Geophysical research: article

In-situ horizontal stress estimation based on the geometrical properties of fractures in well vicinity
N. Dubinya1
K. Ezhov2
1 Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia 2 Naftna Industrija Srbije Science and Technology Center, Novi Sad, Serbia
Journal: Geophysical research
Tome: 18
Number: 2
Year: 2017
Pages: 5-26
UDK: 539.219.2
DOI: 10.21455/gr2017.2-1
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Keywords: geomechanics, in-situ stress, well logging
Аnnotation: A great amount of information regarding the in-situ stresses acting in the upper layers of the Earth’s crust is provided by the geophysical well surveys. Presently, the methods for determination of the mechanical properties of rocks surrounding the wells and estimation of in-situ stress state are well developed. Nevertheless numerical evaluation of maximum horizontal stresses causes significant problems. The study is devoted to the problem of decreasing the uncertainty appearing in the inverse problem of horizontal stresses reconstruction. The additional data on the inner structure of surrounding rocks obtained with borehole microimagers are used for solving the problem. The microimagers provide information on the structural heterogeneities in rocks and to distinguish natural and drilling-induced fractures. The approach described in the study makes it possible to group the fractures according to their filtration properties. The model connecting the geometry of fractures, their spatial orientations, and in-situ horizontal stresses is proposed, conceptualized, and formalized in the paper. As a result, a novel approach to microimager data interpretation for horizontal stress estimation is developed. The approach was verified using synthetic data. The uncertainty analysis revealed that the approach proves its usefulness as the uncertainty in horizontal stress estimation decreases drastically. The study carried out makes it possible to introduce the new parameter into solution of the stress estimation problem. This parameter characterizes the features of fracture orientations and is connected with the in-situ stresses. Its application leads to a significant increase in accuracy of estimation of maximum horizontal stresses.