Andalucia Sur Field: a simulation study

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ANDALUCIA SUR FIELD

A SIMULATION STUDY

ARTHUR LAKES LIBRARY COLORADO SCHOOL of MINES

GOLDEN, COLORADO 80401

by

Carlos Portela

April 6, 1983

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An engineering report submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Engineering (Petroleum Engineer )

Golden, Colorado Carlos A. Portela Approved: D Thesis Advisor Golden, Colorado Department Head Petroleum Engineering ii

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ABSTRACT

A r e s e r v o i r - s i m u l a t i o n study of the Andalucia Sur Field, using a 3-D, 3-phase black oil simulation system, was undertaken to determine the original oil in place (OOIP) and

the production p e r f o r m a n c e of a group of five sands

collectively known as the Doima Formation.

The field is located in the Upper Magdalena Basin in

C o l o m b i a , S o u t h A m e r i c a . It c o n t a i n s a h i g h l y

undersaturated black oil. The five sands are found spanning

an interval b e t w e e n +175 feet and -900 feet subsea.

Structurally, the Andalucia Sur reservoir is a faulted

anticline. Oil production is commingled from all five sands

and is being produced from fourteen wells.

Results from the s i m u l a t i o n study show that the original oil in place for all five sands is 72.02 MMSTB and that only 3*85 MMSTB (5.4/6 of OOIP) as of December 31, 1991,

would be recovered by the primary production mechanism. It

is also shown that the lower "D” and ”E” sands are being depleted a lot faster than the other zones.

The feasibility of a waterflood project was studied. Results show that for the optimum case, 9*59 MMSTB (13*3% of OOIP), as of December 31, 1991, (8'years) can be recovered. Downdip and updip injection of water to flood all five sands is recommended using a peripheral line drive pattern.

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TABLE OF CONTENTS

Page

ABSTRACT iii

LIST OF FIGURES vii

LIST OF TABLES xii

ACKNOWLEDGEMENTS xiii

I. INTRODUCTION 1

II. GEOLOGY 4

III. THE ANDALUCIA SUR RESERVOIR 8

1. The Structure 8

2. Rock Properties 8

2.1 Permeability 8

2.2 Porosity 20

2.3 Thickness 20

2.4 Rock Pore-Volume Compressibility 20

2.5 Resistivity of the Formation Water 27

2.6 Initial Water Saturation 28

2.7 Initial Oil Saturation 28

2.8 Capillary Pressure 28

3. Fluid Properties 41

4. C o m p l e t i o n M e t h o d 42

5. Production History 42

6. Pressure History 66

7. Workovers and Production Problems 67

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IV. OPEN HOLE LOG INTERPRETATION 69

V. THE RESERVOIR SIMULATION STUDY 73

1. The Grid Network 75

2. Reservoir Zonation 77

3. The History Matching 81

3.1 Initialization 82

3.2 Pressure Match 83

3.3 Producing Fluid Ratio Match 84

3.4 Productivity Index Match 87

4. Prediction Cases 102 4.1 Prediction Case 1 103 4.2 Prediction Case 2 103 4.3 Prediction Case 3 105 4.4 Prediction Case 4 109 4.5 Prediction Case 5 111 4.6 Prediction Case 6 114

VI. RESULTS AND DISCUSSION OF RESULTS 120

1. Log Interpretation 120 2. Simulation Study 120 3. Comments on Predictions 130 VII. CONCLUSIONS 151 VIII. RECOMMENDATIONS 152 REFERENCES 153 v

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APPENDIX B

APPENDIX C

TRACY ET AL METHOD ( 156

COMPUTER ROUTINE OF THE LOG INTERPRETATION

METHOD 164

INPUT DATA FILE FOR BOSS 227

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2 5 9 10 11 12 13 19 21 22 23 24 25 26 29 30 31 32 33 34 35 36 37 Geographi c Lo cation

Columnar Sect ion

Structure Map Top A Sand

Structure Map Top B Sand

Structure Map Top C Sand

Structure Map Top D Sand

Structure Map Top E Sand

Permeabil ity- Poros ity Cr

Thickness Map A Sand

Thickness Map B Sand

Thickness Map C Sand Thickness Map D Sand Thickness Map E Sand Ro ck Compress ibility

In itial Water Saturation Map A Sand

In i t ial Water Saturation Map B Sand

In itial Water Saturation Map C Sand

In itial Water Saturation Map D Sand

In itial Water Saturation Map E Sand

In itial Oil Saturation Map A Sand

In itial Oil Saturation Map B Sand

In itial Oil Saturation Map C Sand

In itial Oil Saturation Map D Sand

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24. Initial Oil Saturation Map E Sand 38

25. Oil- Water Capillary Pressure Curv es 39

26. Selected Capillary Pressure Curve 40

•

t-co _Oil _{and Water} _Production _{History: A S - 1} ₄₄

28. Oil and Water Production History: AS-2 45

33. Oil and Water Production History: A S - 10 50

38. Oil and Water Production History: AS-1 8 55

40. Oil and Water Production Hi story: AS-22 57

41 . Oil and Water Production Hi story: Field 58

42. Cumulative Oil and Water Production 59

43. Gross Flow Diagram 72

44. Grid Network 76

45. Permeability Barrier Map 78

46. Pressure Performance: Field 86

47. Relative Permeability Curves from Lab 88

48. Adjusted Relative Permeability: A Sand 89

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49. Adjusted Relative Permeability: B Sand 90

50. Adjusted Relative Permeability: C Sand 91

51. Adjusted Relative Permeability: D Sand 92

52. Adjusted Relative Permeability: E Sand 93

53. Water Cut History Match: Field 94

54. Water Cut History Match: AS- 4 95

59. Water Cut Hi story Match: AS- 12 100

61 . Prediction Case 1: Results 104

62. Proposed Plan: Cases 2 & 3 107

63. Prediction Case 2: Results 108

65. Proposed Plan: Case 4 112

71. Initial Reservoir Analysis 119

72. Oil Saturation Map : Case _{1, A Sand} 123

73. Oil Saturation Map : Case _1, B Sand 124

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74. Oil Saturation Map : Case _1, C Sand 125

75. Oil Saturation Map : Case _{1, D Sand} 126

76. , Oil Saturation Map : Case _1, E Sand 127

77. Oil Pressure Map: Case 2, A Sand 131

78. Oil Pressure Map: Case 2, B Sand 132

79. Oil Pressure Map: Case 2, C Sand 133

o

o _o _• _Oil _{Pressure Map:} _Case

2, D Sand 134

81. Oil Pressure Map: Case 2, E Sand 135

82. Oil Saturation Map : Case _5, A Sand 138

83. Oil Saturation Map : Case 5, B Sand 139

.

C

O _Oil

Saturation Map : Case 5, C Sand 140

85. Oil Saturation Map : Case 5, D Sand 141

86. Oil Saturation Map : Case _5, E Sand 142

0

0 _• _Oil _{Pressure Map:} _Case

5, A Sand 143

88. Oil Pressure Map: Case 5, B Sand 144

0

vO • Oil Pressure Map: Case 5, C Sand 145

90. Oil Pressure Map: Case 5, D Sand 146

91. Oil Pressure Map: Case 5, E Sand 147

A 1 Pressure Build-Up Test : Field Data 162

A2 Pressure Build-Up Analysis 163

B1 Neutron Porosity Histogram 166

B2 Bulk Density Histogram 167

B3 Neutron Porosity-Density Porosity Cross Plot 169

B4 Neutron Porosity-Bulk Density Cross Plot 170

B5 Gamma Ray-(Neu. Por.-Den. Por.) Cross Plot 171

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B6 Gamma Ray-Deep Induction Cross Plot 172

B7 Determination of Gamma Ray Value for Clean

Formation 179

B8 Vol. Shale Cross Plot-Vol. Shale Gamma Ray

Cross Plot 180

B9 Determination of the Amounts of the Three

Types of Shale 183

B10 RWA-Normalized Gamma Ray Cross Plot 187

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14 15 16 17 43 68 74 85 106 121 148 150 197 RANGE OF POROSITY AND PERMEABILITY VALUES

AS CALCULATED FROM FIELD DATA

RESISTIVITY OF THE FORMATION WATER PVT PROPERTIES OF RESERVOIR FLUID HYDROCARBON COMPOSITION OF SEPARATOR LIQUID AND GAS

WELL COMPLETION

WORKOVERS PERFORMED THROUGH 12-31-82 REQUIRED INPUT FOR THE SIMULATION

POROSITY AND PERMEABILITY FOR EACH SAND INJECTION RATE IN EACH SAND

VOLUMETRIC SUMMARY ON SAND-BY-SAND BASIS

PRODUCTION FORECAST. OPTIMUM CASE

SUMMARY OF ESTIMATED RECOVERY AS OF 12-31- 91 ON SAND-BY-SAND BASIS

PERMEABILITY INDEX MULTIPLIER

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ACKNOWLEDGEMENTS

The author wishes to express his gratitude to Dr. Daniel Bass Jr. for serving as his advisor and for being most generous with his time.

The author also wishes to thank Dr. James W. Crafton for his valuable c o m m e n t s during the d e v e l o p m e n t of this

study and for serving on the thesis committee. Appreciation

is also extended to Professor Donald Davis for his help and c r i t i c a l e x a m i n a t i o n of the r e s u l t s d u r i n g the log i n t e r p r e t a t i o n stage, and for s e r v i n g on the t h e s i s committee.

Many thanks are extended to Professor Donald Dickinson for serving on the thesis committee.

Special thanks are expressed to Dr. Luis G. Morales, President of Petroleos Colombianos Ltd., who provided the scholarship that made this study possible, and to whom the author will always be indebted.

The author also wishes to express his thankfulness to

Mr. Luis F. Mendoza and to Mr. Pedro Ruiz for their

willingness in providing the author with all the available data for the study.

The author wishes to dedicate this work to his wife, Gloria, his daughter, Maria del Mar, and his parents Jose and Luz.

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INTRODUCTION

The Andalucia Sur Field is located in the upper valley of the Magdalena River in the Department of Huila, Republic

of Colombia, Figure 1. The field was discovered on the

basis of seismic investigation. The well Andalucia Sur-1,

drilled in May, 1980, was the discovery well. Oil was

found in the fourth sand of a group of five Tertiary sands k nown as the Doima For m a t i o n in the faulted anticline of Andalucia.

The reservoir is bounded on the eastern flank by a thrust fault striking southwest by northeast, known as the Andalucia Thrust, and on the south by the underlying water

bearing zones. To the west, the sediments pinch out against

the Jurassic Basement. The northern limit is not well

established as of this date. Nineteen wells, fourteen oil

producers and five dry holes, have been drilled. All five

sands have been shown to be oil productive. The lithology

of the reservoir can be defined as sand-shale sequences

spanning an interval b e t w e e n +175 feet and -900 feet

subsea.

The field contains a highly undersaturated black oil. It was put on production in May, 1981, with ten producing

wells. The m a x i m u m oil production rate of 3»799 BPD was

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9lo Ciro AND A L U C I A SUR F I E L D COLOMBIA E C U A D O R

LOCATION MAP

ANDALUCIA SUR FIELD

R E P U B L I C OF C O L O M B I A

> 160

KILOMETERS

640 460

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current average of 1,750 B P D , despite the drilling of four

more wells. All wells are on sucker rod pumps with

commingled production from all exposed sands.

Fluid level measurements have been used as the method to d e t e r m i n e average reservoir pressures. Although the

results so obtained are highly questionable, a severe

pressure decline is suspected.

The purpose of this study is to evaluate the original

oil in place (OOIP) for each sand, s imulate the p r i m a r y

production performance and contemplate the feasibility of a water injection project to increase the ultimate recoverable

r e s e r v e s . To a c c o m p l i s h this, a t h r e e p h a s e - t h r e e

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GEOLOGY

The Magdalena River Basin in Colombia, South America is divided into the Upper, Middle and Lower Magdalena Basins. The Upper Magdalena Basin(1), where the Andalucia Sur Field is located, has an area of 4,9^0,000 acres and is a tectonic depression 31 miles long and 12 to 31 miles wide between the

Central and Eastern Andes. It is a marginal, but integral

part, of the Great C o l o m b i a n - V e n e z u e l a G e o s y ncline (2),

which generated the largest part of South American oil.

More exactly, the Upper Magdalena Basin is part of its

western shelf, region flooded by Cretaceous Seas. A

columnar section of the Upper Magdalena Basin is presented

in Figure 2. Morales(3) states that the generating beds of

Villeta K-3 (shales), which are black and bituminous, were

c o m p r e s s e d through tectonic m o v e m e n t s and m o u n t a i n -

building into a horst and graben sequence, forcing the m i g r a t i o n of oil into the K-4 reservoirs or the Caballos

Sands. In some circumstances, he says, this oil has gone

into the Doima Sands, as in the Andalucia Sur Field, or into the Honda Formation, acting as the host rock.

The D o i m a F o r m a t i o n , a T e r t i a r y d e p o s i t w i t h a continental environment, is divided into three sections, as follows:

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A U T O * I C A I T A iO c i c a l a i m o o o •I S a d i a a r t o a l n g g n a o l i d a d o a : t t r r « M i P l r o o i M t 4 4 g r a d ; c i a a i W. R a o ia a l C g ra d e a l u v i o n a a y a in a n t a a ha ■ i n l o c l l a t i h r a n l t e a a f l u v i a t l l a a y l a c u a t r a a , c u i r • 0 4 4 • , l f t i e a a , c o n g la o e r a d o a p o l l m i c - t i e o a c o n a h u n d a iu a e u a r t o y f r a g o e n t o a d a r o c a a v a l c l n l c a a - A r c i l l o l i t a a y l l a w l i t a a p a r d o r e ) ! M i , g r l a a a y v g r d a a - * A r c i l l o l i t a a p a rO e n ] i u a « v a r d a a , b l a n d a a , a a l ^ i a a . A r e r . ia e a a g r l a t > p a a a > » f r o c u a n t a o a n t a c o n g l o M r i t i c a a , H t i a a t , O M n o t a a , A r c i l l o l i t a a y 1 l A o l i t a a o u i t i c o l o r e a p a r d o r o ] i u i , g r l a a a y v a r d a a . N i v a l p e t r o l l f o r o o n A r c i l l o l i t a a o u l t l o a l e v ^ a r o j i a a a g r a d o • i n a n t a a . b l a n d a a . I g t a n e a l a c l o n a a d a _ l* g a d a a d a a r o n l a c a a g r i a v a r d o a o , l l t l o a a g r a i w f i a o a o a d i o , f r i a l l a a . A r a n l a o a a c u a r t o a a d b lo a c a o y o o a r l l l a a . f i r a n o a t d l o , l i A p l a a , b i o * a o r t a a d a a , g r a n o a a u b r a d o n d a a d a a . S h a la a n a g r o a , b l t i m l a o a o a o g l o f r o o a , o g n M t a r i a o p g i n l M . t i v a i a a d a a l c r l t a e o n t a r r i g a n o a . g r i a a l a r o . L l a e l i t a a g r l a c l a n ? y g r i a a a o a r o ■ F r a o u a n t a . A r a n i a g a a c u a r s o a b l a n a a l # e h o a a . g r a • a d l e a g r w a a o , a o b o n g a ^ g r » l l a f i a a . S a d l o o n t l t a a r e j a a , d u r a a , f r a c u o a t a A a n t a a i l u r i J i o a i l M . F r e e w e iit a e i n t m a i o n a a * a e i d a a ■

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2. Mid-section, consisting of clays 3. Upper sand section

The lower sand section com p r i s e s the five producing

h o r i z o n s in the A n d a l u c i a Sur Field. Its g e o l o g i c

description is that it is composed of fine to coarse-grain

sandstone with an abundance of fragments of igneous rocks,

mica and chert. It has a shaly matrix and good porosity and

permeability.

The mid-section is described as multi-colored, soft and soluble clays.

The upper sand section has a similar lithology to the lower sand section.

The interpretation of the geological features and the morphology of the SP and Resistivity curves of the electric

l o g s s u g g e s t t h a t t h e s a n d d e p o s i t i o n m o d e l is

charact e r i s t i c of a fluvial channel with the sediments thickening in a southward direction.

The lower two sands, called ”D" and "E" sands, pinch out against the basement toward the north and east and are cut by the Andalucia Thrust Fault running on the east side

of the structure. These two sands are described as medium-

to-coarse grain with poor to good sorting, which fit the

l a m i n a t e d - b e d load zones of the fluvial model. Their

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The three upper productive sands in the Andalucia Sur

Field, called "A”, MB" and ”C,f sands, are found throughout

the entire structure. Their average thicknesses range from

10 to 25 feet.

These three upper sands are very fine grained, with

poor sorting and a high content of silt and clay. This

description fits the flood plain or natural levee portion of the model.

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THE ANDALUCIA SUR RESERVOIR

1. THE STRUCTURE

Structurally, the Andalucia Sur Field is a faulted anticline elongated in the northeast by southwest direction, bounded on the east flank by a thrust fault called the Andalucia Thrust.

Structural contour maps of the top of each one of the five sand layers producing in the field are presented in Figures 3 through 7.

2. ROCK PROPERTIES

All reservoir parameters needed as input data for the simulation and the calculation methods and sources used are

b r i e f l y d i s c u s s e d in the f o l l o w i n g s e c t i o n s . T h e s e

reservoir parameters are also presented in Tables 1 through 4.

2.1 Permeability

A b s o l u t e p e r m e a b i l i t y v a l u e s r a n g i n g f r o m 5

m i l l i d a r c i e s to 240 m i l l i d a r c i e s were obtained from

Drillstem Test data. The calculation method as recommended by Odeh and Selig(4) was used. The fact that in most cases

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. « s > \ 0 LEGEND o PR OJ E CTE D L O C A T IO N • PR OD UC IN G OIL W ELL + DRY HOLE 9 S H U T - I N OR AB AN DONED W ELL

— PERM EAB ILITY BARRIER

F i g u r e 3.

C o lo ra d o S c h o o l o l M in e s UPPER M A G D A L E N A BASIN

C O L U M B IA . S O U T H A M E R IC A

ANDALUCIA SUR FIELD

STRUCTURAL MAP Top "A* Sand

m e t e r s

S C A L t 1: 1 0 . 0 0 0 C O N T O U R IN T E R V A L 90*

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ITT LEGEND O P R O JE C T E D L O C A T IO N • P R O D UC IN G OIL W EL L 4- DRY HOLE • S H U T - I N OR A BA NDO NE D W ELL

'-'PE RME AB ILITY BARRIER

Figure 4.

C o lo ra d o S c h o o l o l M ine s UPPER M A G D A L E N A BASIN

STR UC TUR AL MAP To p * B* Sand m e t e r s s c a l ei lo.ooo C O NTOUR W T E R V A l 6 0 C A R L O S R O R T El* J A N U A R Y iftBS

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■121 ■8 0 S ■878 LEGEND 0 P ROJ E C TE D LO C A T IO N • PR OD UC IN G OIL WEL L 4- DRY HOLE • S H U T - I N OR ABANDO NED WELL -^ P E R M E AB IL IT Y BARRIER Figure 5. C o lo ra d o S c h o o l o f M in e s UPPER M A G D A L E N A BASIN C O L U M B IA . S O U T H A M E R IC A

S TRUCTURAL MAP To p * C * Sand 300 ’ 000 M E T E R S SCALE 1 10 .0 00 CONTOUR N T E R V A L SO' C A RlO S P O R T E L A J A N U A R Y . 1 8 8 1

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/ •»«

LEGEND

c P R O JE C TE D L O C A T IO N • P RO D UC IN G OIL WELL 4- DRY HOLE

» S H U T - I N OR ABA NDO NED W ELL

Figure 6

C o lo ra d o S c h o o l o f M in e s UPPER M A G D A L E N A BASIN

STR UC TU RAL MAP To p * D* Sand 1 0 0 0 M E T E R S S C A L E 1: 1 0 .0 0 0 CONTOUR MTERVAL 9 0 ' C A R l O S P O B T E L A JAN UA R Y . I M S

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-aoi LEGEND O P R O JE C T E D L O C A T IO N • P R O D UC IN G OIL WELL ♦ DRV HOLE » S H U T - I N OR AB ANDO NED WEL L Figure 7. C o lo ra d o S c h o o l o t M in e s UPPER M A G D A L E N A BASIN C O L U M B IA . S O U T H A M E R IC A

S TR UC TUR AL MAP To p ‘ E* S end 5 0 0 1 0 0 0 M E T E R S S C A L E 1: 1 0 0 0 0 C O N T O U R IN T E R V A L SO' IR I OS P O R T E L A JANU A R Y . 1*63

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TABLE 1

RANGE OF POROSITY AND PERMEABILITY VALUES AS CALCULATED FROM FIELD DATA

SflMO ABS. PERHERBILITY POROSITY (MILLJDARCIESJ (FRAC.l A 5. TO 33. 0.19 TO 0.24 B 33. TO 117. 0.17 TO 0.22 C 9. TO 117. 0.15 TO 0.21 0 22. TO 240. 0.22 TO 0.24 E NO OATA 0.20 TO 0.24 M M

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TABLE 2

RESISTIVITY OF THE FORMATION WATER

SAND WATER RESIST. (OHH-M) A O.ilO TO 0.33 B 0.35 TO 0.31 C 0.33 TO 0.30 0 0.27 TO 0.25 E 0.27 TO 0.25 M M M

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TABLE 3

PVT PROPERTIES OF RESERVOIR FLUID

(DIFFERENTIAL LIBERATION AT 114 OEG. FAREN.)

PRESSURE BO RS OIL VIS. GAS VIS. (PSIG) (RB/STB) (SCF/STB) (CP) (CP) 5000. 1.0357 58. 4.1 4000. 1.0409 58. -3000. 1.0465 58. -2000. 1.0553 58. -1500. 1.0555 58. -1000. 1.0586 58. -900. 1.0594 58. -700. 1.0605 58. 3.36 500. 1.0618 58. 3.31 300. 1.0632 58. 3.27 200. 1.0638 58. 3.25 100. 1.0647 58. 3.23 68. 1.0650 58. 3.2 2 0.0105 37. 1.0500 36. 4.25 0.0105 0. M X H 1.0250 0. 5.54 0.0105 M X H X

STANOARO CONDITIONS - 14.7 PSI ANO 60 OEG. FAREN.

BC (SCF/CFI

5.24 3.56

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TABLE 4

HYDROCARBON COMPOSITION OF SEPARATOR LIQUID AND GAS

MOL PERCENT

COMPONENT SEPARATOR LIQUID SEPARATOR GAS

C02 0.01 0.08 N2 0.25 20.39 Cl 0.52 7.68 C2 1.1U 12.32 C3 6. H8 38.23 I cu 2.13 5.91 NCU 6.75 11.0 IC5 3.39 2.2<J NC5 U. 19 1.9U C6 6.23 0.09 C 7 + 68.91 0,. 12 M H H H M

MOL HEIGHT 2U2. M

M M

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data from the initial flow and closed in periods had to be used (the wells killed by themselves making the final build up d a t a u s e l e s s for c a l c u l a t i n g p u r p o s e s ) m a d e the

p e r m e a b i l i t y values so c alculated rather unreliable.

Besides, the pressure gauges ran in those tests showed a h y ste res is effect so pronounced that the c alc ula tion of fluid produced during the first flow period was quite questionable.

Another attempt to calculate absolute permeabilities for each sand was made by using build-up data from static fluid level m e a s u r e m e n t s as furnished by the operating

company. The method recommended by Tracy et al (5)for low

productivity pumping wells was implemented in a computer

routine. The computer routine and a calculation example are

presented in Appendix A.

An additional source of p e r m e a b i l i t y values was the special core analysis and the con ventional core analysis carried out on samples from the "B” sand in well Andalucia

Sur-22 by two service companies (6,7). The plot of absolute

c o r e p e r m e a b i l i t y v e r s u s c or e p o r o s i t y f r o m t h e s e

references is presented in Figure 8. The ranges of absolute

permeability values for each sand determined by using field data are presented in Table 1.

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C

O

R

E

P

E

R

M

E

A

B

.

TO

A

IR

(M

IL

L

ID

.)

io iV

CORE P O R O S IT Y V.S CORE P E R M E A B I L I T Y

I I ! I I I I I ! I I I I T I I n I ! ! I I I ! I I r !' I I 1 I ! I I II I I I I 10 20 30 40 50

CORE P O R O S IT Y

(P E R C E N T .)

F i g u r e 8. P e r m e a b i l i t y - P o r o s i t y C r o s s P l o t

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2.2 Porosity

Porosity values from the above-mentioned core analyses and from open hole log data were a vailable for the study.

The latter were used as input for the simulator. The

calculation approaches are explained in detail in the log

interpretation section. Weighted average values of porosity

for each sand are presented in Table 1.

2.3 Thickness

Net thicknesses, rather than gross thicknesses, as determined from induction log data were used in this study. Unlike most cases, the SP curve could not be used as a good

lithology marker, because of the high shale content of the

sands. T hickness maps for each sand are presented in

Figures 9 through 13.

2.4 Rock Pore Volume Compressibility

Although rock c o m p r e s s i b i l i t i e s as d e t e rm in e d by Ecopetrol(8) were excessively high (see Figure 14), they can be seen as a q u al i ta tive indication of the degree of

uncompaction or friability of the formation. On the other

hand, when sonic logs were run, the transit time was in the range of 120-160 microsec/ft. i ndicating an u n c o m pa c te d formation.

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a • • • I N D O O I - * r ^ r s j h r f • • • • ! • X * M -s jO -vjO « * N ' X f ^ ' n f n • • • • ! • hoN^b h g is i i M i \ ir < i •ri r"*'^ rg»sir*l ^ r > o — ■*’<*’ ^ ^ r s j i s i Kj • • • *j • o o » -* -r^o * 4 t m- * 'N 'N j r g « • • • « • •#sr-r x • • • • • j • • • • • « • • Xs 8 a > O x d O X “S J -* — - 4 - 4 - —- * • • • • • * • • » O J X O • • • •• * • « 3 ^ « O O d O X ( ■ ^ ^ - * • > 4 IX -^PMPM • • • • • « • * /3N3odo^ ^ ?*> PMPM <N» <N 'V P M • • • • • 4 • • T'^O^xdQrf' rsg f n «\J nu <N fS4 • • • • • « • « o x a x x r > n ^ \ \ •m'M '-w 'M • • • • • 4 « * ^ O i M A < X X * X 'X >' <C o * / ' ^vn p'Jt m <‘M pm f « > n 4 • • • « • • • • • • 4 * « < r < « x - r x O X * 4 • • • 4 • • • • • • ♦ • • H O C O O C f * O X ' tA F i g u r e 9. Thi ck ne ss M a p a S a n d

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S V - 4 * ! • • • • * f ^ ^ i r ^ e o p o ( + • • • ♦ • • • ! • • • IN> b^ÔOOOON I ^ < n f n m n / n i > j c g ^ r g p g 9_| _{, • • • • ' * • • • ! - • • •} I« b^<r»ir»rv04Nopo^ | # * m ^ m m n ^ N N N O J N • { • • • • . ♦ • • • ( • • • • »f> irb^^NirNÔpONO * 4 r t p j n m w n m M N N N N N • • ♦ • •! • • • •!• • • • # • * s | © i f M f ^ i r ' M t f H © p © o m % *4 <*> ^ { o ^ i A N > T 0 9 0 p •4 • ! • • • « O ^ N J lO o j f V i r g • ! • • • • ; • • • • ! • • • *J tfNffN^NNdOObON • | • • • • ; • • • • ] • • • ^N^N^NOCDObO^ *4 • | • • • • • • • • ! • • • O i/>pr4©®iAi/N®©po© • # . # • • • = • • • • ; • # • ôôo«noooopô r > <*\ m <n r g oj j si r g f>j r vj h j f g f*> | © O ^ D O i T ^ O O O O l r O O | m m m r ^ r g r g f> g rw r N jf w r g 4 > f^ > f «•<••••:••••'••# I ro«-inoooiîrM/Mnob«*to I fnmpr*fnrgiMr>if\a»n»nmfn I I | • * • • • »• • • • ' • • • I ©NoiÔNOoooNhoo I nmpff wmnmnnpmrt I 9 | • • ' • • • •■ • • • • ! • • • wNhoo ^ ^ w w w n N o o t r ^ w n h c • • • • • » . • • • • ) • • • ■e »r> o o n o i ^ m it\p4n h r * o r ^ ^ m m < n m r n f n f n m | m < n r > 4* ss • • ! • • • • • • • « « • • N O C V ' O O O O O O O p O O ^ ^ i m r > < * > m fn < * % < n fn in m # n • • > • • • « • • • • ! • • • «OOOCDrgOOOOObOO ^ r v i n < i r ^ r * 0 D O ' sersifc F i g u r e 1 0 . Thickness M a p B S a n d

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*4 <0 • ; • • • • < • • « « « r i r » ^ o < * - < Un n * ^ - < ^ > ^ - K « M / \ Q 0 w 0 ^ * r ® C D ^ > O —« » 4 « 4 f ^ r s 4 * ^ 4 ^ 4 « « N • • • • • ( • • • • • # • %J K N ^ K O W ^ ^ ' B H / ' N •4 — • 4 ^ ® K ^ 9 K% I N O O ^ IT» f*>*> r4 md~4+4 N ^ * N N <"W ->gfNjr><*> ® < n i ^ o o o ^ o o - * —»—**-* N < N n n <•* ^ <*■ < r • • « • • » • • • « • • • B D O O i A O O O ^ O o O O O ^«DvPN / ' O O / ' if* -g<,w <c « c o ^ o t f M O • • # * • < • • • • • • • -C A04T ® 00*0^* 3C*W\tfSO O ^ ' T U ^ ' O AC'G'G t r s u v O 'C < e u > t 'r < r > < £ 0 * 0 ■£.< • • ! • • • « • • • 4 • • • ~ C 3iTM 00»r k ^ O O O * ' ^ 0 0 £ O ^ C <6 <c ’O 'C O O O < 0 <6 « » - o o o o o ^ o o & a Q ^ o —USk+'+lA O N ® ^ B ’i a u r e 1 1 . Th ic kness M a p C S a n d

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• ♦ • 0 0 9 I I • • ♦ I 9 O N O | - 4 ‘V J 'V tf'V « • • • r*r f i o o / ' * • • *■ « r i © * \ « * i • • 1 • • t T O / ' •N^ Q i T iO ^ > - * is i^ w 9 0 ^ 9 9 i T ^ A J -S J-* • o o ^ o o j i^ ooo -# •^1 *W eoo^Jo aoooaj • I • • • 4 • • « 4 o o d ^ * n o r f 1 *■>•# ^ ,ij* «r rw • ♦ •• • « • * • X> O ^ C O i r t t T ' O ^ 1 p ^ * * ^ A . N . 4n * , -r< *> • « • • • f • • • 'NiO 9 ^ ^ oirv c o * * • 9^ ^ • # • • * j • • • « * c o o o ^ n o o « i > 0000^91fr«N F i g u r e 1 2 . Th ic kness M a p D S a n d

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• I • V • • « troool • i • • » • > • • • • ! O O * * f 4 • * • • • • • • • • » WOIT'OO^'0D^^*^>l 4 W > f c n o c b ® ^ f | F i g u r e 1 3 . Th ickness M a p E S a n d

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ROCK C O M P R E S S IB IL IT Y

AS F U N C T IO N OF PRESSURE

o P Q R 0 $ m « Q . 2 5 6 * POROSITT.Q.2U2 P0R0SITY«0.281 POROSITT-O.222 o P0R0SITYa0.236 750 250 500 1000 125C

PRESSURE

( P S I)

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The first estimation of the rock compressibility was

made by using the correlation reported by Hall(9). During

the first hi story m a t c h i n g runs, it was found that the pressure drop caused by fluid production was too high, making the calculated pressures reach negative values after the first six months of production. Therefore, the value for

compressibility as estimated from Hallfs correlation, 3.6 x

10“6p s i” ‘1 was believed to be quite low and the rock

compressibility became another variable during the history matching.

This c on f ir m ed what N e w m a n ( 10) has shown, that the Hall(11) and Knaap(12) correlations do not apply to a very

wide range of reservoir rocks. Since this particular

reservoir rock can be classified as friable (samples could be cut into cylinders but the edges could be broken off by hand), different values from the study by Newman were tried

during the history matching. 15 x 10”6psi“ 'l was accepted as

the most probable value of rock pore volume compressibility for the field.

2.5 Resistivity of the Formation Water

F o r m a t i o n w a t e r r e s i s t i v i t y for e ac h san d w a s calculated using three different approaches as explained in

detail in the log interpretation section. It was found that

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increasing with depth. Water resistivity values for each sand are presented in Table 2.

2.6 Initial Water Saturation

Initial water saturation values were calculated using

f iv e d i f f e r e n t o p t i o n s , as e x p l a i n e d in the log

interpretation section. The initial water saturation maps

are presented in Figures 15 through 19.

2.7 Initial Oil Saturation

Since there was no free gas in the reservoir at the time of discovery, and most probably the amount of free gas

will not reach app rec iab le amounts, the initial oil

saturation is calculated based on the fact that water and

oil are the only saturating fluids. Oil saturation maps are

presented in figures 20 through 24.

2.8 Capillary Pressures

A set of ten o i l - w a t e r capillary pressure curves determined by the porous-plate method in an air-brine system were available from the conventional core analysis made by EcopetrolC13)• These capillary pressure curves are presented

in Figure 25. The c api lla ry pressure curve used for the

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i m m m m i i " i n r t [•^■r -r ►r • • • • • • • • :<r # t • r ’ - r ^ < r * r ^ * > •OKT * » - » f» V < -o 9 -+r v «< M n h m m m ( m m m JTO“ 4 • r > r • r ^ m . r . e + ■f\++»r\'i . • • • • • • • ^ • • » • H im m m * v m m -r •r'C T ^ > n a r < r < # < # - * # T ' r , ^ r j / ' « r » « o •+ *4'■w- • **H9 ^ • 4X «*^*r -r -r +>*■ -r v*-rj^r .r\irv«j j-f <r *r +-r -r *r - ^ . v . v . ^ ^ r a T « m iT> +"■ m m m j i f \ i • * ? • • r / / / » j t r .n.0 » ■ » w j ' . r * ^ • » > • * • * - r J - - r . i A 5 o : - a e r * '* • ! « * ■ - r - r -r>< -r> : c —*c s>-r + * •t'.-r -r ■* ■»•>■ r / -f # - r >r -r .r . r i f ^ ^ S a*>i^03 n y vr <■ -r-r .»■ j- j o -vo Q j / f j j f / j ’ r j j O O a e - H ^ m f f ' O ^ S 9 9 9 0 ^ 0 1 » " » f l j j • r a o o a j^f^roooq j / i o - M a * M N O O O o d n a ? j ' j > ^ ( 3 o o q r f ' i r t j j - r ■#• j »■ j j - o o o a ^ ■ r N y o j i i P j r o o o d ^ n o o j n £ « i i v ^ o o o q •T' . m r ^ -r j>, -r -r j r o o o c ^ • • • • • ^ • • • « :3 ® N » » * « o ^ » / i o o o q * 0 0 s o q f r o o o q ^ -*c^ ^ C 1 ^NiO O O O Q N N « ? a N « H Q X o o q ® ^ i i r v r ^ « n ^ i ^ t r s q o o o q va^tpaa"* a*w 4 o q o o o a ^ o a o o o d o a e o o N J x - . i q o o o q i q o o o c i ^ o o o o o q <>J • J • • • !• • § <• • • j o . j o o o a c u d o o ocj o 0 0 o o a o o o 0 0 0 0 a c a o o o a o c 0 0 0 0 o q . m r g m ^ H i 4| r>- « &■ d « " * m < J u ^ F i g u r e 1 5 . I n i t i a l W a t e r Sa tu ra ti o n M a p A S a n d

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13 ifS++ * + ♦ < r • • * • • > C ^ < 1 *■ «r + + *(•* + • • 4 • • - r < r 3 * + + * • • 4 • ' -*lT S - 4 > '“' J —< d o o » * * ® ^ - c * * * , 4 ^ • • • « • « • ® ^iC -o -Q * * * . r * » , r < r , * j t * r > r , C ‘# |« r * « f * * * 4 * * # ^ * {J» •*• ?*> » * © « » ® r * £ ^ £ N/ t N £ ^ / > f - r - f «4 ■»• - 4 4 O - * ® ^ <A - * ^ * • m ^ o ^ * ! * r T ' * 3 * - » > 0 * 4 ® »fN 0 ^ ^ Qr* O ' T O ® j i r N i p ^ « • • • • • « 4 « « * ^ « o ® o **u*> o o o * r *nj^ «y o ? x > r ^ / t* *'*»/' ^ • • • + • • •« •• • « • O 3 0 0 J « N 4 0 0 < n | N o o a a o - r - C J ' - r - J - r d a 3 0 0 l J ? ® -3-0 .OX>tn.n f * • • • j • • • t • • • 1 • 0 0 3 9 0 O O O O O * ' ® . ^ 3 3 0 0 3 0 3 0 0 0 J N 3 j o o o o o q 300 4 • • • f • • • • • • • ♦ • Q O O O O O 0 0 0 0 ^ 4 - 0 0 0 0 0 0 0 3 0 0 / ^ 3 0 0 0 3 0 C c i 0 C * 4 # 1TV • * • t • * * J | J • • * • O O OO OO OO O ON ^ o o o o o o c o o o ^ i r t N O O O O O O O O O O ^ * ^ t • • • • • • • ^ • • • I • -4 D O O O O O O O O O O O O 0 0 0 0 ^ 3 0 0 9 0 0 0 0 3 o o 4 o c o O o o o O j < * % • • • » • • • « • • • « • ••4 pa*prt «4I «4 e O 3 C > C 3 0 3 0 3 0 0 0 3 0 0 3 O O 3 3 3 0 0 0 0 O O O O C O - . 9 3 9 0 0 3 ! ■ > ! • • • » • • .. O 3 O 0 3 8 O 9 O O O 0 0 o o o o o o o o o o o o o O O O 3 C O 3 0 C O O 0 O ^ •• • » • • • f • • • t • F i g u r e 1 7 . I n i t i a l W a t e r Sa t u r a t io n M a p C S a n d

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r v f s j - N # r ■* • ! • • • I * • N N N < * • <r « ® i C <0 '" W 'N ’Nrf-V <r'K • *1. r > ^ r > * r * i r • •! • + +ir K i T i r t <r « r /i t e* • • • • *■ ■r / -r-i* -r *® • • • • • S B S < C >r -t -t-t -r ■n-npn .*n<-n ■r t f * o ^ * v o o o ® * ♦ e s r <* • * <r • * e ^ -r t <r r *r + *r + ® N * “N j I S i ^ O ^ «r **sr -r -r j- •* <r * ■t ^ «*sr -r r ^'J' ^ «# ^ • « • • •• • • • O O CTflO 30 O ^ ' C ^ N •C lT ' T ' T *r T T + *r ^ r s f • r - r ^ < r / # ^ O 'dr* 7 o > ^ j»> ^ / f * i s r T sT >?*T <r ^ • • ^ • • • • • * « ^ - w o ^ -* * ■ * 7 - It** «r. j> > / v * r * * - * r *■ j r * • • « • • • » • • C O C V ' ? ^ -rr^irw O O O M ^ «r r e c ^ O O C e f i ^ i T > f -# U-J •••'•• F i g u r e 1 8 . I n i t i a l W a t e r S a t u r at io n M a p D S a n d

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m © r g u > © n o - a h * - * © ^ © © • - * - * l A O - n - C < ^ ^ •© ‘■r n - tijn © © © r v * * - ^ •^rg .#• jn & **• © © n j r g ^ n s .Tv £ r v rN .r s .r s , ifS'f*'TsiT\ «/> </MT't/"1 v/' ^ © - H l T ' U ^ r s j x ? © 0“«r Oir © -sji'n 7 3 « « O C ^ ® m O® OOM ^ -/> rfMTV .Ti-r/^ J M /"' i M / ' fs .rs .fN . «# . r t . r > ir ' - r ^ r * -#■ •rwr> *rv © ^ i © r v j x \ ® f v ^ ) r > © -r c ® © m*#** ^ — © © 4 T N -* -g © -fr- —» o - n *■ ^ © - * © r v r s j m u> i/> ^ r » * » ^ » r s » r > r f > f c n ^ r f ^ j ^ i f > i S m X ' N O H CiT / ' / E O «■* rfN O © © r g n * * - ^ r - i ' s j ^ © rstr* *•* ^ f n » ^ v © r v ^ - f v © rs+~<C - * * » n~ £ c * • ^ a o © * » e e ^ ^ k T ' a ^ ^ O O * ^ ^ r f ' £ * £ £ r w > r * < v r X ' ^ i / * ' 4 r ' ^ r g w w "* *r* © 0 © < * > — 9*0 •* f > ^ © o © o*—«® * r n ^ -*©<** OtJO^J^ ? «TW> 'N# ©*-*-* ® *"vo© O O O ^ O r f ' ^ O O ©sC£ w o o o p - ^ ^ - n f ' ^ - * rf> r> kr> • • « • • • « • • « * • • • O O Q F i g u r e 2 3 . I n i t i a l O i l Sat ur at i o n M a p D S a n d

(52)

* r u > j n d ^ ’J ^ U > i/^ ® ® * n '7 J C^iT» —• d —« —• -Ni rs . * • tr» - * X O ^ ' ^ i S t ' T ' O j^<r> j~\ d r \ j n*t*i/ \ • * ^ - r ^ o !-> i T O O d d * - ?g / o 3 ^ ® » 4 —* - * : ■ " j * m j * * d . A d d d i d d T ! d d A d d d d d d d ® , r » ^ * ' * » 0 ,'■ O ^ * - ^ ^ 9 N \ « 4 > 0 4 r * •T X - * ^ d •# od • r / ' r u / ' i T m d d d d d d d d d O O p-rs. x d—»^S4 0 d O i r ^ ^ * ^ > ^ 0 O rsrf^Ni-^ 0«T • O N O < - r d d l i A d o O C C C * ' M^ ^ N O C O C ' C C T l N ^ O o o c ? - r - f , ^ c D O 3 0 O C d - O - ^ d ? 0 o c > o c c «<■ *»>* • 4 0 O O O O / ^ r f ' F i g u r e 2 4 . I n i t i a l O i l S a t u ra ti on M a p E S a n d

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C A P I L L A R Y PR ESS URE C U R V E S

POR. P L A T E M E T H . A I R —B R IN E SYST

1. K*17 HO P0FU0.251 2. K*60 HO P0R=0.23S 3. K=89 HD P0R-0.27H U. K= 137 HO P0R=0.27 5. K-199 HO P0R=0.261 6. K=21H HO P0Rs0.25 7. K= 132 HD P0Ra0.252 8. K= 118 HD P0R=0.2U6 9. K= 116 HD PORsO.255 10. K= 138 HD P0Rs0.28 0.20 0.40 0 60

W A T E R S A T U R A T I O N

(F R A C .)

0 80 1.00

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C A P I L L A R Y PRESSURE C U R V E

POR. P L A T E M E TH . A I R —B R IN E SYST.

I— l ^

CO

K = 199 HD P0R=O.261 Oh 0.60 0.20 0.40 ___ ___

W A T E R S A T U R A T I O N

(F R A C .)

0 8 0 1.00 0.00

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3. FLUID PROPERTIES

Data from the reservoir fluid study (PVT analysis) p e r fo r me d on fluid sa mpl es from well Andalucia Sur-1, c om p l e t e d in "D" sand, using the r e c o m b i n a t i o n sa mp li ng

technique were available for this study. Results are

presented in Tables 3 and 4. The smoothing of laboratory

data was accomplished by using the Y function and the best fitting line was determined by using the mean least-squares

as recommended by Amyx, Bass and Whiting(14). The bubble

point pressure was found to be 68 psig with a solution gas-

oil ratio of 58 scf/stb. The oil density at the bubble

point was 0.8828 gm/ cc (40.5°API) and the density of

residual oil was 0.856 gm/cc (33.8°API).

For the simulation study, it was assumed that the same kind of oil was present in all five sands. Water properties were calculated by the si mu l at or using actual values for density and compressibility at reservoir conditions.

Likewise, gas p roperties were calculated by the

simulator. The specific gravity of the gas was assumed to

be 0.7, since the value of 1.401 from the PVT data could not

be handled by the simulator. (It fell outside the range for calculation purposes.)

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4. COMPLETION METHOD

C om p le t io n reports were furnished by the operating

company. The type of completion is commingled production

from the different zones. Details regarding in which zones

the wells are c om p l e t e d are provided in the production history section and presented in Table 5.

5. PRODUCTION HISTORY

Daily oil and water production rates for each well from the beginning through December, 1982, are presented in

Figures 27 through 40. Total daily oil and water production

for the field are presented in Figure 41.

It is important to say that the production water as

r e p o r t e d by the o p e r a t i n g c o m p a n y is i n f e r r e d f r o m prod uct ion tests done once or twice each m onth for each

well. Cumulative oil and water production for the field are

shown in Figure 42.

Following is a brief summary of the production history on a well-by-well basis.

Well A S -1

Completed in the "D” sand, its cumulative oil and water

production values through December, 1982, are 225,648 STB

and 304 STB respectively. The current pumping fluid level

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TABLE 5

WELL COMPLETIONS

HELL A SAND 8 SAND C SAND D SANO E SAND

A S - 1 NO NO NO YES M

RS-2 YES YES YES YES M

AS-U YES YES YES m M

RS-5 YES (♦> YES YES M M

AS-6 YES YES (♦> NO YES (♦) YES C+J

AS-7 NO NO NO YES NO

AS-10 YES YES YES YES M

A S - 11 NO NO NO YES YES

AS-12 NO YES YES (♦) M M

A S - 13 NO YES YES M M

A S - 17 YES (♦) YES (♦) YES M M

A S - 18 NO YES M M M

AS-20 (n n) NO YES NO H M

AS-22 YES YES NO YES M

M M M M M M M M M M

REMARKS - n - SAND DOES NOT EXIST IN THIS HELL (♦) - OPENEO BUT ISOLATED (HIGH HATER-CUT)

* * - HELL IN SHUT-IN STATUS DUE TO LOH PRODUCTIVITY

M

(58)

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SUR

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