Gas Field Engineering - Gas Well Performance

8/9/2019 Gas Field Engineering - Gas Well Performance

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GAS FIELD ENGINEERING

Gas Well Performance


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CONTENTS

6.1 Gas Well Performance

6.2 Static Bottom-hole Pressure(static BHP)

6.3 Flowing Bottom-hole Pressure(flowing BHP)


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LESSON LEARNING OUTCOME

At the end of the session, students should be able to:

Determine static bottom-hole pressure(static BHP) usingdifferent methods

Determine flowing bottom-hole pressure(flowing BHP) using

different methods


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Figure (6.1) Gas Production Schematic


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Deliverability

Theability of reservoirto deliver a certain quantity

of gasdependsupon:

1.inflow performance relationship(IPR)

2. flowing bottom-hole pressure(FBHP)

Well & Facilities Performance

Flowing bottom-hole pressuredependsupon:

1. Separator pressure

2. Configuration of the piping system


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These conditions can be expressed as:

(8.1)

(8.2)


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Thebottom hole pressure (BHP) must be known in order to

predictthe productivity or absolute open flow potential(AOF)of

gas wells.

Preferred method is aBHP gauge(down-hole pressure gauge).

However,BHPcan be estimated if following is known: well head pressure,

well head temperature,

formation temperature,

well depth

gas specific gravity

Bottom-Hole Pressures (BHP)


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Basic Energy Equation when no flow

For a static gas column, the basic energy balance is:

Further assume that the local g equals

the g constant (g = gc) and re-arrange:

OR


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Static BHP for Slanted Wells

For slanted wells as shown below, total

length L and depth Z are related:

Relates Inclination to

Pipe Length & angle


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BHP for slanted wells

In differential form:

Where dZ is the change in the elevation in the upward

direction and dL is positive upwards.

-- Assuming a single-phase fluid that obeys the real gas

equation of state (EOS), gas density can be expressed as a

function of pressure:


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BHP for slanted wells

Combining the equations yields:

Combine with: AND

To get:


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Root of all methods for BHSP calc.

Relates the change in wellbore pressure

as a function of depth and gas density.

Derived from Energy Balance

Assumed static conditions (no kinetic

energy, friction loss or work done)

Replaced density with EOS (equation of

state)


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Average Temp. & z-Factor Method

Both gas density & z factor are p & T

dependent and change with well depth

Solving the root equation is thus difficult

If T & z-factor are assumed constant then

a solution can be obtained as follows:

whose solution is


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Solution Technique

Because depends on p which is unknown,

solution requires an iterative process.

1. Assume a value of BHSP, , A good

guess can be obtained from:

2. Compute avg pressure & temperature & use it

to find avg z-factor

3. Calculate with the earlier equation.

4. Iterate on steps 2 through 4 until converges.


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Example for Class Participation

Since depends on p which is unknown,

solution requires an iterative process.

1. Assume a value of BHSP, . A good

guess can be obtained from:

2. Compute avg pressure & temperature

& use it to find avg z-factor

3. Calculate with the earlier equation.

4. Iterate on steps 2 to 4 until converges.


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Example Solution


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Example Solution

Because of the simplifying assumptions made in its

development, this method is not accurate for deeper

wells and alternate methods should be used.


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Q & A


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Thank You

Documents

Gas Field Engineering - Gas Well Performance