Flow assurance is associated with the transport of hydrocarbons from the subsurface to surface facilities, and solid formation is one of the most common subsurface and surface flow assurance fluid-related challenges. Therefore, extensive, and integrated studies of fluid phase behaviour and precipitating solids chemistry in multiphase flow are required. This paper presents an extensive phase behaviour study of a complex fluid mixture from a reservoir that located at offshore field in Southeast Asia to observe flow assurance issues, especially organic solid formation.
There was a concern over possible solid formation in the well and surface network from neighbour fields, and it is required to perform an extensive pressure-volume-temperature (PVT) study with a fluid-related flow assurance study from targeted reservoir. Extensive PVT and fluid analysis experiments have been carried out. Complex fluid compositions analyses were measured until dodecane plus with additional complex mixture components. The comprehensive fluid properties were also measured. The laboratory measurement followed standard industry methods (ASTM, UOP, ICP, IP). The API Gravity, density, pour point, solid content (wax, ash, asphaltene), mercury and other metal contents, water content and basic sediment & water (BS&W), total acid number (TAN) were performed without wax appearance temperature (WAT) and Saturates-Aromatics-Resins-Asphaltenes (SARA) analysis measurements. Standard PVT experiments such as constant composition expansion (CCE), differential liberation (DLE), viscosity, and separator tests were performed as well and will be validated through thermodynamic modelling equation of states (EOS).
The complex mixture of fluid composition measured mixture components of naphthenic complexes, aromatic complexes, and contaminants such as CO2, N2, mercury, and metal components. The Watson characterization factor (Kw) is calculated at 11.4 (predominantly naphthenic and aromatic complexes) and consistent with compositional analysis. It can be used to classify the crude oil since it is consistent with compositional analysis if the sample predominantly naphthenic (~6 mol.%) and it might give low pour point at 6°C measured in the laboratory. A thermodynamical model EOS was developed using PVT Software and fine-tuned phase volume and viscosities properties, to achieve an acceptable match against the PVT experiments (CCE, DLE, viscosity, separator, and solid content). The solid content between laboratory measurements and model prediction achieved a good matched as well. Based on this study, it can predict WAT and be concluded that organic solid formation is unlikely to be an issue from targeted reservoir, especially in the wellbore since WAT is far below than tubing head temperature. The validated EOS model can be confidently used for further phase behaviour and flow assurance prediction because numerous laboratory experiments were involved in matching processes.
This study demonstrates how vital and necessary extensive PVT experiments and analysis are prior to well put on-stream to anticipate any flow assurance issues that may cause decreased and prohibited oil production. The thermodynamic modelling can be used for fluid phase behaviour analysis and flow assurance prediction to give better management in flow assurance.
