Abstract

In order to study the flow properties of asphaltenic crudes, corefloods with an oil asphaltene content in the range 0.1% to 6.0 % weight, were systematically performed in various rock material.

These laboratory tests carried out at reservoir temperature, have shown evidence of core damage occurring under dynamic flowing conditions. Plugging effects due to asphaltene deposition were evaluated in each case through comparison with the reference oil permeability measured with a selected hydrocarbon, prior to and after crude flow. Chemical nature and amount of organic deposits found in-situ at the end of tests, were determined by means of the Rock-Eval pyrolysis technique. This method allowed both to characterize the asphaltene fraction in deposits and to determine their distribution along the core.

Core impairment resulting from in-situ asphalt accumulation, was found to cause a 20% to 90% loss of initial oil permeability, depending on rock morphology, mineralogy and crude asphaltene content.

It turns out that trends in permeability reduction related to asphaltene deposition exhibit clear similarities with formation damage caused by solid fines migration. So pore blocking mechanisms models which have been proposed to describe fines migration effects have been successfully applied to the results obtained with asphaltenic crudes. Such an approach leads to an interpretation of the more or less fast permeability reductions observed with the different couples (crude oil/rock material) considered in this work.

Introduction

Production problems related to asphaltene deposition generally appeared in the fields first in surface facilities, especially in separators, during the oil final depressurization step. Another critical point along the production chain is within tubing in which deposits form at depth corresponding to the bubble pressure of produced oil. Afterwards the asphaltene deposit zone can migrate to bottomhole and well neighbouring formation as reservoir depletion proceeds. It is the known and long story of Hassi Messaoud field.

However in some recent fields, well impairment has begun even in early stage of production and seems to concern the reservoir itself.

In vitro flocculation phenomenon and asphaltene precipitation have been the topics of many papers. But the effects in porous medium of asphaltene flocculation have just come under investigation.

Published work deals with experiments and observations carried out in micromodels. A few ones only were performed in sandpacks or cores, but with isolated asphaltenes redissolved into an aromatic solvent.

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