Chapter 5 Flashcards
What are the main objectives for well logging
To provide information for reservoir evaluation.
To gather data for well completion and repair.
Describe how well logging works
➢ A logging set-up consists of the wire, a wireline tool, a
winching gear and a vehicle which contains appropriate
data analysis and recording equipment.
➢ The actual running of a log involves lowering a tool at
the end of a logging cable into an oil/gas well. A
sensor, incorporated in a sonde together with its
associated electronics, is suspended in the hole (well)
by a multiconductor cable.
➢ Data is transmitted to the control panel at surface
through the wire and recorded digitally. All data
recording and processing is now done digitally using
powerful computers and processors.
➢ As the cable is raised or lowered, it activates some
depth-measuring device, which in turn activates a
recording device.
➢ Finally, some form of reproduction takes place to
provide a hard copy of the recorded data which is
called the well log.
The Sonde was the first well log tool. What did it measure
It measures electrical resistivity
List well logging applications
➢ Lithology identification.
➢ Determination of reservoir characteristics (e.g. porosity, saturation, and
permeability.
➢Identification the fluid type in the pore space of reservoir rock ( gas, oil,
water).
➢ Identification of productive zones and reserves.
➢ Determination the depth and thickness of productive zones.
➢ Reservoir properties mapping.
➢Determination formation dip and hole angle and size
➢Monitoring the reservoir parameters when production is in progress.
What is non-conductive boreholes
oil-based and air-based muds and
cased holes
What is Conductive boreholes
Water-based drilling mud
What are the types of well logging
Mud logging
Open hole logging
cased hole logging
production logging
Describe mud logging
During drilling mud is pumped down the drill string forcing the rock cuttings
up to the surface. These cuttings are analyzed by laboratory analysis working
in a transportable laboratory known as a mud logging unit installed at the well
site.
What an the samples from mud logging tell us about the well
✓ Rate of penetration (ROP)
✓ Determination of lithology
✓ Presence of hydrocarbons
✓ Preliminary indication of the well location (seismic data)
✓ Indication of pressure conditions
✓ Monitoring of bit performance
✓ Weight on bit
✓ Mud weight
✓ Estimated pore pressure
What are the types of well logging used for open hole logging
a. Wireline Logging (WL): Electrical logs, Sonic logs, Caliper logs,
Dipmeter logs and Radioactive logs
b. Logging while drilling (LWD)
Describe wireline logging
➢ The tools are introduced into the well on a cable, the
obtained data are transmitt to the surface recording system via
cable.
➢ Performed after interuption or termination of drilling in this
situation, drilling pipes and bit should be out and well be empty.
Describe logging while drilling
➢ The logging device is introduced on the drill pipe and
collected data are memorized in the tool, the data are
downloaded to the surface recording system after termination
or interuption of drilling.
➢ Very efficient in horizontal drilling.
➢Indications of reservoir rock and fluid quality while drilling.
➢ Some tools also are able to record drilling parameters such
as RPM and drilling speed.
What do electrical logs measure
electrical properties of the
formation rock and fluid.
What do caliper logs measure
Measure the geometry of the wellbore.
What do dipmeter logs measure
Measure the dip of the formation.
Wat do sonic logs measure
Measure the elastic or wave properties of the formation
What do radioactive logs measure
Gamma ray measures the radioactive absorption properties
Fill in the blanks
Cased hole and production logging:
This type is used ______ well completion.
A concrete lining or casing has be inserted to ________ the wellbore.
The portion of the well bore that has had metal casing placed and
cemented to protect the open hole from _______, _______, well bore
_________ problems or a combination of these
after
stabilize
fluids, pressures, well bore stability
What are the two most important cased hole logs
cement bound logging (CBL) and variable density logs (VDL)
Fill in the blanks:
Drilling a hole in the formation will cause a disturbance in the vicinity of
bore hole by the invasion of drilling mud into the formation.
➢ Ideally the size of the borehole is ______ to the size of the drill bit.
➢ Shale swelling, salt dissolution and collapse of poorly cemented rocks
may ________ the borehole diameter.
➢ Mud cake build up may ________ the size of the borehole diameter.
➢ The change in the borehole diameter and the contamination caused by
the drilling mud will affect the ________ ______ and appropriate corrections
should be considered.
Equal
increase
decrease
logging tools
What are the characteristics that affect log quality
Depth of investigation
Logging speed
Vertical resolution
Investigation geometry
Describe how depth of investigation affects log quality
Depth of investigation: Depends on the porosity of formation. Different
logging tools, has different characteristics, however, most of them have
shallow depth of investigation which can mostly reach the flushed zone or
transition zone.
Describe how logging speed affects log quality
The running speed of the tools will cause statistical
fluctuations and sampling interval variations. These can affect the vertical
resolution.
Describe how vertical resolution affects log quality
This is related to the depth of investigation. The bed
thickness should be larger than the distance between the source and
detector of each logging tool. Generally, logging tools with large depth of
investigation have low vertical resolution.
Describe how investigation geometry affects log quality
Different logging tools have different measurement
geometries.
What does invasion represent
The difference between the fluid pressure and drilling
mud pressure will cause a flow of the drilling fluid to the
formation in the permeable zones of the borehole
What does mud cake represent
The formation rock acts as a filter and keeps the
particulates of the mud at the borehole wall, this particle
build up on the wall is called mud cake
What does mud filtrate represent
The remaining liquid part of the mud which enters the
formation is called mud filtrate
What does the flushed zone represent
Mud filtrate will replace the reservoir fluid and enters the
formation, this zone where the reservoir fluid is replaced
is called flushed zone
What does the transition zone represent
The zone next to the flushed zone further into the
formation where the mud invasion is incomplete is called
transition zone.
What does the uninvaded zone represent
The untouched portion of the formation by the mud is
called uninvaded zone
Fill in the blanks:
High permeability formations results in _______(shallow or deep)
invasion and ______(thin or thick) layer of mud cake.
deep
thick
Fill in the blanks:
High porosity formations results in _______(more or less) storage
of mud filtrate per invasion distance and the
________(smaller or larger) depth of invasion.
more
smaller
Wireline companies provide correction graphs for
their logging tools to consider the effect of
__________ on well logging readings.
invasion
What does the log display and structure include
- Logging company and log name.
- Well identification and location information.
- Other log and services run in the well.
- Depth and elevation details.
- The log run number.
- The depth of the bottom of the hole.
- The depth of the top and bottom of the logged interval.
- Casing information
- Bit information.
- Drilling mud information
- Mud, mud filtrate and mud cake resistivities.
- Time between end of logging circulation before logging and when
logging tool reached the bottom of the hole. - Temperature.
- The logging truck information.
- The logging company representatives information
What does the bubble point curve represent?
Represents the conditions of temperature and pressure at which the first bubble occurs when u drop the pressure or increase the temperature.
The bubble-point curve (line BC) is defined as the
line separating the liquid-phase region from the two-phase region.
What does the dew-point curve
Represents the conditions of pressure and temperature at which the first droplet of liquid forms when a gas is cooled and/or the pressure is increased.
The dew-point curve (line AC) is defined as the line
separating the vapor-phase region from the two-phase region.
What is the Circondentherm (Tct)
—The Cricondentherm is defined as the maximum
temperature above which liquid cannot be formed regardless of pressure.
The corresponding pressure is termed the Cricondentherm pressure pct.
What is the Circondenbar (Pcb)
The Cricondenbar is the maximum pressure above
which no gas can be formed regardless of temperature. The corresponding
temperature is called the Cricondenbar temperature Tcb.
What does the critical point represent on a P-T diagram
The critical point for a multicomponent mixture is referred
to as the state of pressure and temperature at which all intensive properties
of the gas and liquid phases are equal (point C). For the two-phase system
at this point both phases coexist. At the critical point, the corresponding
pressure and temperature are called the critical pressure pc and critical
temperature Tc of the mixture.
Describe an undersaturated oil reservoir
In these reservoirs the initial reservoir pressure is greater than the bubble
point pressure of the reservoir fluid (pi> pb). No free gas exists until the
reservoir pressure falls below the bubble point pressure.
This includes when PR < Pb(gas section and oil section - gas cap reservoir) and also when PR > Pb (No gas section, all is dissolved in the oil).
Describe a saturated oil reservoir
In these reservoirs the initial reservoir pressure is equal to the bubble-point
pressure of the reservoir fluid (pi= pb). At this point the gas begins to separate from the oil (PR = Pb) and form a gas cap.
What are the types of crude oils
Ordinary black oil
Low-shrinkage black oil
Volatile crude oil
Near critical crude oil
What is the gas-oil ratio, oil gravity, and colour for ordinary black oil
200-700 scf/STB
15-40 API
Brown to dark green
What is the oil formation volume factor, gas-oil ratio, oil gravity, and colour for low-shrinkage black oil
less than 1.2 bbl/STB
less than 200 scf/STB
less than 35 API
black or deeply coloured
What is the oil formation volume factor, gas-oil ratio, oil gravity, and colour for volatile crude oil
less than 2 bbl/STB
2000 - 3200 scf/STB
45-55 API
greenish to orange
What is the oil formation volume factor, gas-oil ratio, and how much heptane’s and ethane’s for near critical crude oil
higher than 2 bbl/STB
excess of 3000 scf/STB
12.5 to 20 mol% heptanes-plus,
35% or more of ethane through
hexanes, and the remainder
methane.
What do we classify the reservoir if it is above critical point
This is a natural gas reservoir
What are the types of natural gas reservoirs
Retrograde gas-condensate reservoir
Near critical gas-condensate reservoir
Wet-gas reservoir
Dry-gas reservoir
What is the gas oil ratio, condensate gravity and colour of a retrograde gas-condensate reservoir
- Gas-oil ratios between 8,000 to 70,000 scf/STB.
- Condensate gravity above 50°API
- Stock-tank liquid is usually water-white or slightly colored.
What is the gas oil ratio, condensate gravity and colour of a near critical gas-condensate reservoir
- Gas-oil ratios between 8,000 to 70,000 scf/STB.
- Condensate gravity above 50°API
- Stock-tank liquid is usually water-white or slightly colored.
What is the gas oil ratio, condensate gravity and colour of a wet-gas reservoir
- Gas oil ratios between 60,000 to 100,000 scf/STB
- Stock-tank oil gravity above 60°API
- Liquid is water-white in color
What is the gas oil ratio of a dry-gas reservoir
greater than 100,000scf/STB
As we go from a liquid to a gas in a reservoir, the gas-oil ratio increases or decreases?
increases
As we go from a liquid to a gas in a reservoir, the stock tank oil gravity (API) increases or decreases?
increases
As we go from a liquid to a gas in a reservoir, the colour becomes lighter or darker?
lighter
For a retrograde gas-condensate reservoir, where does the T lie?
the reservoir temperature T lies between the critical
temperature Tc and cricondentherm Tct of the reservoir fluid.
For a near critical gas-condensate reservoir, where does the T lie?
the reservoir temperature T is close to the critical
temperature of the reservoir fluid
For a wat-gas reservoir, where does the T lie?
the reservoir temperature T is above the
cricondentherm of the reservoir fluid. They contain significant heavy
hydrocarbons such as propane, butane and others