مقاله انگلیسی رایگان در مورد مدلی برای تراوایی آسیب به دلیل ته نشینی آسفالتین – الزویر 2019

The existing theoretical and empirical models to describe asphaltene deposition in porous media do not consider the complicated structure of pore network. Permeability reduction due to asphaltene deposition has been mainly attributed to pore volume shrinkage (porosity reduction). However, asphaltene particles can also block pore throats which will lead to severe permeability reduction even when a large fraction of total pore volume still remains intact. Thus, there is a need for permeability models that are explicitly function of pore/hydraulic connectivity. This paper provides a review of the existing models and examines a permeability model that explain permeability impairment due to asphaltene deposition. In this study, we propose a new permeability model based on Critical Path Analysis (CPA) which is a function of average coordination number (average number of available/connected neighbor pores). Furthermore, experimental data in the literature related to limestone, sandstone and carbonate (dolomite) samples are utilized to understand combined effects of surface deposition and interconnectivity loss due to pore blockage on permeability reduction. We observed that surface deposition is the dominant mechanism in the limestone samples studied here owing to large pore throat size compared to the particle size. In the sandstone samples, both the surface deposition and pore throat plugging mechanisms contribute fairly the same in the observed permeability reduction. For the carbonate (dolomite) samples, the pore blockage is the dominant mechanism, which results in rapid sharp decrease of the permeability. It is expected that the outcome of this work improves prediction of the asphaltene deposition in the near wellbore region.

Introduction

The issue of asphaltene deposition has plagued the oil and gas industry for decades since it has been identified and named as “asphaltenes” in 1837 [7]. Due to the huge costs associated with remediation, it is extremely important to understand the issue of asphaltene deposition and the factors affecting it [14]. Crude oil has several fractions, and asphaltenes essentially tend to be its heaviest, polarizable fractions. They are known as the “cholesterol of petroleum” due to their ability to precipitate as solids and subsequently deposit with changing pressure, temperature and oil composition [3]. Asphaltene precipitation is called the process when asphaltenes become a separate phase from the crude oil. They remain suspended in the liquid phase where the quantity and the size of the asphaltenes are relatively small. The precipitated asphaltenes clump together (aggregation) and form larger particles, also called flocs. The asphaltene aggregates are initially suspended in the crude oil. Subsequently, the flocs may attach to and accumulate on various surfaces, a process which is called asphaltene deposition [28]. In both up and downstream operations deposition may cause severe problems. Asphaltenes may precipitate and deposit on surface of pipelines, bottom of distillation column and heat exchangers as well, affecting efficiency and creating added economic costs to remediate [18,10]. Also, during production, asphaltene particles can deposit in reservoir, leading to possible blocking of flow, particularly in the near wellbore region. Asphaltene deposition problems encountered deep down in rock reservoirs are extremely problematic, and very challenging to tackle, as opposed to production tubing deposition problems. Minssieux [22] studied various core samples with different rock characteristics in core-flooding experiments, with regards to porous media. He concluded that porous sample plugging only seemed to occur after enough oil had flown through the sample, and that damage at earlier times was only observed in samples with a lower initial permeability [28]. The mechanisms through which formation damage due to asphaltene deposition can occur are surface deposition, and pore throat plugging. As asphaltene deposits accumulate on the pore surface, the pore surface area decreases leading to porosity reduction.