Pracss May 2012

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Predicting reservoir architecture in channelized slope settings

(PRACSS)

Ben Kneller, University of Aberdeenwith

Bryan Cronin, Deep Marine, AberdeenFabiano Gamberi, Istituto di Scienze del Mar, Bologna

Rationale

This project will use a threefold approach to the prediction of reservoirarchitecture in slope channels, including their associated levees and other thinbeds. The philosophy is to use subsurface data, modern systems, outcrop data

and mathematical simulations to calibrate quantitative architectural models forcanyons, channel fills and levees. It will leverage previous outcrop and modeling

work undertaken at Aberdeen under the Slopes consortium, a current PhDstudentship on the Buzzard field, and previous consortium-funded outcrop

studies in Turkey.

Deliverables

The project will deliver quantitative architectural models for the fills of slope

channels and their associated levees, with in-house discussions, field trips andworkshops. The work will be undertaken by three PhD students and a full-time

post-doctoral research fellow (PDRF).

Current status

Two PhD students (Themes 2 & 3) and the PDRF commenced April 2012; thethird PhD student will commence August 2012. Field work in Turkey will beginlate May 2012, with further fieldwork in the southern Alps and Mexico in August

and September respectively.

Cost

35k p.a.per sponsor over three years. The project is currently supported byBG, DONG, RWE Dea, Statoil and Tullow.

Outline of research

1. Channel architectures from wireline logs

Deepwater channel-fill sandstones and conglomerates form important but

variable reservoirs. A number of generic models for slope channel architecturehave been proposed, but uncertainties remain concerning, for example, reservoir

compartmentalization at sub-seismic level. The first strand of the researchapproaches this problem by using wireline logs to predict channel architecture,

using two parallel approaches.

A. Channel architectures can be reconstructed using the probability of a

transition from one facies to another in a vertical section such a well, especially ifcalibrated to good outcrop sections where the relationships are visible in two (or

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PRACSS status: 6thMay, 2012

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2) dimensions rather than one; large amounts of such outcrop data already

exist. Much larger numbers of such facies transitions occur in wells than are everseen in core; if such transitions could be identified, the statistical basis for

architectural models would be significantly improved. The first step is to identify

lithofacies (that can subsequently be grouped into reservoir facies) from wells

using neural-net analysis of wireline log data, calibrated to core. If the softwareis well trained to core, and if the core includes the full range of facies, this allows

facies recognition throughout the entire penetrated section rather than just thecored interval, and also in uncored adjacent wells. This gives a much larger

geostatistical base on which to calculate the facies architectures. The resultingtransition matrix would be compared with transitions in outcrop for verification

(starting with existing PhD thesis data from the Slopes consortium at Aberdeen).

B. The second and parallel approach is via spectral analysis of wireline logs. This

will commence with a controlled experiment using outcrop data (largely based

on existing data) to generate synthetic logs, and establishing the distinctiveness

of the spectral signatures of lithofacies assemblages associated with particulararchitectural elements of a channel fill or associated levee/overbank. This will

then be applied to well data with progressively decreasing levels of core control.

Proof-of-concept studies were carried out under the Slopes consortium using

continuous wavelet transforms. An alternative approach could involve the use ofmatching pursuit spectral decomposition, as has already been applied to

synthetic seismic data under the Slopes consortium.

The work will require access to sponsors well data from slope channels

(wireline logs, image logs and dipmeter, and core or high-resolution corephotographs), and collaboration with petrophysicists and geo-statisticians in the

sponsor companies.

2. Reservoir prediction in channel-related thin bedded turbidites

Submarine channels are commonly associated spatially with genetically-related,

thin-bedded turbidites deposited by overbank flow. They may form levees,

terraces or other overbank bodies. Despite their thin-bedded nature they may

contain large volumes of connected sand and thus form significant reservoir. It istherefore important to have robust models for prediction of sand distributionand properties that can be applied in the subsurface. Preliminary models have

been proposed for levees that predict these properties via the levee geometry.However these models draw largely on relatively limited outcrop data and on

shallow seismic data that have not been lithologically calibrated, and have notbeen tested in the subsurface.

This study proposes to erect a more general model for thin bed prediction by (1)utilising sea floor data from thin bed environments where the physical context

can be understood; (2) applying both analytical and state-of-the-art numerical

models to the prediction of over-bank (sensu lato) deposition, calibrated to (1)and (3); (3) broadening the outcrop base on which the model draws; and (4)

testing the model against production data from thin-bedded reservoirs.1) Modern systems.

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A comparative modern data set will be provided by cores, high-resolution swath

bathymetry and sub-bottom (CHIRP) profiles from modern leveed channels ofthe Cefalu basin of the Tyrrhenian Sea, Italy, gathered by Istituto de Scienze

Marine (ISMAR), with possible opportunities to participate in oceanographic

cruises with ISMAR. Public domain Ocean Drilling Program (ODP) data for the

Amazon levee may also be utilised, possibly involving visits to the ODP corerepository in Bremen. Additional data may be available from Institut Francais de

Recherche du Mer (IFREMER) from the levees of the modern Var submarinevalley; other public domain data may also be utilised for non-levee settings.

2) ModellingThe analytical model of Birman et al. (2009)1

3) Outcrop

predicts an association between

levee geometry and grain-size that has yet to be calibrated; the data yielded by(1) and (2) may be used to test and if necessary refine this model. Also, a directnumerical simulation (DNS) model for turbidity currents, developed by

Meiburgs group at Santa Barbara under the Slopes consortium, can be applied to

the prediction of geometries and grain-size distributions across levees. The

model can be tested against a range of geologically reasonable flow parametersand levee geometries; a student would be embedded within Meiburgs group in

Santa Barbara for a short to run this code alongside its developers.

The study will build on the data collected under the Slopes consortium in the

large, compound, slope channel levees of the Maastrichtian Rosario Formation(Baja California, Mexico), and also in the Alikayasi Canyon, Turkey (this study)

using thin section image analysis of levee sandstones in combination with thin-

section-calibrated laser grain-size data, gathered both from new samples and theexisting sample suite. The geological context of both these systems and the field

work logistics are both well-established. Outcrop data will also be gathered froma unit of channel-associated thin beds in the Oligocene Champsaur sandstones

(France), which we interpret as a single-cycle levee package. This will involvemapping the external geometry of the package, gathering bed thickness andpalaeocurrent data, and sampling for grain-size. Possible additional limited

outcrop studies may be undertaken in the Cretaceous Wheeler Gorge section of

California, and the Cretaceous of the Cerro Toro Formation, Southern Chile, both

of which Kneller has reconnoitred.4) The refined models will be tested against subsurface data provided bysponsor companies.

3. Calibration of large-scale reservoir variation in a complete dip profileExisting models for slope channels largely neglect downslope transitions in

architecture style from canyon through channel complexes to splays and sheetsands. The sequence stratigraphic framework of such downslope transitions is

also poorly known.

The Alikayasi Canyon in eastern Turkey represents exceptional exposure of a

multiphase canyon fill, and is one of very few outcrop systems with a complete

1Birman, V.K., Meiburg, E. & B. Kneller, B., 2009. The shape of submarine levees:exponential or power law?Journal of Fluid Mechanics, 619, 367376

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dip section, where the exposure potentially allows the transition from shelf

break to basin floor to be mapped directly.

The system has been studied since 1997 by Cronin and colleagues at the

University of Aberdeen during two sponsored projects, the second of which was

managed by Cronin. With logistical support from local universities we are ideallyplaced to manage such a project based on 15 years of experience in the area.

Specific Technical Objectives:

1) Changes in slope channel complex/canyon fill architecture in high and lownet:gross (coarse-grained and fine-grained) deep water slope systems, from fills,

through margins, levee shoulder and other overbank (thin bed) settings. All areexposed in the vicinity of the Alikayasi Canyon2) Mapping facies distribution within these fill margin and overbank settings to

predict facies variation (both potential reservoir and non reservoir) in both

strike and dip sections of slope channel / canyon complexes.

3) Mapping the downslope transition from canyon to confined or entrenchedslope channel complexes, into basin floor lobes, splays, or coalesced sheets type

architectures.4) Sequence stratigraphic analysis of canyon confined slope channel complex

sheet/lobe/frontal splay development. The Alikayasi Canyon and its downdip

sheet equivalents are known to cover at least eight phases of erosion, bypass andbackfill over a 1.5 Ma interval of the Miocene, which correspond to eight

(Galloway type 3rd Order or Mitchum type 4th order) sea level cycles that are

direct matches for Atlantic or Indian Ocean type Neogene continental margincycles.

5) Use of Petrel or equivalent static modelling package to illustrate an accuraterange of static model builds that reflect true variation in facies and architecture

range, and therefore real potential dynamic fluid sensitivity, to rock propertyvariation in deep water slope exploration targets or development cases.

Field Objectives:

1) Mapping of the architecture of the Miocene Alikayasi Canyon from its slope

position in a dip direction to its mouth, recording the downslope changes incanyon fill architecture into sheet and other architectural elements.2) Mapping of the main 7.5km + ridge of Alikayasi Canyon in the vicinity of

Menzelet Dam Lake. Substantial cliff exposures show the canyon fill to haverecognisable divisions, separated by substantial intervening wedges of

heterolithics that pinch out towards the canyon axis, and thicken away it, passinginto sandier architectural elements interpreted as substantial splay caps oroverbank shoulders, the full extent of which at present is not fully known.

3) Examination of intra-canyon wing heterolithic wedges for further dating andenvironmental significance of fine-grained sediments during these shut-down

periods of canyon evolution.4) Examination of the upper parts of the canyon fill, where more fully evolved

fan delta foresets are recognised.

5) Examination of the architecture of sediment facies beyond the mouth of the

canyon, which currently are thought to represent mouth splays that may bewalkable into the canyon fill.

Documents

Pracss May 2012