correlate zones, assist with structure and isopach mapping, and help define physical rock characteristics such as lithology, porosity, pore geometry, permeability, identify productive zones, determine depth and thickness of zones, distinguish between oil, gas and water in a reservoir, estimate HC reserves, determine facies relationships and drilling locations
Two types of logs?
Open hole logs and cased hole logs
open hole logs
run in newly drilled, uncased wells, used to determine whether or not to run casing
cased hole logs
used to perforate the well
two primary parameters determined from well log analysis are:
porosity and fraction of pore space filled with HC (HC saturation)
Three general types of logs
Electrical, nuclear, acoustic or sonic log
word log may refer to:
a particular curve, a group of curves, the physical record of the measurements, a logging tool (sonde), or the process of logging
Rock properties or characteristics that affect logging measurements are:
porosity, lithology, mineralogy, permeability, water saturation, resistivity of the rock
ratio of voids to the total volume of the rock
the amount of void space that is interconnected.
used to describe the solid portion of the rock
describes the minerals in a particular rock
shale in sandstone causes log readings to change
some measurements, primarily nuclear are...
made as a result of molecular level interactions between the formation and the logging tool
acoustic measurements interact...
with the formation on a bulk level so it is more affected by lithology
parameter that has been used to account for the lithology effects
ability of a rock to transmit fluids, controlled by the size of the connecting passages between pores
ability of a rock to transmit a single fluid, when completely saturated with that fluid
the ability of the rock to transmit one fluid in the presence of another fluid when the two fluids are immiscible
amount of pore volume in a rock that is occupied by formation water
Irreducible water saturation
the water saturation at which all the water is absorbed on the grains in a rock or is held in the capillaries by capillary pressure
Hydrocarbons, the rock, and the fresh water of the formation are all assumed to have a _____ resistivity
_______ is the rock property on which the entire science of logging first developed
______ is the inherent property of all materials, regardless of their shape and size, to resist the flow of an electric current
Salt water has a _____ resistivity
The measurement of resistivity is a measure of the...
amount of salinity of the formation water
Resistivity is a basic measurement of a reservoir's...
fluid saturation, and is a function of porosity, type of fluid, and type of rock.
resistivity logs run in salty mud
resisitivity logs run in fresh mud
First electric log was run in...
France by the Schlumberger brothers in 1927
Ro=F*Rw, F=a/Phi^m, where a=tortuousity factor, and m=cementation factor
What is Rxo, Rmf, Sxo, Rt, Rw, and Sw?
Rxo=resistivity of flushed zone, Rmf= resistivity of the mud filtrate, Sxo=water saturation of the flushed zone, Rt=resistivity of the uninvaded zone, Rw=resistivity of formation water, Sw=water saturation of uninvaded zone
zone in which much of the original formation fluid is replaced by mud filtrate
resistivity of the transition zone
The bulk resistivities are...
Rxo, Ri, Rt
Diameter of invasion
depth of mud filtrate invasion into the invaded zone
The amount of invasion that takes place is dependent on...
the permeability of the mud cake, not the porosity of the formation.
The diameter of invasion is greatest in _____ porosity rocks
dj/dh for high, intermediate, and low porosity rocks.
high=2, intermediate=5, low=10
Ri, Rz, Si
Ri=resistivity of transition zone, Rz=resistivity of the fluid in the transition zone, Si=water saturation of the transition zone
If invasion is deep or moderate, the flushed zone is...
most likely completely cleared of its formation water by mud filtrate.
When oil is present in the flushed zone, the degree of flushing by mud filtrate can be determined from the...
difference between water saturation in the flushed zone(Sxo) and the water saturation in the uninvaded zone(Sw)
Usually about ___ to ___ percent of the oil is flushed out
The ratio of the uninvaded zone's water saturation to the flushed zone's water saturation is an indicator of
hydrocarbon moveability (MHI)
There are 3 commonly recognized invasion profiles:
Step, transition, annulus
The transition profile has a _____ geometry, with two parameters:
cylindrical, di (diameter of flushed zone) and dj (diameter of transition zone)
The transition profile needs at least ____ resistivity measurements, each a different diameter away from the wellbore
The 3 resisitivity measurements of the transition zone are:
Rxo, Ri, Rt
The ability to estimate the invasion in a formation was
made possible with the introduction of the...
dual induction log and dual laterolog
“dual” means that each tool made
tow induction or two laterolog measurements, one at medium and one at deep distance from the wellbore
The dual induction and laterolog made a third measurement which was...
shallower than the medium and deep measurements
Distances for Rxo, Ri, and Rt
Rxo=.5-1.5ft, Ri=1.5-3ft, Rt=3ft+
only present in HC bearing zones, indicate high relative permeability to HC, will dissipate with time, and can only be observed on fresh mud resistivity logs
An annulus profile is detected only by an _____ run soon after a well is drilled
Annulus profile can only occur....
in HC bearing zones
is detected by a higher resistivity reading on the deep induction log than the one on the medium induction log, Rt>Ri
How many resistivity measurements does a step profile and transition profile have?
3 facts about an annulus profile-
Rt>Ri, only in induction logs, and indicates HC productivity
Fresh water based mud has resistivity profile of:
Salt water based mud has resistivity profile for:
A saltwater mud results in a wet profile where
shallow, medium, and deep resistivity measurements all read low resistivity
2 reasons why it is important to know lithology
-porosity logs require a lithology constant before the porosity of the zone can be calculated
-the formation factor also varies with lithology
3 parameters that vary with temperature are
resistivities of the drilling mud, mud filtrate, and formation water
The formation temperature is determined by knowing:
formation depth, bottom hole temperature, total depth of a well, and surface temperature
formation temperature is calculated by using
linear regression y=mx+c where x=depth, y=temperature, m=geothermal gradient, c= mean annual surface temperature
Arp's Formula can be used to
correct fluid resistivities to formation temperature
four most fundamental rock properties use in well logging are
porosity, permeability, lithology, and water saturation
Lithology of a formation must be known because
it is needed to determine porosity, the formation factor varies with lithology, and water saturation varies with the formation factor
The four fluids that affect logging measurements are
drilling mud, mud filtrate, formation water, and hydrocarbons
Resistivity profiles for Wet Zones:
For fresh mud where (Rmf>>Rw)
For salt mud where (Rmf=Rw)
Resistivity profiles for HC zones:
For fresh mud where (Rmf>>Rw)
For salt mud where (Rmf=Rw)
Rxo>Ri<Rt, annulus profile: Rt>Ri, all read high
The SP log is used for
determining gross lithology, to correlate zones
SP log is used to:
detect permeable beds, detect boundaries of permeable beds, determine formation water resistivity(Rw), determine the volume of shale in permeable beds