Marine Geophysical Researches

Integrating discrete distribution of lithofacies into the petrophysical property modeling is essential to preserve reservoir heterogeneity and improve flow modeling. Specifically, various studies have been implemented to model the permeability as a function of well logging data without taking into account the effect of lithofacies, which is rational to produce distinct regression lines given each facies type. In this paper, advanced statistical learning approaches were adopted as an integrated workflow to model the core permeability given well logging records and discrete lithofacies classification for a well in the South Rumaila oil field, located in Iraq. In particular, the probabilistic neural networks was first applied for modeling and predicting the discrete lithofacies classification given the well logging records: neutron porosity, shale volume, and water saturation. Next, smooth generalized additive model (SGAM) was used to model the core permeability as a function of the same well logging records. In addition, the predicted lithofacies was included as a discrete independent variable in the core permeability modeling to provide different regression lines given each lithotype. The SGAM was also modeled for three subset data given each separate lithofacies to verify the efficiency of SGAM and to provide more accurate prediction of permeability. The same procedure of SGAM was completely repeated by the generalized linear model (GLM) to prove the higher effectiveness of SGAM for permeability modeling and prediction. The root mean square prediction error in SGAM was lower than in GLM in all the combined and separate lithofacies models. In addition, the SGAM model overcame the multicollinearity between shale volume and water saturation variables by using the smoothed terms. Finally, making accurate permeability prediction for all wells in the field should ensure capturing the spatial variation and correlation between the data and then preserving the reservoir heterogeneity.

Bathymetric and magnetic data from the mouth of the Gulf of California show an early episode of spreading between ±6 mybp and 3.5 mybp which rifted crust at the foot of the Tres Marias Islands from Baja California. Fracture zones from this episode do not offset the present East Pacific Rise (EPR). A reorganization of spreading beginning 3.5 mybp has led to the present configuration; its initiation is marked in the topography by a valley partially filled by a NS trending turbidite plain.

The study of modern seafloor hydrothermal activity and its mineralization has become one of the focuses of global geoscience. Accurate prediction of possible seafloor hydrothermal active fields is the basis of all research work. The detecting method for new seafloor hydrothermal activity still is mainly dependent on marine site investigation. This includes a series of temperature, turbidity, and geochemical anomaly investigations using submarine cameras and manned diving investigation. Both of these require expensive financial, human, and material resources. In order to realize the accurate prediction of potential hydrothermal activity areas in a low cost manner, with strong pertinence, and a wide range, we propose a prediction method of seafloor hydrothermal active region based on Wavelet Neural Network. First, we integrated the hydrothermal position information from the InterRidge Vents Database with the hydrothermal temperature information form the Argo Database to construct a data set. Then, we combined wavelet analysis with an artificial neural network to create a wavelet neural network optimization algorithm. Finally, the temperature and salinity data were input to the wavelet neural network to predict the seafloor hydrothermal active region. Sevenfold cross validation was used to evaluate the performance of the model and 90.43% prediction accuracy was achieved. The results of experiments show that salinity is not related to the existence of hydrothermal activity fields but rather that the surrounding water temperature has a strong correlation with hydrothermal existence. Therefore, it is effectively feasible to use the wavelet neural network model with an input of seawater temperature to predict seafloor hydrothermal activity fields. Although artificial neural network cannot completely replace traditional hydrothermal exploration technology, it can provide a valuable reference with a strong target.

Sources of very low frequency (0.01 to 1.0 Hz) ambient seismic noise in the shallow (<100 m) water continental margin sediments are investigated using Ocean Bottom Seismometers (OBS). The predominant seismic motions are found to be due to surface gravity (water) waves and water-sediment interface waves. Actual experimental measurements of seabed acceleration and hydrodynamic pressure are given, including side by side comparisons between buried and plate-mounted OBS units. OBS-sediment resonant effects are found to be negligible at the low frequencies under investigation. Wherever there exists relative motion between the seabed and the water, however, an exposed OBS is subject to ‘added mass’ forces that cause it to move with the water rather than the sediments. Calculations based on measured seabed motions show that a neutral density, buried seismometer has superior sediment coupling charactersitics to any exposed OBS design.

The Marine Physical Laboratory of the Scripps Institution of Oceanography has developed an acoustic relay transponder for precise relative positioning of near-bottom instruments and geologic sampling devices. Although specifically designed to position equipment lowered on standard wire ropes without a need to maintain direct electrical contact with the surface ship, the relay transponder may be used to track free vehicles, such as deep submersibles, from the surface. The relay transponder is positioned relative to an array of bottom-anchored acoustic transponders. It is interrogated acoustically from the surface ship; it then sequentially interrogates the bottom transponders which, in turn, reply to the ship. From the measurement of the total travel time (ship to relay transponder to bottom transponder to ship) and assuming, or knowing, the sound velocity of the water, we obtain a relayed range measurement. These relayed ranges, used in conjunction with ship to bottom-transponder ranges, allow us to calculate the position of the relay transponder. A recent application of this technique is described in which several gravity core samples from the crest of the Horizon Guyot were positioned with respect to the detailed bathymetry and the geology within the area. The estimated error in positioning the samples is less than 20 m inside a navigational net extending over 100 km2.

The morphology of the Gulf of Oman Basin, a 3,400 m deep oceanic basin between Oman and southern Pakistan and southern Iran, ranges from a convergent margin (Makran margin) along the north side, a passive type (Oman margin) along the south side, translation types along the basin's west (Zendan Fault-Oman Line) and east (Murray Ridge) sides and a narrow continental rise and a wide abyssal plain in the centre of the basin. Sediment input into the basin during the Late Quaternary has been mainly from the north as a result of the uplift of the Coast Makran Mountains in the Late Miocene-Pliocene. Today most of this detritrus is deposited on the shelf and upper continental slope and perched basins behind the fold/fault ridges on the lower slope. The presence of fans and channels on the continental rise on the north side of the basin indicate, however, that continental derived debris was, and possibly is, being transported to the deep-sea by turbidity currents via gaps in the ridges on the lower slope. In addition to land derived terrigenous sediments, the basin deposits also contain biogenic (organic matter and calcium carbonate), eolian detritus and hydrates and authigenic carbonates from the tectonic dewatering of the Makran accretionary wedge. The eolian sediment is carried into the Gulf of Oman Basin from Arabia and the Mesopotamia Valley by the northwesterly Shamal winds. This type of detritus was particularly abundant during the glacial arid periods 21,000–20,000 and 11,000 (Younger Dryas) years ago when exposure of the Persian (Arabian) Gulf increased the area of dust entrainment and shifted the position of the source of the eolian sediments closer to the basin.

A palynological analysis was carried out for the first time on sediments from Hupo Basin, East Sea, offshore Korea, to locate the Pliocene–Pleistocene boundary and thus determine the depositional age of this stratigraphic unit. Core 19ESDP-101, taken from Hupo Basin, yielded diverse, abundant to common pollen and dinocysts. Age-diagnostic palynomorphs were present in certain core intervals (Zone I, depths 120–63.96 mbsf). However, those age indicators were dark brown, heavily broken representatives that appeared together with poorly sorted, opaque, dark phytoclasts in the lower part of Zone II (63.96–38.76 mbsf), and they were considered to have been recycled from reworked late Pliocene strata due to contour currents during the transgression. Biostratigraphically meaningful taxa were the pollen Carya, Liquidambar, and Fagus and the dinocysts Filisphaera filifera subsp. pilosa and Spiniferites pachyderma. The latest stratigraphic occurrence of these pollen taxa in northeast Asia is the Late Pliocene, and that of the dinocysts is the Late Pliocene across a wide range of aquatic areas, especially in the Pacific. The last appearance datum of the age indicators in this study suggested 63.96 mbsf (top boundary of Zone I) as the Pliocene–Pleistocene boundary in core 19ESDP-101.

Mud volcanoes, mud cones, and mud ridges have been identified on the inner portion of the crestal area, and possibly on the inner escarpment, of the Mediterranean Ridge accretionary complex. Four areas containing one or more mud diapirs have been investigated through bathymetric profiling, single channel seismic reflection profiling, heat flow measurements, and coring. A sequence of events is identified in the evolution of the mud diapirs: initially the expulsion on the seafloor of gasrich mud produces a seafloor depression outlined in the seismic record by downward dip of the host sediment reflectors towards the mud conduit; subsequent eruptions of fluid mud may create a flat topped mud volcano with step-like profile; finally, the intrusion of viscous mud produces a mud cone. The origin of the diapirs is deep within the Mediterranean Ridge. Although a minimum depth of about 400 m below the seafloor has been computed from the hydrostatic balance between the diapiric sediments and the host sediments, a maximum depth, suggested by geometric considerations, ranges between 5.3 and 7 km. The presence of thermogenic gas in the diapiric sediments suggests a better constrained origin depth of at least 2.2 km. The heat flow measured within the Olimpi mud diapir field and along a transect orthogonal to the diapiric field is low, ranging between 16 ± 5 and 41 ± 6 mW m−2. Due to the presence of gas, the thermal conductivity of the diapiric sediments is lower than that of the host hemipelagic oozes (0.6–0.9 and 1.0–1.15 W m−1 K−1 respectively). We consider the distribution of mud diapirs to be controlled by the presence of tectonic features such as reverse faults or thrusts (inner escarpment) that develop where the thickness of the Late Miocene evaporites appears to be minimum. An upward migration through time of the position of the décollement within the stratigraphic column from the Upper Oligocene (diapiric sediments) to the Upper Miocene (present position) is identified.