New ocean survey technology may change subsea positioning

From complex deepwater pipeline route selection to real-time remote navigation, the days of guesswork offshore may be over. With a combination of StarFix.Nav, global positioning systems (GPS), subsea acoustic positioning systems, and the latest PC-based visualization tools, subsea construction, inspection and mapping has become significantly more accurate and visual.

From complex deepwater pipeline route selection to real-time remote navigation, the days of guesswork offshore may be over. With a combination of StarFix.Nav, global positioning systems (GPS), subsea acoustic positioning systems, and the latest PC-based visualization tools, subsea construction, inspection and mapping has become significantly more accurate and visual.

These new tools offer a unique combination of features to perform virtually any ocean-based activity in a speedy, safe, and cost-effective manner. They are widely recognized as being the key to real-time monitoring of subsea activities, right from the manager's desktop computer - back in the office or on the vessel.

The first such commercially available product is from John E. Chance and Associates, Inc. (Houston, Texas). It combines proprietary deepwater data collection methods, instrumentation and analysis tools with HydroVista, a real-time data visualization technology developed jointly by John E. Chance and Associates, Inc. and Spectra Precision Software (Atlanta, Georgia).

Visualization products such as HydroVista work interactively with advanced modeling systems to gather, analyze, and visually present a wide variety of complicated data. This flexible software is specifically designed to manage and display very large files of multiparameter data. Such information might be provided from geophysical surveys containing multibeam bathymetry, sidescan sonar mosaics, sub-bottom profiler data and magnetometer records. Other sources of data incorporated into the virtual environment typically come from engineering 3D models, tiff images, VRML objects, and other CAD-based renderings.

HydroVista then displays all of this information geo-referenced in a virtual environment. The resulting display is a real-world survey accurate location that can be navigated acoustically in three dimensions. This product is ideal for subsea construction and engineering applications, particularly those that involve remotely operated vehicles (ROVs).

Virtual ROV navigation

Typically, ROV pilots must work on visual pictures from cameras placed on the vehicle itself, manipulating the ROV deep into the sea and navigating in two dimensions to the desired location. With HydroVista, a three-dimensional straight line can be displayed and taken to the point of interest. This significantly reduces the travel time. JECA's Starfix.Nav software package displays all the calculations, distance cross course, distance to target, and difference in present elevation and desired location.

Another common problem pertaining to deepwater ROV operation is little or no visibility, typically caused by the ROV itself. The ROV thrusters, for instance, often force large amounts of silt into the water column. Ordinarily, the operator must wait - or sometimes even abandon the site - until the project area clears.

HydroVista eliminates this problem by utilizing strategically placed virtual cameras. These provide required perspectives to the appropriate parties. Through the vessel's video distribution system or dedicated cable, the operator is able to "see" the desired seafloor features or structures. The system has the ability to ship multiple perspectives to different locations on the vessel, keeping all parties up-to-date with the latest survey information and ROV location. Any one of those cameras can be recorded and played back using standard Microsoft products. This information included in a typical e-mail provides remote personnel a unique opportunity to view the offshore operation.

However, it's the ROV operator that derives the most benefit from this virtual environment. "With offshore construction vessels costing thousands of dollars per hour, small increases in efficiency of activities falling along the project's critical path save large amounts of money for the oil company or installation contractor. The ROV pilot actually feels as though he can navigate with little or no visibility," emphasizes Kevin Belcher, Operations Manager of Marine Construction Survey.

"With multiple cameras offering all-around perspectives, navigating successfully through various man-made and natural obstacles that typically hamper construction activities becomes safer and more cost-effective."

Applications for this innovative tool include pipeline investigations, structure and pipeline installations, precise bathymetric surveys, and template and subsea structure placement. This package not only allows navigation of the project area but can also provide visual quality control checks of the subsea positioning data.

Other activities

Deep-sea engineering and construction firms often spend large amounts of time and money designing and selecting the optimum routes for pipelines and the placement of subsea structures. Accomplishing this task in one of the most hostile environments in the world, the deep ocean, simply compounds the problem.

One large US-based oil company is taking advantage of this "virtual" deep-sea technology to best analyze and select the optimum route for a pipeline installation in 3,200 ft water depth. Engineers at this firm were faced with the daunting task of avoiding such natural obstacles as chemosynthetic communities, outcrops, escarpments, and steep inclines, while maintaining design criteria of minimizing spans and overall pipeline length.

The first step involved incorporating all of the previously collected geophysical information into the HydroVista virtual environment. This data consisted of multibeam bathymetric data, magnetometer data, side scan sonar targets, and sub-bottom profiler data. Importing data from Chance's proprietary Gulf of Mexico database provided additional information.

The initial proposed route was draped on the digital terrain model (DTM) in the HydroVista environment. Profiles were output in a proprietary format compatible with the customers span analysis software. In the past, subcontract personnel painstakingly compiled and converted data to a compatible format using Microsoft Excel.

Often times, this process would take days or even weeks to accomplish. Now, this labor intense process has been reduced to a quick DTM generation and route definition on the model. The station/elevation file is exported for analysis in a matter of seconds.

In addition, the software offers a broad range of versatility. The parameters for the output files can be at set stations, grade breaks, or in a custom format defined by the client. After the span analysis is run and an output file generated, the points representing the pipeline are imported into the virtual project environment of HydroVista. A geotypical is applied to the line, giving it the appearance of a pipeline of proper dimensions. After incorporating this information into the environment, engineers went one step further and created a movie along the proposed route to better enable the client to interpret the data.

In this circumstance, it took a single iteration of the proposed pipeline to satisfy the customer's requirements, and the pipeline was designed to fit into a previously impenetrable area. The savings from this project are estimated to be in the millions of dollars.

Copyright 1999 Oil & Gas Journal. All Rights Reserved.

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