Estimating average reservoir pressure

Well Test Analysis, Pressure and Production Monitoring........ etc.

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shahid
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Estimating average reservoir pressure

Post by shahid »

Hello everybody,

Could you please help me on this topic

How to estimate average reservoir pressure with limited SGS data at well basis for a particular reservoir? The pressure will be used for MBAL study

The reservoir is small and without static and dynamic model.

Thanks.
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FANARCO
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Post by FANARCO »

You can RIH in any well with wireline equipped with downhole memory gauges
This will measure the static reservoir pressure
If the well was closed for a long time 3-5 days depends on permeability, the resulted static reservoir pressure will be equal to the average reservoir pressure
mshokrey
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Joined: Fri Mar 16, 2007 11:39 pm

Average reservoir perssure estimate (1) Bounded Reservoir

Post by mshokrey »

Dear shahid,

Here you are the detailed answer for your quires from PIE site:

http://www.welltestsolutions.com/faq.htm#FAQ_17

It is in the form of two questions. the first is for bounded reservoir without any support (i.e. no gas cap or water drive or injection). The second question is related to reservoirs with voidage replacement

How Do I Find The Average Reservoir Pressure?

This is one area of well-testing that is loaded with myths, opinions, and downright lies. There are innumerable "special" analysis methods that take a particular slant on this problem. While this provides endless opportunities for well-test specialists to discuss the merits of these special methods, this analysis proliferation is not very helpful for the engineer trying to get an answer.

PIE attempts to simplify the problem by dealing with closed reservoirs as simply another type-curve model to match to the measured data. When the program detects that you are using a closed reservoir model for the analysis, the results displayed after a type-curve simulation will include the average pressure for the cumulative production and the pore-volume of the specified reservoir geometry.

The average-pressure problem breaks down into three distinct cases:

* The test shows no evidence of reservoir boundaries or drainage-area limits. The calculation of the average-pressure will have to be based on an ASSUMED reservoir size obtained from other sources of information.
* The test does show some effects from reservoir boundaries, but does not show any closed reservoir characteristics. The calculation of the average-pressure will be constrained to a reservoir geometry that honours the location of these boundaries and an ASSUMED reservoir size.
* The test shows closed reservoir effects. The average pressure and reservoir geometry are determined from a best match of the model to the measured data.

It is important to note that when a test DOES NOT show closed reservoir effects, you MUST make an assumption about reservoir size in order to calculate the average reservoir pressure. This is true even for the specialised analysis methods. There is no escape from the fact that you cannot determine the reservoir size if a test does not show closed reservoir effects.

If you cannot make a reasonable assumption about the reservoir size and the test does not show closed reservoir effects, then you can carry out a "Minimum reservoir volume" calculation. This is simply the smallest reservoir size that DOES NOT affect the match of the measured data i.e. all the unknown reservoir boundaries are outside of the radius-of-investigation of the test. This calculation is particularly useful for exploration wells as it defines the minimum "proven reserves" for the test.

PIE does include an MBH analysis as an option under the "MAIN" pull-down menu. The methodology for this special analysis is described in the SPE Monograph "Pressure Build-up and Flow Tests in Wells" by Matthews and Russell.
mshokrey
Posts: 13
Joined: Fri Mar 16, 2007 11:39 pm

Average reservoir perssure estimate (2) voidage replacement

Post by mshokrey »

Dear shahid,

Here you are the detailed answer for your quires from PIE site:

http://www.welltestsolutions.com/faq.htm#FAQ_17

It is in the form of two questions. the first is for bounded reservoir without any support (i.e. no gas cap or water drive or injection). The second question is related to reservoirs with voidage replacement


How Do I Find The Average Pressure In A Field With Voidage-Replacement?

When there is voidage replacement (i.e. water or gas injection) in a developed field, the drainage area around each well takes on a very peculiar geometry (see the chapter on determining average reservoir pressure in the SPE Monograph "Pressure Build-up and Flow Tests in Wells" by Matthews and Russell). What is important to note for this type of problem is that each production well has a connection to one or more of the injection wells. This connection creates one or more "constant pressure boundaries" in the drainage area for the well. For example, the drainage-area for each producer in a balanced 5-spot water-flood is a rectangle with half the pattern area and a constant-pressure boundary on all four sides.

For all practical purposes, the average pressure for a well with constant-pressure boundaries is the pressure AT the constant-pressure boundary. The pressure at the constant pressure boundary is exactly equal to the initial-pressure used for the type-curve simulation in PIE with a constant-pressure boundary model.

Therefore, when you analyse a test for a well in a field with voidage replacement, match the test data with a closed reservoir model with one or more constant pressure boundaries. The initial-pressure from this match will be the average reservoir pressure in the drainage area of the well.
geeker
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Post by geeker »

THANKS! I needed to know this too :D
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