Lecture items - Logging Up? - Wireline Log Services. - What Logs can measure? - The role of the Well Log Analyst - Creating the Well Log “Logging Operation”

Sound waves through open hole logging operation.

LWD & MWD

Logging Up To log the well, drilling must be stopped and the drill string must be removed from the borehole. Typically, the winch lowers the wireline cable and sonde to the bottom of the borehole. When the sonde is on the bottom, the winch slowly rises it up to the surface. When it moves up through the borehole, the sonde takes formation measurements. This is called "logging up. In some cases, measurements may be taken as the sonde is lowered into the borehole. The electrical cable carries power to the sonde. Measurements are not stored in the sonde. Instead, formation measurements are transmitted uphole through the cable to the logging unit for processing.

Wireline Log Services There are several wireline logging services, some of which are similar to LWD, such as (gamma ray (GR), resistivity, and nuclear ( (porosity and bulk density). Other services that wireline log measurements have, not offered by LWD as Seismic. This service uses a device, such as an air gun, at the surface to produce sound waves in the formation. A geophone is lowered into the borehole. As it is rises up to the surface, the geophone detects the sound waves and converts them into an electric voltage. Logs produced by this service are used to determine the lithology and porosity of the formation

Formation testing and sampling The wireline tool has the capability of taking samples of the formation. There are two methods for taking samples. In both methods, the samples are brought to the surface and analyzed to accurately determine the properties of the formation. i-Side wall coring - A hollow cylinder is shot into the formation and pulled out to retrieve a core sample. ii-Fluid sampling - The sonde has pads attached to legs. The legs are extended so that the pads are forced against the walls of the borehole. This allows formation fluid to flow into one or more tanks inside the sonde.

Cased-hole logging Wireline logging can be done in cased holes. Casing is thin-walled, steel pipe that is run in the hole to prevent borehole collapse as drilling progresses. The casing is cemented to the borehole wall. Wireline has developed instruments that can take formation measurements without interference from the casing and cement

Creating the Well Log “Logging Operation”

Wireline Logging Basically, the equipment needed for wireline logging consists of the following: Up-hole instruments (Logging Unit and Rig) Down- hole instruments (Sondes and cables)A logging unit and an instrument for taking measurements. For land rigs, the unit is mounted on a truck. The unit has a winch and an electrical wireline cable. The Downhole logging instrument, called a sonde, is attached to the end of the cable. The unit also includes equipment to power the sonde and to make a permanent record of the log.

Recording the Well Log

Inside a Modern Logging Unit