M
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matrix |
The solid framework of rock which surrounds pore volume. |
maximum-reading thermometer |
A mercury-filled thermometer with a constriction in the capillary tube which registers the maximum temperature attained. When in use, it is contained in a protective case and attached to the downhole instrument or bridle. |
measurements-while-drilling |
MWD. A wireless system for making downhole measurements of azimuth, inclination, and tool facing from sensors mounted inside of a nonmagnetic drill collar located near the drill bit. Formation properties can be measured, such as: natural radioactivity, resistivity, and temperature. These measurements are sent to the surface by means of pressure pulses induced in the drilling mud by a mud-pulse transmitter, or stored downhole and brought to the surface when the bit and MWD collar are brought out of the hole. |
measure point |
A depth reference point on a logging tool at which measurements are taken. Usually the lowermost sensor or lowermost measure point. Static measure point. Compare dynamic measure point. |
meteoric water |
A term applied to water which penetrates the rocks from above, i.e. rain, dew hail, snow and also the water of rivers and streams |
microannulus |
A type of impairment in cement bond quality. Can occur opposite poorly consolidated formations after cemented casing has been subjected to internal pressure. The application of internal pressure results in an expansion of the casing and the cement sheath into soft formations. Removal of the pressure and the resultant contraction of the pipe leaves a microannulus between the casing and the cement sheath. Can be produced. for example, by pressure testing, perforating, fracturing, or cement squeeze operations. |
microlaterolog |
An electrode device with small spacings from which the current flow, and hence the measurement, is focused a short distance into the formation. Introduced in 1953, the microlaterolog measures the resistivity of the flushed zone with minimum influence from the mudcake or the undisturbed zone. The central current emitting electrode (A0) is surrounded by a guard electrode that emits sufficient current to focus the current from A0 a certain distance into the formation. The electrodes are mounted on a pad that is pressed against the borehole wall. In a typical tool design, 90% of the signal comes from within 3 in. [7.6 cm] of the pad, ensuring that the undisturbed zone rarely has an effect. |
microlog |
An unfocused electrode device with small spacings, mounted on a pad and pressed against the borehole wall. The typical microlog has one current-emitting electrode and two measure electrodes in line above it, one at 1 in. [2.5 cm], the other at 2 in. [5 cm]. The potential at the 2-in. electrode gives a 2-in. micronormal log. The difference in potential between the two measure electrodes gives a 1-in. x 1-in. microinverse log. The micronormal reads deeper than the microinverse. |
mist flow |
A producing flow condition in a well bore in which gas and oil flow at very high velocities. The oil film on the pipe wall becomes very thin and most of the oil is transported in the form of very small droplets nearly homogeneously dispersed in the gas. Therefore, the two phases move at essentially the same velocity. |
mobility |
The ratio of permeability to viscosity. Well productivity is directly proportional to the mobility-thickness product. |
moldic porosity |
Porosity formed by the preferential dissolution of a former constituent of sedimentary rock. Once the constituent (such as a shell. other detrital material, or oölith) has dissolved, a void or empty mold remains which bears the shape of the former material. |
mud |
A term that is generally synonymous with drilling fluid and that encompasses most fluids used in hydrocarbon drilling operations, especially fluids that contain significant amounts of suspended solids, emulsified water or oil. Mud includes all types of water-base, oil-base and synthetic-base drilling fluids. Drill-in, completion and workover fluids are sometimes called muds, although a fluid that is essentially free of solids is not strictly considered mud. |
mud ball |
An accumulation of mud solids that sometimes builds up on the drilling bit during circulation prior to logging. It can present a problem to logging if the ball should become dislodged in the borehole or scrape off on the face of porous and permeable reservoir rock. |
mud cake |
Filter cake. The residue deposited on the borehole wall as the mud loses filtrate into porous, permeable formations. The mud cake generally has very low permeability and hence tends to retard further loss of fluid to the formation. See invaded zone. |
mud density |
The density of the drilling mud usually measured in pounds per U.S. gallon or pounds per cubic foot. |
mud filtrate |
The effluent of the continuous (external) phase liquid of drilling mud which penetrates porous and permeable rock, leaving a mud cake on the drilled face of the rock. |
mud log |
A record of information derived from examination of drilling fluid and cuttings from the formation. |
mud logging |
Hydrocarbon well logging. The analysis of samples of the circulated drilling fluid (or mud) and formation cuttings to detect signs of fluids which have entered the mud from the formations. Hydrocarbons may be detected by fluorescence, by chromatographic analysis, gas, and other ways. Also, the mud may be monitored for salinity and viscosity. Plots of such data often include a sample log and a drill time curve. |
mud pit |
tank near the rig into which drilling mud is circulated. Mud pumps withdraw the mud from one end of the pit as the circulated mud (bearing rock chips from the borehole) flows in at the other end. As the mud moves to the suction line, the cuttings drop out leaving the mud "clean" and ready for another trip to the bottom of the borehole. |
mud pump |
A large, reciprocating pump used to circulate the mud on a drilling rig. |
mud viscosity |
Viscosity of drilling mud. |
mud weight |
mud density. |
multiphase flow |
A flow regime in which gas, oil, and water are all flowing. |
multiple completion |
An arrangement for producing a well in which one wellbore penetrates two or more petroleum-bearing reservoirs that lie one over the other. The tubing strings are suspended side by side in the production casing string. each a different length and each packed off to prevent the commingling of different reservoir fluids. Each reservoir is then produced through its own tubing string. |
multishot survey |
directional survey. |
