Page 253 - Handbook Of Multiphase Flow Assurance

252 10. Research methods in flow assurance

structure of water using a polygons counting approach. A potential new hydrate inhibitor
was proposed, based on this study.

Computer study of hydrate inhibition mechanism
Overview of the computer simulations
Reasons for the computer study
The mechanism for kinetic inhibition of hydrates can be studied on a micron scale when
hydrate nuclei are sterically prevented by polymeric inhibitors from agglomeration. It also
can be viewed on the scale of nanometers when the inhibitor affects the microstructure of
water and defers hydrate formation.
Today's experimental techniques do not allow the dynamic study of the properties of ma-
terials in time on a microscopic basis. Computer simulation (molecular dynamics) is a widely
used tool which possesses several advantages over the real experiment. The first advantage
is the ability to look into the dynamics of the processes on a scale of angstroms. Other advan-
tages include 100% repeatability, ease of modification of parameters, and a safe environment.
Among the disadvantages are the use of simplified, theoretical models of the real processes,
high computing and data storage requirements, and computational round-off errors.
Modern high-powered computers permit more complex simulations, such as phase be-
havior and structural properties of fluids and solids. Examples of computational research
are discussed in an ever increasing number of publications. Guidelines for writing the com-
puter simulation programs may be found in books by Allen and Tildesley (1987) and by Haile
(1992). Many commercial software packages for state-of-the-art simulations are available,
such as BIOSYM®, SYBYL®, and HyperChem®.
SYBYL® is an extensive suite of software focused on computational molecular and bio-
molecular design. A modular program, SYBYL® features software for applications in drug
design, biochemical research, homologous chemical modeling, property prediction, molecu-
lar dynamics, polymer research, and conformational analysis. SYBYL® includes a molecular
spreadsheet which can store the obtained information. A molecular spreadsheet allows the
analysis of stored information using one or more parameters. SYBYL® functions in a number
of modes: command line, graphical, and a combined mode which mixes command line access
with graphical selection of objects directly from the screen.
The central role of SYBYL® is to enable the researcher to answer the question: “What
chemical structure or structures should I synthesize next in order to more fully understand
my research problem or produce more active agents?” The search for the best gas hydrate
inhibitor requires the answer of this question. In order to synthesize a chemical to prevent
hydrate formation completely, the mechanism of hydrate inhibition has to be known. It is nec-
essary to determine the function of the kinetic inhibitors in preventing hydrates' formation.
SYBYL® has been used previously to model SPC water. The results of previous simulations
(Clark, 1992) are in good agreement with the original SPC model results (Berendsen et al., 1981).

Results of the computer simulation
This work attempted to provide a qualitative explanation of kinetic inhibition phenomena
for hydrate formation. Two hypotheses for the inhibition mechanism were tested.