Emulsified acids are conventionally utilized in acid fracturing operations in tight gas reservoirs. 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. Moreover, high viscosity of conventional emulsified acids often results in high friction losses limiting the pumping rate in acid fracturing treatments.

In this paper we demonstrate the development and successful field applications of enhanced acid emulsion system that incorporates surface modified nanoparticles. The unique morphology of the nanoparticles along with their selective organic modification facilitates formation of a high temperature stable acid system with lower viscosity compared to conventional emulsified acids. The fluid exhibited reduced pumping pressures leading to higher pumping rates for deeper penetration in multistage horizontal wells. 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 nanoparticles stabilized emulsified acid system, targeting high temperature carbonate gas reservoirs in multistage horizontal wells. 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 reservoir 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. The stimulation operation utilizing the enhanced acid emulsion showcased excellent flowback performance without indication of any formation damage.

The novelty of this paper is the development of the enhanced emulsified acid stabilized with the surface modified nanoparticles having a unique morphology. The main advantages of this enhanced acid system were its high temperature stability and lower friction pressure pressures facilitating higher pumping rates and maintaining continuous net pressure, thus, deeper reservoir penetration resulting in excellent stimulation of carbonate reservoirs.

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