Drilling Engineering

1. Mud logging
operations
Part 3: Formation
Evaluation
BY:MohaMed elfteh
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2. By: M.Elfateh
q Hydrocarbons Shows Evaluation:
v Oil Shows Evaluation:
§ Visual stain:
Staining of the cuttings by oil is an indication that hydrocarbons have
been in the formation at some point in time. The lack of sample staining,
however, does not prove that a reservoir lacks producible hydrocarbons.
The amount and distribution of staining is a function of the reservoir
porosity and permeability. Stain color can be related to oil gravity, with
darker staining indicating heavier hydrocarbons. If a stained sample does
not fluorescence or cut, then this indicator is classified as thermally
“dead oil” and is not considered a show. Staining is described in terms of
its color, distribution, percentage of stained sample.
§ Direct Fluorescence:
Fluorescence refers to the color of the drill cuttings under UV light of
various wavelengths. A lack of fluorescence, however, does not prove the
absence of hydrocarbons in the zone of interest. Care must be taken to
distinguish hydrocarbon fluorescence from natural minerals (Calcite) or
artificial materials. Fluorescence is described in terms of its color,
intensity, distribution, and percentage of sample fluorescing.
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3. By: M.Elfateh
§ Solvent Cut fluorescence:
A cut is the oil liberated from drill cuttings when a solvent is added. A
common solvent used for inducing cuts is chloroform; others include
acetone, petroleum ether, alcohol, hot water, and acid. Most solvents
are flammable, and great care must be taken to handle these materials
safely. A cut is performed while viewing the rock samples under both
normal and UV light. A cut is described in terms of its percentage,
reaction speed and type, color intensity and color. All suspected
hydrocarbon-bearing intervals should be tested for a cut fluorescence.
This is because there may be a positive cut fluorescence test when other
hydrocarbon detection methods fail.
§ Residual Oil: Dissolving sample by adding solvent to sample on a
filter paper, which can be described on term of percentage and color.
§ Oil Odor:
The odor of hydrocarbons may be present even in the absence of any
other hydrocarbon indicators. This condition is most noticeable during
the sample drying process, when lighter hydrocarbons are driven off.
Odor is described as slight, mod, or strong (indicative of heavier
hydrocarbons). Keep in mind that methane through butane have no odor.
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4. By: M.Elfateh
v Oil Shows Evaluation Steps:
§ Step 1: OIL STAIN; Under Microscope: (rr, tr, occ, mnr, com, abdnt, pred) +
(lt brn, brn, dk brn) o stn or n vis o stn.
§ Step 2: FLUORESCENCE DISTRIBUATION; Under UV Box: (rr, tr, occ) spt/
(mnr, com) patchy/ (abdnt, pred) even + (dl, fnt, bri) + (yel, yelshwh, wh,
mlkywh….) fluor.
§ Step 3: CUT FLUORESCENCE; By adding solvent (Chloroform) (rr, tr, occ,
mnr, com, abdnt, pred) + (slo/mod / fst) + (strmg/blmg) + (dl, fnt, bri) +
(yel, wh, mlkywh) ct fluor.
§ Step 4: RESIDUAL OIL; Dissolving sample by adding solvent to sample on
a filter paper:(rr, tr, occ, mnr, com, abdnt, pred) + (lt brn, brn, dk brn)
+ resd o or n vis resd o.
§ Oil Odor: The first indication of the presence of hydrocarbon the odor
(smell) may present in the cutting; you can use general term such as slight,
mod, or strong oil odor.
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5. By: M.Elfateh
v Oil shows evaluation Formula :
Quantity Direct fluor Cut fluor
Modifier Distribution Reaction speed
Distribution
<1% Rr
Spt. weak……….1
(slo/mod/fst )
strmg
1-3% Tr
3-10% Occ
10-25% Mnr
Patchy. fair………2 Strmg - blmg
25-50% Com
50-75% Abdnt
Even. good………3 blmg
>75% Pred
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§ Oil Shows Evaluation Example

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v Gas Shows Evaluation: (Mud Logger):
Onsite extraction and analysis of gas from the drilling fluid to determine the Total Gas,
C1–nC5 components, H2S and CO2 of Formations.
§ Gas Sampling: (On-line Sampling):
Gas readings are obtained from the mud system by placing a separator or gas trap in the
ditch (possum belly) or flow-line. Extracted gas is drawn into the mud logging unit where
it's contents are measured by a variety of gas detectors; usually a total hydrocarbon
detector, a chromatograph, a CO2 detector and a H2S detector.
Total Gas and C1–nC5 components (in ppm) are determined by Flame ionization detector
(FID) or Thermal Conductivity Detector (TCD). The acquisition system records the results in
the database at the depth corresponding to the origin of the gas and displays them on the
rig monitors and surface logs.
The amount of gas recorded is dependent upon many variables, including:
• Volume of gas per unit volume of formation.
• Degree of formation flushing.
• Rate of penetration.
• Mud Density and Mud Viscosity.
• Formation pressure.
• Gas trap efficiency.
• Gas detector efficiency.
• Variability of mud flow rate.
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8. By: M.Elfateh 8
§ Mud Density and Mud Viscosity Cross-Check

9. By: M.Elfateh
§ Types Of Gases during drilling:
• True Zero Gas: The value recorded by the gas detectors when pure air
is passed over the detection block (generally done during calibration).
• Background Gas: Is the gas recorded while drilling through a
consistent lithology (constant).
• liberate Gas (Gas Show): Is the gas that mechanically liberated by the
bit into the drilling fluid as the bit penetrates the formation.
• Produced Gas: Is the gas that enters the annulus out of rock
formations exposed in the wellbore from a specific zone.
• Connection Gas: Is the gas peaks produced during stopping the pumps
to make a connection.
• Trip Gases: Is the gas peaks recorded after circulation has been
stopped for a considerable time for either a bit trip or a wiper trip.
• Recycled Gas: Is the gas that pumped back into the borehole by
circulating mud to appears a second time at the surface.
• Contaminant Gas: Is the gas that artificially introduced in the mud
system ( Adding Diesel, Lubricant or Crude oil).
• The Total gas volume of gas available for liberation is proportion to
(The volume of rock drilled, the porosity of that rock and the gas
saturation within that porosity).
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§ Gas Shows Evaluation Equipment
• Gas Sampling Equipment:
Hydrogen Generator
Gas Regulator
Vacuum Pump
Tubing (Gas Line) Filter
Helium Gas

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• Gas Detecting and Analysis Equipment:
FID GC “Selective”
TCD GC “Universal”
CO2
&TG
H2S Sensor
Gas Detection Equipment

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§ Gas System: TCD System:
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Main Panel
Gas connector and filter for gas panel
Gas Chromatograph
CH4 Sensor
Gas System TCD
Helium Cylinder

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Gas System FID
§ Gas System: FID System:
Gas connector and filter for gas panel
Hydrogen Generator

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§ Gas System Calibration Gas line Check: by injecting sample from TG or Components, Every 250m.

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• Source Rock: High Gas Readings with full Components in Shale Section.
• Dead Oil/ Degradated Oil: Oil shows with very low Gas readings.

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v Gas Ratio Analysis:
In mud logging, mainly interested in the five lightest alkanes (C1-
C5),by examining the ratios of the gas chromatograph data, can
identify what types of hydrocarbons are present in the reservoir
and also identify features such as the gas-oil contact.
Two ratio methods are used: the “Rectangular Plot” and the
“Baker Hughes INTEQ Gas Ratio Method”, When using either plot,
the following corrections must be made:
• Removal of all contamination gas readings, such as diesel, trip
gas, connection gas, recycled gas.
• Correction for background gas, the relative concentrations
must be read above background gas.
• More than one reading must be done to have any
interpretative value.
§ Rectangular Plots:
The rectangular plot uses the ratios C1/C2, C1/C3, C1/C4 and
C2/C3
(or C1/C5) and plots the results on a semi-logarithmic grid.
Values of these ratios are allocated to potential productivity.
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The rectangular plot:

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§ Baker Hughes INTEQ Gas Ratio Method:
Is a combination of three ratios, which when are
plotted together suggest a fluid character.
• Hydrocarbon Wetness Ratio (Wh).
• Hydrocarbon Balance Ratio (Bh).
• Hydrocarbon Character Ratio (Ch).
• Hydrocarbon Wetness Ratio (Wh):
Is a Liquid portion of C1 to C5 alkanes. WH increases
with an increase in both gas and oil densities.
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20. By: M.Elfateh
• Hydrocarbon Balance Ratio (Bh): This parameter is
related to the density of the reservoir fluid,
decreasing with an increase in fluid density.
• Hydrocarbon Character Ratio (Ch): This parameter
is used when excessive methane is present, which
tends to retard the Wh and Bh ratios.
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21. By: M.Elfateh
The interpretation of these ratios is a study of the relationships of the Wh, Ch and
Ch curves and values. The first step is the study of the Wh, using the previously
mentioned set points to determine the fluid character. Secondly, Comparing the
relationship of the Bh To the Wh Will assist in confirming the fluid character in the
following manner:
1. If the Bh is > 100, the zone is excessively dry gas.
2. If the Wh is in the gas phase and the Bh > Wh, the closer the values/curves, the
denser the gas
3. If the Wh is in the gas phase and the Bh< Wh, gas/oil or gas/ condensate is
indicated
4. If the Wh is in the oil phase and the Bh < Wh, the greater the
difference/separation, the denser the oil.
5. If the Wh is in the residual oil phase and Bh < Wh, residual oil is indicated.
After comparing the Wh and Bh values/curves, the Ch is checked if situation 2 or 3
occur.
1. If the Ch < 0.5, gas potential is indicated and the Wh vs. Bh interpretation is
correct.
2. If the Ch > 0.5, gas/light oil or condensate is indicated.
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25. By: M.Elfateh
v Advanced Mud Gas Technology: GC Tracer:
It is the most advanced technology in surface gas
extraction, can accurately analyzes alkane compounds
from methane to octane (C1 up to C8) and aromatic
compounds such as benzene and toluene, plus nitrogen
and carbon dioxide.
GC Tracer uses a semi-permeable membrane for gas
extraction this technology is unique in its field,
particularly when combined with a reliable gas
chromatograph, The entire system allows the
acquisition of each real gas concentration relative to
its concentration in the drilling fluid.
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v GC Tracer Applications:
§ Delineation of Top and Bottom of the Reservoir.
§ porosity behavior in the Reservoir.
§ Estimation of the first characterization of Formation fluids.
§ Identification of changes in fluid type, possible contacts.
§ Connectivity and compartmentalization.
§ Fluid sampling optimization.
§ Support Geosteering to navigate on the fluid.