A Geomechanical Study of the Gorm Field, Danish Central Graben: Using Innovative Technology to Predict Fracture Density, Orientation and Hydraulic Behaviour in a Chalk Reservoir

Quinn, David ¹; Arnhild, Michael ²; Jaarsma, Bastiaan ²; Freeman, Brett ¹
(1)Badley Geoscience Ltd, Hundleby, United Kingdom. (2) Maersk Oil, Copenhagen, Denmark.

The Maersk Oil-operated Gorm Field began production from fractured Danian and Maastrichtian Chalk in 1981. Porosity ranges from 15 to 45%, with matrix permeability from 0.5 to 8 mD. Faults and fractures contribute significantly to enhance effective permeability. With ~ 1000 MMstb STOIIP current production of 16,000 stb/d, infill well accuracy and optimising well interventions are important for continued development of the field.

We have employed a 3-phase strategy involving structural analysis, elastostatic modelling and static stress analysis in order to predict the density, orientation and hydraulic signature of sub-seismic fractures. The primary aim of phase one was to deliver a structurally robust framework model. This involves validation of the structural interpretation using displacement analysis of fault/horizon intersections from multiple horizons (TrapTester software).

The second phase ran forward models of mechanical response to fault slip, underlying salt movement and regional strain using elastic dislocation modelling software (FaultED). This analysis predicts the stress/strain perturbations around the set of mapped faults. At each calculation point in the reservoir, a wide range of mechanical attributes are calculated, including fracture mode and orientation, and proxies for fracture intensity. The application of FaultED to the effects of salt movement is a new technology relevant to most reservoirs where salt is in play. Image log data from 13 wells provide a first order, independent assessment of the predictive method. Comparison between the predicted and observed fault/fracture orientations and densities in the wells yields encouraging correlations. Ultimately these fracture model results are used to condition permeabilities in the fluid flow simulations.

The third phase of the project used the StressTester software to resolve in-situ stresses onto the predicted (and image log) fractures. This analysis estimates the proximity to failure hence likely hydraulic conductivity/resistivity. We find a positive correlation between observed hydraulic signatures in the image logs and our geomechanical predictions.

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