Abstract

The near wellbore damage due to asphaltenes deposition is one of the major flow assurance issues currently faced by the petroleum industry. This study examines the pore scale flocculation and deposition processes of asphaltenes onto rock matrices. The effect of sand-grain size, clay presence in the reservoir rock, crude oil type, and precipitated asphaltenes type on the depositional behavior of asphaltenes is investigated. The porous media is prepared using sands with two different grain sizes or using sand-clay mixtures. Reservoir rocks were fully saturated with two different oil samples. 8 samples was prepared and they were washed by using either n-pentane or n-heptane, which are known as asphaltene insoluble solvents. In total, 16 experimental samples washed with solvents were subjected to optical microscopy and Scanning Electron Microscopy (SEM) – Energy Dispersive Spectroscopy (EDS) analyses to assess the asphaltene depositional mechanism. For all cases, porosity variations were measured experimentally. Our results suggest that asphaltene-clay interaction can increase the near-wellbore damage due to the strong polar ends in asphaltenes which are attached to clay surfaces and/or asphaltenes that are stuck in clay layers. Porosity of the sand has been found to decrease after the injection of solvents, indicating pore blockage due to asphaltene deposition. While the n-pentane precipitated more asphaltenes than n-heptane, n-heptane asphaltenes occupied more volume and resulted in higher porosity reduction due to higher polarity of n-heptane asphaltenes than n-pentane asphaltenes. Furthermore, the presence of clays and non-uniformity of grain sizes are observed to aggravate formation damage by asphaltenes. The SEM images showed that the interaction of clays with asphaltenes mainly reduces the permeability rather than porosity. The EDS analyses indicate that the impurity content of asphaltenes affect mainly the interaction of asphaltenes and clays.

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