Geology

Introduction Petroleum geology

taufiqmoh — Tue, 23 Sep 2008 06:57:17 +0000

From Wikipedia, the free encyclopedia
Petroleum geology is principally concerned with the evaluation of seven key elements in sedimentary basins:

A structural trap, where a fault has juxtaposed a porous and permeable reservoir against an impermeable seal. Oil (shown in red) accumulates against the seal, to the depth of the base of the seal. Any further oil migrating in from the source will escape to the surface and seep.
• Source
• Reservoir
• Seal
• Trap
• Timing
• Maturation
• Migration
In general, all these elements must be assessed via a limited ‘window’ into the subsurface world, provided by one (or possibly more) exploration wells. These wells present only a 1-dimensional segment through the Earth and the skill of inferring 3-dimensional characteristics from them is one of the most fundamental in petroleum geology. Recently, the availability of cheap and high quality 3D seismic data (from reflection seismology) has greatly aided the accuracy of such interpretation. The following section discusses these elements in brief.
Evaluation of the source uses the methods of geochemistry to quantify the nature of organic-rich rocks which contain the precursors to hydrocarbons, such that the type and quality of expelled hydrocarbon can be assessed.

The reservoir is a porous and permeable lithological unit or set of units that holds the hydrocarbon reserves. Analysis of reservoirs at the simplest level requires an assessment of their porosity (to calculate the volume of in situ hydrocarbons) and their permeability (to calculate how easily hydrocarbons will flow out of them). Some of the key disciplines used in reservoir analysis are the fields of stratigraphy, sedimentology, and reservoir engineering.

The seal, or cap rock, is a unit with low permeability that impedes the escape of hydrocarbons from the reservoir rock. Common seals include evaporites, chalks and shales. Analysis of seals involves assessment of their thickness and extent, such that their effectiveness can be quantified.

The trap is the stratigraphic or structural feature that ensures the juxtaposition of reservoir and seal such that hydrocarbons remain trapped in the subsurface, rather than escaping (due to their natural buoyancy) and being lost.

Analysis of maturation involves assessing the thermal history of the source rock in order to make predictions of the amount and timing of hydrocarbon generation and expulsion.

Finally, careful studies of migration reveal information on how hydrocarbons move from source to reservoir and help quantify the source (or kitchen) of hydrocarbons in a particular area.

Introduction Mining

taufiqmoh — Tue, 23 Sep 2008 06:54:09 +0000

From Wikipedia, the free encyclopedia

Mining is the extraction of valuable minerals or other geological materials from the earth, usually (but not always) from an ore body, vein or (coal) seam. Materials recovered by mining include bauxite, coal, copper, gold, silver, diamonds, iron, precious metals, lead, limestone, magnesite, nickel, phosphate, oil shale, rock salt, tin, uranium and molybdenum. Any material that cannot be grown from agricultural processes, or created artificially in a laboratory or factory, is usually mined. Mining in a wider sense comprises extraction of any non-renewable resource (e.g., petroleum, natural gas, or even water).
History

Since the beginning of civilization people have used stone, ceramics and, later, metals found on or close to the Earth’s surface. These were used to manufacture early tools and weapons. For example, high quality flint found in northern France and southern England were used to set fire and break rock.[1] Flint mines have been found in chalk areas where seams of the stone were followed underground by shafts and galleries. The mines at Grimes Graves are especially famous, and like most other flint mines, are Neolithic in origin (ca 4000 BC-ca 3000 BC). Other hard rocks mined or collected for axes included the greenstone of the Langdale axe industry based in the English Lake District.

The oldest known mine on archaeological record is the “Lion Cave” in Swaziland. At this site, which by radiocarbon dating proves the mine to be about 43,000 years old, paleolithic humans mined mineral hematite, which contained iron and was ground to produce the red pigment ochre.[2][3] Mines of a similar age in Hungary and are believed to be sites where Neanderthals may have mined flint for weapons and tools.
Ancient Egyptians mined malachite at Maadi.[4] At first, Egyptians used the bright green malachite stones for ornamentations and pottery. Later, between 2,613 and 2,494 BC, large building projects required expeditions abroad to the area of Wadi Maghara in order “to secure minerals and other resources not available in Egypt itself.”[5] Quarries for turqoise and copper were also found at “Wadi Hamamat, Tura, Aswan and various other Nubian sites”[6] on the Sinai Peninsula and at Timna. Mining in Egypt occurred in the earliest dynasties, and the gold mines of Nubia were among the largest and most extensive of any in Ancient Egypt, and are described by the Greek author Diodorus Siculus. He mentions that fire-setting was one method used to break down the hard rock holding the gold. One of the complexes is shown in one of earliest known maps. They crushed the ore and ground it to a fine powder before washing the powder for the gold dust.

Introduction Economic geology

taufiqmoh — Tue, 23 Sep 2008 04:21:48 +0000

From Wikipedia, the free encyclopedia
Economic geology is concerned with earth materials that can be utilized for economic and/or industrial purposes. These materials include precious and base metals, nonmetallic minerals, construction-grade stone, petroleum minerals, coal, and water. The term commonly refers to metallic mineral deposits and mineral resources. The techniques employed by other earth science disciplines (such as geochemistry, mineralogy, geophysics, and structural geology) might all be used to understand, describe, and exploit an ore deposit.

Economic geology is studied and practiced by geologists; however it is of prime interest to investment bankers, stock analysts and other professions such as engineers, environmental scientists and conservationists because of the far-reaching impact which extractive industries have upon society, the economy and the environment.

Mineral resources
Mineral resources are concentrations of minerals which are of note for current and future societal needs. Ore is classified as mineralization economically and technically feasible for extraction. Not all mineralization meets these criteria for various reasons. The specific categories of mineralization in an economic sense are:
• mineral occurrences or prospects which are of geological interest but may not be economic interest
• mineral resources, include those which are potentially economically and technically feasible, and those which are not
• ore reserves, must be economically and technically feasible to extract

Ore geology
Geologists are involved in the study of ore deposits, which includes the study of ore genesis and the processes within the Earth’s crust which form and concentrate ore minerals into economically viable quantities.
Study of metallic ore deposits involves the use of structural geology, geochemistry, the study of metamorphism and its processes, as well as understanding metasomatism and other processes related to ore genesis.
Ore deposits are delineated by mineral exploration, which utilizes geochemical prospecting, drilling and resource estimation via geostatistics to quantify economic ore bodies. The ultimate aim of this process is mining.

Coal and petroleum geology
The study of sedimentology is of prime importance to the delineation of economic reserves of petroleum and coal energy resources

Introduction Tectonics

taufiqmoh — Tue, 23 Sep 2008 04:15:50 +0000

From Wikipedia, the free encyclopedia
Tectonics, (from the Greek for “builder”, tekton), is a field of study within geology concerned generally with the structures within the crust of the Earth (or other planets) and particularly with the forces and movements that have operated in a region to create these structures.
Tectonics is concerned with the orogenies and tectonic development of cratons and tectonic terranes as well as the earthquake and volcanic belts which directly affect much of the global population. Tectonic studies are also important for understanding erosion patterns in geomorphology and as guides for the economic geologist searching for petroleum and metallic ores.
A subfield of tectonics that deals with tectonic phenomena in the geologically recent period is called neotectonics.
Tectonic studies have application to lunar and planetary studies, whether or not those bodies have active tectonic plate systems.
Since the 1960s, plate tectonics has become by far the dominant theory to explain the origin and forces responsible for the tectonic features of the continents and ocean basins.
There are three main types of tectonic regime
• Extensional tectonics
• Thrust (Contractional) tectonics
• Strike-slip tectonics
Extensional tectonics is concerned with the structures formed, and the tectonic processes associated with, the stretching of the crust or lithosphere.
Areas of extensional tectonics are typically associated with:
• The development of continental rifts, with or without the effects of mantle upwelling
• The gravitational spreading of zones of thickened crust formed during continent-continent collision
• Tensional flexures along strike-slip faults
• On passive margins where an effective basal detachment layer is present at the upper end of a linked system
Extensional structures
The main structures formed in areas of extensional tectonics are normal faults and graben structures.
Prominent examples include:
• The East African Rift, a major continental rift system
• The Basin and Range province of western North America
• The global mid-ocean ridge system
• The Dead Sea basin formed at a releasing bend along a continental transform boundary
Thrust tectonics is concerned with the structures formed, and the tectonic processes associated with, the shortening of the crust or lithosphere.
Areas of thrust tectonics are typically associated with:
• The collision of two continents or a continent and an island arc at a destructive plate boundary
• Restraining bends on strike-slip faults
• On passive margins, balancing up-dip extension, where an effective detachment layer is present
Strike-slip tectonics is concerned with the structures formed by, and the tectonic processes associated with, zones of lateral displacement within the crust or lithosphere.
Areas of strike-slip tectonics are associated with
• Continental transform (conservative) plate boundaries
• Lateral ramps in areas of extensional or contractional tectonics accommodating lateral offsets between major extensional or thrust faults
• Zones of oblique continent-continent collision
• The deforming foreland of a zone of continent-continent collision, a process sometimes known as escape tectonics

Introduction Geology

taufiqmoh — Tue, 23 Sep 2008 03:59:14 +0000

From Wikipedia
Geology (from Greek: γη, gê, “earth”; and λόγος, logos, “speech” lit. to talk about the earth) is the science and study of the solid matter that constitutes the Earth. Encompassing such things as rocks, soil, and gemstones, geology studies the composition, structure, physical properties, history, and the processes that shape Earth’s components. It is one of the Earth sciences. Geologists have established the age of the Earth at about 4.6 billion (4.6×109) years, and have determined that the Earth’s lithosphere, which includes the crust, is fragmented into tectonic plates that move over a rheic upper mantle (asthenosphere) via processes that are collectively referred to as plate tectonics. Geologists help locate and manage the Earth’s natural resources, such as petroleum and coal, as well as metals such as iron, copper, and uranium. Additional economic interests include gemstones and many minerals such as asbestos, perlite, mica, phosphates, zeolites, clay, pumice, quartz, and silica, as well as elements such as sulfur, chlorine, and helium. Geology is also of great importance in the applied fields of civil engineering, soil mechanics, hydrology, environmental engineering and geohazards.
Planetary geology (sometimes known as Astrogeology) refers to the application of geologic principles to other bodies of the solar system. Specialised terms such as selenology (studies of the moon), areology (of Mars), etc., are also in use. Colloquially, geology is most often used with another noun when indicating extra-Earth bodies (e.g. “the geology of Mars”).
The word “geology” was first used by Jean-André Deluc in the year 1778 and introduced as a fixed term by Horace-Bénédict de Saussure in the year 1779. The science was not included in Encyclopædia Britannica’s third edition completed in 1797, but had a lengthy entry in the fourth edition completed by 1809.[1] An older meaning of the word was first used by Richard de Bury to distinguish between earthly and theological jurisprudence.

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