The role of the stress regime on microseismicity induced by overpressure and cooling in geologic carbon storage

Fluid injection in deep geological formations usually induces microseismicity. In particular, industrial‐scale injection of CO₂ may induce a large number of microseismic events. Since CO₂ is likely to reach the storage formation at a lower temperature than that corresponding to the geothermal gradient, both overpressure and cooling decrease the effective stresses and may induce microseismicity. Here, we investigate the effect of the stress regime on the effective stress evolution and fracture stability when injecting cold CO₂ through a horizontal well in a deep saline formation. Simulation results show that when only overpressure occurs, the vertical total stress remains practically constant, but the horizontal total stresses increase proportionally to overpressure. These hydro‐mechanical stress changes result in a slight improvement in fracture stability in normal faulting stress regimes because the decrease in deviatoric stress offsets the decrease in effective stresses produced by overpressure. However, fracture stability significantly decreases in reverse faulting stress regimes because the size of the Mohr circle increases in addition to being displaced towards failure conditions. Fracture stability also decreases in strike slip stress regimes because the Mohr circle maintains its size and is shifted towards the yield surface a magnitude equal to overpressure minus the increase in the horizontal total stresses. Additionally, cooling induces a thermal stress reduction in all directions, but larger in the out‐of‐plane direction. This stress anisotropy causes, apart from a displacement of the Mohr circle towards the yield surface, an increase in the size of the Mohr circle. These two effects decrease fracture stability, resulting in the strike slip being the least stable stress regime when cooling occurs, followed by the reverse faulting and the normal faulting stress regimes. Thus, characterizing the stress state is crucial to determine the maximum sustainable injection pressure and maximum temperature drop to safely inject CO₂.     

Simulation of the impact of faults on CO2 injection into sandstone reservoirs

Numerical simulations of multiphase CO₂ behavior within faulted sandstone reservoirs examine the impact of fractures and faults on CO₂ migration in potential subsurface injection systems. In southeastern Utah, some natural CO₂ reservoirs are breached and CO₂‐charged water flows to the surface along permeable damage zones adjacent to faults; in other sites, faulted sandstones form barriers to flow and large CO₂‐filled reservoirs result. These end‐members serve as the guides for our modeling, both at sites where nature offers ‘successful’ storage and at sites where leakage has occurred. We consider two end‐member fault types: low‐permeability faults dominated by deformation‐band networks and high‐permeability faults dominated by fracture networks in damage zones adjacent to clay‐rich gouge. Equivalent permeability (k) values for the fault zones can range from <10^?14 m² for deformation‐band‐dominated faults to >10^?12 m² for fracture‐dominated faults regardless of the permeability of unfaulted sandstone. Water–CO₂ fluid‐flow simulations model the injection of CO₂ into high‐k sandstone (5 × 10^?13 m²) with low‐k (5 × 10^?17 m²) or high‐k (5 × 10^?12 m²) fault zones that correspond to deformation‐band‐ or fracture‐dominated faults, respectively. After 500 days, CO₂ rises to produce an inverted cone of free and dissolved CO₂ that spreads laterally away from the injection well. Free CO₂ fills no more than 41% of the pore space behind the advancing CO₂ front, where dissolved CO₂ is at or near geochemical saturation. The low‐k fault zone exerts the greatest impact on the shape of the advancing CO₂ front and restricts the bulk of the dissolved and free CO₂ to the region upstream of the fault barrier. In the high‐k aquifer, the high‐k fault zone exerts a small influence on the shape of the advancing CO₂ front. We also model stacked reservoir seal pairs, and the fracture‐dominated fault acts as a vertical bypass, allowing upward movement of CO₂ into overlying strata. High‐permeability fault zones are important pathways for CO₂ to bypass unfaulted sandstone, which leads to reduce sequestration efficiency. Aquifer compartmentalization by low‐permeability fault barriers leads to improved storativity because the barriers restrict lateral CO₂ migration and maximize the volume and pressure of CO₂ that might be emplaced in each fault‐bound compartment. As much as a 3.5‐MPa pressure increase may develop in the injected reservoir in this model domain, which under certain conditions may lead to pressures close to the fracture pressure of the top seal.     

译名之争与早期的《圣经》中译

在早期的《圣经》中译史上,“译名之争”是一个影响颇为深远的事件。这个争论的起源可以追溯到清代前期的“礼仪之争”,直到现在也还没有形成统一的意见。这场围绕着God或Theos等基督教核心名词如何中译而产生的争论,在1843—1851年来华基督教新教传教士集体合作修订《圣经》中译本期间达到高潮。在这期间,英国传教士与美国传教士各自坚持己见,展开长期的论战。“译名之争”导致了早期新教传教士合作译经事业的结束,但也促使多种《圣经》中译本相继问世。它不仅在中国近代基督教传播史上留下深刻的印记,而且波及近代中西化交流的其他方面。     

Significance of large-scale sand injectites as long-term fluid conduits: evidence from seismic data

Sand injectites and related features that are interpreted to have formed by large‐scale, often sudden, fluid escape in the shallow (typically <500 m) crust are readily imaged on modern seismic data. Many of the features have geometrical similarity to igneous dykes and sills and cross‐cut the depositional stratigraphy. Sand injectites may be multiphase and form connected, high‐permeability networks that transect kilometre‐scale intervals of otherwise fine‐grained, low‐permeability strata. North Sea examples often form significant hydrocarbon reservoirs and typically contain degraded, low‐gravity crude oil. Fluid inclusion and stable isotope data from cements in sand injectites record a mixing of aqueous fluids of deep and shallow origin.     

La mobilité forcée des personnes utilisatrices de drogue par injection et inhalation en situation d'itinérance à Montréal

This article focuses on the various actors in the urban setting who contribute to the increase in the forced mobility of homeless injection drug users and crack smokers in Montréal, Canada. The objective is to analyze who these actors are and how they contribute to increasing this forced mobility from the perspective of homeless injection drug users and crack smokers in relation to three needs : basic needs, acquisition of financial resources, and drug use. One hundred and six semi-structured interviews were conducted among this population. The results indicate that various actors—police officers, community organization, peers, municipal administration, storekeepers, and residents—contribute to the forced mobility of this population in their daily activities. As for their needs, it is when they use drugs, sleep, or loiter that they are more likely to experience events of forced mobility. Police officers are by far the actors who contribute the most to this, often in a repressive way. The role of the municipality is also a determining factor in the daily activities of homeless injection drug users and crack smokers.     

Injection‐induced seismicity in Carbon and Emery Counties,central Utah

Utah is one of the top producers of oil and natural gas in the United States. Over the past 18 years, more than 4.2 billion gallons of wastewater from the petroleum industry has been injected into the Navajo Sandstone, Kayenta Formation, and Wingate Sandstone in Carbon and Emery Counties, central Utah, where seismicity has increased during the same period. Previous studies have attributed this seismicity to coal mining. Here, we present evidence for wastewater injection being a major cause of the increased seismicity. We show that, in the coal mining area, seismicity rate increased significantly 1–5 years following the wastewater injection, and the earthquakes, mostly with magnitudes <3.0, are concentrated in areas seismically active prior to the injection. Using simple analytical and numerical models, we show that the injection in central Utah can sufficiently raise pore pressure to trigger seismicity within 10–20 km of the injection wells, and the time needed for the diffusion of pore pressure may explain the observed lag of seismicity increase behind the commencement of injection. The b‐value of these earthquakes increased following the wastewater injection, which is consistent with these events being injection‐induced. We conclude that the marked increase in seismicity rate in central Utah is induced by both mining activity and wastewater injection, which raised pore pressure along preexisting faults.     

Fluid injection and surface deformation at the KTB location: modelling of expected tilt effects

This investigation is indented to explore the relationship between changes in pore fluid pressure and deformation of the land surface induced by a large‐scale injection experiment at the KTB site. Deformation will be monitored by ASKANIA borehole tiltmeters at five locations. During the year 2003, a network of borehole tiltmeters was installed, data transmission links established and tested, and recording of tilt data started. Our first main interest was to receive data sets of all stations well before the injection experiment to start in May 2004, to be able to evaluate local site effects. Thus, the separation of injection‐induced effects will be more reliable. Principal 3D numerical modelling (poro‐elastic modelling and investigations, using the finite element method, FEM) of poro‐elastic behaviour showed that significant tilt amplitudes can be expected during controlled fluid injection. Observed deformation will be investigated within the framework of the fluid flow behaviour and resulting deformation. Two models have been used: a coupled hydro geomechanical finite element model (abaqus ) and, as a first step, also a multi‐layered poro‐elastic crust (poel ). With the numerical model two effects can be quantified: (i) the deformation of the upper crust (tilt measurements) and (ii) the spatial distribution and the changes of material properties in the KTB area. The main aim of the project is to improve the knowledge of coupled geomechanic–hydraulic processes and to quantify important parameters. Thus, the understanding of fracture‐dominated changes of the hydrogeological parameters will be enhanced, geomechanical parameter changes and the heterogeneity of the parameter field quantified. In addition, the induced stress field variation can be explained, which is believed to be mainly responsible for the increase of local seismic activity. Here, we introduce the tiltmeter array at the KTB site, the modelling for a poro‐elastic crust and the preliminary FEM modelling.     

Pliocene sand injectites from a submarine lobe fringe during hydrocarbon migration and salt diapirism: a seismic example from the Lower Congo Basin

Large‐scale conical and saucer‐shaped sand injectites have been identified in the Upper Miocene sediments of the Lower Congo Basin. These structures are evidenced on the 3D high‐resolution seismic data at about 600 ms TWT (two‐way traveltime) beneath the seabed. The conical and saucer‐shaped anomalies range from 20 to 80 m in height, 50 to 300 m in diameter, and 10 to 20 ms TWT in thickness. They are located within a sedimentary interval of about 100 m in thickness and are aligned over 20 km in dip direction (NE‐SW), above the NW margin of an underlying Upper Miocene submarine fan. We have interpreted the conical and saucer‐shaped anomalies as upward‐emplaced sand injectites sourced from the Upper Miocene fan because of their discordant character, the postsedimentary uplifting of the sediments overlying the cones and saucer‐shaped bodies, the alignment with the lateral fringe of the Upper Miocene submarine fan, and the geological context. Sand injection dates from the Miocene–Pliocene transition (approximately 5.3 Ma). The prerequisite overpressure to the sand injection process may be due to the buoyancy effect of hydrocarbons accumulated in the margins of the fan. Additionally, overpressure could have been enhanced by the lateral transfer of fluids operating in the inclined margins of the lobe. The short duration of sand injection and the presence of many sandstone intrusions suggested that the process of injection was triggered by an event, likely due to a nearby fault displacement related to diapiric movements. This is the first time that sand injectites of seismic scale have been described from the Lower Congo Basin. The localized nature of these injectites has led to a change in the migration path of fluids through the sedimentary cover. Consequently, the sand intrusions are both evidence and vectors of fluid migration within the basin fill.     

The connectivity of pore space in mudstones: insights from high‐pressure Wood's metal injection,BIB‐SEM imaging,and mercury intrusion porosimetry

Study of the pore space in mudstones by mercury intrusion porosimetry is a common but indirect technique and it is not clear which part of the pore space is actually filled with mercury. We studied samples from the Opalinus Clay, Boom Clay, Haynesville Shale, and Bossier Shale Formations using Wood's metal injection at 316 MPa, followed by novel ion beam polishing and high‐resolution scanning electron microscopy. This method allowed us to analyze at high resolution which parts of a rock are intruded by the liquid alloy at mm to cm scale. Results from the Opalinus Clay and Haynesville Shale show Wood's Metal in cracks, but the majority of the pore space is not filled although mercury intrusion data suggests that this is the case. In the silt‐rich Boom Clay sample, the majority of the pore space was filled Wood's metal, with unfilled islands of smaller pores. Bossier Shale shows heterogeneous impregnation with local filling of pores as small as 10 nm. We infer that mercury intrusion data from these samples is partly due to crack filling and compression of the sample. This compaction is caused by effective stress developed by mercury pressure and capillary resistance; it can close small pore throats, prevent injection of the liquid metal, and indicate an apparent porosity. Our results suggest that many published MIP data on mudstones could contain serious artifacts and reliable metal intrusion porosimetry requires a demonstration that the metal has entered the pores, for example by Wood's metal injection, broad ion beam polishing, and scanning electron microscopy.     

Increasing livelihood vulnerabilities to coastal erosion and wastewater intrusion: The political ecology of Thai aquaculture in peri-urban Bangkok

Most livelihood research focuses on micro-level decisions affecting occupations but fails to examine wider scale processes that shape markets, institutions, and thus livelihood choices. A political ecology framework can help address this gap by providing ways to analyse how multi-scalar and extra-local practices, policies, and discourses affect local-level socio-environmental outcomes. In the qualitative research reported here, that framework is applied to Tha Kam, a peri-urban coastal sub-district of Bangkok, where most residents are small-scale aquaculture farmers. These farmers have experienced precipitous drops in incomes because of two major environmental changes: coastal erosion and wastewater intrusion. The causes are multiple and complex, and many originate not from practices within Tha Kham but from challenges present at a larger scale or that start upstream. The political and economic drivers of these problems stem from Thailand’s fragmented vertical and horizontal governance structure, unequal class relations in which smallholder farmers and peri-urban residents are marginalised, and lack of accountability and representation. This combination of multi-scalar factors and power imbalances has contributed to evolving injustices of peri-urbanisation, all of which are profoundly geographical in their significance.