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**Tubing limited wells. | **Tubing limited wells. | ||
===Nominal and Effective decline=== | === Nominal and Effective decline === | ||
*There are two types of decline factors (often called the decline rate). | |||
*The nominal decline factor d is defined as the negative slope of the curve representing the natural logarithm of the production rate q vs. time t or : | |||
*[[File:Nominal and Effective decline.PNG|middle|Rate q vs. time t]] | |||
*Nominal decline is a continuous function and it is the decline factor that is used in the various mathematical equations relating to decline curve analysis. For exponential decline it is a constant with time. | |||
*The effective decline factor D is a stepwise function that is in better agreement with data recording practices. It is the drop in production rate from qi to q1 over a specific time period. | |||
*It is defined as | |||
*[[File:Factor D.PNG|middle|Factor D]] | |||
*D is the effective decline rate = the decline rate over a time period. | |||
**This is the decline often quoted in e.g. commercial software decline graphs. Such software may, at users discretion, report nominal decline. | |||
**It is the proportion by which the production rate reduces over a given time period. | |||
**D is a constant only for constant percentage or exponential decline. | |||
**D decreases with time for hyperbolic and harmonic decline | |||
**(1> b > 0) | |||
*It is easy to convert from a nominal decline factor to an effective decline factor and vice versa. | |||
*[[File:Nominal decline factor d to the effective decline factor.PNG|middle|Nominal decline factor (d) to the effective decline factor ]] | |||
*Thus an ‘effective’ decline of 10 % per year is equivalent to a nominal decline of 10.54% per year and vice versa | |||
INSERT Figure 6 Effective and Nominal Decline, Shape and Relationship | |||
=== Hyperbolic Decline === | === Hyperbolic Decline === | ||
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