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Petrophysics (from the Greek πέτρα, ''petra'', "rock" and φύσις, ''physis'', "nature") is the study of physical and chemical rock properties and their interactions with fluids. A major application of petrophysics is in studying reservoirs for the hydrocarbon industry. Petrophysicists are employed to help reservoir engineers and geoscientists understand the rock properties of the reservoir, particularly how pores in the subsurface are interconnected, controlling the accumulation and migration of hydrocarbons.〔 Some of the key properties studied in petrophysics are lithology, porosity, water saturation, permeability and density. A key aspect of petrophysics is measuring and evaluating these rock properties by acquiring well log measurements - in which a string of measurement tools are inserted in the borehole, core measurements - in which rock samples are retrieved from subsurface, and seismic measurements. These studies are then combined with geological and geophysical studies and reservoir engineering to give a complete picture of the reservoir. While most petrophysicists work in the hydrocarbon industry, some also work in the mining and water resource industries. The properties measured or computed fall into three broad categories: conventional petrophysical properties, rock mechanical properties, and ore quality. Petrophysical studies are used by petroleum engineering, geology, mineralogy, exploration geophysics and other related studies. ==Conventional petrophysical properties== Most petrophysicists are employed to compute what are commonly called conventional (or reservoir) petrophysical properties. These are: ''Lithology:'' A description of the rock's physical characteristics, such as grain size, composition and texture. By studying the lithology of local geological outcrops and core samples, geoscientists can use a combination of log measurements, such as natural gamma, neutron, density and resistivity, to determine the lithology down the well. ''Porosity:'' The percentage of a given volume of rock that is pore space and can therefore contain fluids.〔(Schlumberger Oilfield Glossary - Porosity )〕 This is typically calculated using data from an instrument that measures the reaction of the rock to bombardment by neutrons or by gamma rays but can also be derived from sonic and NMR logging. ''Water saturation:'' The fraction of the pore space occupied by water.〔(Schlumberger Oilfield Glossary - Water saturation )〕 This is typically calculated using data from an instrument that measures the resistivity of the rock and is known by the symbol . ''Permeability:'' The quantity of fluid (usually hydrocarbon) that can flow through a rock as a function of time and pressure, related to how interconnected the pores are. Formation testing is so far the only tool that can directly measure a rock formation's permeability down a well. In case of its absence, which is common in most cases, an estimate for permeability can be derived from empirical relationships with other measurements such as porosity, NMR and sonic logging. ''Thickness'' of rock with enough permeability to deliver fluids to a well bore. This property is often called “''Net reservoir rock''.” In the oil and gas industry, another quantity “''Net Pay''” is computed which is the thickness of rock that can deliver hydrocarbons to the well bore at a profitable rate. Reservoir models are built upon their measured and derived properties to estimate the amount of hydrocarbon present in the reservoir, the rate at which that hydrocarbon can be produced to the Earth’s surface through wellbores and the fluid flow in rocks. In the water resource industry, similar models are used to compute how much water can be produced to the surface over long periods of time, without depleting the aquifer. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Petrophysics」の詳細全文を読む スポンサード リンク
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