Deposition apparatus to study the effects of polymers and asphaltenes upon wax deposition

摘要

The ability to predict and control the deposition of wax (also called paraffin) is critical to the efficient recovery of crude oil from cold environments, as part of the broader discipline of "flow assurance" in the petroleum industry. To this end laboratory-scale deposition tests have been useful to understand wax deposition. Previous studies have shown that wax deposition depends on temperature, flow stresses, oil composition (including wax) and the nature of the deposition surface. Furthermore, wax deposition is assessed not only through measurement of the amount of deposited wax, but also by the deposit composition as well as observation of microscopic structure and macroscopic effects on the wax deposit. We present here the first deposition system suitable for testing small volumes (～750 mL) that provides control over the shear conditions and temperature field, and has the ability to measure and observe deposit height, composition, microscopic morphology and macroscopic structure of the deposit. Due to the parallel-plate geometry and the fact that deposition occurs only on one surface in this system, the shear stress at the wall can be varied over an order of magnitude from 2 to 60 Pa, and increases in stress during testing are lower than systems with pipe geometries. Deposit thicknesses to ～150μm are measured continuously via differential pressure, and the deposit samples are readily accessible at the end of testing for subsequent compositional and microscopic analyses. The parallel-plate geometry allows the wax deposit to be visually observed during testing. The thinness of the deposition channel allows observation of deposits for solutions with asphaltenes that are normally opaque. The small sample volume allows selective testing of special wax-inhibiting polymers and asphaltenes, which may be difficult to obtain in larger quantities required for other deposition devices. The temperature field inside the deposition cell is well defined and easily modeled. Tests with multi-component wax solutions showed results that were consistent with previous studies on wax deposition and wax gelation.