NATURAL GAS - a highly compressible, highly expansible mixture of hydrocarbons with a low specific gravity and occurring naturally in a gaseous form.
NET PROFIT SHARE LEASE - An OCS lease that provides for payment to the U.S. of a percentage share of the net profits for production of oil and gas from the tract. The percentage share may be fixed in the notice of the lease sale or may be a variable of the bid, depending on the bidding system used for the lease sale.
NEUTRON LOG - a radioactivity well log used to determine formation porosity. The logging tool bombards the formation with neutrons. When the neutrons strike hydrogen atoms in water or oil, gamma rays are released. Since water or oil exists only in pore spaces, a measurement of the gamma rays indicates formation porosity. See radioactivity well logging.
NIGHT TOOLPUSHER - an assistant toolpusher whose duty hours are typically during nighttime hours. Also known as a tourpusher.
NIPPLE - a tubular pipe fitting threaded on both ends used for making connections between pipe joints and other tools.
NIPPLE UP - in drilling, to assemble the blowout preventer stack on the wellhead at the surface.
NITRO SHOOTING - a formation-stimulation process first used about 100 years ago in Pennsylvania. Nitroglycerine is placed in a well and exploded to fracture.
NORMAL CIRCULATION - the smooth, uninterrupted circulation of drilling fluid down the drill stem, out the bit, up the annular space between the pipe and the hole, and back to the surface.
NOZZLE - 1. a passageway through jet bits that causes the drilling fluid to be ejected from the bit at high velocity.
NRI (Net Revenue Interest) - That percent of the production revenue allocated to the working interest after first deducting proceeds allocated to royalty and overriding interest.
NUCLEAR TRACER - a gas, liquid, or solid material that emits gamma rays.