The solitary wave is a localized hydrodynamic phenomenon that can occur because of a balance between nonlinear cohesive and linear dispersive forces in a fluid. It has been shown theoretically, and observed experimentally, that some solitary waves have properties analogous to those of elementary particles, and the waves have therefore been named solitons. During a measurement program in the Andaman Sea near northern Sumatra, large-amplitude, long internal waves were observed with associated surface waves called tide rips. Using theoretical results from the physics of nonlinear waves, it is shown that the internal waves are solitons and their interactions with surface waves are described.
Internal waves were observed during drilling by the drillship Discoverer 534 in the Andaman Sea, offshore Thailand, in water depths ranging from 1,900ft to more than 3,400ft. An engineering analysis was conducted on measured internal wave data and simultaneous measured drillship response. Knowledge of internal waves will be required for designing production facilities in deep water. Introduction This paper describes a new environmental loading factor that may influence future deep-water operations internal waves. Our experience has verified that internal waves are present in the Andaman Sea, and the literature indicates that internal waves exist in all oceans. The Discoverer 534, under contract to Esso Exploration Inc., operated successfully in the Andaman Sea in water depths ranging from 1,900 ft to more than 3,400 ft. While internal waves were present during much of the operating period, they had no significant impact on drillship period, they had no significant impact on drillship operations. However, because internal waves of magnitude greater than those observed by the Discoverer 534 are possible, Exxon Production Research Co. began a possible, Exxon Production Research Co. began a measuring and modeling program to obtain a detailed engineering description of internal waves. The measuring program, conducted during Oct. 1976, was designed to program, conducted during Oct. 1976, was designed to measure simultaneously internal waves and the corresponding drillship response. A subsequent internal wave-modeling effort now is under way. In the next sections, we briefly review the properties of internal waves, discuss the measurements of internal waves in the Andaman Sea, and describe typical drillship response to moderately sized internal waves. Characteristics of Internal Waves Background Internal waves are water waves that propagate beneath the ocean's surface. Just as surface waves propagate along the boundary layer formed between the ocean and the atmosphere, internal waves propagate along the boundary layer between water of greater and lesser density. Such boundary layers are associated with the oceanic thermocline and normally are characterized by warm, less-saline water lying over cold, more-saline water. Internal waves may exist in any body of water stratified by temperature and/or mineral content. However, energy sources must be available to generate the waves. For example, current flow over uneven bathymetry, shear current flow, and atmospheric disturbances may cause internal waves to form. Internal waves may have a finite amplitude everywhere in the water column except at the bottom, where it is zero. The internal wave amplitude on the ocean's surface is usually small, preventing easy surface observation. The maximum amplitude normally is found near the average depth of the main thermocline. Internal waves commonly are found everywhere in the world and range in size from small-scale microstructures to waves with measured amplitudes as great as 180 m. However, these waves cannot have amplitudes greater than the average thermocline depth and, just as surface waves, they are limited in height by water depth. Normally, internal waves in shallow water are moderately sized, only a few meters or tens of meters high, being limited primarily by available energy sources, thermocline depth, and water depth. JPT P. 1497
Shipboard observations during deepwater drilling operations by the Discoverer 534 and a simultaneous oceanographic measurement program have confirmed the presence of large internal waves in the Andaman Sea, offshore Thailand. The Discoverer 534 has provided measurements of dri11ship response to internal wave activity in water depths ranging from 1900 ft to greater than 3400 ft; internal wave currents as high as 2.6 knots have been measured. As a result of the analysis of internal wave and dri11ship data it is concluded that internal waves may have an impact on dri11ship operations, and knowledge of their forces on offshore structures will be required to design production facilities in some deep water areas of the world. INTRODUCTION The purpose of this paper is to bring to the attention of the offshore industry a new environmental loading factor which may influence future deepwater operations: internal waves. Exxon experience has verified that internal waves are present in the Andaman Sea, and a search of the literature indicates that internal waves exist in all the world's oceans (1). The Discoverer 534 under contract to Esso Exploration Inc., operated successfully in the Andaman Sea in water depths ranging from 1900 ft to greater than 3400 ft. While internal waves were present during much of the operating period, they had no significant impact on drillship operations. However, because internal waves of magnitude greater than those observed by the Discoverer 534 are possible, Exxon Production Research Co. initiated a measurement and modeling program to obtain a detailed engineering description of internal waves. The measurement program, conducted during October 1976, was designed to simultaneously measure internal waves and the corresponding dril1ship response. A subsequent internal wave modeling effort is now underway. In the sections which follow we (1) briefly review the properties of internal waves, (2) discuss the measurements of internal waves in the Andaman Sea, and (3) describe typical dril1ship response to moderately sized internal waves. CHARACTERISTICS OF INTERNAL WAVES Background Internal waves are water waves which propagate beneath the ocean's surface. Just as surface waves propagate along the boundary layer formed between the ocean and the atmosphere, internal waves propagate along the boundary layer between water of greater and lesser density. Such boundary layers are associated with the oceanic thermocline and are normally characterized by warm, less saline water lying over cold, more saline water. Internal waves may exist in any body of water which is stratified by temperature and/or mineral content. However, energy sources must be available to generate the waves. For example, current flow over uneven bathymetry, shear current flow, and atmospheric disturbances may cause internal waves to form. Internal waves may have a finite amplitude everywhere in the water column except at the bottom where it is zero. The internal wave amplitude on the ocean's surface is usually very small, preventing easy surface observation of them. The maximum amplitude is normally found near the average depth of the main thermocline.
At Deimos Field in the deepwater Gulf of Mexico, surface seismic imaging cannot fully image sedimentary structure near the steeply dipping base of salt. 3D vertical seismic profile (VSP) imaging was introduced to the deepwater GOM to improve seismic imaging of complex structural and stratigraphic features (Ray et al., 2003; Hornby et al., 2006) and recently has been used for imaging “blind spots” in surface seismic coverage (Hornby et al., 2005; Hornby et al., 2007). With this method, 3D surveys are conducted using a surface source vessel and downhole geophones. Here we investigate the use of 3D VSP imaging to complement the surface results with additional coverage beyond that of the surface seismic adjacent to the complex salt body.
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