GAS WATER DELIVERABILITY CONSIDERATIONS

J.M. MANDHANA

this article begins on the next page

PETFIOLEUM SOCIETY OF CIM

PAPER NO. 89-40-18 THIS IS A PREPRINT - SUBJECT TO CORRECTION GAS WATER DELIVERABILITY CONSIDERATIONS BY J.M. Mandhane Mandhane Consuking Servkme PUBLICATION RIGHTS RESERVED THIS PAPER IS TO BE PRESENTED AT THE 40th ANNUAL TECHNICAL MEETING OF THE PETROLEUM SOCIETY OF CIM HELD IN BANFF, MAY 28 TO 31,1989. DISCUSSION OF THIS PAPER IS INVITED. SUCH DISCUSSION MAY BE PRESENTED AT THE TECHNICAL MEETING AND WILL BE CONSIDERED FOR PUBLICATION IN CIM JOURNALS IF FILED IN WRITING WITH THE TECHNICAL PROGRAM CHAIRMAN PRIOR TO THE CONCLUSION OF THE
MEETING. Abstract When natural gas from high pressure and temperature reservoir is produced, due to cooling of gas in wellbore tubing and in gas gathering pipelines, the amount of
saturation water dropout .increases. Furthermore, as gas reser- voir pressure declines
due to gas depletion, amount
of connate water production also increases. If aquifer exits, it also adds to the amount of water
production
The
problem of lifting and carrying increasing amount of either saturation
or mobile connate and aquifer water while gas production rate is declining, poses an
interesting problem of maximizing both gas deliver- ability and gas recovery considering wellbore and surface gathering network.
For example, large tubing diameter will result in initial higher gas deliver- ability due to lower frictional drop when gas rate is high and able to lift and carry water, but it will also result in inability to lift and carry water when gas rate declines in future, and thereby, limiting gas recovery. 18 -1 Factors affecting gas deliverability, such as,
tubing diameter, delivery pressure, compression ratio, water dehy /separator/line
heater installation
pipeline diameter, pipeline contour, amount of free water, etc. are studied with view to offer certain guidelines on gas field development aspects when saturation
and/or
mobile
water production
problem
is
expected. Specifically, this paper deals with: o
enumeration of the
most
important factors affecting
gas deliverability and its recovery, o
aid in planning and conceptualizing gas pool development, and o
calculation procedure for estimating amount of saturation water dropout. Introduction Production, collection and distribution of natural gas requires interconnected pipeline network because of large gas volume. Mathematical simulation which

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PETROLEUM SOCIETY OF CIM

PAPER NO. 89-4D-18

THIS 15 A PREPRINT - SUBJECT TO CORRECTION

GAS WATER DELIVERABILITY

CONSIDERATIONS

.,

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BY
J.M. Mandhane
MandhanlJ ConBuhlng SElN.Icas

....i:1

PUBLICATION RIGHTS RESERVED

THIS PAPER IS TO BE PRESENTED AT THE 40111 ANNUAL TECHNICAL MEETING OF THE PETROLEUM SOCIETY
OF CIM HELD IN BANFF, MAY 28 TO 31, 1989. DISCUSSION OF THIS PAPER IS INVITED. SUCH DISCUSSION MAY BE
PRESENTED AT THE TECHNICAL MEETING AND WILL BE CONSIDERED FOR PUBLICATION IN CIM JOURNALS IF
FILED IN WRITING WITH THE TECHNICAL PROGRAM CHAIRMAN PRIOR TO THE CONCLUSION OF THE MEETING.

"
Factors affecting gas deliverability,
such aS
tubing diameter, delivery
pressure, compression ratio, water dehy
/separator/line
heater installation,
pipeline diameter, pipeline contour,
amount of free water I etc. are studied
with view to offer certain guidelines
on gas field development aspects when
saturation
and/or
mobile
water
production
problem
is
expected.
Specifically, this paper deals with:

Abstri!ct

When natural gas from high pressure and

t~mperature reservoir
is produced, due
to cooling of gas in wellbore tubing
and in gas gathering pipelines, the
amount of
saturation water dropout
increases. Furthermore, as gas reservoir pressure declines
due to gas
depletion, amount
of connate water
production also increases. If aquifer
exits, it also adds to the amount of
water
production.
The
problem of
lifting and carrying increasing amount
of either saturation or mobile connate
and aquifer water while gas production
rate is declining, poses an interesting
problem of maximiZing bo~h gas deliverability and gag recovery considering
wellbore and surface gathering network.
For example, large tubing diameter will

result in

initial higher

enumeration of the most important

factors affecting gas deliverability
and its recovery,

aid in planning and conceptualizing

gaB pool development, and

calCUlation procedure for estimating

amount of saturation water dropout.

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Introc2uction

gas deliver-

ability due to lower frictional drop

when gas rate is high and able to lift
and carry water, but it will also
result in inability to lift and carry
water when gas rate declines in future,
and thereby, limiting gas recovery.

Production, collection and distribution

of natural gas requires interconnected
pipeline network because of large gas
volume. Mathematical simUlation Which
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16 -1

simultaneously solvea equations describing fluid flow in reservoir r tubing,

pipelines,
and
associated
surface
equipment, such as, dehy, compressor,
separator, chokes,
etc., and other
contractual constraints, is called gas
network analysis. The objective of the
simulation is to find the maximum gas
deliverability. The mathematical simulation and
solution techniques are
fairly well known, ~nd therefore, will
not be described in this paper.

how gas pressure and temperature could

be controlled to
manage amount of
saturation water dropout.
Deliverability Network simulation

Gas depletion scenario for one gas

reservoir having two wells is simulated
in this paper_ The fluid flow in gas
reservoir
is
simulated using
the
simplified approach
of Rawlins and
Schellhardt(12).
Both wells have the
same IIC and nil constants so that the
production data is affected by the
calCUlated bottomhole flowing pressure,
and not by the type of the rock.

commercially available software(l,2) to

do the gas deliverability analysis are
used in this
paper.
The dry gas
simulator(l)
uses
CUllendar
and
Smith (3)
and
Bureau
of
Mines (-4)
Monograph 10 method for calculating
pressure drop in tubing and gas flow in
pipelines.
As most
user's assign
certain
efficiency
factor to
the
pipeline pressure drop calculations r
the model uses the turbulent region
friction factor with relative roughness
of O.OOOS (partially rough pipe). This
is ~one to simplify the concept.

Well I, labelled as "Highpn because it

produces against higher back pressure,
is connected through a short pipeline
(flOWline 1) to a dehy (node 9), to two
p~pe segments
of equal length but one
going downhill (flOWline 2) whereas the
other going uphill
(flowline J) hy the
same amount, to a separator (node 10),
to a compressor (node 4), to a pipeline
(flOWline 5), to a gas delivery point
(node 6).
The network schematic is
shown in Figure 2.

The gas water deliverability simulator(2) uses two phase pressure drop
calculation
procedures outlined
in
references(5,6,7,B,9). Gas density is
calculated using the Standing(lO) chart
for the compressibility factor.
The
amount of
Yater vapor in
gas is
calculated using the data of McKetta
and Wehe (11) .

'Well 2, labelled as II Low pI! because it

produces against lower back pressure,
is connected through two pipe segments
of equal length and one going uphill
twice as much (flOWline 7) as the other
(flOWline 8), to a separator (node 10),
to a compressor (node ~), to a pipeline
(flOWline 5), to a gas delivery point
(node 6).
The network schematic is
shown in Figure 2.

The calculated gas density and amount

of saturation water is shown in Figure
I at
the pressure
and temperature
ranges encountered while simUlating the
gas deliverability network. Note that
the gas density (inversely, gas volume
and tubing/pipeline gas flow velocity)
could be decreasing in the multiples of
100's as it travels from the reservoir
to a given delivery pOint. This observation is significant in understanding
how gas volume could be managed by
controlling pressure and temperature to
lift and carry vater.

various required data, such as, tubing

depth, inside diameter, etc., is shown
in Table 1 and Figure 2.
The data is
specially designed so that various sensitivity analysis could be attempted.
Deliverabillty Cases
Description of all eleven deliverability cases designed could be seen in
Table 2. Cases 1 and 2 are designed so
that pressure drop calculation methods
could be evaluated. Cases 2 and) are
designed to evaluate impact of line
profile in dry gas environment. Cases
J to 7 are designed to show the impact
of increasing amount of water. Cases 7
to 11 are designed to show what could
be done, i.e., tubing diameter change,
installation
of
dehy/separator/line
heater,
and compressor
change, to
improve gas deliverability.

Figure 1 also shows that the amount of

saturation water in natural gas could
be decreasing in the multiples of 10s
as it travels from the reservoir to a
given delivery point.
The amount of
saturation
water increases
as the
pressure decreases, but it decreases as
gas temperature decreases. Typically,
gas cooling in wellbore results in
water dropout. If gas is cooled to the
ground level, no more yater dropout
shOUld result in gas pipelines, since,
generally, pressure decreases in the
direction of gas flo~.
This observation is significant in understanding

18 - 2