Probabilistic Seismic Hazard Analysis for Offshore Bangladesh Including Fault Sources

This paper presents a probabilistic seismic hazard analysis (PSHA) for a site offshore Maheshkhali Island, Bangladesh. The tectonic setting of the area is complex, and the PSHA includes active crustal faults, megathrust and intraplate subduction faults, and a background gridded seismicity areal source zone based on historical and recorded earthquakes. In addition, we model several rupture scenarios for the closest megathrust source. The peak ground acceleration values for return periods of 475 years and 2475 years are 0.33 g and 0.63 g, respectively. These values are higher than previous studies conducted in the area, however, past studies only included areal source zones based on recorded seismicity whereas this study takes advantage of recent research to include more detailed fault data. The deaggregation plots show that the main contributors to the hazard are a magnitude 6.5–7.1 earthquake 15–20 km from the site on the Maheshkhali fault and a magnitude 8.0–8.8 earthquake 120–250 km from the site on the Ramree megathrust.Probabilistic Seismic Hazard Analysis for Offshore Bangladesh Including Fault SourcesacceptedVersio

Subsurface fracture analysis and determination of in-situ stress direction using FMI logs: An example from the Santonian carbonates (Ilam Formation) in the Abadan Plain, Iran

The relationship between the present-day stress field and natural fractures can have significant implications for subsurface fluid flow. In particular, fractures that are aligned in orientations favourable for reactivation by either shear or tensile failure in the in-situ stress field often exhibit higher hydraulic conductivities. The Ilam Formation of southwestern Iran is an important hydrocarbon reservoir containing numerous natural fractures. However, little is known about the state of stress in this region, or any of Iran's petroleum provinces. We conducted analysis of the present-day maximum horizontal stress orientation and the density, orientation and hydraulic conductivity of natural fractures in the Ilam carbonates using high resolution Formation Micro Imager resistivity logs in two wells. A total of 51 breakouts with an overall length of 215 m were observed in the two wells, indicating a maximum horizontal stress orientation of 68°N (± 7.6°) in well A and 58°N (± 6.3°) in well B. Furthermore, the wellbore-derived stress orientations determined herein are consistent with those inferred from nearby earthquake focal mechanism solutions, indicating that stresses in the sedimentary cover are linked to the resistance forces generated by Arabia–Eurasia collision. Furthermore, the correlation between stress orientations estimated from earthquake focal mechanism solutions and breakouts indicates that focal mechanism solution data, which is often considered to be unreliable for stress field analysis near transform margins, may provide reliable information on the stress orientation near continental collision zones. The image log data also reveals three sets of open, and presumably hydraulically conductive, fractures with strikes of (i) 160–170°N, (ii) 110–140°N and (iii) 070–080°N. Fracture set (iii) is consistent with being formed and open in the present-day stress field. However, fracture sets (i) and (ii) strike at a high angle to the present-day maximum horizontal stress, and are interpreted herein to be the result of either pre- or syn-folding related forces. The observation that different sets of open fractures in the field can be either sensitive or insensitive to the present-day stress is critical for improving hydrocarbon recovery.Mojtaba Rajabi, Shahram Sherkati, Bahman Bohloli and Mark Tinga

Microseismic monitoring and interpretation of injection data from the In Salah CO2 storage site (Krechba), Algeria

-Microseismic data analysis together with interpretation of injection data at the In Salah CO2 storage site provides a valuable tool for improved understanding of the subsurface injection and storage processes. More than 1500 microseismic events have been detected semi-automatically between August 2009 and May 2012 and the occurrence of the events correlates clearly with increased injection rates and well-head pressures. Most likely the fracture pressure has been exceeded temporarily, resulting in a sudden increase of microseismicity. Waveform cross- correlation of the events demonstrates that most events occur in three distinct clusters. Clusters with shorter S-P wave differential travel times clearly correlate with the CO2 injection at KB502, whereas events with larger S-P wave times do not. An uncertainty analysis and a network design study conclude that a more extensive microseismic network would be needed to resolve locations and potential correlations with injection data

Probabilistic Seismic Hazard Analysis for Offshore Bangladesh Including Fault Sources

This paper presents a probabilistic seismic hazard analysis (PSHA) for a site offshore Maheshkhali Island, Bangladesh. The tectonic setting of the area is complex, and the PSHA includes active crustal faults, megathrust and intraplate subduction faults, and a background gridded seismicity areal source zone based on historical and recorded earthquakes. In addition, we model several rupture scenarios for the closest megathrust source. The peak ground acceleration values for return periods of 475 years and 2475 years are 0.33 g and 0.63 g, respectively. These values are higher than previous studies conducted in the area, however, past studies only included areal source zones based on recorded seismicity whereas this study takes advantage of recent research to include more detailed fault data. The deaggregation plots show that the main contributors to the hazard are a magnitude 6.5–7.1 earthquake 15–20 km from the site on the Maheshkhali fault and a magnitude 8.0–8.8 earthquake 120–250 km from the site on the Ramree megathrust

The effects of hyperbaric oxygen treatment on oxidant and antioxidants levels during liver regeneration in rats

The effects of hyperbaric oxygen (HBO) therapy on oxidant/antioxidant metabolism are controversial and its effects on hepatic regeneration are not known. In this study, we investigated a possible beneficial effect of HBO therapy on oxidant and antioxidants levels during liver regeneration. To conduct this study, seventy percent hepatectomy was performed on forty-eight Spraggue-Dawley rats and the rats were divided into two equal groups: HBO-treated group and untreated group (non-HBO group). We determined the levels of malondialdehyde (MDA), an oxidative stress marker, and the levels of antioxidant enzymes/reagents, including glutathione (GSH), superoxide dismutase (SOD) activitiy, copper (Cu) and zinc (Zn), in the remnant liver samples. We also measured mitotic index (MI) and proliferating cell nuclear antigen (PCNA) levels to assess the degree of liver regeneration. HBO treatment significantly decreased MDA levels, whereas it increased SOD activity, GSH and Zn levels. In contrast, Cu levels were lower in the HBO-treated livers than the levels in the untreated remnant livers. The effect of HBO treatment may be mediated by the suppression of certain enzymes that are responsible for lipid peroxidation. In addition, HBO treatment may induce the production of antioxidant enzymes/reagents by remnant liver tissues. The HBO-treated rats maintained their body weights but the untreated rats lost body weights. HBO treatment also increased MI and PCNA levels, indicating HBO treatment enhances liver regeneration. These results indicate that HBO treatment has beneficial effects on liver regeneration by decreasing MDA and by increasing antioxidant activities. We therefore suggest that HBO therapy may be useful after liver resection

Monitoring CO2 Storage Sites Onshore and Offshore using InSAR Data and Strain Sensing Fibre Optics Cables

A key requirement for geological CO2 storage is site integrity management and monitoring during operation through to the post decommissioning period. This paper focuses on monitoring deformation of the ground surface and seabed as a proxy for overall deformation in the reservoir and surrounding layers. The objective is to inform, based on deformation data, on how the reservoir is responding to CO2 injection and to ensure any issues with regard to storage integrity are rapidly detected. The magnitude and pattern of deformation at the surface reveals geomechanical/hydromechanical processes that occur in reservoir due to CO2 injection. We acquired deformation data from the In Salah CO2 injection site and from four additional study cases during the course of this study; one in the onshore UK, the other a combined campaign onshore Norway and offshore Germany, and the third in onshore Japan. Significant developments in measurement techniques, processing tools and interpretation algorithms were developed through this project. Models were then developed to simulate the observed data and to couple surface deformation to displacement in the subsurface. The results show millimeter-scale deformations in the subsurface have a signature at the surface that can be captured by the tools and workflows developed in this project. These deformations, particularly the patterns, are important factors to consider when monitoring a CO2 storage site