Glossary

wall sticking	See differential-pressure sticking.

washout	Excessive borehole enlargement caused by solvent and erosional action by the drilling fluid.

washover	Pertaining to part of the fishing operation to free stuck drill pipe or tubing.

wash over	To release pipe that is stuck in the hole by running washover pipe. The washover pipe must have an outside diameter small enough to fit into the borehole but an inside diameter large enough to fit over the outside diameter of the stuck pipe. A rotary shoe, which cuts away the formation, mud, or whatever is sticking the pipe, is made up on the bottom joint of the washover pipe, and the assembly is lowered into the hole. Rotation of the assembly frees the stuck pipe. Several washovers may have to be made if the stuck portion is very long.

water analysis	(1) A chemical analysis of water in which the quantity of ions in solution is determined for the common cations and anions (e.g., Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, S0₄^--, Cl^-, CO₃^--, HCO₃^-). The character of the solution can be described in terms of the ion concentrations in parts per million, milligrams per liter, or its reaction value. The unit of concentration, parts per million, is related to the weights of positive and negative ions in solution, and the combined weight of the positive ions does not balance the combined weight of the negative ions. The reaction value relates the weight of each ion to its valence and atomic (or radical) weight. For example, The reaction values of positive and negative ions are exactly equal when all ions have been considered. (2) An electrical resistivity analysis of water. Resistivity values of water solutions of interest, as determined by actual measurement of each sample in a conductivity or resistivity cell, are important in the analysis of resistivity well logs.

water-base mud	A drilling mud in which the continuous phase is water. Compare oil-base mud.

water block	A reduction in the relative permeability to oil or gas due to the increase in water saturation near the borehole caused by the invasion of water from a water-base mud.

water cone	See cone and coning.

water cut	The volume fraction of water in the total volume of liquid produced from a well.

watercutmeter	An annular capacitor. Water holdup is determined indirectly by measuring a frequency which depends on the dielectric constant of the fluid flowing through the annular gap of the instrument.

water-drive	The reservoir-drive mechanism in which oil is produced by the expansion of the volume of the underlying water, which forces the oil into the wellbore. In general, there are two types of water drive: bottom-water drive, in which the oil is totally underlain by water, and edgewater drive, in which only the edge of the oil is in contact with the water. Bottom-water drive is more efficient.

watered-out	Of a well, having gone to water.

water encroachment	The movement of water into a producing formation as the formation is depleted of oil and gas by production.

water entry survey	A survey technique used to determine points of water entry in a producing well. One such survey involves three different types of operations. Under dynamic well conditions, the three surveys are run as follows: (1) Temperature log. A continuous temperature profile is recorded over the interval of interest. (2) Radioactive-tracer log: Ejected slugs of radioactive tracer material are monitored in order to determine the flow rate and direction. (3) A conditioning survey is performed. To run a conditioning survey, a tool with a gamma-ray detector and an isotope ejector is run into the borehole. The isotope ejector is turned on, and the tool is lowered through the production interval at constant speed. A gamma-ray log is run during the "conditioning" run in order to provide a base log to which subsequent gamma-ray logs can be compared. Several subsequent gamma-ray logging runs are then made through the conditioned interval. Water from the formation entering theborehole will produce dilution of the isotope-treated fluid in the borehole, and an upward displacement of the treated water column will occur. The combination of surveys is then interpreted.

water flooding	A method of secondary recovery in which water is injected into a reservoir in order to move additional quantities of oil toward producing wells.

water loss	A mud property. The measure of filtrate loss in a water base (water external phase) drilling mud.

water saturation	The fraction or percentage of the pore volume of a rock occupied by water. The occupation may take different forms; i.e., funicular, insular, or pendular saturation See saturation.

water table	The undistorted upper surface of the saturated zone. The pressure everywhere on this surface is at atmospheric pressure.

water wet	hydrophilic. A solid surface is water wet when the adhesive attraction of water molecules for the solid substance is greater than the attraction between water molecules. The angle of contact of a water droplet on a water-wet solid surface will be less than 90° (measured inside the water phase). A mobile nonwetting oil phase would advance over the adhesive layer of water.

wavelength	The distance between two points having the same phase in two consecutive cycles of a periodic wave, along a line in the direction of propagation.

wavelet	See wave train.

wave train	The response of an elastic system to an acoustic energy impulse describes a wavelet of several cycles of sinusoidal character. At the onset, the wavelet will be rich in all frequencies but the high frequency components are attenuated rapidly by transit through earth materials because of inelastic absorption and conversion to heat. Wavelets are generated for each energy mode and the composite particle motion resulting from the compressional, shear, fluid, and boundary waves becomes the wave train with characteristics of the transmitting source, coupling, and the transmission media. See acoustic wave and wave train display, also Stoneley wave and tube wave.

wave train display	The acoustic wave train can be displayed in different modes on some acoustic well logs. For example: (1)The intensity modulated-time mode in which the wave train is shown in the variable photographic density form. See Micro-Seismogram. (2) The amplitude-time mode in which the wave train is shown as a full wave form.

wave train log	An acoustic log in which the acoustic wave train is displayed in either the intensity modulated-time mode or the amplitude-time mode.

weak point	A machined connector or calibrated cable designed to break under specific tensile stress. It is connected to the cable inside the neck of the fishing bell. The weak point will part well below the breaking tension required for new or wellworn logging cables. When the weak point is broken intentionally (or accidentally), it leaves the fishing bell pointed up for fishing purposes, unobstructed by coils of broken cable and wire. See also fishing bell and rope socket.

weight indicator	A surface panel on which the total weight or tension on the cable is metered and can be monitored during the survey.

well bore	A borehole. The bore of a well, whether cased or uncased. Often modernized to one word, wellbore, particularly when the term is used as an adjective.

wellbore storage effect	Afterflow or afterinjection, continuing for a short time after the well bore is shut in at the surface, in the form of wellbore loading or unloading due to the compressibility of fluids inside the well bore. The well bore has storage capacity equal to the volume within the well bore in direct communication with the porous and permeable formation. When the well bore is shut in at the wellhead, fluid will continue to flow into or out of the well bore until pressure is equalized between the well bore and formation. No wellbore storage effect can occur if the well bore is shut in at the bottom of the well at the face of the formation.

well completion	The activities and methods necessary to prepare a well for the production of oil and gas; the method by which a flow line for hydrocarbons is established between the reservoir and the surface. The method of well completion used by the operator depends on the individual characteristics of the producing formation of formations. These techniques include open-hole completions. conventional perforated completions, sand-exclusion conmpletions, tubingless comple tions, multiple completions, and miniaturized completions.

wellhead	Of or pertaining to the equipment at the top of the well bore which is used to maintain surface control of the well. Includes casinghead, tubing head, Christmas tree, etc.

well log	wireline log, borehole log. The product of a survey operation, also called a survey, consisting of one or more curves. Provides a permanent record of one or more physical measurements as a function of depth in a well bore. Well logs are used to identify and correlate underground rocks, and to determine the mineralogy and physical properties of potential reservoir rocks and the nature of the fluids they contain. (1) A well log is recorded during a survey operation in which a sonde is lowered into the well bore by a survey cable. The measurement made by the downhole instrument will be of a physical nature (i.e., electrical, acoustical, nuclear, thermal, dimensional, etc.) pertaining to some part of the wellbore environment or the well bore itself. (2) Other types of well logs are made of data collected at the surface; examples are core logs, drilling-time logs, mud sample logs, hydrocarbon well logs, etc. (3) Still other logs show quantities calculated from other measurements; examples are movable oil plots, computed logs. etc.

well logging cable	See logging cable.

well seismic recording	The well seismic recording is a checkshot service which provides a depth-vs.-time calibration for the seismic reflection technique. Seismic velocities are measured at the well by recording the time required for a wavelet generated by a surface energy source to reach the geophones in a tool anchored in the well. The recorded travel times of the direct arrival are used to calibrate the sonic log, which then becomes the basic seismic reference and allows a surface seismic cross section to be scaled to depth.

well spacing	The regulation of the number and location of wells over a reservoir as a conservation measure.

wettability	The ability of any solid surface to be wetted when in contact with a liquid; that is, the surface tension of the liquid is reduced so that the liquid spreads over the surface. See water wet and oil wet.

whipstock	A long, steel casing that uses an inclined plane to cause the bit to deflect from the original borehole at a slight angle. Whipstocks are commonly used in controlled directional drilling, to straighten crooked boreholes, or to sidetrack to avoid unretrieved fish.

wiggle trace	Obsolete term, see full waveform recording.

wildcat	A well drilled in an area where no oil or gas production exists.

wild well	A well which has blown out of control and from which oil, water, or gas is escaping with great force. Also called a gusher.

winch	A machine that pulls or hoists by winding a cable around a spool.

wireline log	See well log.

work over	To perform one or more of a variety of remedial operations on a producing oil well to try to increase production. Examples of workover operations are deepening, plugging back, pulling and resetting liner, squeeze cementing, etc.