Nov. 1, 1999
PGS completed two surveys in the North Sea for BP Amoco.

EXPLORATION: North Sea surveys

PGS completed two surveys in the North Sea for BP Amoco. The Ramform Vanguard completed a 375-sq-km 3D streamer survey over Schiehallion, Loyal, and Foinaven fields west of the Shetland Islands. In the Norwegian sector, a separate 810-sq-km 3D survey was gathered over BP Amoco's Ula and Gyda fields by the Atlamtic Explorer. Both surveys will be used for 4D seismic analysis.

Regional assessments

The US Minerals Management Service (MMS) has released OCS report MMS 99-0034, Assessment of Conventianally Recoverable Hydrocarbon Resources of the Gulf of Mexico and Atlantic Outer Continental Shelf as of January 1, 1995, on CD-ROM. The study delineates 72 plays: 52 in the GOM Cenozoic; nine in the Gulf of Mexico Mesozoic; and 11 in the Atlantic Mesozoic. These plays account for a mean total endowment of nearly 26 billion bbl of oil and 300 tcf of natural gas. Of this approximately 11 billion bbl and 123 tcf are undiscovered reserves, 80% in the Gulf of Mexico.

The CD is a completely digital, interactive, programmed report that describes and illustrates the assessment methodologies, geologic, and economic results. It includes:

  • PDF-formatted file for viewing, printing, navigating, and searching the report
  • GIS data including shape files of reserves and hydrocarbon-limit maps
  • Tabular data files in spreadsheet or data base formats.

Copies of the CD are free and can be ordered from MMS at Tel: 1-800-200-GULF, Fax: 1-504-736-2620. A PDF file is available at:[email protected].

TECHNOLOGY: Australian expansion

Veritas DGC Asia Pacific is expanding its offerings in the Perth, Australia office. A new Hewlett Packard N-class computer system is planned for the Veritas Centre, which will have 16 gigabytes of memory and 3.5 terabytes of Amdahl fiber channel RAID disk. The expanded center will be online with Veritas' Singapore NEC SX-5 supercomputer. This will allow routine processing of prestack Kirkoff imaging in Perth, which is not currently available there. Provision has also been made for a large format visualization center. The Brisbane office will be consolidated to Perth.

OBC-4C seismic

Fugro's new towed seismic reflection sled system GAMBAS® maps the velocity, nature, and thickness of the very shallow surface layers of subsea sediments.
Click here to enlarge image

Fugro launched a package of support services to enhance the quality and efficiency of ocean bottom cable (OBC), four-component (4C) surveying. The new services are designed to deal with the physical factors that have an impact on OBC operations, which include:

  • Seabed coupling due to seabed hardness or irregularity
  • Cable damage due to abrasion/obstructions
  • Seismic wave velocities in near-surface sediments
  • Weather, waves, and currents
  • Accurate positioning.

The new services draw on the capabilities of the company's geophysical, geotechnical, meta-ocean, and positioning divisions to support OBC operations and alleviate potential problems.

VoxelGeo extensions

Foster Findlay Associates released three FFApplets, which enhance Paradigm Geo physical's VoxelGeo, 3D seismic interpretation software. The first two applets can automatically select sub-volumes and bodies. They enhance multi-volume analysis by extracting data values from one volume to correspond with sub-volumes detected in another volume. The third is a morphology applet, which manipulates the shape, and hence the connectivity, of detected sub-volumes.

Everything old is new

A new program Seismic Plugin is available to analyze scanned seismic images with Adobe Photoshop. Developed by Jay Lieske, the program gives geoscientists the ability to scan a seismic profile and perform calculations on the scanned images to simulate seismic processing. According to Lieske, "(Geologists) might not have access to the digital data that generated the printouts, if the data even exists digitally. But the printouts may not be in a convenient format for performing analysis." This tech-nique is an alternative to traditional reprocess-ing and extends the useful life of older seismic displays without the need for the original digital media.

Early SWF detection

The importance of forehand knowledge in detecting shallow water flows (SWF) prior to drilling was emphasized in the recent 1999 Shallow Water Flows conference, sponsored by the Oil & Gas Journal, PennWell, and Offshore. Presentations focused on the correlation between high sedimentation rates and the incidents of SWF, ways to locate problem zones, prevention and control strategies, state of the art technology to deal with SWF, and case histories that tied the theory to real-world practice and experience.

Most SWF zones are located in regions where sedimentation rates exceed 1,500 ft per million years. These high rates normally occur in rapidly subsiding mini-basins on the continental shelf. High sedimentation rates result in high relative pore pressures that easily move sand grains when a well penetrates the overburden above a shallow overpressured zone.

Safe drilling of SWF zones is a balancing act between rock physics and rock mechanics. One key is to identify the narrow, safe, hydrostatic pressure range before entering the SWF zone with the bit. To identify these limits, high-resolution seismic surveys are the current state-of-the-art. Using analysis of depositioned environments on a horizon basis, pressure wave velocities, shear wave velocities, time slices, sub-crop maps, and inferred flow paths are a few of the tools brought to bear on the wellsite.

Key information included:

  • Planning - Appraisal wells should be designed to collect data on SWF sand strength, porosity, permeability, pore pressure, seismic proper-ties, and overlying fracture gradients.
  • Remediation - New strategies can overcome SWF both while drilling and after the drilling of a well.

The industry spends an average $1.6 million per well for prevention or remediation of SWF-induced problems.