Reservoir souring: sulfur chemistry in reservoir

Reservoir souring is a widespread phenomenon in reservoirs undergoing seawater injection. During this process, the sulfate in the seawater promotes the growth of sulfate reducing bacteria and archaea generating hydrogen sulfide. However, other reactions involving formation of different sulfur species with intermediate valence states such as elemental sulfur, sulfite, polysulfide ions, and polythionates can occur. These sulfur species have implications in both chemical and microbial processes and impact the treatment approaches for soured reservoirs. A predictive reactive model was developed in this study to investigate the chemical reactivity of sulfur species and their partitioning behaviour as a function of temperature, pressure, and pH in a seawater-flooded reservoir. The presence of sulfur species with different oxidation states impacts the amount and partitioning behaviour of H₂S. The model predicts at pH values less than 5, sulfur is predominantly in the form of sulfate, polysulfide, hydrogen sulfide and approximately 10% of the total sulfur is thiosalts. There is also elemental sulfur precipitation. At pH above neutral, the bulk of the sulfur is sulfate and thiosalts and less than 10% polysulfide is formed. The amount of sulfur deposited as elemental sulfur is also less compared to pH lower than 5. Without considering sulfur speciation and assuming that all the initial sulfate in the injected seawater (2454 mg/L) is converted to H₂S microbially and the formed H₂S partitions between phases, the gas phase under test separator conditions on the surface contains 1080 ppm H₂S which is in equilibrium with the oil phase containing 295.7 ppm H₂S and water phase with H₂S content of 8.8 ppm. These values are higher than those obtained from reactivity analysis (i.e., H₂S content of the gas, oil, and aqueous phases are 487 ppm, 134 ppm, and 4 ppm, respectively). Therefore, ignoring sulfur speciation in investigating reservoir souring leads to over-prediction of H₂S content of reservoir fluid. The developed reactivity model enables one the investigation of sulfur chemistry when injection of sulfate-containing seawater is used in recovery processes. This model can be used as a tool to study sulfur speciation and H₂S amounts as a function of reservoir temperature, pressure and pH and therefore, could be used in developing souring mitigation measures

Comparative evaluation of the effect of Er:YAG laser and low level laser irradiation combined with CPP-ACPF cream on treatment of enamel caries

Objectives: This study investigated the effectiveness of low power red and infrared lasers and that of Er:YAG laser, in association with CPP-ACPF cream, on remineralization of white spot lesions. Study Design: Fifty intact premolars were immersed in a demineralization solution for 10 weeks to induce caries like lesions and then were divided into five groups. In group 1, the teeth were covered with a CPP-ACPF cream for 3 minutes and then irradiated with a low power red laser (660 nm, 200 mW) for 1 minute through the cream. In group 2, the treatment was the same as that in group 1, but an infrared laser (810 nm, 200 mW) was employed. The specimens in group 3 were irradiated with an Er:YAG laser (100 mJ, 10 Hz) combined with CPP-ACPF. In group 4, the CPP-ACPF cream was applied for 4 minutes and group 5 was submitted to neither laser nor CPP-ACPF. The micro Vickers hardness was compared at 20, 60 and 100 ì from the enamel surface among the groups. Results: The highest microhardness was observed in the low power red and Er:YAG laser groups and the lowest one belonged to the CPP-ACPF alone and control groups. However, no significant difference was found in microhardness of the experimental groups at any of the evaluation depths (p>0.05). Conclusion: With the laser parameters used in this study, neither the combined application of Er:YAG laser with CPP-ACPF nor the combination of low power lasers with CPP-ACPF provided a significant increase in remineralization of enamel caries

The Production Process of Lithics in Late Bronze Age at Shahrake Firouzeh Site in Neyshabur, North East of Iran

Nowadays, the study of lithics has gained a special status in prehistoric archaeology and even archaeology of later periods. Shahrake Firouzeh is one of the most important prehistoric settlements ever detected in Neyshabur Plain in Khorasan Razavi Province. In general, based on the past excavation seasons, Shahrake Firouzeh site represents the Bronze Age and probably Iron Age cultures in the region and the bulk of cultural materials indicates a culture known as BMAC (Bactria-Margiana Archaeological Complex). This paper analyzes the typology of Shahrake Firouzeh lithics, which is a key typical site related to Late Bronze Age in Northeast of Iran. The collection of stone artifacts from Shahrake Firouzeh excavations includes 66 pieces. These tools have been recovered from nine trenches in different parts of the site during four excavation seasons, all of which belong to Late Bronze Age. The majority of lithics in this site are of debitage type. In addition to producing sickle blades bearing signs of sickle gloss, the main feature of this collection is production of arrowheads retouched in two sides. It should be noted that all the stone artifacts from Shahrake Firouzeh have been made from high quality chert stone in a color range of cream, honey, and transparent with semi-glossy surface. In general, the raw material used is of good quality, although it does not seem to have large dimensions. The raw material source is unknown, and thus no data can be presented on usage patterns of raw material

An Analysis of the Cultural Landscape and Settlement Pattern of the Kashafrud Basin (Mashhad Plain) in the Iron Age

The Khorasan region, especially the Kashafrud basin, has culturally retained a strategic position by virtue of its location between three major cultural spheres of southwestern Central Asia, the Central Plateau of Iran, and northeastern Iran. The Iron Age still remains a mainly unknown period in this region. In northeast Iran, particularly in the Greater Khorasan, the period is characterized by cultural attributes utterly different from those of the other parts of the Iranian Plateau. Coeval archaeological evidence from Khorasan shows affinities with the Yaz and Dahistan cultures of Central Asia. The major topics considered in this study are: the distribution pattern and major influential factors in the formation of the Iron Age settlements in the Kashafrud basin (Mashhad Plain), the nature of Iron Age cultural material in the region, and the characteristics shared between the contemporary settlements in Mashhad and the adjacent regions. Further major research objectives include proposing a comparative chronology, analyzing the regional cultural landscape, and specifying the Iron Age settlement patterns in the region. Thus, attempts have been made to answer the research questions through ArcGIS maps, analysis of surface ceramics, and the landscape archaeology approach. The results indicate the impressive role of environmental factors, especially the Kashafrud River as the leading regional resource, in the advent of Iron Age settlements. Moreover, the regional material culture exhibits strong affinities with the Iron Age culture of “Yaz” in Central Asia, and indicates relations and population movements between the different regions that were under the influence of this culture

Incorporating Microporous Zn3 and Zn2Cd MOFs into Pebax/PVDF Mixed Matrix Membranes for Improved Carbon Dioxide Separation Performance

A pair of related metal–organic frameworks (Zn3 and Zn2Cd) developed in our group were incorporated into Pebax 30R51 and PVDF Kynar 761 polymers to fabricate mixed matrix membranes (MMMs). These MOFs were chosen due to the carbon dioxide molecular sieving ability of Zn3, and the slightly larger pore aperture of Zn2Cd that allows carbon dioxide and larger gases to enter the pores. For Pebax-based MMMs, this work demonstrated an over two-fold and four-and-a-half-fold increase in carbon dioxide permeability for Zn3- (15 wt %) and Zn2Cd-containing (10 wt %) MMMs over the pristine polymer. Separation selectivity (CO2:N2) of 4.21 and 7.33 were observed for Zn3 and Zn2Cd (10 wt %). For PVDF-based MMMs, the incorporation of Zn3 and Zn2Cd (10 wt %) increased the carbon dioxide permeability approximately two- and three-fold. The CO2/N2 selectivity of the PVDF membranes increased 73% (1.01 to 1.86) and 68% (1.01 to 1.68) when 15 wt % Zn3 and Zn2Cd were incorporated into PVDF. The improved performance of Pebax over PVDF based MMMs is attributed to matching the permeability of the polymer bulk phase (Pebax over PVDF) and the dispersed phase (Zn3 and Zn2Cd). The lower permeability allows the MOF, which has slow kinetics associated with molecular sieving, to participate in the permeation process better. With regards to Zn3 vs Zn2Cd, while Zn3 acts as a molecular sieve and Zn2Cd does not, we hypothesize that the faster diffusion of carbon dioxide gas in Zn2Cd can outcompete the lower nitrogen gas permeability and molecular sieving properties of Zn3. However, we expect that further increasing the pore aperture would increase the permeabilities of nitrogen gas such that differences in diffusion kinetics due to molecular size would be unimportant

A Particle Model for Prediction of Cement Infiltration of Cancellous Bone in Osteoporotic Bone Augmentation.

PMC3693961Femoroplasty is a potential preventive treatment for osteoporotic hip fractures. It involves augmenting mechanical properties of the femur by injecting Polymethylmethacrylate (PMMA) bone cement. To reduce the risks involved and maximize the outcome, however, the procedure needs to be carefully planned and executed. An important part of the planning system is predicting infiltration of cement into the porous medium of cancellous bone. We used the method of Smoothed Particle Hydrodynamics (SPH) to model the flow of PMMA inside porous media. We modified the standard formulation of SPH to incorporate the extreme viscosities associated with bone cement. Darcy creeping flow of fluids through isotropic porous media was simulated and the results were compared with those reported in the literature. Further validation involved injecting PMMA cement inside porous foam blocks - osteoporotic cancellous bone surrogates - and simulating the injections using our proposed SPH model. Millimeter accuracy was obtained in comparing the simulated and actual cement shapes. Also, strong correlations were found between the simulated and the experimental data of spreading distance (R2 = 0.86) and normalized pressure (R2 = 0.90). Results suggest that the proposed model is suitable for use in an osteoporotic femoral augmentation planning framework.JH Libraries Open Access Fun

Computer-Assisted Femoral Augmentation For Osteoporotic Hip Fracture Prevention

Osteoporosis is the severe reduction in bone mineral density and load bearing capabilities. Individuals with osteoporosis, especially the elderly, are at a higher risk of bone fracture as a result of trauma, with hip fractures being the most prevalent and life threatening. There are currently a number of preventive treatments available; however the side effects, long delays in restoring bone strength or other issues associated with these treatments inhibit their efficacy. A promising new approach to preventing fracture is augmentation of the mechanical properties of the femur by injecting it with acrylic bone cement-femoroplasty. There are risks and limitations associated with femoroplasty, however, that need to be addressed through pre-operative planning and careful execution as well as experimental validation before it finds its way to the operating room. This thesis describes the methods and tools developed for effectively planning and performing femoroplasty. To this end, computational models were developed to simulate various augmentation scenarios and to predict how those affect the mechanical strength of the femur. Those tools were then used to plan femoroplasty for paired cadaveric osteoporotic femur specimens. Experimental tests performed on those specimens showed significant improvements in the load and energy absorbed to fracture the augmented specimens compared to those left intact. We therefore conclude that effective femoroplasty is possible by using computer planning and controlled execution. Although geared towards femoroplasty, these methods and tools can be extended to other types of augmentation surgeries using bone cement including vertebral body augmentation (vertebroplasty) or augmentation of distal radius for prevention of osteoporotic wrist fractures

Color Stability of Enamel following Different Acid Etching and Color Exposure Times

Background and aims. The aim of this study was to evaluate the effect of different etching times on enamel color stability after immediate versus delayed exposure to colored artificial saliva (CAS). Materials and methods. Human first premolars were divided into five groups of twenty. A colorimeter was used according to the CIE system on the mid-buccal and mid-lingual surfaces to evaluate initial tooth color. Samples in group A remained unetched. In groups B to E, buccal and lingual surfaces were initially etched with phosphoric acid for 15 and 60 seconds, respectively. Then, the samples in groups A and C were immersed in colored artificial saliva (cola+saliva). In group B, the teeth were immersed in simple artificial saliva (AS). Samples in groups D and E were immersed in AS for 24 and 72 hours, respectively before being immersed in colored AS. The teeth were immersed for one month in each solution before color measurement. During the test period, the teeth were retrieved from the staining solution and stored in AS for five minutes. This was repeated 60 times. Color changes of buccal and lingual surfaces were calculated. Kruskal-Wallis and Wilcoxon tests were used for statistical analysis (α ≤ 0.05). Results. There were no significant differences between the groups in term of ΔE of buccal (P = 0.148) and lingual surfaces (P = 0.73). Conclusion. Extended time of etching did not result in significant enamel color change. Immediate and delayed exposure of etched enamel to staining solutions did not result in clinically detectable tooth color changes

Reservoir souring: sulfur chemistry in offshore oil and gas reservoir fluids

Abstract The injection of sulfate-containing seawater into an oil reservoir, for maintaining the reservoir pressure, can promote the growth of sulfate reducing bacteria and archaea near the injection wells, leading to the formation of sulfides such as hydrogen sulfide. However, intermediate sulfur species with different valence states, such as polythionates and polysulfides have been detected in several produced water samples, likely a result of phase partitioning, and chemical and microbial reactions. These sulfur species could affect the microbial communities (e.g., microbially influenced corrosion) and will impact the efficiency of souring mitigation methods. In addition, the presence of these sulfur species can result in operational, environmental, and treatment problems. Therefore, development and implementation of souring control strategies during production cycle of oil and gas reservoirs require identifying the origins, reactivity, and the partitioning behaviour of these compounds. This paper presents an overview of the known mechanisms responsible for reservoir souring and then focuses on the chemical reactions and sulfur species associated with production and consumption of hydrogen sulfide. In this work we highlight complexity of the sulfur chemistry and that the assumption that all the sulfate is reduced to hydrogen sulfide can lead to inappropriate souring management methods. The paper also reviews the detection and analysis methods used for sulfur compounds. The review demonstrates that there is a gap in the current souring models and methods due to the exclusion of key sulfur compounds and challenges in identifying and quantifying these compounds with respect to speed of analysis and sample stability