What is Well Deliverability?

    In order to discuss deliverability, the reservoir and the wells wil lbe considered as a unit. So let us explain what well deliverability is. 

    Well deliverability is defined as  the maximum rate at which fluids ( oil, gas , or water) can flow the reservoir to the surface while maintaning reservoir and wellbore stability. The key paramaters influencing well deliverability include:

-Reservoir pressıure

-Permeability

-Fluid properties

-Wellbore hydraulics

-Skin factor ( damage of near wellbore affecting flow efficiency)

Factor Influncing Well Deliverability

1. Reservoir Pressure

High reservoir pressure develop the well's ability to deliver fluids. As production continues, reesrvoir pressure decreasesi reducing deliverability over time.

2. Permeability

Permeability determines the ease with which fluids can flow through the reservoir rock. Higher permeability leads to higher deliverability.

3. Wellbore Damage (Skin Factor)

Due to formation damage, improper drilling or well completion practices, the near-wellbore permeability can decrease, negatively impacting flow efficiency.

4. Fluid Propersties

Density, viscosity, compressibility, capillary pressure, and gas-oil ratio (GOR), etc. affect the well deliverability of oil and gas wells.

5. Well Completion and Design

Open hole, cased hole, or horizontal completions influence the flow rates. Proper stimulation or perforation can improve the deliverability.

6. Surface Equipment Constraints

Limitations in tubing, chokes, and seperators can restrict well performance, even if the reservoir can transfer more.

Measuring Well Deliverability

Well deliverability is typically calculated by well testing, which includes:

1. Flow Tests

The well's performance under various operating pressures can be determined by measuring a range of flow rates. Typical flow testing consist of:

-Single-Point Test

-Multi-Point Test

-Isochronal Test

2. Pressure Transient Analysis (PTA)

Examining a test's pressure build-up or drawdown in order to determine the skin factor, permeability, and reservoir properties.

3. Inflow Performance Relationship (IPR)

The IPR curve shows the relationship between the reservoir and the well's flow rate. It is fundamental for determining well deliverability and designing artificial lift systems.

Well Deliverability for Gas Wells

Any gas well has an unique deliverability characteristics because of the compressibility of natural gas. The flow of gas is described using non-Darcy flow equations, particularly at high velocities.

Important Equations for Gas Well Deliverability

1. Rawlins and Schellhardt Equation ( for steady-state deliverability):

Figure.1

 

Taking the logarithm of both sides of the equation of Figure.1 yields the equation that forms the basis for the Rawlins-Schellhardt analysis technique:

Figure.2

The form of the equation of Figure.2 suggests that a plot of log (Δpp) vs. log (q) will yield a straight line of slop 1/n and an intercept of (-1/n[log(C)]). The AOF potential is estimated from the extrapolation of the staright line to Δpp evaluated at a pwf equal to atmospheric pressure ( sometimes called base pressure)


2. Backpressure Tests

Backpressure tests are conducted to evaluate the flow rates under varying wellhead pressures. Deliverability curves are generated to predict well performance.



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