Abstracts for Carbonates & Evaporites, v. 14, no. 1, 1999, June
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UNDERDEVELOPED OIL FIELDS - UPPER PENNSYLVANIAN AND
LOWER
WOLFCAMPIAN CARBONATE RESERVOIRS OF SOUTHEAST NEW MEXICO
Ronald F. Broadhead
New Mexico Bureau of Mines and Mineral Resources,
a Division of New Mexico Tech,
Socorro, NM 87801
ABSTRACT: Carbonate reservoirs in the Cisco and Canyon
(Upper Pennsylvanian) and lower
Wolfcampian (Permian) sections in the
Permian Basin of southeast New Mexico, U.S.A. are
significant reservoirs for
oil and gas. The approximately 400 fields that have produced from these
reservoirs have yielded a cumulative production of 490 million bbls oil
(MMBO; 78 million m3)
and 3.2 trillion ft3 (91 billion
m3) gas, 12% of the oil and 16% of the gas produced in southeast
New Mexico. Sixteen of these fields have been identified that were
underdeveloped at some stage
in their history. Cumulative production ranges
from Milnesand West (0.210 MMBO; 0.033 million
m3) to Dagger Draw
(31 MMBO; 4.9 million m3).
Although initially underdeveloped, subsequent redevelopment of these 16
fields added significantly
to reserves and production. Statistical analysis
of production decline curves was used to estimate
reserves developed during
initial drilling of these fields and during subsequent phases of
redevelopment. For the 16 fields studied, redevelopment accounted for a
total of 65% of developed
reserves. Redevelopment accounted for more than
90% of total reserves at Dagger Draw and 99%
at Baum.
Redevelopment in these fields was generally in undrilled portions of the
fields, and not in bypassed
pay zones. The fields are formed by
stratigraphic traps but were initially thought to be structural
traps and
were developed on structural culminations. Because initial development was based
on
the premise of structural entrapment, the majority of reserves in these
fields remained unproduced
until redevelopment. Redevelopment generally
resulted in a fivefold to tenfold increase in numbers
of producing wells and
productive acreage. Because 84% of Upper Pennsylvanian and lower
Wolfcampian
fields have less than 10 producing wells and 57% have less than three producing
wells, it would appear that significant reserves may remain undeveloped in
most existing fields. For
those fields that have been developed only on
structures, additional study of carbonate facies and
environments is needed
to fully delineate the reservoirs and identify full potential.
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TIDAL FLAT ROCKS AND SEDIMENTS ALONG THE EASTERN COAST OF THE
UNITED ARAB EMIRATES
Mohamed I. El-Sayed
Geology Department, United Arab Emirates
University, P.O. Box 17551, Al Ain, United Arab
Emirates
ABSTRACT: The geomorphologic and petrographic
characteristics of the calcareous hard rocks in
the intertidal and
supratidal zones of the eastern coast of the United Arab Emirates, where it
faces the
Gulf of Oman, were investigated. The tidal zone can be broadly
classified into two major physiographic
provinces. A northern province that
has a rather steep profile and a tidal flat that is very narrow and is
characterized by lithoclasts of gravelly sand sediments. It is formed of
beachrocks, well-developed
coastal terraces and cliffs and is bounded
landward by mountains composed mainly of peridotite and
gabbros. The
southern province tidal flat is much wider than the north province with a
shallow, tide
dominated and sheltered coast where sandy bioclasts
accumulate. The mountains surrounding such
areas are located several
kilometers from the coast and are largely formed by gabbros.
Beachrocks are developed as discontinuous beds in narrow belts of pavement,
limited essentially to
the intertidal zone and with a surface, which is
generally sloping seaward. These rocks are partly
covered by beach sand,
skeletal debris, algae and other rock fragments encrusted by living organisms.
They rest on dense to friable loose beach sand mainly composed of biogenic
fragments strongly bonded
by carbonate cements. Tidal terraces are almost
flat benches that vary in their geomorphologic pattern
and three
well-developed terraces are recognized. Based on the composition of framework
grains,
beachrocks can be grouped into two types: lithic and bioclastic. The
lithoclasts are mainly composed of
peridotite, gabbros, pyroxenes,
calcareous rock fragments and washed sediments derived from wadi-fill
and
dust storms. The bioclastic sediments are chiefly fragments of corals,
foraminifera, pelecypods,
gastropods, crabs, echnoids and algae. The
beachrock cement is mainly formed by aragonite, micrite
and coarsely
crystalline calcite with a subordinate amount of dolomite. Precipitation of
aragonite appears
to be mainly controlled by the micrite substrate and at
least three successive stages of cement fill are
observed.
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THE ISOTOPIC COMPOSITION AND DIAGENETIC HISTORY OF PLEISTOCENE
CARBONATES, NORTH QATAR
Hanafy Holail
Geology Department, Faculty of Science, Alexandria
University, Alexandria, Egypt
ABSTRACT: Field, petrographic, and geochemical data for
Pleistocene oolitic carbonates from
North Qatar suggest that the ooids
formed in a marine environment separating the open Gulf from the
coastal
sabkhas. Locally, the more homogeneous granulometry and abundant cross-bedding
of these
rocks reveal an aeolian depositional environment. Petrographic
examination shows that these rocks
are ooid grainstones with low-Mg calcite
cements. The sequence of petrographic features suggests a
progression of
diagenetic fluids from more marine to more meteoric. Early marine cementation
was
followed by partial dissolution of the ooids and cements. Dissolution
and cementation processes
redistributed the primary porosity. After
mineralogical stabilization was completed, subsequent meteoric
flow caused
very localized cementation. The final diagenetic phase precipitated was a low-Mg
calcite
spar cement, representing diagenesis in a fresh-water zone. There is
no indication for the presence of
dolomites. This sequence of diagenetic
features was the result of a fall in eustatic sea-level following
deposition.
Stable isotopic evidence suggests that diagenetic fluids dominated by
meteoric water were responsible for
dissolution and cementation processes.
Oxygen isotopes of ooid grains and low-Mg calcite cements range
from +0.9 ‰
to -2.1 ‰ PDB and from -3.6 ‰ to -8.0 ‰ PDB, respectively. The 13C
values of the ooid
grains (+4.8 ‰ to +2.5 ‰ PDB) are slightly heavier than
those of the low-Mg calcite cements (+3.4 ‰ to
-1.7 ‰ PDB). This may suggest
that the diagenetic system was closed with respect to carbon, with little
introduction of carbon from a non-carbonate source.
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SEQUENCE STRATIGRAPHY OF THE MIDDLE DEVONIAN
WINNIPEGOSIS
CARBONATE-PRAIRIE EVAPORITE TRANSITION, SOUTHERN ELK POINT
BASIN
1Jisuo Jin and 2Katherine M.
Bergman
1Department of Earth Sciences, University of
Western Ontario, Ontario, Canada, N6A
5B7
2Department of Geology, University of
Regina, Regina, Saskatchewan, Canada, S4S 0A2
ABSTRACT: The Middle Devonian Winnipegosis reefs in the
southern Saskatchewan portion of the Elk
Point Basin contain extensive
vadose diagenetic features, such as dissolution breccia, and cavities/caves
filled
by microbialite, pisolite and anhydrite. Basinal facies adjacent to
reef buildups are characterized by the Ratner
laminite, which consists of
three brining-upward successions of laterally continuous, laminated dolomite and
anhydrite. The basal cycle starts with a relatively thick unit of
anhydrite-free, millimeter-scale dololaminite,
changing upward into
interlaminated carbonate and anhydrite, and ending with enterolithic, nodular to
mosaic
anhydrite. Subsequent cycles generally lack the dololaminite of the
basal cycle. The Ratner laminite grades
upward into the bedded to massive
mosaic anhydrite of the Whitkow Member (lower Prairie Evaporite) in
areas
adjacent to reefs. Deposition of the Ratner laminite and the Whitkow Anhydrite
is interpreted as genetically
related to the vadose diagenetic processes,
when the Elk Point Basin became restricted. The carbonate laminite
in the
basal Ratner was accumulated when seepage of fresh marine water through the
barrier kept pace with the
rate of evaporation, preventing a complete
drawdown and desiccation of the basin. Precipitation of the laminated
carbonate was stimulated by vadose diagenesis of the carbonate buildups and
by microbial activity. Each Ratner
brining-upward succession represents a
progressive drawdown when the rate of basin brine evaporation exceeded
seepage of marine water into the basin. Marine water seeping through the
reefs was enriched in calcium cations by
Mg++-Ca++
exchange with the limestone (dolomitization) and by dissolution of reef rocks,
and was responsible for
the precipitation of calcium sulphate in areas
adjacent to the carbonate reefs through brine mixing processes. During
vadose diagenesis of the Winnipegosis reefs and deposition of the Ratner
laminite and Whitkow Anhydrite, brine
level in the barred Elk Point Basin
was controlled by the rate of seepage of marine water through the barrier, which
in turn was controlled by eustatic sea level changes in the open ocean. The
basal anhydrite-free dololaminite of the
Ratner represents a Falling Stage
System Tract when evaporative drawdown was largely compensated by seepage
of
marine water into the basin. The interlaminated carbonate and anhydrite of the
middle and upper Ratner are
interpreted as a Lowstand System Tract
associated with evaporative drawdown and increased cyanobacterial
activity
under near-desiccation conditions when evaporation exceeded seepage. The Whitkow
Anhydrite represents
a Transgressive System Tract deposited during sea level
rise in the open ocean that led to an increased rate of
seepage, higher
basin brine level and diminished microbial influence on bedding structures.
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PATTERNS IN THE COMPOSITIONS, PROPERTIES, AND GEOCHEMISTRY OF CARBONATE MINERALS
L. Bruce Railsback
Department of Geology, University of Georgia,
Athens, Georgia 30602-2501 USA
ABSTRACT: The diversity of carbonate minerals is remarkable,
if largely unappreciated. For example, 277
carbonate-bearing minerals have
been recognized, and among them are 158 pure carbonates of cations with
valences from 1+ to 6+. The other 119 minerals additionally contain
chloride, fluoride, borate, sulfate, phosphate,
arsenate, arsenite,
antimonate, or silicate groups, or combinations of those anions. However,
combinations of
anions with cations are not uniformly distributed, so that
there are no bicarbonates or simple carbonates of highly-
charged cations,
few hydrated or OH-bearing minerals of monovalent cations, and few U-bearing
carbonates with
anions other than CO32,
OH-, and O2-. On the other hand, simple carbonates of
divalent cations, OH-bearing Al
carbonates, and fluoride-bearing carbonates
of rare-earth elements are remarkably numerous. Many of these trends
can be
related to the coordination chemistry of cations in the solutions from which
these minerals form.
Among nearly all the carbonate-bearing minerals, ionic potential of the
cations is a major control on the extent of
hydration. Degree of hydration
is in turn a major control on hardness, density, and solubility.
Among the simple carbonates, hardness, density, and positions of
spectroscopic peaks vary linearly with cation radius
or mass, although such
trends usually exist only within crystallographic groups or only within cation
groups defined by
the periodic table. In contrast, geochemical parameters,
such as solubility and fractionation of oxygen isotopes, vary
with degree of
cation fit in the 6-fold or 9-fold site of the rhombohedral and
orthorhombic simple carbonates, so that
there is not a linear variation with
cation size. The same is true for the distribution coefficients of cations in
calcite and aragonite.
Patterns thus emerge among the compositions, properties, and geochemistry of
the carbonate minerals, with cationic
potential and type as a major
influence on composition, with degree of hydration and cation radius or mass as
a control
on physical and spectroscopic properties, but with cation fit as
the major control on geochemical parameters. These
patterns allow
qualitative prediction of mineral properties and help explain the origins of
some of the major problems in carbonate petrology.
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COLD WATER POLAR ARAGONITIC BIVALVE ELEMENTAL COMPOSITION, EAST
ANTARCTICA
C. Prasada Rao
School of Earth Sciences, University of Tasmania, GPO
Box 252- 79, Hobart, Tasmania, Australia 7001
ABSTRACT: Aragonitic bivalves and abiotic aragonite are
common in cold water Antarctic environments.
Aragonitic bivalves have lower
Mg, Sr, Fe and Mn and higher Na concentrations than those in abiotic polar
aragonite. MgCO3 values in polar aragonitic bivalves and abiotic
aragonite are related to pCO2. Sr values vary
with aragonite
types, seawater temperature and seawater content in the fluid precipitating
aragonite. Abiotic polar
aragonite contains much larger concentrations of Fe
and Mn than those in aragonitic polar bivalves because abiotic
aragonite
formed subglacially below the zone of O2 minimum at very shallow
water depths. Na values in aragonitic
bivalves are indicative of both
salinity and rates of crystal growth, whereas Na values in abiotic aragonite
decrease
with decreasing salinity. The concentrations of Mn, Na and Sr
indicate that aragonitic bivalves formed faster than
abiotic aragonite. The
abiotic aragonite forms rapidly and precipitates significant amount in less than
a year. This
comparative study enables an understanding of cold water polar
biotic and abiotic aragonites related to environment,
water temperature, ice
cover, pCO2 levels, redox potential, meltwater dilution, salinity and
rate of carbonate formation.
These aspects are essential in understanding
modern and ancient glacial sedimentation and diagenesis.
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ELEMENTAL SULFUR FORMATION RELATED TO CELESTINE REDUCTION: AN EXAMPLE OF BIOMINERALIZATION OF BACTERIAL ORIGIN
E. Tekin, B. Varol, *G.M. Friedman, and A.U. Dogan
Department of
Geological Engineering, Ankara University, Tandogan, 06100, Ankara,
Turkey
*Department of Geology, Brooklyn College and Graduate School of the
City University of New York,
Brooklyn, NY; Northeastern Science Foundation,
Inc. affiliated with Brooklyn College of the City University
of New York,
Rensselaer Center of Applied Geology, Troy, NY; For correspondence: Northeastern
Science Foundation, Inc., 15 Third Street, P.O. Box 746, Troy, NY 12181; [email protected]
ABSTRACT: This study investigates the disseminated elemental
sulfur formation in celestine mineralization in the
upper member of the
Bozbel Formation (Eocene) in the Sivas basin, Turkey. Optical and scanning
electron
microscope studies indicate that the sulfur minerals have three
main morphologies including lacy, grape-like, and
spheroidal - lobous types
structures. These sulfur structures are occasionally coated with organic matter.
Total
organic carbon and infrared spectrometry studies indicate that an
average of 1 % organic matter in this sulfur is of
biogenic origin. Detailed
studies on these elemental sulfur deposits suggest that the sulfur was formed by
the
reduction of celestine through the metabolic activities of sulfate
reducing bacteria. This observation is supported by
the trace element values
obtained through x-ray fluorescence analyses on both the celestine and the
elemental sulfur
samples.
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SEDIMENTOLOGY AND EVAPORITE GENESIS OF NEOGENE CONTINENTAL SABKHA PLAYA COMPLEX, KARAKEÇILI BASIN, CENTRAL ANATOLIA, TURKEY
1Ibrahim TÜRKMEN and 2Mehmet
ÖZKUL
1Firat Üniv. Müh. Fakültesi, Jeoloji Müh.
Bölümü, Elazig, Turkey
2Pamukkale Üniv. Müh.
Fakültesi, Jeoloji Müh. Bölümü, Denizli, Turkey
ABSTRACT: The Karakeçili basin is an intermontane basin
located about 60 km SE of Ankara in central Turkey
and covers an area of
approximately 200 km2. This Neogene basin is bordered by granite and
gabbro of the Kirsehir
massif to the north-northeast and east, and massive
gypsum of the Mezgit Formation (Oligocene) to the west and
southwest.
Facies associations characterizing a playa complex crop out in this Neogene
basin. These facies associations include,
from the basin margin to the
center, 1-Red massive conglomerate and pebbly mudstone (alluvial fan),
2-Organically
rich mudstone, bearing sparse gypsum crystals (marsh),
3-Cross-laminated-bedded gypsarenite (eolian), 4-Brown-
gray mudstone bearing
gypsum-roses and discoidal and radial gypsum crystals (saline mudflat), and
5-Bedded-
laminated gypsum (ephemeral salt lake).
Evaporites occur commonly as discoidal crystals, sigmoidal crystals,
rosettes, and nodular forms. These were formed displacively within mudstone from
calcium sulphate - rich groundwater during the arid conditions. Stratified
gypsum
represented by macrocrystalline aspects is generally restricted
laterally and is precipitated by the evaporation of brine
sheets on
mudflats.
The source of evaporites in the Karakeçili basin is the gypsum of the Oligocene Mezgit Formation.
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