Experimental And Theoretical Studies Of Solids Precipitation From Reservoir Fluid
Authors: Thomas F.B. , Bennion D.B. , Bennion D.W. , Hunter B.E. 
Published: March 2010

Abstract
Solids precipitation from reservoir crudes has been recognized as a serious detriment in numerous oil systems world wide. Precipitation may result in in situ permeability reductions as well as contributing to serious plugging problems in surface facilities. The latter can be treated with periodic cleaning techniques (xylene or toluene injection and/or mechanical treatment) but, rather than concentrate on remedies, prevention would be a preferable approach.
This paper describes experimentally determined solids precipitation trends as a function of hydrocarbon solvents added. Techniques for the measurement of solids precipitation at reservoir conditions are reviewed and the implementation of a high-pressure high temperatureLASER cell is described.
Three solids precipitation models were developed as companions to the experimental program. The models co1l.Sisted of an EOS methodology to calculate vapour-liquid equilibria but then three different models were evaluated for the liquid-solid interaction. The first was a pure component solid phase fugacity correlation, the second a regular-solution-theory multi component model found in the literature and the third was the same multi component solid model but was modified for pressure and temperature influences based on theoretical constructs. A comparison of the three models is included with quantitative comparisons between some experimental data sets and Theory. Future direction of this project is also discussed.

Introduction
Solids precipitation from reservoir fluids has been a problem for many years. Katz and Beau(1) were some of the first to begin researching the problem and many worthy groups have continued to study the phenomenon. The range of research efforts has been broad but there has been basically two approaches: the first has been associated with clean-up methods such as improved means of unplugging Lines or solids dissolution, whereas the second has been interested in mitigating solids precipitation before it happens, One approach is remedial and the other preventative and many centres are now applying a combination of the two.
The significance of the solids precipitation has been established by many and Leontaritis and Mansoori(2) have reported the technical and economic impact with respect to numerous oils throughout the world. The unanimous conclusions of all who have researched the phenomenon indicate that the economic impact, due to reduced productivity, is substantial and requires efficient resolution but that the problem is very complex and has to date resisted an adequate description. Experimentation has yielded a number of general trends but their quantification appears to be intractable as yet. Complex molecular-scale theories incorporating resin-asphaltene interaction and electrokinetic phenomena are beyond present analysis. There are, however applied methods which can be used in semi-quantitative analysis of the solids precipitation problem.
Over the last five years Hycal Energy Research Laboratories Ltd. has performed experimental and theoretical research into solids precipitation and considerable insight into the phenomena has been acquired. This paper describes the experimentation done to determine important trends and provides an overview of three theoretical equation-of-state models developed.

Previous Work
Initial research into solids precipitation concentrated on structure and characterization of the compounds.