X-ray detection of pipeline slugs
A multiphase fluid flow is characterized by the commingled flow of different phase immiscible fluids, such as water, oil and gas. The form in which the different fluids exist inside the pipe, known as flow regime, plays an important role in the hydrodynamic behaviour of a production system in both oil and gas wells. Slug flow is a flow regime, commonly encountered in offshore multiphase flow lines. It is characterized by a series of liquid plugs (slugs) separated by large gas pockets (bubbles). Slug flow, due to its transient and intermittent nature, can cause severe instabilities and operational problems to a production system. Flow mathematical models and simulation software tools have been deployed, producing valuable instruments in the analysis and realization of transportation systems based on multiphase technology. In the context of an EU-sponsored project, THREEPLEX, new gamma and X-ray instrumentation has been developed in order to measure the characteristics of three-phase flow or their distribution within the slugs. This instrumentation includes a wide range of gamma densitometers (single and multi-beam, dual and single energy, traversing and fixed). It also comprises of an X-ray tomography system, including the development of relative tomographic algorithms for the interpretation of the data. The novel instrumentation allowed the determination of average and time varying fractions (oil, water and gas) and the tracking and measurement of slugs along a test section. In addition to this, data has been collected on the processes leading to slug formation and the development in the horizontal and V-geometries. In horizontal flow, both two and three phase, a high occurrence of slugs was found at the pipe inlet, with the number of slugs decreasing as the distance along the pipe increased. In three-phase flow it was also found that the occurrence of slugs increased with the viscosity of the liquid. For V-shaped pipes, it was found that slug formation was dependent on water cut. Where the water cut was high, slugs were formed in the descending side of the V. However if the water cut was low, stratified (layered) flow was predominant. The equipment developed and the slug evolution data have a broad range of potential applications in the flow metering of complex multiphase flows. This opens new opportunities for collaboration with manufacturers of similar instrumentation or researchers in the respective area.
