Monitoring - Pulse Testing

Pulse Testing

Contacts

Ahmed Abou-Sayed ahmed@advantekinternational.com Advantek International

Summary

A pulse test is a modification of standard interference testing that is designed to assist in identification of the signal produced by the stimulus. It can be considered as a special form of multi-well interference testing.

A pulse test uses shorter pulses (with smaller observed pressure changes) than an interference test. The test is carried out between two wells, one of which is an observation well and the other well is subjected to a series of injection or production “pulses” followed by shut-in. The process generates an identifiable pressure pattern, which can be detected by the observation well and can be isolated from the general field pressure trends.

Key Issues

Basic Concepts Design References

Key Issue 1: Basic Concepts

Concept 1.1:

If asked, "What are some of the advantages?"

Only two wells need to be involved in the test at a time, and the other wells in the field can continue injection/production. One well is the active well that is pulsed and the other is the passive (measurement) well.
The test time for determining formation properties is much shorter than for conventional interference testing.
There is a basis (as in conventional interference testing) for determining storage (fc_th), diffusivity (k/fmc_t) and interval transmissibility (kh/m).
Since an identifiable pressure pattern is used, there is more certainty for discriminating noise. Nevertheless, sensitive and reliable pressure recording is necessary!
Wells other than the observation well do not need to be monitored.

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Key Issue 2: Design

Design 2.1:

Do you only send one pulse?

If the standard assumptions of an infinite, homogeneous and isotropic reservoir are made (which likely are approximations only), storage and transmissibility can be determined relatively easily from a single pulse measurement.
General solutions exist for situations where a train (multiple) of pulses is sent. These solutions all depend on the time lag and the amplitude of the pulses. A good reference on the specifics for the calculations is Sabet, 1991.
Simulation might be the preferable method for interpreting pulse data.

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Design 2.2:

Skin and Storage

If there is only skin at the active well, this does not change the observed pressure drop at the observation well (whether the skin is positive or negative).
The presence of infinitesimal skin at the observation well does not impact the calculations.
Substantial skin at the observation well delays the arrival of the pressure wave (for positive skin and vice versa for negative skin).
to account for wellbore storage, you need to assume that the reservoir is homogeneous and isotropic. Precautionary measures can include packers in both the active and observation wells and the use of late time data in reservoir simulation matching of the observed data.

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References

Daltaban, T.S., and Wall, C.G.: Fundamental and Applied Pressure Analysis, Imperial College Press, London (1998).
Earlougher, R.C. Jr.: Advances in Well Test Analysis, Henry L. Doherty Memorial Fund of AIME, SPE, Dallas (1977).
Matthews, C.S. and Russell, D.G.: Pressure Buildup and Flow Tests in Wells, Henry L. Doherty Memorial Fund of AIME, SPE, Dallas (1967).
Sabet, M.A.: Well Test Analysis, Gulf Publishing Company, Houston (1991).

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