Exercises in Sequence Stratigraphy

Exercises

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The modules below are tied to lectures, movies and exercises accessible from this web site for professional, academic and educational purposes. They are organized in systematic order for persons with little understanding of so they improve vocabulary, understanding and experience. Initial materials and exercises are introductory but later modules are more sophisticated and challenging. Completion of the modules provides an understanding of so studies of well, seismic and outcrop data lead to mature interpretations of the sedimentary sections. The last item listed at the base of the page are links to exercises put together by Fred Schroeder of ExxonMobil on the application fo geology and geophysics to exploration.

If you need immediate access click here for the listing of printable exercise images and exercise solutions but if you want to know more about the exercises it is better to retrieve them from the modules listed below.

Introduction - Rational for Sequence Stratigraphic Exercises
Earth scientists characterizing reservoirs and exploring for hydrocarbons in carbonate and/or clastic use a sequence stratigraphic framework of layers, that coupled to their character and origin is now at the heart of reservoir modeling. The identification of the appropriate layering geometry is crucial to the construction of 3D exploration models and static reservoir model reservoir models. Needless to say the blind rote application of the rules of sequence stratigraphy without understanding of depositional systems can be a disaster waiting to happen. This is because the resulting stratigraphic grid becomes the template for distribution of clastic and/or carbonate facies, their diagenetic alterations, their associated petrophysical properties, and final input for engineering models for flow simulation. Poor clastic and/or carbonate models are often the result of misunderstanding of the rules and terminology of sequence stratigraphy as well as the principles and workflows for building stochastic models.

The exercises below should help those who build reservoir and exploration models and should clarify the rules of sequence stratigraphy for clastic and/or carbonate settings. This site, with its exercises, lectures, and descriptive text, can be used to retrieve critical reservoir for professionals while teaching principles of sequence stratigraphy based reservoir characterization to novitiates. The accompanying text on the site ties relevant data including images, text links, and movies of sedimentary simulations.

Concepts

Before starting the exercises you might wish to view the following sections on line.

• Introduction to Sequence Stratigraphy: the critical stratigraphic surfaces used in sequence stratigraphy with their relationship to the exercises briefly outlined.

• Basics: Introduction to sequence stratigraphy with a Real Time lecture describing the ideal ‘sequence' of Vail et al 1977 and its associated terminology.

• Clastic Sequence Hierarchies : uses a movie to show the clastic sedimentary response to changing sea level and rates of sedimentation focusing on the hierachies of geometry found in clastic sequences.

• Mixed Carbonate & Clastic Basin: a movie of the fill of a sided sedimentary basin with carbonate and clastic sediment reviewed.

• Carbonate Sequence Hierarchies: examines the hierarchy of scales expressed by carbonate strata and provides movies that track the fill of basins and shelves by carbonate sediment

Exercises

The paradigms of sequence stratigraphy that the exercises teach include:
• sequence stratigraphy provides a framework that subdivides the sedimentary section into geometric packages bounded by unconformities and internal surfaces
• Sedimentary geometries enclosed by this framework are related to changes in base level (sea level and/or tectonic movement) and rates of sedimentation
• The extent and character of sedimentary geometries can be predicted
• sequence stratigraphy has economic implications in that it can be used to make predictions as to the extent and character of the rocks containing hydrocarbon and water resources
• The best of interpretations are preferably made with a tie between local outcrops, local wells and local seismic.
• If one or two of these data sources are missing the resulting models may be diminished by their absence.
• Outcrop studies of sedimentary rocks are used to predict the continuity and extent of their lithology and provide an even more detailed understanding of the lithology of these geometries.
• Seismic cross-sections can provide regional control on the geometries of sequences
• Well logs can be used to determine the lithology of these geometries

The exercises using outcrops indicate how:
• Outcrops are the ultimate ground truth to the correlation of parasequences
• Major surfaces that include transgressive surfaces (TS), maximum flooding surfaceaximum flooding surfaces (mfs), and sequence boundaries (SB) facilitate this correlation.
• stacking patterns of parasequences help determine the continuity of the reservoir quality & depositional setting of the sediments they bound.
• The high-frequency "cycle" or "parasequence" is the smallest set of genetically related facies deposited during a single base-level cycle.
• cycle boundaries mark the turnaround from base-level fall to base-level rise (a period of time during which sea level rises from a highstand position, through a lowstand, and returns to a highstand).
• cycles can be mapped across multiple facies tracts and include multiple vertical facies successions (VFS) and chronostratigraphic units (Kerans & Tinker, 1997 and Mitchum & Van Wagoner, 1991).
• The commonest parasequence is the shoaling upward cycle, with finer deeper water facies at their base and coarser better-sorted facies towards their top.
• parasequence set; parasequence sets identified in outcrop can be used to identify potential acquifers, aquicludes, hydrocarbon source rocks, reservoirs and seals.

The exercises using well log character
• Correlate parasequence set; parasequence sets at the scale of feet to tens of feet
• Determine the depositional setting of the component sytems tracts
• Determine the sequence stratigraphy of the section being studied
• parasequences are identified and correlated from well log character, particularly when planktonic or palynologic biostratigraphy are available.
• The resulting parasequences are often at the same scale as the components of local hydrocarbon reservoirs
• Find, map and exploit these reservoirs more effectively by relating them to eustatic events

The exercises using seismic cross-section display how
• To determine the sequence stratigraphy of a basin from discontinuity surfaces that coincide with seismic reflector terminations
• Those surfaces that form the sequence boundaries are correlated
• The enveloped sytems tracts are correlated
• Both sequence boundaries and sytems tracts are traced from line to line to establish the sedimentary architecture of the basin and infer the origins of the sytems tracts
• clinoform geometries can be used to show evidence of delta switching, slumping and migration and related to the shifting of the source areas
• The effects of variable rates of sediment supply in the area of study can be examined
• To determine evidence for widespread changes in base level
• To locate basin floor fans, slope fans and incised valleys and find evidence to demonstrate that these latter were produced during changes in base level.

Chronostratigraphy

1• Exercise 1 - chronostratigraphy: construction of a chronostratigraphic chart with the support of a movie that tracks an evolving chronostratigraphic chart and the fill of the associated sedimentary basin.

Outcrop sequence stratigraphy - carbonates

Introduction to Sequence Stratigraphy of Carbonates Sections - Miocene Carbonates of Mallorca, Spain: the first steps in the use of measured sections to build sequences stratigraphic models of carbonate platform and reef depositional systems, using measure sections from the sea cliffs lining the south eastern shore of Mallorca.

Exercise 1 - Measured Sections at Cap Blanc- Cliffs of Late Miocene Reef Complex: introduction to carbonate cycle identification on the basis of the carbonate lithofacies within outcrops of the Llucmajor reef. Identification of a vertical set of parasequences and cycles within a measured section.

Exercise 2 - Measured Sections at Cap Blanc- Cliffs of Late Miocene Reef Complex: two to three measured sections are correlated using a combination of predicted trajectories of parasequence stacking patterns in the Llucmajor reef, changes in carbonate facies, and major tied from section to section.

Exercise 3 - Measured Sections and Wells in the Llucmajor Late Miocene Reef Complex: correlation of wells and measured sections in the Llucmajor using predicted reef trajectories to construct a regional sequence stratigraphic interpretation of facies geometries that involve lithofacies, major surfaces, and parasequences that tie them together.

Outcrop sequence stratigraphy - Clastics

Introduction to Sequence Stratigraphy of Clastic Sections - Book Cliffs, Utah: the first steps in the use of measured sections to build sequences stratigraphic models of clastic shoreline depositional systems, using measure sections from the Book Cliffs in Utah.

Exercise 1 - Measured Section at Kennilworth - Book Cliffs, Utah: introduction to parasequence identification on the basis of the lithologies within outcrops. One section is considered and used to identify a vertical set of parasequences within a measured section.

Exercise 2 - Measured Sections at Panther, Kennilworth & Coal Canyons - Book Cliffs, Utah: three measured sections are correlated using a combination of changes in grain size and depositionals facies to identify the major and parasequence stacking patterns that are tied from section to section.

Exercise 3 - Measured Sections from Gilson Gulch to Coal Canyon - Book Cliffs, Utah: correlation of twelve measured sections in the Book Cliffs and construction of a regional sequence stratigraphic interpretation of facies geometries using lithofacies, major surfaces, and parasequences to tie these together.

Well Log sequence stratigraphy - General Preamble

1• Introduction to Sequence Stratigraphy with Well Logs: the first steps in the use of well logs to build sequences stratigraphic models of depositional system.

2• Well Log Suites: brief description of how different types of well log are used to interpret sedimentary geology.

3• Well Log Response Character: explanation of the use of the shapes of well log curves to track changes in mineral content, and grain size and so interpret sedimentary geology.

4• Well Log Stacking Patterns: explanation of how aggradational, retrogradational and progradational stacking patterns identified on well logs can be used to interpret sedimentary depositional settings.

Well Log sequence stratigraphy - Clastic High-Frequency Signals

1• The Geologic setting of the La Pascua Formation - Guarico Sub-Basin: general geological setting of the nearshore clastics of the Lower Oligocene La Pascua formation of the Las Mercedes Field in the West Guarico Block, Venezuela, their lithology, relationship to sea level and plate tectonic setting.

2• Introduction to Sequence Stratigraphy of the La Pascua Formation - Guarico Sub-Basin: first steps in the use of well logs to build sequences stratigraphic models of clastic shoreline depositional systems for the Lower Oligocene La Pascua formation of the Las Mercedes Field in the West Guarico Block, Venezuela.

Exercise 1 - Well log correlation using SP & RES logs: interpretation of local north eastern Venezuelan clastic stratigraphy using three wells (W-1, W-2, W-3) that penetrate the Lower Oligocene La Pascua formation of the Las Mercedes Field in the West Guarico Block.

Exercise 2 - Well log correlation using SP & RES logs: interpretation of local north eastern Venezuelan stratigraphy and identification of a clastic sequence in an incised valley using 10 wells (W-1 to W-10) that penetrate the Lower Oligocene La Pascua formation of the Las Mercedes Field in the West Guarico Block.

Exercise 3 - Well log correlation using SP & RES logs: interpretation of local north eastern Venezuelan stratigraphy and identification of a clastic sequence of an incised valley, and its relationship to sea level from 22 wells (W-1 - W-22) that penetrate in the Lower Oligocene La Pascua formation of the Las Mercedes Field in the West Guarico Block.

Exercise 4 - Well log correlation using SP & RES logs: interpretation of local north eastern Venezuelan stratigraphy and identification of a clastic sequence of an incised valley, and its relationship to sea level from 5 Wells (me333, me296, me428, me313 and me 486) within the central portion of the Northern Strike Line that penetrate in the Lower Oligocene La Pascua formation of the Las Mercedes Field in the West Guarico Block.

Exercise 5 - Well log correlation using SP & RES logs: interpretation of local north eastern Venezuelan stratigraphy and identification of the clastic coastal and incised valley sequences, and their relationship to sea level from wells that penetrate in the Lower Oligocene La Pascua formation of the Las Mercedes Field in the West Guarico Block on a North-South Dip line , a Northern Strike Line and a Southern Strike Line.

Solutions for Exercise 1, 2, 3, 4 and 5: interpretation of well log cross-sections of coastal sedimentation and incised valley fill explained with a movie of the evolving clastic sequences.

3• References: References for the interpretation of Well logs and References for the Guarico Sub-basin geological framework and regional stratigraphy.

Core & Well Log sequence stratigraphy - carbonate High Frequency Signals

1) Introduction to high frequency Carbonate Sequence Stratigraphy: an explanation of why cycles and parasequences are used to study ancient carbonate systems

2) Correlation of cycles and/or sequence parasequences; cycles and/or parasequence sets; and systems tracts in the Hanifa formation: based on stacking patterns & log character. A description of the surfaces that bound and subdivide parasequences and how they are identified on well logs. How to construct Fischer Diagrams.

Exercise 1: Introduction to parasequence identification on the basis of the lithologies within cored wells. Well # 1 penetrates a shallow shelf region and Well # 2 a deeper region.

Exercise 2: Four well logs correlated using a combination of well logs and cores to identify the major <stratigraphic surfaces and parasequence stacking patterns that are tied from well to well.

Exercise 3: The use of 14 (Fourteen) well logs to make a regional sequence stratigraphic interpretation of facies geometries by identifying major surfaces, establishing the lithofacies, building a Fisher diagram.

Exercise 4: Improve high frequency cycle correlation using the Fischer Diagram.

3) A well log cross-section across the margin of "NE shelf of the Delaware Basin of the Permian Basin" in New Mexico and the NW flank of the Central basin Platform (After Harris & Saller 1999).

Exercise 1: Introduction to cycle (and/or ParaSequence) identification on the basis well logs to identify the major stratigraphic surfaces and cycle (and/or parasequence) stacking patterns

Exercise 2: Well logs correlated using a combination of well logs and seismic tied to synthetic to identify the geometry of major stratigraphic surfaces and cycle (and/or parasequence) stacking patterns that are tied from well to well.

Exercise 3: Fill in details of lithofaceis on partly interpreted well log section with information gleaned from interpreted seismic and establish cycle (and/or parasequence) stacking patterns that are tied from well to well.

4) "Beltzaren Lurraldean Field in NW Syldavia" (After Hergé 1939). Exercises that introduce high frequency carbonate sequence stratigraphy with an "hypothetical" example: introduction to use of well log interpretation of carbonates using awell-log section across the imaginary Ordovician carbonate margin of the Beltzarin basin.

Exercise 1: Introduction to surfaces and parasequence stacking patterns tied from well to well.

Exercise 2: Well logs correlated using a combination of well logs and cores to identify the major stratigraphic surfaces and cycle (and/or parasequence) stacking patterns that are tied from well to well.

Seismic sequence stratigraphy

1• Introduction to Seismic Sequence Analysis: the first steps that need to be taken to make a seismic stratigraphy interpretation and the definition and illustration of genetic reflection packages that envelope seismic sequences and systems tracts.

2• Exercise 1- Tying a Well Synthetic to a Seismic Line: a seismic cross-section through Little Knife Field tied to a synthetic seismic trace made from velocity log from the Zablotny #1well so determining the local stratigraphy of the Williston basin.

3• Exercise 2- Seismic Sequence Analysis: sequence stratigraphy of a seismic line across the lower Cretaceous of the offshore of South Africa.

4• Exercise 3- Seismic Sequence Analysis: sequence stratigraphy of five regional seismic lines from the National Petroleum Reserve of Alaska (NPRA):

a) Objectives & Data: seismic used to determine the geometric relationship of sequences, delta migration, local and regional tectonics, and the eustatic signal.

b) Geological Setting: Colville "foreland" basin initiated in the Jurassic and filled by prograding clinoforms of siliciclastics through the Cretaceous and Tertiary.

c) Class Answer - sequence stratigraphy of Lower Cretaceous: slow and constant rate of subsidence with a steady inflow of clastics responding to second and third order eustatic signals in the Cretaceous section with localized higher-frequency (4th order?) events related to delta migration.

5• Exercise 4 - Seismic Sequence Analysis: carbonate sequence stratigraphy of a regional seismic line from the western Great Bahamas Bank:

a) Objectives & Data: carbonate sequence stratigraphy of the shelf, reef crest, slope and down slope basin floor fans related to local changes in base level and the Haq et al (1987) sea level chart.

b) Seismic Line: Cretaceous and Tertiary carbonate sediments of the western Great Bahamas Bank reflect the effects of changes in sea level.

c) Class Answer - The tie of Sequence Stratigraphy of the Neogene Section to Eustasy: A slow and constant rate of subsidence, and steady flux of carbonates sediments onto the Great Bahamas Bank caused a close balance between aggradation and progradation, while small changes in the rate of relative sea level movement and/or carbonate accumulation causing immediate switches from aggradation to progradation at the margin.

An Introduction to the Hunt For Oil provides a link to a series of lectures and exercises compiled by Fred W. Schroeder when he worked for ExxonMobil to introduce earth scientists to the geology and geophysics applied in hydrocarbon exploration.Topics range from a background to the oil industry; the basics of prospecting; well log data; seismic and their Interpretation; structural and stratigraphic analysis; drilling prospects and a lease sale. The site is provided courtesy of ExxonMobil.

Sunday, February 10, 2013