92 Journal of Applied Sciences.
Management and Engineering Technology.
Vol 6.
No 2, 2025: 92 - 106 Linking Carbonate Facies to Stylolite Distribution of Middle Jurassic Limestone.
Onshore Abu Dhabi Oil Field Mochammad Prahastomi1.
Sadoon Morad2 Aisha Al Suwaidi3 Mohammed Ali4 Budi Muljana5 Ryandi Adlan6 Geology Department.
Universitas Pembangunan Nasional Veteran Yogyakarta.
Special Region of Yogyakarta.
Indonesia
2,3,4
Earth Science Department.
Khalifa University of Science and Technology.
Abu Dhabi.
United Arab Emirates Geological Engineering Department.
Universitas Padjadjaran.
West Java.
Indonesia Center of Geological Survey.
Geological Agency.
Ministry of Energy and Mineral Resources.
West Java.
Indonesia Email: 1moch.
prahastomi@upnyk.
id, 2sadoon.
morad@ku.
ae, 3aisha.
alsuwaidi@ku.
ali@ku.
ae, 5budi.
muljana@unpad.
id, 6ryandi.
adlan@esdm.
Received: 2025-08-25 Received in revised from 2025-09-03 Accepted: 2025-09-10 Abstract This study examines the relationship between facies and stylolitization in the Upper Araej Member carbonates of onshore Abu Dhabi.
Analysis of core and thin sections identified four facies: wispylaminated skeletal wackestone (F-.
, peloidal skeletal mud-dominated packstone (F-.
, coated-grain skeletal grainstone (F-.
, and peloidal skeletal floatstone (F-.
, deposited across a shallow carbonate Stylolites were described and measured for vertical offset amplitude to assess facies Results show facies-related tendencies in stylolite amplitude and morphology.
Mudsupported facies .
specially floatstones and wackestone.
tend to display higher variability, with floatstones reaching amplitudes of up to 20 mm, whereas grainstones may also contain isolated highamplitude stylolites .
p to 14 m.
Packstones and wackestones, by contrast, rarely exceed 10-13 Boxplots highlight greater variability in mud-rich facies, whereas grainstones exhibit narrower Statistical testing (ANOVA, p = 0.
KruskalAeWallis.
H = 3.
38, p = 0.
indicates no statistically significant differences in mean stylolite amplitude across facies, although descriptive data reveal trends in variability and extremity.
Jagged stylolites occur in both mud-rich and grainsupported facies, whereas wispy seams are strongly associated with micrite-rich facies and are largely absent in grainstones.
Stylolites in these carbonates may act as both vertical barriers and localized porosity enhancers.
Their facies-associated occurrence emphasizes the need to integrate stylolitization into reservoir models to better predict connectivity, compartmentalization, and flow behavior in Middle Jurassic carbonates.
Keywords: Carbonate Facies.
Middle Jurassic Limestone.
Onshore Abu Dhabi.
Stylolite.
Upper Araej Member.
Introduction Carbonate rocks constitute more than half of the worldAos hydrocarbon reserves .
and form significant aquifers .
and COCC storage sites .
Their reservoir quality, however, is not solely a product of depositional fabric but is strongly influenced by post-depositional diagenetic The interplay between depositional facies and diagenetic overprint generates a highly complex and spatially heterogeneous porosity-permeability system that cannot be predicted from depositional textures alone .
Among these diagenesis process, cementation, dissolution, dolomitization, and pressure solution play crucial roles in modifying primary porosity and permeability.
Moreover, pressure-solution processes are responsible for the generation of stylolites, which are among the most common diagenetic features in carbonate successions .
Understanding the distribution Prahastomi.
Linking Carbonate Facies to Stylolite Distribution of Middle Jurassic Limestone.
Onshore Abu Dhabi Oil Field and development of stylolites is therefore critical to evaluating reservoir heterogeneity and performance in carbonate systems.
Stylolites are serrated dissolution seams formed through stress-induced pressure solution, where insoluble residues such as clays and organic matter accumulate along irregular solution surfaces .
They typically form perpendicular to the maximum stress direction and are easily recognized by their characteristic jagged morphology.
Stylolites may have a dual impact on reservoir properties.
On one hand, stylolites can form barriers or baffles to vertical fluid flow due to their concentration of insoluble material, thereby reducing permeability .
On the other hand, they may enhance porosity locally through dissolution and leaching of carbonate minerals adjacent to the stylolite seam .
This duality highlights their importance in reservoir characterization, where stylolitization can either impede or facilitate hydrocarbon production depending on facies context and spatial continuity.
Considerable research has been devoted to stylolite morphology, classification, and scaling Early classifications by .
and refinements by .
provided frameworks for categorizing stylolite shapes and roughness patterns.
Other studies have examined the role of burial depth and stress conditions in controlling stylolite amplitude and spacing, as well as their implications for fluid flow and mechanical stratigraphy .
Much of this work has been carried out in European carbonate systems .
, .
) and to some extent in the Middle East .
, .
However, despite this body of literature, relatively few studies have quantitatively examined facies-dependent stylolitization patterns within Arabian Plate carbonates, especially the Middle Jurassic Carbonate.
particular, systematic analyses linking stylolite frequency and amplitude to specific facies types in platform carbonates remain limited.
This study aims to address this gap by quantifying stylolite occurrence across different carbonate facies, including mud-rich facies and grain-supported facies.
By analyzing stylolite frequency and amplitude distributions in relation to depositional facies, this work aims to identify facies-dependent trends in stylolitization intensity.
The findings will provide insights into how depositional fabric and diagenetic processes interact to influence stylolite development.
Furthermore, the potential implications for reservoir quality, particularly permeability anisotropy, compartmentalization, and fluid-flow behaviour will be discussed.
Ultimately, this study contributes to a better understanding of styloliterelated heterogeneity in Upper Araej Member and may provide a predictive framework for evaluating similar carbonate reservoirs across the Arabian Plate.
Geological Settings The United Arab Emirates (UAE) lies on the eastern margin of the Arabian Plate, bounded by the QatarAeSouth Fars Arch to the west and the Oman foreland fold-and-thrust belt to the east .
The region is dominated by shallow-marine epeiric carbonates interbedded with minor evaporites and siliciclastics, reflecting repeated transgressions and regressions throughout the Phanerozoic.
The tectonostratigraphic evolution of the UAE is marked by three major events: .
pre-ophiolite rifting, .
emplacement of the Semail Ophiolite, and .
the Zagros Orogeny .
The rifting history, associated with the opening of the Neo-Tethys Ocean, occurred in two main phases: the late Permian and from the Early Jurassic to Late Cretaceous.
These extensional phases generated widespread shallowmarine carbonate platforms across the Arabian microcontinent under relatively stable conditions.
Stability ended in the Late Cretaceous with emplacement of the SW-directed Semail Ophiolite.
Obduction placed ophiolitic nappes above the pre-Cenomanian passive-margin carbonates, causing flexural loading, thrusting, and folding .
Despite this, most of the Mesozoic carbonate shelf remained undeformed, apart from minor faulting .
Peripheral bulge development induced uplift and erosion, particularly along the Lekhwair High and Sharjah.
Sedimentation during this period shifted to deep-marine mudstones in the Upper Cretaceous, overlain by shallow-marine carbonates of the Simsima Formation .
The subsequent compressional phase, the Zagros Orogeny, occurred during the Late Eocene to Miocene and is linked to collision between the Arabian and Eurasian plates following closure of the Neo-Tethys .
Some studies, however, place initial collision in the Late EoceneAeOligocene .
94 Journal of Applied Sciences.
Management and Engineering Technology.
Vol 6.
No 2, 2025: 92 - 106 This event reactivated deep-seated faults in the frontal thrust belt and triggered uplift along the northern Oman Mountains, leading to erosion of pre-Eocene carbonates .
The study concentrates on the Araej Formation which comprises mainly of ooid-peloidal grainstones, foraminiferal packstones, wackestones, and argillaceous lime mudstones.
The study based on Ammonite content suggested the age of this formation from Bathonian to Callovian .
However, .
suggested a slightly older age, which is Bajocian to Callovian (Offshore Abu Dhab.
and supported by the work of .
which suggest a late Bajocian to Callovian (Onshore Abu Dhab.
Additionally, its equivalent formation is upper and middle Dhruma in Saudi Arabia.
The Upper Araej Member made up of argillaceous mudstones which grade upwards to cemented bioclastic, ooid-peloidal packstones and foraminiferal grainstones with minor wackestone units .
Benthic foraminifera.
Trocholina sp.
, were found pervasively in grain dominated limestone units.
The depositional facies and textural pattern of Lower Araej and Upper Araej members are relatively similar to each other.
However, a study conducted by .
suggested that in terms of diagenesis, dolomitization occurred more frequent in Upper Araej .
specially in topmost par.
than in Lower Araej Member.
Pyrite and anhydrite replacement were reported to be present as well.
A study based on onshore well Abu Dhabi reported that the topmost of Upper Araej Member made up of dolomitic packstones which coincide with residual oil and oil stain .
Figure 1.
Research location (Modified from .
) Prahastomi.
Linking Carbonate Facies to Stylolite Distribution of Middle Jurassic Limestone.
Onshore Abu Dhabi Oil Field Figure 2.
Stratigraphic column of Upper Araej Member .
Method This study focuses on the Upper Araej Member (Middle Jurassi.
from an oil well located onshore Abu Dhabi (Figure .
The well is situated on the flank of an anticline.
Data and interpretation presented were derived from the investigation of 36 core boxes totalling 90 feet.
The carbonate classification applied in this study follows .
However, for analytical and practical purposes.
Packstone facies are further categorized using .
terminology as Mud-Dominated Packstone (MDP) and Grain-dominated Packstone (GDP).
The petrographic analyses of 63 half-stained thin sections were performed to characterize rock textures, grain types, lime mud percentages, calcite-dolomite percentages, mineral types, fracture, and also stylolite morphology.
The depositional environment of each microfacies was interpreted based on the thin section and core description.
To evaluate the relationship between carbonate facies and stylolite development, a statistical analysis of stylolite amplitude was carried out on data collected from Floatstone.
Wackestone.
Packstone, and Grainstone facies in the onshore Abu Dhabi oil field.
Stylolite amplitude values .
n millimeter.
were compiled for each facies from thin-section and core descriptions, and grouped according to petrographic classification.
This work focuses on the measurement of vertical offset, a critical indicator of pressure-solution processes in carbonate rocks.
The offset values, illustrated in Figure 3, are used to evaluate the relative magnitude of stylolitization and to link these features with facies-dependent patterns.
For each facies, basic descriptive statistics for the styolite were computed, including:
Mean amplitude .
: arithmetic average, representing the central tendency of stylolite size.
Median .
: the 50th percentile, used to account for potential skewness in Standard deviation and variance: measures of variability around the mean.
Minimum and maximum values .
: identifying the observed range of stylolite 96 Journal of Applied Sciences.
Management and Engineering Technology.
Vol 6.
No 2, 2025: 92 - 106 Sample count .
: indicating the number of stylolite measurements per facies.
Figure 3.
Stylolite type and morphology modified from .
The measurement of stylolte amplitude is indicated by the vertical offset (V.
The amplitude data were visualized using boxplots to highlight distributional properties across In these plots, the lower and upper box boundaries represent the 25th percentile (Q.
and 75th percentile (Q.
, the line within the box marks the median, and whiskers extend to the minimum and maximum within 1.
5 y IQR.
Data points outside this range were considered outliers.
To test for statistically significant differences in stylolite amplitude between facies, one complementary approach was applied: One-way ANOVA, a parametric test comparing mean amplitudes across facies.
One-way ANOVA is used to test whether the means of more than two groups are significantly different.
The test compares between-group variance .
ariation of group means relative to the overall mea.
with within-group variance .
ariation of values within each grou.
The computed Fvalue is compared against the critical value of the F-distribution at a chosen significance level () to determine whether the group means differ significantly .
The total variation in the data is partitioned as:
SS_Total = SSBetween SSWithin Between-group sum of squares:
SSBetween = .
i * (XEi - XE).
I = 1,A,k .
Within-group sum of squares:
Prahastomi.
Linking Carbonate Facies to Stylolite Distribution of Middle Jurassic Limestone.
Onshore Abu Dhabi Oil Field SSWithin = (Xij - XE.
2 , j =1,A, n_i .
i=1,A,k .
k = number of groups .
ni = number of samples in group i XEi = mean of group i XE = overall mean Xij = observation in group i The mean squares (MS) are defined as:
MSBetween = SSBetween / .
MSWithin = SSWithin / (N-.
The F-ratio is then calculated as:
F = MSBetween / MSWithin where N is the total number of observations.
The KruskalAeWallis H test was employed to evaluate whether the mean stylolite amplitude differs significantly among the four carbonate facies (Floatstone.
Wackestone.
Packstone, and Grainston.
This non-parametric test is an extension of the MannAeWhitney U test to more than two independent groups.
It is particularly well suited to geological and petrographic data, which often violate the assumptions of parametric tests due to skewed distributions, unequal variances, and the presence of The KruskalAeWallis test operates by ranking all observations from all groups together, then assessing whether the sum of ranks differs more than expected under the null hypothesis .
The null hypothesis (HCA) states that the distribution of stylolite amplitude is identical across all facies.
The alternative hypothesis (HCA) is that at least one facies differs in distribution.
The test statistic is calculated as:
H = .
/ (N(N .
)] * (RiA / n.
Ae 3(N .
k = number of groups .
our facie.
N = total number of observations across all groups ni = number of observations in group i Ri = sum of the ranks for group i The statistic H is approximately chi-square distributed with .
Ae .
degrees of freedom, provided that each group contains at least five observations.
The corresponding p-value is used to determine statistical significance at the chosen threshold ( = 0.
If p < , the null hypothesis is rejected, indicating that at least one facies differs in mean stylolite amplitude distribution.
Results and Discussion 1 Facies Characteristics and Depositional Environment Based on optical petrographic analysis and core logging description, the studied interval was divided into four facies.
The shallowing upward sequences were observed which comprises muddominated limestone units deposited on the subtidal open marine and grading upward into coarse graindominated limestone units deposited on the shoal setting.
Several high frequency cycles were recorded in the succession.
98 Journal of Applied Sciences.
Management and Engineering Technology.
Vol 6.
No 2, 2025: 92 - 106 Wispy-laminated Skeletal Wackestone (F-.
This facies, developed predominantly in the basal to middle portions of the Upper Araej, is typified by pervasive wispy lamination.
Contacts with the overlying packstones are most commonly Bioclasts are dominated by planktonic foraminifera, sponge spicules, and gastropods, with subordinate benthic foraminifera and echinoderm fragments (Figure 5.
Non-skeletal components consist chiefly of peloids.
The high lime-mud content indicates deposition below the fair-weather wave base in a low-energy environment.
The frequent occurrence of planktonic foraminifera is consistent with deposition in a relatively deeper, subtidal setting.
The absence of restricted-lagoonal indicators .
dasycladacean alga.
implies open-marine circulation.
Consequently, this facies is interpreted as having accumulated in a low-energy, open-platform environment, within the middle to outer ramp.
Peloidal Skeletal Mud-dominated Packstone (F-.
Mud-dominated packstones .
3Ae2.
8 ft thic.
are among the most widespread lithologies in the studied succession.
They are typically bioturbated and stylolitized, with gradational transitions into overlying wackestones.
In the middle interval, they are interbedded with massive grainstones and wackestones, whereas in the upper interval they alternate with floatstones and grainstones.
The allochem assemblage is dominated by peloids and large benthic foraminifera (Trocholina sp.
), with additional contributions from echinoderms, gastropods, and bivalves (Figure 5.
Bioturbation indicates deposition under shallow-marine conditions with relatively low sedimentation rates.
The absence of miliolids and dasycladacean algae, together with the relatively high faunal diversity, supports interpretation in terms of an open-marine setting.
This facies is therefore considered to represent subtidal sedimentation on an open platform, most likely within the upper to middle ramp.
Coated-grain Skeletal Grainstone (F-.
Grainstones are concentrated in the upper part of the studied succession, where they are typically overlain by wackestones or packstones.
Bed thickness varies between 0.
2 and 2.
6 ft.
In the upper interval, grainstones occur as relatively thick and laterally continuous beds, whereas in the middle interval they are restricted to thinner and less continuous horizons.
The assemblage is dominated by benthic foraminifera (Trocholina sp.
) (Figure 5.
, accompanied by bivalves, echinoderms, and gastropods, with only rare ooids.
Stylolites are generally absent, but when present are jagged to rectangular and filled with cement.
The absence of lime mud and bioturbation suggests deposition under high-energy conditions, likely within a shoal or beachAebarrier island complex.
Such hydrodynamic regimes are unfavorable for the preservation of bioturbation structures owing to persistent wave and current activity.
Thin interbedded grainstones in the middle interval, however, may represent spillover lobes or low-amplitude sandwaves within a lagoonal, shallow-subtidal setting.
Peloidal Skeletal Floatstone (F-.
Floatstones occur predominantly in the upper interval, where they are interbedded with grainstones and packstones, and less commonly in the basal interval, where they alternate with wackestones and packstones.
Bed thickness ranges from 0.
1 to 2.
4 ft.
This microfacies is characterized by a substantial lime-mud matrix.
Allochems consist mainly of peloids, large bivalves, benthic foraminifera (Trocholina sp.
), echinoderms, and gastropods, with minor bryozoans (Figure 5.
The high taxonomic diversity of the faunal assemblage suggests deposition under open-marine conditions.
The abundance of peloids is consistent with a shallow-subtidal setting, while partially fragmented bivalves indicate episodic reworking by waves or currents.
This facies is therefore interpreted to reflect deposition in an open-platform, shallow-subtidal environment, on the upper to middle ramp, in association with a beachAebarrier island complex.
Prahastomi.
Linking Carbonate Facies to Stylolite Distribution of Middle Jurassic Limestone.
Onshore Abu Dhabi Oil Field 2 mm 2 mm 2 mm 2 mm Figure 5.
Optical photomicrograph in ppl showing 4 different facies in Upper Araej Member.
Wispy laminated skeletal wackestone, note the subtle appearance of low amplitude stylolite/wispy seams shown in blue arrow which is typically found in this facies .
Peloidalskeletal mud-dominated packstone facies, in this facies peloids are abundant .
lue arro.
Coated grain-skeletal grainstone with abundant benthic forams (Trocholina sp.
) shown in blue arrow, micrite envelopes are common .
Peloidal skeletal floatstone, the occurrence of peloid, extraclast, benthic forams .
lue arro.
are significant with much larger size.
2 Stylolite Two types of stylolites are recognized in the studied limestones, which are jagged/rectangular stylolite and wispy seams.
Stylolites have amplitude of millimetre to centimeters and are more common in packstones, wackestones, floatstone than in grainstone.
Stylolites are pervasive in the middle part of the studied interval (Figure 6.
Stylolites occurred throughout the studied interval where those with higher amplitudes (>1 c.
are encountered in the upper interval.
Stylolites with low to medium amplitude .
3 Ae 1 c.
are common throughout the section particularly in the upper and middle interval.
Wispy seams were observed mostly in the middle and lower interval.
Jagged/rectangular stylolites (Figure 7a and 7.
, which are characterized by varied amplitudes .
p to 20 m.
are encountered mainly in packstones and wackestones and more rarely in grainstone.
Wispy seams (Figure 7.
which are characterized by multiple anastomosing surfaces of low relief with relatively thick dark materials are encountered mainly in packstone and wackestone, and rarely in Wispy seams in the Upper Araej Member are frequently filled with thick clay laminae, for example shown in Figure 7c.
100 Journal of Applied Sciences.
Management and Engineering Technology.
Vol 6.
No 2, 2025: 92 - 106 Figure 6.
Stylolite distribution in Upper Araej Member.
Note that middle section has significant stylolite development.
The chart showing the stylolite frequency across different Note that packstone facies has exhibits extensive development of stylolites .
Figure 7.
The core photograph showing .
The occurrence of jagged stylolite in packstone, note that the stylolites are often filled with calcite cement and clay .
Jagged stylolite in Floatstone .
Low amplitude stylolite .
ispy seam.
in mud-dominated packstone.
Prahastomi.
Linking Carbonate Facies to Stylolite Distribution of Middle Jurassic Limestone.
Onshore Abu Dhabi Oil Field 3 Statistical Analysis The statistical assessment of stylolite amplitude across the principal carbonate facies (Floatstone.
Wackestone.
Packstone, and Grainston.
yields important insights into facies-dependent diagenetic behavior (Table .
Descriptive statistics indicate that mean amplitudes are broadly comparable, ranging between 3.
0 and 4.
1 mm, while median values cluster tightly between 2.
5 and 3.
This convergence suggests that the central tendency of stylolite development is largely insensitive to depositional texture.
However, examination of variability and extreme values reveals a more nuanced Floatstones and Grainstones record the largest maximum amplitudes .
mm and 14 mm, respectivel.
, whereas Packstones and Wackestones rarely exceed 10Ae13 mm.
Such patterns imply that local heterogeneities and stress concentration effects are critical in driving extreme stylolite growth in specific facies.
Table 1.
Statistical parameters of stylolite amplitude across different facies Facies Mean Median Std_Dev Variance Floatstone* Grainstone Min Max Count Packstone* Wackestone* *mud-rich facies Boxplot visualization (Figure .
further underscores these contrasts.
Packstones and Grainstones display narrow interquartile ranges, reflecting relatively uniform textural frameworks and more predictable stylolite amplitude.
In contrast.
Floatstones and Wackestones exhibit broader distributions, consistent with the capacity of mud-supported matrix to facilitate heterogeneous nucleation and irregular propagation.
This greater variability in mud-rich facies not only highlights the sensitivity of stylolite development to matrix composition but also underscores their potential to act as permeability barriers and to promote reservoir heterogeneity and anisotropy.
Despite these distinctions in variability, formal hypothesis testing demonstrates no statistically significant differences in stylolite amplitude across facies.
One-way ANOVA returned a p value of 109, and the non-parametric KruskalAeWallis test yielded H = 3.
38 with p = 0.
Both results confirm that amplitude distributions are statistically indistinguishable among facies.
Collectively, these findings point to a dual conclusion: while the mean expression of stylolite amplitude is broadly uniform across depositional textures, facies exert a pronounced influence on amplitude variability and extremity.
Figure 8.
Box plot of stylolite amplitude .
ertical offse.
across different facies.
102 Journal of Applied Sciences.
Management and Engineering Technology.
Vol 6.
No 2, 2025: 92 - 106 4 Discussions Stylolites are a well-known diagenetic feature in carbonate reservoirs, and their development plays an important role in shaping porosity, permeability, and overall reservoir quality.
In the onshore Abu Dhabi oil field, our analysis of stylolite amplitudes across different carbonate facies (Floatstone.
Wackestone.
Packstone, and Grainston.
reveals facies-related tendencies rather than statistically significant differences.
Descriptive statistics show that mud-rich facies are generally more prone to stylolite development, with Floatstones and Wackestones yielding higher maximum amplitudes .
p to 20 mm and 13 mm, respectivel.
By contrast.
Grainstones exhibit lower average amplitudes, though occasional high-amplitude stylolites .
p to 14 m.
are present.
These observations suggest that depositional texture influences the variability and extremity of stylolite development, even if mean values are broadly comparable across facies.
Stylolitization in Mud-Rich Facies The results show that mud-rich facies are most prone to stylolite development.
Wackestones and Floatstones yield the highest average amplitudes of stylolite, around 4.
1 mm and 4.
0 mm respectively, with maximum values reaching 13 mm in wackestones and as much as 20 mm in Such high values highlight the sensitivity of these facies to pressure-solution processes.
Their fine-grained micritic matrix provides abundant surface area for dissolution, which makes it easier for stylolites to nucleate and propagate during compaction.
Stylolite in packstone which dominate the dataset .
(Figure 6.
, have an average amplitude of about 3.
0 mm, with values spanning 1 to 10 mm.
In this study, packstone are generally mud-dominated packstone .
which implied that high heterogeneity of this facies.
Furthermore, this broad spread points to heterogeneous stylolite development, more likely linked to local variations in grain packing, matrix content, and early Stylolitization in Grain-Dominated Facies Grain-dominated facies has less abundant stylolite development.
Furthermore, this facies shows low average stylolite amplitudes, even though variability is significant.
Grainstones display a slightly higher mean amplitude of 3.
7 mm compared to packstone, with some stylolites reaching 14 mm.
In some intervals, these stylolites may sharply reduce vertical permeability, creating small-scale barriers or baffles within otherwise high-quality reservoir rock.
Stylolitization.
Facies and Reservoir Implications Jagged stylolites in Upper Araej Member, characterized by sharp peaks and rectangular geometries, are present in both mud-rich and grain-dominated facies, whereas wispy seams are either poorly developed or entirely absent in grainstones.
This distribution may suggest that jagged stylolites are controlled primarily by stress concentration along bedding planes and could form regardless of depositional texture, while wispy seams are more strongly associated with micrite-rich facies .
wackstone and packston.
The absence of wispy seams in grainstones possibly reflects the scarcity of clay, which limits the development of diffuse dissolution seams and favors the localization of pressuresolution into discrete, jagged stylolites.
Consequently, stylolite morphology in these carbonates provides important insights into the interplay between depositional fabric and diagenetic pressure-solution processes, with implications for reservoir heterogeneity and compartmentalization.
During stylolitization, grains in limestone dissolve at grain-to-grain contacts, and ions migrate by diffusion from zones of dissolution to zones of lower pressure where they precipitate from the solution as intergranular cement .
Thus, stylotization can greatly impact on the porosity and Prahastomi.
Linking Carbonate Facies to Stylolite Distribution of Middle Jurassic Limestone.
Onshore Abu Dhabi Oil Field The considerable amount of carbonate mass, which is expected to be released upon stylolitization of the limestone is commonly assumed to re-precipitate within the succession .
- .
In terms of the occurrence of stylolite in the anticline structure, intensive stylolitization in the flanks would imply a release of larger mass than in the crest .
The density of stylolite can be impacted by the lithology with a higher abundance of stylolites in clay-rich limestone .
A higher stylolite density was also observed in the clay-rich facies of the Amuri Limestone in the Canterbury Basin by .
However.
It was reported by .
that no significant difference in stylolite density was observed between limestone and dolostone within the Khuff Carbonates from offshore Abu Dhabi.
In evaluating the impact of stylolitization on the carbonate reservoir quality, .
reported that porosity in pelagic carbonates appears nearly absent in thin section analysis.
however, core plug measurements indicate porosity values ranging from 5 to 15%, suggesting the presence of microporosity within the micrite matrix.
Moreover, studies conducted on compacted chalk buried to a depth of 1 km in the North Sea have shown that it generally retains around 40% porosity, primarily associated with It is noteworthy that the chalk described by .
exhibits significantly lower porosity, which is likely associated with the subsequent effects of stylolite development, particularly the cementation of adjacent micropores.
Our results suggest that stylolite development in this Middle Jurassic Limestone shows faciesrelated tendencies, though not statistically significant.
Mud-supported facies, with their micrite-rich composition, provide favorable conditions for the formation of thicker, more continuous stylolites.
Grain-supported facies, by contrast, host more variable and locally controlled stylolite networks.
These findings are consistent with earlier work .
, .
), showing that facies architecture plays a central role in diagenetic modification.
In wackestones, packstones and floatstones, stylolites may act as vertical baffles that reduce connectivity and promote reservoir heterogeneity and anisotropy.
This might reduce sweep efficiency during secondary recovery.
In grainstones, stylolites are less pervasive but still may introduce local anisotropy which baffle fluid flow within the same reservoir unit.
Overall, our findings underscore the complex interplay between facies, lithology, and stylolite development in Jurassic limestones of Upper Araej Member.
While micrite-rich, mud-supported facies tend to favor the development of more continuous, high to low amplitude stylolites, the effect of stylolitization on the original microporosity remains unknown.
Further investigation using highresolution techniques, such as scanning electron microscopy (SEM), is recommended to clarify this Conclussion This study demonstrates that stylolitization in the Upper Araej Member carbonates of onshore Abu Dhabi exhibits facies-related tendencies.
Mud-supported facies, particularly wackestones, floatstones, and mud-dominated packstones, tend to develop thicker and more continuous stylolites, in some cases exceeding 20 mm.
Grain-supported facies, especially grainstones, show lower average amplitudes and less pervasive stylolitization, although isolated high-amplitude stylolites .
p to 14 m.
can still occur locally and may introduce small-scale flow anisotropy that reduces vertical permeability.
Statistical analysis (ANOVA, p = 0.
KruskalAeWallis.
H = 3.
38, p = 0.
confirms that these differences are not statistically significant.
Nevertheless, descriptive data highlight faciesassociated variability and extreme values, suggesting that while average stylolite development is broadly similar across depositional textures, rare but extreme cases in certain facies exert a strong influence on reservoir quality.
Jagged stylolites, which occur in both mud-rich and grain-supported facies, may reflect stress concentration along bedding planes and a relative independence from depositional texture.
By contrast, wispy seams are strongly associated with micrite-rich facies .
, wackestone and packston.
and are largely absent in grainstones due to the scarcity of clay and fine matrix.
This morphological tendency underscores the interplay between depositional fabric and diagenetic pressure-solution processes, 104 Journal of Applied Sciences.
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reinforcing the need to consider both stylolite amplitude and morphology when evaluating reservoir
Reference