Oilfield Glossary

L to N

Lateral bore – normally referred to as the deviated or horizontal extension in the drilling of a horizontal well or multilateral well.

Liner – a string of pipe used to case open hole below existing casing, overlapping inside the upper string and held in place by a liner hanger packer.

Lithology - 1. the study of rocks, usually macroscopic. 2. the individual character of a rock in terms of mineral composition, structure, and so forth.

Logging-While-Drilling (LWD) – a variation of measurement-while-drilling in which the LWD tool gathers information (i.e.; resistivity, density, porosity, gamma ray) about the formation while the well is being drilled.

Main bore – the main casing string from which subsequent directional drilling operations or openhole operations are initiated. Lateral bores extend from the main bore to the desired target depth.

Measurement-While-Drilling (MWD) – measuring directional information (azimuth, inclination, and tool orientation) downhole to adjust the drilling process and guide the wellbore to a specific target.

Migration – a computational process applied to seismic data that returns reflection events to their origin in the subsurface.

Minerals Management Service (MMS) – Branch of the US Department of Interior that governs oil operations in US waters on the Outer Continental Shelf.

Moveout – the difference in arrival times of reflected seismic data at different detectors.

Mud – see drilling fluid

Multicomponent Seismic – a survey conducted using 3-component (3-C) geophones for sensing seismic reflections in the vertical, horizontal, and crossline directions. In the marine environment, a hydrophone is included to acquire 4-component (4-C) data.

Multi-Cycle Tool (MCT) - is primarily a circulating device that is operated hydraulically from the surface using internal tubing pressure.

Multilateral – the construction of two or more wellbores into one or more reservoirs for the purpose of managing and optimizing fluid movement within the reservoir(s). These lateral wellbores are connected back to a common main bore that extends to surface. Various levels of completion systems can be installed in a multilateral well to enable it to produce from several zones simultaneously.

NMO – Normal moveout offset – the difference in arrival times of reflected seismic data at different detectors due to different source and detector separations.

North Sea Brent – crude oil produce from the Brent field in the British sector of the North Sea. Often quoted as a benchmark for world oil prices.