Final Review: Theory

Question 1

what is a well log?

Answer 1

a continuous record of measurements made in a bore hole to detect variations of some physical properties of subsurface rocks

Question 2

what is a passive log

Answer 2

a log that measures naturally occurring phenomena (ex, radioactivity)

Question 3

what is an active log

Answer 3

a log that induces a medium into the formation

Question 4

name the 3 different kinds of open hole logs

Answer 4

natural detection (SP, gamma ray), Porosity (neutron, density, sonic log), Resitivity (induction log, laterolog)

Question 5

what is a Spontaneous Potential Log?

Answer 5

measures the electrochemical reaction between mud filtrate and formation water (passive)

Question 6

what is a Gamma Ray Log?

Answer 6

measures natural radioactivity of the formation, good reservoir indicator (passive)

Question 7

what is a Neutron Log?

Answer 7

bombards the formation with neutrons, and measures hydrogen content of a formation displaying porosity. (active)

Question 8

what is a Density Log?

Answer 8

emits gamma rays, and measures the attenuation of the returning gamma. displays porosity (active)

Question 9

what is a Sonic Log?

Answer 9

emits sound waves, records the transit tome of sound waves through the formation (active)

Question 10

what is a Resistivity Log?

Answer 10

measures the ability of the formation fluids to resist electrical conduction by producing a current in adjacent formations and measuring the response of the formation (active)

Question 11

what is an Induction Log?

Answer 11

indirectly measures resistivity by measuring conductivity of a formation, inverse of a resistivity log (active)

Question 12

what is a Laterolog?

Answer 12

measures the resistivity of the formation by passing a current between two electrodes (active)

Question 13

which log identifies zones of permeability?

Answer 13

MicroLog & Caliper (identifies mud cake = permeability & porosity)

Question 14

be able to label/draw the well bore invasion profile diagram

Answer 14

have diagrams for it

Question 15

what are the 3 most important logs for determining hydrocarbons?

Answer 15

Resistivity, Porosity, and Gamma Ray

Question 16

know the Archie Equation & how to use it

Answer 16

might be brain damaged if you don’t know this by now

Question 17

which logs show lithology/minerology (shale-non shale indicators)

Answer 17

gamma ray, SP

Question 18

which logs best show porosity?

Answer 18

sonic, density, neutron

Question 19

which logs are best for fluid type?

Answer 19

density, neutron, resistivity

Question 20

if you can only use 1 porosity log, which would you pick and why?

Answer 20

density porosity log, most accurate and not affected by gas

Question 21

which resistivity curve is used to find truer values?

Answer 21

deep induction curve

Question 22

on a particular log, the SP is deflecting left when it reaches a non shale zone. what does this indicate

Answer 22

a reservoir and that the well was drilled using a freshwater mud

Question 23

why would a company choose not to use a SP log?

Answer 23

used an oil based mud system, provides no deflection

Question 24

be familiar on using cross plots

Answer 24

practise practise practise

Question 25

True or False: salt water has high conductivity?

Answer 25

True, it has a low resistivity

Question 26

what does neutron porosity and density porosity crossover show?

Answer 26

gas!

Question 27

what is the calliper log showing if it deflects right of the gauge line?

Answer 27

right deflection shows mud cake or sloughing depending on formation

Question 28

which log is best for identifying lithology?

Answer 28

PE (photoelectric effect). Values: SS: 1.8ish DS: 3.1ish LS: 5.1ish

Question 29

why is it critical to know lithology before calculating water saturation?

Answer 29

need lithology to select correct F equation, if that is incorrect the Sw will be wrong

Question 30

when do resistivity logs become obsolete?

Answer 30

when mud invasion is so deep that the deep induction log is reading invaded zone

Question 31

what is the relationship between fluid resistivity formation and fluid resistivity when it comes to SP deflection?

Answer 31

mud resistivity > formation = left deflection (fresh water)

mud resistivity < formation= right deflection (salt water)

Question 32

name 5 of the 10 factors affecting density logs?

Answer 32

drilling mud, borehole shape, presence of thin beds, presence of volcanic ash layers, gas effects shale effect, oil effect, fractures, overpressure, and unconformity