New Methods Analyze Asphaltene Deposition and Fouling in Reservoirs

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27933, “Asphaltene Deposition and Fouling in Reservoirs,” by Mohammad Tavakkoli, Peng He, Pei-Hsuan Lin, Sara Rezaee, Maura Puerto, Rocio Doherty, Jefferson Creek, SPE, Walter Chapman, Sibani Lisa Biswal, and Francisco M. Vargas, Rice University; Jianxin Wang, SPE, and Greg Kusinski, SPE, Chevron; and Joseph Gomes, Deepstar, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. Asphaltene precipitation and deposition in production tubing and surface facilities are well-documented issues, and different methods are available to manage them. However, the problems that asphaltenes may cause in the reservoir, especially in the near-wellbore region, are much less understood. This project aimed to develop experimental procedures and modeling methods to establish whether impairment caused by asphaltene deposition in reservoirs is a real problem and to develop an understanding of the mechanisms by which asphaltene precipitates, alters wettability, and obstructs flow by potentially depositing in the formation. Introduction Asphaltenes are a polydisperse mixture of the heaviest and most polarizable fractions of crude oil. Understanding the asphaltene-deposition problem and the factors affecting it is of great importance to the oil industry because of the costs associated with production loss and remediation activities, such as solvent wash and removal of deposited asphaltenes. Several modeling approaches in the literature are used to model asphaltene deposition in porous media. Different mechanisms, such as adsorption, surface deposition, entrainment of deposits, pore-throat plugging, and pore-throat opening, have been considered in these approaches. However, which mechanisms play the most significant role and which mechanisms can be neglected in modeling asphaltene deposition inside porous reservoir rocks remains unclear. In this work, a series of tools has been developed and used to deepen the understanding of the mechanisms by which asphaltenes can precipitate and deposit in the reservoir. A new technique based on an automated chromatographic method was implemented to separate and quantify the content of saturates, aromatics, resins, and asphaltenes (SARA) in two crude-oil samples. Microfluidic devices were used to visualize the formation of asphaltene deposits in the porous media under various experimental conditions. Also, a quick and inexpensive novel technique to cast core holders using a special epoxy resin was developed to accelerate the execution of coreflood experiments. Finally, a simulation tool based on the lattice Boltzmann method (LBM) was developed for modeling asphaltene deposition in porous media. Crude-Oil Characterization Because of the complex nature of crude oils, performing a detailed compositional analysis for every substance in the oil is not readily achievable. Instead, a hydrocarbon-group analysis is preferred. SARA separation is one of the approaches for the hydrocarbon-group analysis. It separates the crude-oil components, on the basis of their solubility and polarity, into four parts: saturates, aromatics, resins, and asphaltenes.