The rapid development of a surfactant blend using statistical software tools to drastically reduce the number of laboratory experiments associated with more traditional Edisonian-type approaches is discussed. The study evaluates performance of various surfactant blends for fracturing applications in most major North American shale formation materials and crude oils.
The study entailed identifying key surfactant characteristics, such as hydrophilic-lipophilic balance (HLB), relative solubility number (RSN), and solvency. The parameters were used to create a design of experiments (DoE) with statistical software. Formulating experiments were performed as recommended by the DoE, and selected blends were subjected to tensiometer and petroleum industry application testing. Critical micelle concentration (CMC) and interfacial tension (IFT) values were captured to better understand blend physical properties. Additionally, sand pack column flow (SCF) and emulsion break time (EBT) experiments were conducted to assess blend efficacy when exposed to Niobrara, Bakken, Permian, Mid-Conn, Eagle Ford, and Gulf of Mexico (GOM) reservoir materials and crude oils. Spontaneous imbibition experiments were performed on outcrop cores.
Using a custom DoE optimized for interactions and mixtures, the formulation design space was covered with 162 formulations compared to 576 necessary for a full factorial evaluation. Analysis of the surfactant formulation with the regional specific materials revealed primary components for treatment optimization within each area. With respect to SCF experiments, incorporating proppant, fracturing fluid, and regional specific formation cuttings-to-crude oil combinations revealed that the nature of the crude oil dominated the effects of the surfactant formulations. Data analysis revealed blends that lowered the hydrocarbon/water IFT below 2 mN/M outperformed formulations that resulted in higher IFTs. With respect to EBT, progressing from Bakken to Eagle Ford crude oils, API gravities varied significantly, and these changes in chemical properties greatly impacted the testing results. Formulations with higher concentrations of demulsifier-type components performed better as crude oil API gravities decrease because of increased amounts of asphaltenes, resins, paraffins, and naphthenic acid content. When using the DoE results for ranking of surfactants, experiments in porous media revealed all surfactants formulated through the DoE outperformed the standard offerings by greater than 30% when evaluating the efficacy of the blends to displace oil from cores. However, the addition of some demulsifier-type components to the blends adversely impacted the magnitude of improved hydrocarbon recovery, which was attributed to premature adsorption onto the rock surface.
In an industry where the effect of stimulation chemicals on complex downhole environments remains uncertain, processes to identify the most import factors that impact the performance of chemical additives are of utmost importance. This exercise used statistical software to evaluate multiple complex variables associated with surfactant formulation and suggested blends that improve hydrocarbon recovery.