 16,79Relación Gas / Petróleo (RGP) scf/bbl N/A N/A N/A N/AAgua y Sedimentos (BS&W) % 0,00 0,00 50,00 45,00Presión de Cabezal Psig 3632,00 3272,00 2612,00 2360,00Temperatura de Cabezal º F 120,00 148,30 178,80 208,00Presión de fondo @ 8050' Psia 4368,98 4176,97 3969,61 3844,29Temperatura de fondo @ 8050' º F 266,52 267,84 267,21 266,91CO2 % 1,00 2,00 2,00 2,00H2S ppm 1,00 2,00 2,00 2,00Volumenes Acumulados en Tanques bbl 0,00 0,00 20,03 73,43Volumen de líquidos bbl/d 0,00 0,00 92,56 142,40Volumen de condensado bbl/d 0,00 0,00 46,28 78,32Volumen de agua bbl/d 0,00 0,00 46,28 64,08

Separador de AltaPresión psig 702,60 679,70 879,60 920,00Temperatura º F 38,10 72,00 128,44 166,61Presion Diferencial Pulgadas de agua 40,25 77,00 58,10 83,67Placa Orificio Pulgadas 2,25 3,50 4,25 4,25 H2S ppm 1,00 2,00 2,00 2,00CO2 % 1,00 2,00 2,00 2,00Total de Gas contabilizado: 0,80 3,71 8,23 25,24

17

The volume involved in the test, is the poral volume included inside the

investigation radius, which would be equivalent to 7,68 * 107 bbl, and is equal to

91,86 BSCF under surface conditions.

Log-Log plot: dm(p) y dm(p)’ [psi2/cp] vs dt[hr]

History plot (Pressure [psia], Gas Rate [Mscf/D] vs Time [hr])

Semi-Log plot: m(p) [psi2/cp] vs Superposition timeLog-Log plot: dm(p) y dm(p)’ [psi2/cp] vs dt[hr]

History plot (Pressure [psia], Gas Rate [Mscf/D] vs Time [hr])

Semi-Log plot: m(p) [psi2/cp] vs Superposition time

Figure 8 Isochronal test Interpretation. Well SIP-2X.

Calculated Production for the well With the data from the Isochronal test, the calculation of the curve of contribution

of production of the reservoir, IPR (Inflow performance), and the maximum rate of

production of the well for a THP = 0 lpc, AOF (Absolute Open Flow) was carried

out.

18

Back Pressure Equation

Q = C x (Ps^2 - Pf̂ 2)^n

C: 0.242982 [Mscfd/D]/[psi]**2N

n: 0.763844 Dimensionless

AOF: 93.087 MMPCND

Figure 9. IPR Analysis and AOF calculation. Well SIP-2X.

Based on the results of the Modified Isochronal Test an AOF (Absolute Open

Flow) of 93.1 MMSCFD was determined through the equation of Back Pressure

(Figure 9). With ¾" choke, the well has the capacity to produce about 30

MMPCND with a well head pressure of 2685 lpc.

PRODUCTION LOG, PLT:

A production Log (PLT) was performed with the purpose of knowing the individual

contribution from each sand body to the production of the whole well. It was

carried out in several attempts because the well was obstructed at 8769 feet and it

was necessary to clean the well with Coiled Tubing up to 9621 feet.

It was found that the main contribution to the production of the well comes from the

Gobernador Formation, followed by the Member Arenas P-R of the Escandalosa

Formation.

Table 7 shows the results of the PLT.

19

It is important to mention that according to the level of obstruction in the well,

during the isochronal test, the only formation contributing to the production of the

well was the Gobernador Formation.

ZONE INTERVAL

(Feet)

FORMATION GAS RATE

(MMSCFD)

%

PRODUCTION

1 8288 - 8297 Masparrito 0.584 1.89

2 8450 - 8472 Gobernador 20.120 64.98

3 9160 - 9167 Escandalosa 0.682 2.20

4 9236 - 9250 Escandalosa 9.576 30.93

TOTAL 30.96 100.00 Table 7 Production Log Summary. Well SIP-2X.

5.2 WELL SIP-3X 5.2.1 Drilling Phase

The well SIP-3X was drilled as an exploratory well in the Block 3 of the Sipororo

Field to a final depth of 10608 feet MD.

The mechanical completion initially proposed consisted of drilling the objective

reservoir with a hole diameter of 8-1/2" and to cover it with a 7" casing, which

could be pre-perforated for an open hole completion or blank pipe cemented,

depending on the results of the petrophysical evaluation and the open hole DST

(Drill Stem Test).

While drilling the 8 1/2" hole, there were severe circulation losses in the reservoir

section. Approximately 1.300 bls of mud and loss control material with carbonates

of variable grain size were pumped.

Drilling was stopped @ 9211 feet, the programmed electric logs were run, and the

7-inch casing was set and cemented @ 9210'. This way the well was prepared for

a hydraulic fracturing job to communicate the well with the area of the formation

not damaged by the mud invasion.

20

Drilling continued to the lower formations with a hole diameter of 6" until the final

depth 10608 feet MD. The electric logs were run and this section was completed

with a pre-perforated liner of 5 inches.

The drilling mud was similar to the one used in the well SIP-2X and the

overbalance level (Hydrostatic Pressure minus Reservoir Pressure), was in an

average of 450 psi (Table 8).

Depth (feet)

Density (ppg)

Hydrostatic Pressure (psi)

Reservoir Pressure

(psi)

∆P (psi)

8858 10.6 4883 4450 433

8873 10.6 4891 4450 441

8912 10.6 4912 4453 459

8970 10.6 4944 4456 488

8983 10.6 4951 4458 493 Table 8 Mud Hydrostatic Pressure vs. Reservoir Pressure. Well SIP-3X

5.2.2 Petrophysical Evaluation

Table 9 summarizes the petrophysical evaluation of the well SIP-3X.

SIP-3X

Formation MD TVDSS

GrossTVDThickness A.N. ANG ANG/G PHIE Av Sg CMR

Member feet feet feet feet feet % % % K md Masparrito 8642 -7783 168 168 0 0,0% 2,5% 0% Gobernador 8810 -7951 427 292 120 28,0% 6,5% 77% 5 Burguita? 9238 -8378 329 15 1 2,0% 5,5% 58% 10 Navay Quevedo 9567 -8707 83 0 0 0,0% 0,0% - - La Morita 9649 -8790 56 0 0 0,0% 0,0% - - Escandalosa Caliza O 9706 -8846 74 64 0 0,0% 2,5% - - Arenas P-R 9780 -8920 268 93 11,4 4,2% 4,0% 80% 15 Aguardiente Caliza de 10049 -9188 133 108 0 0,0% 2,5% 80% - Arenisca de 10181 -9321 80 50 0 0,0% 4,0% - -

Table 9. Petrophysical Evaluation Summary. Well SIP-3X

21

In Table 10 the results of the Formation Pressures and Temperature determined

with the MDT are shown. SIP-3X

TVD 9Punto Depth Depth SS Hidrostatica BU final Temperatura

(PIES) (PIES) (Lpc) (lpc) (° F) MD TVDFALSO FALSO FALSO FALSO FALSO FALSOFALSO FALSO FALSO FALSO FALSO FALSO Masparrito 8642 8594FALSO FALSO FALSO FALSO FALSO FALSOFALSO FALSO FALSO FALSO FALSO FALSO Gobernador 8810 8762FALSO FALSO FALSO FALSO FALSO FALSO

6 8858 8047 4764 4449,70 267 Burguita 9238 91897 8873 8062 4774 4449,70 268

FALSO FALSO FALSO FALSO FALSO FALSO Navay 9567 9518FALSO FALSO FALSO FALSO FALSO FALSOFALSO FALSO FALSO FALSO FALSO FALSO Escandalosa 9706 9657FALSO FALSO FALSO FALSO FALSO FALSO

12 8912 8101 4787 4452,80 270,5 Aguardiente 10049 999913 8970 8159 4818 4456 270,7

FALSO FALSO FALSO FALSO FALSO FALSO Cuarcita-Alterada 10261 1021215 8983 8172 4824 4458 271

FALSO FALSO FALSO FALSO FALSO FALSO Basamento 10590 10541FALSO FALSO FALSO FALSO FALSO FALSO

TD 10608 10559

Topes Geologicos

Table 10. Pressures and Temperatures measured with MDT, Well SIP-3X

5.2.3 Mechanical Completion

The well SIP-3X was completed in the Gobernador Formation with a 7-inch casing

of, seated at 9210 feet, which was cemented in a 8-1/2" hole, to condition it to

carry out a hydraulic fracturing.

The quality of the cement in this section shows a bad adherence to the casing

(Fig. 10). It is considered that there is cement but due to the circulation losses,

and/or insufficient cleaning, it is a cement with bad quality, and in consequence it

would be difficult to repair it. In addition, to perform a cement squeeze in this area

would weaken the pipe and it could even hinder the fracture operation. It was

considered that the current condition of the cement should not prevent the fracture

job.

In the Escandalosa, Aguardiente Formations and Basement the hole of 6" was

completed with a pre-perforated liner of 5", without cement to avoid the formation

damage and/or to plug the natural fractures with cement.

Figure 11 shows the final casing schedule.

22

The design of the production equipment was carried out to allows selectivity

between the Gobernador Formation and the lower Formations, with a permanent

pressure/temperature gauge in the bottom to monitor reservoir behavior. Figure 12 shows the mechanical completion.

Figure 10 Well SIP-3X. Cement Log in Gobernador Formation.

23

Río Yuca

ParángulaRío Yuca

Parángula

GobernadorGobernador

Hoyo 17 1/2”Rev. 13 3/8” @ 2110

Hoyo 12 1/4”Rev. 9 5/8” @ 8632’

Rayos Gamma / Dual LaterologAcústico Dipolar / Cáliper Orientado


Inducción / Rayos Gamma / Densidad / NeutrónAcústico Dipolar CruzadoCáliper Orientado


Hoyo 8 1/2”Liner 7´´ @ 9210

1. Rayos Gamma / Resistividad / Gamma Ray Espectral/ Acústico Dipolar / Cáliper 6 Brazos 2. Densidad /Neutrón Resonancia Magnética 3. Imagen Resistiva & Acústica5. Puntos de Presión 6. Registro Sísmico (VSP)


Navay EscandalosaAguardiente


Liner Perforado 5”Hoyo 6’’ @ 10608’

PagueyPaguey

Río Yuca ParángulaRío Yuca

Parángula

GobernadorGobernador

Hoyo 17 1/2”Rev. 13 3/8” @ 2110

Hoyo 12 1/4”Rev. 9 5/8” @ 8632’





Hoyo 8 1/2”Liner 7´´ @ 9210





Liner Perforado 5”Hoyo 6’’ @ 10608’

PagueyPaguey

Figure 11. Well SIP-3X. Casing Schedule and electrical logs

8.820’ – 8.835’ = 15’ Cañoneados

Zapata de 13 3/8Zapata de 13 3/8”” @ 2.135 @ 2.135 ftft..

Zapata de 9Zapata de 9--5/85/8”” @ 8.632 @ 8.632 ftft..

Zapata de 7Zapata de 7”” @ 9.210 @ 9.210 ftft..

8.865’ – 8.880’ = 15’ Cañoneados

8.920’ – 8.950’ = 30’ Cañoneados8.950’ – 8.956’ = 14’ Cañoneados9.015’ – 9.045’ = 30’ Cañoneados

Zapata de 5Zapata de 5”” @ 10.606 @ 10.606 ftft..

8.890’ – 8.910’ = 20’ Cañoneados

Realizó MiniFrac y Fracturo (180 SXS en FM).

Base Gobernador 9.050’

Base Gobernador 9.050’

Masparrito 8.642’

Masparrito 8.642’

Gobernador 8.809’

Gobernador 8.809’

Burguita 9.300’

Burguita 9.300’

Escandalosa 9.710’

Escandalosa 9.710’

Aguardiente 10.050’

Aguardiente 10.050’

Basamento 10.600’

Basamento 10.600’

Figure 12. Well SIP-3X. Mechanical Completion

24

5.2.4 Hydraulic Fracturing

It was carried out with the purpose of obtaining production of gas from the

Gobernador Formation which was considered damaged by effect of the high mud

losses during the perforation.

For the execution of the hydraulic fracture, the interval 8950'-8960' was perforated.

It was selected because is the one with better conditions of the cement natural or

induced fissures are not present, in the log images, in the lower part of this body of

sand there is a shale with high fracture gradient and in its upper partthere is a

body of dirty sand with a smaller fracture gradient. That is why it would be

expected that the fracture would grow first in the area of interest and then extend

to the upper layer.

Although natural or induced fissures are not seen in the interval of interest in the

Image Logs, but they are seen in the upper and lower intervals that also have

bigger content of clays, it is supposed that all the layers were subjected to the

same tectonic movements, so it is expected that the sands of the Gobernador

Formation are also fissured, probably with a bigger frequency. For this reason it

was decided to limit the perforated interval to only 10 feet.

In the interval 8915'-8917', located immediately above the level of interest, a fault

was observed. The effect that it will have on the hydraulic fracture is unknown as it

can act like a barrier, or on the contrary like a thief zone.

Previous to the fracturing work, and with the purpose of determining real

parameters for the best design, a Step Up Rate Test (SURT) was carried out to

determine the propagation pressure of fracture, followed by a Step Down Rate

Test (SDRT) to quantify the losses of load in the system, estimating tortuosities in

the NWB and frictions in the perforated holes. Finally, a Minifrac was carried out to

determine the following critical parameters for the final design of the fracture:

• Coefficient of loss of fluid, Ct

• Pressure of closing of the formation, Pc

25

• Young Module, E,

• Relationship of Poisson, ν

• Fracture height, H

• Efficiency of the fracture fluid, η

From the SURT it was not possible to obtain the value of the propagation pressure

of the fracture, since the same one disguises as a a flow inside a system of

fissures. The behavior observed during the SDRT suggests that the presence of

tortuosity, according to the geologic data, can be associated it to the presence of

multiple fractures.

To reduce the effect of the fissures on the loss of fluid, Silica Mesh 100 was used

together with the crosslinked gel at concentration of 40 ppt.

The Minifrac was carried out in two attempts due to premature screen out in the

NWB, which was associated to the presence of multiple fractures. In the second

attempt, the pressure was stabilized to a top value as in the previous Minifrac

(7200 psi vs. 6200 psi) possibly as a consequence of plugging of the perforated

intervals. When the proppant slug enters in the holes, a strong increment of

pressure is observed, but at this time the slug can be over displaced (Figure 13).

The rounded behavior of the pressure once stopped the pumping shows the lack

of a good communication between the well and the induced fracture(s).

26

0 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.000

2500.0

5000.0

7500.0

10000.0

12500.0

0

5.00

10.00

15.00

20.00Treating Pressure(psi)

BHP (Default)

Slurry Rate(bbl/min)

Proppant Conc(PPA)

Prop Conc (BH)(PPA)

Treatment Time(min)

PSI BP

M

+

+

Comienza bombeo de

crosslinkeado

Cortan crosslinkeado

Crosslinkeado en fondo

Figure 13 Well SIP-3X. Observed behavior during the Minifrac Test

A temperature log was run before the SURT and after the Minifrac to determine

the fracture height (Figure 14), and it showed that the fracture would have been in

the interval 8864' - 8918' inside the Gobernador Formation. It was contained in its

base by a shale body determined in the geomechanical logs with the biggest

stresses and in its end it would be contained by the fault observed in the

interpretation of the images logs.

From these previous tests it was concluded that the concept of a hydraulic fracture

in a homogeneous reservoir with a wing of each side of the well is not applicable.

Due to the presence of a system of fissures in the rock in which fluid gets in and

proppant is lost, it was decided to pump in long steps at low concentration as a

way of filling the system of fissures in the vicinity of the well and to keep it

conductive.

In Figure 15 the behavior during the fracturing job is observed, showing an abrupt

increment of the pressure until obtaining a screen out with 180 sacks of Carbolite

20/40 in the formation.

The interpretation of the image logs reported that the direction of the PFP is similar

to the direction of one of the group of fissures. Then it can be inferred that the fluid

27

did not generate a new fracture but it took the one on the way to existing fissures.

This coincides with the lack of rupture evidence in the SURT. As the fissures they

have an inclination from 60 to 80° it is very likely that the "induced" fractures are

also sub-vertical.

Perfil previo

Perfil post

Minifra

Figure 14 Well SIP-3X. Temperature Log, before and after the Minifrac

0 10 20 30 40 50 600

2500

5000

7500

10000

12500

0

5.0

10.0

15.0

20.0

Treating Pressure(psi)

BHP (Default)

Slurry Rate(bbl/min)

Proppant Conc(PPA)

Prop Conc (BH)(PPA)

Treatment Time(min)

PSI BPM

+

+

Crosslinkeado en cañoneaos

Figure 15 Well SIP-3X. Fracturing Process

28

5.2.5 Production Evaluation After the fracturing job the following intervals of the Gobernador Formation were

perforated:

Top (feet) Bottom (feet) Thickness (feet) 8820 8835 15

8865 8880 15

8890 8910 20

8920 8950 30

9015 9045 30

A DST string was run into the hole to begin the evaluation of the production of the

Gobernador Formation. It was carried out with the Rig on site, after a period of

cleaning up of 2 days and before running the completion pipe to allow running a

production Log (PLT) and to be able to evaluate the individual contribution of each

one of the perforated intervals. A "Flow after Flow" test was made with different

chokes in order to able to determine the production potential (AOF) of the

Gobernador Formation.

In Table 11 the obtained results of the production tests are shown with different

choke sizes and in Figure 16 the results of the nodal analysis of this test are

shown, and an AOF of 67.2 MMPCND of gas was determined.

SIP-3X – Flow After Flow Test, Fm. Gobernador

Choke (inches) Qgas (MMSCFD) WHP (psi) Pwf (psi)

¼ 5.11 3709 4356

½ 15.9 3087 4114

¾ 23.9 2168 3881 Table 11. Flow after Flow test, Gobernador Formation, well SIP-3X.

29

Figure 16. Nodal Analysis from Flow after Flow test, Gobernador Formation, SIP-3X

After finishing the Flow after Flow test, a production log was run under statics

conditions to identify the existence of cross flow, as well as dynamic conditions to

measure the contribution of each one of the completed intervals, before

completion of the well, in which all the intervals of the Gorbenador Formation

would flow together from behind of the sleeve.

With the closed well it was determined that crossed flow did not exist. With the well

in production with a choke of 7/8" and a total production rate of 24.8 MMSCFD of

gas it was found that the main production (68.2%) comes from the interval 8920' -

8960', which corresponds to the body of sand subjected to hydraulic fracturing.

Figure 17 and Table 12 show the results interpretation of the PLT.

30

Figure 17. Production Log results, Gobernador Formation, well SIP-3X

Interval (feet)

Water (BWPD)

Condensated (BCPD)

Gas (MSCFD)

(%) Production

8820 - 8835 0 0 816 3.29 8865 - 8880 0 0 459 1.85 8890 – 8910 0 0 3111 12.55 8920 – 8960 0 0 16906 68.21 9015 - 9045 152 38 3493 14.09

TOTAL 152 38 24785 100.00

Table 12. Production Log results, Gobernador Formation, well SIP-3X

31

Once the well was completed, a modified isochronal test was carried out with

periods of flow and closing of 4 hrs (Table 13) with a final closing period of 142 hrs

for pressure build up. From this test an AOF of 89.8 MMPCND was determined

(Figure 18), and it was largerthan the one calculated during the Flow after Flow

test due to better cleaning in the well.

Choke (inches) Gas rate (MMSCFD) WHP (psi) Pwf (psi) ¼ 5.37 3717 4327 3/8 11.34 3563 4233 1/2 24.92 3351 4106 3/4 29.14 2644 3770 7/8 33.51 2270 3629

Table 13 Well SIP-3X. Modified Isochronal test summary.

Figure 18 Nodal Analysis of the Isochronal Test, well SIP-3X

The interpretation of the test offers enough difficulties due to the fact that it is a

reservoir of naturally fractured sandstones with 5 open layers contributing to the

total production and one of them has been hydraulically fractured. For these

reasons the best way to model it was through a multilayer, double porosity

reservoir, and modeling the fractured interval with a well model of finite

32

conductivity. A good fit was achieved in terms of times of reservoir and limits, but

not in early stages (Wellbore Storage), which could be an effect of the fluids in the

well or some bubbles of gas trapped in the tool (Fig. 19).

A P* of 4386 lpc was calculated, which is 10 psi below the initial pressure of the

reservoir of 4396 psi @ 8240 feet (depth of the pressure gauge).

Table 14 shows the parameters calculated for each

layer.

Log-Log plot: dm(p) and dm(p)' [psi2/cp] vs dt [hr] Semi-Log plot: m(p) [psi2/cp] vs Superposition time

H i s t o r y p lo t ( P r e s s u r e [ p s i a ] , G a s R a t e [ M s c f / D ] v s T i m e [ h r ] )

Log-Log plot: dm(p) and dm(p)' [psi2/cp] vs dt [hr] Semi-Log plot: m(p) [psi2/cp] vs Superposition time

H i s t o r y p lo t ( P r e s s u r e [ p s i a ] , G a s R a t e [ M s c f / D ] v s T i m e [ h r ] )H i s t o r y p lo t ( P r e s s u r e [ p s i a ] , G a s R a t e [ M s c f / D ] v s T i m e [ h r ] ) Figure 19 Well SIP-3X. Interpretation of the Isochronal Test.

INTERVALO MODELO H K SKIN Xf Fc

CAPA Pies Pozo Yacimiento Límites Pies mD Pies mD-pie1 8820-8835 Daño+Almacenamiento Doble porosidad Rectángulo 15 3,85 4,99 - -2 8865-8880 Daño+Almacenamiento Doble porosidad Rectángulo 15 1,28 4,99 - -3 8890-8910 Daño+Almacenamiento Doble porosidad Rectángulo 20 0,62 17 - -4 8920-8960 Conductividad finita Doble porosidad Rectángulo 40 65,2 16,8 108 30205 9015-9045 Daño+Almacenamiento Doble porosidad Rectángulo 30 17,9 12 - -

Table 14 Well SIP-3X. Isochronal Test Interpretation.

6. RESULTS ANALYSIS The analyses are directed at the results obtained for the Gobernador

Formation, which is the most important one due to its reservoir characteristics

and because it has the biggest productivity, for that reason comparisons of the

wells SIP-2X and SIP-3X are directed at this formation.

33

• While drilling wells SIP-2X and SIP-3X mud densities which created similar

overbalance to the reservoir pressure were used, an average of 450 psi.

The same type of mud was used for both wells, for that reason this is not a

decisive factor of the behavior observed during drilling.

• The biggest presence of fractures observed in the image logs of the well

SIP-3X (66 fractures) versus those of the well SIP-2X (2 fractures), were

the cause of the loss of fluid in the well SIP-3X.

• The wells SIP-2X and SIP-3X are located in an area associated to the same

regional strengths regime, although in a local way the well SIP-3X is located

in the highest part of the structure and is subjected to bigger strengths, and

this could originate the biggest presence of natural fractures in this well.

• The Gobernador Formation is developed with a bigger thickness in the well

SIP-3X (120 feet of ANG) with regard to the well SIP-2X (75 feet of ANG),

however, the bodies of sand show very similar lithological characteristics.

• Referring to the petrophysical properties, the well SIP-2X shows better

matrix characteristics with a lightly increased porosity (7% vs. 6.5%) and

better permeability (25 MD vs. 5 MD) than the well SIP-3X.

• The better matrix characteristics and lower presence of fractures in the well

SIP-2X explain better production from the matrix of the Gobernador

Formation. This was confirmed through the interpretation of pressure build

up tests carried out at the end of the isochronal test, where the matched

models were the two layers reservoir with storage and damage in the well.

Sensibilities with a double porosity model of the reservoir did not achieve a

good representation of the test.

• The higher presence of natural fractures in the well SIP-3X, caused the loss

of the perforation fluid toward the formation forcing to the change in the

initially proposed mechanical completion. The execution of the hydraulic

fracturing allowed connecting the well with the non damaged area of the

reservoir.

• Due to the higher presence of natural fractures and/or fissures in the well

SIP-3X, it is difficult to calculate the fracture longitude generated during the

fracturing job, if a new fracture was really generated or, on the contrary, the

existing fissures were reopened. However, for the interpretation of the

34

Pressure Build Up tests, a longitude of fracture of 108 feet was calculated

with a limited conductivity of 3020 MD-feet.

• From the pressure build up tests of the well SIP-3X, a bigger contribution of

the fractures is evidenced than form the matrix, and the model that fit the

tests results was of a multilayer-double porosity reservoir.

• The production behavior observed in the wells SIP-2X and SIP-3X is quite

similar, with higher productivities than those originally calculated. However,

it is necessary to highlight that the contribution system to the production of

both wells is different; the first one has contribution from the matrix while

the second contributes through natural and induced fractures. This fact is

the decision point in the final completion of the wells. In the absence of

fractures and with the appropriate overbalance of the hydrostatic pressure

of the mud while drilling, no circulation losses should take place and the

Open hole completion would be the most appropriate to minimize the

formation damage. On the contrary, when the high density of fractures

generates losses of mud toward the formation, the most appropriate

mechanical completion would be with cemented casing to allow a fracturing

work to connect the well with the non damaged area of the formation.

• An alternative to minimize the damage caused during drilling in naturally

fractured reservoirs is underbalance drilling, since a controlled condition of

minimum production rate of the well allows lower hydrostatic pressures of

the drilling fluids, avoiding circulation losses and blow outs.

7. CONCLUSIONS

• The recommended completion scheme for gas wells in naturally

fractured reservoirs is Open Hole, whenever problems of losses

toward the formation of drilling fluids are not present, since the use of

cement is may cause damage to the formation.

• The presence of natural fractures increases the possibility of losses

of the perforation fluid toward the formation.

• The best characteristics of the matrix, in absence of fractures, favors

the open hole completion to minimize formation damage.

35

• If problems of losses of drilling fluids toward the formation occur, the

best option is to complete the well with cemented casing, and to

carry out a hydraulic fracturing job tho connect the well with the non

damaged area of the reservoir.

• Underbalance drilling is a technique that helps minimize the

formation damage that is caused during drilling.

8. REFERENCES

• D’Huteau, Emmanuel: “EVALUACIÓN POST FRACTURA, POZO SIPORORO 3X”, Repsol YPF, 15-12-2005.

• Halleck, Phillip “Studies Reveal Fractured Reservoir Perforating Damage” Petroleum Engineer International, Pennsylvania State

University, April 1996.

• Agilera, Roberto: “Yacimientos Naturalmente Fracturados”, ESP

OIL Workshop Internacional, Mayo 2004.

• Barboza, M.E., González, L: “Informe Final de Completación y Prueba Extendida, pozo SIP-2X”, Repsol YPF, Región Caribe

• Horne, Roland: “Modern Well Test Analysis”, Second Edition.

Petroway, INC. May 1995

• Ceccarelli, Roberto: “Informe Ensayo de Presión del Pozo SIP-3X-Sipororo, Área Barrancas-Venezuela.” Repsol YPF, Febrero 2006.

COMPLETION METHODS COMPARATIVE OF GAS … METHODS COMPARATIVE OF GAS PRODUCER WELLS IN NATURALLY...

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