New Time Lapse Seismic Attribute Linking 4D and Geomechanics

A new time lapse attribute called the “Lateral Gradient of the Overburden Timeshift” (LGOT) has been created to help identify areas potentially impacted by depletion-induced overburden deformation in the Danish North Sea chalk fields. We consider this attribute to be a proxy for shear strain in the overburden. Maximum LGOT values highlight a donut-shaped zone representing the overburden region with higher shear strains and higher likelihood of wellbore deformation. Currently, in the Tyra field there are six wells with known overburden well deformation, all occurring at the inner edge of the LGOT donut. In addition, the delivery of new wells traversing through the donut has also proved challenging. To highlight wells potentially at risk due to overburden deformation in other fields, time strain inversions were run on 4D data from different vintages over several of the Danish chalk fields. Examples of the lateral gradient attribute from Tyra and other Danish chalk fields are presented here.