GEUS has in connection with the exploration and field development in the North Sea area attained substantial experience in reservoir characterization. GEUS has for several years offered services in chalk characterization to the industry as well as being part of several research projects related to the Upper Cretaceous chalk and Lower Cretaceous carbonates.
GEUS conducts research in chalk and carbonate stratigraphy and sedimentology and investigates the link to reservoir architecture, heterogeneity, and performance. In order to create the most comprehensive reservoir understanding, integration of the various geological disciplines is a natural part of the work carried out at GEUS. The applied multidisciplinary research integrates geological, geophysical, petrophysical and other data from outcrop and subsurface studies to describe, characterize, and model the architecture, facies, rock fabric, and heterogeneity of chalk and carbonate reservoirs.
GEUS has an experienced staff covering these various aspects and can offer evaluation on specific topics or integrated into a geological model.
Topics for chalk characterization
A throughout reservoir characterization involves evaluation of measurements at scales from pores to sedimentary basins.
An important aspect in chalk characterization is the sedimentological description. GEUS has highly experienced experts in measuring and describing chalk from outcrops and cores from exploration and production wells. The core description is integrated with the log stratigraphy and GR/DT lithology in order to describe the facies distribution and overall depositional environment. The facies types seen in the cores are illustrated by GR/DT-lithology and correlated to seismic features.
The reservoir properties of the chalk are determined by standard analysis on porosity, permeability, insoluble residue and supplemented with SEM characterization of texture and evaluation of the diagenesis in the rock.
Textural characteristics are correlated to petrophysical (and optionally also to geomechanical) properties.
Interpretation of petrophysical well logs plays a major role in analysis of the chalk reservoirs. The interpretation encompasses determination of lithology, porosity, permeability and hydrocarbon saturation of the drilled section.
Prediction of reservoir quality may be optimized by combining log interpretation with core analysis, petrography and diagenesis data of reservoir sections.
Determination of lithology and reservoir properties in the vast majority of wells rely on interpreting the data stored in a wide range of petrophysical well logs. Detailed lithological information and precise determination of reservoir properties are obtained from evaluation of the cuttings, cores and side wall cores.
Details on the petrophysics and log interpretation
are described separately.
3. Seismic interpretation
In order to illustrate the reservoir in 3D, interpretation of seismic data is an important aspect in the reservoir characterization. The seismic interpretation includes horizon mapping and generation of structure maps and isochore maps. Synthetic seismograms are used to tie well data to the seismic.
The facies types identified from cores and interpreted from well logs are illustrated by GR/DT-lithology and correlated to seismic features. Attribute maps are used to visualise the facies distribution.
Seismic inversion is used for porosity prediction in areas with appropriate data.
Reservoir properties in a chalk section are often stratigraphically controlled and biostratigraphic analysis is therefore routineously part of the reservoir characterization and combined with other geological disciplines, e.g. log-correlation, seismic interpretation, sedimentology, sequence stratigraphy, isotope stratigraphy and organic and inorganic geochemistry.
GEUS provides a large variation of biostratigraphic analyses
on individual well basis or as multidisciplinary regional studies.
Phone: +45 9133 3764
Publications and projects
Lone Klinkby, Lars Kristensen, Erik B. Nielsen, Kim Zinck-Jørgensen, Lars Stemmerik, 2005: Mapping and characterization of thin chalk reservoirs using data integration: the Kraka Field, Danish North Sea. Petroleum Geoscience 11, 113–124.
GEUS has been involved in chalk characterization projects for a large number of companies in the North Sea (UK, Norwegian, German, Dutch and Danish sectors) in addition to research projects such as:
EFP 97 PRIORITY
(Improved oil recovery and productivity from Lower Cretaceous carbonates)
(The Cretaceous Petroleum System in the Danish Central Graben)