The success of chemical enhanced oil recovery (cEOR) is significantly dependent on the type of reservoir and its pressure and temperature conditions. The recovery of heavy oil from carbonate reservoir using cEOR method is still challenging because of its highly complex internal structures and high pressure–high temperature (HPHT) conditions. This research work is the first account of the use of AGA‐97 (viscoelastic surfactant [VES)) along with a chelating agent diethylene triamine penta acetic acid (DTPA) for their application in cEOR method in heavy‐oil‐carbonate reservoirs. Several core flooding experiments were carried out to ascertain the effectiveness of the VES AGA‐97 and chelating agent for cEOR method. The effect of VES on viscosity and interfacial tension was also studied with varying concentration, temperature, and time. The thermal stability of VES was analyzed with the help of thermogravimetric analysis, nuclear magnetic resonance (NMR) and Fourier‐transform infrared spectroscopy. VES AGA‐97 was found to have high thermal stability in short‐term aging. The static adsorption and dynamic adsorption of VES AGA‐97 was studied with the help of total organic carbon analysis. After all the analysis, it was found that VES AGA‐97 and DTPA can be effectively used for cEOR method in carbonate reservoir at HPHT conditions, and the total additional oil recovery of 5.82–9.64% may be achieved.

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Hydrate plug formation is one of the most challenging problems in upstream oilfields. The most preferred option to prevent hydrate plug formation is the use of antiagglomerants in the oil/gas flowlines and in drilling fluids. Antiagglomerants do not prevent hydrate formation but restrict the hydrate crystals from agglomerating. In this study, experiments were conducted on of soy lecithin (biosurfactant) at different concentrations to measure its effectiveness as an antiagglomerant additive. In all the experiments, tetrahydrofuran (THF) hydrate was used, and to study the antiagglomerant efficiency of the additive, visual observation was utilized. Soy lecithin was compared with cetyltrimethylammonium bromide (CTAB), and the former was found as a good environmentally friendly antiagglomerant additive. Soy lecithin at 0.1 wt% in the experimental solution increased the agglomeration time of hydrate crystals by more than 1440 min and showed agglomeration state III at 1 C. Soy lecithin at 0.01 wt% increased the agglomeration time of hydrate crystals to 1000 min. The effect of soy lecithin on the rheological characteristics and filtration properties of drilling fluid was also studied. Even at the highest concentration of 1.0 wt% soy lecithin and at a temperature of 1 C, the rheological parameters of the drilling fluid remained within permissible limits. Soy lecithin was thus found to effectively restrict the agglomeration of hydrate crystals.

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