Casing – a pipe cemented in the well to seal off formation fluids and to keep the hole from caving in. The spaces between the pipes and the well wall are filled with cement. The casing forms a major structural component of the wellbore and prevents the fracturing liquid from penetrating into surface waters.
Deep Gas (gas found at depths with extreme orogen pressure greater than the average for a particular area) - spaces with extreme orogen pressure are underground rock formations created by clay layers, affected by higher than normal pressure at a given level. Water and natural gas which occur in clay are squashed by the sudden compression of clay and pushed into sand or mud under high pressure. Spaces with extreme orogen pressure occur mostly on low levels (3 to 7.5 km underground) which makes extraction even more difficult.
Shale gas - natural gas, commonly referred to as shale gas, obtained from shale rocks, characterized by a high content of organic matter and low values of porosity and permeability. Shale gas is found trapped in small spaces between rock layers. The volume of every space is several times smaller than with conventional resources. Shale gas is not different from natural gas - it contains methane (75 - 95%) and nitrogen as well as ethane, propane, helium, oxygen and carbon monoxide. It is odourless.
Unconventional gas - natural gas resources which require greater than industry-standard levels of technology or investment to harvest. The most common types of unconventional gas resources are:
• shale gas
• tight gas
• coalbed methane CBM
• deep gas
• gas hydrates
Coalbed methane CBM - natural gas consisting of nearly 100% methane, located in underground carbon deposits. Methane particles on the molecular level are attached to carbon and are released in a process called desorption
.
Tight gas - natural gas trapped in tight and dense geological formations with low porosity and low permeability composed of impenetrable, solid rock (sandstone or limestone) with low permeability and porosity.
Natural gas - is a type of organic fossil fuel. A naturally occurring mixture of hydrocarbon and non-hydrocarbon gases in porous formations beneath the Earth’s surface. It is a naturally occurring light hydrocarbon gas mixture consisting of methane in 90%, ethanol and a pair of high-order hydrocarbons. It is used as an energy source to heat buildings, generate electricity and to produce fuel and methanol.
Types of natural gas are:
• conventional gas
• unconventional gas
Geophone - a device that detects ground velocity produced by seismic waves and transforms the motion into electrical impulses.
Wellhead - a device used to control the drill, mounted on top. It consists of pipes, valves and assorted adapters.
Methane hydrates - frozen gas with water. The water particles create a cellular structure in which the gas molecules are trapped. Methane hydrates are found in the shallow lithosphere (to 2000 m deep) Proper forming conditions are in sedimentary rocks located in polar areas (surface temperature below 0 degrees Celsius) or in oceanic sedimentary rocks above 300 m underwater (water temperature approximately 2 degrees Celsius).
Concession - a grant extended by the Polish Ministry of Environment to permit a company to explore for and produce oil, gas or mineral resources within a strictly defined geographic area. Concession granting is regulated by the "Geological and Mining" Act. There are two types of concessions: exploration concession and extraction concession.
Shale - a fine-grained sedimentary rock composed mostly of consolidated clay or mud. Shale is the most frequently occurring sedimentary rock. Shales are usually metamorphic rocks (metamorphic or crystal shale). The term is also used to talk about sedimentary rocks which look similar (sedimentary shale).
Borehole - completed drilling opening, performed in the rock mass for research, exploration, documentation or production purposes reinforced with a head allowing extraction of the mineral. The borehole is cemented and fully sealed. Ensuring full tightness of the borehole is a technological condition for the process of hydrocarbon production. There are vertical and horizontal drillings.
Drilling platform - a construction of several tens of metres high used for drill work. Its components are: a drilling rig, lifts, pumps and containers.
Drilling fluid - fluid which is injected into the borehole. Its function is to remove cuttings from the well and aid the drilling of boreholes into the earth by cooling the drill or flooding the borehole walls.
Stimulation liquid - used in hydraulic fracturing. Its composition is: 90% water, 9.5% sand and 0.5% chemical additives (acid, sodium chloride, polyacrylamide, ethylene glycol, potassium or sodium carbonate, glutaraldehyde, guar gum, citric acid, isopropanol).
Proppant - material that will keep an induced hydraulic fracture open, during or following a fracturing treatment. It prevents the cracks in rocks from closing after lowering the pressure of the liquid pumped into the borehole.
Permeability - a measure of the ability of a porous material (often a rock or unconsolidated material) to allow fluids to pass through it.
Hydraulic fracturing – a process of rock "opening" using water that is pumped in under 600 Pa. The water expands the crack and penetrates it to expand it even more. Next, the fine-grained sand is pumped in which is squeezed in the created crack in the rock in order to prevent it from closing. As the technology develops, water and sand are substituted with more advanced liquids and ceramic materials with regulated viscosity and volume adjusted to the deposit. Hydraulic fracturing is one of the methods of shale gas extraction.
Drill bit – a rotating tool used to crush or cut rock.