PH-responsive wormlike micelles for acid stimulation in carbonate reservoirs

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Stimulation is a technique used for damage removal and to increase the reservoir permeability. For carbonate reservoirs, this process is benefited by the reaction of the fluid with the matrix. However, generally the process is restricted to occurs only in regions of high permeability. In order, to solve this problem, acid diverting fluids based on viscoelastic surfactants (VES) are commonly used. The divergence in this case is caused by viscosity changes of VES triggered by chemical stimulus, such as pH variations. Formulations based in VES can be prepared to respond to [H+] and [Ca2+], tuning the rheological properties of the surfactant solution and producing polymer-like aggregates named as wormlike micelles. When increasing the viscosity due to these responses, the divergence phenomenon occurs, and the fluid changes its direction heading regions of low permeability. As consequence, desirable corrosion patterns known as wormholes are formed. A laboratory scale investigation might be required to properly adopt such special fluids, so a protocol for neutralization of acid fluids was stablished and tested by using two commercial fluids. The rheology of the fluids upon different neutralizing degrees were studied and simulates the rheological behavior when they are flowing and reacting into the carbonate matrix. Additionally, several generations of a new responsive diverting fluid based on VES, named as QuoVadis (from the Latin “Whither goest thou”), were developed and their rheological characteristics, in linear and non-linear regimes, were obtained in different H+ and Ca2+ concentrations. Such formulations are subject of a patent application filed in the National Institute of Industrial Property of Brazil (INPI patent application number BR102020006183-6). The QuoVadis samples were submitted to the neutralizing protocol and their rheological behaviors were considered to evaluate their performance in several core-flooding experiments. The statistical results demonstrate that the desirable dominant wormhole is formed, which was visualized in one of the outcrops through NMR images.