An integrated well data analysis for in-situ stress estimation

Abstract

In this paper we obtain in-situ stress information based on two methods. The first one consists in matching borehole deformations to the modelling of linear poroelasticity equations around a hole in a plate that is subjected to effective compressive horizontal stresses. Knowing the formation parameters, the far field horizontal stress magnitudes can be predicted while the orientation of the minimum horizontal stress is derived from the direction of maximum elongation of the borehole cross section. The second method utilizes the crossover observed in the dispersion of polarized flexural waves to obtain the direction of maximum horizontal stress where the borehole is not deformed. For the particular field data the maximum horizontal stress runs approximately NNW-SSE. The relative principal stress magnitudes are 0.9-1.2 Sv, for the maximum horizontal stress, and 0.8-1 Sv, for the minimal horizontal stress, giving a combination of normal and strike slip tectonics. These results agree with the world stress map and the structural model of the area. The stress magnitudes are highly sensitive to the elastic parameters showing variations up to 25% for the particular data set. Careful velocity estimation, taking into account monopole as well as dipole data, is necessary to reduce uncertainties.