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Confronting CarbonatesBernard Montaron, Theme Director of
Carbonates at Schlumberger writes on the challenges of carbonate
reservoirs.
132 Oil Review Middle East Issue Five 2008
EE NHANCED OIL RECOVERY is a particularly significant factor for carbonate reservoirs, since traditionally recovery tends to be low
from these fields. Bernard Montaron of Schlumberger explains.
Carbonate reservoirs hold around 60 per cent of the world’s oil and 40 per cent of the world’s gas. However, the heterogeneous nature of the rock presents challenges for petroleum engineers. To help address exploration and production issues specific to carbonate fields, Schlumberger has set up a dedicated carbonate R&D centre in Dhahran. This is a region which holds 62 per cent of the world’s hydrocarbon reserves. In fact, the Middle East is dominated by carbonate fields, with around 70 per cent of oil and 90 per cent of gas reserves held within these reservoirs.
Carbonate formations Carbonate reservoirs present a challenge, in part, due to the history of the rock formation. Carbonates rocks are formed locally by the deposition of minute marine organisms, coral and algae, together with the precipitation of calcium carbonate in shallow, warm water. By contrast, the sand and sediment that form sandstone reservoirs tends to be swept long distances by rivers and currents before settling in sites such as deltas and beaches.
One important difference between these two reservoirs types is that sand (a silicon compound) is chemically inert when compared to calcium carbonate. Carbonate rock initially has a high porosity of 35 per cent - 75 per cent, but this decreases sharply as the rock ages. Over
A bu
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at io
Confronting
carbonates
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116_140_ADIPEC:Layout 1 22/10/2008 18:50 Page 132
eons of time, as the rock is compressed deep underground, its character is changed due to a chemical process called diagenesis. During this process, the pores change in size and geometry. Understanding the complex heterogeneous rock matrix can be very problematic.
Diagenesis can create stylolite flow barriers, which extend over large areas, creating a dramatic effect on field performance. The rock may also be fractured by geological processes caused by pressure within the earth‘s crust arising from continental drift. A large fracture corridor may measure 10 m wide, 100 m high and a kilometre long. The history and topography of a carbonate formation provides some idea of the likely position, orientation and direction of these large corridors. Some may run along the crest of a fold where the formation has been subject to bending. But shear stress will tend to result in a crush zone because of the slippage of the rocks on either side of a failure.
This is a very important consideration for reservoir management because major fracture corridors can have a permeability a thousand times greater or more than the surrounding rock matrix. On the positive side, fracture corridors can provide highways for draining the reservoirs. However, the fracture corridors are also an easy
path for water, and injected gas, to break through to production wells. Fractures can also lead to problems during drilling, such as mud losses and stuck pipe.
Fracture cluster mapping workflow Last year the Fracture Cluster Mapping (FCM) workflow was launched to improve fracture characterisation and the modelling of carbonate reservoirs. The workflow integrates Q- Technology services, borehole measurements and Petrel seismic- to-simulation software with expert interpretation and flexible work processes, resulting in improved production performance.
Modelling fracture systems has always been and still is a challenge for geoscientists in the oil industry. The FCM workflow helps to make better decisions for the location of injectors and producers, plan well trajectories, improve production predictions and form a comprehensive Discrete Fracture Network (DFN) model. It makes a clear distinction
133Oil Review Middle East Issue Four 2007
A bu D
habi International Petroleum
Hot Oil Systems for Crude Oil Heating
Hot Oil Heaters for Oil Pumping Systems
Hot Water - Glycol Boilers
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Condensate Polishing Systems
Injection Water Filtration
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Italian Solutions for Heating & Water Treatment in Oil & Gas Applications
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116_140_ADIPEC:Layout 1 22/10/2008 18:50 Page 133
The topography of the field suggested that there would be extensive cracking along a fold running in a NNW to SSW direction. This thesis was supported by an initial run of discontinuity extraction software (DES) when it was used to process high resolution Q-Technology seismic data. However, this was not the full story. Borehole data from one well also showed more
than 400 open fractures running perpendicular to the main fracture cluster. Sequential steps of the workflow were then used, with filter windows, to produce more finely detailed fracture images at a series of azimuths (angles) and inclinations (dips) windows.
The constrained computer runs revealed additional fracture clusters. The filtered images were finally merged together to produce an overall 3D picture of the fracture corridors. The results were correlated with data from the four existing wells, and two new ones. The availability of an accurate fracture corridor map has great benefits for reservoir management, both to enhance production by extending
the area that can be drained by each production well, and to avoid a water breakthrough surprise.
Understanding reservoir producibility FCM addresses production concerns at a reservoir scale; however it is equally important to understand reservoir producibility from a rock-textural perspective at the pore
134 Oil Review Middle East Issue Five 2008
between diffuse fractures that can be modelled using geo-statistical techniques, and fracture corridor 'highways' that must be detected and placed in the reservoir model at their exact field location.
In practice, the frkacture cluster maps can be used in conjunction with technology that allows drillers to steer wells to the most favourable targets within the reservoir. PeriScope directional, deep imaging while drilling, is particularly useful in this respect as it enables petroleum engineers to geosteer horizontal drains using measurement-while- drilling (MWD) and logging-while- drilling (LWD) technology.
Applying the workflow In one example, the FCM workflow was applied to five carbonate fields located in northern Kuwait. One of these fields provided a particularly good test site for validating the workflow, because further drilling was taking place in the complicated structure. Four wells had been drilled at the start of the study, with two further wells drilled as the study progressed.
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Dubai Office: Dubai Internet City, PO Box 500096, Dubai, United Arab Emirates Tel: + 971 4 391 3134 Fax: + 971 4 391 3138 e-mail: [email protected]
Head Office: Alain Charles Publishing Ltd University House, 11-13 Lower Grosvenor Place, London, SW1W 0EX, UK Tel: +44 (0) 20 7834 7676 Fax: +44 (0) 20 7973 0076 e-mail: [email protected]
www.alaincharles.com
Alain Charles Publishing Ltd
Serving the world of business
Be seen by thoseBe seen by those that matter inthat matter in
the region’sthe region’s Oil & Gas sectorsOil & Gas sectors
Be seen by those that matter in
the region’s Oil & Gas sectors
Be seen by those that matter in
the region’s Oil & Gas sectors
The “Lighting
Africa” challenge
Issue Four 2008 NIGERIA
Page 22
Europe m10, Ghana CD18000, Kenya Ksh200, Nigeria N330, South Africa R25, UK £7, USA $12
Nigeria’s Minister for Energy, Odein
Ajumogobia - See page 42
REGULAR FEATURES: News Contracts Events Calendar IT update Company profiles Products & Innovations
Connected porosity
scale. The Schlumberger Carbonate Advisor petrophysics and productivity analysis, launched this year, centers on characterisation and size partitioning of the pore geometry by using texture-sensitive borehole logs, such as nuclear magnetic resonance and capture spectroscopy. It is a comprehensive formation evaluation system that leverages pore geometry analysis to confirm the identification of petrophysical rock types (mineralogy and pore system class), determine fluid saturations and estimate permeabilities and relative permeabilities.
Many different measurements are needed to build-up a picture of the petrophysical properties and producibility of a carbonate formation. Some measurements such as photoelectric effect, gamma ray and nuclear magnetic resonance provide information about the nature of the rock and its pores, while others, such as resistivity, provide information about its fluid content and mobility. It is the integration of all the available data that is key to determining the potential productivity of a formation. Carbonate Advisor is an interpretive methodology that integrates petrophysical data in three sequential steps. The first step determines the lithology and porosity of the rock. This evaluation is then used in the
second step to estimate the pore type and permeability. In the third step, relative permeability and fluid saturations are derived from a detailed analysis of the radial variation of resistivity measurements.
Traditionally, petrophysical properties are often determined from core samples, which are shipped to laboratory for assessment. However, in many cases, key petrophysical characteristics, such as porosity, pore type and permeability from core measurements may not be available for days, weeks or even months. Carbonate
Advisor, log measurements and analysis techniques, goes a long way to providing critical petrophysical information in a fraction of the time. Results, presented continuously as a function of well depth, are available just hours after data has been acquired from logging tools, enabling critical decisions to be made in a timely manner.
The future Today, carbonate reservoirs continue to pose a number of challenges. After all, the recovery factor from these reservoirs is below the 35 per cent average for fields of all types and some fractured carbonate reservoirs have recovery factors below 10 per cent. The challenge in coming years will be to integrate data even more effectively to produce ever-more accurate reservoir models, with an even better definition of features. With continued collaboration to refine existing techniques and the commitment to develop specialist new technologies, the future for carbonate reservoirs is looking more productive.
Further information is available from Schlumberger at ADIPEC 2008.
135Oil Review Middle East Issue Four 2007
A bu D
habi International Petroleum
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Build long term certainty into your
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Many different measurements are needed to build-up
a picture of the petrophysical properties and producibility of a carbonate formation
116_140_ADIPEC:Layout 1 22/10/2008 18:51 Page 135
132 Oil Review Middle East Issue Five 2008
EE NHANCED OIL RECOVERY is a particularly significant factor for carbonate reservoirs, since traditionally recovery tends to be low
from these fields. Bernard Montaron of Schlumberger explains.
Carbonate reservoirs hold around 60 per cent of the world’s oil and 40 per cent of the world’s gas. However, the heterogeneous nature of the rock presents challenges for petroleum engineers. To help address exploration and production issues specific to carbonate fields, Schlumberger has set up a dedicated carbonate R&D centre in Dhahran. This is a region which holds 62 per cent of the world’s hydrocarbon reserves. In fact, the Middle East is dominated by carbonate fields, with around 70 per cent of oil and 90 per cent of gas reserves held within these reservoirs.
Carbonate formations Carbonate reservoirs present a challenge, in part, due to the history of the rock formation. Carbonates rocks are formed locally by the deposition of minute marine organisms, coral and algae, together with the precipitation of calcium carbonate in shallow, warm water. By contrast, the sand and sediment that form sandstone reservoirs tends to be swept long distances by rivers and currents before settling in sites such as deltas and beaches.
One important difference between these two reservoirs types is that sand (a silicon compound) is chemically inert when compared to calcium carbonate. Carbonate rock initially has a high porosity of 35 per cent - 75 per cent, but this decreases sharply as the rock ages. Over
A bu
D ha
bi In
te rn
at io
Confronting
carbonates
United Arab Emirates | Qatar | Kuwait | Saudi Arabia | Oman | Egypt | Sri Lanka
Corporate Office +971 4 885 4449
www.amanabuildings.com
fice +971 4 885 4449e Offf
ldings.commanabui
ka
9
m
116_140_ADIPEC:Layout 1 22/10/2008 18:50 Page 132
eons of time, as the rock is compressed deep underground, its character is changed due to a chemical process called diagenesis. During this process, the pores change in size and geometry. Understanding the complex heterogeneous rock matrix can be very problematic.
Diagenesis can create stylolite flow barriers, which extend over large areas, creating a dramatic effect on field performance. The rock may also be fractured by geological processes caused by pressure within the earth‘s crust arising from continental drift. A large fracture corridor may measure 10 m wide, 100 m high and a kilometre long. The history and topography of a carbonate formation provides some idea of the likely position, orientation and direction of these large corridors. Some may run along the crest of a fold where the formation has been subject to bending. But shear stress will tend to result in a crush zone because of the slippage of the rocks on either side of a failure.
This is a very important consideration for reservoir management because major fracture corridors can have a permeability a thousand times greater or more than the surrounding rock matrix. On the positive side, fracture corridors can provide highways for draining the reservoirs. However, the fracture corridors are also an easy
path for water, and injected gas, to break through to production wells. Fractures can also lead to problems during drilling, such as mud losses and stuck pipe.
Fracture cluster mapping workflow Last year the Fracture Cluster Mapping (FCM) workflow was launched to improve fracture characterisation and the modelling of carbonate reservoirs. The workflow integrates Q- Technology services, borehole measurements and Petrel seismic- to-simulation software with expert interpretation and flexible work processes, resulting in improved production performance.
Modelling fracture systems has always been and still is a challenge for geoscientists in the oil industry. The FCM workflow helps to make better decisions for the location of injectors and producers, plan well trajectories, improve production predictions and form a comprehensive Discrete Fracture Network (DFN) model. It makes a clear distinction
133Oil Review Middle East Issue Four 2007
A bu D
habi International Petroleum
Hot Oil Systems for Crude Oil Heating
Hot Oil Heaters for Oil Pumping Systems
Hot Water - Glycol Boilers
Waste Heat Recovery Boilers
Condensate Polishing Systems
Injection Water Filtration
Desalination & Demineralisation Packages
Drinking Water Makers
Energy & Ecology
Italian Solutions for Heating & Water Treatment in Oil & Gas Applications
Artes Ingegneria S.p.A.
Bono Energia S.p.A.
www.bono.itwww.bono.it [email protected]@bono.it
116_140_ADIPEC:Layout 1 22/10/2008 18:50 Page 133
The topography of the field suggested that there would be extensive cracking along a fold running in a NNW to SSW direction. This thesis was supported by an initial run of discontinuity extraction software (DES) when it was used to process high resolution Q-Technology seismic data. However, this was not the full story. Borehole data from one well also showed more
than 400 open fractures running perpendicular to the main fracture cluster. Sequential steps of the workflow were then used, with filter windows, to produce more finely detailed fracture images at a series of azimuths (angles) and inclinations (dips) windows.
The constrained computer runs revealed additional fracture clusters. The filtered images were finally merged together to produce an overall 3D picture of the fracture corridors. The results were correlated with data from the four existing wells, and two new ones. The availability of an accurate fracture corridor map has great benefits for reservoir management, both to enhance production by extending
the area that can be drained by each production well, and to avoid a water breakthrough surprise.
Understanding reservoir producibility FCM addresses production concerns at a reservoir scale; however it is equally important to understand reservoir producibility from a rock-textural perspective at the pore
134 Oil Review Middle East Issue Five 2008
between diffuse fractures that can be modelled using geo-statistical techniques, and fracture corridor 'highways' that must be detected and placed in the reservoir model at their exact field location.
In practice, the frkacture cluster maps can be used in conjunction with technology that allows drillers to steer wells to the most favourable targets within the reservoir. PeriScope directional, deep imaging while drilling, is particularly useful in this respect as it enables petroleum engineers to geosteer horizontal drains using measurement-while- drilling (MWD) and logging-while- drilling (LWD) technology.
Applying the workflow In one example, the FCM workflow was applied to five carbonate fields located in northern Kuwait. One of these fields provided a particularly good test site for validating the workflow, because further drilling was taking place in the complicated structure. Four wells had been drilled at the start of the study, with two further wells drilled as the study progressed.
A bu
D ha
bi In
te rn
at io
2 0 0 8
Dubai Office: Dubai Internet City, PO Box 500096, Dubai, United Arab Emirates Tel: + 971 4 391 3134 Fax: + 971 4 391 3138 e-mail: [email protected]
Head Office: Alain Charles Publishing Ltd University House, 11-13 Lower Grosvenor Place, London, SW1W 0EX, UK Tel: +44 (0) 20 7834 7676 Fax: +44 (0) 20 7973 0076 e-mail: [email protected]
www.alaincharles.com
Alain Charles Publishing Ltd
Serving the world of business
Be seen by thoseBe seen by those that matter inthat matter in
the region’sthe region’s Oil & Gas sectorsOil & Gas sectors
Be seen by those that matter in
the region’s Oil & Gas sectors
Be seen by those that matter in
the region’s Oil & Gas sectors
The “Lighting
Africa” challenge
Issue Four 2008 NIGERIA
Page 22
Europe m10, Ghana CD18000, Kenya Ksh200, Nigeria N330, South Africa R25, UK £7, USA $12
Nigeria’s Minister for Energy, Odein
Ajumogobia - See page 42
REGULAR FEATURES: News Contracts Events Calendar IT update Company profiles Products & Innovations
Connected porosity
scale. The Schlumberger Carbonate Advisor petrophysics and productivity analysis, launched this year, centers on characterisation and size partitioning of the pore geometry by using texture-sensitive borehole logs, such as nuclear magnetic resonance and capture spectroscopy. It is a comprehensive formation evaluation system that leverages pore geometry analysis to confirm the identification of petrophysical rock types (mineralogy and pore system class), determine fluid saturations and estimate permeabilities and relative permeabilities.
Many different measurements are needed to build-up a picture of the petrophysical properties and producibility of a carbonate formation. Some measurements such as photoelectric effect, gamma ray and nuclear magnetic resonance provide information about the nature of the rock and its pores, while others, such as resistivity, provide information about its fluid content and mobility. It is the integration of all the available data that is key to determining the potential productivity of a formation. Carbonate Advisor is an interpretive methodology that integrates petrophysical data in three sequential steps. The first step determines the lithology and porosity of the rock. This evaluation is then used in the
second step to estimate the pore type and permeability. In the third step, relative permeability and fluid saturations are derived from a detailed analysis of the radial variation of resistivity measurements.
Traditionally, petrophysical properties are often determined from core samples, which are shipped to laboratory for assessment. However, in many cases, key petrophysical characteristics, such as porosity, pore type and permeability from core measurements may not be available for days, weeks or even months. Carbonate
Advisor, log measurements and analysis techniques, goes a long way to providing critical petrophysical information in a fraction of the time. Results, presented continuously as a function of well depth, are available just hours after data has been acquired from logging tools, enabling critical decisions to be made in a timely manner.
The future Today, carbonate reservoirs continue to pose a number of challenges. After all, the recovery factor from these reservoirs is below the 35 per cent average for fields of all types and some fractured carbonate reservoirs have recovery factors below 10 per cent. The challenge in coming years will be to integrate data even more effectively to produce ever-more accurate reservoir models, with an even better definition of features. With continued collaboration to refine existing techniques and the commitment to develop specialist new technologies, the future for carbonate reservoirs is looking more productive.
Further information is available from Schlumberger at ADIPEC 2008.
135Oil Review Middle East Issue Four 2007
A bu D
habi International Petroleum
WeldLink ™ Connector
ww w.
pe tro
log y.c
environments worldwide.
Petrology makes it happen.
new and old pipelines to maximise
life expectancy by eliminating the
risk of internal corrosion. Instead of
replacing an existing pipeline due to
corrosion, Petrology can rehabilitate
Build long term certainty into your
future pipeline OPEX
8/ 13
-1 6
tel: +44 (0) 1389 801700 | fax: +44 (0) 1389 801701 | e-mail: [email protected]
P et
ro lo
gy L
Many different measurements are needed to build-up
a picture of the petrophysical properties and producibility of a carbonate formation
116_140_ADIPEC:Layout 1 22/10/2008 18:51 Page 135
