Some addition to

Logging While Drilling

edited by P. Vassfor Earth Science Engineer MSc

Students

Logging

Log: any data set recorded in a borehole or well and displayed as a function of depth and/or time.

There are three main techniques of acquiring log data:

• Mud Logging

• Wireline Logging

• Logging While Drilling (LWD)

https://wiki.ppdm.org/Well_Logs_Reference_guide#Business_Process_Overview

Mud logging

Mud Logging requires a surface acquisition system and ismanned by a team of 2 to 4 persons. During drillingoperations, sensors are placed to record various drillingdata and samples of the cuttings are caught and analyzed.

The information recorded includes:

• Mechanical, hydraulic, and engineering parameters(Depth, ROP, RPM, WOB, Torque, Drilling Mudparameters etc.)

• Drilled cuttings are analyzed to provide geologic data(lithology, fluorescents

• Gas analysis measured from the mud returns

https://wiki.ppdm.org/Well_Logs_Reference_guide#Business_Process_Overview

http://en.allexperts.com/q/Geology-1359/2013/1/mud-logging-1.htm

Wireline logging

Wireline logging is the acquisition of geophysical data

coming from boreholes as a function of depth.

Wireline logging is performed by lowering a 'logging tool'

- or a string of one or more instruments - on the end of a

wireline into a borehole (or a well) and recording the

values of physical quantities using a variety of sensors.

The measured data can be recorded either at surface

(real-time mode), or in the hole (memory mode) to an

electronic data format.

Well log means the printed or electronic form of

measured datasets which can be analysed and

evaluated to determine the variations of petrophysical

parameters along the borehole.

https://en.wikipedia.org/wiki/Well_logging

Logging while drilling

Logging While Drilling (LWD) requires similar equipment to

Wireline logging. The primary difference is that the down-hole

instruments are an integral part of the Bottom Hole Assembly (BHA)

so the drilling process acts as the hoisting equipment to raise and

lower the instruments. Data transmission usually involves digitally

encoding data and transmitting to the surface as pressure pulses in

the mud system. Additionally, the data is recorded in memory

modules and this data is downloaded once the instruments are

retrieved from the well bore.

https://wiki.ppdm.org/Well_Logs_Reference_guide#Business_Process_Overview

http://theogm.com/2012/06/05/ecoscope-technology-advances-drilling-off-shore-newfoundland/

Logging while drilling

Logging while drilling

LWD tools present a complication for drilling, as well as additionalexpense. However, their use may be justified when:

• real-time information is required for operational reasons, such as steering a well (e.g., a horizontal trajectory) in a particular formation or picking of formation tops, coring points, and/or casing setting depths,

• acquiring data prior to the hole washing out or invasion occurring,

• safeguarding information if there is a risk of losing the hole,

• the trajectory is such as to make wireline acquisition difficult (e.g., in horizontal wells).

Toby Darling: Well Logging and Rormation Evaluation

Logging while drilling

Factors that might limit the ability to fully use both memory data and

pulsed data:

• drilling mode (data may be pulsed only if the drill string is having mud

pumped through it),

• battery life (depending on the tools in the string, tools may work in

memory mode only between 40 and 90 hours),

• memory size (most LWD tools have a memory size limited to a few

megabytes),

• depending on how many parameters are being recorded, the memory

may become full within 20–120 hours,

• tool failure (it is not uncommon for a fault to develop in the tool such

that the pulse data and/or memory data are not transmissible/

recordable).

Toby Darling: Well Logging and Rormation Evaluation

Logging while drilling

There are two ways of mounting logging tools in the

bottom hole assembly:

• collar mounted tools (or fat tools, semi-permanently

mounted in drill collar),

• retrievable tools (or slim tools can be retrieved and

replaced using wireline through the drill string).

https://en.wikipedia.org/wiki/Measurement_while_drilling

Logging while drilling

An incomplete list of available measurement in LWD technology:

• natural gamma ray (GR) (total gamma ray, spectral gamma ray, azimuthal

gamma ray, gamma ray close to drill bit,

• density and photoelectric index,

• neutron porosity,

• borehole caliper (ultra sonic azimuthal caliper, density caliper),

• resistivity (attenuation and phase-shift resistivities at different transmitter

spacings and frequencies, resistivity at the drill bit, deep directional

resistivities),

• sonic (compressional slowness (Δtc), shear slowness (Δts)),

• borehole images (density borehole image, resistivity borehole image),

• formation tester and sampler (formation pressure, formation fluid sample),

• nuclear magnetic resonance (NMR),

• seismic while drilling (SWD), Drillbit-SWD,

https://en.wikipedia.org/wiki/Logging_while_drilling

Measurement while drilling

Measurement while drilling (MWD) refers to directional-drilling

measurements (e.g. for decision support for the smooth operation of

the drilling).

Measured quantities:

• borehole inclination from vertical,

• magnetic direction from north

• natural gamma ray emission from the rock

This information is used to drill in a pre-planned direction into the

formation which contains the oil, gas, water or condensate and

helps to confirm the real-time location of the borehole in relation to

the presence of different types of known formations (by comparison

with existing seismic data).

https://en.wikipedia.org/wiki/Measurement_while_drilling

http://www.weatherford.com/products-services/drilling-formation-evaluation/drilling-services/measurement-while-drilling

Measurement while drilling