Far-Field Lateral Tectonic Strain Prediction from Straddle Packer Formation Stress Measurements

The objective of this work is to provide estimated lateral tectonic strain values to geoscientists and petroleum engineers from easy-to-use subsurface depth correlations. These correlations are obtained from over 600 straddle packer microfrac tests conducted across the world. This methodology does not have the purpose of replacing rigorous in-situ stress derivation from fracture closure measurement tests and borehole failures such as breakouts or induced fractures observed from image logs. These correlations, however, can provide probable tectonic strain ranges vs. depth in exploratory areas where wellbore data and stress tests are not available. Hundreds of microfrac stress testing data collected during the last 30 decades have been analyzed to obtain the far-field tectonic strain values. The lateral strains are obtained by an inversion method using the basic petrophysical formation properties and the straddle packer in-situ stress measurement balancing the elastic tensor relationship of stress equal to stiffness time strain. The average formation porosity, density, compression, and shear slowness across the microfrac testing interval are used to calculate Young’s modulus, Poisson’s ratio, tensile strength, and Biot’s poroelastic coefficient. The minimum and maximum lateral strain values are obtained once the predicted tectonic stress values match the microfrac testing results of each formation breakdown and fracture closure measurements. Finally, basic depth correlations are derived, so lateral strain values can be easily predicted to solve geomechanics challenges across 500 to 18,000 ft deep. The predicted tectonic strain data shows values between 0.01 to 1.6 mStrain. The minimum lateral strain values are more constrained than the maximum lateral strain, which seems to have a higher variability with depth. Both lateral strain profiles exhibit a clear increase at depths higher than 9,000 ft, where the tectonic stress effects amplify in subsurface rock sediments. Multiple pore-pressure gradient conditions varying from 8 to 18 ppg are studied across multiple basins since overpressure zones have poroelastic implications in the effective stress state. This is the first-time lateral Earth strain correlations vs. depth are presented in the industry that could be used to predict tectonic stresses easily at specific depths if the rock stiffness is known. These empirical equations can be used by geophysicists to derive effective stress profiles from seismic attributes with an acceptable uncertainty before a well is drilled.