1

Fault compartment experience from a reservoir structural geologist:

1993-2017.

Signe Ottesen1

1: Statoil ASA

Abstract: Through structural work in Statoil the development of fault seal understanding and workflows

has been followed from 1993 to present day. Over these years our understanding of fault rock types,

fault rock properties and compartmentalization has evolved from a mysterious art form to a quantitative

science. In this presentation highlights of case history experiences and method development will be

shared.

The detailed work on fault seal processes and fault rock properties from RDR, University of Leeds, has

greatly contributed to our current understanding and workflows (Knipe 1992, Fisher & Knipe 1998).

The integration of the SGR method and later clay smear methods (Lindsay et al. 93) in Badleys

modelling tools: FAPS, (Yielding 1997) has also been important, including the focus from Manzocchi et

al. (1999) on the implementation of methods for calculations of fault transmissibility multipliers. Early

work on this will be referred to (Ottesen Ellevset et al. 1998, and other anonymized work), including

inspiring work from colleagues (Knai & Knipe 1998). It rapidly became evident that the uncertainty in

input parameters to fault seal analysis limit the degree of precision in our calculations. Modelling of this

uncertainty investigated in Ottesen et al., (2005), and today we are moving towards more probabilistic

methods.

Challenges are still present, and we will need sharp minds to develop workflows and methods further.

One challenge is that the seismically mapped geometry can never be expected to be exact due to seismic

resolution. Another one is that slip-surfaces has been proven by outcrop studies to change fault

properties (Tueckmantel et al. 2010) compared to small deformation bands without slip-surface

development which are often measured from core samples. How and when to include this effect in our

modelling workflows is not straight forward, and also a larger dataset on the effect of slip-planes would

be beneficial. Overall our current workflows, tools and understanding of fault property modelling are

massively improved since 1993! Calibration against production data also indicate that these methods

provide improved history match (Jolley et al 2007), and as seismic reservoir monitoring becomes more

and more popular, lots of 4D calibration data can be expected in the future.

References:

Fisher, Q,J, & Knipe, R.J., 1998. Fault sealing processes in silisiclastic sediments. In: Jones et al. (eds) Faulting,

Fault Sealing and Fluid Flow in Hydrocarbon Reservoirs. Geol. Soc Spec. Publ., 117-134.

Jolley, S.J., Dijk, H., Lamens, J.H., Fisher, Q.J., Manzocchi, T., Eikmans, H. and Huang, Y., 2007. Faulting and

fault sealing in production simulation models: Brent Province, northern North Sea. Petroleum Geoscience, 13, pp.

321-340.

Knai, T.A. & Knipe., R.J., 1998. The impact of faults on fluid flow in the Heidrun Field. In: Jones et al. (eds)

Faulting, Fault Sealing and Fluid Flow in Hydrocarbon Reservoirs. Geol. Soc Spec. Publ., 147, 269-282.

Knipe, R.J, 1992. Faulting processes and fault seal. In: R.M. Larsen (Ed). Structural and Tectonic modelling and

its application to petroleum geology. NPF spec.publ. 1, pp 325-342.

2

Lindsay, N.G., Murphy,F.C., Walsh, J.J. & Watterson,J, 1993. Outrop studies of shale smears on fault surfaces.

In: Flint, S.,& Bryant, A.D.(eds.) The Geological modelling of Hydrocarbon reservoirs and Outcrop Analogues.

International Association of Sedimentologists Publication, 15, 113-123.

Manzocchi, T., Walsh, J.J., Nell, P and Yielding, G., 1999. Fault transmissibility multipliers for flow simulation

models. Petroleum geosience, 5, pp 55-63.

Ottesen Ellevset, S.O., Knipe, R., J., Svava Olsen, T., Fisher, Q., J., & Jones., G., 1998. Fault controlled

communication in the Sleipner Vest Field, Norwegian Continental Shelf; detailed, quantitative input for reservoir

simulation and well planning. In: Jones et al. (eds) Faulting, Fault Sealing and Fluid Flow in Hydrocarbon

Reservoirs. Geol. Soc Spec. Publ., 147, 283-297.

Ottesen, S., Townsend, C. and Øverland, K.M., 2005, Investigating the effect of varying fault geometry and

transmissibility on recovery. Using a new workflow for structural uncertainty modelling in a clastic reservoir. In:

P.Boult and j. Kaldi , eds., Evaluating fault and cap rock seals: AAPG Headberg Series no. 2, p. 125-136.

Tueckmantel, C., Fisher, Q.J., Knipe, R.J., Lickorish, H., Khalil, S.M., 2010. Fault seal prediction of seismic-

scale normal faults in porous sandstone: A case study from the eastern Gulf of Suez rift, Egypt. In: Marine and

Petroleum Geology 27, 334-350

3

A detailed analysis of fault morphology using seismic from the Snøhvit

Field, Barents Sea

Jennifer Cunningham1, Nestor Cardozo

1, & Chris Townsend

2

1: University of Stavanger

2: PGNiG International Upstream AS

Abstract: Seismic survey ST14M02 is a multi-azimuth survey, shot in the Barents Sea in 2014. The

dataset is post-stack and is chosen because of excellent fault/horizon imaging and good well control near

to the faults. The workflow for this study involves:

Detailed near-fault seismic interpretation

Fault throw analysis using key horizons as throw indicators (using T7)

Apparent dip analysis of key horizons (using T7 and methods similar to (Long and Imber, 2010,

2012)

An analysis of structure enhancing seismic attributes (using Petrel/Geoteric similar to Iacopini et

al., 2016)

An analysis of fault throw and apparent dip will help to establish fault evolution and morphology. A

comparison of structure enhancing attributes will help to identify which attribute best image the location

of fault tips in the seismic data. The same attributes will be used in comparison with apparent dip maps

to understand what attributes are capable of imaging fault segmentation and morphology. The end result

of this study will improve our understanding of fault imaging in seismic data with respect to fault

segmentation and deformation.

References:

Iacopini, D., R. W. H. Butler, S. Purves, N. McArdle, and N. De Freslon, 2016, Exploring the seismic expression

of fault zones in 3D seismic volumes: Journal of Structural Geology, v. 89, p. 54–73.

Long, J. J., and J. Imber, 2010, Geometrically coherent continuous deformation in the volume surrounding a

seismically imaged normal fault-array: Journal of Structural Geology, v. 32, p. 222–234.

Long, J. J., and J. Imber, 2012, Strain compatibility and fault linkage in relay zones on normal faults: Journal of

Sedimentary Petrology, v. 36, p. 16–26.

4

Fault geometry and architecture, insights from seismic and outcrop

studies

Torabi, A1*, Alaei, B., Libak, A.

*Uni Research CIPR, Nygårdsgaten 112, 5008 Bergen; anita.torabi@uni.no

Abstract: The geometry and architecture of faults and fault network is one of the key aspects in

characterization of reservoirs and predicting fluid flow underground. Faults may influence both

hydrocarbon migration and entrapment in petroleum reservoirs (e.g. Knipe 1997; Harris et al., 2003).

Therefore, rigorous and reliable fault network mapping could considerably reduce the exploration risk

and/or production challenges of structurally bounded hydrocarbon traps. Utilizing fault seismic

attributes (Torabi et al., 2016a and b; Libak et al., 2017; Torabi and Alaei, 2017), we are able to extract

fault geometric attributes such as length, height, and damage zone width without a need for subjective

seismic interpretation. We have applied our developed workflow on a large number of 3D surveys from

the Barents Sea and built a fault geometric attribute dataset. These data, together with detailed outcrop

studies of fault core and damage zone of different fault types in a variety of lithologies has increased our

knowledge of fault geometry and architecture.

5

Using Trap Analysis to evaluate uncertainty in column height prediction

in fault-bounded traps

Peter G. Bretan1

1: Badley Geoscience Limited

Abstract: Over the past two decades, a quantitative methodology has been developed to predict column

heights in fault-bounded traps. The method typically involves constructing a best-case 3D fault

framework model; populating the model with well-based (e.g. Vshale) or seismic attributes; predicting

fault-zone clay content using Shale Gouge Ratio (SGR) algorithm at reservoir-on-reservoir

juxtapositions and transforming SGR to hydrocarbon column heights. Column height attributes are

typically displayed on fault plane sections. For complex reservoir juxtapositions or traps bounded by

multiple intersecting faults, visual inspection of column height attributes on fault plane diagrams often

lead to erroneous conclusions regarding the height of the column supported the fault seal.

In this contribution, an automated approach, termed Trap Analysis, for reporting and analysing

hydrocarbon column heights in traps bounded by intersecting faults is described. The method enables

fault leak points and column heights to be quickly derived and evaluated for complex traps or reservoir

juxtapositions. Fault ‘side walls’, defined by fault tip loops and branch lines, are simultaneously

interrogated to derive a unique location of the fault leak point. The fault leak point is that point on the

fault side wall which, when trappable column heights are calculated, implies the shallowest hydrocarbon

contact in the trap. The results of the Trap Analysis are reported as a set of coordinates defining the

location of the leak point together with the maximum column supported at the leak point.

The application of the Trap Analysis approach is illustrated using examples from the North Sea. The

new approach outlined in this contribution enables different input parameters (e.g. published vs in-house

SGR to threshold pressure relationships, water and hydrocarbon densities, model geometries etc.) to be

quickly evaluated in order to derive a range of column heights and trap fill scenarios. Different column

height predictions derived using different SGR to threshold pressure transformations and/or density

values have important implications for migration studies and for estimating the total size of the

hydrocarbon accumulation in a fault-bounded trap.

6

The value of fault analysis for field development planning

Andreas A. Frischbutter1*

, Quentin J. Fisher2, Gyunay Namazova

1 & Sebastien Dufour

1

1: Wintershall Norge AS, Jåttaflåten 27, 4020 Stavanger, Norway

2: School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK

Abstract: Faults play an important role in reservoir compartmentalization and can have a significant

impact on recoverable volumes. A recent petroleum discovery in the Norwegian offshore sector, with an

Upper Jurassic reservoir, is currently in the development planning phase. The reservoir is divided into

several compartments by syndepositional faults that have not been reactivated and do not offset the

petroleum-bearing sandstones completely. A comprehensive fault analysis has been conducted from core

to seismic scale to assess the likely influence of faults on the production performance and recoverable

volumes. The permeability of the small-scale faults from the core were analysed at high confining

pressures using formation-compatible brines. These permeability measurements provide important

calibration points for the fault property assessment, which was used to calculate transmissibility

multipliers (TM) that were incorporated into the dynamic reservoir simulation model in order to account

for the impact of faults on fluid flow. Dynamic simulation results reveal a range of more than 20% for

recoverable volumes, depending on the fault property case applied and for a base case producer–injector

well pattern. Fault properties are one of the key parameters that influence the range of cumulative

recoverable oil volumes and the recovery efficiency.

7

Fault compartmentalization at Goliat field, results from development

drilling

G. Halset1, Lars-Erik Gustafsson

1 & Johan Leutscher

1

1: Eni Norge AS

Abstract: Goliat is an oil field located in the Barents Sea on the Norwegian Continental Shelf, operated

by Eni Norge (65%) with Statoil (35%) as venture partner. The field was discovered in 2000, and since

then 5 additional exploration wells and 21 development wells have been drilled. The field came in

production in March 2016. It consists of two separate reservoirs, both containing oil with an overlaying

gas cap; the Kobbe Formation, at approximately 1800 meters depth and the Realgrunnen Subgroup

(Tubåen Fm and Fruholmen Fm), at approximately 1000 meters depth.

The Goliat structure is formed by a large complex faulted anticline structure located in the south-eastern

part of the Hammerfest Basin bordering the Troms-Finnmark Platform. The field has two dominating

fault set orientations; a SW-NE striking fault set (of local importance related to the crestal part of the

Goliat anticline trend parallel to the Troms-Finnmark Fault Complex) and a WNW-ESE striking fault set

(of more regional importance within the Hammerfest Basin).

Both reservoirs share a complex structural setting characterized by a high number of faults. Seismic

interpretation, formation pressure analysis and geochemistry analysis point to a complex field with

several compartments and fluid barriers.

The main compartments in the field were proven pre-development, and a general trend showing higher

sealing capacity on the WNW-ESE striking fault set were found. For Kobbe reservoir, the SW-NE

trending faults with a vertical throw of up to 40m were proven to be open. Results from a horizontal

development well for the same reservoir level, showed a sealing sub-seismic WNW-ESE trending fault.

Only weak indications from seismic suggest any vertical displacement. Sealing capacity of faults is still

an important uncertainty of the field.

8

The value of modern fault seal analysis and modelling methods: A case

study from the NCS calibrated using high-quality 4D seismic data.

Robert Worthington1

1: Statoil ASA

Abstract: Following its early development phase, this NCS field has presented some unexpected

compartments around two of the three down-flank water injectors, despite appraisal wells indicating

very good reservoir properties and communication. Both compartments experienced high pressure build-

ups (<ca.150 bar) with one reaching critical levels leading to top seal failure. Understanding the role of

faults on reservoir communication and flow pathways quickly became important, aiding the

interpretation of production data and ultimately towards successful and cost efficient development plans.

Following modern fault seal analysis and modelling techniques we have gained important insights on the

sealing and baffling behaviour of faults for this field. All faults in the full field flow simulation model

were provided with a more geologically valid distribution of flow properties and a history match to

production data was quickly achieved, prior to which was difficult using more commonly used

(simplistic) single fault multiplier methods. Furthermore, this study was fortunate in that the dynamic

modelling results could be compared with clear pressure and fluid contact anomalies within high quality

4D seismic data. This work demonstrated that due to the relatively thin thickness and variable flow

properties of the reservoir package, flow is restricted vertically and that even small scale faults can

generate clay-rich fault rock providing effective baffles. The sealing capacity of such faults is adequate

to account for the small static pressure differences between reservoir zones, while the baffling effect was

able to explain the high pressure build-ups in the compartments. Narrow ‘windows’ of more open fault

rock properties, where sand-sand juxtapositions arise can also be clearly accountable to explain the

better communication reservoir zones. This field case is a good example of the value of fault seal

methodology and the importance of fault seal and compartment risking during earlier stages of field

development. Furthermore, that smaller scale faults should not be dismissed as unimportant during early

seismic structural interpretation and reservoir modelling stages.

9