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Logging while drilling (LWD) is a technique of conveying well logging tools into the well borehole downhole as part of the bottom hole assembly (BHA).. Although the terms Measurement while drilling (MWD) and LWD are related, within the context of this section, the term MWD refers to directional-drilling measurements, e.g., for decision support for the smooth operation of the drilling, while ...
Well logging, also known as borehole logging is the practice of making a detailed record (a well log) of the geologic formations penetrated by a borehole.The log may be based either on visual inspection of samples brought to the surface (geological logs) or on physical measurements made by instruments lowered into the hole (geophysical logs).
A drilling rig is used to create a borehole or well (also called a wellbore) in the earth's sub-surface, for example in order to extract natural resources such as gas or oil. During such drilling, data is acquired from the drilling rig sensors for a range of purposes such as: decision-support to monitor and manage the smooth operation of ...
Borehole imaging logs are logging and data-processing methods used to produce two-dimensional, centimeter-scale images of a borehole wall and the rocks that make it up. These tools are limited to the open-hole environment.
The log must run in holes containing electrically conductive mud or water, i.e., with enough ions present in the drilling fluid. Indeed, in the borehole fluids the electrical charge carriers are only ions (cations and anions) present in aqueous solution in the fluid. In the absence of dissolved ions, water is a very poor electrical conductor.
Density logging is a well logging tool that can provide a continuous record of a formation's bulk density along the length of a borehole.In geology, bulk density is a function of the density of the minerals forming a rock (i.e. matrix) and the fluid enclosed in the pore spaces.
Spontaneous potential log, commonly called the self potential log or SP log, is a passive measurement taken by oil industry well loggers to characterise rock formation properties. The log works by measuring small electric potentials (measured in millivolts) between depths with in the borehole and a grounded electrode at the surface.
Mud logging is usually performed by a third-party mud logging company. This provides well owners and producers with information about the lithology and fluid content of the borehole while drilling. Historically it is the earliest type of well log. Under some circumstances compressed air is employed as a circulating fluid, rather than mud.