*for Microsoft
EXCEL*^{®}*
Version 2003 or later*

This spreadsheet can be used to carry out well-test analysis calculations that are typically used for basic well performance surveillance and eliminates the need for a specialised software package (e.g. PIE) for this type of work. The key features in the spreadsheet are:

- Use individual sheets for each set of shut-in data, with up to 32000 data points for each set of data and as many sheets as you want. A data "filter" is included to reduce the input pressure data to a manageable size.
- A pseudo-pressure calculation is included which uses a table of gas viscosity and Z-factor data that you supply. The pseudo-pressure is used to transform the shut-in pressure data so the correct analysis results are obtained.
- A Derivative plot for each shut-in is displayed along with a graphics control that is used to define a derivative stabilisation. This stabilisation is then used to estimate the reservoir permeability-thickness.
- A Superposition plot for each shut-in is displayed along with a graphics control that is used to define a straight-line through the the data. This line is used to estimate the extrapolated reservoir pressure (P*) and the skin-factor.
- Multiple sets of shut-in data can be compared on rate-normalised Derivative and Superposition plots (plot overlay). This comparison shows how well performance and reservoir pressure change over time.
- The "Time to pseudo-steady-state flow" (Tpss) is estimated from a simple radius-of-investigation calculation, and a value of Tpss can be entered to control the length of the rate-history used in the superposition calculations.

All of the calculations are visible and unprotected so you can also use this spreadsheet to learn how basic well-test analysis calculations are carried out. All of the basic algorithms needed to prepare a derivative plot are included as Visual Basic code in the spreadsheet. This includes a general superposition function, and a simple derivative calculation which includes smoothing. Everything in the spreadsheet is open for you to modify as desired.

If you are wondering why this is being made available free of charge, please read the discussion of what is meant by "Basic Surveillance". And some slides describing the theory in more detail are here.

If you want to use the "Basic Surveillance" spreadsheet, please read the following terms, then click on the "I Accept" button below to download a ZIP-file containing the spreadsheet.

® EXCEL is a registered trademark of Microsoft Corporation.