Key terms are defined below. For more information, many terms can be found in the Petroleum Information data Dictionary (PIDD) and at the Schlumberger Oilfield Glossary Entity and attribute definitions are available in the web report.
� BIOSTRATIGRAPHY � The branch of stratigraphy dealing with the paleontologic aspects of rocks, or stratigraphy based on paleontologic methods, specifically the differentiation of rock units on the basis of the description and study of the fossils they contain.
� CHRONOSTRATIGRAPHIC UNIT � A classification of a geologic body based on chronostratigraphy.
� FAULT � A fracture or zone of fractures along which there has been displacement of the sides relative to one another parallel to the fracture.
� FLUID CONTACT � An interface between fluid bodies, such as an oil-water contact.
� FOSSIL ASSEMBLAGE - A group of fossils occurring at the same stratigraphic level and used for geologic interpretations.
� GEOCHEMISTRY � The branch of geology dealing with the chemistry of the earth, including the distribution and abundance of chemical elements and isotopes in minerals, ores, rocks, soils, water, hydrocarbons, and the atmosphere.
� GEOLOGIC LAYER � A volume of rock visibly separated by surfaces. Sedimentary rocks may be visibly separated by surfaces or contacts, which subdivide their geologic history and form the basis for their classification and formal naming.
� GEOLOGIC PICK - The interpreted intersection of a geologic surface and a borehole.
� GEOLOGIC SURFACE � A two-dimensional boundary between geologic features such as formations, structures or the interface between enclosed fluids.
� GEOLOGIC STRUCTURE � A large-scale geologic feature produced by deformation or displacement of rocks masses by geologic compressional or shear forces to yield features such as faults, anticlines, synclines, domes, and basins.
� GEOLOGIC TIME � The period of time dealt with by historical geology, or the time extending from the formative period of the earth as a separate planetary body to the beginning of written or human history. The time of the earth's history that is represented by and recorded in the succession of rocks.
� GEOCHRONOLOGIC UNIT � Name of an event representing a span of continuous time in geologic history, during which a corresponding strata, a chronostratigraphic unit, was formed. Also referred to as Geologic Time Unit.
� GEOCHRONOLOGY � The study of time in relationship to the history of the earth, especially by the absolute age and relative dating systems developed for this purpose.
� GEOPHYSICS � The study of the earth by quantitative physical methods; includes seismology, tectonophysics and engineering geophysics. Examples techniques include: seismic reflection, seismic refraction, gravity, magnetic, electrical, electromagnetic, radiometric, and nuclear.
� INFORMAL STRATIGRAPHIC NAME � An approach to stratigraphic identification dealing with the relative ordering of rock strata on a local basis, using informal stratigraphic nomenclature and guidelines. Frequently, interpreters will recognize local relationships and correlations before they fit them into a formal structure or publish them for general use.
� LITHOLOGY � The description of rocks, especially in hand specimen and in outcrop, on the basis of characteristics; e.g., color; mineralogic composition; grain size.
� LITHOSTRATIGRAPHY � The branch of stratigraphy dealing with the lithology of strata and with their organization into units based on lithologic character. Also referred to as rock stratigraphy.
� PALEONTOLOGY � The branch of geology dealing with the study of life in past geologic time, based on fossil plants and animals and including phylogeny, their relationships to existing plants, animals and environments, and the chronology of earth's history.
� PETROPHYSICS � The study of physical properties of reservoir rocks, especially porosity and permeability.
� RESERVOIR � A volume of reservoir rock containing a contiguous natural accumulation of producible fluids and characterized by a single pressure system.
� SEDIMENTOLOGY � The branch of geology dealing with the study of sedimentary rocks and of the processes by which they were formed; the description, classification, origin, and interpretation of sediments.
� STRATIGRAPHIC CLASSIFICATION � An arbitrary but systematic arrangement, zonation or partioning of the sequence of rock strata into units with reference to any or all of the many different characteristics, properties, or attributes the strata may have. The American Code of Stratigraphic Nomenclature is an example of a formal stratigraphic classification.
� STRATIGRAPHIC CORRELATION � Correlation of indicators of stratigraphy from multiple sources, such as wells, outcrops or seismic.
� STRATIGRAPHIC CORRELATION � A stratum or body of adjacent strata recognized as a unit in the classification of a rock sequence with respect to some specified characteristics.
� STRATIGRAPHY � The branch of geology dealing with the relationships of rock strata. Stratigraphy includes interpretation of succession and age relationships of rock strata, as well as their internal composition.
� STRUCTURAL GEOLOGY � The branch of geology dealing with the general disposition, attitude, arrangement or relative positions of rock masses of a region, consequent upon deformational processes, such as faulting, folding and intrusion.
� TECTONICS � The branch of geology dealing with the broad architecture of the outer part of the earth; i.e., the regional assembling of structural or deformational features, including their mutual relations, origin and historical evolution.
� UNCONFORMITY � The surface of contact between rock units at which is indicate a substantial nonstructural break or gap in the stratigraphic record. At the unconformity, the stratigraphically older rock unit is not succeeded by the next younger unit in the expected stratigraphic sequence. Such breaks are usually indications of extensive periods of erosion, with loss of the intervening rock record. An unconformity can also be formed by an extended period of nondeposition.
� ZONE � An interval, layer or stratum to which are assigned interpretive attributes, transforming the interval into a zone of specific characteristics; e.g., pay zone; fossiliferous zone; porosity zone.