Any pore pressure which differs from normal pore pressure. It may be either higher than normal pore pressure (super-normal) or lower than normal pore pressure (subnormal). See overpressure and underpressure.

°K = °C + 273.16
°R = °F + 459.69

(1) The process of soaking up or taking in by capillary, osmotic, chemical, or solvent action.

(2) The process by which radiation loses some or all of its energy to any material through which it passes. See also photoelectric absorption.

A record of a well-logging measurement of one or more specific characteristics of acoustic waves propagated in and around the liquid-filled wellbore.

(1) The interval transit time, usually of the compressional wave, is recorded on such logs as the sonic log, continuous velocity logs, and borehole compensated sonic and Acoustilogs.

(2) The amplitude of part of the propagated acoustic wave, such as the compressional wave or shear wave is the measurement recorded on other well logs. These are the amplitude log, cement bond log, and fracture logs.

(3) The acoustic wave train of the propagated acoustic wave is displayed in the amplitude-time mode on full wave train logs such as signature logs or character logs; whereas the wave train is shown in the intensity modulated-time mode on variable density logs, variable intensity logs, 3-D Velocity Logs, or Micro-Seismogram Logs.

(4) Includes logs resulting from the measurements of travel time and amplitude of reflected acoustic energy. Tools making such measurements are the borehole televiewer and sonar caliper.

(5) Also includes logs produced by devices which detect and measure the amplitude of sound waves in the audible frequency range. Audible sound might emanate from liquid or gas movements in the wellbore environment. Tools developed to make such measurements are used in audio or noise logging techniques.

(1) The total time required for a specific acoustic wave to travel from one point to another.

(2) interval transit time. The time required for a compressional wave (usually) to travel from one point to another separated by a distance of unit length (usually one foot).

The activity of an ion species is its thermodynamic equivalent concentration; i.e., the ion concentration corrected for the deviation from ideal behavior caused by the interionic attraction of ions. It is this interaction between ions which tends to cause the electrical conductivity of a solution to be less than that predicted from the number of ions present. Only at infinite dilution are the ions completely free of the influence of other ions in solution.

Ionic activity is used in expressing the variation of electrode potentials and other electrochemical phenomena (e.g., SP). At low concentrations, the chemical activity of a solution of a given salt is roughly proportional to its salt content; i.e., roughly proportional to its conductivity or inversely to its resistivity. In concentrated solutions, the relation between conductivity and concentration is complex and depends on individual solute properties.

(1) Having the properties of a base.

(2) Containing sodium and/or potassium in excess of the amount needed to form feldspar with the available silica; e.g., an alkaline rock-in this sense sometimes written alkalic.

(3) Containing ions of one or more alkali metals.

(4) Waters containing more than average amounts of carbonates of sodium, potassium, magnesium, or calcium.

(1) That space between a drill pipe and the formations through which the drilling fluid (mud) returns to the surface.

(2) The space between tubing and casing or between casing and formation.

(3) A ring of interstitial water produced by invasion processes in hydrocarbon-bearing beds when both hydrocarbon and interstitial water phases have mobility and their mobilities are different.

When R_xo > R_o the annulus will be more conductive than the flushed zone (R_xo) or the uninvaded oil-bearing zone (R_t). When R_xo < R_o, the resistivity of the annulus will be intermediate between that of the flushed zone (R_xo) and the uninvaded oil-bearing zone (R_t).

The measure of gravity of liquid petroleum products on the North American continent, derived from specific gravity in accordance with the following equation:

Calibration pits, located at the API nuclear log calibration facility at the University of Houston, used for the calibration or standardization of gamma-ray logging responses and neutron logging responses into API units.

A unit of counting rate used for scaling gamma-ray logs and neutron logs.

(1) For gamma-ray curves. The difference in curve deflection between zones of low and high radiation in the API gamma-ray calibration pit is 200 API gamma-ray units. One two-hundredth of this deflection is one API gamma-ray unit.

(2) For neutron curves. The difference between electrical zero and the curve deflection opposite a zone of Indiana limestone (19% porosity) in the API neutron calibration pit is 1,000 API units. One one-thousandth of this deflection is one API neutron unit.

(1) A water-bearing stratum of permeable rock, sand, or gravel capable of producing water.

(2) In a petroleum reservoir with a natural water drive, the aquifer is that part of the reservoir containing water.

where	m	=	porosity exponent,
	Ro	=	resistivity of the formation when 100% saturated with formation water,
	Rw	=	formation water resistivity,
	Rt	=	true resistivity of the formation,
	n	=	saturation exponent.

(1) A bow spring or lever on a downhole tool which presses against the borehole wall to centralize the tool, to push the tool to the opposite side of the borehole, or to hold a sensor pad to the borehole wall.

(2) To prepare a perforating gun so that it will fire when the firing switch at the surface is operated. This usually requires connecting the detonator and/or completing the electrical wiring in the gun.

Descriptive of rock constituents and minerals which are formed or generated in the location where they are found.

Authigenic materials ussually are formed subsequent to deposition, but might be formed at the time of deposition. Compare allogenic.

(1) In well logging. In a horizontal plane, it is the clockwise angle of departure from magnetic north. See also magnetic declination.

(2) Curve recorded in dipmeter surveys. Looking down the hole, it is the clockwise angle from magnetic north to the reference electrode number 1 on the sonde or tool.

(3) In land surveying. It is the clockwise angle of departure in a horizontal plane from true north.