Oil and Gas Terms Beginning with “M”

The MBT test (methylene blue test, also called the methylene blue capacity test or cation exchange capacity test) is a drilling fluid quality control procedure that quantifies the concentration of active clay… Read more →

MD (measured depth) is the distance along the actual wellbore trajectory from the surface reference datum, typically the rotary table (RT) or kelly bushing (KB) elevation, to any downhole point of interest, measured by… Read more →

What Is Mixed Metal Hydroxide? Mixed metal hydroxide (MMH) describes a class of positively charged layered crystal compounds containing Al³⁺, Mg²⁺, and OH⁻ ions that associate with negatively charged bentonite particles… Read more →

A product similar to mixed-metal hydroxide, but based on silicate chemistry Read more →

MMscf is the standard oilfield abbreviation for one million standard cubic feet of gas, a volume unit in which the leading M's are Roman numerals: one M means a thousand, so MM means a thousand thousand, that is one… Read more →

MODU stands for mobile offshore drilling unit, a generic term for the several classes of self-contained, floatable or floating machines that drill exploration and development wells offshore and can be moved from one… Read more →

(noun) Abbreviation for Magnetic Reversal Sequence. A chronostratigraphic tool based on the record of periodic reversals in the Earth's magnetic field preserved in sedimentary and volcanic rocks, used in biostratigraphy… Read more →

An MSDS (Material Safety Data Sheet) — now formally replaced in most jurisdictions by the SDS (Safety Data Sheet) under the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) — is a… Read more →

What Is MT (Magnetotelluric)? Magnetotelluric (MT) is a passive electromagnetic geophysical method that maps subsurface resistivity variations by measuring naturally occurring electric and magnetic fields at the Earth's… Read more →

What Is Measurement While Drilling (MWD)? Measurement while drilling (MWD) describes the downhole instrumentation and surface telemetry system that transmits real-time wellbore survey data, including inclination,… Read more →

Abbreviation for millions of years before present. The preferred abbreviation is Ma. Read more →

Mega annum. The abbreviation for million years that is most commonly used in the geologic literature. Read more →

A Marsh funnel is a standardized cone-shaped vessel fitted with a small-bore orifice tube at its apex, used to measure the apparent viscosity of drilling fluid by timing how long it takes a fixed volume of mud to drain… Read more →

A device that fits into the rotary table to accommodate the slips and drive the kelly bushing so that rotating motion can be transmitted to the kelly. Read more →

A Material Safety Data Sheet (MSDS) is a standardized document that communicates the physical properties, chemical composition, health hazards, handling requirements, and emergency response procedures associated with a… Read more →

Maxwell's equations are the four fundamental partial differential equations of classical electromagnetism, formulated by James Clerk Maxwell in 1865 and refined by Oliver Heaviside into their modern vector form, that… Read more →

A drilling rig in which the source of power is diesel engines and the power is distributed through mechanical devices including chains, sprockets, clutches, and shafts. Read more →

Milankovitch cycles are systematic variations in Earth's solar exposure (insolation, the amount of solar radiation received at any latitude on Earth's surface) that arise from periodic variations in three orbital… Read more →

The Minerals Management Service (MMS) was a bureau of the United States Department of the Interior responsible for managing the nation's natural resources on the Outer Continental Shelf (OCS) and collecting royalties on… Read more →

The Moho, formally named the Mohorovicic discontinuity after Croatian seismologist Andrija Mohorovicic who discovered it in 1909, is the seismic velocity boundary that separates the earth's crust (the outermost solid… Read more →

The Moho, formally named the Mohorovicic discontinuity after Croatian seismologist Andrija Mohorovicic who discovered it in 1909, is the seismic velocity boundary that separates the earth's crust (the outermost solid… Read more →

Monte Carlo risk analysis is a quantitative approach to project evaluation under uncertainty in which input parameters are represented as probability distributions rather than fixed values, and the model is solved… Read more →

The sampling of uncertain data for use in Monte Carlo risk analysis or simulation. Read more →

Monte Carlo simulation is a computational technique that models the uncertainty inherent in reservoir and economic parameters by running thousands of iterative calculations, each time drawing input values at random from… Read more →

Mscf/d is the abbreviation for thousand standard cubic feet of gas per day, one of the most common units for expressing the production rate of a natural gas well. The notation trips up newcomers because the leading M is… Read more →

A large, high-pressure reciprocating pump used to circulate the mud on a drilling rig. A typical mud pump is a two- or three-cylinder piston pump. Read more →

Open steel tanks used for holding drilling fluids. Some tanks are used for suction to mud pumps, settling of sediments, and storage of reserve mud. Read more →

A device that removes gas from the mud coming out of a well when a kick is being circulated out. Read more →

Multiazimuth towed streamer acquisition (MATS) is a marine seismic survey acquisition technique in which multiple 3D seismic surveys are recorded over the same area at different sailing directions (azimuths), enabling… Read more →

Abbreviation for million years. The preferred abbreviation is Ma. Read more →