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IGP: Inside casing gravel pack where no gravel is placed into the perforations. IGRF (Seismic): International Geomagnetic Reference Field. II (Injection Well): Injectivity index. ILD (Logging): Deep induction log. Illicit Discharge: The ¤ow of substances other than rainwater or snowmelt to a separate storm sewer system whether by direct subsurface connection, overland ¤ow, dumping, or other means. Illite: A clay type of varying form and composition. Rarely water sensitive. May occur in unusual cases as a brous deposit that can act as a particle trap. ILM (Logging): Medium induction log. Imbalance Penalties: Penalties implemented by a pipeline to provide an incentive for shippers to maintain actual receipts and deliveries at nominated and conrmed levels. Imbalance Trading: Process by which shippers can acquire gas from, or sell gas to, other customers to minimize or avoid cash-out. Imbibition: Absorption and adsorption of ¤uids into the pores of the rock. IMF: Intermediate manifold facilities. Imhoff Cone: A conically shaped, 1 L graduated vessel used to measure the approximate volume of settleable solids in wastewater during various settling periods. Immature Oil: Young crude or crude that has not been thermally “processed” by heat to generate lighter ends (short carbon chains) and gas. Immediately Dangerous to Life or Health: An atmosphere that will not support human life. Impact (in Risk Analysis): Impact (or consequence) is the effect on conditions or people if the hazard is realized (occurs) in practice and probability is the likelihood that the impact will occur. Risk is a function of probability and impact (consequence). Impaction: The action of particles entering into contact with a surface. Impedance: (1) Total opposition (resistance, capacitance, and inductance), expressed in ohms, to the ¤ow of current. (2) The effects placed upon an alternating current circuit by induction, capacitance, and resistance. Total resistance in an alternating current (ac) circuit. Impeller: (1) The rotating pump component that drives the ¤uid in a centrifugal pump. (2) A set of vanes designed to rotate and move a mass of ¤uid. The prime mover in a centrifugal. Impermeable: Rock with passages so small that no effective ¤ow can take place. Note: All man-made and natural substances have some permeability, given high pressure, time, enough surface area, and a low permeability ¤uid. Imported Crude Oil Burned as Fuel: The amount of foreign crude oil burned as a fuel oil, usually as residual fuel oil, without being processed as such. Imported crude oil burned as fuel includes lease condensate and liquid hydrocarbons produced from tar sands, Gilsonite, and oil shale.