Well testing using multiple pressure measurements

Details Well testing using multiple pressure measurements Well testing using multiple pressure measurements

2002-06-13

2004-01-13

Tsay, Frank (Department: 3672)

Wells

Processes

With indicating, testing, measuring or locating

C166S252600

Reexamination Certificate

active

06675892

ABSTRACT:

BACKGROUND
The invention generally relates to well testing using multiple pressure measurements.
After a well is drilled for purposes of hydrocarbon production, the well typically is tested to determine various parameters that characterize the well. For example, the well may be tested to determine the permeability of a particular formation through which the wellbore extends, as well as determining formation damage, often called the “skin.”
The term “skin” may be defined as the alteration of permeability due to fluid and particle invasion that occurs during drilling (fluid and mechanical skin respectively). In this manner, fluid and particle invasion during drilling may alter the permeability of the formation near the wellbore (called the “near wellbore formnation”) and create very low permeability around the wellbore. Excessive skin may cause an excess pressure drop when the well is produced. Thus, one of the main objectives of well completion is to reduce the skin in order to improve production efficiency.
For many wells, such as horizontal wells, establishing well productivity is difficult because near wellbore formation conditions right after drilling and clean up are complex to assess. Different characteristics of the formation properties along the wellbore and their exposure to mudcake and mud filtrate for different time lengths normally creates variable skin along the wellbore that cannot be evaluated easily by using conventional well testing techniques. Furthermore, variable skin may create non-uniform-flow during production tests that hinders the interpretation of these results. Therefore, challenges to accurately assessing the skin using conventional well testing techniques exist.
Wireline techniques to assess the reservoir parameters typically produce an indication of the reservoir parameters along the near wellbore formation. Furthermore, conventional tests typically produce a single average value that characterizes the skin for the entire wellbore. Thus, a conventional test may not produce an indication of the spatial variation of the skin along a particular wellbore. However, determination of the spatial variation of the skin along the wellbore may be useful for purposes of targeting specific zones of the wellbore for cleanup and near-wellbore stimulation, as some zones may have excessive skin damage and should be isolated for purposes of treatments.
FIG. 1
depicts a typical system
10
for measuring the average skin along a wellbore
11
that extends through a formation
14
. In the system
10
, a tubular string
13
extends through the wellbore
11
and the annular space between the string
13
and the interior of the wellbore
11
is sealed off by a packer
12
into two isolated segments. For purposes of measuring the average skin, a flow to the surface of the well may be established through the central passageway (for example) of the tubular string
13
, and in response to this flow, pressure
22
and flow
23
sensors of the string
13
may measure the respective pressure and rate of the flow. This information may be used to deduce an indication of the average skin and formation parameters associated with the whole wellbore
11
that extends through a formation
14
. However, for multi-layer formation and horizontal well with long well hole, the skin and formation parameters can vary significantly. As noted above, the average skin and formation parameters of the formation
11
may not provide the enough resolution needed for proper production development and remedial work. The variations of the skin and formation parameters along well hole in the formation are needed, as average reservoir parameters are not sufficient to plan stimulation treatments or understand spatial variation of formation quality.
Thus, there exists a continuing need for an arrangement and/or technique that addresses one or more of the problems that are stated above and/or possibly addresses problems that are not stated above.
SUMMARY
In an embodiment of the invention, a technique includes measuring the transient pressure in the wellbore at two distinct locations, which we call the first and second regions, with independent pressure sensors as the formation fluid is produced into the first region. The second region may be a passive pressure observation section.
The second region is hydraulically isolated from the first region in the wellbore, and the communication between them takes place through the formation. Formation productivity characteristics (skin, horizontal permeability or vertical permeability, as examples) are determined from the first and second measured pressures.


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Frick, T.P.; Brand, C.W. and Schlager, B.,Horizontal Well Testing of Isolated Segments, SPE Journal, Sep. 1996, pp. 261-273.

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