Leak-off tests for horizontal stress determination?

Determination of in-situ principal stresses still represents a major challenge to the oil industry. Among the methods proposed to estimate horizontal stress magnitudes and directions is the inversion of results from leak-off tests. Previously published work with this method has been based on a procedure where all shear stress components were neglected. This paper presents a procedure based on the complete stress solution and user input from three data sets. Results based on the complete stress solution may in many cases differ considerably from the simplified (linearised) version. The results presented in this paper show that even if a complete stress model is used, the results may contain large uncertainties. These uncertainties are related to several factors, such as the uncertainty of leak-off pressure measurements, stress field homogeneity and the boundary conditions at the borehole (permeable/impermeable borehole wall, existence of cracks and fractures, etc.) during leak-off. Evaluation of the horizontal stress field should therefore be based on several methods and several sources of information.