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salinity |
The concentration of ions in solution (sodium, potassium, chloride, sulphate, etc.) |
sand control |
The installation of equipment or application of techniques to prevent migration of reservoir sand into the wellbore or near-wellbore area. In weak formations, sand control may be necessary to maintain the structure of the reservoir around the wellbore. In other formation types, the migration of sand and fines into the near wellbore area may severely restrict production. Each of these conditions requires different treatments. The principal sand-control techniques include gravel packing and sand consolidation. |
saturation |
The relative amount of water, oil and gas in the pores of a rock, usually as a percentage of volume. |
saturation exponent |
The exponent of the saturation term in Archie's saturation equation. The saturation exponent is related to the influence of insulating fluids on the shape and continuity of the electrically conductive solutions occupying pore volume. |
secondary porosity |
Post depositional porosity. Such porosity results from fractures, vugs, solution channels, diagenesis, dolomitization, etc. |
sedimentary rocks |
Rocks formed from material derived from pre-existing rocks by processes of denudation, together with material of organic origin. The term includes both consolidated and unconsolidated material; the latter is also referred to as 'sediment'. |
seismic |
Pertaining to waves of elastic energy, such as that transmitted by P-waves and S-waves, in the frequency range of approximately 1 to 100 Hz. Seismic energy is studied by scientists to interpret the composition, fluid content, extent and geometry of rocks in the subsurface. "Seismic," used as an adjective, is preferable to "seismics," although "seismics" is used commonly as a noun. |
set casing |
To run and cement casing at a specific depth in a well bore. |
shale |
A fine grained, thinly laminated or fissile, detrital sedimentary rock formed by the compaction and consolidation of clay, silt, or mud. The composition is characterized by an appreciable content of clay minerals, or derivatives from clay minerals, and a high content of detrital quartz. |
shale base line |
A line drawn through the deflections characteristic of shale on an SP or GR curves, which is used as the reference in making measurements to determine the characteristics of permeable rocks and their formation waters. |
shale shaker |
A vibrating screen for sifting out rock cuttings from drilling mud. Drilling mud returning from downhole, carrying rock chips in suspension. Flows over and through the mesh of the shale shaker leaving small fragments of rocks which can be collected and examined for information about the formations being drilled. |
shoulder-bed effect |
Adjacent bed effect. Effect of adjacent beds on a well logging measurement. The amount of the effect is related to the vertical resolution of the measuring tool. |
shut in |
To close the valves at the top of a well bore. To stop flow out of, or injection into, a well bore. |
sidetrack |
To drill a secondary wellbore away from an original wellbore. A sidetracking operation may be done intentionally or may occur accidentally. Intentional sidetracks might bypass an unusable section of the original wellbore or explore a geologic feature nearby. In the bypass case, the secondary wellbore is usually drilled substantially parallel to the original well, which may be inaccessible due to an irretrievable fish, junk in the hole, or a collapsed wellbore. |
sinker bar |
A specialized heavy weight, or series of weights, which can be attached to some downhole logging-tool assemblies in order to add the extra weight necessary for the tool(s) to descend properly through heavy borehole fluids (muds). |
skin |
A zone of reduced permeability around the well bore, resulting from damage due to the drilling. completion, and/or production practices. |
slim-hole drilling |
A means of reducing the cost of a well by drilling a smaller-diameter hole than is customary for the depth and the types of formations to be drilled. A slim hole permits the scaling down of all phases of the drilling and completion operations; i.e., smaller bits, less powerful and smaller rigs (engines pumps, draw works), smaller pipe, and less drilling mud. |
slug |
A volume of mud that is more dense than the mud in the drillpipe and wellbore annulus. A slug is used to displace mud out of the upper part of the drillpipe before pulling pipe out of the hole and is mixed in the pill pit by adding additional weighting material (barite) to a few barrels of mud from the surface pits. The pill is pumped into the top of the drillstring to push mud downward, out of the pipe, thus keeping the upper stands of pipe empty. |
slug flow |
A fluid-flow condition in producing wells in which large bubbles of the lighter fluid move upward faster than small ones and aggregate to form larger bubbles or slugs which reach pipe diameter. |
sonic log |
An acoustic log. |
sour |
Containing hydrogen sulphide. |
source |
In well logging, the source of radiation used in the operation of radioactivity logging or nuclear logging tools. |
spectral gamma-ray log |
Natural gamma-ray spectral log. Unstable isotopes emit particulate (alpha, beta) and electromagnetic (gamma) radiation. Penetrating gamma rays are suitable for borehole detection. Isotopes of specific elements radiate gamma rays exhibiting specific energy levels within the energy spectrum. Identification of the specific energy level(s) and the amount of gamma radiation (at the specific level) provides a means of identifying the isotope and the quantity of the element. |
spherically focused log |
SFL. A log of formation resistivity measured by a tool developed for the limited investigation of the invaded zone. Focusing is used to enforce an approximately spherical shape on the equipotential surfaces within the formation in spite of the presence of the borehole. Borehole effect is virtually eliminated for hole diameters up to 10 in., yet investigation of the tool is kept shallow enough that its response is, in the majority of cases, mostly from the invaded zone. SFL is a mark of Schlumberger. |
spinner |
A device for measuring in situ the velocity of fluid flow in a production or injection well based on the speed of rotation of an impeller, or spinner. The spinner can be helical, that is, longer than it is wide, or like a vane, which is similar to a fan blade. In both cases, the speed of rotation is measured and related to the effective velocity of the fluid. Friction and fluid viscosity cause the relationship to be slightly nonlinear at low effective velocities and introduce a threshold velocity below which the spinner does not turn. Results are interpreted using the multipass, two-pass or single-pass methods. |
spud |
To start drilling the well |
squeeze cementing |
The forcing of cement slurry by pressure to specified points in a well to cause seals at the points of squeeze. It is a secondary-cementing method, used to isolate a producing formation, seal off water, repair casing leaks, etc. |
stimulation |
Any process undertaken to improve production from a subsurface formation. Stimulation may involve acid stimulation, hydraulic fracturing, perforating, or simply cleaning out the well and controlling sand production. |
stock tank barrel |
STB. A 42-gallon barrel of crude oil at standard conditions of temperature and pressure. |
stratigraphic trap |
A type of reservoir capable of trapping oil or gas due to changes in porosity and permeability or to the termination of the reservoir bed. |
stratigraphy |
The study of stratified rocks especially their sequence in time., the character of the rocks and the correlation of beds in different locations |
structure |
A term used to describe the overall relationship of rock masses e.g. folding, faulting, unconformities |
structural trap |
A trap in reservoir rock which has been formed by the deformation (folding or faulting) of the rock layer. Anticlines, salt domes, and faults of different kinds result in barriers which form traps. |
surface casing |
The first string of casing set in a well after the conductor pipe, varying in length from a few hundred to several thousand feet. Some states require a minimum length to protect aquifers containing fresh water. |
swab |
To reduce pressure in a wellbore by moving pipe, wireline tools or rubber-cupped seals up the wellbore. If the pressure is reduced sufficiently, reservoir fluids may flow into the wellbore and towards the surface. Swabbing is generally considered harmful in drilling operations, because it can lead to kicks and wellbore stability problems. In production operations, however, the term is used to describe how the flow of reservoir hydrocarbons is initiated in some completed wells. |
sweet |
Containing little or no hydrogen sulphide or sulphur compounds |
syncline |
A basin shaped fold or fold system |
synthetic seismogram |
synthetic seismogram, commonly called a synthetic, is a direct one-dimensional model of acoustic energy travelling through the layers of the Earth. The synthetic seismogram is generated by convolving the reflectivity derived from digitized acoustic and density logs with the wavelet derived from seismic data. By comparing marker beds or other correlation points picked on well logs with major reflections on the seismic section, interpretations of the data can be improved. The quality of the match between a synthetic seismogram depends on well log quality, seismic data processing quality, and the ability to extract a representative wavelet from seismic data, among other factors. The acoustic log is generally calibrated with check-shot or vertical seismic profile (VSP) first-arrival information before combining with the density log to produce acoustic impedance. |
