Browsing by Subject "Deep water"
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Item Deep water Gulf of Mexico pore pressure estimation utilizing P-SV waves from multicomponent seismic in Atlantis Field(2009-12) Kao, Jeffrey Chung-chen; Tatham, R. H. (Robert H.), 1943; Flemings, Peter B.; Krail, PaulOverpressure, or abnormally low effective pressures, is hazardous in drilling operations and construction of sea-bottom facilities in deepwater environments. Estimation of the locations of overpressure can improve safety in these operations and significantly reduce overall project costs. Propagation velocities of both seismic P and S wave are sensitive to bulk elastic parameters and density of the sediments, which can be related to porosity, pore fluid content, lithology, and effective pressures. Overpressured areas can be analyzed using 4C seismic reflection data, which includes P-P and P-SV reflections. In this thesis, the effects on compressional (P) and shear (S) wave velocities are investigated to estimate the magnitude and location of excess pore pressure utilizing Eaton’s approach for pressure prediction (Eaton, 1969). Eaton’s (1969) method relates changes in pore pressure to changes in seismic P-wave velocity. The underlying assumption of this method utilizes the ratio of observed P-wave velocity obtained from areas of both normal and abnormal pressure. This velocity ratio evaluated through an empirically determined exponent is then related to the ratio of effective stress under normal and abnormal pressure conditions. Effective stress in a normal pressured condition is greater than the effective stress value in abnormally overpressured conditions. Due to an increased sensitivity of variations in effective pressure to seismic interval velocity, Ebrom et al. (2003) employ a modified Eaton equation to incorporate the S-wave velocity in pore pressure prediction. The data preparation and subsequent observations of seismic P and S wave velocity estimates in this thesis represent a preliminary analysis for pore pressure prediction. Six 2D receiver gathers in the regional dip direction are extracted from six individual ocean-bottom 4C seismic recording nodes for P-P and P-SV velocity analysis. The receiver gathers employed have minimal pre-processing procedures applied. The main processing steps applied were: water bottom mute, 2D rotation of horizontal components to SV and SH orientation, deconvolution, and frequency filtering. Most the processing was performed in Matlab with a volume of scripts designed by research scientists from the University of Texas, Bureau of Economic Geology. In this thesis, fluid pressure prediction is estimated utilizing several 4C multicomponent ocean-bottom nodes in the Atlantis Field in deepwater Gulf of Mexico. Velocity analysis is performed through a ray tracing approach utilizing P-P and P-SV registration. A modified Eaton’s Algorithm is then used for pore pressure prediction using both P and S wave velocity values. I was able to successfully observe both compressional and shear wave velocities to sediment depths of approximately 800 m below the seafloor. Using Hamilton (1972, 1976) and Eberhart-Phillips et al. (1989) regressions as background depth dependent velocity values and well-log derived background effective pressure values from deepwater Gulf of Mexico, I am able to solve for predicted effective pressure for the study area. The results show that the Atlantis subsurface study area experiences a degree of overpressure.Item Interplay of salt-influenced structural deformation and submarine channel evolution in the Campos Basin, offshore Brazil(2017-08-10) Ceyhan, Can; Fisher, W. L. (William Lawrence), 1932-; Covault, Jacob A.The Campos Basin, located on the southeastern Brazil passive margin, is one of the most productive basins in the western South Atlantic. The development of many siliciclastic turbidite reservoirs in the southeastern Brazilian margin provided a great interest in submarine channel systems of the Campos Basin for hydrocarbon exploration purposes. Prior research highlights the variation of sediment supply, sea-level fluctuations and tectonic activity as the most critical controls on channel development within the Campos Basin. The Campos Basin is structurally complex as a result of salt movement, and it is an ideal setting in which to investigate the influences of structural deformation on channel evolution and architecture. I investigated the interaction between development of a post-Miocene submarine channel system and structural deformation related to salt tectonics by using structural and stratigraphic analysis of 3D seismic-reflection data, which covers an area of approximately 1750 km². I produced detailed maps and cross sections of the submarine channel system, and compared them to structural maps in order to interpret the control of structural deformation on evolution and architecture of the submarine channel system. I interpreted that a regionally mapped seismic-reflection horizon approximates the paleobathymetry at the time of channel formation and correlated with the trend of the channel system. The paleobathymetry mainly dictated the transport pathway of the submarine channel system, as channels within the system mainly stayed in salt-withdrawal basins and avoided salt-influenced structural highs. However, the submarine channel system was diverted to flow directly on the top of a salt diapir within the southeastern part of the study area, rather than staying within salt-withdrawal basins. I explained this anomaly by two uplift stages of the salt diapir. Aggradation smoothed out much of the paleobathymetry associated with the first growth stage of the salt diapir, and the salt-influenced structural high was not able to divert the submarine channel system. The basal surfaces of channels within the system are deformed as a result of the growth of the salt diapir, which suggests that the salt diapir became active again when the submarine channel system started to develop.Item Quantitative seismic geomorphology of a confined channel complex, southern Atwater fold belt, Gulf of Mexico, U.S.A.(2010-08) Morgan, Jessica Leanne; Wood, Lesli J.; Steel, Ronald; Fisher, William L.The structures along the Atwater Fold belt form important deep-water hydrocarbon traps in the northern Gulf of Mexico. The purpose of this study is to map and quantify the morphology, sedimentology and architecture of Plio-Pleistocene basin floor fan systems outboard of the Poseidon Minibasin, located along the Atwater deep-water fold belt (mid-Miocene to Pliocene), and apply that information to determine the temporal and spatial nature of the fill and its implications as a reservoir analog. The data set includes ~2200 km sq. of 3D seismic data, along with information from several wells. Wireline logs show the Tertiary age deposits outboard of the Sigsbee Escarpment to be several hundred feet thick, sharp-based, dominantly coarse-grained (sandy) but fining up cycles composed of sandy basin floor fans, mass transport complexes and leveed channels developed in a confined setting within deep-water “valleys.” The largest valley formed in five main stages: initiating from narrow channel incision, widening through lateral incision and sidewall slumping, straightening, and finally flooding and infilling. The valley system is ~20,000 feet across and ~ 1,400 feet deep, with what look like well-developed levees ranging from 700 to 1300 feet at their thickest point extending ~19000 feet away from the channel. This system is underlain by a ~700 foot thick mass transport complex and overlain by younger, low sinuosity leveed channel systems. Both of these systems appear to have been sourced by large submarine drainages, originating from a shelf edge sediment source system to feed the rugose slope with deep-water channel pathways uninhibited by salt wall inflation at the time of valley deposition. Major phases of salt thrusting along the southern edge of the Atwater were contemporaneous with the formation of these large, through-going valley system, which appear to be associated with the period of sheet thickening and development of monoclinal basinward dip related to rafted mini-basin docking. Well log signatures show evidence for armored clay drapes along the valley margins as well as a flattening of lateral accretion packages toward the distal end of the system. The flattening of these packages seems to signal proximity to the fan terminus, which would serve as an important indicator of spatial extent of plays in deep-water.Item Shelf-slope sediment transport in medium-sized basin margin clinoforms, with a focus on slope channel facies and architecture(2022-08-10) Gan, Yuqian; Olariu, Cornel; Steel, R. J.; Carvajal, Cristian R; Horton, Brian K; Mohrig, David COnce sediment is brought beyond the shelf-edge, its transport into deep water is dominated by sediment gravity flows passing through slope channels and canyons, as well as from finer grained overbanking systems diverted out of these conduits onto the generally muddy slope. Channels and channel complexes are well studied at the scale of continental-slope clinoforms, albeit often at relatively low resolution. This thesis focus on the facies and architecture of slope-channel fills within medium-sized clinoforms (height < 1km) that were supply-dominated (low-angle progradting shelf edge trajectory). The main study database is a set of well exposed, ‘walkable’ clinoforms in the Early Jurassic, back-arc Neuquén Basin of Argentina. Key results from this work are that (1) upper slope channels have a tendency to be deeper than the lower slope channels within the same clinoform set, (2) a downslope fining of slope channel fill from conglomerate to sandstone, with conglomeratic debris flows accumulated preferentially in upper slope channels, whereas lower slope channels mostly host sand-rich turbidites, except for the cases of coarse sediment (pebble) bypass to lower slope and basin floor (3) individual channel-element infills (especially within upper slope channel complexes) are strikingly dominated by sharp-based, decimeter thick, sediment gravity flow units that internally show an upward change from conglomeratic to sand-rich beds. Clast sizes decrease upwards and sandy matrix percent increases upwards through each infill unit, as debrite beds change upward to sandy turbidites. We found that this prominent multi-flow, fining-upward sequence is especially common on upper slope sites and was possibly related to a eustacy-regulated decreasing sediment supply from the nearby shelf into the slope channels. This tentative explanation uses the landward-stepping action of a transgressive shoreline to explain the decimeter scale upward-fining architecture. The coarse sediment is initially brought to the shelf edge and slope by shoreline regression but sediment flux to the channels then reduced during drowning of the shelf. Autogenic explanations for the channel architecture are also possible, but the very prominent repetition of 10-20m thick regressive-to-transgressive cycles (kms lateral extent) in the adjacent shoreline-shelf stratigraphy make the allogenic drive hypothesis feasible. The slope portion of the Maastrichtian Lewis-Fox Hill clinoforms in Washakie Basin is used as a second case study for analysis of similar, medium-sized, supply-dominated clinoforms, with overall finer grains (sandstone dominant). Sandstone thickness from the slope section is extracted from closely spaced well log data to approximate slope channel thickness. In this case, the impact on channel architecture made by differential lateral subsidence across the basin and of lowering of the shelf-edge trajectory during clinoform growth was a focus of the analysis. Results suggest that (1) channels commonly reduced in thickness from upper to lower-slope sites, (2) more rapid subsidence across the same clinoform set increased the numbers of channels but the channels became relatively small and (3) flattening of the shelf-edge trajectory (from progradation-dominant to aggradation-dominant) caused more deeply downcut channels, (4) greater degree of progradation of the shelf edge is linked with deeper slope channels, explained by greater amount of sediment being ‘forced’ into deep water with a more limiting accommodation on the shelf.