Paleokarst Signatures in the Loppa High, Barents Sea: 3-D Seismic Mapping, Seismic Facies Classification and Core Data Confirm the Presence of Buried Karsts Terrains

Sayago, Jhosnella ¹; Di Lucia, Matteo ¹; Mutti, Maria ¹; Cotti, Axum ²; Sitta, Andrea ²; Broberg, Kjetil ²
(1)Institute of Earth and Environmental Science, University of Potsdam, Potsdam, Germany. (2) Edison International S.p.A., Oil & Gas Exploration, Stavanger, Norway.

In the eastern flank of the Loppa High, located in the Norwegian Barents Sea, a deeply buried paleokarst system overprinting the Upper Palaeozoic carbonate rocks has been recognized through interpretation of seismic data. Assessing the spatial and temporal distribution of these observed features is a key to forecast the reservoir potential of the area, understand the post-depositional processes that have overprinted these sedimentary units and provide important information for the well planning activities. Although the 3D seismic studies have identified the existence of paleokarst features such as major drainage systems, deep canyons and sinkholes, two of the challenges that remain in this area include 1) to map the spatial distribution of these features at a regional scale and 2) to identify the sediments filling the paleokarst relief, which in some cases could represent geological unconformable traps, such as breccias formed by collapse of previous evaporites rocks or dissolved carbonate rocks.

In this work we are seeking to address these two challenges by developing an integrated approach consisting of: 1) manually mapping the unconformities in the 2D and 3D surveys using traditional seismic sequence stratigraphic principles; 2) a volume based multi-attribute seismic facies classification; and 3) a core-based facies descriptions.

The seismic stratigraphic analysis allowed us to recognize the major regional unconformities and the main seismic sequences, as well as, to infer the areas of major aerial exposure that should have experienced most intense karstic processes. The multi-attribute seismic facies classification, using the ‘Train Estimation Model’ from PetrelTM software, was used to map subsurface heterogeneities related to different seismic facies configurations. Finally, the integration of these results with the core-based facies description allowed the identification of sedimentary units that can be related to paleocave-systems deposits.

The integrated seismic approach has yielded interesting results regarding the probable distribution of this buried paleokarst system. The core-based facies description has play a key role in the interpretation of the seismic results and allows to make comparisons to known examples of modern and ancient caves systems related with hydrocarbon exploration settings.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.