# What is mud resistivity?

## What is mud resistivity?

In a permeable formation, mud resistivity is commonly 1 to 3 orders of magnitude lower than the formation resistivity, or, in the case of oil-based mud (OBM), it can be much higher.

## What is resistivity in oil field?

Resistivity is a fundamental material property which represents how strongly a material opposes the flow of electric current. In these logs, resistivity is measured using four electrical probes to eliminate the resistance of the contact leads.

Why is determination of mud resistivity important?

It is necessary to measure resistivity because the mud, mud cake, mud filtrate resistivity exert a strong effect on the electric logs taken in that mud. The mud resistivity varies greatly from the actual resistivity values due to the various factors encountered in the actual operation.

### What are the types of resistivity logs?

Resistivity Logging. There are three main categories of well Logging: Electrical, Nuclear and Acoustic/Sonic.

### What is the resistivity of water?

What is resistivity in water?

Type of Water Approximate resistivity in Ohms (Ω)
Pure Water 20,000,000
Distilled Water 500,000
Rain Water 20,000
Tap Water 1,000 – 5,000 Ω

What is formation resistivity?

The formation resistivity factor measure the influence of pore structure on the resistance of sample. In the absence of a conductive mineral layer the electrical current can flow only through the fluid in the rock interconnected pores. This implies that F is related to the porosity of the rock.

## What does high resistivity mean?

Electrical resistivity is a measure of a material’s property to oppose the flow of electric current. The symbol of resistivity is usually the Greek letter ρ (rho). A high resistivity means that a material does not conduct electric charge well.

## Does water have high resistivity?

Water with a high concentration of dissolved salts will have a low resistivity, and vice versa. Resistivity is measured in Ohms….What is resistivity in water?

Type of Water Approximate resistivity in Ohms (Ω)
Pure Water 20,000,000
Distilled Water 500,000
Rain Water 20,000
Tap Water 1,000 – 5,000 Ω

What can affect resistivity?

The general rule is resistivity increases with increasing temperature in conductors and decreases with increasing temperature in insulators.

### Does salt water have high resistivity?

Water with a high concentration of dissolved salts will have a low resistivity, and vice versa. Resistivity is measured in Ohms….What is resistivity in water?

Type of Water Approximate resistivity in Ohms (Ω)
Tap Water 1,000 – 5,000 Ω
Brackish river water 200
Coastal seawater 30
Open seawater 20 – 25

### What should the fluid loss be in oil based mud?

Only the oil phase in oil based mud is free to form a filtrate, making an oil based mud suitable for formations which must not be damaged. The fluid loss is generally very small with oil based muds (less than 3cc at 500 psi and 300 degrees F). During the test there should never be water present in the filtrate (indicates a poor emulsion).

How is the resistivity of downhole mud determined?

The downhole mud resistivity can be estimated approximately by measuring the resistivity of a surface sample taken just before mud circulation was stopped before logging and adjusting it for the difference in temperature using an appropriate chart or equation.

## Which is an important number in the resistivity log?

An important number in log interpretation therefore is the particular formation resistivity factor ( F ), defined as where Ro is the resistivity of rock 100% saturated with water of resistivity Rw. Note that Rw decreases with increasing salinity and temperature, as, therefore, does Ro. The value of F increases with decreasing porosity.

## What kind of mud is used in OBMs?

In recent years the base oil in OBMs has been replaced by synthetic muds such as esters and ethers. These muds are generally called synthetic or psuedo oil based muds. The water in invert emulsion muds is dispersed as small droplets throughout the oil.