Lecture 2 - Exploration: Part 2 Flashcards
What is used to control mud viscosity?
Bentonite
What is used to control mud density?
Baryte
How is mud lost?
Mud penetrating rock formation and subsequent loss
What is the consequence of ‘formation kicks’?
Could lead to a blowout
Penetration of formation fluids into mud
What are mud samples analysed for? How?
Hydrocarbon gases using gas chromatography
Why is drill-stem testing done?
Good indication of reservoir characteristics (poroperm, nature of gases) from analysis of flow rate, amount of formation fluid recovered in drill string and the formation pressures recorded.
What is LWD?
Logging while drilling
- logging after each section is drilled usually prior to inserting casing
What are gamma rays?
High-energy electromagnetic waves which are emitted by atomic nuclei as a form of radiation
What does a gamma ray log measure? Where does the radiation come from?
Measurement of natural radioactivity in formation versus depth
Radiation from element such as U, Th and K
What does the spontaneous potential (SP) curve record?
The natural occurring electrical potential produced by the interaction of formation connate water, conductive drilling fluid and shale
What does the spontaneous potential (SP) curve reflect?
The difference in electrical potential between a moveable electrode in the borehole and a fixed reference electrode at the surface
The spontaneous potential is primarily used as a Lithology indicator. What else can it be used for?
Permeability indicator
Shale volume indicator
Porosity indicator
Measurement of Rw (hence formation water salinity)
What is the neutron log used for?
Evaluating formation porosity (although it is essentially just a hydrogen detector)
What does the capture of hydrogen atoms result in?
Emission of a secondary gamma ray
What is the formation density log used to measure?
Porosity log measuring the electron density of a formation
How do dense and low density formations compare in a formation density log?
Dense formations absorb many gamma rays so have low count rates
Low density formations absorb fewer gamma rays so have high count rates
What does resistivity measure?
Electrical properties of the rock
What three factors affect the ability of a material to conduct an electric current?
Volume of water
Temperature of formation
Salinity of formation
What do resistivity logs measure?
Ability of rocks to conduct electrical current
What do acoustic tools measure?
Speed of soundwaves in subsurface formations
How do acoustic logs indicate Lithology?
Using the ratio of compressional velocity over shear velocity
Name two types of image logs and the companies that use them
FMI (Schlumberger) STAR Imager (Baker)
What are image logs based on and what do they show?
Based upon electrical resistivity/conductivity of units
Shows up internal character of units e.g. bedding, fractures
How do high resistivity units appear on image logs? Give examples of these
Show up as bright
E.g. lava and sills
What does STAR Imager provide?
High-resolution resistivity formation images in conductive mud systems
What does abandonment mean?
Converting a well to a state that can be left indefinitely, will not damage water supplies, potential hydrocarbon or the environment
What two methods of abandonment are there?
P + A: Plugged (cement plug) and abandoned
Suspended: left in state with sealed well head cover for later activity
