Evaluation of Reservoir Performance Using Decline Type Curves Improve Reservoir Description - Area Central Norte (ACN)

Region, El Tordillo Field Argentina

Final Project for

Carlos Alejandro BertoMaster of Engineering

Chair of Advisory Committee:

Dr. Thomas. A. Blasingame

Department of Petroleum Engineering

Texas A&M University – College Station, Texas

Outline

• El Tordillo Field Description.

• Area Central Norte Waterflood Project Description.

• Data Acquisition and Preparation.

• Production and Injection Data Analysis.

• Integration of Results.

• Conclusions and Recommendations

Objectives

• To present a description of El Tordillo Field and the Area Central Norte waterflood project.

• To show the preparation of the production and injection data.

• To analyze and interpret the reallocated production data.

• To demonstrate the various analyses.

• To integrate the results (as maps and crossplots).

• To make recommendations for future waterflood projects in El Tordillo Field.

El Tordillo Field

El Tordillo Field is located in The San Jorge Basin, Patagonia (Argentina)

C O M O D O R O R I V A D A V I A

A R G E N T I N A

7 1 ° 7 0 ° 6 9 ° 6 8 ° 6 7 ° 6 6 °

7 1 ° 6 9 °7 0 ° 6 8 ° 6 7 ° 6 6 °

ATLA

NTIC

OCE

AN

D E S E A D O M A S S I F

S O M O C U R A M A S S I F4 4 °

4 5 °

4 6 °

4 7 °

4 4 °

4 5 °

4 6 °

4 7 °

0 3 0

M I L E SCH

ILE

N O R T H -W E S T E R N

A R E A

N O R T H C E N T R A L

A R E A

C E N T R A L B A S I N

W E S T E R N A R E A

S O U T H F L A N K

S O U T H -W E S T E R N

A R E A

ANDE

AN

BELT

O F F S H O R E

C O M O D O R O R I V A D A V I A Area: 29000 Acres

El Tordillo Field is recognized as one of the major oil fields in Argentina.

El Tordillo Field – Reservoir Data

• Total numbers of wells 850• Production oil wells 420• Injection water wells 69• Average final depth 9,840 ft• Area 29,000 acres• Cumulative oil (Aug. 1999) 189 MMSTB• OOIP 1,800 MMSTB

Reservoir Description

• El Tordillo Field reservoir consists of a complex of fluvial-dominated sandstone sequences comprised of multiple layers with distinctive shale zones.

• Sandstones bodies are concentrated in groups, locally called “complejos”.

• Normal faults are the most common and most important structures in the reservoir.

• Trébol, Comodoro Rivadavia, Mina El Carmen are principal producing formations in the stratigraphic column in the reservoir.

El Tordillo Field – Waterflood Performance

There are several producing regions within El Tordillo Field with:

• Excellent continuity of oil-bearing sands,

• Sequence development, and

• A high cumulative oil recovery.

These three characteristics are sufficient to define El Tordillo Field as “feasible” for waterflooding.

• Area Central Norte project (ACN) has an excellent secondary response.

EL TORDILLOPRODUCCION POR SECUNDARIA

0

200

400

600

800

1000

1200

1400

Ju

l-9

1

Oct-

91

En

e-9

2

Ab

r-9

2

Ju

l-9

2

Oct-

92

En

e-9

3

Ab

r-9

3

Ju

l-9

3

Oct-

93

En

e-9

4

Ab

r-9

4

Ju

l-9

4

Oct-

94

En

e-9

5

Ab

r-9

5

Ju

l-9

5

Oct-

95

En

e-9

6

Ab

r-9

6

Ju

l-9

6

Oct-

96

En

e-9

7

Ab

r-9

7

Ju

l-9

7

Oct-

97

En

e-9

8

Ab

r-9

8

Ju

l-9

8

Oct-

98

En

e-9

9

Ab

r-9

9

Ju

l-9

9

MESES

CA

UD

AL

[m

3/d

]

T.SUR TN ACN LPE BLOQUE D ACNE LPS ACNSOM TSPROF.

Waterflood Oil Rate in ACN (Aug ’99) = 2200 STB/D

El Tordillo Field – Waterflood Performance

Area Central Norte (Region Map)

Area Central Norte

• Stratigraphic Cross Section A-A’ for ACN Project Area

MINA EL CARMEN FORMATION

S-667 S-678 S-537 S-691 S-694 S-637 S-624 S-572 S-634 S-632 S-631 S-682 S-782

EL TREBOL FORMATION

PATAGONIA FORMATION

SARMIENTO-RIO CHICO FORMATION

COMODORO RIVADAVIA FORMATION

SALAMANCA FORMATION

8141 ft

Ew

0 ft

1000 ft

2000 ft

3000 ft

4000 ft

5000 ft

6000 ft

7000 ft

8000 ft

10000 ft

9000 ft

0 ft 1300 ft 2600 ft 3900 ft 5200ft 6500 ft 7800 ft 9100 ft 10500 ft

8443 ft8095 ft

8787 ft

7993 ft

8532 ft

8207 ft

8580 ft

8450 ft8532 ft 8472 ft 8561 ft 8521 ft

Dry Horizon (No production)

Gas, Oil, and Water production

Injection horizon

Gas production

Oil and Water production

Oil production

Converted water injection well

Project Area Cross-Sections

Area Central Norte (Region Map)

Area Central Norte

Project Area Cross-Sections

• Stratigraphic Cross Section B-B’ for ACN Project Area

MINA EL CARMEN FORMATION

S-554

EL TREBOL FORMATION

PATAGONIA FORMATION

SARMIENTO-RIO CHICO FORMATION

COMODORO RIVADAVIA FORMATION

SALAMANCA FORMATION

9000 ft9073 ft 8991 ft

8476 ft8498 ft 8630 ft

8334 ft

8056 ft

S-720S-719 S-693 S-637 S-638 S-516 S-642

N S

0 ft

1000 ft

2000 ft

3000 ft

4000 ft

5000 ft

6000 ft

7000 ft

8000 ft

10000 ft

9000 ft

0 ft 650 ft 1300 ft 1950 ft 2600 ft 3250 ft 3900 ft 4550 ft 5200 ft 5600 ft

Dry Horizon (No production)

Gas, Oil, and Water production

Injection horizon

Gas production

Oil and Water production

Oil production

Converted water injection well

Top of Reservoir Contour Plot (ft) – ACN Study RegionEl Tordillo Field – Patagonia, Argentina

Reservoir Thickness Contour Plot (ft) – ACN Study RegionEl Tordillo Field – Patagonia, Argentina

Data Preparation

Production Data

Injection Data

Static Reservoir Data

Data Preparation – Production Data

The fact that the production data are commingled may significantly affect our ability to analyze and interpret the production for each well:

It is impossible to provide an analysis for each individual layer.

The production data is “re-allocated” in Area Central Norte (ACN) zones: Comodoro Rivadavia and Mina El Carmen formations

Data Preparation – Production Data

Re-allocated Production Data

Well Production

Data

FluidProperties Geological

Markers

NeighborWellsData

WellboreDiagrams

Available information used to “re-allocate “ production on a per-well basis after each completion and each re-completion.

Data Preparation - Steps

• Identify errors or anomalies in the production and injection data.

• Locate and annotate changes in the completion practices.

• Reinitialize the production data in time.

• Reallocate the total production for each reservoir interval.

1.E+00

1.E+01

1.E+02

1.E+03

1962 1966 1970 1974 1978 1982 1986 1990 1994 1998

Data Preparation – “Re-allocation”O

il P

rod

uct

ion

Rat

es ,

ST

B/D

Date, year

ACN sandsOil Production Non -ACN sands

Oil Production

Production Performance Plot for Well –516Comparison of Total Oil Rate and ACN Project Zones Oil Rate

Data Preparation

Production Data

Injection Data

Static Reservoir Data

Data Preparation – Injection Data

Although the injection wells are injecting in a “multi-stage” fashion (i.e., injection over several layers simultaneously), the total injection per well is used in the analysis because the oil production could not be identified sand by sand.

Data Preparation

Production Data

Injection Data

Static Reservoir Data

Data Preparation – Static Reservoir Data

To estimate the static reservoir pressure as a func-tion of date, we used the fluid level measured in swab tests (performed on individual sands (or groups of sands)) during the productive life of each well.

Although the pressure data show a poor correlation with date, we believe that the data are reasonable, and as such, we have used the average trend for our analysis.

0

500

1000

1500

2000

2500

3000

1960 1965 1970 1975 1980 1985 1990 1995 2000

Data Preparation – Static Reservoir Data

Pressure (avg.) = 84426 - 41.8 * yearDatum : 7664 ft

Sta

tic

Res

ervo

ir P

ress

ure,

psi

Date, year

Static Reservoir Pressure Assigned by DateEl Tordillo Field, Argentina – ACN Region

high

avg.

low

Data Result Using Decline Type Curves

Production WellsThe material balance type curve analyses yield two types of results: “flow” and “volumetric” parameters.

• Reservoir properties Skin factor for near well damage or stimulation, s Effective permeability, k

• In-place fluid volumes Original oil-in-place, N Movable oil at current conditions, N p,mov

Reservoir drainage area, A

Example: Well S-677 (Oil)

The well data used in these analyses are:

Reservoir PropertiesPorosity: 0.15 (fraction)

Irreducible Water Saturation : 0.25 (fraction)

Net Pay Interval : 131 ft

Initial Reservoir Pressure: 1,830 psia

Fluid PropertiesOil Formation Volume Factor: 1.2 RB/STB

Oil Viscosity: 1.0 cp

Total Compressibility 25 E-6 psia-1

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1975 1979 1983 1987 1991 1995 1999

Production Performance Plot for Well S-677ACN Project - Blue, Junior, Brown Zones

Prod

ucti

on R

ates

, S

TB

/D

Date, yearW

orko

ver

(A

ug. 9

3)

PrimarySecondary

Oil

Water

Com

plet

ion

(Oct

. 76)

Wor

kove

r (

Jun.

82)

Trend #1

Well S-677 (Oil) – Match Trend #1

We note a good match of all the production data, for both the transient and boundary-dominated flow periods in trend #1.

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1975 1979 1983 1987 1991 1995 1999

Production Performance Plot for Well S-677ACN Project - Blue, Junior, Brown Zones

Prod

ucti

on R

ates

, S

TB

/D

Date, yearW

orko

ver

(A

ug. 9

3)

PrimarySecondary

Oil

Water

Com

plet

ion

(Oct

. 76)

Wor

kove

r (

Jun.

82)

Trend #2

Well S-677 (Oil) – Match Trend #2

We note an excellent match of all the production data, for both the transient and boundary-dominated flow periods (Trend #2).

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1975 1979 1983 1987 1991 1995 1999

Production Performance Plot for Well S-677ACN Project - Blue, Junior, Brown Zones

Prod

ucti

on R

ates

, S

TB

/D

Date, yearW

orko

ver

(A

ug. 9

3)

PrimarySecondary

Oil

Water

Com

plet

ion

(Oct

. 76)

Wor

kove

r (

Jun.

82)

Secondary Trend

Well S-677 (Oil) – Match Secondary Trend

We note a good match of all the production data in the boundary-domi-nated flow periods during the secondary production trend.

Results: Well S-677 (Oil)

The production rate (and pressure) functions were plotted versus “material balance time” (Np/q) on the Fetkovich-McCray type curve. The following average results are obtained:

• Volumetric PropertiesOriginal Oil in Place, N = 5,485 MSTBDrainage Area, A = 92.8 acres

• Flow PropertiesPermeability, k = 0.452 md

Skin factor, s = -5.57

Estimated Ultimate Recovery Analysis

qo vs. Np (Semi-Empirical-Approach) (S-677) (This plotting approach is used when bottomhole pressure data

are not available).

Primary Performance

Extrapolating the trends prior to

waterflood response to qo=0,

the primary movable oil is

obtained.

Estimated Ultimate Recovery Analysis

qo vs. Np (Semi-Empirical-Approach) (S-677) “This plotting approach is used when bottomhole pressure data

are not available”.

Secondary Performance

Extrapolating the trends in the

waterflood period to qo=0, the secondary

movable oil is obtained.

EUR Analysis: Results – Well S-677 (Oil)

Primary PerformanceNp,mov: 328.9 MSTBRecovery factor: 6.0 %

Secondary Performance Np,mov: 201.7 MSTBRecovery factor: 3.68 %

Secondary/Primary Recovery Ratio = 0.613

Data Result Using Decline Type Curves

Injection WellsAs for oil cases performed previously, the material balance type curve analyses yield two types of results: “flow” and “volumetric” parameters.

• Reservoir properties• Skin factor for near well damage or stimulation, s• Effective permeability, kw

• In-place fluid volumes• Total system volume available for injection, W• Injectable water, Winj

• Injection area, A

Example : Well S-638 (Water Injection)

The well data used in the analysis are:

Reservoir PropertiesPorosity: 0.15 (fraction)

Irreducible Water Saturation : 0.25 (fraction)

Net Pay Interval : 166 ft

Initial Reservoir Pressure: 1,000 psia

Fluid PropertiesOil Formation Volume Factor: 1.01 RB/STB

Oil Viscosity: 1.0 cp

Total Compressibility 40 E-6 psia-1

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

9401 9501 9601 9701 9801 9901

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

5,500

6,000

Injection Performance Plot for Well S-638ACN Project - Blue, Junior, Brown Zones

Wat

er I

njec

tion

Rat

es ,

ST

B/D

Date, year

Wor

kove

r (

Oct

. 98)

Pwf

qwi

Con

vers

ion

(Oct

. 93)

Wor

kove

r (

Oct

. 95)

Wor

kove

r (

Apr

. 97)

Flo

win

g B

otto

mho

le P

ress

ure

, psi

a

Well S-638 (Inj.) – Match Injection Trend

• We note a good match of the injection data—for both the transient and transition flow periods.

Results: Well S-638 (Injection Well)

The injection rate (and pressure) functions were plotted versus “material balance time” on the Fetkovich/McCray type curve .The following results were obtained:

• Volumetric PropertiesTotal system volume available for injection, W = 42,040 MSTBWInjection Area, A = 439.6 acres

• Flow PropertiesPermeability, kw = 1.848 md

Skin factor, s = -6.498

Estimated Injectable Water Analysis – S-638

We note a reasonably linear trend with sig-nificant data scatter. The extrapolation of this trend yields Winj = 11.1 x 106 STBW

Injection Performance

By plotting the injectivity index, (qwi/p), versus

cumulative water injection, we can

estimate the injectable water volume when

(qwi/p)=0.

(qwi/p) vs. Wi

Integration of Results - Maps

The following maps are presented as a mechan-ism to integrate the results from our individual well analyses:

•Flow Capacity, kh

•Original Oil-in-Place,OOIP

•Primary and Secondary EUR

•Total Recovery Factor

•Secondary/Primary Recovery Ratio.

Flow Capacity (kh) Contour Map

OOIP

EUR(p)

Original-Oil-in-Place (OOIP) Contour Map

kh

EUR(p)

Primary EUR - Contour Map

OOIP

kh

Secondary EUR - Contour Map

Total Recovery Factor - Contour Map

Secondary/Primary Ratio - Contour Map

Integration of Results - Crossplots

•Crosplots are presented to estimate average values for the primary and secondary recovery factors and secondary/ primary recovery ratio:

EURPrimary vs. OOIP

EURSecondary vs. OOIPEURSecondary vs. EURPrimary

•Log-log correlation plots were prepared as an attempt to obtain meaningful relations between the computed flow capacity and the oil recovery versus initial oil rate in order to estimate the performance of infill wells in the ACN Region:

kh, OOIP, EURPrimary , EURSecondary vs. Oil Rates.

Comparison of Estimated Ultimate Recovery (Primary)Versus Oil-in-Place (OOIP ) Computed from Decline Type Curve Analysis

El Tordillo Field, Argentina(ACN Region- Zones : Blue, Junior, and Brown)

1.E+04

1.E+05

1.E+06

1.E+07

1.E+05 1.E+06 1.E+07 1.E+08

Computed Oil-in-Place, STB

Es

tim

ate

d U

ltim

ate

Re

co

ve

ry

(Pri

ma

ry),

ST

B

EUR PRIMARY = 0.1 OOIP

Crossplot: Primary EUR versus OOIP

Crossplot: Secondary EUR versus OOIP Comparison of Estimated Ultimate Recovery (Secondary)

Versus Oil-in-Place (OOIP ) Computed from Decline Type Curve AnalysisEl Tordillo Field, Argentina

(ACN Region- Zones : Blue, Junior, and Brown)

1.E+03

1.E+04

1.E+05

1.E+06

1.E+05 1.E+06 1.E+07 1.E+08

Computed Oil-in-Place, STB

Es

tim

ate

d U

ltim

ate

Re

co

ve

ry

(Se

co

nd

ary

), S

TB

EUR SECONDARY = 0.047 OOIP

Crossplot: Secondary EUR versus Primary EUR Comparison of Secondary Estimated Ultimate Recovery

Versus Primary Estimated Ultimate RecoveryEl Tordillo Field, Argentina

(ACN Region- Zones : Blue, Junior, and Brown)

1.E+04

1.E+05

1.E+06

1.E+07

1.E+04 1.E+05 1.E+06 1.E+07

Estimated Ultimate Recovery (Primary), STB

Es

tim

ate

d U

ltim

ate

Re

co

ve

ry (

Se

co

nd

ary

), S

TB

EUR Secondary = 0.47 EUR Primary

Crossplot: kh versus Initial Oil Rate (qoi) Comparison of Flow Capacity (kh )

Versus Initial Oil RateEl Tordillo Field, Argentina

(ACN Region- Zones : Blue, Junior, and Brown)

1.E+00

1.E+01

1.E+02

1.E+03

1.E+01 1.E+02 1.E+03 1.E+04

Initial Oil Rate, STB/D

Co

mp

ute

d F

low

Ca

pa

cit

y (kh

), m

d-f

t

kh (avg) = 4.7624 q oi 0.4944

Low

Avg

High

Crossplot: OOIP versus Initial Oil Rate (qoi) Comparison of Oil-in-Place (OOIP ) Computed from DeclineType Curve Analysis

Versus Initial Oil RateEl Tordillo Field, Argentina

(ACN Region- Zones : Blue, Junior, and Brown)

1.E+05

1.E+06

1.E+07

1.E+08

1.E+01 1.E+02 1.E+03 1.E+04

Initial Oil Rate, STB/D

Co

mp

ute

d O

il-i

n-P

lac

e,

ST

B

OOIP (avg) = 119017 q oi 0.6681

Low

Avg

High

Crossplot: EURprimary versus Initial Oil Rate (qoi) Comparison of Estimated Ultimate Recovery (Primary)

Versus Initial Oil RateEl Tordillo Field, Argentina

(ACN Region- Zones : Blue, Junior, and Brown)

1.E+04

1.E+05

1.E+06

1.E+07

1.E+01 1.E+02 1.E+03 1.E+04

Initial Oil Rate, STB/D

Es

tim

ate

d U

ltim

ate

Re

co

ve

ry

(Pri

ma

ry),

ST

B

EUR (primary)(avg) = 25010 q oi

0.5243

High

Avg

Low

Crossplot: EURsecondary versus Initial Oil Rate (qoi) Comparison of Estimated Ultimate Recovery (Secondary)

Versus Initial Oil RateEl Tordillo Field, Argentina

(ACN Region- Zones : Blue, Junior, and Brown)

1.E+03

1.E+04

1.E+05

1.E+06

1.E+01 1.E+02 1.E+03 1.E+04

Initial Oil Rate, STB/D

Es

tim

ate

d U

ltim

ate

Re

co

ve

ry

(Se

co

nd

ary

), S

TB

EUR (Secondary)(avg)

= 14299 q oi 0.4538

Low

Avg

High

Integration of Results – Time Dependency

Integration of Results – Time Dependency

Integration of Results – Time Dependency

Integration of Results – Time Dependency

•We note that the previous comparisons do not show any specific trends. The lack of any specific time dependency of the results clearly confirms that the reservoir is highly heterogeneous and probably of a low, to very low permeability.

Conclusions

The following conclusions are noted:

• The guidelines to set the production and injection realloca-tion are well established an all of the necessary information/ data was identified and sorted.

• The decline type curve and volumetric analyses yielded acceptable estimates of original oil-in-place, as well as primary and secondary movable oil.

• The calculation of movable oil volume using the q versus Np plot yields acceptable results (unless pwf varies significantly).

Conclusions (Cont.)

• Integrating the results of this study, we identified areas with favorable conditions for additional oil reserves. We believe that a detailed analysis (on a well-by-well basis) of these zones will support the drilling of new infill wells in the ACN Region.

• We observed relatively constant trends of OOIP and primary EUR versus completion date, which confirms that the reser-voir is highly heterogeneous, is of low permeability, and infill wells should improve overall recovery.

• Crossplots of results developed in this study can be used as predictive tools for estimating the recovery of infill wells of the ACN Region.

Conclusions (Cont.)

• The secondary/primary recovery ratio for the ACN Region (0.47) is a useful parameter for predicting secondary EUR in the preliminary evaluation of other projects with similar characteristics as El Tordillo Field.

RecommendationsIn order to enhance the recovery in the ACN Region, a detailed surveillance program is proposed:

• Monitoring of production by sands or by groups of sands.

• Periodic measurements of static reservoir pressure.

• Pressure and rate monitoring of water injection.

• Periodic step rate tests to optimize injection pressures and rates.

• Injection profile logging (for routing of injections fluids).

• Periodically perform specific production tests.

• Periodically check fluid levels to ensure pump-off in producing wells.

This work is dedicated to my lovely wife, Diana and to my two beautiful children, Lucia y Manuel.

Dedication

I would like to thank Tecpetrol S.A for providing me the opportunity and the financial support to pursue my Master of Engineering degree at Texas A&M University.

I would also like to thank the following individuals for their contributions to this work:

Dr. T.A. Blasingame , for serving as Committee Chairman, and for his advise, support, and encouragement during this investigation.

Dr. A. Datta-Gupta, Dr. R. Thompsen and Dr. J. Watkins for serving as Committee Members.

Acknowledgments

Evaluation of Reservoir Performance Using Decline Type Curves Improve Reservoir Description - Area Central Norte (ACN)

Region, El Tordillo Field Argentina

Final Project for

Carlos Alejandro BertoMaster of Engineering

Chair of Advisory Committee:

Dr. Thomas. A. Blasingame

Department of Petroleum Engineering

Texas A&M University – College Station, Texas