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The Reservoir Diagnosis

The Reservoir Diagnosis

via

Well Testing

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Reservoir Complexity

The reservoir is a complex

unknown system to be explored

and described

?

?

?? ?

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Reservoir Knowledge

Knowledge of the reservoir is required to:

Understand the present product ion

performance

Optimise the production potential

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Reservoir Knowledge

In addition to the reservoir complexity, there are more

phenomena in the reservoir which can have an impact on

the production potential.

For example, changing reservoir pressures can have an impact

on:

fluid properties

downhole gas-oil ratios

water flow from the aquifer

breakthrough of previously sealing faults

This requires Reservoir Monitoring.

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The liberated gas can create secondary gas caps

GasOil

The migrating gas can

reach the production well

Possible Production Problems

The well test can help to forecast the effect (k, PVT)

Monitoring shows the current status

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Possible Production Problems

Gas

Oil

A gas cap extension or

gas coning can be observed

The well test can help to forecast the effect (kv)

Monitoring specifies production policies

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Source of water can be:

Aquifer water moving laterally to the well

A water cone is drawn up (bottom water)

Possible Production Problems

Water

flow

The well test can help to forecast the effect (kv, krw )

Monitoring specifies production policies

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Contact with the Reservoir

The well is the only direct link

between the reservoir and

surface, separated by several

thousand feet.

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Reservoir Surveillance and Monitoring

The well is:

A communication tool:

- The reservoir can be evaluated by testing the well

- The reservoir is monitored through the well

A product ion tool:

The reservoir production capacity depends on the quality of thewell/reservoir communication

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The Well Test Concept

During a well test, we send a

signal into the reservoir by

changing the rate...

and we receive its response:

the bottom hole pressure

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The Well Test Concept

First we receive the response

from the wellbore

From its behaviour we evaluate the

(near) wellbore properties

The longer we observe the response, the further we look into the

system: well / formation / limits

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The Well Test Concept

Secondly we receive the response

from the formation

From its pressure behaviour we get the

permeability value

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The Well Test Concept

Thirdly we receive the

response from a boundary

From the time delay we get the distance

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The Well Test Concept

we get information on

the hydrocarbons properties

From the fluid samples...

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Standard Well Test Set-up

Surface rates

Surface samples

BHP & BHT

Downhole rates

Bottom hole samples

Acquisition

Interpretation

WHP

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Reservoir Evaluation by WT

The well testing objectives.

There are numerous WT objectives, depending on the

specific problems/questions related with the

well/reservoir system.

Following are some typical objectives:

The well/reservoir production capacity

Reservoir boundaries / size (STOIIP)

Hydrocarbon properties (PVT samples)

Reservoir properties (dual porosity systems)

etc.

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Data to Be Acquired

Well Testing Interpretation

Required input data for analysis:

Pressure data P

Production rate history q

Basic fluid parameters Bo, , (cfluids)

Reservoir data h, , ct, model parameters..

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Reservoir Evaluation

The Well Testing Interpretation

results are :

Well production capacity (well damage)

Reservoir production capacity (transmissibility)

Reservoir porous volume (reservoir limits)

Reservoir specific behaviours

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