Transient Pressure BuildUp Analysis (PBU Test)

THEORY & FORMULA

Transient Pressure BuildUp Analysis (Oilwell)
Pressure buildup (PBU) survey involves measuring the changes in wellbore pressure with time after a well has been shut in. PBU requires that the well produce at a stabilized rate before shut-in. The PBU equation introduced by Horner is given by:

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where pws = sandface pressure, psig pi = initial reservoir pressure, psig Qo = stabilized oil rate, STB/day μo = oil viscosity, cp Bo = formation volume factor, rB/STB k = permeability of formation rock, mD h = formation thickness, ft tp = flowing time before shut-in, hr Δt = shut-in time, hr.
A plot of pws versus (tp+Δt)/Δt would ideally produce a straight line with an intercept at pi (or p*) and a slope of ,strong>-m. This plot is known as the Horner plot, a semi-log plot. In practice, there is a deviation from a straight line in the initial section of the plot due to skin and wellbore storage effects. The straightline portion of the plot can be graphically identified by interactively ignoring a number of early plot points and performing a straightline fit on the rest.
When a satisfactory straight line is obtained, the initial reservoir pressure pi is estimated by extrapolation to the pressure corresponding to (tp+Δt)/Δt = 1. That is, the extrapolated pressure (p*) = (pi) for an infinite reservoir or for wells tested early in the life of the reservoir.
Another pressure point of importance on the fitted straightline is the pressure corresponding to Δt = 1 hour. Also computed is the slope (m) of the straight line in units of psi/log cycle.
Finally, the permeability of the formation (k) and the skin factor (s) can be calculated according to the relationships:

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where m = slope of semi-log straight line, psi/log10cycle p1hr = pressure at time 1-hour on semi-log straight line, psig pwf(Δt=0) = sandface pressure immediately prior to shut-in, psig ct = total compressibility coefficient, 1/psi

Tips:

◊ Use link

EXAMPLE Of Input/Output to demo data entry expectations and results; you may edit & use it as starting point

◊ Between 15 to 30 measurements points may be entered

◊ Up to 11 points may be ingored in the staright-line fitting process

◊ If the required Java plug-in not installed on your computer, an auto-download of this plug-in will be initiated before the plot is displayed.

BIBLIOGRAPHY
Dake L.P.; Fundamentals Of Reservoir Engineering; Elsevier Scientific Publ. Co., Amsterdam, Netherlands, 1978.
Horne R.N.; Modern Well Test Analysis - A Computer-Aided Approach; Petroway Inc., Palo Alto, California, 1995.
Earlougher R; Advanced Well Test Analysis; Monograph Series Vol 5, SPE, Dallas, 1977.
Kansas Geological Survey, Oil & Gas Information, Gemini Project, Lawrence, Kansas, 2002.

Recreated by @Abrar2009

Use link:

* Effect of Oil Production Rate

* Science Direct Journal

* Haliburton Public Data

* Petroleum Engineering Calculator