NPI Typecurve Analysis

Boundary-Dominated Match

Transient Match

Normalized pressure integral (NPI) typecurves are the inverse of Agarwal-Gardner typecurves. The NPI analysis is often preferred by those who come from a pressure transient analysis domain, and are accustomed to seeing log-log plots using normalized pressure, instead of normalized rates.

Note:   For information on the NPI typecurve theory and equations, see NPI Typecurve Analysis Theory.

The NPI typecurve analysis method uses the following models:

Boundary-Dominated Match

To obtain information about reserves and drainage areas, we recommend that you focus on the boundary-dominated (depletion) stems of typecurves. These are located on the right-side of the plot, where each set of typecurve converges to a single line. The NPI typecurve analysis does not require hyperbolic exponent values. Instead, the data is matched on the single depletion stem. As the data is moved about the plot, the OGIP / OOIP is continuously updated on the Analysis tab. 

For gas reservoirs whose fluid properties are strongly a function of pressure, the data points appear to "stretch" and "contract" as they are moved around the screen. This is because of the pseudo-time effect. Harmony recalculates gas properties at average reservoir pressures based on the calculated OGIP from the typecurve match. As the match is modified, OGIP, average reservoir pressure, and material balance pseudo-time are automatically recalculated, and the data points are repositioned accordingly.

Transient Match

To obtain information about permeability and skin, you should focus on the transient stems of the typecurves. On the NPI typecurve plot, these open on the left-side of the plot as a “fan” of different reD values for the radial and water-drive models, re / xf values for the fracture model. You can select the best matching typecurve, which provides an associated reD (or re / xf) value.

From the selection, Harmony calculates: