Optimizing the drilling and completion phases of a typical oil or gas wellbore requires geomechanical analysis to characterize the in-situ stresses. Stress profiles and lateral tectonic stresses can be determined and calibrated through MicroFrac testing and by modeling borehole breakouts observed in borehole image logs.
Several wells in the Campamento 1 field (the first field in the Neuquén Basin) were drilled with the tight basement formation in the Neuquén province in Argentina as the primary target. These wells were evaluated to estimate the stress profile using anisotropic mechanical properties and to identify suitable intervals to fracture. There are several tests and analyses that can typically be used to calibrate horizontal stresses. These tests and analyses include leak-off test (LOT), extended leak-off test (XLOT), minifrac test, step-rate-injection test (SRT), MicroFrac test, core strain measurement (Anelastic Strain Recovery, ASR), analysis of borehole breakouts and induced fractures from specific image logs.
The objective of this paper is to show the use of borehole breakouts and hydraulically induced fracture initiation and closure pressures to calibrate the magnitude of the horizontal stresses in a vertical well. Breakouts are typically more visible in an acoustic image log and are expected to occur in formations with lower strength and/or lower internal friction coefficient but sometimes they occur in intervals with high strength and stiffness sustaining high horizontal tectonic stresses.
Examples are shown in the Campamento 1 field wells with borehole breakouts and minifrac data used in constraining the magnitude of the lateral tectonic strains. The horizontal stress profiles obtained from these vertical wellbores provide valuable information for predicting hydraulic fracture geometry, propagation and containment for subsequent reservoir stimulation jobs. Two vertical wells where coupled calibration with minifrac data and breakout modeling were done are presented to show how this calibration is achieved and how it helps to constrain the magnitude of the horizontal stresses in a vertical well.
The results show how observed borehole breakouts and fracture pressures can help in constraining the magnitude of the lateral tectonic strains. These are important parameters in estimating the horizontal stress profile in the target reservoir and the stress contrast over the sub-adjacent and supra-adjacent formations.