The interpretation of image data for depositional facies

The interpretation of image data for depositional

facies orientation used in building a Static

Model for the Harvey CO2 sequestration area.

A Report by ODIN Reservoir Consultants

For

Department of Minerals and Petroleum

April 2016

DMP/2016/2

Jon Willem Roestenburg

South West Hub CO2 Sequestration Confidential

Page 2 of 15 April 2016

LIST OF FIGURES .................................................................................................................................. 3

DECLARATION ....................................................................................................................................... 4

NOTE: ...................................................................................................................................................... 4

1. SUMMARY AND CONCLUSIONS .................................................................................................. 5

2. INTRODUCTION .............................................................................................................................. 6

2.1 OBJECTIVES OF THE EVALUATION ................................................................................................. 6 2.2 SCOPE OF WORK – GEOLOGICAL MODELLING ............................................................................... 6 2.3 DATA PACKAGE ........................................................................................................................... 6 2.4 PROCESSING AND METHODOLOGY ............................................................................................... 6 2.5 INTERPRETATION ......................................................................................................................... 8

2.5.1 Cross referencing to real rock and analogue data ............................................................. 8 2.6 DEFINING ORIENTATION ON PLANAR FEATURES ............................................................................. 9

2.6.1 Non planar features ......................................................................................................... 10 2.7 STRUCTURAL DIP DETERMINATION AND COMPENSATION ............................................................... 11 2.8 INCORPORATING IMAGE DERIVED DATA WITH THE STATIC MODEL .................................................. 11

2.8.1 Depositional facies generation ......................................................................................... 11 2.8.2 Depositional Orientation ................................................................................................... 13

2.9 CONCLUSION ............................................................................................................................. 15



List of Figures

Figure 1 Distribution or XRMI buttons representing individual log curves from which a interpolated

image is generated ........................................................................................................ 7 Figure 2 Results of depth adjustments by depth shifting buttons and rows and remove irregular tool

motion to align well crossing features. Pre depth shift image is on the left. ................. 8 Figure 3 Computing dip and azimuth along planar bedding and classification into geological dip sets

such as planar bedding and fractures ........................................................................... 9 Figure 4 Stereographic presentation of dip and azimuth data by classified dip sets showing fracture

populations at left and crossbedding at right ............................................................... 10 Figure 5 Non planar image features and their geological classification ............................. 11 Figure 6 Presentation of image log data, derived dip sets and depositional facies ........... 12 Figure 7 Depositional orientation ........................................................................................ 14



Declaration

ODIN Reservoir Consultants has been commissioned to undertake to provide a review of the GSWA Harvey-1 Reservoir Simulation for Carbon Capture and Storage – Western Australia on Project on behalf of The Department of Minerals and Petroleum, (DMP) The evaluation of Carbon Capture and Storage is subject to uncertainty because it involves judgments on many variables that cannot be precisely assessed, including CO2 sequestration rates and capture, the costs associated with storing these volumes, sequestration gas distribution and potential impact of fiscal/regulatory changes. The statements and opinions attributable to us are given in good faith and in the belief that such statements are neither false nor misleading. In carrying out our tasks, we have considered and relied upon information supplied by the DMP and available in the public domain. Whilst every effort has been made to verify data and resolve apparent inconsistencies, neither ODIN Reservoir Consultants nor its servants accept any liability for its accuracy, nor do we warrant that our enquiries have revealed all of the matters, which an extensive examination should disclose. We believe our review and conclusions are sound but no warranty of accuracy or reliability is given to our conclusions. Neither ODIN Reservoir Consultants nor its employees has any pecuniary interest or other interest in the assets evaluated other than to the extent of the professional fees receivable for the preparation of this report Note: ODIN has conducted the attached independent technical evaluation with the following internationally recognised specialists: Jon Roestenburg Jon is a Petroleum Geologist and Leadership advocate with global experience involving technical, managerial, educational and corporate roles. Jon has worked in large, multi-national corporations with experience in onshore USA, Central Asia, Russia, China, Japan, Southeast Asia and Australasia. Jon is an expert in the application of borehole log and Image log data to the reconstruction of contextual subsurface geological architecture. Jon has applied his borehole image analysis expertise to a diverse range of geological applications ranging from depositional environment analysis, sedimentology, diagenesis, brittle deformation styles, structural geology and geobody orientation in a wide variety of basins, deformational terrains, conventional and unconventional petroleum systems and mineral deposits.



1. SUMMARY AND CONCLUSIONS

A key component of building a facies property in a static model is the orientation of the

facies units based on the understanding or interpretation of the depositional

environment. Both Harvey-1 and Harvey-4 wells of the South West Hub CO2

sequestration project contain image log data from which depositional facies units and

their orientation were derived. Dip and azimuth measurements on bedding planes and

sedimentary structures that have been recognised on image log data are critical to

determining the orientation of the bedding, the structural setting, the brittle deformation

and the facies orientation for use in the static model.

Both well data sets were processed (reprocessed in the case of Harvey-1) so that a

consistent interpretation and outcome would be achieved. Over 16,000 dip and

azimuth measurements were made and form the basis of the depositional models and

their orientation after structural dip compensation. These depositional units in turn

were used to develop the oriented facies units that are imported into the static model.

Conformable and stratigraphically persistent dips and azimuths were derived from

image data acquired over nearly three kilometres of vertical section.

The results indicate that the dominant pre structural orientation of braided fluvial

depositional facies in the Wonnerup Member is E and NE derived from planar cross

bedding, co-sets, vertically consistent and cumulative cross strata and depositional

facies. A consistent palaeo-depostional orientation exists for the fluvial point bar

sandstone units that dominate the Yalgorup Member. For the purposes of modelling,

the two environments are classified as “fluvial” since the respective geobodies are in

the same direction.



2. INTRODUCTION

2.1 Objectives of the Evaluation

The objective of this study is to derive depositional facies and their orientation from the

Harvey-1 and Harvey-4 borehole image data, and to develop a reservoir linked facies

unit distribution that can be used in the static model of the Harvey area.

2.2 Scope of Work – Geological Modelling

The scope of this project is to derive dip and azimuth data from processed image logs,

determine the structural dip and remove it, then establish the depositional facies and

orientation based on Harvey-4 XRMI and Harvey-1 STAR data.

2.3 Data Package

Both Harvey-1 and Harvey-4 have image log data that has been utilised in this project:

Harvey-1: Harvey-1_STAR_RAW_1285-2723m

Harvey-4: Harvey 4_S2R2_XRMI_Main_250-1784.0m

In addition to these log data files the derived image based dip, azimuth and facies data,

the project referenced facies distribution within the accepted analogue models for the

Wonnerup Member based on the Brahmaputra River Braided fluvial systems and

channel orientation models and analogues for meandering fluvial systems for the

overlying Yalgorup Member.

2.4 Processing and Methodology

Image Log Processing is an involved and computationally intensive process requiring

specialist software and processing to allow the accurate spatial alignment of individual

current curves or acoustic impulses necessary to create the circumferential borehole

image – a suitable colour scale, such as “earth tones” is then applied to the individual

curves to generate an image through interpolation.



Processing starts with data loading, button to button and pad to pad alignments through

tilt arm corrections, borehole eccentricity corrections including borehole erosion

(washout) and corrections for hole deviation, relative bearing and azimuth (rotation

away from true and magnetic north – essential for orientation and dip computation) and

instantaneous tool acceleration corrections.

Depending on the tool type, pad and button configuration up to 192 channels are

corrected. In the case of the XRMI – a 6 arm tool there are 150 individual button curves

requiring spatial correction as seen in Figure 1

Figure 1 Distribution or XRMI buttons representing individual log curves from which a interpolated image is generated

Image generation is based on the correct spatial alignment of raw data curves that

have been adjusted using tool accelerometer, cable speed, hole deviation, relative

bearing and tool centering (eccentricity) and caliper corrections. Figure 2(left) shows

the colour map in “earth tones” applied along a three-dimensional bedding contact that

tracks across the wellbore and is displayed in two dimensions. However, the alignment

is occasionally imperfect, hence the individual pads are shifted resulting in a correctly

aligned image as shown in Figure 2 (right). This figure also shows the difference

between a “static” and “dynamic” processing routines with more detailed geology

exposed in the dynamic image. The benefit of the more detailed dynamic processing is

to change the visual colour range associated with contrasting bed boundaries,

revealing more detail, the static processing is used for stratigraphy, tectonic elements

and diagenetic zones, hence both types of presentations at various vertical scales and

colour maps are used for interpretation.



Figure 2 Results of depth adjustments by depth shifting buttons and rows and remove irregular tool motion to align well crossing features. Pre depth shift image is on the left.

2.5 Interpretation

2.5.1 Cross referencing to real rock and analogue data

The fundamental aspect of any image interpretation or analysis is the application of a

specific borehole image log database (interpreter), as there are a series of non-unique

interpretation outcomes possible for any image feature. Hence prior to a final

interpretation all outside data is referenced to provide the context for the analysis. In

the case of the Harvey Project a large amount of geological and geophysical data was

made available which included several whole cores, their descriptions and analyses.

Several visits to the core store were made to ascertain the extent of the Wonnerup and

Yalgorup Member cored intervals and the details of sedimentary bedding shown in the

cores. In addition, the modern depositional analogue used is the Brahmaputra fluvial

system and in particular the upstream braided intervals with transverse and linguoid

sand bars being the dominant depositional unit in the Wonnerup Member and

meandering point bars in the Yalgorup Member. The main sedimentary features seen

on the image logs were planar parallel and tangential cross bedding in definitive cross-

bed strata and cosets separated by truncation surfaces and paleosol horizons in the

Wonnerup Member and thalweg oriented planar crossbedding in the point bars

between palaeosols of the Yalgorup Member.

In image log interpretation, sandbody (geobody) orientation is defined using the internal

architecture, particularly the spatial orientation of sedimentary structures and bedding.



In addition, primary sedimentary structures are related to the depositional process and

the energy (which is classified using the dip magnitude). In the Harvey Project, the

direction of planar and tangential cross bedding is the most informative sedimentary

structure for defining the depositional orientation.

2.6 Defining Orientation on planar features

All planar geological features identified on the image logs were measured to derive dip

and azimuth, which were classified into sedimentary (primary and process related)

structures and post depositional (brittle deformation and diagenetic) structures. An

example of dip and azimuth on two expressions of these planar events, planar cross

bedding and fractures are shown in Figure 2 and Figure 3.

Figure 3 Computing dip and azimuth along planar bedding and classification into geological dip sets such as planar bedding and fractures

In this case the orientation of the sedimentary bedding is ENE at a dip angle of about

30 degrees before removing post-depositional structural dip. The resultant dip and

azimuth values in relation to specific geological features over a larger vertical interval

can also be shown in the usual stereonet manner for accurate analysis as shown in

Figure 4. From these analyses, fracture orientation and sets have been derived



indicating two populations striking N-S and NW-SE and a dominant NE dip direction for

cross bedding.

Figure 4 Stereographic presentation of dip and azimuth data by classified dip sets showing fracture populations at left and crossbedding at right

2.6.1 Non planar features

In addition to planar features there are many non-planar features shown on the image

logs in both wells. Most of these are due to the non-preservation (destruction) of

primary sedimentary structures, non-existence of bedding (planar structures) in the first

place and post depositional diagenetic processes. Figure 5 shows non-planar siderite

nodules on the left and cross cutting “boudins” in siderite layers or zones on the right.



Figure 5 Non planar image features and their geological classification

2.7 Structural dip determination and compensation

The section across both the Wonnerup and Yalgorup Members in the Harvey area

shows significant post depositional structuring in the form of faulting and associated tilt

seen on seismic and on the dip meter logs. To establish the pre-structural sedimentary

orientation structural dip has been removed (palynspasticly) by vectorial rotation based

on structural bedding dip and azimuth values derived from preserved claystone

bedding and truncation surfaces.

In the Harvey-4 well, structural dip is 10° @ 022° azimuth and in Harvey-1 it is 7° at

035° azimuth.

2.8 Incorporating Image derived data with the static model

2.8.1 Depositional facies generation

After classifying all image based bedding (and non bedding into dip sets and type, and

removing structural dip, the results are displayed along the well trajectory as a logs in

the usual manner at various scales (1:500 and 1:40). The integration of curve shape

analysis or well log based sequence stratigraphy, (primarily on the GR log and log



derived lithology), dipmeter interpretation (pattern analysis) and geological setting

characteristics are then used to interpret the log and dip response as depositional

facies.

Figure 6 Presentation of image log data, derived dip sets and depositional facies

Figure 6 shows an example of the Harvey-4 classified dip and azimuth measurements

into colour coded dip sets; log derived lithology and depositional facies. Two dip

columns are shown where the left most dip track is post structural bedding and the right

dip track in the figure, there structural bedding orientation after structural dip removal.

The complete interval logs are shown in the accompanying enclosures.

Dip sets and Gamma Ray generated lithologies are grouped into intervals that are

architecturally and genetically related in terms of stacking patterns, sedimentary

evolution (logical depositional succession), process energy (similarly dipping

magnitudes that indicate current force or energy) and conforming (or un-conforming)

relationships. This method has generated the oriented and classified depositional

facies, calibrated to the log and rock information available. In the Harvey Project, the

section is dominated by fluvial facies, which are classified into braided fluvial, point

bars, palaeosols, and overbank claystones and further into high and low energy units

on the image logs and then grouped ad fluvial for the geomodel since the sandstone

geobodies have the same orientation. Orientation based on internal bedding is a linked

to known sedimentological deposition processes in modern analogues, for example, in

a braided fluvial environment, the dominant depositional unit is the transverse, or



linguiod bars, whose orientation, given by downstream (slope) avalanching cross

bedding is oblique to the downstream elongation direction of the braid plain. Generally,

an azimuth spread of around 35° – 45° occurs between successive bar orientations and

the main downstream depositional vector direction. Most of the Wonnerup Member

cross bedding is of this type. Within the younger Yalgorup Member, dominated by a

meandering fluvial system the cross-bedding is within point bars with helicoidal cross

bedding, dipping towards the channel thalweg. The geobody elongation direction is

orthogonal to the direction of internal bedding dip.

2.8.2 Depositional Orientation

The dip vectors (dip and azimuth) have been grouped according to a range in azimuth.

Three groups or azimuthal classes are defined as: E-NE (red), NE-N (Orange), and N-

NW (yellow). These groups were assigned based on their vertical occurrence along the

well trajectory as shown in Figure 7. This classification was applied to both Harvey-1

and Harvey-4 for consistency and vertical continuity.



Figure 7 Depositional orientation

In order to reduce the number of discrete intervals, the thinner azimuthal classes have

been grouped prior to importing into the static model. The dominant azimuthal group is

coded red and represents the E-NE dipping current bedding, indicating a sedimentary

provenance for the area in the west/south-west. Both the Wonnerup Member braided

fluvial and the Yalgorup Member meandering fluvial systems are elongate deposits

oriented west – east and southwest to northeast in the Harvey area. There is a limited

occurrence of northwest oriented bedding (yellow), which indicate a local change

during deposition, possibly due to short duration current shifting due to accommodation

space generated by local faulting (tilting) or storm events that have an alternate source

or provenance.



2.9 Conclusion

Over 16000 dip and azimuth measurements were made over the Wonnerup and

Yalgorup Members at the Harvey-1 and Harvey-4 locations. The image log data sets

from Harvey-1 and Harvey-4 - which cover nearly three kilometres of vertical section

(2972m) - have been processed, analysed and interpreted to derive azimuthal

classes/groups for inclusion in the static model. The orientation is dominated by east to

northeast depositional units with a sub dominant northeast to north facies distribution

for both members. This information has been incorporated into the static geological

model of the Harvey area.

Documents

The interpretation of image data for depositional facies