1. 5
Company ReposlYPF
Speaker Juan José Rodriguez, Eduardo Ibarra & Jean-Marc Morisseau
Title Underground Gas Storage in Diadema – Argentina. Applied Technology and Systems for Operation
and Monitoring

2. 6
INTRODUCTION
The Diadema project is aimed at optimizing natural gas and oil development and production in Golfo San Jorge
basin fields, since this is an area producing oil with associated gas, with limited operation flexibility for normal
supply of gas demand during the winter season, as well as for the management of surplus volumes of summer
production (Fig. 2).
Besides the General San Martín gas pipeline is being used at its full capacity in winter, thus becoming a ‘bottleneck’
for gas coming from the Austral and Golfo San Jorge basins, and limiting the transportation of the available gas in
the producing fields to meet the consumption areas demand.
The situation is exactly the opposite in summer, a period during which there is idle transport capacity available
resulting from the strong reduction in gas demand.
The Diadema Project allows storing surplus gas from producing fields during the summertime and contributes to the
optimization of the production of liquid hydrocarbons and associated gas in the fields connected to the General San
Martín main gas pipeline, thus avoiding gas flaring and / or shutting off high GOR wells in those fields. The natural
gas stored in the reservoir during the summertime will be later on withdrawn during high demand periods.
This project will also increase the gas supply to Comodoro Rivadavia city, so Diadema will be a new point-of-
delivery into the gas distribution system. This will contribute to improve the reliability and quality of the natural gas
supply to the city, thus allowing reducing or avoiding (with future expansions) current gas supply shortages to “large
users” (power plants, industrial plants, etc.).
Normal injection/withdrawal cycles for the Diadema gas storage facility consist of an injection period of about 7
months, from October to March, and a production period of about 4 to 5 months, between May and September. The
injection/withdrawal cycles may however vary significantly from one year to another depending on the actual
weather conditions in the region during winter, which can change drastically.
GAS STORAGE CHARACTERIZATION
The Diadema field is located 40 km Northwest to the city of Comodoro Rivadavia on the Northern flank of the San
Jorge basin.
Among various hydrocarbon productive levels, lies a gas bearing layer called the “Banco Verde” horizon, belonging
to the Salamanca Formation of the cretaceous-tertiary age, at an average depth of 500 meters below surface. This
geological horizon is made up of high porosity and high permeability sandstone, deposited by a marine
transgression in an estuary environment. It is covered by clays deposited on a coastal lagoon environment. Its
average net thickness is about 15 meters. Structurally, the field is divided into compartments formed by sub-vertical
faults with generally East-West and Northeast-Southwest strikes.
Gas was produced from the Banco Verde horizon since around 1950 and continued until 2000. During that period
of time, the reservoir pressure dropped from its initial 25 bar down to about 5 bars. A part of the depleted gas
reservoir was then converted into natural gas storage.
The gas storage operations are carried out in the so-called Repsol-YPF licensed block. Seven operation wells are
used for gas injection and withdrawal. These wells are located on two adjacent reservoir compartments which
constitutes the useful volume for the gas storage facility which operates between 15 and 25 bar providing a working
gas volume of some 75 M std m
3
. Gas is injected into the reservoir during summer using the gas pipeline pressure.
It is withdrawn during winter and sent to the pipeline by means of compressors.
Due to the very low pressure prevailing into the reservoir after the production period, it was necessary to inject a
volume of cushion gas in order to raise the reservoir pressure before starting operating the storage facility. This
cushion gas injection was performed during the year 2001. During the winter period of 2002 the facility was
operational for the first gas withdrawal operation.
EXISTING FACILITIES AND CURRENT EXPANSION
Gas Pipeline. This is a 10” - 12” diameter and 7.1 km length gas pipeline, fit for high-pressure (up to 65 bar)
operation, which connects the reservoir with the 12” diameter branch pipe owned by Camuzzi Gas del Sur S.A. gas
distribution company. In turn, this pipeline also connects to the General San Martín main pipeline, downstream the
Manantiales Behr Compression Plant.
The 10” - 12” interconnection gas pipeline that provides for natural gas flow to and from the reservoir, connects to
gas injection/production wells and to a gas line for the field’s internal consumption.
Metering. The metering system used is the orifice plate system to control the injection flow into the wells, and a bi-
directional ultrasound flow-metering system has been installed at the interconnection point with the gas distribution
company, with state-of-the-art technology for on-line controls and operation monitoring functions (SCADA).

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Injection System. For distributing the in-coming gas towards the 7 injection/production wells, a manifold and
connection pipes were built with a flow-metering system with a 300,000 m3/day capacity per well, at a 26 bar
pressure.
Withdrawal System. To provide a maximum withdrawal rate of about 600,000 m3/day during winter season, a
2,000 HP compressor plant was built, with a suction pressure of 7 to 15 bar and a discharge pressure of 60 bar, a
dehydration plant with TEG absorption, gas / liquid separator, gas metering and regulation systems, manifolds, on-
line gas quality control systems (chromatograph and hygrometer) and data transmission and communications
systems (RTU). The gas to be produced from the storage facility is compressed and dehydrated for its re-entry into
the distribution system under the quality specifications required by the ENARGAS (gas regulatory agency).
Current Expansion. The UGS facilities have been expanded in order to be used in winter 2005, both in the gas
field area and the compressor and treatment plant, as follows:
Wells: In order to expand the gas injection and withdrawal, 2 additional wells have been drilled in the western zone
of the reservoir, which will be used during the following operating cycle. Such wells are connected to an existing
gas pipeline, which joins other storage wells with the compressor plant.
Gas Plant: To double the withdrawal rate (up to 1,200,000 m3/day) 2 compressors of about 1,300 HP each one
have been installed, and an additional TEG dehydration plant for treating the maximum gas deliverability.
RESERVOIR MONITORING AND NUMERICAL SIMULATION
Underground storage facilities in depleted gas fields have the advantage that the gas containment quality of the
caprock is already proven for gas pressure below the discovery (or initial) reservoir pressure. It is therefore not
necessary to undertake specific studies to verify that the characteristics of the caprock, including the faults or other
geological heterogeneities that it may encompass, are appropriate for impeding vertical gas migration, providing
that the maximum operating pressure of the storage facility is maintained below or equal to the discovery pressure
and that the level of the gas/water contact inside the reservoir is kept above the initial gas/water contact.
However, it is often necessary to implement an underground monitoring system for the operation of these facilities
in order to follow the behavior of the reservoirs and to verify that the storage operations have no significant impact
on the surrounding aquifers. A typical scheme of underground gas storage in depleted gas field is shown by Figure
3.
In the case of the underground storage facility of Diadema, the necessity of monitoring was dictated by several
important aspects which are:
- Large number of wells which were drilled through the Banco Verde layer in the area of the storage facility,
- The conditions of these wells, some of them drilled more than 70 years ago and many of them abandoned
- Presence of barriers created by the faults which could impede or severely limit the horizontal flow of the gas
inside the reservoir,
- Heterogeneous distribution of the permeable intervals thickness of the Banco Verde sandstone
- Lack of reliable data on the gas production from the Banco Verde layer
- Uncertainties relative to the actual limits of the reservoir used for the gas storage facility.
The underground monitoring is performed through dedicated wells drilled into the reservoir and into the aquifers
layers located above.
For the reservoir the present monitoring wells network includes 13 wells for measuring the gas pressure in various
areas of the reservoir and for some of them the gas/water contact depths.
The aquifers layers located above the Banco Verde, are being monitored by 3 wells drilled to allow the
measurement of the aquifer pressures or their hydrostatic levels and to take water samples for chemical analysis.
In order to predict the behavior of the Diadema reservoir and to optimize the storage operating conditions, a
computerized numerical modeling has been developed during 2001. The model was built up using the geological
information and gas production data, though scarce, which were available at the time. The model had to take into
account the structural features of the porous layer and particularly the more or less impervious barriers formed by
the faults and creating compartments within the reservoir.
At the early stage of gas injection, some parameters of the model were adjusted to match the predicted gas
pressure distribution within the reservoir and the pressures observed on the monitoring wells. Afterwards, the
model was periodically updated with the latest gas movement data and on-site pressure measurements. This
follow-up allowed monitoring the deviations between the theoretical behavior forecast by the model and the actual
evolution of the reservoir data, and therefore to identify possible inaccuracies in the reservoir characteristics
introduced in the model.

4. 8
The model allowed to evaluate the amount of gas present in each reservoir compartment and to optimize the
location of the new injection/production wells. Along with the increase of the injected gas volume, it was also found
that the actual reservoir area occupied by the stored gas extended beyond the originally considered limits, thus
requiring additional monitoring wells.
APPLIED TECHNOLOGY AND SYSTEMS FOR OPERATION AND MONITORING
Using an information system that involves state-of-the-art technologies, operating data on natural gas production,
processing, and mobilization are made available before product delivery to trunk gas pipelines. The system, known
as Gasmed, has been specially adapted to meet the needs of Repsol YPF’s natural gas business. It allows to
significantly improving natural gas management.
System Description
Until start-up of Gasmed, the areas comprising the Natural Gas Director’s Office had several process control
devices in place for their operations. These systems, i.e. .DCS, SCADA, remote monitoring and remote control, as
applied to gas production, processing, transport, storage, shipment, distribution, and sale, were located around
each plant, across the field, between compressor and control stations or at business centers .Information
technology applications were based on Models which provided safe but expensive and inflexible solutions.
Both information from field measuring devices and operating data were not fully automated and only rarely were
they made available to management.
Under these conditions, field data security and integrity were of a limited nature. In addition, the temporal
relationship between the process or event and the data reviewed did not always hold appropriately.
Advances in information technology, as incorporated into the new system, resulted in radical changes which
ensured continuous data availability and caused a favorable impact on business performance and costs.
On the basis of a combination and integration program, procedures, protocols, applications, and standardizations
were successfully revised, which resulted in a value-added business. Such significant changes allow for
reestablishment of automation strategies, execution of standards, and adaptation of standards to global information
systems for company-wide use.
In Figures 4 and 5, we can see schematics of Gasmed system. How plant information is arranged and processed
is shown in the four system tiers.
Change factors and added value
Automation can be a key factor to improve and drive results. These solutions offer the best return on investment.
The active development which drives this ongoing improvement, are made possible due to advances in numerous
fields, communication and computer capabilities, open software and embedded sensor technologies.
This also implies expertise availability and special knowledge 247 , which have to be supported by remote
connectivity tools in order to diagnose, spot and fix problems.
The objective of real time data management expedites the decision making process across the whole organization.
It encourages the trend towards a solid integration of third party systems such as TOW, ERP, GIS, SAP, etc.
The value of real time information and the field devices intelligence provide accurate data measurements and have
self-diagnosis capabilities. The trend towards more complex measurements, carried out with self-calibration
equipment, is also driving and targeting process quality.
Each equipment installed carries loads of information, historical operating records, etc. Data consistency is
essential to achieve process optimization and modernization.
Last but not least, it is important to keep data quality and consistency.
Mass balancing techniques can make up measurement errors caused by diversions or failures in sensors, assuring
a certain degree of consistency.
TOW application records daily and monthly operation of UGS Diadema, obtaining quality and auditable data from
the corporate Gasmed software application.
Volumetric Online Balancing
As follows we will point-out the steps we have taken in order to implement TOW as a system tool aimed at solving
the difficulties to control the gas injection and withdrawal operations at Diadema.

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Up to date Implementation feasibility Analysis.
Need Concerns Application
used
Application
proposed
Record daily and monthly
operation in corporate filing
system.
-
Data availability.
- Inconsistencies
Several excel
files
Implement TOW
Distribute the injected and
withdrawn gas volumes
among reservoir wells.
- Consistent calculations Ditto
Through TOW to
determine gas
volumes, it can be
used both to configure
and audit.
TOW system (The Oilfield Workstation) is being company-wide implemented by Repsol YPF (Upstream E&P).
The main objectives of the system are:
-Keep data availability of the whole process of the fluids (Oil, Gas and water), from its extraction through the wells
to its delivery and trading operations.
-Act as data source for all the corporate applications and other external agencies when needed.
After analyzing its implementation in UGS Diadema we have reached to the following conclusions:
-Record data in TOW, this would provide excellent data availability.
-Avoid data inconsistencies.
- Calculate in a consistent and auditable way the injectedwithdrawn gas volumes among the different wells.
-In order to display results another corporate application would be used (Oracle Discoverer).
During the set-up process several value-added tasks were carried out:
- Defined variables can be checked by the users.
- Results can be efficiently revised through the Terminal Server Client (remote access).
- In order to avoid data flow intervention by users, an interface with Gasmed system was implemented (automatic
data input).
1.1. - The system was configured so that daily closing runs automatically (gas volumes balance and wells
distribution).
With TOW we daily measure injected or withdrawn gas volumes from the reservoir, and distribute these volumes in
the Storage wells, taking into account how long they have been in operation (Fig. 6).
As a complement to TOW we have an automatic method to calculate gas volumes distribution to and from the
wells. This requirement can be fully achieved with TOW application, using the theoretical measure for the wells
according to the latest controls and timing.
The system allows inputting data of all the plant measurements, wells controls and obtain conciliation of volumes
on a daily and monthly basis.
Two separate collecting systems have been developed for UGS Diadema. One of them was used to record
withdrawal information and the other one to record gas injection to the reservoir data and supply to distributors;
each of them with its corresponding measuring controls.
We can see in Figure 7 the volumetric differences (%) in gas balancing, for injection & withdrawal during 2004.
Currently the volumetric differences have been reduced up to 0,2 – 0,3 % by using Gasmed - TOW, whereas in
2003 applying a manual method (excel) the differences were about 0,5 % for both operations.

6. 10
Apart from that, regarding the necessary time for the gas balancing administrative processes, we have drastically
reduced the labor time (approx. 90%), because of the automatic methodology applied (Fig.8).
Minor differences in gas balancing and less time of human resources, positively impact in the economy of UGS
Diadema.
Future System Implementation
New applications will eventually be implemented in UGS Diadema, both in the reservoir control optimization and in
activities linked with operating techniques in wells and compressor plant, which are outlined as follows:
- Modelization of storage capacity, linked with working gas and deliverability, taking into account wells production
potential and compression power availability.
- Remote control of key valves for injecting and withdrawal wells in order to improve the response to the different
flow-rate fluctuations as for reservoir injection or gas supply to our customers.
At present, the automatization project is under way to be implemented along 2005 / 2006.
CONCLUSIONS
1.- UGS Diadema is aligned with technological advances worldwide by using processes automation into the
decision making process in a smoothly and operative way, getting to know the risks levels to drive the best results.
2.- Because of the efficiency and accuracy of our systems we are able to minimize errors caused by human
intervention, obtaining quality and auditable data from the corporate Gasmed software application.
3.- Gasmed and TOW systems have been specially adapted to meet the needs of Repsol YPF’s natural gas
business and particularly the management of UGS Diadema. All in all, the procedures and adjustments we have
been developing have proved to be very successful for our business.
1.2.ACKNOWLEDGEMENTS
The authors extend their acknowledgment to Repsol YPF for allowing them to present and publish this paper.
Additionally, we would like to thank Mr. Esteban Rigoni and Mr. Alejandro Simeoni for their valuable contribution in
TOW-Gasmed applications.
1.3.REFERENCES
1. Integrated Management System for Quality, Safety and Environment at the First Underground Storage
Facility in Argentina. . Second Quality Latin-American Congress. Bariloche – Argentina. March, 2004.
Rodríguez J.J and Santistevan P.
2 Diadema, The First Underground Storage Facility For Natural Gas in Argentina. Considerations Regarding
Environmental Protection, Safety And Quality. WGC Tokio 2003. Rodríguez J.J. and Morisseau J.M.
3 Diadema Project – Underground Gas Storage in a Depleted Field in Patagonia, Argentina, SPE 69522.
2001. Rodríguez J.J and Santistevan P.
4 Underground Gas Storage in the World. Situation in the Argentine Republic. SPE 382243. Bariloche –
Argentina, 1997. Correa Nacul, Evandro and Rodríguez, J.J
5 Use of a depleted field as a natural underground storage facility.- Second Natural Gas Lat. Congress –
November 15 through 20-1992, Salta – Argentina. Weiner, Adolfo G. And Arguello, Jorge
Figure 1.- Location of the UGS Diadema

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Figure 2.- Interconnection of Diadema facilities with Gas Pipelines
Figure 3.- Typical Scheme of an UGS in a Depleted Gas Field
PORTO ALEGRE
CORNEJO
TUCUMAN
CORNEJO
TUCUMAN
MONTEVIDEOMONTEVIDEO
SAN SEBASTIAN
BUENOS AIRES
SAN SEBASTIANSAN SEBASTIAN
BUENOS AIRESBUENOS AIRES
METHANEXMETHANEX
SANTIAGOSANTIAGOSANTIAGO
CUIABA
SANTA CRUZ
CUIABA
SANTA CRUZ
TALTAL
TOCOPILLA
TALTAL
TOCOPILLA
LOMA LA LATALOMA LA LATA
SAN PABLOSAN PABLO
PARANA
COMODORO RIVADAVIA
DIADEMA U. G. S.
RIO DE JANEIRO
GENERAL SAN MARTIN
GAS PIPELINE
BAHIA BLANCA
CONCEPCION
LA MORA
BEAZLEY
PERU BOLIVIA
ARGENTINA
BRASIL
CHILE
URUGUAY
MENDOZA
P C
C O M O D O R O
R IV A D A V IA
C IT Y
D IA D E M A
U N D E R G R O U N D
G A S S T O R AG E
C am uzzi G a s d el S ur
P ipelin e 12”
10”
12”
G ral S an M artín
P ipelin e 30” (TG S )
T o B uen os A ires
PM -
100
M . B ehr
W inter
Sum m er

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Figure 4.- Triangle of Gasmed Info
RESERVOIR
STORAGE
WELL
MONITORING
WELL
MONITORING
WELL

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Figure 5.- Gasmed System General Scheme
SQL
Server
Central
Dato
SCADA
Intranet
Repsol YPF
Servidor
Intranet
PC de Escritorio con
Web Browser
SCADA Server
SCADA Viewer
WAN
Repsol YPF
TCP/IP
Dato
SQL
Figure 6.- Gasmed – TOW Screens Display
1.2.Diadema
Dispatch
ing
GASODUCTO
TRANSMISOR DE TEMPERATURA
TRANS.DETEMP.
TRANS.DEPRESION
PUNTODEROCIO
PUNTO DE ROCIO
MEDI DOR
TRANSMI SOR DE PRESION
TOMAMUESTRA
Field Key
Sensors
RTU
LEVEL 4
LEVEL 3
LEVEL 2
Intranet
Server
Desk PC
with

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a.- Daily Gas Plant Balancing
b.- Daily Gas Wells Balancing
Figure 7.- Volumetric Differences in Gas Balancing (Gasmed – TOW)

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Figure 8.- Time optimization by using Gasmed – TOW
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0
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HORAS
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