Breaking Dogma on the Single-Stress-Gradient Based Mechanical Earth Modeling – Wireline Formation Testers Micro-Frac, Not Just an Input… It's a Fact!

Abstract

Measuring in-situ stresses in unconventional formations constitutes a cornerstone for reservoir-quality and completion-quality evaluation. Challenges of succeeding these tests are related to difficulties to break these formations and propagate the created fracture allowing fracture gradient estimation. Moreover, formation heterogeneities and properties anisotropy, often lead to model inaccuracies and expose drilling or fracking operations to "avoidable" failures. Hence earlier in unconventional reservoir exploration, successful in-situ stresses become a must have for geomechanical model and Fracturing design calibrations. While cross-discipline integration is key to building a representative and comprehensive MEMs, since the early 2000's, Wireline Formation Testers are used to collect localized in-situ stress measurements that constitute a valuable input to fine-tune MEMs. However, with limited knowledge and inadequate planning, these operations known as "Micro-Frac/Stress Testing" are often challenged with high failure rate, especially with legacy tools physical limits. A combination of a novel stochastic planning approach involving the multidomain integration of Petrophysics, Borehole-Images and Geomechanics, coupled with Cutting-Edge WFTs technologies significantly increases the success likelihood for Stress Testing providing thereby an unfailing calibration source for MEMs. This new approach allowed first to define the depths to test with higher rate of success to break the formations and then, to communicate to drillers and client supervisor the test duration and potential adjustment such as mud weight, to break the rock and propagate the created fractures in the formations. The above enables, from operational standpoint, successful risk-free stress test measurement, allowing the calibration of the Mechanical Earth Model and Frac Design in the hydrocarbons embedded Source Rocks across South Algerian Basins. Furthermore, stress mapping allowed the identification of a lateral variability of stress gradients within the same field, confirming the unreliability of single-stress-gradient based models and highlighting the importance of multi-well modeling of mechanical earth properties. By using a well calibrated MEMs leading to a keen understanding of stress state, chances of stimulation operations success were significantly increased. The benefit of utilizing this new method with advanced logging technologies among which the new generation of WFTs, combined with a multidomain data integration as well as a novel planning approach based on stochastic simulation enabled the achievement of a failure-free Stress Testing operations, yielding fine-tuning of MEMs in the challenging South Algerian Hot Shale. Through a keen knowledge of stress state, stimulation operations success was significantly increased.