A Diagnostic Approach to Predict Asphaltene Deposition in Reservoir and Wellbore

摘要

Despite the myriad of published literature on asphaltene, true understanding of its characterization, and deposition is still lacking. There have been many proposed models based on principles in thermodynamics, hydrodynamics, and many empirical equations proposed, however, further work still needs to be done to have a better grasp of the asphaltene deposition. In this study, we examine an integrated approach to evaluate asphaletene deposition in both the reservoir and wellbore as a function of fluid velocity. We discuss the effect of permeability reduction as a function of combined effects of surface deposition and interconnectivity loss due to pore blockage in the reservoir. The effects of pore surface deposition and pore blockage are evaluated based on published experimental data on sandstone and carbonate rock samples. Next, based on different wellbore/tubing configurations (uniform and tapered) and fluid types, the asphlatene deposition is evaluated within the wellbore considering both favorable and non-favorable regions. Simulated values obtained from OLGATM are used to define these regions and critical particle sizes where there is a shift from Region I to Region II. Results indicate that in terms of asphaletene deposition in the reservoir, for sandstone samples, both surface deposition and pore throat plugging seem to contribute fairly equally to permeability reduction. In the case of carbonate however, pore blockage seems to be mainly dominant, which results in an almost instantaneous sharp decrease in sample permeability. Moreover, increasing fluid velocity, positively contributes to diminishing permeability reduction in sandstone samples, whereas it has no effect in case of carbonate samples. In case of deposition in the wellbore, asphaltene deposition rate is inversely related to fluid velocity in Region I whereas in Region II, it is directly proportional. More importantly however, this study determines particle size cutoff values for the two regions and does a systematic study of the impact that uniform and tapered wellbore configurations have on asphaltene deposition. Results of this study may change the industry's predictions of asphaltene deposition in both reservoir and wellbore. Improved understanding of asphaletene deposition leads to better production and far more accurate economic predictions.