SCP in UGS reservoir in HungaryThe Hungarian oil and gas group MOL, one of the largest corporations in Central Europe, converted the Szoreg reservoir in Hungary’s Algyo Basin to a UGS facility. Because there is evidence of SCP in other UGS fields in the area, MOL contacted Schlumberger for a solution to

■■ ensure long-term zonal isolation across the UGS reservoir to withstand the stresses caused by gas storage cycles

■■ bring cement to surface across the low-fracture-gradient formations

■■ control gas migration during cement setting.

Combination of technologies for primary cementingThe wells in this project included 34 vertical wells and 10 horizontal wells. The CemSTRESS* cement sheath stress analysis software was used to gain a better understanding of the stresses in the cement sheath through analyses of tensile strength, Young’s modulus, and expansion properties. The CemSTRESS analysis led to the selection of FlexSTONE cement technology as the most appropriate cementing system. Under the challenging conditions of the Szoreg reservoir, FlexSTONE cement system reduces the risk to zonal isolation by creating a robust cement sheath matched to the specific stress environment of the reservoir.

Challenge

Control gas migration and ensure long-term zonal isolation across an underground gas storage (UGS) reservoir to withstand the stresses caused by gas storage cycles throughout the life of the well.

Solution

Used the D600G GASBLOK* gas migration control cement additive, in combination with CemNET* advanced fiber technology to control losses, FlexSTONE* advanced flexible cement technology, and AccuSET* broad temperature range engineered cement hydration control system to contain sustained casing pressure (SCP).

Results

Achieved long-term zonal isolation in 44-well campaign with no remedial cementing and no QHSE incidents.

Combined Cementing Technologies Achieve Long-Term Zonal Isolation in MOL’s UGS WellsCase study: Successful primary cementing prevents gas migration to surface in 44-well campaign in Hungary

Cementing

Annaba

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Vi tebsk

Vej le

Parnu

Ioannina

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L iepaja

Bergen

Severodvinsk

Banja Luka

Batna

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Gomel

L idaMogi lev

Tartu

Tampere

Vaasa

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I rak l ion

Khania

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Miskolc

Pecs

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Olsztyn

Arad

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Brai la

Arkhangelsk

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Novgorod

Ordzhonik idze

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Pskov

Smolensk

Sovietsk

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Gavle

Ostersund

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Uppsala

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Simferopol

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Vologda

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Stara Zagora

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Plzen

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Bastia

Bremen

Dresden

Kiel

Magdeburg

Debrecen

Szeged

Enschede

Groningen

Kaliningrad

Malmo

Burgas

Varna

Brno

Ostrava

Lyon

Marseille

Bonn

Frankfurt

Hamburg

Leipzig

Munchen

Nurnberg

Stuttgart

Agrinion

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Mosel

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Firenze

Genova

Turin

Krakow

Lodz

Poznan

Wroclaw Breslau

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Constanta

Timisoara

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Krasnodar

Leningrad

Volgograd

Yaroslavl

Belgrade

Goteborg

Geneva

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Aleppo

Adana

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Istanbul

Izmir

Dnepropetrovsk

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Zaporozhye

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Karlsruhe

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Milano

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Copenhagen

Helsinki

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Athens

Budapest

Rome

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Monaco

Amsterdam

Oslo

Warsaw

Bucharest

Moscow

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Stockholm

Bern

Tunis

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Vienna

Brussels

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Luxembourg

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FINLAND

AUSTRIA

ITALY

SWEDEN

NORWAY

GERMANY

FRANCE HUNGARY

ROMANIA

BULGARIA

TURKEY

DENMARK

POLAND

BYELARUS

UKRAINE

CZECH

SLOVAKIA

GREECE

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Tyrrhenian Sea

Adriatic

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Gulf of Bothnia

Aegean

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Mediterranean Sea

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Szeged reservoir in Hungary’s Algyo Basin.

*Mark of SchlumbergerCopyright © 2009 Schlumberger. All rights reserved. 09-CE-0055

www.slb.com/cementing

The D600G GASBLOK cement additive created an impermeable barrier that prevented gas migration into the cement slurry by improving cement bond to the casing and formation interfaces. When cementing casing, some of the cement can be lost into natural fractures, fissures, vugs, or highly porous zones even when the fracture pressure is not exceeded. CemNET advanced fiber cement was used in the lead slurry to cover low fracture gradient zones to ensure top of cement to surface. CemNET cement is composed of an inert, fibrous material capable of forming a network across the loss zone.

AccuSET smart cement hydration control technology was used to shorten compressive strength development time, a benefit in the horizontal wells where additional drilling occurred for the openhole completion.

Long-term zonal isolationZonal isolation was achieved on all 44 primary cementing jobs, preventing gas migration to surface and requiring no remedial cementing for cement to surface. The cement slurry’s short compressive strength development saved waiting-on-cement time. In addition, there were no QHSE incidents during the process. The success of this combination of services proved that this package can be deployed at any location to ensure safer, properly executed cementing jobs and long-term zonal isolation.

CemSTRESScement sheath stress analysis software

FlexSTONEadvanced flexible cement technology

CemNETadvanced fiber technology to control losses

D600G GASBLOKadditive to pre-vent gas migra-tion in medium-temperature applications

The combination of Schlumberger services helped MOL achieve its goals, ensuring long-term zonal isolation across the UGS reservoir.

Long-term zonal isolation achieved

Gas migration prevented

No remedial cementing required

broad-temperature- range, engineered cement hydration control system

AccuSET

Case study: Successful primary cementing prevents gas migration to surface in 44-well campaign in Hungary