Role of compressive tectonics on gas charging into the Ordovician sandstone reservoirs in the Sbaa Basin,Algeria: constrained by fluid inclusions and mineralogical data

Structure‐ and tectonic‐related gas migration into Ordovician sandstone reservoirs and its impact on diagenesis history were reconstructed in two gas fields in the Sbaa Basin, in SW Algeria. This was accomplished by petrographical observations, fluid inclusion microthermometry and stable isotope geochemistry on quartz, dickite and carbonate cements and veins. Two successive phases of quartz cementation (CQ1 and CQ2) occurred in the reservoirs. Two phase aqueous inclusions show an increase in temperatures and salinities from the first CQ1 diagenetic phase toward CQ2 in both fields. Microthermometric data on gas inclusions in quartz veins reveal the presence of an average of 92 ± 5 mole% of CH₄ considering a CH₄‐CO₂ system, which is similar to the present‐day gas composition in the reservoirs. The presence of primary methane inclusions in early quartz overgrowths and in quartz and calcite veins suggests that hydrocarbon migration into the reservoir occurred synchronically with early quartz cementation in the sandstones located near the contact with the Silurian gas source rock at 100–140°C during the Late Carboniferous period and the late Hercynian episode fracturing at temperatures between 117 and 185°C, which increased in the NW‐direction of the basin. During the fracture filling, three main types of fluids were identified with different salinities and formation temperatures. A supplementary phase of higher fluid temperature (up to 226°C) recorded in late quartz, and calcite veins is related to a Jurassic thermal event. The occurrence of dickite cements close to the Silurian base near the main fault areas in both fields is mainly correlated with the sandstones where the early gas was charged. It implies that dickite precipitation is related to acidic influx. Late carbonate cements and veins (calcite – siderite – ankerite and strontianite) occurred at the same depths resulting from the same groundwater precipitation. The absence of methane inclusions in calcite cements result from methane flushing by saline waters.     

Social Norm Change,Behavioural Approaches and the Politics of Knowledge: A Conversation between the Ivory Tower and the Field

The social norms approach (SNA), the new entrant from the behavioural sciences into the field of development practice, professes a scientific, more accurate, efficient and cost-effective methodology for identifying, measuring and changing harmful social norms. Despite its increasing popularity, no systematic, robust or long-term field evaluations are available to demonstrate the effectiveness and sustainability of using the SNA, nor its superiority over other, pre-existing methods. This article critiques the SNA from the perspective of development praxis, highlighting three concerns: the underlying cultural presumptions about development and its subjects; the problematic methodological design and its complexity; and the lack of contextual framing in the approach and its focus on individual behaviour to the exclusion of the structural constraints embedded in the social and economic environment. The recent drift to broaden the SNA framework is also discussed and assessed. To illustrate a contrasting approach, a case study is presented of MV Foundation, a civil society organization that works on changing social norms on issues of education and child labour. The article concludes that the SNA is arguably yet another instance of colonization of the field of development through hegemonic control of the creation of knowledge.