igneous rock: Solidified rock formed by cooling and solidifying of magma underground or lava on the surface of the ground. Examples are basalt and granite.
illite: A potassium, aluminum silicate. Exhibits the highest radioactivity level of the clays. Density 2.52 g/cm3 . Diagenetic or authigenic Illite is typified by fragile, leafy, feathery crystals and long delicate fibers adhering to and covering grain surfaces. Such crystals easily can be broken at vigorous production rates or injection rates. See brushpile.
immobile water: See irreducible water.
impermeable: Impervious to the flow of water or other geofluids. An impermeable rock has extreme resistance to flow. The rock might be porous, but the pores must be connected to provide permeability. Also see permeability.
infiltration: (1) Of water on the ground surface, water percolating into the ground from a source such as precipitation or irrigation. See percolation.
(2) In drilling wells, it is the penetration of filtrate from drilling mud into the drilled face of porous and permeable strata.
injection of potable water for storage purposes: This is the most complicated of all the operations relative to water treatment and handling. There are many parts to be considered in the injection process for it to be successful and economical.
(1) The highest efficiency is achieved when the water is injected into a reservoir aquifer where the boundaries are finite and measurable, and there is no natural relief for the excess water and resulting reservoir pressure. Under these conditions, the water pressure generated during the injection process will not dissipate, thus ensuring later recovery of a large percentage of the injected water. The lowest efficiency will be found where water is injected into boundless aquifers containing renewable water, and where the excess water and water pressure generated during the injection process will divert renewal water away from the region influenced by the injection well, and the excess pressure will find natural relief and will dissipate over time. Dissipation of the excess water pressure will turn the water storage operation into an unnatural recharge or augmentation operation where the injected water becomes available in various degrees to all other wells producing water from the same aquifer, and at its worst, a water disposal operation. See formation damage.
(2) When water is injected into an aquifer that is overlain by the aerated zone, the injection pressure might not rise appreciably and a clean, clay-free aquifer might take water freely, and the storage operation will be a put-and-take operation over the short term. Over the long term any excess pressure from the injection process will find relief in the aerated zone which is at atmospheric pressure. This will turn the storage operation into an augmentation or recharge operation, increasing the life of the aquifer for all wells producing from the same aquifer.
If the injection into an unconfined aquifer causes the water table to rise, the injected water is being stored. If there appears to be no change in the water table after injection, the injected water is being disposed of. In this case, the quantity of water recovered in later production probably would be nearly the same whether or not injection took place. Also see formation damage.
The changes in water pressure in any case can be monitored under static conditions in the injection well or monitoring wells by measurements of the potentiometric surface.
injection of waste liquids for disposal purposes: There are many parts to be considered in the waste disposal process for it to be successful and economical. This is the most complicated of the injection operations from the standpoint of well completion and zonal isolation. The efficiencies are the reverse of the water storage operation. The highest efficiency is attained in continuous and boundless strata where injection pressure does not build up the pore pressure within the formation, but dissipates freely. The poorest efficiency is observed in zones with low permeability and poor relief, where pore pressures built up in the formation become increasingly difficult to overcome and do not dissipate rapidly. In such cases, injection has caused fracturing, lubrication of fault interfaces, and mini earthquakes. Also see formation damage and hydraulic fracturing.
in place: Relative to aquifers, it refers to all molecular water that occupies the pores in the bed, stratum, gravel, sand, or rock whether before or after production. Includes both irreducible and mobile water. See depleted (2).
InSAR: Interferometric Synthetic Aperture Radar. See under subsidence (1).
instream flow: The amount of water necessary to maintain flowing streams to support marine life or other activity.
instream use: The use of water for beneficial purposes that does not require its withdrawal or diversion from its natural water course.
in situ: In place at its natural location, at existing physical and chemical conditions within the formation.
interbasin transfer: The physical transfer of water from one watershed to another. GWAC.
interbedded: Said of beds lying between or alternating with others of different character; especially said of rock material or sediments laid down in sequence between other beds, such as sands and gravels. NSSH.
interface: Usually, the surface of contact between two unlike materials. The contact surface between air and water, water and oil, sand and carbonate, erosional surface at an unconformity.
Interferometric Synthetic Aperture Radar: InSAR. See under subsidence (1).
intermediate casing string: One or more protective casing strings sometimes set between the surface casing and the production casing in order to protect portions of the formation that are sensitive to drilling mud chemicals and drilling mud pressures in order to prevent lost circulation; or, in formations exhibiting overpressure, to prevent collapse of the borehole opposite plastic shale or to prevent blowouts of oil or gas from permeable hydrocarbon-bearing beds.
intermittent flow: Recurrent. Periodic. Usually, seasonal flow.
interstitial water: Formation water. The water that occupies space within the interstices and pores of rock, regardless of the water’s source or origin. See formation water and compare connate water.
interstices: The spaces between the grains of sedimentary rock.
intrusive rock: Igneous rock that has been formed from magma forced into openings between older rock, and then solidified before reaching the ground surface. See igneous rock.
invaded zone: The permeable zone surrounding the drilled hole where mud filtrate, under the pressure of drilling mud, fully penetrates and displaces formation water in individual beds or strata. The efficiency and radial depth of displacement can vary depending on the spurt loss and the permeability of the filter cake. The flushed zone is that part of the invaded zone where the displacement of formation water has been most efficient. Also see flushed zone.
invasion diameter: See diameter of invasion.
ions: In water. When acids, bases, or salts are dissolved in water solutions, they break up into charged particles called ions. These particles are atoms or groups of atoms. The metal atoms are positively charged because they give up electrons, and non-metals and their clusters, called radicals, become negatively charged because they accept electrons. The solution is electrically neutral because of the equally balanced charges. Positively charged ions are called cations, negatively charged ions are called anions.
iron bacteria: Microorganisms that feed on iron in the water or on the pipe. They may appear as a slimy rust-colored coating on the interior surface of a toilet flush tank or as a glob of gelatinous material in the water. CSU.
irreducible water: In aquifers, it represents both the immobile water residing within fine pores and other fine interstices, and the water residing on the surfaces of all grains and particles as a result of the respective forces of capillarity (wettability, adhesion), buoyancy, gravity, surface tension (cohesion), and evaporation. Capillarity, grain surface wettability, and buoyancy are opposed by gravity, surface tension, and evaporation. The in situ quantity of irreducible water residing in waterwet soils, gravels, sands and other rock materials is directly related to the superior forces of capillarity, wettability, adhesion, and buoyancy, and inversely related to the inferior forces of gravity and evaporation. The greater the combined grain and particle surface area, capillarity, and buoyant force, the greater will be the volume of irreducible water. Irreducible water is immobile and part of water in place and cannot be made to move while under in situ conditions; and, therefore, is not producible. Irreducible water is expressed as a fraction or percentage of porosity. Compare specific retention. See buoyancy, capillarity, surface tension, and compare mobile water.
The in situ value of irreducible water saturation can be quite different from that determined from the extracted rock sample taken from a different environment or examined in a different environment. The determination of the correct amount of irreducible water is important in determining the recovery factor.
irrigation: The application of water to crops, lawns and gardens by artificial means to supplement natural precipitation. Water can be applied by sprinkling, flooding, or dripping. Douglas Co.
irrigation district: A legal entity created by statute in order to develop large irrigation projects. CSU.
irrigation efficiency: The ratio of the volume of water required for a specific beneficial use divided by the volume of water delivered. It is commonly interpreted as the volume of water stored in the soil for evapotranspiration compared to the volume of water delivered, but may be defined and used in different ways. Douglas Co.
irrigation water requirement: The quantity of water, exclusive of effective precipitation, that is required for various beneficial uses. Douglas Co.
irrigation year: The irrigation year for the purposes of recording annual diversions of water for irrigation in Colorado begins November 1 and ends on October 31 of each year. CSU.
isolation: (1) Related to the effectiveness of the completion of a water well to prevent communication inside the borehole. It is the quality or degree that an aquifer has been cemented, or grouted, to prevent pressure depletion in the aquifer and/or water from crossflowing from the aquifer to another part of the well bore, or to prevent the contamination of the aquifer from crossflow from another aquifer or from the well bore. See thief zone, thief level, and back pressure.
(2)Also see lens for isolated sedimentary deposits that form reservoirs .
isotopes: Atoms of a single element which have differing masses. Isotopes are either stable or unstable (radioactive). Radioisotopes emit particulate (alpha, beta) or electromagnetic (gamma) radiation as they transform or decay into stable isotopes. Daughter products produced by primary disintegration or irradiation are isotopes. SPWLA
Compiled and Edited by Robert C. Ransom
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