F
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facies |
The sum total of features such as sedimentary rock type, mineral content, sedimentary structure, bedding characteristics, fossil content, etc. Which characterise a sediment as having been deposited in a given environment. |
fault |
A fracture in rock along which there has been an observable amount of displacement. Faults are rarely single planar units; normally they occur as parallel to sub-parallel sets of planes along which movement has taken place to a greater or lesser extent. |
fault block |
A mass bounded on at least two opposite sides by faults. It may be elevated or depressed relative to the adjoining regions, or it may be elevated relative to the region on one side and depressed relative to that on the other. See illustration in fault definition. |
fault trap |
A subsurface hydrocarbon trap created by faulting, which causes an impermeable rock layer to be moved to a location opposite the reservoir bed. |
feldspar |
A group of abundant rock-forming minerals of the general formula, MAl (Al,Si)3O8 where M can be K, Na, Ca, Ba, Rb, Sr, and Fe. Most widespread of any mineral group, feldspar may constitute 60% of the earth's crust, occurring in all types of rock. When the positive ion is K+, the mineral is orthoclase; when it is Na+, it is albite; when it is Ca+2, it is anosthite. |
field |
A geographical area in which a number of oil or gas wells produce from a continuous reservoir. A field may refer to surface area only or to underground productive formations as well. In a single field, there may be several separate reservoirs at varying depths. |
field print |
A preliminary print of the well log presented in the field at the completion of the survey operation. |
field tape |
A magnetic tape on which well-log data were recorded during the logging operation. |
fines |
Fragments or particles of rock or mineral which are too minute to be treated as ordinary coarse material. When found in pore spaces of reservoir rock, fines sometimes can be moved by produced fluids to cause formation damage. |
first reading |
The depth of the first useable reading or value recorded on a curve at the onset of the survey. |
fish |
Anything left in a wellbore. It does not matter whether the fish consists of junk metal, a hand tool, a length of drillpipe or drill collars, or an expensive MWD and directional drilling package. Once the component is lost, it is properly referred to as simply "the fish." Typically, anything put into the hole is accurately measured and sketched, so that appropriate fishing tools can be selected if the item must be fished out of the hole. |
float collar |
A special coupling device. inserted one or two joints above the bottom of the casing string, that contains a check valve to permit fluid to pass downward but not upward through the casing. The float collar prevents drilling mud from entering the casing while it is being lowered, allowing the casing to float during its descent and also decreasing the load on the derrick. The float collar also prevents a backflow of cement during the cementing operation. |
flowing pressure |
The pressure registered at the wellhead of a flowing well. |
flowing well |
A well that produces oil or gas by its own reservoir pressure rather than by use of artificial means |
flowline |
Large-diameter pipe which conducts mud coming out of the hole from the annulus to the shale shaker and mud tanks. |
flushed zone |
The volume close to the borehole wall in which all of the moveable fluids have been displaced by mud filtrate. The flushed zone contains filtrate and the remaining hydrocarbons, the percentage of the former being the flushed-zone water saturation, Sxo. In simple models, the flushed zone and the invaded zone are synonymous. |
fold |
A flexure in rocks; that is, a change in the amount of sip of a bed, and also often a change in the direction of dip. |
formation |
(1) A general term applied in the well-logging industry to the external environment of the drilled well bore without stratigraphic connotation. |
formation evaluation |
The analysis and interpretation of well-log data, drill-stem tests, etc. in terms of the nature of the formations and their fluid content. The objectives of formation evaluation are (1) to ascertain if commercially producible hydrocarbons (or other forms of energy and minerals) are present, (2) to determine the best means for their recovery, and (3) to derive lithology and other information on formation characteristics for use in further exploration and development. |
formation pressure |
The pore pressure existing within reservoir rock or non-reservoir rock at a specified time. The pressure exerted by fluids in a formation, recorded in the hole at the level of the formation with the well shut in. It is also called reservoir pressure or shut-in bottom-hole pressure. |
formation resistivity factor |
Formation factor, F. Equal to the ratio of the resistivity of the l00% water-saturated rock framework to the resistivity of the water solution contained in the rock. The limiting formation factor is an intrinsic characteristic of the rock, obtainable with reliability only when the interpore water solution is highly salt saturated. The apparent formation factor most often obtained, is a function of porosity, salinity of water filling the pores, pore geometry, clay content, and presence of electrically conductive solid matter. |
formation testing |
The gathering of data on a formation to determine its potential productivity before installing casing in a well. The conventional method is the drill-stem test. Incorporated in the drill-stem-testing tool are a packer. valves, or ports that can be opened and closed from the surface, and a pressure-recording device. The tool is lowered to bottom on a string of drill pipe and the packer set, isolating the formation to be tested from the formations above and supporting the fluid column above the packer. A port on the tool is opened to allow the trapped pressure below the packer to bleed off into the drill pipe, gradually exposing the formation to atmospheric pressure and allowing the well to produce to the surface, where the well fluids can be sampled and inspected. From a record of the pressure readings, a number of facts about the formation can be inferred. |
formation volume factor |
The ratio of the volume of gas or liquid with its dissolved gas at reservoir conditions of temperature and pressure to its volume at standard conditions. |
formation water |
See interstitial water. |
fracture gradient |
Is the pressure per unit depth required to fracture or cause the rock of the formation to separate. |
fracture porosity |
Porosity resulting from the presence of openings produced by the breaking or shattering of brittle rocks. |
free fluid index |
FFI. The percent of the bulk volume occupied by fluids which are free to flow, as recorded on the nuclear magnetism log. Gas gives a low FFI. |
free pipe |
Pipe or casing in a well bore which is free to vibrate or respond to stress. Casing or tubing which is free of the restraint of a cement sheath or formation materials. |
fullbore-spinner flowmeter |
A flowmeter with retractable impeller blades which can be used below the bottom of tubing where the impeller blades open to almost full inside diameter of the casing. |
full waveform recording |
A representation of the acoustic wave train in the amplitude-time mode. A trace in the X-Y plane illustrating the wave amplitude vs. time. |
