Prediction of temperature drop
accompanying a given pressure drop for
natural gas wellstreams
A. Bahadori and H. B. Vuthaluru
PROFESSIONAL PAPER
Accurate prediction of the temperature drop accompanying a given pressure drop for the natural gas
production systems is necessary in the effective design of natural gas production facilities. Current rigorous
compositional models depend on many variables and require information about fluid composition. In this
paper, a simple-to-use method which is easier than current available models, is presented to predict
accurately the appropriate temperature drop accompanying a given pressure drop in natural gas production
systems based on the black-oil model to get a quick approximate solution for the temperature drop of a
natural gas streams in gas production systems. Considering the results, the new developed correlation is
recommended for rapid estimation of temperature drops in gas production systems for pressures up to 45
MPa and pressure drops up to 25 MPa. The obtained results illustrate that good agreement is observed
between the reported data and the values calculated using the new developed method. The average absolute
deviation between reported data and the proposed correlation is around 4.6%. The proposed method
appears to be superior owing to its accuracy and clear numerical background, wherein the relevant
coefficients can be retuned quickly for various data.
Key words: natural gas, liquid content, temperature drop, Black-Oil model, simulation
1. Introduction
Predicting accurate temperature profiles in gas-produc-
tion systems can improve the design of production facili-
ties. As an example, temperature profiles in systems
have application in accurate two-phase flow pressure
drop prediction, gas-lift designs, and etc. If composition
of gas is available, engineers predict the temperature
drop by using a computer simulation program based on
a fully compositional equation of state (EOS) pVT formu-
lation and flash calculation. The program will perform a
flash calculation, internally balancing enthalpy. It will
calculate the temperature downstream of the choke,
which assures that the enthalpy of the mixture of gas and
liquid upstream of the choke equals the enthalpy of the
new mixture of more gas and less liquid downstream of
the choke. Otherwise, the gas production system can be
modeled with the use of a black–oil model, which is also
a tool for modeling the gas reservoir exploitation and for
calculating the resources.12 Black-oil simulators repre-
sent a high percentage of all simulation applications and
they can model immiscible flow under conditions such
that fluid properties can be treated as functions of pres-
sure.1Coats6presented radial well simulations of a gas
condensate that showed a modified black-oil pVT formu-
lation giving the same results as a fully compositional
equation of state (EOS) pVT formulation for natural de-
pletion above and below dew point. Under certain condi-
tions, he found that the modified black-oil model could
reproduce the results of compositional simulation for cy-
cling above the dew point.12,10
Fevang et al.10,11 obtained results which mostly support
the conclusions by Coats.6However, they found differ-
ences in oil recoveries predicted by compositional and
modified black oil (MBO) models when the reservoir is a
very rich gas condensate and has increasing permeability
downwards.12 According to their final conclusions, a
black oil simulator may be adequate where the effect of
gravity is negligible, and for gas injection studies black oil
model can only be used for lean to medium-rich gas con-
densate reservoirs undergoing cycling above dew point.12
El-banbi and McCain7,8 suggested that modified black oil
(MBO) approach could be used regardless of the com-
plexity of the fluid. Their paper presented the results of a
full field simulation study for a rich gas condensate res-
ervoir. The modified black oil (MBO) model performance
was compared with the performance of a compositional
model in the presence of water influx and also a field
wide history match study was conducted for above and
below the dew point.7,8 Their paper presents an accurate
match of average reservoir pressure and water produc-
tion rates. They also mentioned contrary to the common
belief, the modified black oil (MBO) approach proves to
be sufficient for modelling gas condensate behaviour be-
low the dew point and using the modified black oil (MBO)
approach, instead of a fully compositional approach,
may result in significant time saving especially in
full-field simulation studies.7
El-Banbi et al.9presented the set of correlations to gen-
erate modified black-oil pVT properties without the need
for fluid samples or elaborate procedure for equation of
states (EOS) calculations.
Choking, or expansion of gas from a high pressure to a
lower pressure, is generally required for control of gas
well flow rates. Choking is achieved by the use of a choke
or a control valve.1The pressure drop causes a decrease
NAFTA61 (7-8) 347-351 (2010) 347
