Abnormally high formation pressures are encountered worldwide, ranging in geological age from Cenozoic to Paleozoic, within a depth range of few hundred meters to as deep as six thousand meters while carrying out exploratory drilling by E and P companies. Several causes can increase formation fluid pressure i.e. rapid loading of sediments results compaction disequilibrium, thermal expansion of fluids, compression and/or upliftment of strata by tectonic forces, generation of oil and gas from organic matter and its volume expansion due to high thermal stress within the restricted pore volume in subsurface condition. Few global examples on overpressure occurrences have been compiled in the paper with special reference to Bengal Basin. Emphasis has been given on methodology and interpretation on abnormal pressure detection in Bengal Basin with a compiled data package on generated curves (Geologs), charts, tables in a systematic way to understand the depth/stratigraphic horizons proved/interpreted as proved or likely to be within transition and overpressure regime. The integrated analysis indicates that the wells drilled in the east of Eocene hinge zone in the onshore and offshore parts of Bengal Basin have penetrated overpressure formation within Miocene in the depth range of 2800 m to 5340 m and the mud weight used to control this overpressure zone was more than 2.0 sp gr mud. The generated Geologs can be used as reference to understand the regime of transition and overpressure, as a valuable document for exploration drilling planning and monitoring. The generated model curve (modified using available data after Hottman and Johnson,1956 curve) using sonic departure (i.e. 't ob(sh) -'t n(sh) ) from drilled wells may be used as an additional tool to find out the expected formation pressure gradient and equivalent mud weight in all future wells. The correlation of wells based on the trend of dcs and V logs will be useful for predicting transition and overpressure top provided all the parameters required for calculating dcs and V log recorded smoothly during drilling phase. The study has brought out the detail procedure to generate the pressure profile in the future wells. The generation of pressure profile of a well prior to drilling has got immense importance in oil industry. The drilling of the well should be done by maintaining the optimum mud weight generated from the pressure profile. In case, during drilling, formation pressure is more than the mud pressure, resulted gas kicks or worse, blowouts of the well. Excessively high mud pressure can fracture the formation and cause lost circulation. The oil and gas companies, worldwide, attributed 15% losses due to various problems associated with drilling complications, mostly related to improper pressure prediction of a well. The losses include loss of material as well as drilling process continuity, called non-productive time (NPT). The generation of accurate pressure profile reduces drilling problems, cuts exploration and development costs and allows billions of doll...

Abstract. The Lesser Himalaya exposed in the Kishtwar Window (KW) of the Kashmir Himalaya exhibits rapid rock uplift and exhumation (∼3 mm yr−1) at least since the late Miocene. However, it has remained unclear if it is still actively deforming. Here, we combine new field, morphometric and structural analyses with dating of geomorphic markers to discuss the spatial pattern of deformation across the window. We found two steep stream segments, one at the core and the other along the western margin of the KW, which strongly suggest ongoing differential uplift and may possibly be linked to either crustal ramps on the Main Himalayan Thrust (MHT) or active surface-breaking faults. High bedrock incision rates (>3 mm yr−1) on Holocene–Pleistocene timescales are deduced from dated strath terraces along the deeply incised Chenab River valley. In contrast, farther downstream on the hanging wall of the MCT, fluvial bedrock incision rates are lower (<0.8 mm yr−1) and are in the range of long-term exhumation rates. Bedrock incision rates largely correlate with previously published thermochronologic data. In summary, our study highlights a structural and tectonic control on landscape evolution over millennial timescales in the Himalaya.

No abstract

Abstract. The Kishtwar Window (KW) of the NW Himalaya exposes the northwestern termination of the orogen-parallel anticlinal stack of thrust nappes, termed as the Lesser Himalayan Duplex and its evolution portrays rapid exhumation at least over the last 2–3 Myr. However, speculations remain if it still actively deforming. Here we combine morphometric analyses with structural and field evidences to describe the spatial pattern of internal deformation of the duplex. We suggest that the variations in the geometry of the basal décollement, the Main Himalayan Thrust (MHT) and internal faulting within the duplex define the observed neotectonic deformation. We recognize two significant steep stream segments/ knickzones, one in center of the window, and a second one along its western margin, which we relate to fault-ramps emerging from the MHT. The larger of the knickzones, in the core of the window, show an increase in the angle of foliations towards downstream. Highly-fractured and folded rocks at the base of the steep stream segment, suggest internal deformation of the duplex, possibly linked to surface-breaking thrust fault-ramp at the core of the duplex. The second steepened knickzone coincides with the western margin of the window and is identified by a narrow channel through a comparatively weaker bedrock gorge. Summarizing our findings, we favor a structural and active tectonic control on the growth of the duplex even over geomorphic timescales. Corroborating with previous studies, we suggest that the differential uplift and growth of the duplex is linked to several flat-ramp structures along the MHT.