the formation of carbonate cements in the forth and balmoral fields northern north sea a case for biodegradation carbonate cementation and oil leakage during early burial

giant irregular pockmark craters in the palaeogene of the outer moray firth basin uk north sea a cluster of irregular pockmark craters of palaeogene age in block 15 18 in the outer moray firth uk north sea have been mapped on 3d seismic data with well control the craters range from 0 5 to 4 km in diameter between 50 and 200 m in depth and have been buried by tertiary subsidence and sedimentation to present day depths of between 1000 and 1400 m sub sea they are circular to elliptical in plan view and are located in a delta front and upper pro deltaic slope position on the dornoch delta the structures are confined to the top of the lower eocene balder formation and regional mapping across the moray firth basin shows they are restricted to an area of ca 15 15 km2 well data show that the craters are sand filled and have excavated an argillaceous and tuffaceous unit the crater filling sands are sealed by overlying mudstone units planar wing like features emanate from the margins of the craters well control indicates that these seismically identified wings consist of sandstone suggesting that the craters have been modified by an episode of sand remobilisation and injection the proposed mechanism for the formation of these structures is large scale fluid eruption probably shallow gas at the early eocene seafloor these craters are significantly larger in size than those typically observed on contemporary sea floors we argue that the gas is more likely to have been sourced from deeper jurassic or carboniferous sediments within the witch ground graben than from shallow biogenic origins these structures rank in scale alongside the largest known pockmarks and demonstrate that natural fluid and hydrocarbon seeps have a long ancestry in this basin

clastic intrusions in deep sea fan deposits of the rosroe formation lower ordovician western ireland abstract the rosroe formation contains discordant elastic intrusions and essentially stratiform clastic intrusions up to 40 cm thick that display little evidence of injection features of the elastic intrusions such as upper surface irregularities and tapered lateral margins also occur in wedged clastic layers up to 30 cm thick in the rosroe formation and suggest they may be injected sheets a few of the mostly granule grade injected sheets in the rosroe formation contain banding that is remarkably similar to the banding in the formation s stratified pebbly sandstone together with the existence of essentially stratiform injected sheets the banding suggests that some elastic sills in deep sea fan deposits may be indistinguishable from normally deposited beds contactual features sharp upper contacts upper surface irregularities truncation of superjacent strata upper surface inclusions nesting and blunt steep and tapered lateral margins and internal characters lenticular breccia and trains of aligned laminite clasts of the elastic intrusions in the rosroe formation provide tentative criteria for the identification of clastic sills that simulate normally dep sited beds in deep sea fan deposits

regional sand injectite architecture as a record of pore pressure evolution and sand redistribution in the shallow crust insights from the panoche giant injection complex california abstract observations on outcrop of a regionally developed sand injectite are used to infer and estimate the pore pressure conditions in the shallow crust that caused the fluidization and injection of tens of cubic kilometres of sand the estimated pore fluid pressures at the base of the injection complex at 1500 m burial depth below a regionally developed shale dominated seal are from 22 26 to 25 08 mpa which respectively correspond to 0 81 and 0 95 lithostatic pressure a theoretical basis for prediction of sand injection is defined and applied to the prediction of pore pressure at the time of sand injection the depth at which seal failure occurred and the density and granular content of the fluidized flow lateral variations in the style and abundance of sandstone intrusions are described and these all fit into a remarkably uniform tripartite division of parent units an intrusive complex and an extrusive complex a sill zone intrusions are dominated by sills occurs in a restricted stratigraphic interval 200 270 m thick location of the base of the sill zone is directly related to the thickness of the overburden and an isobaric surface at the time of sand injection the lithostatic equilibrium surface is defined at the base of the sill zone when the sills formed an extended period of supra lithostatic pressure occurred within the sill zone

the transformation of sediment into rock insights from iodp site u1352 canterbury basin new zealand abstract at integrated ocean drilling program iodp expedition 317 site u1352 east of the south island new zealand we continuously cored a 1927 m thick holocene to eocene section where we can uniquely document downhole changes in induration and lithification in siliciclastic to calcareous fine grained sediment using a wide range of petrological physical property and geochemical data sets porosity decreases from around 50 at the surface to 5 10 at the base of the deepest hole with a corresponding increase in density from 2 to 2 5 g cm 3 there are progressive bulk mineral changes with depth including an increase in carbonate and decrease in quartz and clay content grain compaction is first seen in thin section at 347 m below sea floor and intensifies downhole pressure solution chemical compaction begins at 380 m and is common below 1440 m with stylolite development below 1600 m and sediment injection features below 1680 m porewater geochemistry and petrographic observations document two active zones of cementation one shallow eogenetic down to 50 m as evidenced by micritic nodules and pore water geochemistry driven by methane oxidation by sulfate and another burial related cementation zone mesogenetic starting at 300 m a transitional zone occurs between 50 and 300 m our results quantify downhole diagenetic changes and verify depth estimates for these processes inferred from outcrop studies and provide an actualistic example of cementation and compaction trends in a slope setting

the geometry and emplacement of conical sandstone intrusions conical sandstone intrusions with a geometry comparable with that of many igneous sills have been identified using 3d seismic data from large areas of the north sea and faeroe shetland basins these intrusions are of reservoir scale ranging from 100 to 2000 m or so in diameter 50 300 m in height and 1 80 m in thickness aperture they are concentrated in specific stratigraphic intervals in the cenozoic fills of both basins two geometrical end members are recognised and defined here apical cones and flat based bowls the former consist of inward dipping conical inclined sheets meeting at a prominent apex and the latter of similarly dipping discordant margins climbing from the edges of a concordant sheet both end members are associated with domal folds that are interpreted as resulting from the hydraulic elevation of the overburden during intrusion and which are analogous to similar structures associated with bowl shaped igneous sills measurements of aperture versus distance exhibit systematic relationships with the structural relief of these folds offering a potentially predictive method for estimation of sandstone intrusion aperture and reservoir volume prior to drilling a growth model for these end member geometries is presented drawing on existing theory for igneous sill emplacement aperture versus distance plots x are used to illustrate two contrasting models for aperture inflation during propagation but these require much further data before any specific growth model can be adopted

physical modelling of sand injectites abstract sand injectites are structures that result from intrusion of fluidized sand into fractures we have studied them in the tampen spur area of the north sea and have reproduced them experimentally by driving compressed air through layers of sand glass microspheres and silica powder the silica powder was cohesive and capable of hydraulic fracturing whereas the sand and glass microspheres were almost non cohesive and therefore able to fluidize the models were dynamically similar to their natural counterparts for as long as equilibrium was static when the processes became dynamic so that inertial forces were significant the scaling was approximate and the corresponding reynolds numbers differed the experimental apparatus was a square box 1 m 1 m wide resting on a grid of fluid diffusers during the experiments the fluid pressure increased until it attained and surpassed the weight of overburden flat lying hydraulic fractures containing air formed within cohesive and least permeable layers heterogeneities in material properties and layer thicknesses were responsible for localizing fracture networks when any one network broke through to the surface rapid flow of air through the fractures fluidized the underlying mobile materials and even depleted some of the layers some of the fluidized material extruded at the surface through vents forming volcanoes and sheets the remainder lodged at depth forming sand injectites or laccoliths conical sand injectites formed preferentially where layers had high resistance to bending laccoliths formed nearer the surface where overlying layers had low resistance to bending the experimental sand injectites were broadly similar to those in the tampen spur area of the north sea as well as other areas

complex reservoir geometries in a deep water clastic sequence gryphon field ukcs injection structures geological modelling and reservoir simulation abstract the balder formation sandstone reservoir of the gryphon field was deposited during the late paleocene early eocene while the background sedimentation comprised pelagic shales and tuffs sediment gravity flows transported sands from the shelf area in the west the crawford ridge acted as a barrier to sediment transport in the east causing the sands to be deposited predominantly as massive sand bodies as flow velocities decreased during burial sand remobilisation and injection occurred possibly localised around faults cored intervals show a range of injection structures from thin cm scale dykes to more massive metre scale chaotic intrusive features the cross cutting nature of the injection structures as observed in core and in seismic sections accounts for the high degree of reservoir connectivity observed in the field a study was undertaken with the objective of constructing a 3d geological model for dynamic reservoir simulation in order to evaluate future development activities in the field as previous purely deterministic models had proven unsuitable the complex depositional and post depositional history of the gryphon field reservoir has resulted in a system for which there is no published analogue to aid in 3d reservoir modelling preliminary stochastic models based on analogues chosen to reflect the reservoir sand body geometries did not match the field production history the fact that both the deterministic and fully stochastic models were unsuitable suggested that a novel approach was required to model this field subsequent models constructed using a combination of stochastic and deterministic models have proven successful in matching the production history of the field and evaluating infill opportunities

large scale liquefaction and fluidization in the cap chat melange quebec appalachians the cap chat melange crops out discontinuously for 200 km along the south shore of the st lawrence river in the gaspe peninsula it is located just south of logan s line the northern limit of the humber zone with the taconian foreland basin this melange is composed of dismembered rocks of the adjacent formations in particular the lower ordovician riviere ouelle and middle ordovician tourelle formations with lesser contributions by the middle ordovician des landes and the cambrian orignal formations blocks in the melange vary in size from a few centimetres to several kilometres with well preserved internal stratigraphy in the larger blocks the distribution of blocks is not uniform and the composition of the surrounding matrix changes with corresponding changes in block composition tectonic processes mostly extensional and compressional faulting are responsible for some of the chaotic aspects of the melange however the main mechanism was as follows i large scale liquefaction of the mudstone rich riviere ouelle formation ii sinking with consequent dismembering of the tourelle formation into this underlying weakened riviere ouelle formation and iii fluidization of the lowermost sand beds of the tourelle formation resulting in abundant sandstone sills and dikes in the riviere ouelle formation

mechanism of instantaneous coal outbursts thousands of mine workers die every year from mining accidents and instantaneous coal outbursts in underground coal mines are one of the major killers various models for these outbursts have been proposed but the precise mechanism is still unknown we hypothesize that the mechanism of coal outbursts is similar to magma fragmentation during explosive volcanic eruptions i e it is caused by high gas pressure inside coal but low ambient pressure on it breaking coal into pieces and releasing the high pressure gas in a shock wave hence coal outbursts may be regarded as another type of gas driven eruption in addition to explosive volcanic lake and possible ocean eruptions we verify the hypothesis by experiments using a shock tube apparatus knowing the mechanism of coal outbursts is the first step in developing prediction and mitigation measures the new concept of gas driven solid eruption is also important to a better understanding of salt gas outbursts rock gas outbursts and mud volcano eruptions

fluid flow features in hydrocarbon plumbing systems what do they tell us about the basin evolution abstract fluid flow features such as sandstone intrusions mud volcano systems and pockmarks represent well known geological structures generated due to flow of fluids in the subsurface however the integration of fluid flow features in quantitative and qualitative basin analysis is still in its infancy this study presents a review and a qualitative integration of fluid flow features in basin analysis of the danish north sea area and of salt mini basins offshore angola based on results from six case studies focusing on the detection mapping and evaluation of features related to focused fluid flow in these areas in the study the diversity of seismically imaged fluid flow features in hydrocarbon plumbing systems is reviewed and their utility is demonstrated this is done by focusing on the aspects of fluid flow related features that can be integrated into basin analysis studies and how these may help us increase the understanding of basin evolution and to achieve the major goals of basin analysis such as understanding the depositional and tectonic context of the basin and the presence and extent of hydrocarbons particularly concerning the determination of fluid flow timing triggers sources and routes fluid flow features represent a major but underused tool in basin analysis

the process of sand injection internal structures and relationships with host strata yellowbank creek injectite complex california u s a abstract the yellowbank creek injectite complex ycic has excellent exposure of the external geometries and internal structures in a large scale sandstone injectite the ycic has an irregular geometry that can be defined neither as a sandstone dike nor as a sill substantial erosion occurred along the margins between the ycic sandstone and host mudstones that includes scoured basal margins and a scalloped upper margin that cuts up to 5 m into the overlying host mudstones erosion of host mudstone has incorporated significant volumes of mudstone clasts into sandstones at the margins of the injectite using microtextural data corrasion is identified as a typical process by which mudstone is eroded during sand injection corrasion occurs when particles of mudstone are either cut or broken from a cohesive bed as the result of high velocity turbulent flow of sand grains acting as tools corrasion together with scouring and the general erosion of the host mudstone imply high velocity turbulent flow conditions and confirm that the fluidized sand had a sufficiently low viscosity during sand injection to allow turbulence internal structures include laminae of more tightly packed sand grains than occur in the surrounding sandstones and are interpreted to have formed by flow and deposition of injecting sands during waning of flow thus reflecting an overall reduction of pore fluid pressure deformation of laminae into folds defines bands which are aligned parallel to the margins of the sandstone the force driving deformation is likely to have been shear stresses induced between the injected sandstone and the more rigid host mudstone the principal style of deformation is hydroplastic oversteepened laminae and pipes are interpreted to have formed due to post sand injection consolidation and resulted in only minor mobilization of sand