Table Of ContentDevelopments in Petroleum Science, 4
GEOMORPHOLOGY OF
OIL AND GAS FIELDS IN
SANDSTONE BODIES
C.E.B. CONYBEARE
Australian National University, Canberra (A.C . T.)
ELSEVIER SCIENTIFIC PUBLISHING COMPANY
Amsterdam - Oxford - New York 1976
ELSEVIER SCIENTIFIC PUBLISHING COMPANY
335 Jan van Galenstraat
P.O. Box 211, Amsterdam, The Netherlands
AMERICAN ELSEVIER PUBLISHING COMPANY, INC.
52 Vanderbilt Avenue
New York, New York 10017
Library 01 C0ngrr.a Calaloging in Publication Data
Conyheare, C E B
Geomorphology of oil and gas fields in sandstone
bodies.
(Developments in petroleum science ; 4)
Includes hibliographical references and indexes.
1. Geornorphology. 2. Rock traps (Hydraulic
engineering) 3. Sandstone. 4. Petroleum-Geology.
5. Gas, Natural-Geology. I. Title. 11. Series.
GB406. c63 553' .B 7537974
ISBN O-~!+I&-lJ.398-7
Copyright b 1976 by Elsevier Scientific Publishing Company, Amsterdam
AH rights reserved. No part of this publication may be reproduced, stored in a
retrieval system, or transmitted in any form or by any means, electronic,
mechanical, photocopying, recording, or otherwise, without the prior written
permission of the publisher,
Elsevier Scientific Publishing Company, Jan van Galenstraat 335, Amsterdam
Printed in The Netherlands
ACKNOWLEDGEMENTS
The author wishes to acknowledge the assistance of Ms P.M. Carle,
Ms E.A. Kilner, Mr L. Seeuwen and Mr G.R. Harper in the preparation of the
typescript and illustrations. Acknowledgement is also due to the following
organizations, institutions, and publishers from whose publications the quota-
tions and many of the illustrations in this book have been drawn: Geological
Society of America, American Association of Petroleum Geologists, Society
of Economic Paleontologists and Mineralogists, Canadian Society of Petroleum
Geologists, Canadian Institute of Mining and Metallurgy, Royal Geological and
Mining Society of the Netherlands, Australian Petroleum Exploration
Association, Four Corners Geological Society, Delaware Geological Society,
Rocky Mountains Association of Geologists, Wyoming Geological Association,
Houston Geological Society, Gulf Coast Association of Geological Societies,
Dallas Geological Society, Tulsa Geological Society, Kansas Geological Society-
United States Geological Survey, U.S. Bureau of Reclamation, U.S. Navy
Hydrographic Office, Mississippi River Commission, Illinois Geological Survey,
Indiana Geologcal Survey, Geologische Dienst der Nederlanden, U.S.S.R.
Ministry of Oil Industries, University of Texas, Schlumberger Well Services,
Nedra Press (U.S.S.R.), John Wiley and Sons, Prentice-H'dl, Princeton
University Press, Chapman and Hall, Springer-Verlag, Gulf Publishing Company,
Tracer Petroleum and Mining Publications, and Elsevier Scientific Publishing
Company.
The author also wishes to acknowledge the facilities offered to him during
visiting appointments at the University of Calgary and the Colorado School of
Mines.
PREFACE
This book is essentially about stratigraphic traps for oil and gas. Many of
the examples discussed are geomorphologic features having inherent closures
without any secondary structural element; others are primarily geomorpho-
logic features modified by folding or faulting to produce local closures. The
first category comprises traps that are purely stratigraphic, although the accu-
mulation of hydrocarbons may have been assisted by regional or local tilting
of the strata, or by deformation caused by compaction of the underlying sedi-
ments. The second category, which includes a much larger number of known
examples, comprises structural-stratigraphic traps. Many of these traps have
proved to be elusive, particularly those of the first category which commonly
defy detection by seismic methods. In some cases, discovery has been ac-
cidental, and further exploration to delineate the accumulation has been
empirical.
The purport of this book is to briefly present examples illustrating the main
geological characteristics of geomorphologic features that have controlled or
influenced the accumulation of oil and gas in particular fields, with a view to
using such examples as models in the search for new fields in sandstone bodies.
Many of the examples presented have been so well documented that they
stand as classic examples of stratigraphic fields in which oil and gas accumula-
tions are controlled by geomorphologic features. Others have yet to be defined
unequivocally, but are included as additional references to assist in the inter-
pretation of geophysical and sub-surface geological data.
The author is indebted to the many geologists who have written about the
hydrocarbon accumulations and geological features described herein, without
whose efforts it would not have been possible to compile this book.
Canberra, A.C.T. C.E.B. CONYBEARE
1
INTRODUCTION
Accumulation of oil and gas in a sandstone body depends on several
factors including the state of generation and time of migration of
hydrocarbons or their precursors, directional variations in porosity
and permeability, the existence of stratigraphic or structural closure
with a suitable seal, and the geometry of the sandstone body. Many
holes have been drilled on the basis of geophysical inteqretations that
indicated structural closure within a prospective section, only to find
the section lacking in suitable source beds for hydrocarbons, or with
no impermeable seal above the potential sandstone reservoir. The
sandstone itself may be locally tight. Further, the spatial relation-
ships of depositional trends and geometry to permeable zones within the
sandstone body are commonly unknown. To complicate our understanding of
the situation, the depositional trends and geometry of the sandstone body
itself may not be known. With these possibilities in mind, the following
comments are offered on the classification of sandstone bodies.
A sheet or blanket sandstone body may be designated as a mappable
stratigraphic unit, such as a member or formation, and yet lack continuity
and homogeneity. At one locality it may consist of a single sandstone
unit, and at another it may comprise two or more sandstone beds that have
individual depositional trends, shapes, and petrophysical characteristics.
At a particular location oil or gas may be encountered in Sandstone "A",
where it occurs below the up-dip edge, but not in adjacent Sandstone "B"
that pinches out elsewhere. This type of situation is common in alluvial
point bar and channel-fill sands, in anastomosing delta distributary sands,
and in off-lapoing marine shoreline sands.
2
A classification of sand body shapes is proposed by Pettijohn,
Potter and Siever (1972) after the classification of Potter (1962, b).
They say that there are at least four different basic recurring shapes
to sand bodies, illustrated by Fig. 1-1, and make the following statement
on p. 440, "Equidimensional sand bodies have length-width ratios of
approximately 1:l and may cover a few to thousands of square kilometers.
These have been called sheets and blankets. Elongate sand bodies, on
the other hand, are those with long dimension notably exceeding width
and are one of three types: pods, ribbons and dendroids (Potter, 1962,
Fig. 3). -have length-width ratios of three or less where ribbons
are much more elongate with length-width ratios of three or more and
possibly as high as 20 to 1 or more. Rich (1923, p. 103) used the term
shoestring for such bodies. Dendroids are commonly more sinuous and
have branches, either tributaries or distributaries. By lateral migration,
coalescent ribbons and dendroids may form belts, dendritic belts being the
more common. 'I
Sheets
E Ion gate
Fig. 1-1 Classification of sand body shapes. (Modified by Pettijohn,
Potter and Siever, 1972, after Potter, 1962b).
3
These designations are based on the geometry of the sandstone bodies
and do not have any implicit connotation as to depositional environment
or geomorphology. Also, they can be misconstrued and misapplied, with
particular reference to some so-called sheet or blanket sandstones.
Nevertheless, they serve a useful purpose in qualifying and to some extent
quantifying the shapes of sandstone bodies.
Sheet-like stratigraphic units, consisting essentially of sandstone,
may have originated as transgressive or regressive shoreline sands, as
eolian sands, as widespread sand beds within coalescing alluvial fans, as
braided and laterally migrating estuarine deposits, as river sediments on
a broad plain, or as layers of sand swept out on abyssal plains of the ocean.
Apart from the similarity of their gross dimensions, these units are
markedly different in their internal structure and stratigraphic
relationships. All are diachronous to some degree, although a layer
of sand swept rapidly on to an abyssal plain will represent so short
a period of time that it can be regarded as a stratigraphic marker bed.
Internally, a sheet-like stratigraphic unit may consist of several
distinct sandstone bodies that may be locally connected or entirely
separated by impermeable shale layers. These separate bodies may be
nearly equidimensional or elongate in shape. A sequence of off-lapping,
elongate shoreline sands may have a wide areal distribution within a
comparatively thin stratigraphic interval, and consequently form a sheet-
-like unit in gross dimensions. Within such an interval the preferred
orientations of these elongate sandstone bodies are parallel to the
original coastline; but the interval may also include other elongate
sandstone bodies, oriented approximately normal to the coastline, that
were formed as distributary sands filling channels cut into the shoreline
sands. In many cases the distributary sands cannot readily be distinguished
from the shoreline sands with which they are associated, although variations
4
ENVIRONM E NTS
CHANNELS
STREAM
SHEET F LOODS
ALLUVIAL FLOWS
4
FANS “SIEVE DEPOSITS”
(APEX, MIDDLE I
DEBRIS FLOWS
8 BASE OF FAN) VlSCOUS
4
FLOWS
MUD FLOWS
CHANNELS
(VARYING SIZES)
BRA I DED
ALLUVIAL STREAMS ,,, LONGlTUDlNAl
,x
(FLUVIAL) Q
TRANSVERSE
CHANNELS
MEANDER
MEANDERING NATURAL LEVEES
BELTS
STREAMS
(ALLUVIAL
POlNT BARS
VALLEY)
1
STREAMS, LAKES
F LOODBASINS
8 SWAMPS
1
TYPES:
COASTAL DUNES
TRANSVERSE
SElF
EOLIAN DUNES DESERT DUNES ( LONGlTUDlN AL )
BARCHAN
PARABOLIC
OTHER DUNES
DOME-SHAPED
Figs. 1-2, 1-3 and 1-4
Classification of depositional environments of sand bodies
and their related geomorphologic features. (After Le Blanc,
1972, and Bernard and Le Blanc, 1965).
5
DEPOSIT IONA L MODELS
ORAlDtD CHANNtLS IWAIHtll
AND AOANDONfD CMANNfL5
ALLUVIAL FAN
UfN,
MEANDERING STREAM
COASTAL
DUNES
6
E NVI RO N M E NTS
~~
CHANNELS
MEANDER
NATURAL LEVEES
BELTS
UPPER
DELTAll POINT BARS
PLAIN
ST REAMS,
F LOODB A S INS LAKES
& SWAMPS
CHANN EL5
DlSTR IBUTARY
2a C HANN ELS
NATURAL LEVEE!
Z
0-
c- LOWER
DELTAIC
DELTAIC
v,
Z PLAIN MARSH,
a INTER-
LAKES,
DISTRIBUTARY
pi TIDAL CHANNEL:
I- AREAS
& TIDAL FLATS
R IV ER-MOUTH
BARS
-
INNER BEACHES &
?:
F RlNGE 1 BEACH RIDGES
L
L TIDAL FLATS
DISTAL
Fig. 1-3. For caption see p.4.
