Finn Hallstein Fadnes

Detection of asphaltene precipitation and amounts precipitated by measurement of electrical conductivity

Abstract Asphaltene deposition during oil production might lead to expensive clean up operations. The production plans may also have to be reviewed. It is therefore necessary to investigate the potential for asphaltene deposition prior to field development. Reliable techniques for detection of asphaltene precipitation are needed in order to test existing theoretical models. The available experimental techniques are elaborate and not suited for high pressure work. A novel technique to determine asphaltene precipitation and relative amounts precipitated is presented. The technique is based on measurement of electrical conductivity, of the crude oil. It is seen that the electrical conductivity changes abruptly at the point of precipitation. Both gravimetric analysis and microscopy has been used to verify the results obtained by conductivity. The principle has been checked for a number of oils with varying asphaltene content from 0.3wt% to 9wt%. Results from four different oils are reported.

Natural hydrate inhibiting components in crude oils

Abstract Reservoir fluids have been observed to show significant variations in their ability to form hydrate plugs. It is therefore likely that the different oils contains components that effect their tendency to form plugs. A procedure for evaluation of the plugging potential and for identifcation and extraction of naturally hydrate inhibiting components in crude oils is presented. The actual oil is characterized with respect to emulgating properties, content of polar components (resins and asphaltenes), interfacial tension, hydrate equilibrium, kinetics and potential of plug formation. The oil is then modified, by extracting the polar components. The modified oil is characterized, in the same manner as described above. The extracted polar components are used as a base for secondary extraction and fractionation of surface active components. Component fractions having high surface activity will be tested as hydrate inhibitors. The results indicate that it is possible to identify naturally inhibiting components in crude oils having a low potential of forming hydrate plugs.

Measurements and Predictions of Hydrate Equilibrium Conditions

Abstract: The main objective of this study was to demonstrate the importance of reliable hydrate equilibrium data for thorough mitigation and remediation of hydrate problems. Hydrate prevention strategies generally rely on extensive use of different hydrate simulators that, in turn, are based on experimental data. Erroneous hydrate predictions may severely jeopardize the established hydrate strategy and can have severe economic implications. In this study the hydrate equilibrium conditions for eight different hydrocarbon systems were investigated by experimental measurements and by hydrate simulator predictions. The results clearly verify the importance of having due control over the experimental parameters, especially the heating gradient. The error in the determination of the hydrate equilibrium temperature seems to increase with the complexity of the system; for example, when inhibitors are added to the aqueous phase.

Experimental Characterization of Hydrate Formation and Decomposition in Reservoir Fluids

Future oil production in the North Sea area will make extended use of subsea production. Transport of unprocessed, multiphase well streams over long distances at sea bottom temperatures give a high potential for hydrate formation. As a part of the strategy for handling the hydrate problem, an experimental facility for characterization of hydrate formation and decomposition in reservoir fluids has been established. The measured characterization parameters are the thermodynamic hydrate equilibrium conditions, the required amount of subcooling, the rate of hydrate formation, the degree of conversion, and the rheology change. Also performed are visual observations of the emulsion properties of the oil, the tendency to form hydrate plugs, and in general the appearance of the hydrates. The experimental variables are the pressure, the number of hydrocarbon phases present, the water cut, the cooling rate, the stirring rate, and finally the type and concentration of inhibitor. The measurements obtained in this system are gathered together with results from dynamic flow rigs and other studies to form a total base for evaluation of the possible hydrate problems of a given project.