3D Microporosity Characterizations in the Heterogeneous Middle Jurassic Tuwaiq Mountain Formation: Insights into an Unconventional Sweet Spot.

Carbonate microporosity can vary significantly across depositional lithofacies and cycles, owing primarily to the high degree of heterogeneity in their pore sizes, pore throat radius, geometry, and connectivity. This is further compounded by the complex diagenetic alterations during various stages of burial. In addition, the presence of micropores, which are abundant in carbonate rocks, but not visible using conventional techniques, is challenging to characterize. To address this issue, our study focused on the Middle Jurassic Tuwaiq Mountain Formation (TMF) due to its importance as an analogue to subsurface conventional and unconventional reservoirs. Here, we utilized eight samples and performed pore network modeling to quantify microporosity distribution and connectivity from high-resolution microcomputed tomography images of different microfacies (MF) in the TMF from both mud- and grain-dominated facies. These results were then validated with petrographic, SEM images, and porosity-permeability measurements. Our study revealed that, in the high-energy, grain-supported microfacies of the shallow lagoon depositional cycle, micropores dominated by interparticle and microvug types were abundant and well-connected, with mean pore and throat sizes of 7 and 4 µm. Conversely, micropores within the low-energy mud-dominated microfacies of the deep lagoon depositional cycle dominated by intraparticle and intercrystalline types were isolated and rarely connected, even at the microscale (1-4 µm in diameter, with an average of 2 µm). This result suggests that pore connectivity at the microscale is not always related to matrix porosity, and the pore connectivity is present in submicron scale, which goes against common concepts in unconventional carbonate reservoirs. Furthermore, our observations indicate that primary depositional processes play a major role in controlling the distribution and connectivity of the Tuwaiq Mountain Formation's microporosity, while diagenetic processes only have minor controls. Our study emphasizes the importance of characterizing microporosity and its connectivity in heterogeneous carbonate rocks, which may reduce the uncertainty in exploring the properties of complex carbonate reservoirs worldwide.

CO2-Rock-Brine Interactions in Feldspar-Rich Sandstones That Underwent Intense Heating.

The success of any carbon capture and storage method largely depends on, among other factors, its safety, reliability, and thorough understanding of the interactions among CO2, underground geological formation, and resident brine. Upon injection into the subsurface rock formation, CO2 interacts with the host geological formation and brine, initiating complex geochemical reactions that are often poorly understood and could potentially affect the overall stability and storage capacity of the geological formation, particularly those in close proximity to an intense heat source. For instance, the impact of intense and prolonged heat due to, say, magmatic intrusion on sandstones' framework, authigenic mineralogies, and CO2-storage potentials is still poorly understood. Consequently, in this study, we have investigated the impact of firing on CO2-rock-brine reactions in the Bandera Gray (BG) sandstone. Prior to the CO2 injection using 60 000 ppm brine at 75 °C and 28.7 MPa for 30 days, two samples of the BG sandstone were fired for 6 h in a muffle furnace at 700 and 1100 °C each. The BG samples were then studied for XRD, SEM, and ICP-OES analyses before and after the CO2 injection, mainly to investigate any changes in mineralogical compositions and fluid chemistry. To determine the impact of the CO2-rock-brine interactions on the authigenic and framework mineralogies of the BG sandstones under low pH (∼3) conditions, powdered samples of the pre- and postfired BG sandstones were treated with nitric acid. The findings of the study indicate that there were no observable reactions involving rock-forming minerals and carbonate cement in the unfired and fired (at 700 °C) sandstones after the CO2 injection. However, pervasive feldspar-dissolution porosity was formed in the postfired BG sandstone (1100 °C) after CO2 injection. This was mainly because albite was partly to pervasively transformed into anorthite during firing at 1100 °C, making the feldspar highly susceptible to dissolution under CO2 conditions. This implies that the conversion of albite into chemically unstable anorthite in natural sandstones that underwent intense and prolonged heating could develop significant amounts of secondary dissolution porosity due to CO2 injection, thereby impacting their storage capacities and overall petrophysical properties. This dissolution was separately corroborated using a nitric acid treatment. The findings of the study will provide a better understanding of the CO2-rock-brine reactions involving sandstones that experienced intense heat due to, for instance, magmatic activity over a long geologic time scale, which has largely transformed the chemistry of their feldspars, particularly plagioclase.

Deciphering the impact of decabromodiphenyl ether (BDE-209) on benthic foraminiferal communities: Insights from Cell-Tracker Green staining and eDNA metabarcoding.

This study investigates the ecotoxicological effects of BDE-209, a persistent organic pollutant (POP) prevalent in Kuwait's coastal-industrial areas, on benthic foraminiferal communities. We conducted a mesocosm experiment in which we exposed benthic foraminiferal communities sampled from the coastal-industrial areas of Kuwait to a gradient of BDE-209 concentrations (0.01 to 20 mg/kg). The impact of exposure was assessed using live-staining and metabarcoding techniques. Despite the significantly different taxonomic compositions detected by the two techniques, our results show that BDE-209 significantly affects foraminiferal communities, with moderately high concentrations leading to reduced α-diversity and considerable taxonomic shifts in both molecular and morphological assemblages. At concentrations of 10 and 20 mg/kg, no living foraminifera were detected after 8 weeks, suggesting a threshold for their survival under BDE-209 exposure. The parallel responses of molecular and morphological communities confirm the reliability of both assessment methods. This study is the first to investigate the reaction of eukaryotic communities, specifically foraminifera, to POPs such as BDE-209, generating valuable insights that have the potential to enhance field studies and aid the refinement of sediment quality guidelines.

In-situ micro-CT scanning and compressive strength assessment of diammonium hydrogen phosphate (DAP) treated chalk.

The occurrence of wellbore mechanical failure is a consequence of the interaction among factors such as in situ stress, rock strength, and engineering procedures. The process of hydrocarbons production, causing reduction of pore pressure, alters the effective stresses in the vicinity of a borehole, leading to borehole instability issues. Estimating the rocks' elastic modulus and compressive strength is essential to comprehend the rock matrix's mechanical response during drilling and production operations. This study aimed to assess the practicality of Diammonium Hydrogen Phosphate (DAP) application as a chemical for strengthening chalk in hydrocarbon reservoirs, to make it resistant to high stresses and failure during drilling and production. The mechanical and physical properties of Austin chalk rock samples treated with DAP under mimicked reservoir conditions were studied. The results showed that DAP is a highly effective carbonate rock consolidating agent that improves the mechanical strength of the chalk. Compressive test measurements conducted on rocks treated at two different temperatures (ambient and 50 °C) showed that DAP effectively strengthened the rock matrix, resulting in an increase in its compressive strength (22-24%) and elastic modulus (up to 115%) compared to the untreated sample. The favorable outcomes of this research suggest that the DAP solution holds promise as a consolidation agent in hydrocarbon reservoirs. This contributes to the advancement of knowledge regarding effective strategies for mitigating mechanical failures of the wellbore during drilling and production.

Evidence for the early Toarcian Carbon Isotope Excursion (T-CIE) from the shallow marine siliciclastic red beds of Arabia.

The Toarcian Oceanic Anoxic Event (T-OAE) and its corresponding Carbon Isotope Excursion (CIE) have been reported widely across the Tethyan region and globally. In Arabia, and based on ammonite dating, the time window of the T-OAE coincided with the deposition of the reddish siliciclastic unit of the Marrat Formation. However, no evidence of the T-OAE/CIE was ever reported from Arabia because these red beds were previously interpreted as continental deposits. Recently, these red beds have been recognized as shallow marine deposits which opened an opportunity to assess the occurrence and expression of T-OAE-CIE in Arabia. In this study, a multiproxy geochemical characterization was performed on the Toarcian Marrat Formation to infer the chemistry of the paleowater column and identify intervals of possible T-OAE/CIE in Arabia. While the low concentrations of redox-sensitive elements (Mo, U, V, Cr) may indicate a shallow oxic marine settings, the coupled negative δ13Corganic excursion and apparent increase in the chemical weathering suggests that the deposition of Marrat red beds coincided with the development of T-CIE and possibly time-equivalent to the T-OAE globally. The origin of reddening is interpreted to have occurred during the middle Marrat deposition due to the stabilization of unstable hydrous iron oxides to hematite under oxic marine conditions. The proposed model further indicates the possible development of source rocks in the deep, anoxic environment counterpart where the T-OAE may be expressed. Since our study documents the first record of the T-CIE and discuss the origin of shallow marine siliciclastic red beds in the Arabian Plate, this will have significant implications for the overall understanding of the T-CIE globally and for hydrocarbon exploration through realizations of potential new source rocks associated with the OAEs in the Toarcian and other time intervals.

High-resolution X-ray diffraction datasets: Carbonates.

X-ray diffraction (XRD) analysis is a versatile and reliable method used in the identification of minerals in solid samples. It is one of the primary techniques geoscientists, mineralogist, solid-state chemists depend on to characterize the composition of unknown samples. In recent years there has been a growing interest among researchers to have readily accessible and large dataset to use to calibrate their experiment or to simply build various statistical models. Sadly, this is difficult to come by. Most well-curated datasets are propriety in nature and often too expensive for the average researcher. Additionally, when these datasets are available, they might not be suitable for purpose due to lack of proper coverage for certain a mineral of interest. For these reasons, we have carefully selected and curated samples rich in calcium carbonate that will be useful for various applications. Our dataset includes 1680 X-ray diffraction scans of samples collected from carbonate rich rock formations outcrops in Spain, Italy, and Saudi Arabia. They represent materials with total carbonate concentration range between 30-99%. The spectra were acquired on a Malvern PANalytical EMPYREAN Diffractometer system at two theta range 2- 70 and 0.01 step size. This dataset will be valuable to geoscientists, mineralogist, solid-state chemists, data scientists alike looking to design experiments, build mineralogical reference databases or statistical models with sufficient data points. We currently use the dataset in our own projects to develop comprehensive carbonate library and felt compelled to share.

Dataset showing the abundance and distribution of benthic foraminifera in relation to marine sediment parameters from western Arabian Gulf.

This dataset supports the paper entitled "A baseline investigation of benthic foraminifera in relation to marine sediments parameters in western parts of the Arabian Gulf". Duplicate sediment samples (sets A and B) were collected from 30 stations in an area covering approximately 25000 km2 in the offshore northern Arabian Gulf, using a van Veen grab (0.1 m2 area) and the top 1 cm was analysed for living benthic foraminifera. A set of samples was devoted to foraminiferal analysis while the other, set B, for sediment analyses. In situ hydrographical parameters such as temperature, salinity, pH, turbidity and DO were measured at surface waters. The top 1 cm was subsampled for foraminiferal analyses from the grab and preserved using 70% ethanol with Rose-Bengal stain. Potentially Toxic Elements (PTE) levels in sediment and grain size distributions were analysed. The dataset is expected to provide a baseline for PTE levels in sediment, benthic foraminiferal communities, and identify endemic species adapted to extremes of temperature and saline conditions typical of the Gulf. It can also be used by environmental managers, micropaleotologists, students in environmental/geology/marine science as reference background conditions based on sediment toxicity and benthic community information in revising environmental guidelines in the region. Data from this study suggest that PTEs are within the range of background values, and the sediments support highly diversified and stable benthic foraminiferal communities adapted to the unique environmental conditions in the Gulf. To date, this dataset documents the highest number of living benthic foraminifera species reported from the Gulf, and the most diverse living community compared to all previous studies. It also provides evidence for the full recovery of areas impacted during the 1991 Gulf oil spill which is evident by the diverse and flourishing assemblages of living benthic foraminifera documented.

A baseline investigation of benthic foraminifera in relation to marine sediments parameters in western parts of the Arabian Gulf.

This baseline paper discusses the distribution and abundance of living benthic foraminifera in relation to Potentially Toxic Elements (PTEs) such as As, Al, Fe Cd, Co, Cr, Cu, V, Ni, Hg, Pb, and Zn in marine sediments collected from 30 stations in the offshore Arabian Gulf to define baseline environmental conditions for the implementation of future biomonitoring programs. A total of 271 living benthic foraminiferal species were identified belonging to 66 genera, 37 families and 6 orders. Data from this work suggest that PTEs are within the range of background values, and the sediments support highly diversified and stable benthic foraminiferal communities adapted to the unique environmental conditions in the Gulf. Thus, the effect of anthropogenic activities is deemed negligible. This study is expected to provide a baseline dataset for PTE levels in sediment, benthic foraminiferal communities, and identify endemic species adapted to extremes of temperature and saline conditions typical of the Gulf.