Glossary

rack pipe	To stand pipe on the derrick floor when coming out of the hole.

radial flow	The flow of fluids into a wellbore from the surrounding drainage area. Also, could be descriptive of the flow from an injection well to the surrounding area.

radiation	The emission and propagation of energy through space or matter, distinguished by the fact that the speed of propagation equals that of light and requires no intervening medium for its transmission. Any form of energy propagated as rays, waves, or streams of particles; especially light and other electromagnetic waves, sound waves, and the emissions from radioactive substances. See alpha particle, beta particle, gamma ray, neutron generator, gamma ray source, and neutron source.

radioactive tracer	A radioactive material put into a well to allow observation of fluid or gas movements by means of a radioactive-tracer survey.

radioactive-tracer log	A form of radioactivity log used in production logging for the study of tracer movements and, therefore, fluid movements in the immediate vicinity of the well bore (e.g., in casing. tubing, annulus, open hole). Usually one or more slugs of radioactive material are ejected into the fluid phase to be studied, and the direction and velocity of the introduced slug is monitored over different parts of the well bore. Tracer logs are helpful in estimating fluid flowrates, points of fluid exit or entry into the well bore, crossflow, leaks, etc.

radioactivity	A property of unstable isotopes. which undergo spontaneous atomic readjustment with the liberation of particles and/or energy (e.g., alpha or beta particles, neutrons, and gamma rays). Alpha and beta enmission change the chemical nature of the element involved. The loss of energy will result in the decay or transformation of the unstable isotope into a stable isotope; or transmutation into an isotope of another element, sometimes giving rise to emission of neutrons. The process of radioactive decay is one of conversion of mass to energy in accordance with Einstein's relationship, E = mc². Nearly all of the energy of emitted particles and photons is converted to heat in the near vicinity of the radioactive parent. This is one means by which the temperature of the earth is maintained.

radioactivity log	A well log of natural or induced radiation. Usually refers to a gamma-ray log; but, sometimes the expression radioactivity log is used to refer to a density log, neutron log. or other nuclear logs.

radioisotope	A nuclide. A radioactive isotope (unstable isotope) which spontaneously emits particulate (alpha beta) or electromagnetic (gamma) radiation as it decays to a stable state.

radiometric grade	Grade ore determined by radioactivity measurement in the borehole (Sgrade ´ thickness/ Sthickness). It is the weighted mean of the grades, with the thickness of each grade taken as the weight.

rams	(1) Heavy rubber seals in a blowout preventer which can be closed to provide pressure control. One of three types – blind, pipe, or shear – may be installed in several preventers mounted in a stack on top of the wellbore. (a) Blind rams, when closed, form a seal on a hole which has no part of equipment extending through the blowout preventer. (b) Pipe rams, when closed, seal around any pipe standing in the hole. (c) Shear rams, cut through drill pipe and then form a seal. (2) Well-logging companies furnish blowout preventers with modified rams which can be closed down over logging cable to provide pressure control. Will not damage cable.

Rankine temperature scale	A temperature scale with the degree interval of the Fahrenheit scale and the zero point at absolute zero. On the Rankine scale, water freezes at 491.60° and boils at 671.69°. See absolute temperature scale.

rate of penetration	ROP. The measured distance that the drill bit or other drilling tool penetrates subsurface formations in a unit length of time.

rathole	(1) A hole in the rig floor 30 to 35 feet deep. Lined with casing that projects above the floor into which the kelly is placed when hoisting operations are in progress. (2) A hole of a diameter smaller than the main hole. It is drilled in the bottom of the main hole.

ratio	(1) A mathematical relationship between two values, where one value is divided by the other, commonly expressed as a fraction. (2) In Thermal Decay Time Logging. A measurement recorded with the Dual-Spacing Thermal Decay Time tool which is derived from the counting rates of the two detectors. The ratio measurement has characteristics similar to those of a neutron log and for specific cases can be calibrated to serve as such. Used with the measurement of the Thermal Decay Time tool, it provides an apparent porosity and an apparent formation water salinity, useful for cased-hole formation evaluation. (3) With other dual-spaced radiation detector systems, it is the count-rate ratio (of near to far detector) sometimes recorded with two-detector tools such as the compensated neutron log.

Rayleigh wave	A surface acoustic wave (propagated along a flat surface; e.g., a ground surface) in which the particle motion is elliptical and retrograde with respect to the direction of propagation. Rayleigh waves probably are induced by shear wave components and result from differential velocities between the surface layer and deeper layers within the medium.

RDB	Rotary drill bushing.

reaction value	See water analysis.

reading	A value taken from a recorded curve for a specific depth in the well.

ream	To enlarge the wellbore by drilling it again with a special bit. Often a rathole is reamed or opened to the same size as the main wellhore.

reamer	A tool used in drilling to smooth the wall of the borehole, enlarge the hole to the specified size, stabilize the bit, straighten the wellbore if kinks or doglegs are encountered, and drill directionally. See ream.

receiver	A transducer used to receive a form of energy which has been propagated through the formation or induced in the formation. Used in the acoustic logging, induction logging, induced polarization methods, etc. Compare transmitter.

reciprocal sonde	A sonde (and associated equipment) in which the current and measure electrodes are interchanged according to a specific rule; i.e., A electrode for M electrode and B electrode for N electrode with no resulting change in logging measurements. An unexplained exception may be the lateral curve in thick salt sections.

reciprocator	An electronic module designed for the reciprocation of conductivity measurements into resistivity (e.g., induction conductivity signals to resistivity).

record	(1) A print of a well log. (2) A sequence of data on magnetic tape.

recorder	A device which records well-log data on film, chart, or tape. See camera.

recovery	(1) The amount of core recovered compared to the amount cut. (2) The height of fluid in the drill pipe on a drill-stem test which did not produce enough fluid to rise to tlme surface. (3) The total volume of hydrocarbons that has been or is anticipated to be produced from a well or field.

recovery factor	The percentage of oil or gas in place in a reservoir that ultimately can be withdrawn by primary and/or secondary techniques. The percentage of the oil or gas in place (expressed in stock tank barrels or in cubic feet) that will ultimately be recovered.

rectify	An obsolete term meaning to adjust records on a borehole log for true vertical depth. Logs in slant holes are usually recorded in distance measured along the well bore, which makes them difficult to correlate with other logs from other wells which intersect the formations differently. This adjustment is necessary in order to observe the true structural relationships between corresponding strata in different wells. See true vertical depth.

redox logging	The continuous measurement of the oxidation-reduction potential of formation penetrated by the well bore. Chemical reactions depending on the transfer of protons and electrons depend on the pH and Eh of the systems in which the reactions cccur. A measurement of the oxidation-reduction potential is a measurement of the tendency for such reactions to occur.

redox potential	See oxidation-reduction potential.

red pattern	A convention used in dipmeter interpretation to denote increasing formation dip with increasing depth with a constant average azimuth. The red color is sometimes drafted on the tadpole plot of the computed dipmeter log. Compare blue pattern and green pattern, See dip for illustration.

reef	A type of reservoir composed of rock (usually limestone) formed from the skeletal remains of marine plants and animals.

reference point	(1) measure point. A mark or position on a tool to which all measurements are related. A tool zero. See measure point. (2) A depth datum.

reflection peak	An increase in the value of resistivity recorded on a lateral curve as the A electrode passes a thin highly resistive bed (of thickness less than AO spacing). The recorded location of the reflection peak is one AO spacing removed from the actual depth of the thin resistive bed. See illustration under blind zone or lateral curve.

reinjection	The process of pumping produced water back into a porous and permeable formation by means of an injection well.

relative bearing	In dipmeter interpretation. Looking down the hole, it is the clockwise azimuthal angle from the upper side of the tool to the reference electrode number 1.

relative permeability	The ratio between the effective permeability to a given fluid at a partial saturation and the permeability at 100% saturation. The ratio of the amount of a specific fluid that will flow at a given saturation, in the presence of other fluids, to the amount that would flow at a saturation of 100%, other factors remaining the same. It ranges in value from zero at low saturation to 1.0 at 100% saturation of the specific fluid. Since different fluid phases inhibit the flow of each other, the sum of the relative permeabilities of all phases is always less than unity.

relief well	A well drilled near and deflected into a well that is out of control, making it possible to bring the wild well under control.

reluctance	The characteristic of a magnetic circuit which determines the total magnetic flux in the circuit when a given magnetomotive force is applied.

repeat formation tester	The repeat formation tester (RFT) is operated by an electrically driven hydraulic system so that it can be set and retracted as often as necessary to pressure test all zones of interest on one trip in the well. Two separate fluid tests can also be taken on one trip. Formation pressures are recorded at the surface in both digital and analog form. See formation tester. RFT is a mark of Schlumberger.

repeat section	A log rerun over a short section of hole, generally 200 feet, to enable comparison of similarity with the main survey to show instrument stability and repeatability.

reserves	The unproduced but recoverable oil or gas in place, in a formation, that has been proved by production.

reservoir	A subsurface, porous, permeable rock body in which oil or gas or both can be stored. Most reservoir rocks are limestones, dolomites, sandstones, or a combination of these. The three basic types of hydrocarbon reservoirs are oil, gas, and condensate. An oil reservoir generally contains three fluids: gas, oil, and water, with oil the dominant product. In the typical oil reservoir, these fluids occur in different phases as a result of the variation in their gravities. Gas, the lightest, occupies the upper part of the reservoir rocks; water, the lower part; and oil, the intermediate section. In addition to occurring as a cap or in solution, gas may accumulate independently of the oil. If so, the reservoir is called a gas reservoir. Associated with the gas, in most instances, are salt water and some oil. In a condensate reservoir, the hydrocarbons may exist as a gas, but, when brought to the surface, some of the heavier gases condense to a liquid or condensate. At the surface, the hydrocarbons from a condensate reservoir consist of gas and a high-gravity crude (i.e., the condensate). Condensate wells are sometimes called gas-condensate reservoirs.

reservoir-drive mechanism	The natural energy by which reservoir fluids are caused to flow out of the reservoir rock and into a wellbore. Solution-gas drives depend on the fact that, as the reservoir is produced, pressure is reduced, allowing the gas to expand and provide the driving energy. Water-drive reservoirs depend on water pressure to force the hydrocarbons out of the reservoir and into the wellbore.

reservoir pressure	Formation pressure. The pressure found within a reservoir at a specific point in time. Sometimes reservoir pressure is thought of as original pressure or geopressure (prior to disturbance) but at other times is thought of as pressure existing after disturbance. Reservoir or formation pressure should be qualified as to time, condition, and place.

reservoir temperature	The field average temperature encountered in the particular phase being investigated. In a liquid analysis of a reservoir containing an extensive gas cap, it would be the average temperature of the oil zone.

residual	That which remains after a removal or displacement process.

residual oil	Oil remaining in the reservoir rock after the flushing or invasion process, or at the end of a specific recovery process or escape process.

resistance	(1) The opposition to the flow of direct current. Equal to the voltage drop (E) across the material in which the current is flowing divided by the current (I) flowing through the material. See Ohm's law and IR drop. Also, see impedance. (2) In fluid flow, see viscosity.

resistivity	Specific resistance. The property of a material which resists the flow of electrical current. The reciprocal of resistivity is conductivity. See ohm meter. See also apparent resistivity.

resistivity index	R_t/R_o. The ratio of the resistivity of a formation bearing hydrocarbons to the resistivity it would have if 100% saturated with formation water. See also Archie's formulas.

resistivity logs	Any of a number of basic logs on which some aspect of formation resistivity has been recorded. (1) Most resistivity logs derive their readings from 10 to 100 ft³ of material about the sonde. See electrical survey, laterolog, and induction log. (2) microresistivity logs, on the other hand, derive their readings from a few cubic inches of material near the borehole wall.

returns	The drilling fluid, cuttings, etc. which circulate up the hole to the surface.

reversal	An interval of characteristic distortion on a normal curve across a resistive bed which has a thickness less than the AM spacing. The distortion is in the form of a depression of resistivity opposite the bed and two small symmetrical peaks located to either side of the depression outside the bed boundaries. The two peaks are separated by a distance equal to the AM spacing plus the bed thickness. The resistivity value of the depression is lower than the actual bed resistivity and, therefore, is deceptive.

rig	The derrick, drawworks, and attendant surface equipment of a drilling or workover unit. See also rotary rig and platform.

rig down	To dismantle equipment after the completion of an operation.

rig floor	The area immediately around the rotary table and extending to each corner of the derrick or mast. The area immediately above the substructure on which the drawworks, rotary table, etc. rest.

rig up	To prepare equipment for an operation.

riser	Length(s) of pipe mounted between the wireline blowout preventer and the stuffing box (or hydraulic packing head). Sometimes long enough to enclose the entire downhole instrument. Usually between 2 and 3 feet long. Should be equipped with 2 in. outlet through which the well can be killed or flowed if necessary. Under pressure, when broken cable strands bunch up under glands in the stuffing box, the blowout preventer can be closed and wires removed. If the downhole tool assembly is too long to fit inside a short (2-3 ft riser), the blowout preventer can be closed, the cable can be cut at a specific distance measured from the blowout preventer and a long riser with stuffing box installed. See illustration at lubricator. Also compare marine drilling riser.

riser pipe	See riser. Also see marine drilling riser.

roentgen	The basic unit of gamma ray exposure. One roentgen is the exposure resulting from the generation of one electrostatic unit (esu) of charge per 0.001293 g (1 cm³ at STP) of dry air. A fixed exposure rate exists at every point in space surrounding a source of fixed intensity.

roller-cone bit	A drilling bit made of three cones, or cutters, that are mounted on extremely rugged bearings. They are also called rock bits. The surface of each cone is made up of rows of steel teeth or rows of tungsten carbide inserts.

ROP	Abbreviation of rate of penetration.

rope socket	A metal component that clamps some of the cable armor strands at the tool end of the cable. It seats inside of the cable connector or fishing neck to support the weight of the tool. By the number of armor strands used, it can be made the weak point or pull-out point of the cable-to-tool mechanical connection. Sometimes called cable clamp. See weak point.

rose diagram	A polar plot or diagram in which radial distance indicates the relative frequency of an observation at a certain azimuth. Used in dipmeter interpretation. Compare azimuth frequency diagram.

rotary bushing	See master bushing, also kelly bushing.

rotary drill bushing	RDB. See kelly bushing.

rotary drilling	A drilling method in which a hole is drilled by a rotating bit to which a downward force is applied. The bit is fastened to and rotated by the drill stem, which also provides a passageway through which the drilling fluid is circulated. Additional joints of drill pipe are added as drilling progresses.

rotary rig	A derrick equipped with rotary drilling equipment; ie., drilling engines, draw works, rotary table, mud pumps, and auxiliary equipment. A modern drilling unit capable of drilling a borehole with a bit attached to a rotating column of steel pipe.

rotary table	The rotating steel platform on the derrick floor with an opening in the center through which the drill pipe and casing must pass. The table is rotated by power transmitted from the drilling engines. In drilling, the kelly bushing fits into the master bushing of the table. As the table rotates, the kelly is turned, rotating the drill column and the drill bit.

roughneck	Roustabout, floorhand. Members of the drilling crew. The driller's assistants who work on the derrick floor, in the derrick to rack pipe, tend the drilling engines and mud pumps, and operate the pipe tongs.

roundtrip	The action of pulling the drill pipe out of the hole and subsequently running the pipe back into the hole to the same depth. Roundtrips are made each time the drill bit is changed, for example.

rugosity	The quality of roughness or irregularity of a solid surface such as the borehole wall. The measurements of logging tools which must be held in close contact with the formation face (e.g., density and microresistivity logs) can be affected by rugosity.

run pipe	To lower a string of casing into the hole.