Directional data from cores must be referred to geographic North before they can be used in reservoir models. Few cores are oriented during drilling, but fortunately most can be re-oriented subsequently by the paleomagnetic method. This uses the remanent magnetism of the rock to define North.

The horizontal component, JH, of the mean paleomagnetic vector, JT,in a run of core defines the direction of North within that run. Directional properties of the core (such as Fracture plane orientations ) are returned to their in-situ orientations by effectively turning the core about its axis until JH points to gegraphic North.