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| *There are two types of decline factors (often called the decline rate). | | *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 : | | *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]]
| | [[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. | | *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. | | *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 | | *It is defined as |
| *[[File:Factor D.PNG|middle|Factor D]]
| | [[File:Factor D.PNG|middle|Factor D]] |
| *D is the effective decline rate = the decline rate over a time period. | | *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. | | **This is the decline often quoted in e.g. commercial software decline graphs. Such software may, at users discretion, report nominal decline. |
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| **(1> b > 0) | | **(1> b > 0) |
| *It is easy to convert from a nominal decline factor to an effective decline factor and vice versa. | | *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]]
| | [[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 | | *Thus an ‘effective’ decline of 10 % per year is equivalent to a nominal decline of 10.54% per year and vice versa |
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