Formation Evaluation
Drilling Essential
SCHLUMBERGER LEARNING
Schlumberger-Private
Objectives
At the end of this session, you should be able to describe the
measurement and application of main logs
SCHLUMBERGER LEARNING
Schlumberger-Private
Topics
• Mud Logging
• Cores
• Gamma Ray
• Caliper
• SP
• Resistivity
• Porosity
• MDT
• LWD
SCHLUMBERGER LEARNING
Schlumberger-Private
Mud Logging
• Mud logging is one of the first direct evaluation methods available.
• The rate of penetration gives qualitative information about the lithology being drilled. i.e, in a hard shale the ROP
will be slower than in a porous sandstone.
• The formation cuttings travel upward with the mud and are caught and analyzed at the surface providing
information about the lithology and porosity.
SCHLUMBERGER LEARNING
Schlumberger-Private
Mud Logging
• If hydrocarbons are present, they will show in the cuttings, and in the mud. The gas in the mud is monitored with a
gas detector. A chromatograph analyzes the composition of the gas.
• Challenge is to account for the delay time that cuttings arrive on surface, therefore when drillers are entering the
target zone they will decrease speed, to allow time for the mud logger to survey.
SCHLUMBERGER LEARNING
Schlumberger-Private
Mud Logging
Drilling Rate Hydrocarbon Analysis
Chromotograph PPM
Interpreted
Visual Porosity
Master log
Lithology
M. per Hr.
Depth (m)
Cuttings Continuous Total Analysis
Lithology Gas in air % Methane--- Ethane---
Propane--- Butane---
Remarks
Pentane---
20 15 10 5 1 10 PPM 1 K 10 K
LS: wht, dk, br, vf, xin, cin, hd
w tr foss
SH: dk gy, gy, frm, occ sft,
occ sity
SS: lt gy, cir, xin, sb ang, sb,
rnd, m grn, oil stn, bri yel
flour, bri gid stng cut
SH: dk gy, gy, frm, occ sft,
occ sity
SS: lt gy, cir, xin, sb ang, sb,
rnd, m grn, oil stn, bri yel
flour, bri gid stng cut
SH: dk gy, gy, frm, occ sft,
occ sity
SCHLUMBERGER LEARNING
Schlumberger-Private
Cores
Used to:
• Allow direct measurement of reservoir properties
• Correlate indirect measurements (wireline/LWD logs).
• Test compatibility of injection fluids
• Predict the borehole stability
• Estimate probability of formation failure and sand production
SCHLUMBERGER LEARNING
Schlumberger-Private
Information from Cores
Standard Analysis Special Core Analysis
• Porosity • Vertical permeability to air
• Horizontal permeability to air • Relative permeability
• Grain density • Capillary pressure
• Cementation exponent (m) and saturation exponent
(n)
SCHLUMBERGER LEARNING
Schlumberger-Private
Coring Assembly and Core Bit
Drill collar
connection
PDC Cutters
Thrust bearing
Outer barrel
Inner barrel
Fluid
vent
Core retaining
ring
Core bit
SCHLUMBERGER LEARNING
Schlumberger-Private
Whole Core
SCHLUMBERGER LEARNING
Schlumberger-Private
Whole Core
Whole Core Photograph,
Misoa Sandstone, Venezuela
SCHLUMBERGER LEARNING
Schlumberger-Private
Sidewall Sampling Gun
• The tool is run on a wireline.
• 20 to 30 bullets are fired from each gun.
• The hollow bullet will penetrate the formation and a
Core bullets rock sample will be trapped inside the cylinder.
• When the tool is pulled, wires will pull the bullet and
Formation rock sample from the borehole wall.
Core sample
SCHLUMBERGER LEARNING
Schlumberger-Private
Sidewall Coring Tool
• Newer wireline tool.
• Drills a plug out of the borehole wall.
• Avoids crushing the sample.
Coring bit
• Up to 30 samples can be individually cut and
are stored inside the tool.
Samples
SCHLUMBERGER LEARNING
Schlumberger-Private
Modular Dynamic Tester (MDT)
Positioned across the formation and set against the borehole.
The probes are pushed through the mud cake and against
the formation. Electric power module
A drawdown that can be controlled from surface is created at Hydraulic power module
one probe and observed in the two observation probes.
Probe module
Test data provide estimates of Preservoir, Kh and Kv and
allow us to evaluate anisotropy.
Dual probe module
Fluids can also be sampled.
Flow control module
Sample module
SCHLUMBERGER LEARNING
Schlumberger-Private
Openhole Log Evaluation
• Wireline or LWD
Well Log
• Correlation curves: (Gamma ray, Spontaneous
potential) SP Resistivity
• Resistivity curves
• Porosity logs (Bulk density, Neutron, Acoustic)
SCHLUMBERGER LEARNING
Schlumberger-Private
Gamma Ray
Measures natural radioactivity of formation
• Potassium (K)
• Uranium (U)
• Thorium (Th)
• Radioactive elements tend to concentrate
in clays -shales.
• Clean formations (such as sandstones or
limestones,) usually have a very low level
of radioactivity
• Used barely to differentiate “shaly” from
“no-shaly” formations.
• Posterior use for depth correlation.
SCHLUMBERGER LEARNING
Schlumberger-Private
Example GR Log 001) BONANZA 1
GRC ILDC RHOC DT
0 150 0.2 200 1.95 2.95 150 us/f 50
SPC SNC CNLLC
-160 MV 40 0.2 200 0.45 -0.15
GRC ACAL MLLCF
6 16 0.2 200
0 150
10700
Units=GAPI 10800
GR
Log
10900
SCHLUMBERGER LEARNING
Schlumberger-Private
Spontaneous Potential (SP)
The SP log must be run in a conductive drilling mud. It cannot be
run in oil-base mud.
The SP log has several oilfield applications:
• The most common is shale indication
• Is generally an indicator of permeability.
• Depth correlation
• Identify the fresh/salt water interface
• Determination of formation water resistivity.
SCHLUMBERGER LEARNING
Schlumberger-Private
SP Log
001) BONANZA 1
GRC ILDC RHOC DT
0 150 0.2 200 1.95 2.95 150 us/f 50
SPC SNC CNLLC
-160 MV 40 0.2 200 0.45 -0.15
ACAL MLLCF
6 16 0.2 200
SPC 10700
-160 MV 40
10800
SP
Log
10900
SCHLUMBERGER LEARNING
Schlumberger-Private
Caliper Log
• Continuous measure of the actual borehole diameter.
• To identify washouts, tight zones
• Also used to calculate the volume of cement required for cementing
• In combination with GR may give qualitative indication of lithology
SCHLUMBERGER LEARNING
Schlumberger-Private
Caliper Log 001) BONANZA 1
0
GRC
150 0.2
ILDC
200 1.95
RHOC
2.95
DT
150 us/f 50
SPC SNC CNLLC
-160 MV 40 0.2 200 0.45 -0.15
ACAL MLLCF
6 16 0.2 200
10700
ACAL
6 16
Units= inches 10800
Caliper
Log
10900
SCHLUMBERGER LEARNING
Schlumberger-Private
Resistivity Logs
Resistivity of zone
• Measures the resistivity (inversely to conductivity) Resistivity of the water in the zone
Water saturation in the zone
of the formation water. Mud
Rm
Adjacent bed
• Therefore, it gives the fluid type indication such as Rs
water or HC.
Uninvaded
hmc Flushed zone
• Does not indicate type of HC. Rmc zone Zone of
transition
R1
(Bed dh or Rw
• Measure at different depths (of invasion) to thickness) Mudcake Rxd annulus
Sw
determine the resistivity of the flushed zone and the h Rm1
virgin zone
Sxo
Rs
di
dj
Adjacent bed
(Invasion diameters)
rj
dh
Hole
diameter
SCHLUMBERGER LEARNING
Schlumberger-Private
Resistivity Logs
SCHLUMBERGER LEARNING
Schlumberger-Private
Resistivity Logs
SCHLUMBERGER LEARNING
Schlumberger-Private
Example of Resistivity Log
001) BONANZA 1
GRC ILDC RHOC DT
0 150 0.2 200 1.95 2.95 150 us/f 50
SPC SNC CNLLC
-160 MV 40 0.2 200 0.45 -0.15
Units=(OHMM) 6
ACAL
16 0.2
MLLCF
200
10700
• Black: Shallow
• Red: Medium
• Green: Deep Investigation of resistivity
10800
10900
SCHLUMBERGER LEARNING
Schlumberger-Private
Porosity Logs
None of them measures porosity directly!
• Density
Measure the density of both the rock matrix.
• Neutron Porosity
Function of the hydrogen content within the fluids.
• Sonic
Measures the fastest path for sonic waves through the solid rock
SCHLUMBERGER LEARNING
Schlumberger-Private
Density Logs
Measure the formation bulk density:
• Gamma ray collides with electrons in formation, losing energy.
• A detector measures the intensity of gamma rays returning and so
the electron density of the formation can be predicted
• Low GR counts means a high bulk density, thus Low f.
Density = 1 / Porosity
SCHLUMBERGER LEARNING
Schlumberger-Private
Density Logs
ma − b
= d =
ma − f
Density Dolomite 2.83
Density Sandstone 2.65
Density Limestone 2.71
Density of fluid =1
sandstone = 2.65-2.2 / 2.65-1 = 0.45 / 1.65 = 27 %
dolomite = 2.83-2.2 / 2.83 -1 = 0.63 / 1.83 = 34.4 %
Limestone = 2.71 – 2.2 / 2.71 -1 = 0.51/1.71 = 29.8%
SCHLUMBERGER LEARNING
Schlumberger-Private
Bulk Density Log Example
001) BONANZA 1
GRC ILDC RHOC
0 150 0.2 200 1.95 2.95
SPC SNC
-160 MV 40 0.2 200
6
ACAL
16 0.2
MLLCF
200
Units = Gram/cc
10700
Bulk Density
Log
10800
10900
SCHLUMBERGER LEARNING
Schlumberger-Private
Neutron Logs
• Logging tool emits high energy neutrons into formation
• Neutrons collide with formation (including fluids) and lose
energy with each collision
• Most energy is lost when colliding with a hydrogen.
• Low count rate of neutron returning indicates large number of
H atoms present in oil or water, therefore, high Φ
SCHLUMBERGER LEARNING
Schlumberger-Private
Porosity From Neutron Log
001) BONANZA 1
GRC ILDC RHOC
0 150 0.2 200 1.95 2.95
SPC SNC CNLLC
-160 MV 40 0.2 200 0.45 -0.15
ACAL MLLCF
6 16 0.2 200
10700 Unit = Count per
second
Neutron
10800 Log
10900
SCHLUMBERGER LEARNING
Schlumberger-Private
Sonic Tool
Two receivers eliminate the
• The sonic tools create an acoustic signal and measure how long it travel in the borehole
takes to pass through a rock.
• By simply measuring this time we get an indication of the formation
properties.
Distance
between Receive
two rs
receivers
• The amplitude of the signal will also give information about the
Acoustic
formation. signal
travels
through the
formation
Transmitter
SCHLUMBERGER LEARNING
Schlumberger-Private
Sonic Log Applications
Mechanical properties: To measure or predict:
• Rock strength
• Earth stress
• Rock failure mechanisms
Perforating stability or sanding analysis
• Hydraulic fracture height determination
• Wellbore stability
Formation evaluation
• Porosity estimation
• Gas identification
• Lithology determination
Cement bond logging
SCHLUMBERGER LEARNING
Schlumberger-Private
Common Lithology Matrix Travel Times Used
Lithology Typical Matrix
Travel Time,
tma, sec/ft
Sandstone 55 t log − t ma
Limestone 47 s =
Dolomite 43 t f − t ma
Anydridte 50
Salt 67
Steel 57
• tlog is log reading, sec/ft
• tma is the matrix travel time, sec/ft
• tf is the fluid travel time, sec/ft
• is porosity
SCHLUMBERGER LEARNING
Schlumberger-Private
Sonic Log
001) BONANZA 1
G
GRC R90
ILDC RH
RHOC D
DT
0 R 15
150 0.2 200 1.9
1.95O 2.9
2.95 15
150 us/
us/f
T 5
50
S
SPC 0 R30
SNC 5 CNCNLLC5 0 f 0
-
-160 PM
MV 4
40 0.2 200 0.4
0.45L --0.15
160 CAV
ACAL 0 R10
MLLCF 5 0.15
6 L 1
16 0.2 200
6 DT
10700
150 us/f 50
10800
Sonic
Log
10900
SCHLUMBERGER LEARNING
Schlumberger-Private
Logging While Drilling
• All LWD tools have a power supply and data transmission system.
• Data transmission may be within the downhole assembly from the sensors to a memory device or from the
sensors to the surface (telemetry).
Azimuthal resistivity
(depth of investigation Gamma ray Transmitter for
12 in. or less) detector wireless telemetry
Measurement and measurement
antenna of current
3/4º fixed Surface-adjustable
bent housing Motor
Stabilizer bent housing
and bearings Inclination RPM
gravity toolface
SCHLUMBERGER LEARNING
Schlumberger-Private
Logging While Drilling
A pressure pulse in the mud is created by opening and shutting a valve in the drillstring. This is usually done by using
a rotating device at a given RPM.
In this manner, a binary data string is transmitted to the surface and received by a transducer. The binary data string
is then interpreted by a computer.
Provides depth, pressure, GR, resistivity.
• Real time correlation for picking coring and casing points
• Real time overpressure detection in exploration wells
• Real time logging to minimize “out of target” sections (geosteering)
• Real time formation evaluation to facilitate “stop drilling” decisions
• Sidewall coring
• Porosity logs
SCHLUMBERGER LEARNING
Schlumberger-Private
