The influence of pH on sorption characteristics of organic indicators in tracer analysis

Abstract

In the process of oil field development, oil wells are losing pressure. In order to maintain the existing oil yield, some extraction wells are transferred to the injection mode. For this purpose technical water, seawater or sewage water is used. Well water flooding is posing a serious challenge. In order to minimize water recirculation, tracer analyses are employed to determine impact of a waterinjection well on extraction wells. Fluorescent dyes and organic compounds are commonly used as the tracers. The article deals with influence of pH on sorption characteristics of fluorescein disodium, ethacridine lactate, rhodamine B, rhodamine 6G and sodium rhodanate. The dependences of absorption and desorption of markers in oil upon change of hydrogen index of formation water have been demonstrated. Emphasis is made on uranine, its absorption and desorption in the presence of nitrogen-containing compounds. Thus, the analyses have revealed that fluorescein disodium is actively absorbed by oil even at pH = 7.3, the concentration of which in the formation water has decreased 30-fold. Uranine absorption is due in no small part to high mineralization of formation water. During desorption, the best results have been obtained in the presence of ammonia. Thus, to obtain good results in tracer analyses when using fluorescein disodium, the tracer fluid must be transferred to the alkaline region. Fluorescein can also be used to determine oil movement from a water-injection well. The use of such cationic fluorescent dyes as ethacridine lactate, rhodamine B, and rhodamine 6G for carrying out tracer analyses is not advisable due to significant migration of the latter into oil. If salts of thiofulminic acid are used as tracers, it should be considered that 10–20% of the salt can “escape” into oil when passing through the formation.