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Abstract

Liquid droplets that load in gas wells cause several
serious issues. To solve these problems, different lifting method were
developed. Lifting system that are used now for horizontal gas well were
originally developed for oil wells. Moreover, this research is targeted mainly toward
gas well deliquification (remove liquid loading from wellbore or dewatering).

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Introduction

In natural gas well, the produced gas particles are
attached to a load of liquid droplets (oil condensate or water). Moreover, the
produced gas can lift liquid droplets to the surface at the early stage of the
production when the gas pressure is high enough to provide such critical
velocity to carry the liquid to surface.

After period of production when the well become mature, an
amount of liquid that present inside the tubing along with gas produced result
in disperse within gas that drag gas flow downward by gravity. Therefore, gas
velocity falls and leads to extra decreases in extracted liquid volume that
cause accumulation which rise the burden of the ability to carry up liquid
droplets, which lead to gather more liquid and extra builds up accumulation of
liquid that cause a reduction or complete stop of the gas production.

 

Objective

·        
To discuss the improvement
in deliquification.

·        
To discuss new design
method of lift system.

 

 

Methodology

I collected the data for a research in Well completion
course that is about summarizing some latest improvement in lifting in gas
wells. Moreover, I collected data using OnePetro website from different
journals and SPE papers. The main methodology that I followed is to explain the
main difference between lift systems and to summarize a real gas well case that
undergoes different lifting technique.

 

 

 

 

 

Discussion
& Result

Gas well deliquification or gas well dewatering is a method
of lifting that used to get rid of liquid (oil condensate or water) that occur
within gas during production from gas well. To deliquefy liquid in well, there
are different possible solutions such as:

·        
Natural flow.

·        
Compression.

·        
Gas lift.

·        
Beam lift.

·        
Plunger lift.

·        
Foam lift.

 

In this research we will focus on foamer injection that is
used to increase gas production. The foam performance depends on different
parameters such as pressure, temperature, hydrocarbon fraction, and foamer
agitation velocity. In addition, Foam Assisted Gas Lift may be used and it is
considered to be an economical choice due to its increased gas production
rate and it requires less injected gas. There are three types of tests that
applies on foam to test its performance that are:

·        
Foam buildup test.

·        
Collapse test.

·        
Liquid carryover test.

 

In addition to that there are system consideration that
control the validity of lifting solution such as:

·        
Cost of production and
amount of pay.

·        
Solution life.

·        
CO2 and H2S corrosion.

·        
Acid resistant.

·        
Amount of water and the
ability to control it.

·        
The cause and depth of
condensation.

·        
The power required.

·        
The costs and risks of
workover.

In addition, the gas velocity is affected by the design of
the well bore (such as sudden expansion/contraction). Moreover, the gas
condensate is affected by the rate of production

Slower velocity => poorer lift => longer transit time
=> more heat loss => water condensate.

Some of the methods are depend on recharging the well from
near formation Recharging from low permeability zones to higher permeable zone.
In methods such as:

·        
High permeability streaks.

·        
Natural fracture.

·        
Stimulated fractures.

 

Nevertheless, liquid behavior is affected by the deviation
of the well, where in the vertical well, all the liquid droplets are lifted by
flowing gas. However, in a deviated well, a separation is possible due gravity
where liquid droplets will be accumulating down hole at an angle.  However, the proposed gas well case is
vertical well and it undergoes these methods:

 

 

A.     Gas Lift

The method of gas lift is used to improve the production
rate and to deliquefy the gas well as an artificial lift technique by
decreasing the hydrostatic pressure of the liquid. This method is applied by
injecting high pressure gas in the well pipe through valves on the annulus
string.

 

 

 

 

 

 

 

B.     Foam Assisted Lift

Foam assisted lift is a new technique that is used to
dewater the gas well by decreasing the liquid surface tension and its density.
This method depends on injecting soap from surface in the tubing through capillary
string. Moreover, the system components are:

·        
Capillary
soap

·        
Stainless
steel capillary string

·        
Foot valve
(soap injection valve)

·        
Capillary
hanger

·        
Soap pump

·        
Soap tank

 

 

And
the systematic process of Foam assisted lift is:

 

C.     Foam Assisted Gas Lift

It
is a hybrid technique that use both Gas lift and Foam assisted lift to improve
the effectiveness of the two methods by injecting soap and gas. In other words,
the soap is increasing the liquid column and the injected gas energize the
flow. This method is most effective when:

·        
The well
flow is very low, and much liquid was accumulated

·        
The liquid
column is lower than gas valve.

 

 

D.     The study case

This is the example of natural flow gas well that well be
focused on in this research paper and its recovery technique was changed three times
after depletion. The following figures show main information about the proposed
gas well in it production profile.

(Tayyab, 2016)

        
i.           
Production
with Natural Flow

The cumulative production after perforation of Sand Y is around
18 MMMCF and around 1 MMSCFD initially that is increasing with time and loads
in the tubing. After 8 years of production, the flow rate of gas fall to 1
MMSCF per day and the Water-Gas ratio was 300 STB/MMSCF. Therefore, Sand Z was
perforated to comminglally produce around 7 MMSCFD. Moreover, wellhead gas
compression systems was applied for 10 years to rise flow up to 12 MMSCFD and
30STBMMSCF of Water-Gas ratio. In 2011, the was depleted due to loss of energy
to flow the gas with around 57% recovery rate.

 

       ii.           
Production
with Gas Lift

The Gas lift system was introduced in M-1 well in 2012 to
deliquefy the gas well by inject 0.4 MMSCFD of gas the produced around 1.7
MMSCFD and 225 STBD of water. Shortly, the gas flow dropped to 1.2 MMSCFD with
larger Water-Gas ratio that show liquid droplets are loading in the tubing.
After 6 Months, Gas lift system has produced only 1.6 BCF that is 2.4 %
recovery.

 

     iii.           
Production
with Foam Assisted Lift

After Gas lift system was suspended, a Foam assisted lift
was introduced in the gas well. Soap was injected close to the perforation
using capillary string. In the beginning of injection, Soap was injected at
rate of a half-gallon per day and raised gradually to a rate of 5 gallons per
day that result in 1.5 MMSCFD of gas. However, any further increment of
injected soap leads to drop in the production rate. After three months, a
liquid droplets load occurs and requires gas lift to provide sufficient energy
to flow the gas well. Therefore, new lifting system were introduced in the
well. One of limitation of foam that is affected by temperature.

 

     iv.           
Production
with Foam Assisted Gas Lift

After 5 months in 2013, a combined system of Gas lift and
Foam assisted lift was applied to dissolve the liquid loading of the gas well.
In fact, it was a challenge to determine the optimum rate of soap and gas
injection rate at that time because there were no standard values for this
combined system. Therefore, several trial and error were applied and the best
values for M1 well were 2 Gallon per day of soap and 0.3 MMSCFD of injected gas.
After 21 days of instable production, the production stabilizes at 1.3 MMSCFD
with 300 BBL of water per day.

       v.           
Result

This a table shows an efficiency of each system that has been
used in this gas well over four years of production after depletion of natural flow
and liquid loading occurrence:

(Tayyab, 2016)

It Shows that Foam assisted gas lift provides most profitability
per year of 3.0 $MM/year. In contrast, Gas lift and Foam assisted lift achieve 1.6
$MM and 1.5 $MM of profit per year respectively.

 

Conclusion

·        
It is advantageous to use a
combined system of Gas lift and Foam assisted lift that optimize production rate
of gas well and overcomes limitation of two methods alone.

·        
Soap injection has an
optimum rate; any variation affects the production negatively.

·        
High temperature reduce the
effectiveness of Foam performance.

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