Improvement of wellbore stability in shale using nanoparticles

Wellbore instability causes many difficulties including costly drilling operation. Many wellbore instabilities occur due to sloughing or swelling shales and abnormal pressured shale formations. Showing different degrees of influence, pore pressure transmission and chemical osmosis are the main mechanisms in shale instabilities, with regard to physical and chemical properties of shale and thermodynamics condition. Both of these mechanisms are investigated in this paper to evaluate their significance in wellbore stability consideration. For wellbore stability maintenance, a logical approach to prevent pressure increase at near wellbore is pore throat physical plugging. Nano-particles have been used for this intent. To evaluate performance of different water based drilling fluids on pore pressure; Membrane Efficiency Screening Equipment (MESE) set up has been used. Three different drilling fluids, containing different additives, in contact with Gurpi formation were studied with and without the addition of nano-particles. Gurpi formation is located in sedimentary basins of western and southwestern regions of Iran. Much better physical plugging was achieved by using nano-particles which caused reduction in permeability and pressure increment. One of the mud formulations using nano-particles reduced pressure increment in near wellbore, up to 97%.