Wellbore Image Analysis Applied to Reservoir Characterization
Wellbore image data is key to reservoir characterization -- it can be used to determine both the in situ state of stress and the orientation and distribution of the natural fracture and fault population within the basin. Knowledge of the magnitude and orientation of the in situ stress field is invaluable to well completion design, borehole stability, reservoir production and fracture completion. Fracture permeability, permeability anisotropy and overall reservoir hydrology are related to the in situ stress field. In situ stress and fracture measurements are crucial for answering many outstanding questions: "Why is a reservoir fault zone permeable at some locations and not at others?", "Can we predict spatial variations in permeability and the nature and orientation of permeability anisotropy from surface-based or borehole measurements?", "Can direct measurements of in situ stress magnitude and orientation be used to predict borehole stability in tectonically stressed areas?"
Studies of the orientation of the in situ stress field have had wide application in the oil and gas industry, from the analysis of stress induced wellbore breakouts measured in dipmeter and acoustic image data to analysis of drilling induced tensile cracks observed in electrical image data. New methods are available to exploit observations of wellbore failure (used in conjunction with available drilling and well test data) that extend these observations of stress orientation to determination of the full stress tensor. The methods utilize analyses of tensile (drilling induced tensile cracks) and compressional (wellbore breakouts) failures in vertical and inclined boreholes to constrain the orientation and magnitudes of in situ stresses, predict borehole stability, and to predict the subset of hydraulically conductive fractures from a reservoir fracture population.