The Role Of Acid-Additive Mixtures On Asphaltene Precipitation
Authors: Knobloch Timothy S. , Ali S.M. Farouq , Diaz Manuel J. Trevino 
Published: December 2007

Introduction

Asphaltene precipitation is currently undergoing a major observation by the petroleum industry due to the problem it can create, such as the reduction of fluid flow passages. In particular, this could include the reduction of formation permeability.

This experimental study encompasses the role the acid, and the chemicals often added during formation stimulation could have in precipitating asphaltenes from some crude oils. That is, sometimes unstable colloidal materials in asphaltic base crudes coagulate when subjected to acid stimulation and form deposits on the wellbore and on the formation faces. These deposits have been found to consist of paraffins, resins, maltenes, and asphaltenes. The paraffins, resins, maltenes, and asphaltenes. The asphaltenes that precipitate out are not single molecules, but clusters of molecules often coated with paraffin and resin molecules strongly bonded to the exterior of the clusters.

To investigate sufficiently the role played by acid-additive mixtures on asphaltene precipitation in open systems and in porous media, a study was first made to determine the total amount of asphaltene precipitation as a function of solvent concentration precipitation as a function of solvent concentration using asphaltic base crudes. Further studies were made to determine the amount of asphaltene precipitation of the same crudes, using acid-additive mixtures precipitation of the same crudes, using acid-additive mixtures commonly used in acid-stimulation treatments. Additional investigation was completed to attempt determination of the extent of plugging due to asphaltene precipitation during the acidizing of a linear model using consolidated Berea sandstone cores.

CRUDES USED FOR STUDY

The crudes used for this study were the Lloydminster crude from Alberta, Canada, and the Lake Maracaibo and Mouchal crudes from Venezuela. The Lloydminster was used to check the effects of all the available acid-additive mixtures and to observe the possible effects of asphaltene precipitation on flow possible effects of asphaltene precipitation on flow in a porous media; whereas the Lake Maracaibo and the Morichal crudes were used for a complete solvent study and also checked with the acid-additive mixtures that precipitated significant amounts of asphaltenes.

APPARATUS AND EXPERIMENTAL PROCEDURE

The separation of the asphaltenes from the crudes was completed by the following equipment: a Ruska Mercury Displacement Pump, a Millipore Filter, and a high-pressure sample reservoir, according to Fig. 1.

The procedure for separating the asphaltenes is begun by first weighing out samples of the test crude into preweighed sample bottles. Next, determine the amount of solvent to be mixed volumetrically with the crudes in 20, 40, 60, and 80% solvent-to-crude concentrations. Add the desired amount of solvent to the appropriate crude sample and mix thoroughly. In this study, Talboys Instrument Corp. magnetic, variable-speed mixer was utilized at 15 minutes per sample.

The actual separation of the asphaltenes from a crude sample was achieved by emptying the contents of one sample bottle into the stainless-steel reservoir. Any crude remaining in the sample bottle should be washed with 5 ml of naphtha and emptied into the reservoir. A Millipore Filter containing a 5-micro p filter paper was attached to the outlet end of the p filter paper was attached to the outlet end of the reservoir and the sample bottle positioned to collect the filtered crude. The Ruska Mercury Pump now is used to displace the crude out of the sample reservoir and through the Millipore Filter, there all particles 5-micro p and larger were collected on the filter paper. The 5-micro 4 filter paper is removed now and paper. The 5-micro 4 filter paper is removed now and replaced with a 1-mu filter paper. The crude sample then is re-emptied into the reservoir and the same procedure repeated with a 1-micro 4 filter paper. procedure repeated with a 1-micro 4 filter paper.

FRACTIONAL DISTILLATION OF THE ASPHALTIC MIXTURES

In order to isolate the asphaltenes, the following apparatus was implemented: 250-ml flasks, a distillation chamber, and a sample chamber, according to Fig. 2.