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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 ...
LWD tools are able to measure a suite of geological characteristics including density, porosity, resistivity, acoustic-caliper, inclination at the drill bit (NBI), magnetic resonance and formation pressure. [6] The MWD tool allows these measurements to be taken and evaluated while the well is being drilled.
Many modern oil and gas wells are drilled directionally. At first, loggers had to run their tools somehow attached to the drill pipe if the well was not vertical. Modern techniques now permit continuous information at the surface. This is known as logging while drilling (LWD) or measurement-while-drilling (MWD).
Rotary assemblies [2] are commonly used where formations are predictable and the rig economics are an issue. In such an assembly the weight of the drill collars gives the BHA the tendency to sag or flex to the low side of the hole, collar stiffness length and stabiliser diameter and placement are engineered as a means of controlling the flex of the BHA.
Geosteering only practically became possible with the advent of deep reading 2 MHz resistivity LWD tools from the major LWD vendors (BakerHughes Reservoir Navigation Tool, SperrySun and Schlumberger) and other tools in the early 1990s, and the forward modeling software from a number of vendors capable of predicting resistivity tool responses for different relative angles and formation ...
For this reason, several resistivity tools with different investigation lengths are used to measure the formation resistivity. If water based mud is used and oil is displaced, "deeper" resistivity logs (or those of the "intact zone" sufficiently away from the borehole disturbed zone) will show lower conductivity than the invaded zone.
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.
1" (5 foot average) mud log showing heavy (hydrocarbons) (large area of yellow)Mud logging includes observation and microscopic examination of drill cuttings (formation rock chips), and evaluation of gas hydrocarbon and its constituents, basic chemical and mechanical parameters of drilling fluid or drilling mud (such as chlorides and temperature), as well as compiling other information about ...