Drilling Operations & Well Logging Flashcards

What is the primary purpose of drilling mud in well operations?

Answer: To lubricate the drill bit and maintain pressure

The primary purpose of drilling mud in well operations is to lubricate and cool the drill bit, carry rock cuttings to the surface, and crucially, maintain hydrostatic pressure in the wellbore. This pressure prevents formation fluids from flowing uncontrollably into the well, which is known as a 'kick,' thus ensuring drilling safety and wellbore stability.

What does the term 'kick' refer to in drilling?

Answer: An influx of formation fluids into the wellbore

In drilling, a 'kick' refers to an influx of formation fluids (oil, gas, or water) into the wellbore. This occurs when the pressure exerted by the drilling mud column is insufficient to counteract the pressure of fluids within the rock formation. If not quickly controlled, a kick can escalate into a dangerous blowout, posing significant safety and environmental risks.

What is the function of well logging?

Answer: To record geological data about the subsurface

The function of well logging is to record geological and petrophysical data about the subsurface formations encountered during drilling. Specialized tools are lowered into the wellbore to measure various properties, such as resistivity, radioactivity, and acoustic velocity. This data is crucial for identifying hydrocarbon zones, evaluating reservoir quality, and making informed decisions for well completion and production.

Which tool is used to measure formation resistivity?

Answer: Resistivity log

A resistivity log is the tool used to measure formation resistivity, which is the ability of a material to oppose the flow of electric current. Hydrocarbons and gas are highly resistive, while saline formation water is conductive. By analyzing resistivity measurements, geologists can identify hydrocarbon-bearing zones and determine water saturation within the reservoir.

Why is casing used in a well?

Answer: To prevent formation collapse and fluid migration

Casing is used in a well to prevent formation collapse and fluid migration, providing structural integrity to the wellbore. Steel pipes are inserted and cemented in place, isolating different geological formations and preventing unwanted fluids from moving between zones or into the wellbore. This ensures well stability, safety, and environmental protection.

What does a gamma ray log detect?

Answer: Radioactivity to identify rock types

A gamma ray log detects natural radioactivity to identify different rock types in the subsurface. Shales and clays typically exhibit higher natural radioactivity due to their content of potassium, uranium, and thorium, while sandstones and carbonates are generally less radioactive. This log is fundamental for distinguishing lithologies, identifying shale content, and correlating formations.

Which log measures the acoustic properties of the formation?

Answer: Sonic log

A sonic log measures the acoustic properties of the formation by recording the time it takes for an acoustic wave to travel through a specific length of rock. This travel time is inversely related to the rock's acoustic velocity, which is influenced by porosity, lithology, and fluid content. Sonic logs are valuable for porosity determination, lithology identification, and seismic-well ties.

What is the purpose of cementing in drilling operations?

Answer: To bond casing to the borehole and isolate zones

The purpose of cementing in drilling operations is to bond the casing to the borehole wall and isolate different geological zones. Cement slurry is pumped into the annulus between the casing and the formation, creating an impermeable seal. This process provides structural support for the casing, prevents fluid migration between formations, and protects the casing from corrosion.

Which well log helps determine the porosity of formations?

Answer: Porosity log

Porosity logs, such as neutron logs and density logs, are specifically designed to help determine the porosity of formations. These logs measure properties related to the amount of pore space within the rock, which can be filled with fluids. By analyzing these measurements, geologists can calculate the percentage of pore volume available for hydrocarbon accumulation.