Jurassic. LaVilla. Los Ranchos. El Fausto. Paleocene. Eocene. Post-Miocene. La Puerta. Lagunillas. Misoa ... PDVSA's "Tercera Ronda" bid in December 1997.
PART 1 NEW GEOLOGIC MODEL FOR THE CRETACEOUS RESERVOIR OF THE LA CONCEPCIÓ N MATURE OIL FIELD, MARACAIBO BASIN, VENEZUELA Denis MARCHAL, Elmer FERRO and Enrique PERALTA Pérez Companc de Venezuela S.A.
Eastern Venezuela Basin
n oco
ar am
Maracaibo Basin
C iudad B oliva r
ang
B Merida mountains
a Fa
We established a new structural model based on faulted en echelon folds. It exhibits a set of structures caused by strike-slip to w rench tectonics processes. The field is mainly composed of tw o dextral transpressive relay zones striking NE-SW, forming up-lifted blocks bounded by opposite reverse faults w hich curve tow ards each other. The presence of such a relay zone explains the changing dip of folds along the general strike of the structures, and the various fracture directions. The productive fractures strike NW-SE and seem to be linked to contemporary tectonic stress acting in this part of the Maracaibo basin.
ul t
The regional tectonostratigraphic setting for the Cretaceous in the Maracaibo Basin is one of a pass i ve m a r g i n s i t t i n g o n t h e G u a y a n a S h i e l d (Audemard, 1991). The geological history of the Maracaibo basin is closely related to the strike-slip m o ve m e n t o f t h e C a r i b e a n p l a t e , i n d u c i n g transpressional deformation during the andean tectonic event (early Tertiary). Other contributors to the development of the basin are the formation of the Perija mountains (Oligo-M iocene) and Mérida andean mountains (Plio-Pleistocene).
0
50
The interaction betw een these multiple tectonic events generated the foredeep basin in the w estern Venezuela (Audemard & Lugo 1996). These events, associated to the sea level variations and the great amount of sediment available, originated a very thick sedimentary section, w hich suffered various cycles of thermal maturation, forming numerous petrol eum fi el ds such as those i n the La Concepción area.
100 km
Location map - La Concepción Area Modified from http://www.npagroup.com/dataservices/imagegallery/colo_ven.html
LITHOLOGY
ARENISCAS SUP.
Average depht of Fm . Tops
PTA. GORDA
RAM ILLETE
1,8 km
Sandstones intercalated with shales and lignites
F. MISOA ARENISCAS INF. F. GUASARE
7200’
8000’
Shaly claystones intercalated with sandstones Intercalated sandstones and claystones Limestones (Mudstone and Grainstone) Sandstones
Shales / Silty claystones
SOCUY LA LUNA
MARACA
LISURE
Limestones, calcarenites dolomitized fractured limestones 11700’
R. NEGRO
Pm - Tr
BASEMENT
11750’
Conglomerates Gneiss - schist
“C”
Eocene
“C” ji l Tru
Cretaceous
4
Basement 10 km
5
?? ??
lo
Later, acquisition and processing of 376 km 2 of recently acquired 3D post-stack time migrated seismic w as completed at the end of 2000. The corresponding 3D seismic interpretation tied to w ell log, core analysis, pressure tests, and image / PLT logs are being used to build an integrated model.
6
AGE
Shales (seal)
Limestones
Sandstones / Conglomerates
Source Rock
Pleistocene Pliocene
N West Mérida W Falcón
N
Miocene Oligocene
Sandstone/Seal couples From WEC 1997, modified from Parnaud et al 1995
TECTONOSEQUENCES
TECTONIC SETTING
Central
ACTIVE MARGIN
Carúpano E
W
Maracaibo
East Orinoco
3D Seismic Survey Programs
N S
Rifts and inversions
Venezuelan Foredeeps
N S
Atlantic type facing north
Paleocene
S
Foredeep
Maturín
Guárico
Barinas
Eocene
S
E
Perijá
Maracaibo Basin
N
Cretaceous
PASSIV E M ARGIN
Jurassic
RIFT
Triassic Paleozoic
PRE-RIFT
Back-arc rifts Peneplaned Paleozoic folded-belts
M odified from Audemard and Lugo, 1996
Schematical Cross-Section NW
SE
Stratigraphy
Structure
10000’ 10100’ 10400’
APON
SOURCE ROCK
“B” Misoa
In La Concepción Field, the basement consists of Permo-Triassic granites and schists. The base of the Cretaceous is composed by quartzfeldspar conglomerates and sandstones of the Rio Negro Formation. Overlying this formation are the Cogollo Group and La Luna Formation. The Cogollo Group is composed from bottom to top by the Apon, Lisure, and M araca Formations. The Apon Formation consists of limestone, locally dolomitized, intercalated w ith shales. The Lisure and Maraca formations are made of interbedded bioclastic limestones. La Luna Formation, considered the main source rock, represents the maximum flooding member of the area and consist of black shales and limestones. Capping La Luna Formation is a thin section of marine carbonates, named Socuy M ember, composed by hard limestones and calcareous shales. This member is overlain by the Colon-Mito Juan Formation composed by thick black shales that constitutes the seal for the reservoir.
2500’ 2700’
25 00
PALEOCENE
OIL
Sandstones intercalated with shales
3500’
F. COLON/ Mito Juan
OIL RESERVOIRS FLUID SUMMARY API : 35 Initial Pressure : 4,800 psi @ 10,000 ft. Bubble Point : 3,500 psi Rsi (scf/Bbl) : 834 Viscosity : 0.9 cp Temperature : 240 F Current Pressure : 3900 psi @ 10,000’ft. Cum. @12/01 (MMbbl) 78.53
SERIES
Gr. COGOLLO
OIL RESERVOIRS PARAMETERS SUMMARY Average TD : 12,000 ft. Drive mechanism : Solution Gas Trap type : Structural Productive Unit : Cogollo Group Net thickness (feet) : 400-800 Porosity (%) : 3-9% (Matrix) Permeability (md) : naturally fractured
SYST.
EOCENE
FIELD SUMMARY Field Surface: 248 km2 Drilled Wells: 16 before Perez Companc de Venezuela SA (PCSA) 12 Cretaceous PCSA wells Total: 28 Cretaceous wells (Jan - 02)
UPPER
There is special interest in developing the Cretaceous limestones to their maximum potential due to their large production rates per w ell. The data appears to confirm that fault-associated fractures seem to be the fundamental oil conduits. How ever, their identification and targeting can prove to be a highly eluding task. Many fractures fall below the seismic resolution, and w ell information is too discrete to be the only tool to rely on. In spite of these difficulties, the combination of 3D seismic and w ell information can significantly optimize new drilling locations w hen above-seismic-resolution fractures are sought.
3
GEOLOGICAL SETTING
TYPE WELL
LOWER
The Cretaceous field w as discovered in 1948. Perez Companc received the field w ith a daily oil production of 2,650 bopd, w ith 1,878 barrels coming from 9 w ells in the Cretaceous reservoir. In about four years of operation, and through reactivations and drilling of 4 new Cretaceous w ells and 6 sidetracks, the company increased production by about 7,000 bopd. This successful drilling campaign designed possible using w ell correlations and 2D seismic interpretation. The interpretation of the recently acquired 3D seismic boosted up the success in optimizing the new drilling locations.
General Information - La Concepción Area
TERTIARY
La Concepcion is a mature oilfield located in the Maracaibo Basin that initiated activities in 1924 (Venezuela Oil Consortium Ltd. - Shell) w ith the discovery of the Eocene siliciclastic reservoir (Misoa Formation). Thereafter, it continued to be operated by PDV SA, prior to being aw arded to Perez Companc through PDVSA's "Tercera Ronda" bid in December 1997.
Stratigraphic Column
CRETACEOUS
INTRODUCTION
“B” Misoa
Paleocene
Initially, the data included 1,100 km of 2D seismic data and w ell log information from 13 w ells drilled in the Cretaceous reservoirs. In a first step, most of the seismic lines w ere successfully reprocessed, greatly improving the seismic image and therefore the quality of the interpretation.
Paují La Puerta Lagunillas
Miocene
Trujillo mountains E
Bachaquero fault
Post-Miocene
S
Build-up tests exhibit a short radial flow period follow ed by bilinear flow w hich can be attributed to the presence of microfissures near the w ell that are connected to major fractures distant from the w ell. Analysis of geologic and production data suggests the spatial distribution of productive fracture zones is controlled by a combination of tectonics and stratigraphy. The new geologic model allow ed us to increase reserves by 100 % .
o
lt Fau
Lagunillas
c
M aracaibo Lake
Atlantic Ocean
Lama Icotea High
Urdañeta
si
M aturín
Perija mountains
La Concepción
Perijá W mountains 0 La Los Vill a Ra n 1 cho s E l Fa us to 2
DATA
as
C aracas M ara caibo
La Concepción field is located in the northw estern part of a triangular structural block delimited by major basement involved w rench fault systems, respectively the Oca fault to the north, the Bucaramanga fault to the SW, and the Bocono fault to the SE.
Regional Cross-section
Ju r
O ca Fau lt
Caribbean Sea
B uc
Discovered in 1948, the Cretaceous reservoir of La Concepción field (Maracaibo basin) has produced 68 MMbbls of oil from 16 w ells up until 1997. In 1998 a w ork program w as undertaken, resulting in increased oil rates (2,000 to 17,000 bopd). The main reservoir is composed of an 1,100 ft thick section of Cretaceous carbonate rocks. N ew data (3D seismic, new boreholes, 900 ft of one w ell core, image and production logs, litho-biostratigraphic data, etc) w as used in updated field studies.
D
Two Way Time, (s)
ABSTRACT
REGIONAL STRUCTURAL FRAMEWORK
Composite Satellite Picture
La Concepción Area
The structural style of the La Concepción field corresponds principally to a deformation induced by w rench faulting involving high angle basement faults. The Cretaceous section is mainly affected by localized major reverse faults producing pop-ups. The overlying shales of the Mito-Juan Formation act as a ductile layer, responsible for the partitioning of the deformation betw een the Cretaceous and the Tertiary section. The Tertiary section is characterized by reverse-fault-limited folds w here normal faulting is common.
MIOCENE
LEG EN D Field Boundary City (La Concepción) Boundary 3D Seism ic Survey Program - Focused on Cretaceous (201 km 2) 3D Seism ic Survey Program - Focused on Cretaceous+ Eocene (175 km2)
UPPER EOCENE
Comparison Between 2D and 3D LOWER EOCENE
Guasare PALEOCENE Mito Juan / Colon La Luna Cogollo
CRETACEOUS
Río Negro 2000 m
BASEMENT
2000 m
Depth Cross-Sections in the Three Main Structures
A NEW IMAGE OF THE STRUCTURES GENERAL TRENDS The structural geology follows the regional trends observed in several oil fields in the M aracaibo basin (Nelson et al., 2000). NE-SW oriented reverse faults dom inate the structural fram ework, form ing folds as they dissipate upwards. Subordinate faults with reverse and, in less proportion, norm al offsets affect the main structures. Am ong these faults, the NW-SE oriented norm al faults are the most conspicuous.
FAULT-ASSOCIATED FRACTURES Our main objective is to cross the fractures network associated to the faults. To help us detect and delineate faults in the reservoir, we use the standard seismic display (am plitude) as w ell as seism ic attributes (e.g., coherency). Since the acquisition of the 3D seism ic, we plan each well to cross a "seism ically visible" fault in order to cross the associated fracture network. Through the com bination of PLT and Acoustic Image logs, we have observed that the m ain well production comes from clearly im aged open fracture zones, frequently oriented NW-SE.
THREE MAIN STRUCTURES Because the Top Socuy M ember (Top Cretaceous Limestones) makes a strong and continuous seism ic reflection, it was chosen as a level of reference. Interpretation of the 3D seism ic on the top of Socuy reveals three main structures in the field, named "Cretaceous South", "Cretaceous North" and "Cretaceous Los Lanudos".
NE view
Cretaceous Los Lanudos
Cretaceous North
The "Cretaceous South" and "Cretaceous North" structures are flower structures, each of them composed by three sub-structures: (1) the NW flank dipping to the NW, (2) the central pop-up planar or dipping gently to the SE and, (3) the SE flank dipping to the SE. In plan view, each central pop-up is bounded by tw o m ajor opposite reverse faults (maxim um throw around 2000 ft.) which curve toward each other and get connected. This feature is especially visible for the "Cretaceous North" structure. Each sub-structure is affected by subsidiary faults (reverse and normal faults). These two pop-up structures are separated by a depressed area.
Cretaceous South
The "Cretaceous Los Lanudos" structure is limited to the SE by a m ajor reverse fault, and to the west by a m ajor strike-slip fault zone. These features define a faulted "extruded" m onoc linal s tructure dipping gently to the NN W. The m ain reverse fault displays a smaller offset (m aximum throw around 1000 ft.) than those m ajor faults of the "Cretaceous South" and "Cretaceous North" structures. This block is affected m ainly by norm al secondary faults.
Cretaceous Los Lanudos
NW view
Structural Map At The Top Cretaceous Limestone do u n La s o L s u ceo a t Cre
s
rth o s N u o ce a t Cre
Cretaceous North
Cretaceous South
3D view of the Top Cretaceous of La Concepción Field (coherency attribute texture mapping)
Well-A h Cretaceous Sout
Well-A
Well-G
Fault
W ell-G
Fault
K su r-9 C -30 7 (K su r-8)
Reverse Fault Well-A
Vertical Fault
Well-G
Strike-slip Fault
Well-A
Norm al Fault Well-A
Well-G
“in study” Fault
Well-A Well-G
C O HE R E N C Y
Well-G
FRACTURE ORIENTATIONS vs PRESENT-DAY EARTH STRESS FIELD We have compiled and plotted fracture and breakout data. This information comes from different historic sources such as Acoustic Image logs and Caliper logs. Image logs provides fracture characterization (e.g., geometry, direction, aperture) as well as breakout direction. From the Caliper log, we obtained in some cases information about the possible breakout direction.
World Stress Map Maracaibo basin
The analysis of the direction of the open to semi-open fractures shows a dominant NW-SE orientation in most of the wells. Different orientation of the fractures in some wells can be linked directly to the influence of the associated fault. In this case, the resulting fracture direction parallels the fault plane strike. The comparison of the Image log with the core fracture analysis (Well-I) indicates that Acoustic Image logs are mainly sensitive to open and semi-open fractures. The closed ones are barely or never seen.
La Concepción Field
The breakout direction analysis performed in the wells with available logs shows that the maximum borehole-perpendicular component of present-day stress is predominantly oriented NW-SE. Because this direction is predominant in the whole field, we assume that the present-day minimum principal compressive stress is oriented NE-SW. Preliminary investigation of the World Stress Map (WSM) database shows that the western part of the Maracaibo basin is subjected to NE-SW extension. This observation suggests that the dominant NW-SE orientation of the open fractures in the La Concepción field may be directly linked to the direction and nature of the extensional present-day stress field acting in the Maracaibo basin.
Projection: Mercator
Well-F
World Stress Map Rel. 2000-1
Fracture Azim uth Depth Interval (11033‘-11260‘) N
Depth Interval (11260-12335‘) N
n = 29
0
O
N
0
O
38%
S
Depth Interval (12335‘-12445‘)
n = 194
N
0
O
14%
S
Depth Interval (12445‘-12482‘)
n=8
0
O
50%
S
n = 21
19%
S
B reakouts P erpendicular O rientation
Well-Q
Depth Interval (11033‘-12482‘) N
Fracture Az im uth
n = 286
Depth Interval La Luna (10777‘-11003‘) N
Depth Interval Maraca (11003‘-11279‘) N
n=3
Depth Interval Lisure (11279‘-11888‘) N
n =5
Depth Interval Apon (11888‘-11959‘) N
n=2
n=3
0
O
0
O
0
O
0
O
0
O
29%
S
100%
S
60%
S
100%
S
100%
S
B reakouts P erpendi cular O rientation Depth Interval La Luna (10777‘-11003‘) N
Depth Interval Maraca (11003‘-11279‘) N
n=1
Depth Interval Lisure (11279‘-11888‘) N
n = 44
Depth Interval Apon (11888‘-11959‘) N
n = 71
n = 14
Well-O O pen Fracture A zim uth N
Break outs Perpendicular O rientation N
n = 160
0
O
200%
S 0
O
0
O
0
O
0
O
n = 734
S
39%
S
38%
S
0
O
Well-P B reakouts P erpendicular O rientation Depth Interval (9650‘-11100’) S
13%
S
31%
N
n = 19
Note: Datas from the Guasare Unit
0
O
Well-N Fracture Az im uth S
Depth Interval (10386‘-10525‘) N
n = 73
B reakouts P erpendi cular O rientation
C- 257 0
O
Depth Interval (9800‘-10650’) N
27%
S
Well-M
S
75%
Fra cture A zim uth Depth Interval (10824‘-13452’)
Fracture Azim uth
B rea kouts P erpendic ul ar O rientation
Depth Interval ( 11260‘-13164‘)
Depth Interval (11260‘-13164‘)
N
Well-G
O
N
n = 37
0
Structural Map In Depth CRETACEOUS - TOP SOCUY La Concepción Field Reverse Fault Vertical Fault
Well-R
N NE n = 68
n=4
0
O
N
36%
Well-D
n = 418
Strike-slip Fault Normal Fault
Fracture Azim uth Open Fractures Depth Interval (10200‘-12216’) N
Semi-Open Fractures Depth Interval (10200‘-12216’)
0
O
0
O
N
n = 52
n = 69
SSW S
0
O
0
O
“in study” Fault
16%
19%
S
S
17%
Well-I S
S
21%
Fracture A zim uth O n Im age-Log
Fracture Az im uth O n C ore
B reakouts P erpendicular O rientation
Depth Interval (10265‘-11646‘)
Depth Interval (10380‘-11558’)
Depth Interval (10265-11646‘)
16%
N
N
n = 105
N n = 84
n = 758
Well-L Fracture Azim uth
Breakouts P erpendicular O ri entation
Depth Interval (10821‘-12234’)
Depth Interval (10821‘-12234’)
N
n = 68
0
O
0
O
0
O
n = 452 N
0
O
O pen and S em i-O pen S
15%
S
0
O
7%
Well-B S
16%
S
24%
Fracture Azi m uth Depth Interval (9922‘-11400’) N
0
O
N
Breakouts P erpendicular O rientation
Depth Interval (10020‘-10530’)
Depth Interval (10020‘-10530’) N
n = 113
0
O
S
Depth Interval (9922‘-12410’) N
n = xx
n = 98
0
O
0
O
n = 113
SE 0
O
S
27%
13%
Open and Semi-Open Fracture Orientations and Breakouts Directions
NW
Frac ture A zim uth N
n = 78
28%
B rea kouts P erpendic ula r O rientation
Depth Interval (10400‘-11029’)
Well-K
N
16%
S
Well-J B reakouts P erpendicular O rientation
Depth Interval (11400‘-12410‘)
n = 140
S
0
O
S
27%
S
x%
S
(compilation of datasets from the analysis of Acoustic Image Logs and Caliper Logs)
39%
The heterogeneity of the datasets presented on this map depends on the drilling and well-log acquisition conditions.
43%
Adapted from Mueller et al., 2000