Geomechanical characterization of shale samples after pore plugging with nanomaterials

Abstract

Chemical agents capable of sealing pores and micro-fractures can be used to solve wellbore instability in shales. Nanomaterials, as sealing agents, have been applied to test fluids, and their wellbore strengthening effects were evaluated by triaxial tests. A recommended workflow is given to first conduct pore pressure transmission tests, and then perform triaxial tests to evaluate the influence of drilling fluids (sealing agents) on the strength of shales. Due to the low permeability of shales, the small sample (0.25 in. height and one in. diameter) is used in pore pressure transmission tests. This research gives special loading to handle small samples in triaxial testing and innovative calculation procedure to produce stress-strain curves for the shales. After Pore Pressure Transmission (PPT) tests with nanoparticles of various sizes (10, 40 nm), concentrations (3%, 10%), and types (aluminum oxide, magnesium oxide), triaxial tests were performed on Mancos Shale and Eagle Ford Shale. The best combinations for increasing UCS values (Uniaxial Compressive Strengths) are 10% 40-nm Al2O3 for Eagle Ford Shale and 3% 40-nm MgO for Mancos Shale, according to our test matrix. As shown by the experiments, the application of the appropriate nanoparticles on shales will improve their strength and reduce the risk of wellbore collapse. The methodology developed in this research can be extended to triaxial testing on cuttings-size samples, which provides useful rock characterization information for samples that do not meet standard testing conditions.