--> Abstract: Blanket 3-D Coverage-Its Successful Application in Exploring a Mature Area, Central Dutch Offshore, by R. Herber, C. Elders, J. Lamens, M. Bachmann, and F. S. Ferrer; #90990 (1993).

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HERBER, RIEN, CHRIS ELDERS, JO LAMENS, MARTIN BACHMANN, and FERNANDO SANCHEZ FERRER, Nederlandse Aardolie Maatschappij, Assen, Netherlands

ABSTRACT: Blanket 3-D Coverage-Its Successful Application in Exploring a Mature Area, Central Dutch Offshore

In the K and L blocks of the Dutch sector of the southern North Sea, the Rotliegende Sandstone forms the main objective. Drilling started in 1968, and to date 36 Rotliegende gas fields have been discovered in Nederlandse Aardolie Maatschappij (NAM) operated acreage with volumes in place ranging between 2 and 50 x 10{9}cu m.

Approximately 70% of these fields were discovered using two-dimensional seismic, but as exploration progressed an increasing number of wells were found water bearing. The main cause of failure is lack of structural integrity, due to high Rotliegende fault density and highly variable overburden dominated by Zechstein salt and Chalk grabens.

Three-dimensional (3-D) seismic acquisition started in 1981 but at first was typically limited to small production surveys covering existing gas fields. In 1986, acquisition of block-wide exploration 3-D surveys began. This has resulted in a present-day coverage of some 5000 sq km, representing 95% of NAM-operated central offshore K and L blocks. Interpretation of these surveys revealed many undrilled structures, inspiring a second phase of exploration drilling with a high success ratio of 80%.

As drilling activity progressed in the earliest covered blocks, however, a number of structurally conclusive dry wells were drilled, and remaining individual prospects are small. Therefore, a third exploration phase now has started, concentrating on hydrocarbon habitat reviews making use of detailed 3-D interpretation of seismic attributes. The reconstruction of tectonic history and an updated charge model are expected to lead to an improved definition of remaining potential in these mature blocks.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.