Sylvi Høiland

Adhesion force between cyclopentane hydrates and solid surface materials

The mechanisms by which hydrates deposit in a petroleum production line are related to pipeline surface properties, fluid composition and properties, and water cut. In this work, adhesion forces between cyclopentane hydrates and solid surfaces were investigated as a function of the solid material, the presence of water and the presence of petroleum acids in the oil phase. The influence of dissolved water on hydrate adhesion forces was also investigated. The results show that the adhesion force between hydrates and solid surfaces was dependent on the surface material; solids with low surface free energy lead to the lowest adhesion forces. The adhesion force was strongly dependent on the presence of water in the system. When a water drop was deposited on the solid surface, the adhesion force between the hydrate and the solid surface was more than 10 times larger than hydrate-hydrate adhesion forces. The presence of a water-saturated oil phase also led to an increase in adhesion force between hydrate particles. Adhesion forces were highest when the solid surfaces are water-wet. Addition of petroleum acids to the oil phase drastically reduced adhesion forces.

The influence of petroleum acids and solid surface energy on pipeline wettability in relation to hydrate deposition.

The mechanisms by which hydrates deposit in a petroleum production-line are probably related to pipeline surface properties, e.g. pipeline material, surface energy and roughness. In this work, the wettability alteration of pipeline surfaces from contact with oil, and the adhesion energy between water and solid in the presence of oil is investigated. Contact angles for model systems are determined as a function of solid material and oil composition. Although contact angles in oil/brine/solid systems have previously been extensively reported in the literature, the variety of solids that mimic a pipeline surface is limited. In this study, we include various metal surfaces in addition to glass and epoxy coating. The results show that both the presence of petroleum acids in the oil, and low surface free energy of the pipeline material, lead to more oil-wet systems and consequently reduced adhesion energy between water and solid.

ISOLATION AND MOLECULAR IDENTIFICATION OF HYDRATE SURFACE ACTIVE COMPONENTS IN PETROLEUM ACID FRACTIONS

The anti-agglomerating hydrate behavior observed for some crude oils has previously been related to crude oil composition and to surface adsorption mechanisms. Petroleum acids derived from some crude oils have been found able to convert systems with initially high risk of plugging into easily flowable dispersions. In this work, acid fractions are isolated from three oils with low tendency to form hydrate plugs and from two oils associated with high risk of hydrate plugging by using an ion-exchange resin. The extracts are further separated into four sub-fractions by solid phase extraction (SPE). The chemical composition of the fractions is studied by means of HPLC, GPC, FTIRand UV/VIS spectroscopy and elemental analysis. The distribution of chemical compound classes in the fractions differs between the non-plugging and plugging oils, and the differences are most distinctive in one of the sub-fractions. The results imply that acid sub-fractions holding a significant proportion of more weakly polar compounds, like ester functionalities, are important for how the hydrate surfaces and the oil phase interact.

CRITICAL DESCRIPTORS FOR HYDRATE PROPERTIES OF OILS: COMPOSITIONAL FEATURES

In petroleum production systems, hydrate morphology is observed to be influenced by the crude oil composition. This work is aimed at identifying which crude oil compositional parameters that need to be determined in order to evaluate natural anti-agglomerating properties of crude oils, i.e. the critical compositional descriptors. The compositional features of 22 crude oils have been studied, and multivariate data analysis has been used to investigate the possibility for correlations between several crude oil properties. The results show that biodegradation together with a relatively large amount of acids are characteristic for non-plugging crude oils, while excess of basic compounds is characteristic for plugging crude oils. The multivariate data analysis shows a division of the nonbiodegraded oils, which are all plugging, and the biodegraded oils. In addition, the biodegraded oils seem to be divided into two groups, one with plugging oils and one with mostly non-plugging oils. The results show that the wettability can be predicted from the variables biodegradation level, density, asphaltene content and TAN.

PETROLEUM HYDRATE DEPOSITION MECHANISMS: THE INFLUENCE OF PIPELINE WETTABILITY

The mechanisms by which hydrates deposit in a petroleum production-line are likely to be related to pipeline surface properties, e.g. pipeline material, surface energy and roughness. In this work, the wettability alteration of pipeline surfaces from contact with oil, as well as the adhesion energy between water and solid in the presence of oil is investigated. Contact angles are determined as a function of solid material and oil composition, for both model oils and crude oils. Although contact angles in oil/brine/solid systems have been extensively reported in the literature, the variety of solids that may mimic a pipeline is limited. In this study, we include various metal surfaces in addition to glass and a coating. Initial results from using near infrared imaging for collecting contact angle data in non-translucent systems are also presented.