Sand production from gas wells has a significant impact
on the
production of gas wells. This review aims to reveal the reasons for
fracturing sand backflow in Sulige Gas Field gas wells and provide
targeted preventive measures to prevent fracturing sand backflow.
The critical parameters of sand production in gas wells were calculated
through theoretical models, and the reasons and mechanisms of fracturing
sand backflow in Sulige gas wells were analyzed from three major aspects:
production factors, reservoir factors, and process factors. The Analytic
Hierarchy Process was used to analyze the degree of influence of the
sand production factors in gas wells. Research has shown that the
high production rate of gas wells, unreasonable design of fracturing
parameters, and insufficient drainage of fracturing fluid are the
main reasons for sand discharge in the Sulige gas well formation.
Controlling the production of gas wells between the critical flow
rate of fracturing proppant reflux and the critical sand carrying
flow rate of the wellbore, designing fracturing construction parameters
reasonably, prolonging the gas testing time, and allowing the fracturing
fluid to fully reverse flow can effectively prevent sand production
from the gas well.
Owing to limitations
imposed by the experimental requirements,
it is difficult to carry out pressure–volume–temperature
experiments on CO2-containing natural gas in high-temperature
and ultrahigh-pressure gas reservoirs. Relevant research is also insufficient,
which has led to a lack of clarity in current understanding of the
microscopic mechanism of variations in the deviation factor of high-CO2 natural gas under high-temperature and ultrahigh-pressure
conditions. This has greatly limited the development of natural gas
reservoirs containing CO2. To reveal the microscopic mechanism
of variations in the deviation factor of natural gas containing CO2 as a function of pressure under high-temperature and high-pressure
conditions, by physical simulation experiments, the deviation factors
of samples of sour natural gas with known CO2 contents
from the Ledong gas reservoir were determined. Then, according to
the idealized parameters of the physical experiment, a molecular model
of natural gas containing CO2 was established using molecular
simulation methods. Changes in molecular density, molecular volume,
nonbonding interaction energy, potential energy, and kinetic energy
during variations in the deviation factor of a CO2-containing
natural gas system as a function of pressure under high-temperature
and ultrahigh-pressure conditions were quantitatively studied. Using
molecular simulation techniques, it was found that the changes in
total energy, kinetic energy, and potential energy between molecules
are the internal factors that cause variations in the deviation factor
of natural gas systems containing CO2 under ultrahigh-temperature
and high-pressure conditions. The results show that the increase of
carbon dioxide content in natural gas will cause the total energy
of natural gas molecules to decrease when the pressure is constant.
This means that the higher the CO2 content in natural gas,
the easier it will be compressed. This study should lay the foundation
for investigating the mechanisms of the occurrence of CO2-containing natural gas, as well as facilitating the exploitation
of CO2-containing natural gas.
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