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Vocabulary of Formation of Oil Deposits
Reservoir:A volume of rock that has sufficient porosity and permeability to permit the accumulation of crude oil or natural gas under adequate trap conditions.
Crude Oil: Petroleum in its natural state as it emerges from a well, or after passing through a gas-oil separator but before refining or distillation.
Millie Darcy: 0.001 Darcy.
Darcy: Measure of permeability. Equal to the passage of one cubic centimeter of fluid of on centipoise viscosity flowing in one second under a pressure differential of one atmosphere having an area of cross-section of one square centimeter and a length of one centimeter.
Clastic Sedimentary Rocks: Rocks composed principally of broken fragments that are derived from preexisting rocks or minerals and that have been transported some distances from their places of origin.
Paleontology: 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 the Earth’s history.
Stratigraphy: The science of rock strata. It is concerned with the succession, age relationships, form, distribution, lithologic composition, fossil content, geophysical and geochemical properties, and other aspects of stratified rocks.
Organic Reefs: Rocks (often limestones) formed from organic material that grew in place. Some have excellent porosity and permeability and make excellent reservoir rocks. They are known not so much for their size, but for the richness of the oil in some cases.
Seismology: The study of earthquakes, and of the structure of the Earth, by both natural and artificially generated seismic waves.
Seismic Section: Graphic results of a seismic survey which typically plots velocity versus time or velocity versus depth. Reflectors visible on the section are representative of the geometry of subsurface strata.
Geophones: A small electromechanical device which generates a small electrical pulse when seismic waves pass them.
Seismic Timer: An instrument with a sensitive needle which indicates movement on a geophone. The needle leaves a trace on a piece of graph paper mounted to a roller or base which moves at a specified rate (typically one millimeter per millisecond).
Constructing Drill Sections
Vocabulary
Intercept: The depth range of a feature of interest (chemical, mineralogical, etc..) found in a drill hole in which the upper and lower boundaries are specified.
Intersect: To meet and cross at a point.
Collar ********: The ******** of the mouth or opening of a drill hole or mine working.
Ore Deposits
Vocabulary
Extrapolating: Estimate made from set of known values
Plan Map: Map made by projection of information onto a horizontal plane. Different plan maps are made for different mine levels for underground mines. Geologic maps are a type of plan map where the geology is projected onto the horizontal plane corresponding to sea level.
Arithmetic Mean: Values are summed and divided by the total number of values.
Bisector: A straight line that bisects (halves) a line.
Prism: A polyhedron with two faces that are polygons in a parallel planes, and the other faces are parallelograms or rectangles.
Dilution: Waste that is not segregated from ore during mining, thus decreasing the grade of the ore and increasing the tons.
Resource: The amount of a substance, or “endowment”, contained in a deposit and ultimately available for extraction and use.
Magnetic Surveys
Vocabulary
Gamma: The units in which magnetic survey maps are often contoured. 1 gamma = 1 nanotesla.
Magnetic Basement: Crystalline (plutonic igneous), ****morphic rocks which underlie a thick section of non-magnetic, typically sedimentary rocks.
Gravity and Density
Vocabulary
Homogenous: The same or similar material throughout. Uniform in structure or composition.
Amplitude: Half the orthogonal distance between the antiformal and synformal enveloping surfaces.
Station: ******** on a survey line or a survey grid where a measurement is made.
Earth Tide Correction: Cyclic variation in gravity measurements during the course of the day caused by changes in the relative positions of the earth, moon, and sun.
Drift: The gradual change in gravimeter readings with time caused by various factors, including temperature and tidal effects. A correction is made by re-occupying a base station at the end of the day to measure the change which has occurred since the beginning of the day.
Measuring Resistivity
Vocabulary
Apparent” Resistivity: The resistivity which is measured at the surface and calculated making the assumption of a homogenous substance. The apparent resistivity is calculated by measuring the potential drop between two “potential electrodes” positioned between two “current electrodes”. The formula for apparent resistivity is:
AR = (V )(I) / 2 p a
where
V = voltage difference (potential difference) between the two “potential” electrodes
AR = apparent resistivity in ohms
I = current in amps
a = the spacing between electrodes (same spacing for each electrode).
(from Milson 1991)
Transmitter: An instrument which controls and measures current and resistivity and induced polarization surveys.
Receiver: An instrument which measures voltage in resistivity and induced polarization surveys.
Electrodes: Usually ****l stakes driven in the ground with wires attached, but sometimes consisting of “porous pots” which contain salt water to enhance current flow.
Electrical Polarization: To establish a current, voltage and electromagnetic field enhancing the flow of electrons with a specified flow path (highly variable in shape).
Telluric Currents: Naturally occurring electrical currents which travel in large sheets induced just below the earth’s surface, which are influenced by ionospheric currents related to diurnal changes in the earth’s magnetic field.
Rock and Mineral Identification
Vocabulary
Ore and Gangue: The general definition of “ore” is a naturally occurring material from which minerals of economic value can be extracted at a profit. Stating the commodity for which it is mined, for example “gold ore” or “iron ore”, often modifies the term “ore”. Ore minerals are the specific minerals containing the commodity of interest. Many minerals contain elements of commercial interest, but are not ore minerals because the mineral is “refractory”, meaning it is difficult to impossible to extract the commodity from the mineral. “Gangue minerals” refer to material so intimately associated with ore that it has to be mined with it, and later removed by various crushing, grinding and separation processes. The “host rock” is the rock surrounding the ore and gangue, which, like the gangue, has no value. To illustrate these relationships, consider the following example for a gold ore:
A gold-bearing quartz vein 1 foot thick occurs in a granite intrusion. The quartz vein contains arsenopyrite and pyrite in addition to native gold. The “ore” in this example is the quartz vein material where it contains sufficient concentrations of gold . The ore mineral is native gold. The gangue minerals are quartz, arsenopyrite and pyrite. The granite is the host rock.
Ore Deposits: An “ore deposit”, or “ore body”, is a continuous, well-defined mass of material containing a sufficient volume of ore to mine economically. In other words, the length, width and thickness must be determined as well as the concentration of the commodity of interest. Defining an ore body (ore deposit) generally requires drilling to determine the thickness as well as the depth below the surface.
Ore Minerals: Ore minerals are typically categorized as either “****llic” or “non****llic” (also called “industrial”). ****llic minerals, as the name implies, are minerals containing ****ls. We refer to the common ****ls, which are chemically active and commonly alloyed, as “base ****ls” (eg, copper, lead and zinc). In contrast, “precious ****ls” are rare ****ls with high commercial value commonly desired in their isochemical form (e.g., gold, silver, platinum). Non****llic minerals are of course all other types of minerals.
Lode Deposits: Ore deposits can are broadly broken down into two groups, called “lode” and “placer”. Lode deposits are those that occur within consolidated rock, having formed during the original formation of the rock, or some time after that. The processes which form lodes are often implied to be chemical in nature, whether it was due to the original fluids within a magma, or the magma itself, or whether it was due to some hydrous (water rich) fluids which migrated through the rock at a later date and altered its original composition.
Placer Deposits: In contrast, a placer deposit is formed in unconsolidated material, and forms as a result of physical processes at or near the earth’s surface. The processes are secondary in nature and the prime example is weathering. In some environments the climatic and hydraulic (action of water) conditions are just right to create a natural mechanical concentration process. The most typical environment is the stream environment. Where this concentration happens, the unconsolidated sediments in the stream can become enriched enough with valuable minerals to be classified as ore deposits. A large amount of gold is mined from this type of deposit, called a placer gold deposit.
Disseminated: Minerals which are scattered as small particles throughout a rock.
Vein: A tabular or sheet like mineral deposit often filling a fracture or fault.
Aggregate: Crowded or massed together into a dense cluster.
Opaque: Does not allow light to pass through.
Mineralization: To develop a mineral formation
Consolidation: United into one form.
Foliation: Consecutive thin layers
Measuring Rock Structures
Vocabulary
Hanging Wall: The block of rock above an inclined fault surface.
Footwall: The block of rock below an inclined fault surface.
Normal Fault: A fault, generally steeply inclined, along which the hanging wall block has moved relatively downward.
Reverse Fault: A fault, generally steeply inclined, along which the hanging wall block has moved relatively upward.
Thrust Fault: A special type of reverse fault with a very low angle fault plane, typically dipping < 15 degrees.
Strike Slip Fault: A fault which has horizontal movement, or movement parallel to the strike of the fault plane.
Axial Plane: An imaginary plane which intersects the crest or trough in such a manner that the limbs or sides of the fold are more or less symmetrically arranged with reference to it.
Anticline: Fold with limbs dipping away from the fold axis.
Syncline: Fold with limbs dipping towards the fold axis.
Symmetrical Fold: A fold in which both limbs dip equally away from the axial plane.
Asymmetrical Fold: A fold in which one limb dips more steeply than the other.
Overturned Fold: A fold in which one limb is tilted beyond vertical, resulting in both limbs dipping the same direction, but not at the same dip angle.
Isoclinal Fold: A fold in which both limbs are approximately parallel.
Recumbent Fold: A fold with a nearly horizontal axial plane, resulting in overturned beds on one or the other limbs.
