Glossary

packer	A downhole, expanding plug-like device which is used to seal off certain parts of tubing, casing, or open hole when cementing, acidizing, or isolating specific zones of a formation for production or testing. Packers can be run on logging cables, tubing, drill pipe, or casing and when in position can be expanded to form a seal to confine fluid flow to the inside bore of the packer.

packer flowmeter	A spinner-type velocimeter which utilizes an inflatable packer bag. After the proper-size bag is pumped up to fill the annulus between tool and casing, all the fluid is diverted through the spinner assembly which measures the velocity of the fluid, which, in turn, is related to the volumetric flow rate. A profile in bbl/day for either "up or down" flow is recorded; also flow direction. The profiles are determined by fixed point recordings. The tool operates at lower rates than the minimum required for a continuous flowmeter.

pad	See sidewall pad.

pair production	The conversion of a photon (gamma ray), which has more than twice the rest mass energy of an electron (about 0.51 MeV per electron), into an electron and a positron when the incident photon passes through the strong electric field surrounding an atomic nucleus and vanishes. This is an example of creation of matter (the electron pair, one negative and one positive) from energy (the photon) according to Einstein's law: E = mc². Relatively unimportant in density logging because of the high threshold energy (greater than 1.02 MeV) required for the incident gamma ray. Important in the detection of gamma rays in the ionization chamber and Geiger-Mueller counter. One of the three interactions of gamma rays with matter. Compare photoelectric effect and Compton scattering.

paraffin	A hydrocarbon having the formula C_nH_2n+2 (methane, CH₄; ethane, C₂H₆, etc.). Heavier paraffin hydrocarbons (i.e., those of C₁₈H₃₈ and heavier) form a waxlike substance that is called paraffin. Heavier paraffins often accumulate on the walls of tubing and other production equipment, restricting or stopping the flow of desirable lighter paraffins.

paraffinic	Pertains to an oil of the methane series having the formula C_nH_2n+2. Such compounds are chain-like molecules. Compare aromatic.

partition gas chromatograph	A device for quantitative analysis of hydrocarbon constituents. A fixed quantity of sample is carried with a stream of sweep gas through a partition column packed with an inert solid coated with a nonvolatile organic liquid. The lighter fractions traverse the column faster than the heavier fractions so that the components appear separately at the column exit, where their amounts can he measured.

parts per million	ppm. Refers to concentration by weight for both solute and solution. Parts per million (wt./wt.) differs from mg/liter (wt./vol.) when the specific gravity of the solution differs from that of pure water at standard conditions. Many salinities that have been measured in units of mg/liters are reported routinely in ppm without proper conversion to ppm.

patch panel	A surface panel which serves as a junction board between the survey panels and various survey lines. The patch panel allows easy access to all cable and ground line conductors. Conductor functions can be interchanged or checked rapidly for continuity, insulation, or quality of signal brought to the surface. Also, provides easy access to output of surface panels.

pay	The part of a formation which produces or is capable of producing oil or gas, or other economic product.

pendular saturation	See description and illustration under saturation.

perforating	See gun perforating.

perforation record	A log sometimes run after a perforating operation in order to record perforations at actual depths. Usually performed with a casing collar locator.

permafrost	Perenially frozen ground.

permeability	Absolute permeability. A measure of the ability of a rock to conduct a fluid through its interconnected pores when that fluid is at 100% saturation. Measured in darcies or millidarcies. See also effective permeability.

petroleum	Oil or gas obtained from the rocks of the earth.

petroliferous	Containing petroleum (of rocks).

pH	An expression representing the negative logarithm of the effective hydrogen-ion concentration or hydrogen-ion activity (in gram equivalents per liter). The pH value is a unit of measure of the acid or alkaline condition of a substance. A neutral solution (as pure water) has a pH of 7; acid solutions are less than 7; basic, or alkaline solutions are above 7. The pH scale is a logarithmic scale; a substance with a pH of 4 is more than twice as acid as a substance with a pH of 5. Similarly, a substance with a pH of 9 is much more than twice as alkaline as a substance with a pH of 8.

phase	(1) Any portion of a nonhomogeneous system that is bounded by a surface. is homogeneous throughout, and may be mechanically separated from the other phases. The three phases of H₂O, for example, are ice (solid) water (liquid), and steam (gas). (2) In physics, the stage or point in a cycle to which a rotation, oscillation, or variation has advanced.

photoclinometer	A well-logging device which photographically records the borehole azimuth and deviation from the vertical. In the cartridge of the downhole instrument. a compass needle indicates magnetic north and a steel ball rolling freely on a graduated concave glass indicates the hole deviation. A lens focuses these images on photographic film which is exposed, frame by frame, when the tool is held motionless, centered in the borehole at preselected stations. Compare poteclinometer.

photoelectric absorption	When a photon (gamma ray) collides with an atom, it may be completely absorbed and its total energy used to eject one of the orbital electrons from those surrounding the nucleus. Part of the photon's energy is used to overcome the binding energy holding the electron in the atom; the remainder serves to impart a velocity to the recoiling electron. In general, this photoelectric effect is greater for low energy incident gamma rays (below about 100 keV), and occurs at higher energies for atoms of higher atomic number. The rate of absorption varies only with the energy of the incident gamma ray and the nature of the atom. Photoelectric absorption is the process which produces the high-speed ionizing particle (i.e., electron) which causes the scintillation to appear in the phosphors of scintillation detectors. Produces an effect in the formation which influences some density logging measurements.

photoelectric absorption cross section index	P_e. A downhole measurement recorded with the Litho-Density and Compensated Spectral Density tools that is related to the atomic number of the formation and therefore the lithology. See photoelectric absorption also.

photoelectric effect	Changes in the electrical characteristics of substances due to radiation, generally in the form of light. The photoelectric absorption of photons (gamma rays) in the photoelectric effect is one of the interactions between gamma rays and matter. See further explanation under photoelectric absorption, and compare pair production and Compton scattering.

photomultiplier	Used with a scintillation crystal to make up a scintillation counter. The flash of light produced in the phosphor of a radiation detector strikes the sensitive surface of a photocathode in the photomultiplier, causing the emission of a number of primary electrons. These electrons are drawn to an anode maintained at a higher potential, and a number of secondary electrons are emitted for each impinging electron. The secondary electrons are drawn to a second anode maintained at a higher potential than the first. whereupon additional multiplication occurs. This process is repeated in about ten stages until the initial current has been multiplied about a millionfold. The amplitude of the output of the photomultiplier is proportional to the intensity of the scintillation in the phosphor. See also scintillation counter.

photon	A quantity of energy emitted in the form of electromagnetic radiation; e.g., radio waves, light, x-rays, and gamma rays.

photon log	A well log of scattered gamma rays differing from a density log in that the tool is not pressed against the borehole wall and hence is especially sensitive to changes in hole diameter or density of the fluid in the borehole. It has been used for determining changes in the density of fluids in the well bore and location of cement in the casing-formation annulus.

pick-up	(1) On a well log, it is the recorded point on a curve at which the curve begins to vary in response to variations in the wellbore environment. (2) During the survey operation, it is the depth at which the logging tool lifts off the bottom of the borehole. Signified by curve movement and increase in cable tension as shown on the weight indicator.

piercement dome	A mass of material usually salt, that rises and penetrates rock formations. See dome and salt dome.

pinch out	The progressive thinning of a stratum to its point of disappearance.

Pipe Analysis Log	PAL. A well log which combines magnetic-flux-leakage and eddy-current measurements in such a manner as to locate defects or flaws on the inner or outer wall of a casing, as well as to provide a measurement which is indicative of the extent of such defects. Magnetic-flux-leakage testing relies upon the detection of perturbations in a magnetic field caused by defects anywhere on the inside or outside casing wall. For the eddy-current test, the frequency of the eddy current is chosen so that the depth of investigation will be limited to the inner casing wall. The electromagnetic thickness log is frequently run in conjunction with the Pipe Analysis Log where concentric casing strings are set in order to provide information helpful in the analysis of the outer casing string. PAL is a mark of Schlumberger.

pipe inspection log	See casing inspection log and Pipe Analysis Log.

plastic shale	Shale in a state of plasticity which is capable of squeezing or extruding into the well bore. Plastic shale contains a large amount of water and lacks rigidity. Plastic shale flows as a result of the geostatic load it is bearing. Compare heaving shale.

platform	A platform is an immobile structure which provides a base for drilling and producing hydrocarbons in offshore areas. A fixed platform, which is made of steel or concrete, extends above the water surface and is supported by the sea bed by means of piling or spread footings. Other platforms are jack up platforms used in shallow waters and tension-leg platforms used in deep waters.

plug	(1) See plug and abandon. (2) A sample. See sidewall core and core. See also core analysis. (3) A large underground feature such as a salt plug or salt dome. Not a popular usage of the term. See diapir, pluton, and salt dome.

plug and abandon	P&A. To place a cement plug into a dry hole or noneconomic well and abandon the well.

plug back	To place cement in or near the bottom of a well to exclude bottom water, sidetrack, or produce from a formation already drilled through. Plugging back also can be accomplished by a mechanical plug set by wireline, tubing, or drill pipe.

plugged back total depth	PBTD. A depth above the original total depth, to which the well bore has been cemented or plugged .

pluton	In the strictest sense, a body of igneous rock which has formed beneath the surface of the earth by consolidation from magma.

poise	p. The viscosity of a liquid in which a force of 1 dyne (a unit of measurement of small amounts of force) exerted tangentially on a surface of 1 cm² of either of two parallel planes 1 cm apart will move one plane at the rate of 1 cm per second in reference to the other plane with the space between the two planes filled with the liquid.

Poisson's ratio	See elastic properties of rocks.

polar compound	A compound (as water) with a molecule that behaves as a small bar magnet with a positive charge on one end and a negative charge on the other.

polar plot	Plots on polar coordinate paper usually used to aid dipmeter interpretation. Polar plots may take different forms; e.g., modified Schmidt plot, azimuth frequency diagrams, etc.

pool	A reservoir or group of reservoirs. The term is a misnomer in that hydrocarbons seldom exist in pools but rather in the pores of rock.

pore	An opening or void within a rock or mass of rock, usually small and filled with fluid (water oil, gas, or all three). See porosity. Compare vug.

pore pressure	Pressure exerted by fluids contained within the pores of rock. See formation pressure.

porosity	The ratio of void space to the bulk volume of rock containing that void space. Porosity can be expressed as a fraction or percentage of pore volume in a volume of rock. (1) Primary porosity refers to the porosity remaining after the sediments have been compacted but without considering changes resulting from subsequent chemical action or flow of waters through the sediments. See primary porosity. (2) Secondary porosity is the additional porosity created by chemical changes, dissolution, dolomitization, fissures, and fractures. See secondary porosity. (3) Effective porosity is the interconnected pore volume available to free fluids, excluding isolated pores and pore volume occupied by adsorbed water. In petroleum engineering practices, the term porosity usually means effective porosity. (4) Total porosity is all void space in a rock and matrix whether effective or noneffective. Total porosity includes that porosity in isolated pores, adsorbed water on grain or particle surfaces, and associated with clays. It does not include water of crystallization wherein the water molecule becomes part of the crystal structure.

porosity exponent	The exponent (m) of the porosity term in formation resistivity factor-porosity relationship. (See Archie's formulas.) The porosity exponent is influenced by those properties of the rigid rock which influence the shape of the electrically conductive solution occupying the pore volumes. Sometimes referred to as cementation factor and shape factor.

porosity overlay	A log of porosity values computed from different logs plotted on top of each other.

positive separation	A term usually used in reference to microlog curves to describe the condition where the micronormal (deeper) resistivity curve reads a higher value than the microinverse (shallower) curve. This condition usually denotes the presence of mud cake on the face of the drilled formation. Compare negative separation.

poteclinometer	A device for making a continuous measurement of the angle and direction of borehole deviation during a survey. A pendulum moves the wiper arm of a potentiometer so that a simple resistance measurement corresponds with the position of the pendulum and therefore the angle between the tool axis and verticle. A compass moves the wiper arm of another potentiometer so that another resistance measurement corresponds to a measure of azimuth. Another pendulum moves the wiper of a third potentiometer to make a measurement of relative bearing. See deviation, azimuth, and relative bearing. Used in dipmeter surveys. Compare photoclinometer.

potential	(1) Voltage level with respect to a reference level. (2) emf. electromotive force. (3) Potential drop = IR drop. See IR drop and Ohm's law.

pour point	In the case of an oil (or any other liquid), it is a temperature 5�F above that temperature at which the oil is solid. The lowest temperature at which an oil will flow.

ppm	Parts per million.

precession	A comparatively slow gyration of the rotational axis of a spinning body about another (intersecting) axis so as to describe a cone. Caused by the application of a torque tending to change the direction of a rotational axis. See nuclear magnetism log.

pressure	The force per unit area that is exerted on a surface (as that exerted against the inner wall of a container or piping system by a fluid or that exerted on a wellhead by a column of gas in the well). In the U.S., pressure is usually expressed in pounds per square inch (psi).

pressure case	See housing.

pressure drop	A loss of pressure resulting from friction as a fluid passes through a porous medium from one area to another.

pressure gauge	An instrument for measuring fluid pressure that usually registers the difference between atmospheric pressure and the pressure of the fluid by indicating the effect of such pressures on a measuring element (as a column of liquid, a Bourdon tube, a weighted piston, a diaphragm, or other pressure-sensitive device).

pressure gradient	A scale of pressure differences in which there is a uniform variation of pressure from point to point. For example, the pressure gradient of a column of pure water is about 0.433 psi/ft of vertical elevation (9.79 kPa/m).

pressure maintenance	A method for increasing ultimate oil recovery by injecting gas, water, or other fluids into the reservoir before reservoir pressure has dropped appreciably, usually early in the life of the field, to reduce or prevent a decline in pressure.

pressure transient testing and analysis	A pressure transient test is a test during which the flow rate of a well is carefully controlled in order to obtain pressure transient data. Pressure transient analysis is the careful evaluation of pressure variation as a function of time in order to determine qualitatively those parameters which control fluid flow.

pressure, volume, and temperature (PVT) analysis	An examination of reservoir fluids in a laboratory under various pressures, volumes, and temperatures to determine the characteristics and behavior of the fluid.

Primacord	A trade name for a cord containing a core of high explosive material which is used to detonate high explosives or a series of explosive charges; e.g., shaped charges. The cord detonates at the velocity of the detonative wave of the explosive material. Sometimes liquid-proof and pressure-proof for exposed applications.

primary porosity	Porosity which is present in sediment at the time of deposition or formed during sedimentation. Compare secondary porosity.

primary recovery	Recovery of petroleum oil from underground reservoirs by taking advantage of the natural energy (pressures) in these reservoirs. The most common types of these sources of reservoir pressures are solution-gas drive, gas-cap-expansion drive, and water (aquifer) drive. More than one of these natural drives may occur in a single reservoir. See also secondary recovery and tertiary recovery.

probe	In well logging, a probe is a downhole logging instrument. A sonde. A tool.

producibility index log	A computed well log showing a comparison of various parameters important to the producibility of a formation (e.g., effective porosity, clayiness. permeability index. etc.).

production	(1) The amount of oil or gas produced in a given period. (2) That phase of an energy related industry which deals with bringing the formation fluids to the surface and preparing the product for pipeline or other transportation.

production casing	Long string. The last string of casing set in a well prior to production.

production log	A well log run in a production or injection well. Small diameter tools are used so that they can be lowered through tubing. Services and devices include continuous flowmeter, packer flowmeter, gradiomanometer, manometer, densimeter, watercutmeter, thermometer, radioactive-tracer logs, temperature logs, calipers, casing collar locator, fluid sampler, water entry survey, etc.

Prolog	A computed log analysis system. Prolog computer-processed interpretations are designed to be performed at the well site. Prolog is a mark of Dresser Atlas.

prompt gamma ray	Gamma radiation given off "promptly" following a nuclear reaction: ie., fission, or by the interaction of a neutron and a stable nucleus. For example, a nucleus excited by capturing a neutron, or by the inelastic scattering of a very fast neutron. sheds excess energy by the emission of one or more prompt gamma-ray photons. See also delayed gamma ray.

propagation effect	See skin effect.

proportional counter	Similar in construction and operation to an ionization chamber. Usually the proportional counter is a metal chamber. filled with gas, with a central electrode maintained at a positive voltage with respect to the shell. The voltage level of the central electrode is related to the critical voltage value where gas amplification begins. The proportional counter is operated in that limited voltage range where the charge flow across the counter is proportional to the primary ionization. In well logging, it is designed for the detection of neutrons. A gas is used which is suitable for the production of ionizing particles upon reaction with incident neutrons. The gas commonly used is He³ but may be BF₃. The BF₃ gas, maintained at about 1 atmosphere, requires a voltage level of 2400-2500 volts and produces a larger pulse than that in He³; but, the He³ maintained at higher pressure and operating at about 1300 volts is more efficient in the detection of neutrons. Compare ionization chamber, Geiger-Mueller counter, and scintillation counter.

proration	A system enforced by a state or federal agency or by agreement between participants that limits the amount of petroleum that can be produced from a well or field within a given period.

protection casing	A string of casing set to protect a section of the hole and to permit drilling to continue to a greater depth. Intermediate casing.

proton	An elemental particle which is identical to the nucleus of the lightest hydrogen atom. Both proton(s) and neutron(s) are constituents of nuclei of elements heavier than hydrogen. A proton carries a positive charge numerically equal to the charge of an electron and has a mass of 1.6724 × 10^–24 gram or 1.0075 atomic mass unit.

proximity log	A microresistivity log, similar to the microlaterolog, made from a tool which focuses survey current issuing from a sidewall pad. The electrodes are mounted on a wider pad than that used by the microlaterolog, and survey current is focused deeper into the formation. These design features result in measurements which have less sensistivity to the mud cake. A caliper curve usually is recorded simultaneously. Compare microlaterolog and microspherically focused log.

pseudo-geometrical factor	A weighting factor used for estimating uninvaded formation resistivity from the response (R_a) recorded on a laterolog (or guard log). True resistivity can be estimated from the relationship R_a = R_xoJ + R_t(1 - J) where R_xo = flushed zone resistivity, R_t = uncontaminated zone resistivity, and J = pseudo-geometrical factor, a function of invasion depth. It must be emphasized that a pseudogeometrical factor relating to an electrode-type resistivity device is applicable in only one set of conditions, and therefore charts of this type are not valid as general-purpose invaded-zone correction charts. The most useful feature of such a chart is the graphic comparison it allows of the relative contrihution of invaded zones to the responses of the various tools. Compare geometrical factor.

pseudo-static SP	PSP. Similar to static spontaneous potential (SSP), but applies to measurement or calculation in dirty rock, whereas SSP refers to that in clean rock. Compare SSP.

PSP	See pseudo-static SP.

p.u.	Porosity unit: one percent pore volume.

pulsator	A device used in early electrical-resistivity well logging instrumentation to pulsate (or alternate) the survey current and measured signals.

pulsed neutron capture log	Neutron Lifetime Log, Thermal Decay Time Log, or Thermal Multigate Decay Log.

pulsed neutron log	A term with broad application. Includes all logs made while using neutron bursts or pulses. This term quite often is used in referring to neutron decay time logs such as the Thermal Decay Time Log, Neutron Lifetime Log, and Thermal Multigate Decay Log. A neutron generator, which emits neutrons in controlled cyclic pulses, is the source of radiation. The term also applies to other nuclear logs where cyclic neutron pulses must be used; e.g., some induced spectral gamma-ray logs.

pulse-height analyzer	An instrument used to indicate the number of occurrences of counter-output pulses falling within each of one or more specified amplitude (i.e., energy) ranges; used to obtain the energy spectrum of gamma radiations. It is possible to separate and count the pulses corresponding to one or more specific energy ranges which serve as an indicator of some specific radioactive isotope in the formation. See also spectral gamma-ray logging, induced spectral gamma-ray logging, and channel.

PVT analysis	Abbreviation of pressure, volume, and temperature analysis.

P-wave	compression wave.

pyrobitumen	A dark-colored, hard, nonvolatile, native, asphaltic substance which is infusible, is relatively insoluble in carbon disulfide, and destructively decomposes with pyrolysis.