Geosciences

A Class-3 intercept-gradient (AxB) AVO product produced conventionally (below) and with PGS Tensor's constrained approach (above), which shows three anomalies corresponding to known pay sands.

Integrated database

Phillips's Ekofisk Chalk Exploration Project (CEP), a massive multidisciplinary effort by Phillips, its partners Agip, Elf, Fina, and Total, and Landmark Graphics, has produced a semi-regional geoscientific study of Norway's PLO18, in the Greater Ekofisk Area, Phillips's principal production area worldwide, at over 310,000 b/d. The partners are investing almost $3 billion in new infrastructure to prolong production through 2028, when the license expires.

Although all major structural closures and several stratigraphic features in the Chalk have been drilled since Ekofisk's discovery in 1969, recent depositional models indicated significant reserves could remain in stratigraphic traps on the flanks of main fields and beneath existing pay zones. Thus to evaluate this potential, the CEP began in 1994. Together with the other companies, and utilizing Landmark's Open Works, a network of geoscientists was established that built a high quality, regionally consistent database that integrated some 3,000 sq km of 3D seismic data which was the result of merging ten 3D surveys and a regional 2D grid, data on over 400 wells that included petrophysical, lithological, core, DST/RFT, biostratigraphic, and other data, to produce a common database and interpretation environment that facilitated close interaction between disciplines.

Over the following year and a half, the CEP developed a comprehensive regional exploration model for the Chalk that identified more than 40 stratigraphic leads and provided a base on which future exploration is possible.

A cube for all reasons

PGS Tensor's massively parallel processing software, particularly the MPP operating system, CUBE MANAGER, was demonstrated at this year's AAPG and EAGE as an effective means of integrating a multitude of different but related data into a flexible format that facilitates manipulation. The system accelerates the porting of existing code and writing of new applications in the parallel environment, and the scalable nature of MPP permits CUBE MANAGER to make the writing of algorithms without committing to architecture or configuration specifics. As a result, the system is flexible and scales to accommodate large computational problems such as 3D prestack depth migration, yet is user-friendly for interactive processing.

Structural evolution of salt

Ge Hongxing, Martin P.A. Jackson, and Bruno C. Vendeville of the Bureau of Economic Geology at the University of Texas recently completed experiments in which they reproduced the dynamic evolution of the Bohai Bay (China) Wenliu salt diapir and graben. Physical models of basement-involved salt tectonics and salt dissoluton were used to simulate the development of the structure.

In a description of their conclusions published in China's Acta Petrolei Sinica (Vol. 2, 1997), the authors note that the Wenliu structure is localized above the central uplift in the northeast part of the Dongpu depression of the Bohai Bay Basin and consists of a downward simple crestal graben, a thickened salt core, and a basement horst. Their study revealed that, during early Sha-3 Eogene thick-skinned extension, the salt layer partially decoupled deformation above and below the salt. The overburden then formed forced fold that was cored with salt pillow above the central basement horst block, and a graben formed at the crest of the forced anticline due to local arching. Finally, by combination of regional extension and local stretching, the crestal graben widened and triggered reactive diapirism and synkinematic sediments in the flank depressions caused salt to flow upward to the central basement uplift. As regional extension decreased, the reactive diapir ceased to rise and was buried by Neogene and Quaternary sediments.

Greenpeace goes after PGS

The environmental activist organization Greenpeace continues to challenge exploration and development work in the West of Shetland region of the North Atlantic. Last month, six of its members boarded PGS's Atlantic Explorer seismic acquisition vessel in port at Ullapool, Scotland and chained themselves to equipment in an effort to thwart a shoot for Conoco. After 17 hours, they were removed from the vessel, but the next day were out in four inflatables and succeeded in disrupting PGS's Geo Explorer and Malene Ostervold, which were shooting in the area on behalf of Agip. After four days of disruption, the two vessels pulled in their streamers and left the area.

CogniSeis sold to Paradigm

By the end of this month, GeoScience Corporation will have sold its CogniSeis Development subsidiary to Paradigm Geophysical for cash and guaranteed future royalties with a total value of US$19.5-23.0 million. The sale was announced last month by Richard F. Miles, president of GeoScience, as a means of allowing the company to concentrate fully on seismic instrumentation.

EAGE

The LFP (Lithology and Fluid Prediction) division of Ensign presented a demonstration at this year's EAGE conference in Geneva of how changes in lithology and fluid variations can be mapped from seismic data and how such seismic properties as P-wave velocities, acoustic impedance, and Poisson's ratio can be linked to desired rock properties, including porosity, lithology, net pay, fluid fill, and fracture parameters.

At a separate EAGE demo, LCT and CGG-Petrosystems introduced a new system for seismic-gravity integration, their LCTSEIS-3D. The system uses high resolution gravity data to constrain, confirm, and refine seismic velocity models.