Wellbore Stabilizing Nanomaterial Assist to Drill Over-Pressured Formations

Abstract

Abstract As the oil and gas industry looks for more prolific opportunities, the complexities of drilling have become more sophisticated and consequently there is more risk associated with borehole stability, differential sticking, and mud losses. Some wells, despite their very narrow operating window, require high mud weights to prevent borehole collapse. Therefore, wells are drilled with inherent risks of stuck-pipe, fluid losses, and possible set contingency casing string - all of which can be very expensive in terms of equipment, and lost time. Drilling through shale is inevitable. Shale tends to be characterized as high in-situ stresses, fissile, laminated, with low permeability. It has been observed that wellbore stability problems occur due to lack of appropriate inhibition from drilling fluids. The most important variable in maintaining shale stability is the prevention of pressure invasion into the shale matrix. Shale stability is achieved when fluid invasion is reduced, and differential pressure support is maintained using pressure reducing additives that provide borehole support. There are many additives currently being used for this application, but all have their limitations, and not all are properly used for appropriate applications. The latest development in Nanotechnology offers the opportunity to utilise the features of nano-sized particles (sub-micron) in drilling fluids where conventional products fail to deliver required wellbore stability at the target zones. The stabilizing nanoparticle is a dry solid with a particle size of approximately 100-200 nano-meters, deformable, stable, and with a dispersed zeta potential -10 to -20mV. The product can mechanically ‘seal’ micro-fractures and possibly large pore throats in shale thus assisting in forming a semi-permeable membrane. Additionally, the application of these particles could be extended to stabilize weak-bedding planes in geomechanically sensitive formations. This paper will discuss a product that is suitable for use in both water base and oil base muds that functions to improve wellbore stability at high over-balance pressures. Herein, detailed laboratory work will demonstrate the product behaviour in different mud systems while reducing pore pressure transmission. Additionally, the product has shown to have great stability in high salt and high pH environments while being inert with respect to rheological property changes.