Bioclastic Packstone Research Articles

Stratigraphy, Microfacies, Paleoenvironments and Paleoecology of Asmari Formation (Oligocene - Miocene), Zagros Basin, Western Iran

The present work involves the study of the Asmari Formation from the viewpoint of the stratigraphy, microfacies, and depositional environment. The Khorramabad area, Zagros basin, west Iran, has been investigated for the first time. For this purpose, seventy-three samples were taken from the Shurab section. Eight microfacies have been identified in the Asmari Formation: Sandy wackestone (MF1), Peloidal Mudstone (MF2), Bioclastic milina Wackestone-Packstone (MF3), Bioclastic imperforate foraminifera Wackestone-Packstone (MF4), Coral boundstone (MF5), Bioclastic packstone - grainstone (MF6), Bioclastic imperforate foraminifera grainstone (MF7), Mudstone microfacies (MF8). Two benthic foraminiferal biozones were recognized, which are Archaias asparagus- Archaias Henson Assemblage Zone, which is restricted to Chattian, and the Eulepidina- Miogypsina Assemblage Zone, which is restricted to Aquitanian. The biostratigraphic correlation with other studies in and outside Iran, executed across the studied section, enveloping the Chattian to Aquitanian, divulges a progression in the biozone thickness, indicating a migration of the depositional center towards the northwest of the basin. The Asmari Formation is deposited from an outer ramp and open shelf lagoon and is defined as a tropical environment.

Microfacies Analysis and Evolution of Porosity of the Albian-Early Cenomanian Mauddud Formation from Selected Wells in Ratawi Oilfield, Southern Iraq

Mauddud Formation (Albian stage-the Early Cretaceous) is an important oil reservoir in Ratawi field of southern Iraq. Four wells, R T-2, R T-3, R T-6, and R T-7, located 70 km northwest of Basra, were selected to study microfacies properties and petrophysical associations with the probability of oil production. Seventy-seven core samples are collected, and thin sections for petrographic analysis. The self-potential, Gamma-ray, resistivity, and porosity logs are used to determine the top and bottom of the Mauddud Formation. Water saturation of the invaded and uninvaded zones, shale volume, and porosity were calculated. The study area results showed that the quantity of shale is less than 15% for most of the wells, and the dominant porosity is the secondary porosity. In contrast, the primary porosity is low in all study wells, and the formation contains varying proportions of producing hydrocarbons. The results suggest the formation comprises light-colored dolomitized lime and pseudo-oolitic white limestone with green to blue-gray shale. The petrographic analyses of 65 thin sections of the Mauddud Formation reveal that most skeletal grains are shallow marine-derived faunas, while non-skeletal grains include peloids and ooids. The facies analysis showed that the Mauddud Formation was deposited within different sedimentary environments ranging from deep to very shallow environments, which was represented by a large variation in Five microfacies and ten submicrofacies, the microfacies "Mudstone, wackestone, packstone, grainstone, and Rudstone "submicrofacies" Peloidal wackestone to packstone, Bioclastic wackestone to packstone, Miliolids wackestone to packstone,Orbitolina wackestone, Peloidal packstone to grainstone, Orbitolina packstone, Mudstone to wackestone,Bioclastic wackestone, Miliolids and Bioclastic wackestone to packstone, Bioclastic packstone, and Peloidai grainstone". This variance suggested that the formation might be deposited within the carbonate platform's variety of environment, such as "deep sea, restricted, shallow open marine, mid-ramp, rudist biostrome, and shoal." Seven different kinds of pores have been found in the carbonate sideman of the Formation: Interparticle, Intraparticle, moldic, Vuggy and fracture.

Classification of rock types of porous limestone reservoirs: case study of the A oilfield

Rock types with similar lithological components and pore structures form the basic units of porous limestone reservoirs; this influences the reservoir evaluation efficiency and water injection development. As the main oil and gas pay zone in central Iraq, the Cretaceous Khasib Formation reservoirs are influenced by deposition, dissolution, and cementation. There is strong vertical heterogeneity in the most important zone of the Kh2 layer, with diverse rock types and complex pore structures. Based on core observation and casting thin-section identification, the Kh2 layer in the study area was divided into eight lithofacies types as argillaceous bioclastic wackestone, planktic foraminiferium wackestone, lamellar bioclastic wackestone, intraclastic–bioclastic packstone, patchy green algae packstone, green algae and pelletoid packstone, benthic foraminiferium–bioclastic packstone, and intraclastic grainstone. Along with the reservoir void space types of the lithofacies, capillary pressure curves are used to quantitatively analyze the throat and pore features of the different lithofacies. From the porosity–permeability cross-plot characteristics and distribution of pore types, 14 petrophysical facies are obtained. Finally, based on the differences between the lithofacies and petrophysical facies, the Kh2 member is divided into 13 rock types with different geological origins and petrophysical characteristics. Among these, the rock type RT1-8-14 has the best and rock type RT1-1-1 has the worst physical properties among the reservoir rock types. This study provides an optimization method for carbonate reservoir evaluation and is expected to be beneficial for efficient development of similar carbonate reservoirs.

Physico-Mechanical and Petrographic Appraisal of Carbonate Rocks as Construction Aggregate: A Case Study from Lesser Himalaya, Pakistan

Owing to the exceptional role of crushed rock aggregates in construction, their prospective reserves fulfilling qualitative and economic parameters should be identified to meet their ever-increasing demand. This research aims to unlock new sources of high-quality construction materials, thereby optimizing concrete performance and meeting the requirement for sustainable building materials. The study investigated the physicomechanical and petrographic properties of Jurassic, Cretaceous, and Eocene limestones of the Kawagarh Formation (KF), Samana Suk Formation (SSF), and Margalla Hill Limestone (MHL) along the Abbottabad–Nathiagali roadside section, as per the American Society for Testing and Materials (ASTM) and British Standards Institute (BSI). The results of geotechnical investigations are flakiness and elongation index (19.6–34.85% and 17.53–31.2%), specific gravity (2.64 to 2.67), water absorption (0.34–0.63%), unconfined compressive strength (41.72–80.65 MPa), loss angeles abrasion value (15.63–19.08%), impact value (15.38–19.36%), and the soundness (0.9–1.97%). These results showed values within the acceptable range according to ASTM and BSI standards. Petrographically, the KF is classified as mud and wackestone, the SSF was mainly classified as wacke-packstone and grainstone, while the MHL was classified as bioclastic wacke and packstone. The dominancy of micrite matrix favors the strength of aggregate, whereas porosity, microfractures, stylolites, and allochems adversely affect the mechanical properties of rock aggregates. Based on reserve estimation, the studied sections possess significant exploitable reserves and are feasible for quarry operations. The studied rocks can be utilized to produce high-strength concrete, optimizing its performance and quality.

Provenance and paleoenvironmental studies of Bima and Dukul Formations in the Yola Basin, Northern Benue Trough, Nigeria.

Sedimentological studies of some areas located within latitudes 11035’E & 12000’E, and longitudes 9014’N & 9025’N were undertaken to delineate the surface lithologies of the Yola sub-basin, in the Northern Benue Trough. Field observations of the surficial deposits at Mayolope, Taana, Kpasam and Bille revealed that they are Bima Formation while the ones in Abare are Dukul Formation. Paleoenvironmental studies based on the characteristics of lithofacies of these exposed sections and laboratory assessments of some selected samples showed that the Bima Formation was deposited in a continental setting while the Dukul Formation was deposited in a low-energy marine setting. Petrographic studies of framework components showed that the samples of the Bima Formation were predominated by quartz minerals, leading to their identifications as sandstones and classifications as quartzarenites while the samples of the Dukul Formation were limestones and were classified as bioclastic packstones. Heavy mineral compositions of the sandstones revealed their provenance; Zircon and Tourmaline with a combined amount of 60.1% suggested igneous and low-grade metamorphic rocks while rutile and staurolite with a total amount of 27.7% indicated contributions from high-grade metamorphic rocks.

Microfacies and mineralogical analyses of the late cretaceous carbonate rocks from The Central Benue Trough, Nigeria

The Cretaceous limestone facies from Yandev section in the central Benue Trough, Nigeria constitutes parts of the potential reservoirs and sources rocks for petroleum prospects in the basin. The central Benue Trough is the least studied basin among its contemporaries due to lack of subsurface data. Detailed mineralogical, facies analysis and diagenesis of these carbonate rocks in the basin have not received significant study. The aim of this study was to employed multifaceted methodology such as sedimentological, facies analysis petrographic and geochemical approaches which was lacking in previous research in the trough. The sedimentological analysis was done to evaluate fabrics grain sizes, and lithology types. For petrographic analysis, thin sections were prepared and examined under a petrographic microscope and categorized according to Dunham's classification. Geochemical analysis involved X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX) techniques to unveil mineralogical, oxide, and elemental compositions. The sedimentological results revealed light to dark grey medium to fine-grained limestone facies with intercalation of dark grey shales and siltstones. The XRD mineralogy data, revealed calcite (60.00 - 64.10%), quartz (14.30 - 51.00%), albite (12.30 - 19.00%), and chlorite (6.30 - 8.10%). Microfacies results revealed distinct sandy bioclastic wackstone and sparitic intraclastic packstone, as well as micritic intraclastic wackestone and sparitic bioclastic packstone. SEM images highlighted the intricate composition, including elongated structures, whites and dark spots suggesting varying conditions of deposition. Elemental analysis through EDX emphasized significant proportions of carbon, oxygen, sodium, potassium, calcium, silicon, aluminum, iron, and magnesium. Based on sedimentological, biofacies, lithofacies and geochemical evidence we infer that the carbonate sediments were mainly deposited in a shallow marine depositional environment (inner to outer neritic).

The growth and demise of a Middle Miocene carbonate platform in Central Luconia, offshore Malaysia

The evolution and facies distribution of relatively small carbonate platforms, ∼30 km2, are not well documented, even though they are common in ancient and modern carbonate systems. This study investigates depositional facies and evolution of a Miocene carbonate platform in Central Luconia, offshore Malaysia. An integrated approach, including core-described lithofacies, well-log correlation, and seismic analysis, allowed for the mapping of facies through time. The platform was divided into five stratigraphic zones (1 [top], 2 Upper, 2 Lower, 3 Upper, 3 Lower [bottom]) separated by low porosity intervals. Five depositional facies groups were recognized in core samples: (1) bioclastic wacke-packstone facies deposited in a platform interior, (2) bioclastic packstone facies deposited in backreef environments, (3) coral boundstone facies deposited at the reef margin, (4) interbedded shale and carbonate facies deposited on the slope, and (5) argillaceous carbonate facies deposited across the platform as flooding layers. Well D penetrated almost the entire platform, and facies in that well changed upward from mainly bioclastic wacke-packstone at the bottom to mainly bioclastic packstone in the middle to coral boundstone near the top before being covered by interbedded shale and carbonate. Six seismic facies were identified and combined with well data to map the five facies groups through time. The platform shows repeated backstepping of facies at flooding layers followed by aggradation of facies belts up to exposure surfaces, resulting in a long-term backstepping of depositional environments until the platform drowned. Sr-isotopes dating near the top of the platform yielded an age of approximately 12 Ma. This suggests that the platform drowned earlier than other carbonate platforms in Central Luconia (8–10 Ma). More tectonic subsidence in this area during the Middle Miocene is proposed as the main cause of the early demise of this carbonate platform compared to other Luconia platforms.

The geological controlling factors of the heterogeneity of a bioclastic limestone reservoir—a case study of the Cretaceous Kh2 layer in A oilfield, Iraq

Reservoir heterogeneity is one of the key factors affecting the exploration and development of oil and gas reservoirs. The Kh2 layer in the A field of Central Iraq is a major pay zone with strong longitudinal and lateral heterogeneity. The heterogeneity, controlled by geological factors, has not yet been confirmed, which seriously restricts the development of this pay zone. This study aims to establish a geological pattern for the reservoir heterogeneity of bioclastic limestone, providing a geological basis for heterogeneity evaluation. Based on the core observation, thin-section identification, and physical property analysis, the microfacies are classified, and the diagenetic sequences and the pore structure of the Kh2 layer are analyzed. Seven types of microfacies are developed in the Kh2 layer, namely, planktic foraminiferal wackestone (MFT1), lamellar bioclastic wackestone (MFT2), intraclastic–bioclastic packstone (MFT3), green algal packstone (MFT4), green alga–pelletoid packstone (MFT5), bioclastic–intraclastic packstone (MFT6), and intraclastic grainstone (MFT7). The heterogeneity of the different microfacies and heterogeneity within the same microfacies were evaluated using the variation coefficient of permeability tested from cores collected from wells and calculated by well-logging at different intervals. The highest heterogeneity was observed in the lamellar bioclastic wackestone (MFT2), with an average variation coefficient of 0.72. The lowest heterogeneity was observed in the green algal packstone (MFT4), with an average variation coefficient of 0.11. The vertical heterogeneity of the permeability is mainly controlled by sedimentation, while the lateral heterogeneity is mainly influenced by cementation, bioturbation, and the distribution of green algae. Finally, a micro-scale geological pattern for determining the reservoir heterogeneity of bioclastic limestone reservoirs is established. This study can guide the current injection development and remaining oil prediction in oilfields with similar backgrounds.

Sedimentary: Carbonate microfacies and mineralogy of the southern Benue Trough and eastern Dahomey basin, Nigeria

This study presents a detailed investigation into the microfacies, geochemistry, and depositional environments of carbonate rocks from the southern Benue Trough and eastern Dahomey Basin. This analysis involved a combination of techniques, including X-ray diffraction, X-ray fluorescence, scanning electron microscopy with energy-dispersive X-ray spectroscopy and thin-section petrographic examination. Samples from the Igumale Formation of the southern Benue Trough and samples from Ewekoro Formation of the eastern Dahomey Basin were analyzed, offering insights into their mineral compositions, elemental distributions, and depositional environments. In each basin, two carbonate microfacies were identified. The two microfacies found in the Igumale Formation were recognized as micritic bioclastic packstone and sandy bioclastic wackestone. In the Ewekoro Formation, the two microfacies recognized were bioclastic packstone and sparitic peloidal wackestone. The X-ray diffraction analysis of samples from both basins revealed a dominance of calcite. X-ray fluorescence analysis showcased calcium oxide and calcium as the predominant oxide and elements in both basins with varying concentrations. Scanning electron microscopy-energy-dispersive X-ray spectroscopy results unveiled the elemental composition with calcium and silicon emerging as major constituents. The photomicrographs suggest distinct depositional conditions for both samples with those from the Igumale Formation showing evidence of shallow marine and that of the Ewekoro Formation suggesting calm marine environments comprised of fined grained carbonate rocks containing fossils. This study has provided detailed understanding on the nature, microfacies types, mineralogical composition, depositional environment and diagenetic processes of Cretaceous-Paleocene carbonate rocks within the studied basins.

Carbonate Ramp Facies and Porosity Recognition: Case Study of the Late Albian-Early Cenomanian Mauddud Formation in Ratawi Oilfield, Southern Iraq

The carbonate ramp facies of the Late Albian-Early Cenomanian Mauddud Formation were studied in the Ratawi Oilfield, Basra Governorate, south of Iraq using integrated borehole data set that included, core and cutting samples in three drilled wells to analyze the petrography of the Mauddud Formation, two hundred and eighty-one (281) thin sections were prepared and examined for the three selected wells. The results show that the formation is composed of light grey dolomitized limestone and pseudo-oolitic creamy limestone with green to bluish shale. The petrographic observations results show four facies’ associations in the Mauddud Formation. These include: Mid–Ramp environment which is represented by Argillaceous mudstone microfacies, Argillaceous wackestone microfacies and orbitolinid wackestone microfacies; the shallow open marine environment which is assimilated by foraminiferal wackestone microfacies and foraminiferal packstone microfacies; a restricted marine environment that represented by bioclastic fossiliferous wackestone microfacies and miliolid wackestone microfacies and Shoal environment is represented by bioclastic packstone microfacies, bioclastic grainstone microfacies, peloidal foraminiferal pack-grainstone microfacies, and peloidal packstone-grainstone microfacies with diverse skeletal grains. The porosity includes Vuggy, Interparticle, Intraparticle and Fracture porosity.

Rhodolith-forming coralline red algae in the CaCO3 biofactory — A case study from the Serravallian of tropical northeastern Indian Ocean

Rhodolith-forming non-geniculate coralline red algae have been recorded from the Long Formation, exposed in four different outcrops at Little Andaman Island (Hut Bay) in the northeastern Indian Ocean. The non-geniculate corallines are represented by species of Sporolithon Heydrich, 1897, Mesophyllum Lemoine, 1928, Lithothamnion Heydrich, 1897, Phymatolithon Foslie, 1898, Lithoporella (Foslie) Foslie, 1909, Spongites Kützing, 1841, Neogoniolithon Setchell & Mason, 1943 and Lithophyllum Philippi, 1837. The algal assemblages also include geniculate corallines belonging to the genera Amphiroa Lamouroux, 1812 and Corallina Linnaeus, 1758. In addition, larger benthic foraminifers and few planktonic foraminifers also have been identified in thin section analysis. Based on the earlier study carried out on planktonic foraminifers, the Long Formation has been dated as Serravallian (late middle Miocene) and chronostratigraphically, the Long Formation has been included in the Ongeian Regional Stage. In the rhodolith-forming non-geniculate corallines, various growth forms and taphonomic features have been recognized. Diagenesis affected the studied material by micritization, cementation and compaction. The four outcrops are dominated by bioclastic wackestone and packstone composed of coralline red algae, benthic and planktonic foraminifers, echinoid spines and unidentified coral fragments. The rhodolith-forming coralline red algae, the growth forms and taphonomic features in non-geniculate corallines and the characteristic benthic foraminifers are indicative of a moderate energy depositional environment. This study indicates that the carbonate production was considerably high during the Serravallian of the tropical northeastern Indian Ocean.

Microfacies Analysis and Depositional Environment of the Mishrif Formation at Selected Wells in E Oilfield, Southren Iraq

The Mishrif Formation is an important succession that was deposited during the Cenomanian–Early Turonian. More than 79 thin sections of core in addition to well log data for the Mishrif Formation from 2 boreholes within the E oilfield (E-1, and E- 2) were used to determine the different associations facies to interpret the depositional environment of the Mishrif Formation. Six major microfacies were diagnosed the Mishrif Formation, Mudstone, Wackestone, Packstone, Grainstone, Boundstone, and Rudstone and ten submicrofacies include: Bioclastic Packstone submicrofacies with rich Echinodermat, Coral and Rudist fragment and high Dolomitization, Rudstone submicrofacies with large Rudist fragment and vug porosity , Boundstone submicrofacies with very large coral, Plankton Foraminiferal Packstone submicrofacies withe Globigerinelloides and Calcispheres, Bioclastic Wackestone to Packstone submicrofacies with dolomite and calcareous algae, Peloidal Packstone with coral, pillites, pieces of Rudist and Separate-Vug pore, Bioclastic Packstone to Grainstone submicrofacies, Peloidal to Bioclastic Packstone submicrofacies, Benthonic Foraminiferal Mudstone submicrofacies, Rudist fragmented Mudstone. These microfacies were deposited in restricted, shoal, shallow open marine, rudist bioherm, and deep marine environments.

Middle Eocene Succession of Dammam Formation, Biostratigraphy and Microfacies Study, North Karbala Area, Western Iraq

Stratigraphic and sedimentary study to Dammam Formation (Eocene age) at well Kr-1, Karbala Government, Western Desert of Iraq. Lithologically, Dammam Formation consists of Nummulitic limestone and dolomitic limestone. The contact between the upper and lower of Dammam Formation is unconformable, the lower contact is represented by Umm Er-Radhuma Formation by the unconformable surface in the Upper Paleocene age, while the upper is an unconformable surface with Euphrates Formation in the Early Miocene age. The rock section of the well Kr-1 is divided into several beds depending on Petrographical and paleontological contents, the results of the identified foraminifera are indicated to several groups and genera which are: Nummulites, Lindrina, Lockhartia, Rotaliid, Miliolid, also other groups of fossils like Ostracoda, Echinoderms, Bryozoa, Gastropod, Pelecypod, and different fragments. Based on the petrographic study and type of microfacies, the formation was divided into three main and secondary microfacies which are: Nummulitic packstone, Dolomitic and Bioclastic Packstone, and Floatstone. One main biozone was recognized in the studied section which is Nummulites gizehensis- Nummulites planulatus - Nummulites discorbinus Assemblage Zone with age Middle Eocene (Lutetian), this biozone is divided into two secondary biozones: Nummulites millecaput Rang zone Middle Eocene (Middle-Upper Lutetian) age and Nummulites elevate Rang zone Middle Eocene (Late Upper Lutetian) age. After collecting all the sedimentary and planetology data for the studied section, the Dammam Formation was deposited in shallow warm marine, tropical water, as well as, the absence of planktonic foraminifera crowds is another evidence that the environment is a shallow basin close to the coast. The basin is located at the Interior Platform represented by the evaporites basin, the restricted, and then the open sea environments.

Seismic characterization of Cenomanian–Turonian carbonate platform based on sedimentological and geophysical investigation of onshore analogue outcrop (northern Lebanon)

AbstractOutcrop analogues play a key role in the characterization of subsurface carbonate platforms. The lack of well data and relevant outcrop analogues can result in the misinterpretation of seismic data. To address this issue, we apply an integrated workflow based on sedimentology, geophysics and petrophysics on outcrop analogues present onshore Lebanon, to constrain the carbonate platform's properties on onshore seismic data. A thorough sedimentary description is completed for a 400‐m‐thick Cenomanian–Turonian carbonate platform located in Kfarhelda, northern Lebanon. P‐wave velocity is acquired directly on the outcrop, and the petrophysical properties are measured on 44 samples. A 1D synthetic seismogram is computed with Ricker wavelet 25 Hz resembling seismic resolution. The resulting reflectors are mainly (1) high amplitude reflectors at the limit between two facies with contrasting physical properties enhanced by diagenesis, (2) moderate amplitude reflectors corresponding to stratigraphic limits at the transition between facies and (3) very low amplitude reflectors in karstified units. The integration of outcrop and seismic data is based on the generation of the synthetic seismogram to identify the geological origin of reflectors. The best fit between the synthetic seismic and seismic profile is used to interpret a seismic facies representing bedded limestones of Sannine and Maameltain formations (Cenomanian–Turonian). Two other distinctive reflectors are identified at the boundary of the Marly Limestone Zone, and the Channel facies unit characterized by bioclastic packstone to floatstone. This study highlights the importance of using outcrop analogues to identify the seismic signal of stratigraphic sequences and improve the interpretation of onshore seismic data.

Facies, cycle stratigraphy, and heterogeneity of the Clear Fork carbonates in the Eastern Shelf of the Permian Basin, Texas

The Clear Fork carbonate reservoirs at Iatan East Howard field are highly heterogeneous. Facies analysis and cycle stratigraphy are employed to characterize the Clear Fork Formation and reservoir heterogeneity at the field. One-dimensional (1-D), vertical stratigraphic analyses started from meter-scale cycles to cycle sets, system tracts, and then depositional sequences. A reverse process was followed to construct a 2-D framework from a 1-D stratigraphy. In the downdip areas, the Clear Fork Formation is dominated by subtidal facies; toward the updip, peritidal facies become more abundant and depositional facies may alternate between shallow subtidal and tidal-flat facies. Approximately 56 well-developed, meter-scale, upward-shallowing cycles were defined in the Clear Fork cores facilitated by wireline logs. Most of them have bioclast wackestone and packstone in the lower part and are capped by fenestral peloid packstone, silty to sandy dolostone, and/or dark mudrocks. Six cycle sets (high-frequency sequences) were identified, and two depositional sequences were recognized. Sequences are correlatable, but it is challenging to correlate meter-scale cycles. The Clear Fork cycles display relatively consistent thickness and facies stacking pattern plus evidence of subaerial exposure and erosion of subtidal facies, suggesting an allocyclic control and having been the result of eustatic sea-level fluctuations. Reservoir pores (porosity >4%) commonly occur in the transgressive system tracts and lower highstand system tracts (HSTs) within individual high-frequency sequences; the upper HSTs commonly consist of amalgamated peritidal deposits and are generally tight because pores (mostly fenestral and intergranular pores) have been occluded by anhydrite and carbonate cements. These new findings contrast the previous studies showing that porosity is typically higher in the cycle-set-top or cycle-top facies (mainly tidal-flat deposits) in the formation. Reservoirs are areally discontinuous and vertically compartmentalized by multiple nonporous zones. Reservoir characterization is critical to improving recovery efficiency. This case study provides an insight into complex facies and cycle stacking patterns as well as stratigraphic architecture on a carbonate platform during a waning icehouse phase and can help to better understand the controls on the distribution and quality of such carbonate reservoirs.

Palaeobiogeography, palaeoecology, and sequence stratigraphy of the Upper Jurassic carbonate succession of the Lar Formation, central Alborz Zone, Iran

Foraminifera, ammonites, and calcareous dinoflagellates were used for stratigraphy and, together with microfacies, for the assessment of the palaeoenvironmental conditions of the Upper Jurassic deposits in the central Alborz Zone of northern Iran. The Lar Formation (Lar Fm.) in the Polur section is of latest Oxfordian to early Kimmeridgian age. The ammonite Subnebrodites planula and the calcareous dinoflagellate Colomisphaera nagyi have been introduced as new biomarkers of the lower Kimmeridgian in the central Neo-Tethys. The distribution of calcareous dinoflagellates reflects possible dispersal routes along a narrow seaway between the western Neo-Tethys and the Alborz Zone in the central Neo-Tethys. The Terebella-Crescentiella associations of the Lar Fm. represent a low-energy setting under dysoxic conditions in the Central Neo-Tethys Ocean. The benthic foraminiferal assemblages in this formation show a high dominance of infaunal taxa and r-selected strategists. This assemblage is reminiscent of eutrophic conditions and low oxygen levels in the lower part of the Lar Fm. Good preservation of the hexactinellid sponges in the upper part of the Lar Fm. also indicates an oxygen-minimum zone. Three third-order depositional sequences can be distinguished in the study area based on six microfacies. Depositional sequence 1 (DS1) is composed mainly of argillaceous limestone and medium- to thick-bedded limestone, corresponding to an outer ramp-to-middle ramp environment. Depositional sequence 2 (DS2) comprises breccia limestone and thick-bedded limestone facies in its lower part and thin-bedded limestone to massive limestone in its upper part. The breccia limestone facies may be associated with subaerial exposure and reworking of previously deposited sediment during a relative sea level fall. The thin-bedded limestone to massive limestone of DS2 consists mainly of bioclastic mudstone to wackestone (outer ramp). These represent an deep-water outer homoclinal ramp facies. Depositional sequence 3 (DS3) consists mainly of massive limestone to thick-bedded limestone with a bioclastic peloidal microbial Crescentiella packstone (middle ramp). The relative stratigraphic positions of DSs1–3 and sequence boundaries in the uppermost Oxfordian to lower Kimmeridgian of the Polur area show a fair match to the upper Oxfordian to lower Kimmeridgian sequences (JOx7, JOx8, JKi1 and JKi2) on the global sea level curve.

Integrated geophysical, petrophysical and petrographical characterization of the carbonate and clastic reservoirs of the Waihapa Field, Taranaki Basin, New Zealand

Despite the economic importance of the Waihapa Field in Taranaki Basin in New Zealand, the structural setting, petrographic and petrophysical properties of its Cenozoic reservoirs are still poorly understood. This research integrates a 3D seismic survey with core and well logs data, as well as petrographic description in order to discuss the structural setting and the reservoir characterization of the Cenozoic reservoirs along the Waihapa Field, Taranaki Basin, New Zealand. A major thrust fault was interpreted dissecting both the Kapuni (Paleocene- Eocene) and Ngatoro (Oligocene- Early Miocene) groups and another opposite thrust fault affecting the Ngatoro Group and the Waihapa anticline. These compressional structures were resulted from the regional compression which affected the Taranaki Basin during the Miocene. Wai-iti Group (Miocene) is dissected by a set of NE-SW normal faults. These normal faults remark the end of the compressional phase and the beginning of a new extensional phase along the Taranaki Basin.The petrographic data of the studied reservoirs indicate that the Late Miocene Mount Messenger Formation is composed of feldspathic wacke, micaceous feldspathic quartz arenite and mudstone microfacies, whereas the Oligocene Tikorangi Formation is composed of five microfacies (bioclastic grainstone, bioclastic packstone, sandy wackestone, highly fractured silty mudstone and sandy glauconitic packstone microfacies). Downward, the Upper Eocene Mangahewa Formation is composed of ferruginated quartz arenite, micaceous quartz arenite, and ferruginated calcareous quartz arenite microfacies. Cementation and compaction are mostly affected the Mangahewa Formation while fracturing and dissolution are primarily affected the Tikorangi and the Mount Messenger formations respectively. The studied core data was discriminated into four petrophysical static rock types (PSRTs). The PSRT1, representing the Mount Messenger reservoir, has the best reservoir quality (av. porosity = 23.3%, av. permeability = 45.0 md, and meso pores, 2.60 μm) while the PSRT4 of Tikorangi Formation has the lowest reservoir quality (av. porosity = 5.5%, av. permeability = 0.01 md, and nano pores, 0.07 μm). The PSRT2 (av. porosity = 4.17%, av. permeability = 0.26 md, and micro pores, 0.59 μm) and PSRT3 (av. porosity = 5.93%, av. permeability = 0.08 md, and micro pores, 0.22 μm) are petrophysically considered transitional rock types between the PSRT1 and the PSRT4.However, Tikorangi reservoir is already producing oil from the borehole scale fractures. This work represents the workflow applied during integrating seismic, petrographical and petrophysical data in order to characterize carbonate and clastic reservoirs for any further hydrocarbon development plans along the field.

Microfacies and Diagenetic Processes of the Late Jurassic Naokelekan Formation in selected wells at Balad, Ajil and Baiji Oilfields, Central Iraq

This work depends on detailed petrographic and diagenetic processes studies of collected cutting rock samples, from the Late Jurassic Naokelekan Formation from Ajil-8, Balad-1 and Baiji-1 wells. Based on the thin sections study, the formation contains various petrographic components represented by pelecypods, calcispheres, planktonic and benthonic foraminifera, in addition to the groundmass of micrite and microspars. Many diagenetic processes affected the rock successions such as, compaction, micritization, authigenic minerals (pyrite), cementation, neomorphism, dissolution, porosity, replacement and dolomitization. The detailed microfacies analysis reveals that the rock successions consist mainly of three microfacies including; lime mudstone, which is divided into non-fossiliferous lime mudstone, bioclastic lime mudstone and planktonic foraminiferal lime mudstone, lime wackestone which also divided into calcispheres lime wackestone, benthonic lime wackestone, and pelcypodal lime wackestone, and lime packstone include, bioclastic lime packstone, peloidal lime packstone, and calcispheres lime packestone. The overall characters of these microfacies indicate the formation was deposited in two different environments: (1) shallow marine subtidal environment at the lower and upper parts (2) outer shelf in an euxinic environment at its middle part

Microfacies and paleoenvironment of the Mishrif Formation (middle Cenomanian–early Turonian), in Nasiriyah oil field in Southern Iraq

The Microfacies analysis of the Cretaceous Mishrif Formation was studied in Nasiriyah oil field in Nasiriyah Governorate, southern of Iraq using integrated borehole data set that included, core samples and well logs in newly drilled well to analyze the microfacies and the Diagenesis Process of the formation, 100 thin sections for selected well. The results show that the formation composed of: (top to base) a fine-grained, limonitic fresh water limestone containing Charophytae. Four facies’ associations were distinguished in the Mishrif Formation. These include: - These include: - Restricted shallow Open Marin environment is represented by Wackstone and Mudstone to Wackstone. The shallow open marine environment is represented by bioclastic wackestone and packestone, as well as rudistid floastone in rare situations. Shoal Environmentis represented by bioclastic packstone to grainstone, as well as rudstone. Deep Marine environment is represented by mudstone to packstone. six diagenetic processes affected on Mishrif Formation: Cementation, Micritization, Recrystallization, Dissolution, Compaction and Pressure Solution (Stylolization), and Dolomitization, found in thin sections.

UPPER JURASSIC TO LOWERMOST CRETACEOUS MICROFOSSILS FROM THE HĂGHIMAŞ MOUNTAINS (EASTERN CARPATHIANS, ROMANIA)

The limestones of the Upper Jurassic to lowermost Cretaceous from the Hăghimaş Mountains were studied in two sections from the upper part of the Fagu Oltului valley, a tributary of the Olt River. The lower part of the succession is remarkable for the rich brachiopod fauna contained in a red limestone buildup, documented previously as a stromatactis mud-mound. The mound consists of bioclastic wackestones and packstones with numerous brachiopods, crinoids, and sponges. The mud-mound is covered with intraclastic grainstones and fine-grained limestones with pelagic bivalves. The following lithological units pass into shallow water limestone with nerineid gastropods, calcareous algae and foraminifera, in a regressive sequence. The micropaleontological association identified in the Upper Jurassic to lowermost Cretaceous limestones from Fagul Oltului includes calcareous algae, foraminifera, saccocomid crinoid fragments, annelid worm tubes, sponge fragments, rare calpionellids and microorganisms with an uncertain systematic position. The identified microfossils have a wide stratigraphic distribution. The most important stratigraphic landmarks are Trocholina conica (which does not extend younger than Kimmeridgian) and Calpionella alpina (which does not appear before the upper Tithonian). Based on the whole micropaleontological assemblage, the lower part of the succession (the skeletal mud-mound) can be ascribed to the Kimmeridgian – lower-middle Tithonian, and the upper part to the upper Tithonian – Berriasian.