Logging while drilling

Logging while drilling (LWD) is a technique of measuring geologic formation properties in real-time while drilling an oil well.

Description

Logging while drilling, along with measurement while drilling systems provide wellbore directional surveys, petrophysical well logs, and drilling information in real-time while drilling. MWD refers to measurements acquired down hole while drilling that specifically describe directional surveying and drilling-related measurements. LWD refers to petrophysical measurements, similar to open hole wireline logs, acquired while drilling. These systems are based on mud pulse telemetry, where variations in pressure exercised by the tool can be sensed on the surface via a computer or electromagnetic telemetry, and thus communication is established.

Measured parameters

A suite of tools record different parameters of the drilled rocks:
*Natural Gamma Ray (GR)
** Average Gamma Ray
** Gamma Ray Spectrometry
** Indicates sandy or shaly formation layers
*Accoustic Properties (sonic)
** Slowness (Δtc)
** Shear Slowness (Δts)
** Used to correlate seismic data to depth and to acquire formation porosity
*Resistivity of Formation (ohm-m)
** Higher Resistivity is indicative of hydrocarbons (or pure rock)
** Low Resistivity is indicative of salt water
*Estimated Porosity (phi)
** More porisity means more pore space that may contain hydrocarbons
*Density/Lithology (rho and photoelectric factor)
*Pressure/Temperature
*Seismic While Drilling (SWD)
** Drillbit-SWD
** VSP-WD (Vertical Seismic Profile While Drilling)
*Formation Pressure
** Fluid type
** Permeability

ee also

*Geosteering

References

* [http://www.glossary.oilfield.slb.com/Display.cfm?Term=logging%20while%20drilling LWD definition on Schlumberger Oilfield Glossary]
* [http://www.geo365.no/sfiles/5/11/6/file/LoggingDemonstratingCapability_24-26.pdf]