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Campos Basin Tertiary Reservoirs of Barracuda and Caratinga Fields: DevelopmentStrategy and Main Reservoir Management IssuesM.M. Alves, W.B. Maciel, L.C. Reis, M.S. dos Santos Braga, and J.J. Marques, Petrobras

Copyright 2005, Offshore Technology Conference

This paper was prepared for presentation at the 2005 Offshore Technology Conference held inHouston, TX, U.S.A., 25 May 2005.

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Abst ractBarracuda and Caratinga fields, with 1.1 GBOE reserves, areone of the main deep-water discoveries of the late 80s andearly 90s in Campos Basin, southeast of Brazil. At that time,as it is nowadays, the economic feasibility of deep-waterdevelopment projects was very much dependent on the high

productivity of the wells. In despite of the quite goodpetrophysical properties, the thickness of the reservoirs did notprovide enough productivity to make such projects feasible.The horizontal wells technology came over to improveproductivity indexes, making possible the development of

these giant fields. The high quality of the seismic data wouldhelp the positioning and the geosteering of the horizontalwells.

The reservoirs of the fields are sandstone turbiditesand have quite distinct depositional styles and structuralfeatures. Hence, different well patterns and completion

strategy were used for each one. The reserves will be producedby 32 wells and, to maintain the reservoir pressure, 22 water

injection wells will be used.

To reduce the reservoir uncertainty, a productionanticipation project -Pilot Project- was planned. Elevenexploratory wells were completed on the main reservoir units

and blocks. These would permit the observation of thereservoir behavior and the checking of the reservoirs hydraulic

compartmentalization, once the development wells weredrilled.

At the end of the Drilling Phase, the results arehonouring the project initial assumptions. The Original Oil in

Place as well as the productivity / injectivity indexes wereconfirmed. The reservoir pressure dynamic data showed that

the assumed hydraulic model to set the development plan wasvery close to the verified one, regarding the horizontal and

vertical connectivities.

This paper focuses on the key factors that enabled asuccessful project implementation and on the strategy used for

the reservoir development of these deep-water offshore fields.

Introduction Barracuda and Caratinga deep-water giant oil fields are

located on the south-central part of Campos Basin, southeastof Brazil, about 90 km from the Rio de Janeiro State coast, inwater depths of 600 to 1,100 meters for Barracuda and 850 to

1,350 meters for Caratinga (Fig. 1). The reservoir depths rangefrom 2400 to 3200 m.

These fields comprise OOEIP volumes of 4.2 GBOEand reserves of 1.1 GBOER within high quality siliciclasticturbidite reservoirs from the Tertiary. The average gravity ofthe oil ranges from 20 to 26 API.

From the total reserves, about 70% of them are inBarracuda and 30% in Caratinga Field. Barracuda Fieldreserves are divided in an Oligocene / Miocene reservoir,called MRL330 and an Eocene / Paleocene reservoir, called

ENCOBR. On the other hand, most of Caratinga field reserves(about 83%) are within a Lower Oligocene reservoir called

CRT100. The rest of Caratinga Field reserves are withinOligocene/Miocene, MRL330 and Oligocene reservoirs,MRL600 and MRL700.

Barracuda Field was discovered in 1989 andCaratinga, the first Campos Basin field discovered using 3Dseismic, was discovered in 1994. In 1997, using exploratory

wells already drilled to produce from the main blocks, a PilotProduction Project started, through the FPSO P-34 (Fig. 2).

The pilot aimed the reduction of reservoir and surfacefacilities uncertainties. The drilling of the Definitive Project(Fig. 3) development wells started in 1999 and, in 2004, the

last development well was completed. In December the 21st,of 2004, the first well started the production. Two 150,000bbl/day oil capacity FPSOs, P-43 and P-48, will collect the

production from both fields. The production peak will bereached in May and June of 2005, for Barracuda andCaratinga, respectively. See in this volume (Costa Filho, 2005)more details about the two production units.

A further development phase has been studied aimingthe production of a fourth block of Barracuda MRL330

reservoir .

Development StrategyThe development strategy for projects related to deep-water oil

accumulations requires a different approach than the

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The Barracuda ENCOBR reservoir is confined to salttectonics controlled, NW-N oriented, elongated troughs (Fig.6). This troughs are tipically 2-3 kilometers wide, several

kilometers long and are filled with up to a few hundred metersof sand rich deposits. The lowest and thickest parts of thetroughs are water saturated. This sand rich sequences wereemplaced by gravitational turbidite flows that, after

deposition, undertook variable degrees of reworking andredeposition by botton-currents. The highest reservoir quality

and reserves are within the Middle Eocene sequences.The Caratinga Field main reservoir, CRT100 is a

submarine fan formed by two main domains: the amalgamatedchannels and the spill-over lobes. The depositional settingcreated very distinct depositional arquitecture, when thisreservoir is compared with Bararacuda Field MRL330

reservoir. This relatively thin, up to 40 m thick sand richsuccession, was further cut by a NW, early Oligocenesubmarine canyon that segmented it in two blocks. Internally,the CRT100 blocks are faulted mainly by low offset NWoriented faults. The Oligocene canyon was further filled by

several 3rd order stratigraphic sequences, that contains theOligocene MRL700, MRL600 and MRL330 reservoirs (Fig.

7).At both fields the MRL and CRT reservoirs present

average reservoir (net) thickness of about 15-25 m andtipically darci permeabilities. The ENCOBR reservoir showshigher thickness but a few hundred of milidarciespermeabilities. These characteristics of the reservoirs made the

economic feasibility very dependent on the wells PIincrement, provided by horizontal wells technology.

Geological ModellingA huge effort was dispended during and after the appraisal

phase in order to better characterize and reduce the geologicaluncertainties of the development project (Assis et al., 1998).With the Pilot Production Project as well as the new seimicacquisition and the development wells drilling, more detailedreservoir information came up, providing more accuracy andconfidence to the reservoir models built.

The consistent reservoir 3D modeling has been a key

input on the success of the implementation of the developmentproject. To consistently model a reservoir, particularly the

ones subjected to water flooding trough injector wells, a goodgeological conceptual model is very important. To do that, theavailability of a good quality seismic data, in consonance witha set of relevant logs, representative cores and pressure data,

along with the multidisplinary team work of sedimentologist,stratigrapher, structural geologist, geophysicist and

development geologist, among others, are very important. Thezoning of the reservoirs into stratigraphic sequences,organized in a logical hierarquical order, the definition of thedominant facies associations and its respective arquitectural

elements and their conceptual spatial distribution are crucialsteps to build the reservoir model (Fig. 8). The further

petrophysical properties assignment must be in accordancewith that conceptual model. In addition to that, particularlyfor the Oligocene reservoirs, the stochastic 3D simulation wasalways performed with a strong seismic constraint for the

inter-well space (Fig. 9).

The new wells, along with the higher resolutionseismic data, brought up new insights and details for thegeological conceptual models. Besides, there was no surprise

regarding the reservoir petrophysic properties, either from thelogs, cores or well testing.

The new seismic with the much better arealresolution, has improved a lot the arquitectural elements

imaging, mainly for the Oligocene reservoirs, as well as theimaging of the faults, that became much more clear and

accurate. Furthermore, the horizontal well placing andgeosteering processes were also enhanced by the improvementof the quality of the seimic data available.

Faults geometries and transmissibilities, werecarefully modeled, sometimes using specialized software to dothat. The new seismic improved the fault zones geometric

characterization. The new pressure data, provided by theproduction and development wells pressure measurements,gave important insights about fault plane transmissibilities.

The understanding of the fluid contacts and the oilquality distribution, the conceptual model for that and the

consequent volumetrics of each portion of the reservoir isanother key input to the geological model. It, obviously, can

have a great impact on the OOIP estimates. The developmentwells added substantial information on this subject. The MRLand CRT reservoirs have no associated aquifer while theENCOBR reservoir has some associated water volume.Perched oil/water contacts are not uncommon, associated withreservoir base closure, sometimes combined with faults or

erosional features filled with sealing material. These localwater pools are usually small in volume and will havenegligible effect in terms of energy maintenance. Tarmatlayers observed within the ENCOBR Reservoir have beenmodeled as baffles rather than barriers, since it can be

observed with pressure data, production history and welltesting, that they are not continuous.

The development well testing and oil samplingshowed different oil quality distribution patterns for each oneof the main reservoirs. The MRL330 reservoir of BarracudaField, showed no significant oil quality variation within thethree developed blocks. The forth MRL330 Block shows a

lower gravity oil. The ENCOBR Reservoir did not showsignificant oil variation. The CRT100 Reservoir showed an oil

gravity / viscosity variation as a function of the depth.

Reservoir Flow ModelTo set up the development plan of the two fields, numerical

flow model for each reservoir was built and the number andthe position of the wells was fixed. Nevertheless, data from a

new seismic acquisition and dynamic information from thePilot System have allowed significant improvements in thegeological and flow models. In addition, new core and fluidlab analysis have been carried out. The models could still be

enhanced by making use of data from the first group of wellsdrilled. Pressure data from WFT and DST from these wells

have confirmed the isolation among the main blocks and, moreimportant, have showed the very good horizontal and verticalcommunication inside them (Fig. 10).

The new flow model was used for some adjustments

in the well positions. In the former model, the choice of thedirection of the horizontal wells must respect the criteria of the

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minimum net pay due to drilling control limitations. However,the quality of the new seismic data allowed a better controland, thus, some wells had their main direction modified in

order to enhance the sweep efficiency. The new model hasalso permitted some changes in the well pattern, for instance, awell initially planned to inject in the MRL330 Reservoir wasreplaced by a water injector in the western area of the CRT100

Reservoir which has significantly improve the sweep of thisreservoir. Figure 11 shows the final pattern for the main

reservoirs of the two fields.By taking into account the heterogeneities (baffles

and the spatial distribution of porosity, permeability and initialsaturations) the new model became more complex and reliableencouraging new development alternatives. Beyond theordinary approach using finite differential simulators,

complementary studies have been carried out as streamlinessimulation (Fig. 12), fault transmissibility quantification, riskanalysis, Value of Information, etc. As a result of thesestudies, further than the changes in the development planmentioned before, infill drilling wells are planned in the

portfolio of the Caratinga field. For example, one well in theCRT100 Reservoir aims to recover the oil by-passed by water

due to a possible baffle. The existence of the unswept zonemight be confirmed by 4D Seismic or by the results frominjection monitoring using tracers.

Well Planning, Geosteering and Reservoir EvaluationThe success acchieved with the special wells drilling is mainly

a result of the following factors:1) Drilling, reservoirs and geological operation teams

integration;2) Availability of softwares to support planning and

geosteering of the horizontal wells drilling in real time;

3) Use of pilot wells to obtain reservoir data;4) Availability of distinct tools for the reservoirs data

acquisition.The drilling, reservoir and geological operation teams

integration was essential to the Projects success. Thisintegration allowed a common understanding of objectives andlimitation factors of each horizontal well project. Thus, the

reservoir team could transmit to the other teams the geologicalcharacteristics of the area to be drilled, as well as the way that

it should be drilled. On the other hand, the drilling team canclarify the possible limitations to the trajectory proposed bythe reservoir one, while the geological operation team mayproperly monitor the wells drilling.

The teams communication was favoured by somefactors, as the physical closeness, the existence of a commun

database, the use of a 3D visualization room and supportingsoftwares and the real time data availability. The real timedrilling follow up allowed strategic decisions to be takenquickly, as the optimization of the net-thickness by well

trajectory changing (Fig. 13) or even the abandonment of thedrilled leg and its further deviation.

Another important topic for the Project were the pilotwells. They aimed to collect reservoir data and supporthorizontal well drilling. They also intended to evaluate theseismic accuracy in the area. For each pilot well a data

collecting program was established, in order to evaluate fluidand rocks characteristics and pressure values.

This program included logging, wireline formation tests andcoring.

After all, the horizontal wells confirmed the success

of the methodology applied as can be seen when comparingthe predicted and the reached values of the horizontalextension and the porous horizontal extension (Net), (Table 1).

Table 1: Main figures of the horizontal wells drillingcampaign.

Number of Horizontal Wells 33

Total Predicted Horizontal Extension (m) 22756.0

Total Reached Horizontal Extension (m) 22483.0

Reached / Predicted. 0.99

Total Predicted Net Extension (m) 14952.3

Total Reached Net Extension (m) 13411.6

Reached / Predicted. 0.90

This success was essential in terms of well

capacities. The original development plan was elaborated

considering, in the flow model, that the productivity indexwould be equal to 70 m3/day/bar for all the wells. The wellsbehavior, specially for the first years of production, is highlydependent on this parameter. For this reason, the achievementof the estimatives was critical for the Projects success.

After all wells drilling and testing, it can beconsidered that the results were pretty close to the predicted.The Figure 14 shows a histogram of the the observedproductivity and the injectivity indexes. It can be observedthat, in some cases, the indexes were bellow the expectations,but they were compensated by other very expressive values.

This success was a result of two main factors: the drillingeficciency that obtained porous extentions (net-pay) according

the planned and the completion efficiency, that did not reducethe well capacity.

One of the initial issues in the drilling phaseconcerned the evaluation of the horizontal wells. The

intercalations in the reservoir have impaired the evaluation ofthe vertical permeability as well the estimation of the

production inflow profile. A new evaluation strategy wasestablished including the production logging tools and the useof novel test interpretation methods. It has allowed asystematic learning which improved the confidence in the well

tests results and the reduction on the uncertainties with respectto the reservoir parameters.

Human ResourcesThe unavailability of trained and prepared human resources inthe last years was a problem for the Projects implementation.

The available teams presented a desirable profile, with around10 years of experience in the activitity, but the number ofpeople was not enough to attend the demand.

In order to solve this problem, some actions wereplanned:

Use of some service companies for theexecution of some operational jobs;

Use no experienced employess under senior

professional supervision;

Use of new technologies that helped toimprove the multidisciplinary team

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integration making easier and faster dataexchange;

On the Project implementation, which six rigs should

be operating at the same time, these strategies enabled favoredconditions to fast and suitable decision taking.

The aim of the reservoirs team, with a reducednumber of employees, was to avoid the mistakes occurrence in

the wells drilling activities, which cause financial impacts andconsequently, increase the teams stress.

The empowerment and the subsequent increase of theteam members responsibilities allowed a meaningfulperformance improvement of the group. Small teams canmultiply the working ability when managed in a participativeenvironment.

In order to support this process with a strong

multidisciplinary component, it was used a 3D visualizationenvironment. This resource allowed the sharing of severalmodels (seismic, geologic and flow model) information andthe wells projects. These tools clarified the generalunderstanding of the problems, supporting faster and more

efficient operational solutions.The integrated efforts of the project teams have added

value to the wells detailing and execution. This performanceguaranteed the internal and external project milestonesaccomplishment, according to the planned costs and dates.

ConclusionsThe development of deep-water giant fields requires high flowrates wells and pressure maintenance. In this project, specialwells were used to achieve the former requirement and, to the

latter requirement, water injection since the Definitive Projectproduction start up were used.

In order to reduce uncertainties, a Pilot Production

Project was carried out. Data collection was maximized on theearly phases of the project. It was also important thepartnerships with services companies as well as relevant new

technology application.Reservoir focused seismic acquisition and processing

were among the very important data that allowed the successof the project implementation. Yet, the 3D visualization roomswere key technological investment, very useful to sharemultidisciplinary visions and opinions.

The intensive use of the seismic data along with theconsistent integration of the well data and advanced geologicalconcepts made the numerical reservoir models quite accuratein the representation of the reservoir relevant characteristics.

It is of fundamental importance that the flow model isalways updated with the best reservoir knowledge of the

multidisciplinary reservoir group. The application of the basicreservoir engineering concepts along with the extensive use ofinnovative technology either to handle the reservoir data or toact into the reservoir were a key factor to the projectobjectives achievement..

A sounding horizontal well planning, within a

multidisciplinary team, as well as the choice of the rightavailable drilling and log tools and a careful geosteeringduring the drilling are among the key points to achieve successin the development plan implementation.

The drilling phase implementation was done onschedule and on budget. This was credited to the high qualityof the work carried out previous to the field development,

associated to a result-focused management and the integrationof teams and processes.

References

1. Costa Filho, F.H., Barracuda & Caratinga FPSOsDesign. OTC 17058, Offshore Technology Conference.Houston, Texas, 2005.

2. Motta Filho, B.R., S.J. Alves Neto & Reis,L.C.

Optimizing the Barracuda and Caratinga Subsea WellDesign to the Improve Oil production Curve. OTC 17051,

Offshore Technology Conference. Houston, Texas, 2005

3. Rovina, P.S. & G.R. Borin, Drilling and Completion

How to accomplish CAPEX and schedule managing up tosix rigs simultaneously. OTC 17055, Offshore Technology

Conference. Houston, Texas, 2005.

4. Bruhn, C.H.L., J.A.T.Gomes, C. Del Lucchese & P.R.S.Johann. Campos Basin: reservoir characterization and

management Historical overview and future challenges. ,OTC15220, Offshore Technology Conference, Houston,

Texas, 2003.

5. Guardado, L.R., L.A.P. Gamboa & C.F. Lucchesi,Petroleum geology of the Campos basin, Brazil: a model

for a producing Atlantic-type basin, in J.D.Edwards andP.A. Santagrossi, eds., Divergent/passive margin basins,1990.

6. Mohriak, W.U., M.R. Mello, J.F. Dewey & J.R.Maxwell,

1990. in Brooks, J., ed. Classic Petroleum Provinces,

Geological Society Special PublicationN0 50. p 119-141,

1990.

7. Bruhn, C.H.L. & R.G. Walker. High-resolution

stratigraphy and sedimentary evolution of coarse-grainedcanyon-filling turbidites from the upper cretaceous

transgressive megasequence, Campos Basin, offshoreBrazil.Jounall of Sedimentary Research, Vol. B65, N0 4,

p.426-442, 1995.

8. Rangel, H.D., P.T.M. Guimares & A.R. Spadini.

Barracuda and Roncador giant oil fields, deep-waterCampos Basin, Brazil. In Halbouty, M.T., ed., Giant oil and

gas fields of the decade 1990-1999, AAPG Memoir 78, p.123-137, 2003.

AcknowledgmentsThe authors would like to dedicate this paper to all the peoplethat have dealed with Baracuda & Caratinga project reservoirissues and that are the main actors of the significant resultsachieved. We also would like to thank Pilar Martin andAmanda Trajan Cerveira for the important support in the

english version; and Adriana de Oliveira and Mauro RobertoBecker for the careful revisions. We also thank PETROBRAS

for the permission to publish this paper.

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0 a 30 30 a 60 60 a 80 80 a 130 > 30

IP ou II (m3/day/bar)

frequency(%)

Figure 13: Wells Productivity & Injectivity Indexesdistribution obtained.

Figure 12: Caratinga - CRT110 Reservoir Streamlines.

Figure 11 From the top to the botton: a- CaratingaCRT100; b- Caratinga MRL330; c- Barracuda

MRL330 and d- Barracuda ENCOBR.