Novel Principles for Effective Earth Model Grid Management while Geosteering

Abstract

The aim of geosteering is to place the well optimally in the reservoir, based on the available measurements and interpretations of the geology. The interpretations are captured in earth models that are used for decision support. But real-time decision processes such as geosteering are poorly supported by current earth modelling methods. While drilling, new measurements received from the well allow revisions of the pre-drill geological interpretations. However, the current modelling tools are not capable of updating their representations of the interpretations in real-time. 3D earth models are typically kept unchanged during the drilling operation, while updated 2D models capture the geological interpretations only in a simplistic manner. Furthermore, uncertainties in the interpretation of the geological structures are not accounted for. Such strategies are inadequate for geosteering support when drilling in geologically complex regimes, and may lead to poor decisions. Current 3D modelling technologies are typically based on an inflexible, global grid that is used to represent geological structures and petrophysical properties. The management of this grid is slow and time consuming. To pave the way for a more effective earth model management, novel principles for i) local updates of the geological structure in an existing grid, ii) local control of the resolution of the geological structure and consequently the grid, and iii) local scale uncertainty management including the geological structure are proposed. The principles are demonstrated in a 2D software prototype. The ultimate aim is to enable an always updated multi-realization 3D model at optimal resolution while drilling, suitable for real-time decision support under uncertainty.