Insight into the Sealing Capacity of Mudrocks determined using a Digital Rock Physics Workflow

Primary objective: To better understand seal capacity in mudrocks and to determine the conditions under which a mudrock seal fails by allowing a non-wetting fluid to percolate. Hypothesis: Mudrock seals can fail below the fracture pressure if there exists a percolating pathway formed due to a continuous and sufficiently large pore-throat system. Procedure: We used SEM images of uncemented muds obtained at various depths (< 1.1 km burial) in the Kumano Basin offshore Japan for the study. Image mosaics were filtered and segmented using conventional and machine-learning techniques to identify the pore space, silt, and clay grains. We applied a 3D stochastic technique for pore space reconstruction from the SEM images and simulated capillary drainage in the resulting 3D volumes by the lattice Boltzmann method (LBM) using Stampede 2. Conclusion: Results showed that porosity and permeability decreased with depth, and capillary threshold pressure values increased. However, increasing silt content at a particular depth counteracted this behavior, due to better preservation of larger pores and throats.Texas Advanced Computing Center (TACC

Sandstone Consolidation III Year End Report

Two areas of cap rock occurrence have been mapped, one in the upper Texas Coast and the other in South Texas. These may be related to ancient delta systems. Two high-resistivity zones have been identified in Brazoria County. The nature of the high-resistivity intervals remains enigmatic. Most of the carbonate they contain is microscopically and isotopically skeletal in origin. Few authigenic components have been identified. Isotopic data suggest minimal recycling of pore waters between shale and sandstone. Hydrolysis reactions and reactions between key pairs of minerals have been written. The goal is to plot formation waters on stability diagrams for these reaction pairs and to correlate log activity ratios with the presence or absence of cap rock and deep secondary porosity. Mineral compositions are based on microprobe data from earlier Sandstone Consolidation projects and new data collected in this project. Methods have been developed to estimate thermodynamic functions for most of these minerals at elevated temperatures. Methods differ depending on the mineral class and availability of published thermodynamic data.Bureau of Economic Geolog

Late Miocene wood recovered in Bengal–Nicobar submarine fan sediments by IODP Expedition 362

Drilling and coring during IODP Expedition 362 in the eastern Indian Ocean encountered probably the largest wood fragment ever recovered in scientific ocean drilling. The wood is Late Miocene in age and buried beneath ∼800 m of siliciclastic mud and sand of the Bengal–Nicobar Fan. The wood is well preserved. Possible origins include the hinterland to the north, with sediment transported as part of the submarine fan sedimentary processes, or the Sunda subduction zone to the east, potentially as a megathrust tsunami deposit

Release of mineral-bound water prior to subduction tied to shallow seismogenic slip off Sumatra

Plate-boundary fault rupture during the 2004 Sumatra-Andaman subduction earthquake extended closer to the trench than expected, increasing earthquake and tsunami size. International Ocean Discovery Program Expedition 362 sampled incoming sediments offshore northern Sumatra, revealing recent release of fresh water within the deep sediments. Thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial-induced temperature increases in the past 9 million years. Complete dehydration of silicates is expected before plate subduction, contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction. Shallow slip offshore Sumatra appears driven by diagenetic strengthening of deeply buried fault-forming sediments, contrasting with weakening proposed for the shallow Tohoku-Oki 2011 rupture, but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records

Systematic destruction of K-Feldspar in deeply buried rift and passive margin sandstones

Systematic patterns of detrital K-feldspar decline with increasing burial depth are revealed during deep burial (2.5-4.5km) of sandstones in diverse sedimentary basins from three rift and two passive margin setings in the North Sea and USA gulf coast. K-Feldspar destruction is predominantly by dissolution, though in-situ alteration to albite also occurs. Dissolution can remove up to 15% solid volume of the rock by 4.5km, so that primary arkosic snadstones become diagenetic quartzarenites at depth, with increased secondary:primary porosity ratios. Deeply buried sandstones are not reliable records of depositional composition

Quartz types, authigenic and detrital, in the Upper Cretaceous Eagle Ford Formation, South Texas, USA

Lithologic heterogeneity of the Eagle Ford Formation in South Texas arises from mixing of extrabasinal grains of siliciclastic composition with intrabasinal grain assemblages composed dominantly of marine carbonate with a lesser component of biosiliceous debris. Detrital quartz in particular is derived from both extrabasinal and intrabasinal sources, posing a challenge for the use of bulk compositional data for mudrock classification. Extrabasinal detrital quartz supplied along a major axis of siliciclastic influx, the Woodbine depositional system of East Texas, is reduced to a minor part of the grain assemblage in South Texas. Petrographic evidence and point count results indicate that around 85 percent of total quartz in these rocks, equal to about 12.6 volume percent, is authigenic. Thus, significant quantities of authigenic silica are not restricted to siliceous mudrocks, but can be found in carbonate-rich mudrocks as well. Formerly opaline skeletons of radiolaria, the dominant source of silica for authigenic quartz precipitation, are only poorly preserved by replacements including calcite, dolomite, pyrite, and quartz. Dissolved silica released by dissolution of radiolarians, and perhaps also by volcanic glass dissolution is re-precipitated in a variety of forms, including matrix-dispersed microquartz cement, fillings within primary intragranular pores, and grain replacement of both calcareous and siliceous allochems. The mass balance of dissolved silica mobilized from radiolarians and other reactive silicates and the precipitation of authigenic quartz is uncertain because the initial volumes of now-dissolved detrital material versus the final volume of authigenic material (quartz and other authigenic silicates) cannot be determined with accuracy

THE NICOBAR SUBMARINE FAN AND RELATIONSHIP WITH THEBENGAL FAN: PRELIMINARY RESULTS FROM IODP EXPEDITION 362,INDIAN OCEAN

International audienceThe Bengal-Nicobar Fan has been long-studied to investigate possible links between Himalayantectonics and the Asian monsoons. Despite the many DSDP, ODP, and IODP expeditions in the region, theNicobar Fan is largely undersampled, even though it contains key information on the tectonostratigraphicevolution of the eastern Indian Ocean. In contrast to the Bengal Fan that records Holocene sedimentgravityflows (SGF), the Nicobar Fan, lying east of the Ninetyeast Ridge, is inactive because subduction of theridge starting in the Late Pleistocene blocked the sediment supply from the north. IODP Expedition 362(AugustOctober 2016) drilled two boreholes within the sedimentary cover of the Indian Ocean Plate offshorefrom the north Sumatra subduction zone to investigate the role of input materials in the seismogenesis ofmegaearthquakes. Here, the 1-to-5 km-thick sedimentary succession comprises a basal pelagic layer overlainby sediments of the Nicobar submarine fan. Drill sites are located at 3°N 91°E, ~ 250 km southwest of thesubduction zone, on the eastern flank of the Ninetyeast Ridge where the input section is ~1.5 km thick. SitesU1480 and U1481 were drilled, cored and logged to a maximum depth of 1500 m below seafloor (mbsf), andreached the 60-70 Ma igneous oceanic crust of the Indian plate. The recovered sediments represent a nearlycontinuous Late Cretaceous to Recent deep-marine sedimentary section that consists of silicilastic sedimentsdeposited from various SGFs (including turbidity currents and debris flows), interpreted as Nicobar Fan,underlain by a diversity of abyssal-plain environment sediments containing essentially hemipelagic, pelagic,tuffaceous and igneous lithologies overlying ocean crust. The Nicobar Fan represents > 90% of the inputsection on the drill sites and is characterized by a succession of muddy to sandy SGF deposits, includingabundant plant-fragment-rich debrites, with rare interbeds of calcareous mud. Sediment accumulation ratesreached 100-400 m/Ma in the late Miocene to Pliocene (25-1250 mbsf), but were considerably reduced since~1.6 Ma (5-20 m/Ma). Underlying the Nicobar Fan, an Oligocene-Miocene unit composed of siliciclastic mudand rare sandy SGF deposits (turbidites as deep as ~1500 m in Site U1481) may record the early stages of thefan in the abyssal plain. Sediment accumulation rates are low (2-15 m/Ma) and the amount of siliciclasticmaterial tends to decrease with depth. Below this, the Late Cretaceous to Oligocene pre-fan unit comprises asuite of pelagic sediments (tuffaceous mudstones, chalk, calcareous mudstones) characterized by a slow (1-5m/Ma) and erratic (many hiatuses) sedimentation, interbedded with several magmatic intrusions andextrusions. Expedition 362 demonstrates that the Nicobar Fan was active between ~1.6 and ~9 Ma, andpossibly since ~30 Ma. The observed mineralogical assemblage of the SGF deposits is consistent with aprovenance from Himalayan rivers and the succession is interpreted to represent different stages of fandevelopment from initiation to abandonment. Expedition 362 results will enable direct comparison betweenthe Nicobar Fan and records of sedimentation elsewhere in the Bengal and Indus Fan and provide a holisticview of the Indian Ocean fan system history