Calculate Water Resistivity Rw - Western Atlas (1985)

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List of equations assignment

Water Resistivity - Western Atlas (1985)

Western Atlas (1985) proposed an equation for the calculation of water resistivity (Rw) that is compound by some math expressions and values such as equivalent water resistivity (Rwe), bottom hole temperature (BHT). The equation is the following:

Where:
• Rw= water resistivity
• Rwe= equivalent water resistivity
• BHT= Bottom Hole Temperature

Calculate Water Resistivity (Rw) - Western Atlas (1985)
Rwe: ohm-m		BHT: °F

Equivalent Water Resistivity (Rwe)

For the calculation of equivalent water resistivity (Rwe), these are the values that must be known: mud filtrate resistivity, an SP measurement, and bottom hole temperature. The equation is the following:

Where:
• Rmf= resistivity of mud filtrate at formation temperature
• BHT= Bottom Hole Temperature
• SP= SP measurement

Calculate Equivalent Water Resistivity (Rwe)
Rmf: ohm-m		SP: mV
BHT: °F

Mud Filtrate Resistivity (Rmf)

To calculate mud filtrate resistivity, it is important to know the mud filtrate resistivity at surface temperature, the temperature of mud filtrate, and formation temperature. The equation to calculate it, is the following:

Where:
• Rmf= resistivity of mud filtrate at formation temperature
• Rmfsurf= resistivity of mud filtrate at measured temperature
• Tsurf= measured temperature of Rmf
• Tf= formation temperature

Calculate Mud Filtrate Resistivity (Rmf)
Rmfsurf: ohm-m		Tsurf: °F
Tf: °F

Formation Temperature (Tf)

There is an equation to calculate formation temperature if it is unknown or difficult to measure, and this takes into account: the annual mean surface temperature, formation temperature, bottom hole temperature, and formation depth. The equation is the following:

Where:
• AMST= Annual Mean Surface Temperature
• BHT= Bottom Hole Temperature
• FD= Formation Depth
• TD= Total Depth
• Tf= formation temperature

Calculate Formation Temperature (Tf)
BHT: °F		AMST: °F
TD: ft		FD: ft

Made by Henry Herrera