petroleum geology of the cusiana field llanos basin foothills colombia cusiana field is located in the llanos foothills 150 mi 240 km northeast of bogota colombia light oil gas and condensate in cusiana occur at drilling depths that average 15 000 ft 4575 m in an asymmetric hanging wall anticlinal trap 15 mi 25 km long and 3 4 mi 5 6 km across formed during the miocene holocene deformation of the eastern cordillera top and lateral seals are provided by marine mudstones of the oligocene carbonera group and support a hydrocarbon column of over 1500 ft 460 m biomarker data from the hydrocarbons indicate a marine mudstone source interpreted to be the turonian coniacian gacheta formation over 50 of the reserves occur in upper eocene mirador formation sandstones which were deposited predominantly in estuarine environments additional deeper reservoirs include estuarine sandstones of the paleocene barco formation and the shallow marine santonian campanian upper guadalupe sandstone porosity in cusiana is relatively low good permeability is retained however because the reservoirs are pure quartz cemented quartzarenites that lack permeability reducing authigenic clays and carbonate cements core and well test analyses indicate matrix permeability not fracture permeability provides the high deliverability of cusiana wells cusiana hydrocarbon phases exist in a near miscible critical point state reservoir simulation indicates very high liquid hydrocarbon recoveries should be possible from all reservoirs by using the reinjection of produced gas to maintain reservoir pressure and to vaporize residual liquids the field contains up to 1 5 mstb footnote of hydrocarbon liquid reserves and 3 4 tcf footnote of gas

evaluating the mechanical compaction of quartzarenites the importance of sorting llanos foreland basin colombia abstract mechanical compaction is the main porosity reducing process in sandstones including high reservoir quality rigid grain sandstones for such sandstones the extrapolation of theoretical or experimental compaction algorithms needs calibration with rocks having well constrained burial histories evaluating the compaction of these rocks is achieved by comparing current intergranular volume igv with depositional igv which is strongly dependent on sorting however because sandstone sorting is difficult to measure accurately its impact on depositional porosity and compaction state is largely underestimated we use the quartzarenites of the oligocene carbonera formation in the subsurface of the hydrostatically pressured llanos basin to illustrate the importance of sorting when evaluating the compaction of rigid grain sandstones igv and sorting were measured in core samples using a combination of transmitted light and cathodoluminescence images resulting in improved accuracy over standard procedures the compaction state of clean quartzarenites at given depths is best described using igv versus sorting plots which are used to derive compaction curves for specified sorting values the igv versus sorting trends are displaced to lower igv values with increasing burial depth the differences in igv caused by differences in sorting exceed the differences in igv resulting from 1000 m of burial illustrating the high impact of sorting when evaluating compaction contrasting with published experimental results the compaction of the llanos basin ductile grain poor quartzarenites is independent of grain size and grain rearrangement is the main compaction mechanism during the first 1 6 km of burial based on the llanos data we have generated igv versus depth curves for clean pure quartzarenites of specific sorting which can be used to predict their maximum primary porosity up to moderate burial depths differences with other published burial curves are probably related to unaccounted variations in sorting ductile grain content and framework strengthening cements however the llanos basin quartzarenites contain virtually no cements explaining their high degree of compaction relative to other rigid grain sandstones and making them ideal to isolate the effects of compaction on the igv of quartzarenites the llanos basin data suggest that below 2 5 km of depth clean well to moderately well sorted quartzarenites continue reducing their igv by mechanical compaction below the 26 limit which should apply only to extremely well sorted rigid grain uncemented sandstones

physical simulation of ground fissures triggered by underground fault activity abstract numerical modeling and physical simulation experiment are two important steps to investigate the stress and strain fields of overlying strata but sometimes it is very difficult to do the test of the physical experiment on a large scale soil sample due to the financial consideration and the available test site to investigate the features of the ground fissures prevailing in xi an city we undertook in this study a series of physical simulation tests on the large scale soil sample to analyze the stress and displacement fields caused by the underlying normal fault activity comparing with the fracturing modes of the ground fissures and the failure patterns of construction building it is evident that the experiment results coincide with the failure patterns of the building but not with the fracturing modes of the ground fissures which indicate that the ground fissures in xi an may be an old fracture surface having already spread to superficial layer covered by a very thin layer of loose soils and the groundwater over pumping is just a factor to make them exposed on the ground surface

amorphous silica nanofilms result in growth of misoriented microcrystalline quartz cement maintaining porosity in deeply buried sandstones deeply buried sandstones in sedimentary basins typically have low porosity due to cementation and compaction there are several known causes of anomalously high porosity in sandstones one of which is microquartz coatings on sand grains that seem to inhibit growth of quartz cement however there has been no mechanistic understanding of why or how microquartz grows or why it maintains high porosity in sandstones here we have used high resolution scanning electron microscopy electron backscattered diffraction and transmission electron microscopy to study the microquartz cemented late cretaceous heidelberg formation germany we have revealed that a nanofilm of amorphous silica 50 100 nm and a layer of chalcedony are between the detrital grain and microquartz cement the amorphous silica insulates the detrital quartz grains and prevents syntaxial growth while microquartz adopts the orientation of the underlying chalcedony with its fast growth c axis parallel to the grain surface thus preventing growth into the pore now that we know what controls microquartz growth and why it preserves porosity it can be used to help identify rank and appraise deeply buried petroleum accumulations

role of pore structure in the percolation and storage capacities of deeply buried sandstone reservoirs a case study of the junggar basin china abstract deeply buried sandstone reservoirs are characterized by their wide pore throat distributions and varied storage and percolation capacities an integrated analysis comprising casting thin section scanning electron microscopy x ray computed tomography micro ct high pressure mercury intrusion hpmi and constant rate mercury intrusion crmi is performed on thirteen samples from the jurassic sangonghe formation in the junggar basin to investigate the pore structures and their influence on the storage and percolation capacities hpmi crmi and micro ct are combined to determine the full range pore size distributions fpsds which have multimodal distributions between 2 77 nm and 500 m with three broad peaks the right peak ranging from 100 to 500 m is associated with residual and dissolution intergranular pores the middle peak is mainly composed of dissolution intergranular and intragranular pores with radii between 10 and 100 m the left peak exhibited fluctuations and is characterized by dissolution intragranular and intercrystalline pores with radii of 37 nm 10 m according to the pore types sizes and proportions in the fpsd the pores are classified as intercrystalline nanopores 100 m a storage capacity evaluation combining the classifications and fpsd indicates that the macropores and nanopores primarily contribute to porosity albeit with contrasting influences on the storage capacity the contents of macropores determine the storage capacity of a deeply buried sandstone reservoir while the negative effects of nanopores become predominant with decreasing porosity a percolation capacity evaluation on the basis of crmi results suggests that the permeability contribution is dominated by nanopores in tight sandstone controlled by micro small pores in low permeability sandstone and dominated by mesopores in conventional sandstone mesopores always play a favorable role in percolation however the negative impacts of nanopores should be considered in low permeability and tight sandstone micro small pores have a negative influence on the permeability of conventional sandstone but are favorable for the fluid percolation of most low permeability and tight sandstone reservoirs a new empirical equation indicates that r10 of the fpsd is the suitable as the proper pore throat radius for the permeability estimation of deeply buried sandstone reservoirs

anomalous porosity and permeability preservation in deeply buried tertiary and mesozoic sandstones in the cusiana field llanos foothills colombia reply abstract porosity in deeply buried 14000 ft 4200 m sandstones of the lower tertiary mirador formation in the cusiana field llanos foothills colombia is less than 10 porosity units p u however permeability is as much as 1000 md which is believed to be due to the simple quartzose detrital grain composition and large grain size the low porosity has resulted from pervasive quartz cement 10 15 fluid inclusion microthermometry and intergranular grain volumes indicate that the quartz cement precipitated at a temperature of around 100 c during deep burial surprisingly thick 400 ft 120 m sandstones of the underlying upper cretaceous guadalupe group in the cusiana field have porosity as high as 20 p u these sandstones are lithic sandstones composed of quartz and a variety of phosphate grain types and are poorly cemented quartz cement is not abundant and occurs as rims of microcrystalline quartz on quartz and phosphate grains in contrast interbedded quartz arenites within the guadalupe group are heavily cemented by quartz cement and have porosity similar to the overlying mirador formation the major control on porosity in these sandstones appears to be the presence of quartz cement the quartz cement is controlled by grain composition the reasons for the lack of quartz cement in the lithic sandstones of the guadalupe group are uncertain but phosphate poisoning inhibiting quartz cement growth is a possibility the presence of high porosity sweet spots in deeply buried sandstones may be linked to the occurrence of phosphate beds a primary depositional control

diagenetic exaggeration of primary textural variations in incised valley fills cusiana field colombia incised valley fills in the late eocene mirador formation of the cusiana field are dominated by quartz arenite sandstones that vary in grain size from fine sandstones to sandy conglomerates the average porosity of the valley sandstones is approx 8 which reflects significant compaction during deep burial approximately 20 000feet and abundant quartz cement approximately 14 precipitated over a wide temperature range 85 140 degrees c surprisingly the present permeability structure of the valley fill sandstones still reflects grain size variations indeed the effect of the large amounts of quartz cement has been to exaggerate the primary textural variation in permeability very coarse well sorted sandstones at the valley bases possess two orders of magnitude higher permeability than fine grained equivalents of the same porosity this permeability contrast is more than original depositional textures in sandstones would predict and is consistent with predictions from simple sphere pack models which show that at low porosity 12 the contrast in permeability due to grain size is greatly enhanced as a result the reservoir characterization has been based on the primary sedimentary fabric not on diagenesis production logging results show that the coarse grained bases of the valley fills are indeed the major contributors to flow thus the impact of diagenesismore on the flow structure of these valley fills has been to selectively reduce the permeability of finer grained sandstones while maintaining high permeability in the coarsest grained bases of the valley fills less

characteristics of two phreatoplinian ashes and their water flushed origin abstract the whole deposit grain size populations have been determined for two phreatoplinian ashes of the rhyolitic taupo volcano new zealand one is much finer than plinian pumice deposits studied from the same volcano and the other differs in having a lower content of coarse pumice the poor sorting of the two ashes is attributed mainly to water scavenging of the ash cloud the very limited fractionation with distance from source combined with the very regular exponential thickness decrease indicates that the scavenging water was an integral part of the ash cloud and was derived from lake taupo at times when the proportion of erupted water to magma became particularly high erosion of the underlying deposits took place and to this is attributed the striking gullying of the surface which separates the two ashes

experimental investigation of reverse fault rupture propagation through wet granular soil abstract surface fault rupture has been previously investigated in dry cohesionless soil however wet granular soil has not been investigated in detail however apparent cohesion induced by intergranular water causes granular soil to behave differently than dry cohesionless soil field evidence shows that all soil that has been wetted will experience some degree of cohesion in the present study eight experimental faulting tests were conducted on sand in which the water content varied from 0 dry to 15 and the soil layer height ranged from 25 to 35 cm to determine the behavior of the wet sand a series of direct shear tests were carried out at low confining stress corresponds to stresses at different depth of the physical model the results showed that the shear band zone decreased in the wet specimens creating a sharp scarp at the surface the required normalized fault displacement for outcropping decreased significantly in these specimens and reached a minimum value at about a 5 water content the direct shear test results showed that the failure strain of the wet sand can be used for prediction of h0 h surface tension cracks at the hanging wall widened in the zone of distortion at the surface in the wet specimens other aspects of fault rupture also are discussed

petroleum emplacement inhibits quartz cementation and feldspar dissolution in a deeply buried sandstone abstract whether the emplacement of petroleum in sandstone reservoirs can preserve porosity during burial remains controversial in the kessog field uk central north sea average porosities of the crestal sections of the fluvial deltaic pentland formation reservoir can exceed 25 despite burial to 4 km or more the predicted porosity for the reservoir at this depth is only around 14 based on regional data oil saturation data thin section point counts grain size and sorting measurements reservoir pressure and sem images were combined to analyze the cause of the high reservoir porosity petroleum emplacement preventing cementation is the most likely mechanism for porosity preservation facies variation is not responsible as the high porosity sandstones from the crestal well are in terms of average grain size fine grained and sorting coefficient moderately well sorted nearly the same as the lower porosity sandstones from the flanks of the field average porosity 13 15 other potential porosity preservation mechanisms such as overpressure grain coats and feldspar dissolution can be discounted the sandstones with high oil saturations are characterized by 1 most porosity being primary as opposed to secondary 2 there being 2 5 less quartz cement than in the water saturated sandstones 3 there being 2 3 more k feldspar and 2 6 less kaolin than the water saturated counterparts this study demonstrates that petroleum emplacement can effectively inhibit quartz cementation and k feldspar transformation to kaolin in sandstone reservoirs

an integrated analysis of an orogen sedimentary basin pair latest cretaceous cenozoic evolution of the linked eastern cordillera orogen and the llanos foreland basin of colombia the integration of restored basin geometry and internal features of syntectonic units e g stratal architecture thickness sandstone composition with fl exural modeling of the lithosphere constrains the evolution of a basin and its fl exural history related to orogenic growth spatial temporal loading confi guration using this approach we determined the maastrichtian cenozoic polyphase growth of the eastern cordillera of colombia an inverted mesozoic extensional basin the record of this growth occurs in an andean post middle miocene thrust belt the eastern cordillera and in adjacent foreland basins such as the llanos basin to the east this approach permitted the identifi cation of fitectono stratigraphic sequences in the foreland basin and fi ve phases of shortening for the eastern cordillera thermochronological and geochronological data support the spatial and temporal evolution of the orogen foreland basin pair tectono stratigraphic sequences were identifi ed in two restored cross sections one located at a salient and the other in a recess on the eastern fl ank of the eastern cordillera the lower two sequences correspond to late maastrichtian paleocene fl exural events and record the eastward migration of both tectonic loading and depositional zero in the llanos basin these sequences consist of amalgamated quartzarenites that abruptly grade upward to organic rich fi ne grained beds and to the top light colored mudstones interbedded with litharenites in isolated channels amalgamated conglomeratic quartzose sandstones of the third sequence record 15 m y of slow subsidence in the llanos basin and llanos foothills during early to middle eocene time while shortening was taking place farther west in the magdalena valley the fourth sequence of late eocene middle miocene age records a new episode of eastward migration of tectonic loads and depositional zero in the llanos basin this sequence begins with deposition of thick fi ne grained strata to the west whereas to the east in the llanos basin amalgamated quartzarenites unconformably overlie cretaceous and older rocks former forebulge apatite fi ssion tracks in the axial zone of the eastern cordillera growth strata in the

numerical modeling of trishear fault propagation folding in contrast to kink band migration modeling methods trishear numerical models produce fault propagation folds with smooth profiles and rounded hinges modeled fold hinges tighten and converge downward within a triangular zone of distributed deformation which is focused on the fault tip such features have been reported from field studies and are also seen in analogue models of compressional deformation however apart from its initial application to laramide folds little quantitative work has been undertaken on trishear fault propagation folding in other settings in addition no study has been undertaken into the growth strata which might be associated with such structures this paper uses an equivalent velocity description of the geometric model of trishear together with models of erosion and sedimentation to investigate trishear fault propagation folding of both pregrowth and growth strata the trishear model is generalized to include a variety of fault propagation to slip ratios and fault propagation from a flat decollement the models show continuous rotation of the forelimb with the characteristic development of cumulative wedges within growth strata when total slip on a structure is high the model predicts overturned pregrowth and growth strata during the initial stages of deformation beds in the forelimb thicken but later thin when they become steep or overturned the effect of variations in fault propagation to slip ratios on two dimensional finite strain in the models is assessed by the use of initially circular strain markers high fault propagation to slip p s ratios lead to narrow zones of high finite strain while lower p s ratios lead to more ductile deformation and broader zones of high strain in all cases hanging wall anticlines and footwall synclines originate as early ductile folds which are later cut by the propagating fault modeled structures are compared with natural examples

the deformation of overburden soil induced by thrust faulting and its impact on underground tunnels overburden soil beds situated above a fault are often deformed by propagation of bedrock thrusting from the fault during large earthquake the deformed beds formed a triangular shear zone this coseismic faulting often causes damage to underground tunnels located in the shear zone the present research studies the deformation behavior of the overburden soil beds and the tunnel the associated mechanism and the impact on the safety of tunnel linings induced by a large blind thrust slip based on sandbox experimental and numerical studies it is found that results from numerical analysis are in agreement with the sandbox model tests with regard to growths of the shear zones within the soil beds location of the tunnel in this shear zone and deformations of the tunnel the potential major shear zone may be bent or bifurcated into two sub shear zones owing to existence of a tunnel inside the shear zone furthermore the occurrence of back thrust faulting will threaten the safety of nearby structures it was also identified that stiffness of the soil and the fault dip angles are among the major factors controlling the configuration of shear zones the stresses within the soil and the loads on tunnel linings based on the identified mechanisms the strategies for hazard prevention are accordingly suggested and discussed

rupture behavior of the 1999 chi chi taiwan earthquake slips on a curved fault in response to the regional plate convergence abstract simple kinematic modeling of particle motion along a curved fault similar to the ruptured chelungpu fault taiwan indicates a unique spatial slip pattern specifically we find that the large convergent slip on the curve is a result of the minimum deformation scenario of the fault geometry and regional northwestern movement of the philippine sea plate psp the modeled deformation regime portrays an accumulation of deformation in the curved region which coincides very well with a long term observed nw se trending seismogenic zone in the central taiwan this consistence suggests that the chelungpu fault is a preexisting curved fault this is further evidenced by geological and geophysical observations because the spatial slip pattern is locally and regionally tectonically controlled it indicates that the rupture behavior of the chi chi earthquake is repeatable better knowledge of the fault geometry and the regional plate motion may help us to predict the possible spatial slip distribution of large earthquakes this discovery is important for avoiding large buildings and constructions near predicted large slip regions

campanian miocene tectonostratigraphy depocenter evolution and basin development of colombia and western venezuela abstract the position of the central axis of deposition over colombian and venezuelan continental crust has varied markedly through time the axis migrated from west to east from late cretaceous to oligocene but at times secondary drainage divides were established by local uplift events in oligocene times with initial inversion of the eastern cordillera the central axis of deposition was divided into two main axes the proto magdalena and the proto orinoco systems the west to east migration of the central axis of deposition had a tectonic origin and it occurred in combination with tectonically driven changes in accommodation space depocenter evolution can be divided as follows 1 the axis of the campanian and early maastrichtian depocenter was located few km east of the present position of the central cordillera of colombia it migrated east with gradual uplift of the central cordillera 2 the central axis of late maastrichtian deposition is positioned approximately over the present day western foothills of the eastern cordillera possibly crosses the eastern cordillera over the santander massif and continues into the maracaibo lake in western venezuela accommodation space decreased from campanian to maastrichtian times in cretaceous tertiary boundary times parts of the eastern margin of the eastern cordillera were uplifted by an initial phase of inversion of deeply rooted jurassic and early cretaceous normal faults 3 in paleocene times the central axis of deposition was located along the spine of the eastern cordillera and extended into the maracaibo basin and accommodation space continued to decrease 4 in latest paleocene times the central axis of deposition shifted to eastern regions of the eastern cordillera and accommodation space decreased 5 the early eocene central axis of deposition was located along the present day eastern foothills of the eastern cordillera accommodation space continued to decrease and the regional middle eocene unconformity began to develop in middle eocene times a regional unconformity developed marking the climax of the pre andean orogeny deposition during these times was dominant in the maracaibo basin area where large amounts of sediment derived from vast exposed areas accumulated 6 the late eocene central axis of deposition was confined to the present position of the llanos foothills late eocene deposition reflects a regional increase in accommodation space in oligocene times the initial uplift of the eastern cordillera divided the main depocenter into two central axes accommodation space diminished in uplifted regions but continued to increase in the depocenters allowing sporadic marine ingressions into the present position of the llanos foothills as uplift of the eastern cordillera continued the eastern depocenter axis proto orinoco migrated east and the western depocenter axis proto magdalena migrated west this process continued through the rest of the cenozoic

the effect of grain coating microquartz on preservation of reservoir porosity clay coatings have been widely accepted by many workers as an explanation for preserving high porosity in deeply buried sandstones but few workers have realized that similar effects can be produced by microcrystalline quartz coatings this phenomenon can be expected only under special circumstances but in such cases it can have profound consequences for exploration in the central graben area of the southern north sea unusually high porosity 20 27 and permeability 100 1000 md are found in certain zones in upper jurassic sandstones at depths of 3 4 4 4 km the porosity in these zones is 5 15 higher than expected based on average porosity depth trends from brent and haltenbanken sandstones we propose that the high porosity is due to continuous grain coatings of euhedral microcrystalline quartz crystals that are 0 1 2 m thick the distribution of microcrystalline quartz coatings is controlled by the presence of siliceous sponge spicules rhaxella which implies a sedimentological control on the reservoir quality we present a thermodynamic model showing how continuous microcrystalline quartz coatings inhibit development of no mal macrocrystalline quartz overgrowths sourced mainly from stylolites high porosities in parts of various upper jurassic oil fields ula and gyda have previously been explained by inhibition of quartz cementation by early hydrocarbon charge we suggest that the microcrystalline quartz coatings provide a more plausible explanation

reservoir performance of late eocene incised valley fills cusiana field llanos foothills eastern colombia the cusiana field is located in the llanos foothills of eastern colombia the principal reservoir is the late eocene mirador formation which comprises 50 of reserves currently the mirador reservoir is providing nearly all of the 150 00bopd of production from the cusiana field the mirador reservoir comprises a stack of incised valley deposits the fills of the valleys are dominated by quartz arenite sandstones the average porosity of the valley sandstones is 8 which reflects abundant quartz cement approximately 14 and significant compaction during deep burial approximately 20 000feet single valleys are up to 70 feet thick and exhibit a distinctive bipartite fill that reflects changing energy conditions during filling bases of valleys have the coarsest grain size and have sedimentological and trace fossil evidence for deposition in highly stressed brackish water environments the upper parts of the valleys are typically finer grained and were deposited in more saline settings despite the low porosity of the mirador valleys drill stem tests and production log data show that they have phenomenal performance characteristics rates of ge 10 000bopd are achieved from single valleys bases of the valley fills are the key contributors to flow integration of detailed core and pore system analysis with the reservoir performancemore data shows that the permeability fabric of the mirador can be explained by original depositional architecture and simple loss of primary porosity comparison of cusiana with other quartz rich sandstones from around the world suggests that it s low porosity high performance is predictable less

deformation of overburden soil induced by thrust fault slip abstract when the blind thrust fault slips due to earthquakes overburden soil strata may deform and fail leading to a development of a coseismic fault zone how overburden soil strata will deform or be faulted is an essential issue in the evaluation on the safety of ground underground infrastructures located near the potential plastic zone on the basis of previous work by cole and lade cole d a lade p v 1984 influence zones in alluvium over dip slip faults journal of geotechnical engineering 110 599 615 this research further explores the processes of thrust faulting within overburden soil and examines the influences of corresponding factors or parameters under a range of boundary conditions using physical models and numerical analysis for both small scale and full scale configurations factors explored include uplifting rate fault dip angle dilation angle of plastic flow young s modulus poisson ratio cohesive strength frictional angle scaling as well as the location of ground loadings applied on ground surface the experimental results indicate that although one major fault slip surface can be developed subsidiary faults may also form which requires special attention when defining stain patterns young s modulus and the dilation angle are the most influential parameters in our models a stiffer e leads to early fault propagation and the occurrence of back thrusts and causes more significant discrepancies in the deformation behaviors of models with different scales a greater dilation angle of the overburden soil leads to a wider fault zone the above mentioned phenomena highlight that a careful consideration of the applicable young s modulus and the dilation angle is essential in a proper simulation or prediction of the fault zone development for small scale physical models used to simulate the fault development for a full scale problem the stiffness of model soil should be properly scaled down which still requires further study

centrifuge modeling of reverse fault rupture propagation through single layered and stratified soil abstract many buildings have been built over active faults surface faulting as a main effect of earthquakes can cause damage such buildings properties of material over bedrock affect the pattern of rupture propagation through deposits and the width of the rupture zone on ground surface several researchers have primarily studied fault rupture propagation patterns on single layered granular soil however natural geologic deposits are rarely homogeneous and uniform but mostly consist of different layers in this study centrifuge model tests were conducted to investigate the patterns of reverse fault rupture propagation through single and double layered soil stratum it was observed that the soil type and sequence of layers affected the fault rupture propagation pattern as well as the surface rupture zone the results show that the width of deformation zone tends to decrease in stiffer soil in compare to softer soil these findings may help to produce a framework for predicting the occurrence and geometry of surface fault rupture zone that can help us to define a setback zone which is a major concern in building codes

the bude formation lower westphalian sw england siliciclastic shelf sedimentation in a large equatorial lake the 1300 m thick turbiditic bude formation was deposited in a lake lake bude but disagreement persists over whether the environment was a deltaic or deep water fan the tectonic setting of the lake was the northern flank of a northerly advancing variscan foreland basin close to the westphalian palaeo equator palaeocurrents indicate sediment sourcing from all quadrants except the south there is a dm m scale cyclicity whereby sandstone bodies comprising amalgamated event beds alternate with mudstone intervals containing non amalgamated event beds the ideal cycle is a symmetrical coarsening up fining up cycle consisting of three facies i 2 and 3 arranged in 12321 order facies 3 in the middle of the cycle is an amalgamated sandstone body up to 10 m thick which interfingers laterally with thin cm mudstone layers the sandstone body comprises amalgamated beds of very fine sandstone which are largely massive and up to 0 4 m thick channels are absent except for scours up to 0 2 m deep which truncate the interfingering mudstone layers sandstone bodies are inferred to be tongue shaped in three dimensions facies 1 and 2 completing the 12321 cycle are respectively dark grey fine and light grey coarse varved mudstone containing thin 0 4 m sandstone event beds fossils and burrows indicate that facies 1 and 2 were deposited respectively in brackish rarely marine and fresh water hence the ideal cycle 12321 reflects an upward decrease then increase in salinity brackish fresh brackish this is attributed to the lake sill being periodically overtopped by the sea due to glacio euitatic sea level oscillations the resulting oscillations in lake depth produced the coarsening up fining up regressivetransgressive cyclicity the central sandstone body representing the regressive maximum event beds are interpreted as river fed turbidites deposited during catastrophic storm floods combinedflow ripples and other wave influenced structures occur in event beds throughout the ideal cycle suggesting deposition of the entire bude formation above storm wave base the proposed environment is a shelf of continental shelf dimensions but lacustrine instead of marine sandstone bodies are interpreted to be river connected tongues or lobes the absence of cycles containing nearshore or emergent facies is attributed to i the lake sill preventing the water level from falling below sill level thereby insulating the lake floor from eustatically forced emergence and ii relatively distal deposition beyond the reach of shoreline progradations the lack of palaeoflow from the south is attributed to a now eroded deep water trough lying to the south in front of the northerly advancing orogen some facies 2 laminated mudstone beds grade laterally into massive and or contorted beds interpreted as in situ seismites facies 4 consistent with an active foreland basin setting development of seismites was possibly facilitated by gas bubbles and or weak cohesion in the fresh water bottom mud the late quaternary black sea with its broad northwestern shelf is probably a good physiographical analogue of lake bude and was likewise fresh at times

basin development and tectonic history of the llanos basin eastern cordillera and middle magdalena valley colombia the middle magdalena valley eastern cordillera and llanos basin constituted a major regional sedimentary basin from the triassic to the middle miocene basin development began during the triassic to the earliest cretaceous with a synrift megasequence related to the separation of north and south america in the proto caribbean the synrift megasequence began with deposition in a continental environment that became paralic and shallow marine in the early cretaceous basin development continued into the cretaceous in a back arc setting east of the andean subduction zone the back arc megasequence was dominated by shallow marine sedimentation and produced an excellent regional source rock during the turonian coniacian marine deposition was abruptly terminated during the ear y maastrichtian due to the final accretion of the western cordillera accretion of the western cordillera created the early pre andean foreland basin megasequence of late maastrichtian to early eocene age this depositional episode consists of coal rich alluvial plain coastal plain and estuarine deposits throughout the middle magdalena valley eastern cordillera and eastern llanos basin the megasequence was terminated by middle eocene deformation in the magdalena valley which ended sediment deposition throughout colombia loading effects of this deformation reestablished the basin in which the late pre andean foreland basin megasequence was deposited until the early miocene this megasequence also consists of alluvial plain coastal plain and estuarine deposits including the primary reservoir in the llanos foothills the upper eocene mirador fo mation the megasequence also includes a series of four major grossly coarsening upward cycles in the llanos basin these cycles correspond to changes in sea level sediment supply and foreland basin loading the mudstone in the lowermost of these cycles is the regional seal in the llanos basin and foothills the middle miocene onset of andean deformation in the eastern cordillera isolated the middle magdalena valley from the llanos basin the deformation was dominated by inversion of the basin controlling faults the resultant loading of the lithosphere created the accommodation space for the andean foreland basin megasequence a major transgression into the llanos basin coeval with this deformation caused deposition of marine mudstones in the lower part of the megasequence however the majority of the andean foreland basin megasequence consists of the guayabo formation a classic molasse sequence deposited in a high energy coarse grained bed load dominated fluvial system that was supplied by the developing mountains of the eastern cordillera

subsidenz und tektonik des saar nahe beckens sw deutschland the saar nahe basin in sw germany is one of the largest permo carboniferous basins in the internal zone of the variscides its evolution is closely related to movements along the hunsruck boundary fault which separates the rhenohercynian and the saxothuringian zones recent deep seismic surveys indicate that the saar nahe basin formed in the hanging wall of a major detachment which soles out at lower crustal levels at about 16 km depth oblique extension along an inverted variscan thrust resulted in the formation of a half graben within more than 8 km of entirely continental strata accumulated the structural style within the basin is characterized by normal faults parallel to the basin axis and orthogonal transfer fault zones balanced cross section construction and subsidence analysis indicate extension of the orogenically thickened lithosphere by 35 subsidence modeling shows discontinuous depth dependent extension with laterally varying extension factors for crust and mantle lithosphere thus the offset between maximum rift and thermal subsidence can be explained by a zone of mantle extension shifted laterally with respect to the zone of maximum crustal extension

study on reverse fault rupture propagation through sand with inclined ground surface abstract previous studies on faulting were performed on horizontal grounds which were hypothesized implicitly as an increasing number of infrastructures are being built on topographically complex sites such as mountainous areas investigations into fault rupture propagation through soil with an inclined surface have become significant in this study a series of 1 g physical model tests of reverse faulting with inclined ground surfaces were performed the effects of ground inclination on the geometry of fault ruptures displacement at the ground surface and deformation of the sand layer were investigated three classical soil mechanics theories namely the rankine roscoe and vermeer theories were used to predict the directions of fault ruptures in sand with inclined ground surfaces the predicted values were compared with the measured values obtained from the model tests based on the experimental results a configuration of the setback limits for structures on an inclined ground is recommended to prevent destruction by fault ruptures

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

aerodynamic and geometric diameter of airborne particles discussion the paper by chen and fryrear 2001 addresses a much neglected topic in the general field of grain dynamic behavior but it is unfortunately marred by a number of omissions and inaccuracies first some minor errors have to be pointed out which may mislead some readers if not corrected 1 equation 1 should read r f 6 rv without the minus sign 2 equation 7 is valid only for reynolds numbers less than 1 not more than 1 as stated 3 in their table 1 the legend states that t m is the calculated mean settling velocity which should read the calculated mean settling time 4 the legend in fig 2 should read measured average settling times and not settling velocities 5 the values for v t and the geometric particle diameters given in table 1 do not correspond to the graph in fig 5 6 on page 366 it is mentioned that sieve intervals of 75 m were used for particles between 125 and 600 m and 10 m intervals between 125 and 10 m however in table 1 the intervals apparently vary from 105 m to 25 m for the first range and between 19 and 8 m for the second 7 it is implied on the same page that perfect spheres were selected by examining them under a microscope this cannot be done because all the grains would lie on their shortest axes they may therefore just as well

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

surface ruptures induced by the wenchuan earthquake their influence widths and safety distances for construction sites abstract surface ruptures studied in this paper refer to those induced by the 2008 wenchuan earthquake they mostly appear as two prominent surface rupture zones one is about 240 km long distributed along the central fault and another about 70 km long along the front mountain fault the influence width of a surface rupture is an important factor to determine the safety distance for construction sites to keep away from it in measuring the influence width the shortening amount or rate must be paid enough attention to the statistical analysis of 85 sets of practically measured data of surface ruptures shows that the influence widths are concentrated in the scope of 15 m and 60 m and that there is a linear relationship between the vertical displacements h and influence widths d of surface ruptures which can be approximately expressed as d 11 h 14 the influence scopes on both sides of a surface rupture are asymmetric and their proportion between the hanging side and the down side is generally from 3 1 to 2 1

centrifuge and numerical modeling of normal fault rupture propagation in clay with and without a preexisting fracture abstractover the last few decades extensive research has been conducted to investigate fault rupture propagation induced by faulting through uncemented soil while it has long been realized that many natural soils are cemented relatively few publications have been devoted to investigating fault rupture propagation in cemented soil moreover preexisting fracture in soil may be reactivated during earthquakes and its influence on fault rupture propagation is not fully understood in this study three centrifuge model tests are reported on investigating fault rupture propagation induced by normal faulting in uncemented clay and cemented clay with and without a preexisting fracture preliminary numerical analyses of the centrifuge tests are also carried out to study the mechanism of fault rupture propagation in these three ground conditions ground deformation was dominated by a shear mechanism in uncemented clay and a shear zone along the projection of the bedrock fault plane was observed on the other h

magma mixing as the probable origin of some permian volcanic rocks of the saar nahe basin sw germany some permian calc alkaline rocks of the saar nahe basin are briefly described and their origin is discussed in the light of a magma mixing model for the intermediate members

formation of abnormally high porosity permeability in deltaic sandstones oligocene bozhong depression offshore bohai bay basin china abstract the porosity enhancing capability of secondary porosity in a closed sandstone geochemical system has been suggested to be small in past studies however the mechanisms responsible for the formation of abnormally high porosity permeability remain unclear the oligocene dongying formation in the bozhong depression offshore bohai bay basin preserves abnormally high porosity i e 36 4 average or 42 1 median higher than background values this work selects samples with abnormally high porosity ahp samples with normal porosity np and samples with abnormally low porosity alp and compares their differences in physical properties porosities permeabilities and thin section porosities diagenetic minerals pore structures compaction and cementation detrital compositions and grain texture in an attempt to find the real factors controlling this heterogeneity an effective export of dissolution by products al3 and si4 from ahp to np and alp leads to 2 01 average or 2 11 median newly created porosity in ahp which is still significantly lower than the porosity difference between ahp and np in comparison compaction reduction and mechanisms beneficial for compaction reduction should be the major factors controlling ahp formation the content and distribution pattern of early carbonate cements compared to the sedimentary factors grain size and rigid grains have significant influences on compaction reduction only samples with moderate contents 0 5 3 0 of uniformly point distributed early carbonate cements and with effective export of dissolution by products can form ahp three formation models for alp and two formation models for np are also proposed in summary the evolution of porosity permeability is controlled by early carbonate cements and induced compaction reduction major causes and by feldspar dissolution and redistribution of by products minor causes this work provides new constraints on the formation of ahp and heterogeneity and is therefore important for sandstone reservoir quality prediction

intergranular pressure solution in four quartzose sandstones abstract cathodoluminescence petrography and scanning electron microscopy reveal that several geologic variables significantly influenced intergranular pressure solution and quartz cementation in the bromide ordovician oklahoma upper minnelusa permian wyoming nugget jurassic utah and tuscarora silurian pennsylvania sandstones a linear relationship exists between mean grain size and intergranular pressure solution with finer grained samples having experienced more intergranular pressure solution than coarser grained ones samples that display pervasive illite grain coatings have also experienced more intergranular pressure solution than those with no or poorly developed grain coatings sorting and limited framework grain compositional variability have exerted little influence o intergranular pressure solution silica budgets indicate that in the bromide upper minnelusa and nugget sandstones more quartz has been dissolved by intergranular pressure solution than is present as cement these sandstones have exported silica during burial diagenesis in the tuscarora the amount of quartz dissolved by intergranular pressure solution is about equal to the amount of quartz cement present implying approximate mass balance however petrographic evidence suggests that most of the quartz cement in at least three of these sandstones predates most intergranular pressure solution implying that they acted as silica importers during shallow diagenesis and silica exporters during deeper diagenesis intergranular pressure solution has played varying roles in determining the ultimate porosity of these four sandstones in the nugget intergranular pressure solution was the single most important diagenetic process that influenced porosity evolution in the bromide intergranular pressure solution was slightly more important than mechanical compaction and considerably more important than cementation in the tuscarora intergranular pressure solution was slightly more important than mechanical compaction and of about equal importance to quartz cementation in the upper minnelusa intergranular pressure solution was less important than both mechanical compaction and gypsum anhydrite cementation

a structural outline of the yenkahe volcanic resurgent dome tanna island vanuatu arc south pacific abstract a structural study has been conducted on the resurgent yenkahe dome 5 km long by 3 km wide located in the heart of the siwi caldera of tanna island vanuatu arc south pacific this spectacular resurgent dome hosts a small caldera and a very active strombolian cinder cone the yasur volcano in the west and exhibits an intriguing graben in its central part detailed mapping and structural observations make it possible to unravel the volcano tectonic history of the dome it is shown that following the early formation of a resurgent dome in the west a complex collapse caldera plus graben occurred and this was associated with the recent uplift of the eastern part of the present dome eastward migration of the underlying magma related to regional tectonics is proposed to explain this evolution

interaction of shallow foundations with reverse faults a series of centrifuge model tests is reported that investigated the effects of foundation position on the interaction of reverse dip slip faults with shallow foundations resting on sand the model tests have allowed careful examination of both the soil and foundation deformation as a shear localization fault propagates through a 15 m thick sand layer for fault throws up to 5 m by comparing results of the tests with foundations present with those from a free field test the effect of the foundation on the faulting pattern has been observed directly the response of the foundation is very sensitive to the exact position of the fault and even when the fault emerged remotely from the foundation it sometimes caused significant foundation movements detailed results are presented for the tests and it is suggested that these results are used as 1 indications of likely foundation soil fault interaction mechanisms and 2 to allow future validation of numerical models for similar problems finally fou

ground water silicification and leaching in sands example of the fontainebleau sand oligocene in the paris basin in the fontainebleau sand oligocene superposed lenses of quartzite are restricted to outcrops and structurally low zones of the formation the quartzite lenses result from a silicification process controlled by water table levels during the recent geomorphologic evolution of the landscape the quartzite lenses pinch out rapidly under the limestone capped plateaus and are related to the development of a bleached sand profile above the water table the sand is bleached and the former quartzite lenses are corroded along their margins moreover flint pebbles are dissolved and primary smectite and illite are weathered to kaolinite dissolved silica can thus reach supersaturated levels allowing quartz precipitation quartz grains are overgrown at the base of the profile in zones of ground water outflow related to spring lines the adjustment of the water table during the landscape incision led to formation of quartzite lenses at deeper levels this silicification process has no climatic significance but is dependent on the stability of the landscape and on its progressive dissection the rate of quartz cementation indicated by geomorphologic considerations is consistent with hydraulic and geochemical calculations it appears to be very rapid approximately 30 000 yr for a quartzite lens

hyperbolic spiral model for predicting reverse fault ruptures in sand based on centrifuge tests fault deformation can cause severe damage to structures located within the fault zones a logarithmic spiral model was developed by d a cole and p v lade in 1984 to predict the shapes and locat

mechanical models of fault propagation folds and comparison to the trishear kinematic model abstract faults propagating through the earth generate a wave of deformation ahead of their tip lines we have modeled this process to understand the relationship between fold geometry and fault propagation using finite element modeling fem we investigate the response of incompressible frictionless and frictional materials and a compressible frictional material with associated flow to vertical and dipping faults whose tip lines propagate at rates 3 3 5 times their slip rates the fold geometries finite strain and velocity fields in models with incompressible materials are very similar to those produced by the trishear kinematic model even though the latter uses a purely ad hoc linear velocity field furthermore when the trishear grid search is applied to the final geometry of the mechanical folds the best fit kinematic models have approximately the same propagation to slip ratio as was used in the fem experiments however when the compressible frictional material is used the mechanical models exhibit a main triangular shear band in front of the tip line and a conjugate shear band in the fold backlimb both migrating with the propagating tip line the conjugate shear band antithetic to the fault produces a gentle anticlinal back limb even though there is not a bend in the fault

the effect of oil saturation on the mechanism of compaction in granular materials higher oil saturations lead to more grain fracturing and less pressure solution abstract whether addition of oil to sandstones slows stops or has no influence upon pressure solution and quartz cementation has long been disputed despite having major implications for petroleum exploration and appraisal strategies to elucidate the effect of addition of oil to compaction pressure solution and cementation processes this study utilizes an experimental approach simulating isochemical volumetric compaction using granular halite in the presence of variable brine oil mixtures each experiment at 500 kpa effective stress lasted 48 hours and involved repeated measurements of volumetric strain the lithified products of experiments were examined using sem techniques after 30 hours approximately 4 volumetric strain occurs when the brine oil ratio is 100 0 pure brine fractures are rare in samples from experiments undertaken with pure brine so that pressure solution and concomitant cementation must be the compaction mechanism when the brine oil ratio is decreased from 100 0 to 40 60 the volumetric strain remains about 4 but there are more fractures as quantified from sem image analysis these observations suggest that although pressure solution has occurred some of the volumetric strain is the result of fracturing implying that pressure solution has been less effective in the presence of some oil than it is in the presence of pure brine when the brine oil ratio is decreased further from 40 60 to 5 95 the volumetric strain increases up to 7 3 sem image analysis reveals that the strain is predominantly due to grain fracturing this change from pressure solution to grain fracturing is likely due to heterogeneous pressure solution resulting from heterogeneous distribution of stresses brine coated grain contacts undergo pressure solution but oil coated grain contacts experience increasing stress up to the point of failure as the surrounding grain pack compacts when the brine oil ratio is decreased to less than 5 95 volumetric strain decreased to about 1 with few induced fractures and little pressure solution compaction is negligible when the brine oil ratio is 0 100 only oil in the pores and fractures are negligible halite is more water soluble and more hygroscopic than quartz so that water will cling to halite surfaces more tenaciously than to quartz since even halite has its mechanism of volumetric strain affected when the brine oil ratio is less than 40 60 quartz pressure solution and subsequent cementation is even more likely to be affected by oil filling this experimental study suggests that the mechanism and extent of compaction and subsequent cementation in sandstones is strongly affected by the addition of oil

the impact of diagenesis on the heterogeneity of sandstone reservoirs a review of the role of depositional facies and sequence stratigraphy diagenesis exerts a strong control on the quality and heterogeneity of most clastic reservoirs variations in the distribution of diagenetic alterations usually accentuate the variations in depositional porosity and permeability linking the types and distribution of diagenetic processes to the depositional facies and sequence stratigraphic framework of clastic successions provides a powerful tool to predict the distribution of diagenetic alterations controlling quality and heterogeneity the heterogeneity patterns of sandstone reservoirs which determine the volumes flow rates and recovery of hydrocarbons are controlled by geometry and internal structures of sand bodies grain size sorting degree of bioturbation provenance and by the types volumes and distribution of diagenetic alterations variations in the pathways of diagenetic evolution are linked to 1 depositional facies hence pore water chemistry depositional porosity and permeability types and amounts of intrabasinal grains and extent of bioturbation 2 detrital sand composition 3 rate of deposition controlling residence time of sediments at specific near surface geochemical conditions and 4 burial thermal history of the basin the amounts and types of intrabasinal grains are also controlled by changes in the relative sea level and therefore can be predicted in the context of sequence stratigraphy particularly in paralic and shallow marine environments changes in the relative sea level exert significant control on the types and extent of near surface shallow burial diagenetic alterations which in turn influence the pathways of burial diagenetic and reservoir quality evolution of clastic reservoirs carbonate cementation is more extensive in transgressive systems tract tst sandstones particularly below parasequence boundaries transgressive surface and maximum flooding surface because of the abundance of carbonate bioclasts and organic matter bioturbation and prolonged residence time of the sediments at and immediately below the sea floor caused by low sedimentation rates which also enhance the formation of glaucony eogenetic grain coating berthierine odinite and smectite formed mostly in tst and early highstand systems tract deltaic and estuarine sandstones are transformed into ferrous chlorite during mesodiagenesis helping preserve reservoir quality through the inhibition of quartz cementation the infiltration of grain coating smectitic clays is more extensive in braided than in meandering fluvial sandstones forming flow barriers in braided amalgamated reservoirs and may either help preserve porosity during burial because of quartz overgrowth inhibition or reduce it by enhancing intergranular pressure dissolution diagenetic modifications along sequence boundaries are characterized by considerable dissolution and kaolinization of feldspars micas and mud intraclasts under wet and warm climates whereas a semiarid climate may lead to the formation of calcrete dolocrete cemented layers turbidite sandstones are typically cemented by carbonate along the contacts with interbedded mudrocks or carbonate mudstones and marls as well as along layers of concentration of carbonate bioclasts and intraclasts commonly hybrid carbonate turbidite arenites are pervasively cemented proximal massive turbidites normally show only scattered spherical or ovoid carbonate concretions improved geologic models based on the connections among diagenesis depositional facies and sequence stratigraphic surfaces and intervals may not only contribute to optimized production through the design of appropriate simulation models for improved or enhanced oil recovery strategies as well as for co2 geologic sequestration but also support more effective hydrocarbon exploration through reservoir quality prediction

clastic deposition provenance and sequence of andean thrusting in the frontal eastern cordillera and llanos foreland basin of colombia sedimentological provenance and detrital thermochronological results for basin fill at the modern deformation front of the northern andes 6 n latitude provide a long term eocene to pliocene record of foreland basin sedimentation along the eastern cordillera llanos basin boundary in colombia lithofacies assemblages and paleocurrent orientations in the upward coarsening 5 km thick succession of the nunchia syncline reveal a systematic shift from craton derived shallow marine distal foreland back bulge accumulation in the mirador formation to orogen sourced deltaic and coastal influenced sedimentation of the distal to medial foreland foredeep in the carbonera and leon formations to anastomosing fluvial and distributive braided fluvial megafan systems of the proximal foreland foredeep to wedge top basin in the lower and upper guayabo formation these changes in depositional processes and sediment dispersal are supported by up section variations in detrital zircon u pb and u th he ages that record exhumation of evolving compartmentalized sediment source areas in the eastern cordillera the data are interpreted in terms of a progressive eastward advance in fold and thrust deformation with late eocene oligocene deformation in the axial zone of the eastern cordillera along the western edge of floresta basin soapaga thrust early miocene reactivation inversion of the eastern margin of the mesozoic rift system pajarito and guaicaramo thrusts and middle late miocene propagation of a footwall shortcut fault yopal thrust that created the nunchia syncline in a wedge top piggyback setting of the eastern foothills along the transition from the eastern cordillera to llanos foreland basin collectively the data presented here for the frontal eastern cordillera define a general in sequence pattern of eastward advancing fold and thrust deformation during cenozoic east west shortening in the colombian andes

evolution of the surface deformation profile and subsurface distortion zone during reverse faulting through overburden sand abstract the 2d distinct element method was used to investigate the propagation of fault rupture traces through overlying sand during reverse faulting along a range of dip angles and at different vertical throws calibrated micromechanical material parameters were used in the numerical simulations which were validated through a comparison of the simulation results with those obtained from a centrifuge experiment involving acceleration at 80 g the gompertz sigmoid function with three parameters provided the best fit to the normalized surface deformation profiles obtained both from the numerical simulation and from centrifuge experiments the three parameters that characterized the gompertz sigmoid function were the normalized scarp height the maximum slope on the scarp and the location of the reverse fault outcropping a surface deformation profile slope of 1 150 was used as the setback criterion the normalized affected width and fault outcrop relative to the fault tip were determined for reverse faults having a variety of dips and throws the dip angle significantly affected the kinematic mechanism underlying reverse faulting at a given vertical throw the scarp height increased as the dip angle decreased in the cases of 45 as the dip angle decreased the location of the fault outcropping shifted toward the footwall and the maximum slope on the scarp increased the horizontal displacement played a significant role at low dip thrusts 22 5 30 37 5 a back thrust fault developed and an inverted triangle wedge formed in the subsurface

deep burial diagenesis and reservoir quality evolution of high temperature high pressure sandstones examples from lower cretaceous bashijiqike formation in keshen area kuqa depression tarim basin of china the deep high temperature high pressure lower cretaceous bashijiqike sandstone buried to depths as great as 6 5 7 1km is an important natural gas reservoir in keshen gas field kuqa depression of the tarim basin reservoir quality is a critical risk factor in the development of these ultradeep reservoirs integrated approaches incorporating routine core analyses mineralogical petrographic and geochemical analyses have been used to investigate the diagenetic history of these rocks and their impact on reservoir quality with the aim to unravel the mechanisms for maintaining anomalously high porosities in sandstones that are buried to such a great depth these sandstones are dominantly fine to medium grained moderately to good sorted lithic arkoses and feldspathic litharenite most primary pores have been lost by mechanical compaction or carbonate cementation and the reduction of porosity by mechanical compaction was more significant than by cementation dissolution of framework grains contributed to the enhancement of reservoir quality eogenetic diagenetic alterations mainly include mechanical compaction precipitation of calcite cements and grain coating clays mesogenetic diagenesis is characterized by dissolution of framework grain by organic acids and subsequent precipitation of clay minerals and quartz infiltration of meteoric water related to teleodiagenesis would result in dissolution of the framework grains the meteoric leaching events during teleodiagenesis are of great importance for the bashijiqike sandstones grain coating clay minerals mixed layer illite smectite clays help to preserve porosity at depth by retarding quartz cementation and pressure solution the unique burial regime as early stage shallow burial with late stage rapid deep burial contributes to porosity preservation in eodiagenesis fluid overpressure caused by intense structural compression in the middle himalayan movement retarded compaction and helped preserve porosity in the late rapid deep burial stage anomalously high porosities are mainly found in medium grained good sorted sandstones with grain coating clays but with low clay and carbonate cement content of which the porosity is preserved primarily and enhanced secondarily the lowest porosities are associated with sandstones that are tightly compacted or cemented with carbonates or rich in detrital matrix porosity depth trends may vary significantly with lithofacies due to its differences in textural and compositional attributes five lithofacies are defined in terms of detrital composition and texture type and degree of diagenesis the reservoir quality prediction models of various lithofacies are constructed and the results of this study provide insights into mechanisms for maintaining anomalously high porosity and permeability in high temperature high pressure sandstone reservoirs and may help explain hydrocarbon distribution

centrifuge modeling of buried continuous pipelines subjected to reverse faulting seismic ground faulting is a severe hazard for continuous buried pipelines over the years researchers have attempted to understand pipeline behavior mostly via numerical models such as the finite

diagenesis and reservoir quality of lacustrine deep water gravity flow sandstones in the eocene shahejie formation in the dongying sag jiyang depression eastern china the lacustrine deep water gravity flow sandstone reservoirs in the middle of the third member of the shahejie formation 43 7 38 2 ma are the main exploration targets for hydrocarbons in the dongying sag jiyang depression eastern china the impact of diagenesis on reservoir quality of these sandstones has been established by a variety of methods petrographically the sandstones consist mainly of lithic arkose with 43 of quartz 33 of feldspar and 24 of lithic fragment with reservoirs having average porosity and permeability values of 17 1 and 38 1 md respectively in addition to their primary intergranular pores secondary pores are well developed from feldspar dissolution with pore throat radii ranging from 0 01 to 40 m the dissolution of feldspar and transformation of smectite to illite may be the sources of silica for the first phase of quartz overgrowth whereas illitization of kaolinite may be responsible for the second phase of quartz overgrowth in addition pressure dissolution of quartz is also an important source of silica for quartz overgrowth dissolution of feldspar has little impact on reservoir quality whereas compaction and carbonate cementation are the main factors significantly reducing reservoir quality oil charge may have retarded carbonate cementation and generated overpressure that retarded compaction thus preserving porosity precipitation of vermicular kaolinite resulting from feldspar dissolution promoted a change in the wettability of the reservoir from water wet to oil wet which is beneficial for oil entrapment the central parts of medium to thick bedded sandstones that have experienced oil charge twice appear to have the highest quality reservoirs based on petrophysical properties this work provides a new interpretation of the formation mechanism of high quality lacustrine deep water gravity flow sandstones reservoirs that have experienced multiple periods of oil charge

the nahe caldera a resurgent caldera in the permocarboniferous saar nahe basin sw germany in the saar nahe basin sw germany a large resurgent caldera complex of lower permian age was recognized recently for which the name nahe caldera is proposed

paragenesis and conditions of formation of the moschellandsberg mercury deposit sw germany the moschellandsberg mercury deposit sw germany is hosted in a permo carboniferous volcanic caldera and has formed at shallow depths 100 300 m and over a wide temperature range from about 200 c to less than 65 c the deposit shows vertical zonation and the mineral paragenesis is unusually complex and contains significant amounts of sb as cu and ag fahlores are hg and fe rich sb bi and as members displaying a mixing gap vesicular ore textures and limited fluid inclusion evidence prove the existence of an immiscible gas phase during ore deposition the fluid composition can be constrained to ph 4 h2s 10 5 molal co2 10 1 molal and fh2 10 2 10 3 bar by comparing the observed mineral associations with stable phase assemblages calculated from thermodynamic data calculated metal solubilities indicate that hg ag and sb can be transported very efficiently in such a fluid but that the solubility of gold is very low