Well modeling incorporating compositional and non-isothermal effects

Thanyamanta, Worakanok (2007) Well modeling incorporating compositional and non-isothermal effects. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This study proposed a methodology to predicting asphaltene precipitation in wells with advanced completions. A fundamental comprehensive two-phase flow model was proposed to predict asphaltene precipitation in horizontal production wells. The main objective of the research was to incorporate compositional and non-isothermal effects into an isothermal physical flow model and to investigate conditions that promote asphaltene precipitation. The precipitation induced by flow restriction found in equipment installed as parts of advanced well completion was the main focus. The proposed model consisted of a black-oil network model and a compositional asphaltene model allowing investigation of both physical and phase behaviour of flowing fluids in non-isothermal environment. The original network model was an isothermal model. In order to take into account heat transport in wellbores, an approach to predict wellbore temperature profile using a network-type model was proposed. This enabled the proposed network model to predict pressure, temperature, flow rate, and phase fractions of the produced fluid in different parts of the well. Local asphaltene precipitation predictions were able to be conducted at locations where asphaltene formation was likely to occur. In this research an asphaltene model was proposed. The model was developed based on a pseudo-three-phase solid-type asphaltene model. An isenthalpic flash was used to reflect the characteristics of flows through restrictions. By using the proposed asphaltene model, asphaltene onset conditions can be predicted and asphaltene phase behaviour at the conditions of interest can be determined. -- In this study the proposed methodology was used and successfully predicted flow behaviour in example well networks. It was found that different completion schemes have different effects on fluid conditions in the well and, in turn, asphaltene precipitation behaviour. The example simulations suggested that the drastic pressure drop induced by the valve restriction can cause asphaltene to precipitate. In the example cases the precipitation occurred inside the restriction thus downstream and upstream conditions were not sufficient for evaluation of asphaltene precipitation. In addition temperature also has effects on asphaltene precipitation prediction. The isothermal assumption for production systems, where the temperature in the well is always constant and equal to the reservoir temperature, may not be sufficient to accurately describe the asphaltene phase behaviour in the well. An increase in fluid temperature inside the restricted flow path also has effects on prediction of the asphaltene onset pressure. The extent of these temperature effects depend on the shift in the predicted onset pressure compared with the prevailing pressure drops in the entire well network.

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