Novel Organically Modified Nanoparticles Stabilized Emulsified Acid Paves Way for Productivity Enhancement in High Temperature Gas Reservoirs

Abstract

Well stimulation of carbonate reservoirs is conventionally associated with the using of strong mineral acids such as hydrochloric acid (HCl). However, the heterogeneity of the reservoir as well as the fast reaction rate of HCl with the rock will lead to face dissolution rather than achieving deeper wormholes or longer fractures. A commonly used approach to slow down the acid/rock reaction rate is through the use of acid-in-oil emulsions. Unfortunately, the thermal stability of the emulsified acids is significantly impacted at high temperatures (+300 °F), which will result in poor penetration of the reservoir, thus reducing the treatment effectiveness. This paper showcases the development and successful field application of an enhanced emulsified acid system for stimulating high-temperature carbonate reservoirs. The new system utilizes organically modified nanoparticles with the emulsified acid to form a solid stabilized emulsion. The unique morphology of the nanoparticles along with their selective organic modification facilitates formation of a high temperature stable emulsified acid system with lower viscosity compared to conventional emulsified acids. The low viscosity reduces surface pumping pressures leading to higher pumping rates for deeper reservoir penetration. The new system can work with HCl concentration up to 28% and temperatures up to 325 °F. We present here the systematic developmental study and field trial results for the organo-modified nanoparticles stabilized emulsified acid system, targeting high temperature carbonate gas reservoirs. Several laboratory performance tests were judiciously undertaken to compare the performance of the new emulsified acid with conventional systems. Experimental studies including rheological characterization, thermal stability, corrosion mitigation and formation damage profiling are reported. The new emulsified acid displayed lower viscosity, enhanced stability at high temperatures, corrosion loss within industry acceptable limits, superior stimulation effectiveness and minimal formation damage compared to conventional emulsified acid. Stimulation treatments using the enhanced emulsified acid showcased excellent flowback performance with no reservoir damage. The new organo-modified nanoparticles based emulsified acid system not only demonstrated enhanced temperature stability, but also minimized the surface treating pressure facilitating higher pumping rates and deeper reservoir penetration resulting in excellent stimulation of carbonate reservoirs.