Well Logging and Drilling Fluids Lecture Notes

Vocabulary flashcards covering principles, equipment, operations, and petrophysical properties in well logging and drilling fluid technology.

Well Logging

The practice of making a detailed record (well log) of the geologic formations penetrated by a borehole, based either on visual inspection of rock samples brought to the surface or physical measurements made by downhole instruments.

Geological Logs

Well logs based on the visual inspection and physical examination of rock cuttings and core samples brought to the surface.

Geophysical Logs

Well logs based on physical measurements made by specialized instruments lowered directly into the borehole.

Pechelbronn Oil Field

The oil field in France where the Schlumberger brothers first made electrical well measurements in $1928$, establishing electrical well logging in petroleum exploration.

Porosity

The fractional portion of rock volume occupied by pore space, often expressed as a percentage and typically ranging from $10\%$ to $30\%$ in reservoir rocks.

Hydrocarbon Saturation

The fraction of pore space filled by hydrocarbons; when water is the only other fluid present, water saturation plus hydrocarbon saturation equals one ($S_w + S_h = 1$).

Archie's Formulae

Mathematical formulations used to calculate water saturation from downhole resistivity measurements to determine commercial hydrocarbon capability.

Darcy

The standard unit of permeability that allows a fluid flow of $1\,\text{mL/s}$ of fluid with $1\,\text{cP}$ viscosity through $1\,\text{cm}^2$ area under a pressure gradient of $1\,\text{atm/cm}$.

Sag

The settling of heavy weighting materials out of drilling mud, causing wide variations in well fluid density, commonly occurring in high-angle and horizontal wells.

Baryte

The most common weighting material added to drilling mud to increase density, balance formation pressure, and prevent fluid influx.

Kick

An unexpected influx of formation fluids into the wellbore caused when formation pressure exceeds the hydrostatic pressure of the mud column.

Blowout

An uncontrolled eruption and flow of pressurized formation fluids from the wellbore to the surface or another formation.

Mud Filtrate

The liquid effluent of the continuous phase of drilling mud that filters into porous and permeable rock formations under positive pressure differential.

Mud Cake (Filter Cake)

The low-permeability residue of mud solids deposited on the borehole wall as the mud loses filtrate into permeable formations, retarding further fluid invasion.

Bridging Agents

Materials (such as calcium carbonate or ground cellulose) sized to exceed half the opening of pore throats or fractures, forming a tight seal for mud solids.

Wellbore Stability

The condition of maintaining borehole size and cylindrical shape to prevent sloughing, bridging, tight hole conditions, and excessive hole enlargement.

Skin Damage

Any reduction in natural formation porosity and permeability caused by mud or solid invasion, clay swelling, or residual buildup on perforations, causing a pressure drop.

Corrosion Coupon

A small piece of metal exposed directly to the fluid system to evaluate corrosive conditions, monitor metal loss rates, and assess chemical inhibitor effectiveness.

Mud Logging with Sample Logging

A wellsite operation consisting of continuous examination and recording of physical aspects of drill cuttings, core samples, gas content, and drilling parameters.

Penetration Rate Log (Drill Time Log)

A continuous record of the time taken to drill a specific pipe length or penetration rate, acting as an indirect lithology and compaction indicator.

Fluorescence

The glowing response exhibited by hydrocarbon-bearing rock cuttings or cores when subjected to ultraviolet (UV) light examination during sample testing.

Gravel Packing

A well completion method wherein an underreamed section of the borehole contains a slotted or perforated liner packed with sized gravel to prevent sand inflow.

Gravel Pack Log

A dual-detector neutron logging tool used to evaluate the packing condition and porosity of a gravel pack to identify intervals requiring replacement prior to production.

Sonde

The downhole measuring instrument assembly constructed of steel or fiberglass that houses the active or passive logging sensors.

Cartridge

The steel-encased electronic assembly in a downhole tool that supplies power to the sensors, processes raw signals, and transmits telemetry data to the surface.

Measurement While Drilling (MWD)

A downhole system that acquires drilling and directional parameters in real time and transmits data to surface via mud pressure wave pulses at roughly $3\,\text{bits/s}$.

Logging While Drilling (LWD)

A system where formation evaluation sensors integrated into the bottom-hole assembly record petrophysical data into internal memory, retrieved after tripping to the surface.

Data API

The three fundamental operational procedures of geophysical exploration and well logging: Data Acquisition, Processing, and Interpretation.