Potential Reservoir Research Articles

Hydrocarbon production potential of paralic reservoirs from the Niger Delta basin: Evidence from ichnological studies

Reservoir ichnological study was employed to improve on the inconsistencies and poor interpretation of hydrocarbon-bearing strata within the multipartite maturing terrain of the onshore Niger Delta basin. Ichnofacies characterization revealed two distinctive trace fossil suites that both reflected different feeding behaviours and responses to substrate consistency, which assisted in the high-resolution assessment of facies constituting the paralic reservoirs. Fifteen potential reservoir intervals were subdivided into productive and non-productive as revealed on core slabs as well as well log signatures. Fluctuating river sediment influx has been considered to be detrimental to the colonization of the channel deposits and barrier bars, which resulted in excellent hydrocarbon reservoirs in the study area. The sandstone facies, characterized by sparse bioturbation and extensive bedding, displays imprints of Ophiomorpha, Thalassinoides, and Palaeophycus. The removal of these imprints has minimized subtle heterogeneities, resulting in more uniform reservoir characteristics. This uniformity has favored the accumulation of hydrocarbons within the point bars.Biogenicchurning of bedded sediment generated a poorer sorting index thereby reducing the reservoir quality at 9866-9840ft, 9154-9120ft, and 9090- 060ft depth intervals, which has been interpreted to represent poor reservoir potentials. However, it is advised that future investigations should focus on the forced regressive shoreface and delta front reservoirs of the studied interval for its internal continuity that may contain maximum production potential.

Integration of deep-learning fault segmentation, horizontal transverse isotropy analysis, and ambient microseismic methods to enhance fracture prediction in the Crisol Anticline, Colombia

The analysis of fault and fracture systems in the subsurface is crucial for identifying potential reservoirs and optimizing production. However, conventional fault interpretation methods have limitations due to the complexity and amount of data involved. In this study, a multimethod approach was used to analyze fault and fracture systems in the Crisol area of the Valley Middle Magdalena basin. We used deep-learning fault segmentation, horizontal transverse isotropy (HTI), and ambient microseismic methods to identify and characterize fault and fracture systems in the study area. The deep-learning fault segmentation method helped to identify complex fault systems, whereas the HTI method identified areas and orientations of intense fracturing that occurred at any prior period of stress in geologic time. Meanwhile, the ambient microseismic method measured active rock movements and fracturing in the subsurface that occurred during the microseismic trace recording. The application of multiple methods for analyzing fault and fracture systems in the subsurface is demonstrated to offer a more comprehensive understanding of the geology and enhance the accuracy of well placement and production forecasts.

Hospital water environment and antibiotic use: key factors in a nosocomial outbreak of carbapenemase-producing Serratia marcescens

BackgroundThe healthcare water environment is a potential reservoir of carbapenem-resistant organisms (CROs). Here, we report the role of the water environment as a reservoir and the infection control measures applied to suppress a prolonged outbreak of Klebsiella pneumoniae carbapenemase-producing Serratia marcescens (KPC-SM) in two intensive care units (ICUs). MethodsThe outbreak occurred in the ICUs of a tertiary hospital from October 2020 to July 2021. Comprehensive patient contact tracing and environmental assessments were conducted, and a case–control study was performed to identify factors associated with the acquisition of KPC-SM. Associations among isolates were assessed via pulsed-field gel electrophoresis (PFGE). Antibiotic usage was analyzed. . ResultsThe outbreak consisted of two waves involving a total of 30 patients with KPC-SM. Multiple environmental cultures identified KPC-SM in a sink, a dirty utility room, and a communal bathroom shared by the ICUs, together with the waste bucket of a continuous renal replacement therapy (CRRT) system. The genetic similarity of the KPC-SM isolates from patients and the environment was confirmed by PFGE. A retrospective review of 30 cases identified that the use of CRRT and antibiotics were associated with acquisition of KPC-SM (p < 0.05). There was a continuous increase in the use of carbapenems; notably, the use of colistin has increased since 2019. ConclusionOur study demonstrates that CRRT systems, along with other hospital water environments, are significant potential sources of resistant microorganisms, underscoring the necessity of enhancing infection control practices in these areas.

Granitoids of the western Himalaya and Karakoram as potential geothermal reservoirs – A petrological, geochemical and petrophysical study

Hot springs in various granitoid and gneissic complexes in northern Pakistan indicate elevated geothermal gradients, which warrants their evaluation for geothermal applications. Evaluation of such prospects requires extensive knowledge of rock properties and their interaction with reservoir fluids. Our contribution provides first-order information on petrophysical, geochemical, and petrographic descriptions derived from outcrop analogs. About seventy samples of (mostly) granitoids and gneisses from the Nanga Parbat Massif (NPM), the Kohistan-Ladakh Batholith (KLB), and the Karakoram Batholith (KB) were collected. Biotite, K-feldspar, and plagioclase in the granitoid and gneiss show weak to moderate alteration, which increases in shear zones, suggesting fracture-assisted fluid interaction. Geochemical results indicate that the gneisses and granites of the NPM are mostly peraluminous S-type and show enrichment in most LREEs and depletion in HREEs. In addition, depleted Sr and Ba and enriched Rb and U in granites indicate partial melting and high fractionation. On the contrary, granitoids from the KLB are of calc-alkaline I-type and characterized by the depletion of REEs and the enrichment in Ba and Sr. The granitoids of the KB, due to their different magmatic histories, are more diverse, ranging from older I-type calc-alkaline granodiorite, and younger I-type alkaline syenite and S-type calc-alkaline granite. They show an overall enrichment in HREEs along with Ba, Th, Ta, Sr, and Lu. Allanites from syenite of the KB show significant concentrations of Th and U.Petrophysical measurements reveal low matrix porosities (0.6–3.5 %), with primarily average thermal conductivities (1.48–3.37 W m−1K −1) and thermal diffusivities (0.68–1.95 ∙10–6 m2 s−1), with minor variation in specific heat capacities (744–767 J kg−1 K−1). The NPM displays higher average thermal conductivity, thermal diffusivity, and lower porosity than the KB, while the petrophysical properties of the KLB range between these two domains.The geothermal systems in the area operate due to the thickening of a granitoid-dominant crust, which is enriched with radiogenic elements. The fault zones provide channels for meteoric water to access deeply these hot and thermally conductive rocks in the subsurface. After heat exchange, the water is discharged back to the surface as hot springs. The present data set provides a better understanding of regional geothermal regimes from petrological, geochemical, and petrophysical perspectives and assists in numerical modeling for potential geothermal assessment.

Sequence stratigraphic framework and distribution of potential reservoirs: Early Cretaceous Qishn Formation, Dhofar, Southern Oman

Sequence stratigraphic framework and distribution of potential reservoirs: Early Cretaceous Qishn Formation, Dhofar, Southern Oman

Prevalence, antimicrobial resistance and detection of virulence genes of Escherichia coli and Salmonella spp. isolated from white-lipped peccaries and collared peccaries.

Salmonella spp. and Escherichia coli are implicated in human and animal infections and require antimicrobial treatment in many situations. Faecal samples of healthy white-lipped peccaries (Pecari tajacu) (n = 30) and collared peccaries (Tayassu pecari ) (n = 60) obtained in three farms located in the Midwest Brazil. The antimicrobial profiles of commensal E. coli from P. tajacu and T. pecari from commercial herds in Brazil were isolated and analyzed and virulence genes were detected. Among 90 healthy animals, no Salmonella spp. were isolated. However, 30 samples (27%) tested positive for E. coli, with 18 isolates from P. tajacu and 12 from T. pecari, representing frequencies of 58.0% and 38.7%, respectively. Additionally, other Enterobacteriaceae family bacteria were detected but not included in this analysis. However, individual samples from 30 animals tested positive for E. coli, of which 16 were isolated from P. tajacu presenting multidrug resistance and six were isolated from T. pecari presenting a similar pattern. The E. coli virulence genes detected were papC (pilus-associated pyelonephritis) in five isolates, tsh (temperature-sensitive hemagglutinin) in one isolate, and eae (enteric attachment and effacement) in one isolate. The serum resistance gene, iss (increased serum survival), was detected in four isolates. An association between these genes and the presence of hemolysin was also observed in one isolate. Thus, T. pecari and P. tajacu are potential reservoirs of pathogenic and multidrug-resistant and E. coli. Faecal E. coli of healthy P. tajacu and T. pecari could act as a possible reservoir of antimicrobial resistance genes in environment.

Investigating the CO2 Geological Sequestration Potential of Extralow-Permeability Reservoirs: Insights from the Es1 Member of the Shahejie Formation in the Dawa Oilfield

Investigating the CO2 Geological Sequestration Potential of Extralow-Permeability Reservoirs: Insights from the Es1 Member of the Shahejie Formation in the Dawa Oilfield

Regional assessment of the ultra-deep geothermal (UDG) reservoir quality and potential of the Dinantian Zeeland Formation, the Netherlands

Abstract Dinantian carbonates in the NW European Carboniferous Basin (NWECB) in the Netherlands form a target for ultra-deep geothermal (UDG) exploration. The NWECB was a deep water area with shallow water attached carbonate systems in the southwestern Netherlands and isolated carbonate platforms nucleated on horsts in the northern part of the Netherlands. Carbonate platforms in the SW Netherlands contain intra-Dinantian, sub-Namurian and sub-Cretaceous karst systems with irregular cavities, enlarged fracture systems and collapse breccias with relict porosity. Isolated carbonate platforms in the northern Netherlands were not affected by sub-Namurian or sub-Cretaceous karst but contain petrophysical anomalies interpreted as intra-Dinantian karst or fracture systems. The matrix reservoir quality of Dinantian limestones is generally poor but has been improved by a phase of regional dolomitization that affects the lower parts of both isolated and attached carbonate platforms. Dolomitization took place during burial and was associated either with late Carboniferous to early Permian burial or a thermal event during the middle to late Jurassic. Additional reservoir quality is present in a system of hydrofractures in late Tournaisian ramp carbonates in the SW Netherlands that post-date dolomitization; the fracture system may have formed during late Jurassic basin inversion. Present heat flow indicates that two isolated carbonate platforms in the northern Netherlands are buried to sufficient depth to be considered as potential UDG exploration targets. Attached carbonate systems in the SW Netherlands are too shallow to have been heated to the temperature required for industrial applications or for generating electricity from geothermal energy.

Persistent feline coronavirus infection in a cat with cardiac and gastrointestinal signs

Background Feline coronavirus infection causes feline infectious peritonitis in a subset of cats, but can also result in persistent infection. The tissue reservoirs of feline coronavirus and the role of viral persistence in pathogenesis are poorly understood. Aims This study aimed to identify sites of feline coronavirus persistence in a naturally infected cat, identify disease correlates and characterise within-host viral evolution. Methods The study followed a 5-year-old Bengal cat for 6 years and collected non-invasive samples, including faeces and conjunctival, oropharyngeal and saliva swabs. At 11-years-old, the patient was euthanised as a result of respiratory distress, and tissue samples were collected. The authors used hybridisation capture and next-generation sequencing methodologies focused on the feline coronavirus S gene, along with RNA in-situ hybridisation. Results During the study, the patient was diagnosed with inflammatory bowel disease, alimentary small cell lymphoma, chronic rhinitis and mitral valve regurgitation. Feline coronavirus was detected in the nasal cavity, intestine, faeces and conjunctiva in 2017, and in the intestine, faeces and heart in 2022. Sequence analysis showed that the virus adapted to tissue reservoirs over time. Conclusions This study identifies potential feline coronavirus reservoirs. The relationship of persistent feline coronavirus infection to chronic conditions warrants further investigation.

Appendectomy and the Risk of Parkinson's Disease: A Korean Nationwide Study.

The vermiform appendix is considered a potential reservoir for the abnormal α-synuclein aggregate in Parkinson's disease (PD). Previous epidemiologic evidence on the association between appendectomy and PD risk remains inconclusive, especially outside the Western world. To investigate the association between appendectomy and PD risk in Korea. Among 703,831 eligible adult subjects in the National Health Insurance Service sample cohort, we identified 16,122 patients who underwent appendectomy. The rest formed the control group. PD risk was assessed using time-dependent Cox regression analyses. The appendectomy group did not have altered risk of PD compared with the control group in either unadjusted [hazard ratio (HR) 1.32, 95% confidence interval (CI) 0.97-1.80, P = 0.08] or adjusted model (HR 1.42, CI 0.88-2.30, P = 0.15). No further statistical difference appeared when stratified by sex. Appendectomy is not associated with altered risk of PD in the Korean population.

Nemabiome metabarcoding shows a high prevalence of Haemonchus contortus and predominance of Camelostrongylus mentulatus in alpaca herds in the northern UK

Gastrointestinal nematodes (GINs) are a common threat faced by pastoral livestock. Since their major introduction to the UK in the early 1990s, South American camelids have been cograzed with sheep, horses, and other livestock, allowing exposure to a range of GIN species. However, there have been no molecular-based studies to investigate the GIN populations present in these camelids. In the current study, we sampled nine alpaca herds from northern England and southern Scotland and used high-throughput metabarcoded sequencing to describe their GIN species composition. A total of 71 amplicon sequence variants (ASVs) were identified representing eight known GIN species. Haemonchus contortus was the most prevalent species found in almost all herds in significant proportions. The identification of H. contortus in other livestock species is unusual in the northern UK, implying that alpacas may be suitable hosts and potential reservoirs for infection in other hosts. In addition, the camelid-adapted GIN species Camelostrongylus mentulatus was identified predominantly in herds with higher faecal egg counts. These findings highlight the value of applying advanced molecular methods, such as nemabiome metabarcoding to describe the dynamics of gastrointestinal nematode infections in novel situations. The results provide a strong base for further studies involving cograzing animals to confirm the potential role of alpacas in transmitting GIN species between hosts.

One health approach to study human health risks associated with Dermanyssus gallinae mites

Despite the significant health risks associated with Dermanyssus gallinae infestations in humans, they are often overlooked. This study investigated a household case of D. gallinae infestation and explored the resulting clinical manifestations and risk of infection in family members. Microfluidic PCR was employed for high-throughput screening of pathogens in collected mites and blood samples from both chickens and family members. Morphological and molecular examinations confirmed the identity of the mites as D. gallinae sensu stricto (s.s.), with evidence indicating recent blood feeding. Results indicated that the mites exclusively harbored various pathogens, including Bartonella spp., Ehrlichia spp., Apicomplexa, and Theileria spp. Blood samples from family members and poultry tested negative for these pathogens, suggesting a potential reservoir role for D. gallinae. The study further identified haplotypes of D. gallinae, classifying them into D. gallinae s.s., cosmopolitan haplogroup A. Serological analysis revealed elevated IgE seroreactivity against mite proteins in the family member with bite lesions. Antibodies against Bartonella spp. were detected in this individual, indicating exposure to the pathogen. In summary, this study sheds light on the clinical manifestations, pathogen detection, and genetic characterization of D. gallinae infestations, underscoring the necessity of adopting comprehensive approaches to manage such infestations effectively.

Geo-mechanical and geo-morphology characterisation of the cap rocks in the Niger Delta for potential carbon capture and storage

The world has been battling climate change which is caused by an excessive amount of carbon dioxide in the atmosphere. Carbon sequestration in geological sinks was identified as one of the major methods to curb and reduce the amount of carbon dioxide in the atmosphere. The carbon dioxide stored in the geological formations must not escape back into the atmosphere. Characterisation of potential reservoirs for geological sequestration is pertinent for injectivity, capacity, and most importantly containment of carbon dioxide. The cap rock is one of the most important factors determining carbon sequestration success. This study focuses on the preliminary characterisation of the caprocks for evaluating potential subsurface storage of carbon dioxide based on their petrophysical characteristics. X-ray Diffraction and X-ray Fluorescence provided the mineralogical composition and geochemical data of the cap rocks while Scanning Electron Microscopy-EDS was used to identify the qualitative information on the micromorphological textural structure of the cap rocks in the Niger Delta. Conventional Triaxial experiments were used to determine the elastic and geo-mechanical strength of the caprocks. It was identified that the grain skeleton of caprocks in the region is predominated by Quartz, Albite, and Muscovite. The ratio of the tectosilicate and phyllosilicate minerals indicates that the cap rocks are silicate shale. The peak strength of the caprocks ranged from 48.85 to 80.50 MPa and are classified as strong rocks. The cap rocks showed a quasi-elastic behaviour after being subjected to compressive axial force. The elastic modulus of the caprocks was also observed. The characteristics exhibited by the shale caprock at the rock matrix level are highly favourable for sealing carbon dioxide and hence indicate capability for use in carbon sequestration.

Infection and re-infection of Leptospira spp. in stray dogs and cats from Bogota, Colombia.

Leptospirosis is a re-emerging zoonosis that is under-reported in tropical countries, and canines can be a potential reservoir of the disease. The objective of this study was to diagnose Leptospira spp. that is actively infected and re-infected in stray dogs and cats from Bogota, D.C., Colombia. A sample of 200 animals, including dogs and cats from the animal protection programs of Bogota, Colombia, were used in this study. Blood was collected from these animals for serum and DNA analysis. Conventional polymerase chain reaction (PCR) was performed using the 16s rRNA primer set, and higher-quality amplification products were sequenced by Sanger. For serodiagnosis, a group of PCR-positive samples was tested using the microagglutination test (MAT). The overall PCR positivity of stray dogs and cats was 56%, 52.9%, and 65.3% in dogs and cats, respectively. The MAT seropositivity was 77.3%, and only dogs showed titers higher than 1:400. Canicola, Icterohaemorrhagiae, Pomona, Hardjo Prajitno, and Canicola and Hardjo prajitno were the serogroups associated with dogs and cats, respectively. Phylogenetic analysis revealed that the strains belonging to Leptospira interrogans serovars related to isolated samples of American, European, and Asian bats (Myotis myotis), dogs, and bovines of American origin. These results showed that stray dogs and cats were previously exposed to different serovars of Leptospira spp. and re-infected with other serovars that actively participated in the transmission cycle. These findings highlight the importance of actively diagnosing infectious animals to design effective intervention strategies.

Geomechanical responses of sand–clay interbedded gas hydrate-bearing deposits under depressurization-driven gas production at site UBGH2-6 in Ulleung Basin, offshore Korea

This study explores geomechanical responses of sand-clay interbedded hydrate reservoirs subjected to depressurization. A thermo-hydro-mechanically (T-H-M) coupled simulation code was created to simulate T-H-M interactions in layered hydrate reservoirs, utilizing an explicit two-way coupling scheme. The code was then used to model a hydrate reservoir analogous to a hydrate deposit system in Ulleung Basin, Offshore Korea (Site UBGH2-6). Hydrate reservoirs comprising thin and interbedded sand-clay layers exhibit unique geomechanical responses due to the localized gas hydrate dissociation along sand-clay layer interfaces. The localized dissociation pattern leads to accelerated sediment consolidations along the layer interfaces. The simulation results also reveal development of shear deformation along the sand-clay interfaces, which implies the layer interfaces may act as the main sources of sand productions and fines migration within a depressurized hydrate reservoir. Additional simulations are conducted to further investigate the effects of depressurization rate and formation wettability on gas productivity. Although faster depressurization speeds up initial gas production, ultimately, the production rate is governed by the final bottom hole pressure, regardless of the depressurization rate. Nonetheless, slower depressurization appears more favorable, given its capacity to mitigate initial geomechanical responses, such as reservoir compaction and sand production, thus preserving the long-term production potential of a hydrate reservoir. On the other hand, a cyclic depressurization scheme also proves to be able to mitigate the level of initial geomechanical responses, but only at the cost of reduced gas productivity. A comparative analysis with varying wettability indicates that water-wet reservoirs may be more favorable target for gas hydrate exploitation than gas-wet reservoirs. The presented results enhance understanding of complex hydrate reservoir dynamics and contribute to advancement of sustainable and efficient hydrate production techniques.

Is Artemia susceptible to the microsporidium Ecytonucleospora hepatopenaei (EHP) infection?

Following the three-stage approach of the WOAH (World Organisation for Animal Health) standard on the confirmation of susceptible species to a specific pathogen, Artemia franciscana juveniles were challenged with immersion exposure (IM) in a homogenate suspension of Penaeus vannamei hepatopancreas infected with Ecytonucleospora hepatopenaei (EHP) and per os administration (PO) with chlorella soaked in EHP-infected hepatopancreatic homogenate suspension. Using TaqMan probe-based quantitative PCR, we detected that loads of EHP in A. franciscana juveniles from both the IM and PO groups were about 101 copies/ng-DNA on the 3rd day post-exposure (3 dpe). However, no more EHP was detectable in the challenged A. franciscana juveniles on 7 dpe. Nested PCR targeting the EHP spore wall protein gene did not produce a target band in A. franciscana juveniles on either 3 dpe or 7 dpe. The confirmative evidence of the absence of sustained infection with EHP in the exposed Artemia was substantiated using in situ DIG-labeling-loop-mediated DNA amplification (ISDL) on A. franciscana juvenile sections, which revealed a few weak grey-blue positive signals appeared on 3 dpe but disappeared on 7 dpe. The results indicated that exposure to EHP resulted in the invasion of Artemia in intestinal epithelial cells, but the infection was unable to persist, confirming Artemia is not susceptible to EHP. Therefore, the research countered the assertion of Artemia as a potential EHP reservoir.

Assessment of the Upper Cretaceous Abu Roash carbonate source rocks from the Beni Suef field, Western Desert, Egypt

Global sea-level rise during the Early Turonian-Late Cenomanian Bonarelli event resulted in oceanic anoxia and deposition of organic-rich source rocks across Northern Africa, such as the Late Cretaceous Abu Roash-F carbonates. Here, using thin sections, SEM, XRF, standard core analysis, and Rock-Eval pyrolysis data, we examine the petrographic and geochemical properties of the Abu Roash-F (AR-F) carbonate source rocks. These deep marine carbonates consist of dominantly planktonic foraminifera and calcispheres and are classified as wackestone. Extensive micritization, calcite cementation, and ferroan dolomite cement replacement (filling the bioclastic tests and chambers) are identified as the principal diagenetic factors. Core measurements indicate that these carbonates have very low porosity below 3% and horizontal permeability of 0.003 mD (3x10-18 m2), which is also supported by the observed isolated nanopores in SEM. The elemental concentration from the XRF data confirms a highly reducing depositional environment that facilitated the organic richness during the Early Turonian Oceanic Anoxia Event 2 (OAE2). The studied carbonate interval consists of Type-II kerogen in the oil window with a Tmax of about 440 °C and up to 4.2 wt.% TOC indicating ‘fair’ to ‘excellent’ organic richness and a very high probability of active oil generation and expulsion. Following the wireline logs and core data, the self-sourcing unconventional reservoir potential of the AR-F carbonates has been emphasized.

Geochemical Characteristics of the Paleozoic Marine Source Rocks and Ultra-Deep Hydrocarbon Accumulation Mode of the Awati Sag

The Lower Paleozoic of the Awati Sag and its periphery is a region with relatively low levels of exploration and stands as a frontier for ultra-deep hydrocarbon exploration. Based on outcrop and core samples, this study integrated organic geochemical analysis, total organic carbon (TOC) logging interpretation, and one-dimensional and two-dimensional hydrocarbon accumulation simulations, to clarify the primary source rock of the Lower Paleozoic and its characteristics, as well as its hydrocarbon accumulation mode. The findings indicate the following: (1) The Lower Paleozoic features two sets of industrial source rocks. The Yuertusi Formation, with its considerable thickness (approximately 200 m), widespread distribution, and elevated TOC (averaging approximately 5% from experimental data and logging interpretation), stands out as the Lower Paleozoic’s most pivotal source rock. (2) The Yuertusi and Saergan Formations are in a high-to-over-mature stage, with the Yuertusi initiating oil generation in the early Silurian and transitioning to gas by the late Permian. The Saergan began producing oil in the Carboniferous, followed by gas in the late Permian. (3) The potential ultra-deep gas reservoirs in the Awati Sag are mainly distributed in the structural traps closer to the deep faults in five potential target formations. Deep natural gas typically exhibits mixed-source signatures, with the mixing notably pronounced along the Shajingzi Fault Belt due to influential basin-controlling faults.

Further Investigation of CO2 Quasi-Dry Fracturing in Shale Reservoirs—An Experimental Study

The physical properties of shale reservoirs are typically poor, necessitating the use of fracturing technology for effective development. However, the high clay content prevalent in shale formations poses significant challenges for conventional hydraulic fracturing methods. To address this issue, CO2-based fracturing fluid has been proposed as an alternative to mitigate the damage caused by water-based fracturing fluids. In this paper, the applicability of quasi-dry CO2 fracturing in shale reservoirs is examined from three key perspectives: the viscosity of CO2 fracturing fluid, the fracture characteristics induced by the CO2 fracture fluid, and the potential reservoir damage caused by the fracturing fluid. Firstly, the viscosity of CO2 fracturing fluid was determined by a rheological experiment. Rheological tests revealed that the viscosity of CO2 fracturing fluid was significantly influenced by the water–carbon ratio. Specifically, when the water–carbon ratio was 30:70, the maximum viscosity observed could reach 104 mPa·s. Moreover, increasing reservoir temperature resulted in decreased fracturing fluid viscosity, with a 40 °C temperature rise causing a 20% viscosity reduction. Secondly, matrix permeability tests were conducted to investigate permeability alteration during CO2 fracturing fluid invasion. Due to the weak acidity of CO2-based fracturing fluid, the permeability reduction induced by clay hydration was inhibited, and an increase in permeability was observed after a 3-day duration. However, the matrix permeability tends to decrease as the interaction time is prolonged, which means prolonged soaking time can still cause formation damage. Finally, triaxial fracturing experiments facilitated by a three-axis servo pressure device were conducted. The fracture properties were characterized using computed tomography (CT), and 3D reconstruction of fractured samples was conducted based on the CT data. The results demonstrate that CO2 fracturing fluid effectively activates weak cementation surfaces in the rock, promoting the formation of larger and more complex fractures. Hence, CO2 quasi-dry fracturing technology emerges as a method with significant potential, capable of efficiently stimulating shale reservoirs, although a reasonable soaking time is necessary to maximize hydrocarbon production.

Sandstones and red beds in the Lower Cretaceous Sidi Aich Formation, Chotts Basin (Southern Tunisia): facies, architecture and depositional environments

Abstract The Lower Cretaceous deposits of North Africa represent a terrestrial to shallow-marine sandstone-dominated succession often referred to as the ‘Continental Intercalaire’ and Nubian Sandstone informal groups. The upper Barremian Sidi Aich Formation of the Continental Intercalaire is distinguished throughout the Chotts basin of southern Tunisia by sandstone-dominated sequences within conglomerate, calcareous siltstone and palaeosol red bed occurrences. This paper aims to highlight: (1) the facies distribution, internal architecture and depositional environment of the sandbodies; and (2) the origin, spatial distribution and architecture of the red beds that underlined and topped sandbodies. Strata in the Zimlet El Beida anticlinal structure, Chotts basin, offer a good opportunity for detailed field observations and bed-by-bed logging of three representative lithostratigraphic sections. Detailed sedimentological investigation allows the recognition of several lithofacies grouped into three facies associations indicating tidal flat, tidal channel and tidal bar depositional settings characterizing a transgressive tide-dominated estuarine system that developed during an episode of relative sea-level fluctuations in the Early Cretaceous. The high-resolution petrographic, mineralogical and geochemical analyses of the red beds allow the differentiation of three distinct lithofacies sets including: (1) intraformational conglomerates; (2) calcareous siltstones; and (3) palaeosol. Major red beds comprise detrital grains inherited from the host or parent sediment and authigenic minerals (dolomite, calcite and hematite) precipitated during the diagenetic processes. Grain components have been partially or completely cemented and/or replaced by terrestrial phreatic dolomite. The negative δ 13 C and δ 18 O signatures of the dolomite analyses indicate that the dolomitization processes have been influenced by fluctuations of the groundwater table or climate change from semi-arid to semi-humid conditions. This study, therefore, may provide useful data for the better understanding of the internal architecture of the red beds associated with sandbodies that represent the main and significant potential reservoir within the Lower Cretaceous Continental Intercalaire sandstone-dominated groundwater aquifers of the Chotts basin.