Flow Assurance Principles in Oil & Gas Industries



Flow Assurance Principles in Oil & Gas Industries

MOLECULAR BASED STUDY OF
ARTERIAL BLOCKAGE / FOULING in

PETROLEUM and NATURAL GAS INDUSTRIES

( Asphaltene / Bitumen, Resin, Paraffin / Wax , Diamondoids , etc.)

DEPOSITION FROM PETROLEUM FLUIDS

A CONTINUING RESEARCH PROJECT TO STUDY CAUSES OF DEPOSITIONS AND DEVELOP PREVENTIVE, REMEDIAL AND MITIGATING MEASURES


BACKGROUND

One of the major unsolved complex systems confronting the petroleum and natural gas industries at present is the untimely deposition of heavy organic compounds present in the oil. The production, transportation and processing of petroleum, bitumen, and other heavy-organic-containing hydrocarbons could be significantly affected by flocculation and deposition of asphaltene, resin, paraffin / wax, Diamondoids, organo-metallics, etc. in the reservoir rock tubulars, oil well, pumps, storage vessels, transfer pipelines, and refinery and upgrading equipment with devastating economic consequences.

One question of interest in the oil industry is "when" and "how much" heavy organics will flocculate out under certain conditions. Since a petroleum crude generally consists of a mixture of hydrocarbons and heavy organics it has become necessary to look at each of its constituents as a polydisperse or discrete mixture interacting with one another.

Polydispersity in petroleum fluids
The kind and amount of depositions of heavy organics from petroleum fluids vary depending on the hydrocarbons present in oil and the relative amounts of each family of heavy organics. We have developed analytic techniques to identify and measure the percipitates from petroleum fluids.

Four different effects (mechanisms) are recognized for such deposition s. One or more of these mechanisms would describe the organic depositions that may occur during oil production, transportation or processing.

KNOWN MECHANISMS OF DEPOSITIONS

The degree of dispersion of heavy organics in petroleum fluids depends upon the chemical composition of the petroleum. The ratio of polar/non-polar and light/heavy molecules and particles in petroleum (Figure 1) are the factors primarily responsible for maintaining the stability of the polydisperse oil mixture.

Figure 1

I. Solubility Effect

Deposition of heavy organics can be explained by an upset in the polydisperse balance of oil composition. Any change in
(i) temperature
(ii) pressure , or
(iii) composition (such as addition of a miscible solvent to oil as demonstrated by Figure 2) may destabilize the polydisperse oil. Then the heavy and/or polar fractions may separate from the oil mixture into steric colloids, micelles, another liquid phase or into a solid precipitate.

Figure 2: Effect of composition change on heavy organic precipitation.


Visit also Asphaltene Deposition and Its Control
Visit also A Statistical Mechanical Model of Asphaltene Flocculation and Collapse From Petroleum Systems

Click here
for an examples of temperature effect.
Click here
for an example of pressure effect

Segments of the separated fractions which contain sulfur, nitrogen, and/or hydrogen bonds could start to flocculate and as a result produce the irreversible heavy organic deposits which may be insoluble in solvents.

II. Steric Colloidal and Micellar Effects

Some of the heavy organics (specially asphaltenes) will separate from the oil phase into an aggregate (large particles) and then will remain suspended in oil by some peptizing agents, like resins, which will be adsorbed on their surface and keeping them afloat as demonstrated by Figure 3.

Figure 3

Stability of such steric colloids is considered to be a function of concentration of the peptizing agent in the solution, the fraction of heavy organic particle surface sites occupied by the peptizing agent, and the equilibrium conditions between the peptizing agent in solution and on surface of heavy organic particles. The amount of peptizing agent adsorbed is primarily a function of its concentration in the oil. A concentration variation of a peptizing agent (such as resins) in oil will cause its adsorbed amount on surface of heavy organic particles to change. Migration of peptizing molecules (shown by arrows) from the surface of heavy organic particles could take place due to the change in their chemical-potential-balance between the bulk oil phase and the surface phase as shown in Figure 3.

III. Aggregation Growth Effect (aka Depletion Flocculation Mechanism)

The peptizing agent concentration in oil may drop to a point at which its adsorbed amount would not be high enough to cover the entire surface of heavy organic particles. This causes the potential for aggregation of heavy organic particles due to development of free active sites on their surfaces, and their eventual flocculation as shown by Figure 4. This may then permit the heavy organic particles to come together (irreversible aggregation), grow in size, and flocculate. The nature and shape of the resulting aggregates will determine their effect on the behavior of the petroleum fluids.

Figure 4

Visit The Laboratory Procedure to Identify and Measure Heavy Organic Deposits:
1. The Laboratory Procedure to Identify and Measure Heavy Organic Deposits
2. An analysis of methods for determination of onsets of asphaltene phase separations

Various aggregating macromolecules follow different aggregation pattenrs. For example, the irreversible aggregates of asphaltene are considered to follow an aggregation growth pattern shown by Figure 5 which is proven to be a FRACTAL.

Figure 5

According to the above mechanism, at a critical concentration ( Onset of flocculation point), asphaltene is depleted from the crude oil phase after an aspaltene particle collision which gives rise to a chemical potential gradient with respect to the bulk oil phase. Then flocculation starts taking place and the growth of the flocs exhibit characteristics of a fractal based structure above a certain floc volume fraction. The polymeric aggregation of colloidal dispersion of this nature is known as “Depletion Flocculation Mechanism”as described by D.H. Napper in his book entitled "Polymeric Stabilization of Colloidal Dispersions", Academic Press, New York,1983.

IV. Electrokinetic Effect

When a crude oil is flowing in a conduit (porous media, well, pipeline, etc.) there is an additional effect (electrokinetic effect) to be considered in the behavior of its heavy organic constituents. This is because of the development of electrical potential difference along the conduit due to the motion of charged particles. This electrical potential difference could then cause a change in charges of the colloidal particles further down in the pipe, the ultimate result of which is their untimely deposition and plugging of the conduit as shown by Figure 7. The factors influencing this effect are the electrical and thermal characteristics of the conduit, flow regime, flowing oil properties, characteristics of the polar heavy organics and colloidal particles, and blending of the oil.

Figure 6: Electrokinetic deposition in an isothermal-single phase pipeline flow
Click here
for examples of non-isothermal and multi-phase pipeline flows

Depending on the kinds of operation and the heavy organics present in a crude oil one or more of the effects described above will have to be considered in prediction and modeling of any deposition problem.


Click Here to Download
a Demonstration Copy of Asphaltene Aggregation in Petroleum Fluids

COMPUTER SOFTWARE PACKAGES



Petroleum Fluids Static and Dynamic Phase Diagrams:

UIC/TRL PUBLICATIONS

OUR RELATED SHORT COURSE:Flow Assurance Principles in Oil & Gas Industries


Dr. G.A. Mansoori, Bio & Chemical Engineering Departments, THE UNIVERSITY OF ILLINOIS AT CHICAGO, 851 S. Morgan St. (M/C 063), Chicago, IL 60607-7052 USA, Phone (312) 996-5592

OUR ONGOING RESEARCH SUBJECT

The Role of Water on Asphaltene Deposition from Petroleum Fluids (Experiments and Modelings)


RELATED LITERATURE

This page, and all contents, are Copyright © 1995-2014 by the University of Illinois at Chicago

For further information please contact us through our e-mail: TRL at UIC dot edu


Return