Impact of Hydrocarbons on the Rheological Properties of Seawater-Based Fracturing Fluids

The success of extracting hydrocarbons from unconventional reservoirs heavily relies on the properties of the fracturing fluids. These fluids, typically water-based and containing polymers and cross-linkers, are essential for enhancing the solution's viscosity. With concerns over operational costs and resource availability, the oil and gas industry is increasingly turning to seawater as an alternative to freshwater in fracturing processes. The primary focus of this study is to examine how the presence of hydrocarbons affects the rheological properties of polymer-based fracturing fluids. In this study, seawater is mixed with varying concentrations of synthetic and crude oils (50, 100, 250, and 500 ppm), specifically decane (C10H22), dodecane (C12H26), tetradecane (C14H30), and light crude oil. Carboxymethyl hydroxypropyl guar gum (CMHPG) was used as the polymer, which was hydrated in these oil-laden solutions. After polymer hydration, a cross-linker (XL-Z2) was introduced. The rheological properties were analyzed using a Chandler HTHP Viscometer 5550 under the following conditions: a temperature of 70 °C, 500 psi pressure, and a shear rate of 100 s–1. The study reveals an increase in viscosity with increasing concentrations of decane and dodecane and a slight decrease in viscosity with increasing concentrations of tetradecane. The increase in viscosity is attributed to the elongation of carbon chains and the strengthening of intermolecular forces, resulting in enhanced viscosity. However, there is a sharp decrease in the viscosity in the presence of light crude oil. This decrease is due to the presence of heavy hydrocarbon atoms in the crude oil, which can be attributed to the asphaltene content in the crude oil. Additionally, over a period of 180 min, the study observed a significant increase in viscosity in the presence of synthetic oils (decane and dodecane), whereas a decrease was noted with tetradecane and light crude oil, likely due to its heavier hydrocarbon components such as asphaltenes. In conclusion, the study highlights the significant influence of hydrocarbons on the viscosity and overall rheological characteristics of polymer-based fracturing fluids in seawater. These findings offer valuable insights for the oil and gas industry, aiding in the selection and optimization of fracturing fluids by understanding the effects of different hydrocarbon types and concentrations.